ML20117L188
| ML20117L188 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 05/06/1985 |
| From: | Michael Scott COALITION FOR RESPONSIBLE ENERGY EDUCATION |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| CON-#285-015, CON-#285-15 2.206, NUDOCS 8505160126 | |
| Download: ML20117L188 (133) | |
Text
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J..tM COALITION FOR RESPONSIBLE
; ENERGY EDUCATION v
4 315 W. Riviera Drive
/- Tenpe, AZp4M Q
. May 6,1985wc Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation '85 MY 15 A11:25 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 g. . . . . , , , ,
RE: ShowCausePetitionPursuantto10CFR2.206(hkb,$ehatterof Arizona Public Service, et al. (Palo Verde Nuclear Generating Station Nos. 1 and 2) Requesting Suspension of PVNGS No. 1 Operating License Pending Completion of Specified Corrective Actions and Institution of Proceeding on Corrective Actions at PVNGS Nos. 1 and 2. Docket Nos. 50-528, 50-529 (License No. NPF-34 and Construction Permit No. 142).
- 1. This petition is brought by the Coalition for Responsible Energy Education (hereinafter referred to as " Coalition") before the Director, Nuclear Reactor Regulation, pursuant to 10 CFR 2.206(a). The petition alleges that spray pond piping corrosion at Palo Verde Nuclear Generating Station (PVNGS) Nos. 1 and 2 constitutes an unreviewed safety question.
The petition requests service upon Arizona Public Service (APS) of an order to show cause, pursuant to 10 CFR 2.202, why the low power operating license for PVNGS-1 should not be suspended and future licens-ing activity for PVNGS-1 and 2 deferred, pending completion of specific corrective actions, and a proceeding initiated under 42 U.S.C. 2239(a). DESCRIPTION OF PETITIONER
- 2. The Coalition for Responsible Energy Education is a non-profit citizen's organization founded in 1982 to address energy issues in Arizona through public education, research and litigation. The Coalition, through its officers and attorneys, has represented its members through show cause petitions and in meetings with the Commission, as well as in utility rate and financing hearings before the Arizona Corporation Commission. In January, 1985, the Coalition Board of Directors adopted the Palo Verde Intervention Fund as a special project of the Coalition.
The Intervention Fund has previously participated in Atomic Safety and Licensing Board hearings on PVNGS-1, 2 and 3. The Coalition's member-ship consists of individuals and organizations residing in Arizona.
SUMMARY
, 3. In its " Evaluation of Spray Pond Weld Corrosion at PVNGS," filed with the Commission on April 3,1985, Aiizona Nuclear Power Project @
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(APS, et al.) maintains that said corrosion does not constitute an unreviewed safety question. The Coalition has learned of information which contr'dicts a that conclusion. The Coalition alleges that operation with existing and anticipated through-wall pitting of the spray pond welds due'to microbiological 1y influenced corrosion (MIC) will: (1) reduce the margin of safety below acceptable levels and result in essential cooling water system (ECWS) temperatures in excess of design criteria; and (2) increase the probability of accident and malfunction of equipment important to safety through the potential for MIC contamination of other safety-related systems.
- 4. The Coalition further alleges that APS has failed to demonstrate that the MIC problem is or can be confined to the spray pond stainless steel piping, and to establish adequate means to prevent and monitor for further MIC activity. Indeed, based on its information, the Coalition alleges that APS' proposed corrective actions will prove counter-productive.
AUTHORITY
- 5. Title 10 of the Code of Federal Regulations 2.206(a) establishes the right of the public to petition the Commission, Director of Nuclear Reactor Regulation and other specified directors to institute proceed-ings pursuant to 10 CFR 2.202 to modify, suspend or revoke a license or for other relief as may be proper. Such a petition must specify the relief requested and set forth the facts that constitute the basis for the request. The Commission may, pursuant to 10 CFR 2.206(a), institute sudt a proceeding by serving upon the licensee an order to show cause.
- 6. 10 CFR 2.206(b) establishes that the appropriate director shall institute said proceeding or advise the person requesting said proceed-ing in writing of the reasons for denying the request "within a reasonable time."
- 7. The Atomic Energy Act of 1954 gives discretion to revoke, suspend or modify the license or construction permit of an NRC licensee:
A license or construction permit may be revoked, suspended or modified in whole or in part... because of conditions revealed by the application for license or statement of fact or any report, record, inspection, or other means which would warrant the Commission to refuse to grant a license on an original application; or for failure to construct or operate a facility in accordance with the terms of the construction permit or license or the technical specifications
in the application; or for the violation of or failure to observe any of the terms and provisions of this chapter or ;
-of any regulation of the Commission.
42.U.S.C. 2236. Notwithstanding the discretionary aspect of this statute, the NRC has a mandatory duty to exercise its authority when necessary and is required to determine that there will be adequate ' protection of the public health and safety. See Natural-Resource Defense Council vs. U.S. Nuclear Regulatory Commission, 528 F.2d 166 (2d Cir. 1978)..
- 8. The Director and Commission are not obligated under 10 CFR 2.206 to grant the requested relief nor-to hold.a formal hearing on the request. ,
Although such action is discretionary, the Supreme Court has determined that the Atomic Energy Act mandates that "the public safety.is the first, last and. permanent consideration in any decision on the issuance of a construction permit or a license to operate a nuclear facility." Power Reactor Co. v. Electricians, 367 U.S. 196, 402 (1961), quoting In Re Power Reactor Development Co., 1 AEC 128, 136 (1959). How the NRC fulfills this mandate, particularly in determining the benefits of a discretionary hearing, is discussed infra. ,
- 9. First, a hearing should not be ordered when to do so will result'in -
the reconsideration of issues: ! Parties must be prevented from using 10 CFR 2.206 pro- [ cedures as a vehicle for reconsideration of issues pre- ; viously decided, or for avoiding an existing forum in which ther more logically should be presented. > Consolidated Edison Co. of New York et al. (Indian Point Units 1. 2 and 31, CLI-75-8, 2 NRC 173, 177 (1975).
- 10. The instant case deals with an unreviewed safety question first identified in March, 1985, and has never been previously decided. 4 There are no. existing forums. An operating license has been issued for PVNGS-1, and was issued prior to discovery of the spray pond MIC situation.'
Consideration of full-power operation has been scheduled for May 23, 1985 - (50 Fed. Regz 18612 [May 1, 1985]). Normally, consideration of full-
' power operations would not constitute an adjudicatory forum in which -
l all the issues raised herein could be addressed. The Coalition does not i seek to reexamine the issues reviewed in granting the PVNGS-1 and 2 construction permits and PVNGS-1 license (i.e., if APS can meet NRC requirements), but rather, the consideration of whether the licensee now meets and will continue to meet the requirements of said permits and - licenses, the' Safety Analysis Report (SAR), and the Rules and Regulations e ~ - - -~~_-
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m 4 of"the NRC, and further, if there is reasonable assurance that operation , in the current state will not jeopardize the public' health and safety.
- 11. In the instant case, there is no existing forum for determination of issues affecting the prudency of operation of PVNGS-1 in its current l'
- state. The risk of increasing the probability of malfunction of i equipment-important.to safety through MIC contamination of additional systems arises with the operation of PVNGS-1 in its current state; i accordingly the Coalition petitions for postponement of initial criti-cality until such time as this issue is resolved. Even more urgently,
- the increased risk of accident resulting from operation with currently identified and possible additional MIC arises particularly upon full-
; power operation.. Therefore, the Coalition prays that any vote on full-
- power operation of PVNGS-1 should be delayed until such time.as this issue has been resolved. The prolonged period of low-power testing,
{ power ascension and analysis to be undergone prior to actual full-power i ' operation provides an extended period of time during which this issue 1 can be resolved without negatively impacting PVNGS in any way, econom-i ically or otherwise. Definitely, the public safety would be best
- i. served, therefore, by such a delay.
1
- 12. In Indian Point, supra, the Commission considered what existing j forum might be best suited to address the matters at issue. Neither the deliberations on full'-pmer operation of PVNGS-1 nor the NRR's j reently. announced and pending investigation of the spray pond MIC j situation constitute the logical forum, as they are not contested case' ,
) proceedings in which the petitioner, the Coalition, could raise its-l concerns. A request for hearing and petition to intervene at this ?- stage pursuant to 10 CFR 2.714 would be extremely untimely. talen the
- Atomic Safety and Licensing Board hearings were held and the operating l license application noticed, the MIC condition was unknown or non-I exitent.
- 13. The fact that the PVNGS-1 operating license has been issued and other procedural steps completed should not jeopardize this petitioner's l- right to a fair consideration of the issues raised herein. The
! provisions of Indian Point merely address the question of existing forums; they do not alter the fact that a utility with a construction ) permit or-low-power operating license bears-the burden of proof: We think it ineluctable that a utility must bear the burden j of proving compliance with the Commission safety regulations not onlyfat the beginning and and of'the nuclear licensing i
e
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5.-- - proc'ess - but, as in this case - when called upon at some -
' interim point to "show cause" why a construction permit should.not~be lifted for unsafe construction practiced.s Where; nuclear power plants are involved, public safety'is 3 indisputably.better served if a utility must stop con - ,
struction practices.it cannot prove safe; a decision that -i it may continue those practices because someone else-can-
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.not prove'them. unsafe.is manifestly not one which ple.ces public safety considerations first.
Consumer Power Company (Midland Plant, Units 1 and 2), ALAB-315;i3 NRC 101, 104 (1976). Clearly, the same reasoning applies to opergling Thespoi5t is [ practices or conditions as to construction practices. that the paramount importance of public safety places the burden of proof.on the licensee. A petitioner need only provide the NRC staff with "sufficent reason" to look into the matter of suspension of as , license or other relief, but is not required to assume the burden of proof itself. Indian Point, supra. The public's right to due process of law, as well as public safety, dictates that this should be so.
- 14. A petitioner, however, has some responsibility to prove its case:
[T]he standard to be applied in determining whether to issue a show cause order is, as we have said.in Indien Point whether." substantial health or safety issues thive] been raised...." A mere dispute over factual' issues does
.not suffice.
Indian Point, supra at 177. Another test against which any request for - a discretionary hearing must be judged is whether such a proceeding would serve any "useful purpose." Public Service of Indiana (Marble , Hill Nuclear Generating Station, Units 1 and 2), CLI-80-10,'11 NRC 438, 443 (1980).- The dissenting opinion in Marble Hill suggests a two-fold interpretation of "useful purpose," the first of which is the public's right to know the risk with which they live (considered to be predicated on widespread citizen interest).
- 15. In the instant case, such widespread citizen-interest clearlyo -
exists and has been demonstrated, both in regard to Palo Verde generally I and in regard to the specific i sue of spray pond MIC. Citizen concern about Palo Verde has increased markedly since the 1982 Atomic Safety and Licensing Board hearings. At an August 24, 1983 meeting,with Region V Director Jack Martin, a diverse spectrum of local citizens expressed - concerns about both the economics and safety of PVNGS and the candor of ^ APS and, indeed, the NRC. Those last concerns were particularly emphasized by media representatives in attendance, and were occassioned ' in part by PN0's not released to the press on the 1983 reactor coolant system failure at PVNGS-1. (See attached Exhibit 1.) Subsequently, l plant construction quality and cost, APS quality assurance and manage-l
7 n . y g ment control and competence, and nuclear plant safety and economics A generally have all increased. In 1984, a poll by Arizona's leading newspaper, The Arizona Republic, found 49% of local residents surveyed a " dissatisfied" or "very dissatisfied" with PVNGS quality of construc-k 'tlon, compared to 22% who were satisfied." Another 1984 poll, by the t, independent research firm Behavior Research Center of Arizona, showed
^ -
a plurality of residents favoring abandonment of PVNGS and a majority
; ' opposed to any future nuclear plant construction. (Exhibit 2.)
l
'Public concern about plant costs has culminated in initiation of a
$2 million, four-state utility commission construction cost and pru-
- - dency audit and acknowledgement by the chief executive officer of a major ANPP partner, Salt River Project, that construction of PVNGS i was "a mistake." (Exhibit 3.) The state agency regulating APS rates, the Arizona Corporation Commission, expressed its concern about the current MIC situation by calling a special hearing on the question.
A leading metropolitan daily, The Phoenix Gazette, editorially expressed its disapproval of the failure to inform the public of the MIC situation (two PN0's issued in March,1985,were not released to the media and eventual utility disclosure failed to reveal the full extent of the MIC, until the PN0's were released to the press by the Coalition), and of the potential impact on plant costs and safety of APS' proposed corrective actions. The editorial stated:
- Officials at the Palo Verde Nuclear Generating Station and the U.S. Nuclear Regulatory Commission seem to have a rather cavalier attitude about more defects that have been discovered at the facility.
...No problems, of whatever magnitude, can be tolerated at Palo Verde. It should go on-line in as perfect a condition as engineers and competent craftsmen can make it.
(The Phoenix Gazette, March 28, 1985; Exhibit 4.)
- 16. Most importantly, the "useful purpose" to be served by a discre-tionary hearing is the technical resolution of problems which results in a greater degree of safety afforded to the public. As interpreted by the " Proposed General Statement of Policy and Procedure for Enforce-ment Action," 44 Fed. Reg. 66754, October 7, 1980 (implementing 10 CFR
, 2.202 and 2.204), suspending orders can be used to remove a threat to the.public health and safety. Specifically, suspension orders can be used when further work or operation would preclude or significantly hinder the identification and correction of potentially hazardous conditions, or for any other reason for which license suspension,
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c , . a.u. . - - - - - - .; a-e modification or revocation is legally authorized.
- 17. The primary test of "useful purpose" is based on what kind of regulatory action best serves the public welfare. As a general rule, the Commission has held that:
public health and safety is best served by concentrating enforcement resources on actual field inspections and related' scientific and engineering work as opposed to the conduct of legal proceedings. Marble Hill, supra. The Appeals Board elaborated on these roles: [W]here the matter is not one of inevitability of harm but rather of the extent to which the applicant is carrying out its obligations, the Commission's enforcement arm comes into play. It is in the first instance an enforce-ment and not an adjudicatory function to make certain that license conditions are being satisfied. It is left to en-forcement personnel to insure that an unnecessary or avoid-able impact is not incurred because of the applicant's lack of diligence. Public Service Co. of New Hampshire, et al. (Seabrook Station, Units 1 and 2), ALAB-356, 4 NRC 525 (1976). This notwithstanding, the Atomic Energy Act and the implementing regulations of the NRC recognize that the role of enforcement actions is limited by providing for legal pro-ceedings. In the instant case, the petitioner, the Coalition, alleges that an unnecessary and avoidable impact will be incurred by operation of PVNGS in its current state; however, the situation is not one in which the diligence of the operating utility is a point of controversy. Rather, at issue is the technical resolution of problems which would result in a greater degree of safety afforded to the public. Inspection and enforcement activity has already occurred "in the first instance." The situation has advanced to the stage at which a technical determina-tion must be made in favor of one of two courses: early preventative action to preclude an increase in the probability of equipment malfunc-tion or accident, or operation in the current condition, which would preclude or significantly hinder the identification, limitation and correction of potentially hazardous conditions. The general issue is whether MIC in the PVNGS spray ponds constitutes an unreviewed safety question, which was not considered when the Commission issued a low-power operating license. 10 CFR 50.57(a3) and (6) provide findings required for issuance of an operating license: There is reasonable assurance (i) that the activities authorized by the operating License can be conducted without endangering the health and safety of the public,
and (ii) that such activities will be conducted in compliance with the regulations of this chapter and: The issuance of the license will not be inimical to the i common defense and security or to the health and safety
'of the public.
It is precisely the effect on the public health and safety resulting from operating with the existing MIC and pitting conditions (unanalyzed at the time the operating license was issued) and from the likelihood of the creation of additional conditions inimical to the public safety that concerns the petitioner. In addition, it is manifest that previous management and enforcement activities were inadequate to prevent these circumstances from arising. On-going inspection activities have occurred and substantial questions remain. Finally, as discussed infra, the problem of MIC raises several questions on which scientific knowledge is limited or uncertain, and others in which expert scientific opinion is inadequately reflected in APS' " Evaluation" of April 3, 1985. The Appeals Board has explained two reasons to grant a petition for discre-tionary hearings:
...the NRC already provides a separate procedure, under 10 CFR 2.206, for any interested person to seek enforcement actions beyond those adopted; and:
[The request must] state specifically what additional facts might be uncovered by a public hearing that has not been or will not be by pending investigations. Marble Hill, supra at 443. The specific information, based on a review of the state-of-the-art scientific understanding of MIC upon which this petition largely rests,is discussed infra. Generally, it is this infor-mation and a broader exploration of the complexity of MIC problems touch-ing on this issue, which could best be brought out through the presenta-tion of scientific opinion by expert witnesses in an adjudicatory pro-cedure.
- 18. It should also be emphasized that the Coalition's information suggests that APS' " Evaluation" and proposed corrective action fail.in several respects to reflect the scientific state-of-the-art on MIC including ways which are likely to prove counter-productive. (See discussion in " Statement of Facts," infra.) Moreover, APS' public statements on the situation - including characterizing it as a "non-problem" - have, not inappropriately, been characterized as sug-gesting a " cavalier attitude," such as to indicate an abdication of
knowledge and responsibility by the utility. As the Commission has 4 stated: In large part, decisions.about licensees are predictive ! in nature, and the Commission cannot ignore abdication of responsibility or abdication of knowledge by a licen-
.see applicant when it is called upon to decide if a li-
' cense for a nuclear facility should be granted.
Houston Lighting & Power Co. (South Texas Project Units 1 and 2), CLI-80-32,~12 NRC 281, 291 (1980). 1 STATEMENT OF FACTS
- 19. The following summary of the APS-ANPP position on the spray pond piping and weld corrosion at PVNGS-1 and 2 is drawn from APS' "Evalua-tion of Spray Pond Weld Corrosion at PVNGS," filed with the Director, Nuclear Reactor Regulation, on April 3, 1985.
- 20. APS has identified corrosion in over 80% of the welds on the stain-4 less steel spray pond piping at PVNGS-1 and 2, through a combination of radiographic sampling and visual inspection. A small number of indi-
! cations of corrosion were identified in base metal. APS estimates 60% through-wall penetration.
- 21. APS estimates that water leakage due to through-wall penetration under specified LOCA conditions, could increase essential cooling water temperature to as high as 124.6 F (pp. 5-6). The design criteria limit is 125 F.
- 22. APS has identified the-probable'cause of the pitting as MIC and the probable causative agent as Gallionella, on the basis of microscopic analysis of weld sections and analysis of the physical characteristics of the corrosion. APS concludes that the accumulation of stagnant water caused the Gallionella infestation.
'23. As corrective action, APS proposes continuation of its current chemistry control and biocide treatment program. APS proposes to pre-vent future stagnation through routine operation of the spray pumps (aeration).- APS proposes a monitoring program consisting of quarterly pressure drop measurements and re-radiographing welds at the first re-fueling outage.
- 24. To determine whether MIC has affected other-safety related systems, 7
APS visually examined 2 welds and 1 valve from the Unit 1 safety injection system and reviewed prior inspections, concluding that the MIC is iso-lated to the spray pond piping.
- 25. APS concludes that it has established means to prevent further pit-ting initiation and monitor flow, that operation in the current condition l will not reduce the margin of safety or increase the probability of acci- ]
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dent or malfunction of safety related systems, and therefore does not I constitute an unreviewed safety question.
- 26. According to APS' calculations, spray pond operation under specified LOCA conditions could result in a temperature increase to within 0.4*F of design criteria limitations. By definition, the margin of safety built into the design criteria would thus be reduced. Moreover, APS acknowledges that it cannot predict the rate or extent of future pitting, and anticipates further through-wall leakage to develop. APS' calculations appear methodologically sound and conservative at first glance. However, APS' analysis is premised on the critical, non-conservative assumption that there will be no further incidences of spray pond piping MIC; i.e., that there will be no increase in the number and size of the indications of MIC. This assumption lacks clear empirical support. It can only be verified over time, through allowing the MIC condition to run its course, or averted, by removing the corrosion and its causative agent (Exhibit 8). Moreover, APS' statistical methodology for inferring the extent of corrosion in similar systems is vulnerable to error because it fails to account for site-specific differences that could affect the rate of MIC (Exhibit 8).
- 27. In addition, our information establishes that APS' analysis and proposed actions do not provide satisfactory assurance that other safety related systems have not been and will not become affected by the MIC.
- 28. As stated on page 3 of "Microbiologically Influenced Corrosion of Industrial Alloys" (Daniel H. Pope, et al.; Exhibit 5) and page 13 of Microbiologically Influenced Corrosion": A State-of-the-Art Review (MTI Publication Number 13; Daniel H. Pope, et al.; Exhibit 6), microorganisms related to MIC:
...may be motile which aids in migrating to more favor-able conditions or away from less favorable conditions, e.g., toward food sources and away from toxic materials.
It should be noted that APS was in a position to have been aware of this information, Bechtel Power Corporation having forwarded a copy of the Pope, et al. abstract to APS on January 3, 1984, as part of the discus-sion of corrosion of buried piping at PVNGS. (Exhibit 5, cover letter.) Booth, (page 14, Exhibit 7) states that sulfer-oxidizing bacteria (e.g., Gallionella) "are all actively motile." Pope adds: The individuals can be widely and quickly dispersed by wind, water, animals, aircraft, etc., and thus the poten-tial for some of the cells in the population to reach more favorable environments is good.
1
' (Exhibit 5 at p. 4; Exhibit 6 at p. 14). Moreover:
They :(MIC organisms) have specific receptors for certain - chemicals which allows them to seek out higher concen-trations of those substances which may represent. food - s6urces. It is very:important to understand that nu-y trients, especially organic nutrients, are generally in short supply in most aquatic environments; but that
' surfaces, including metals, adsorb these materials, creating areas of relative plenty. Organisms able to. seek out and establish themselves at these sites - will have a distinct advantage in such environments.
(Exh'ibit 5 at p. 3; Exhibit 6 at p. 13.) Gallionella (as well as other ; ^ microorganisms associated with MIC) can be spread by water movement through plant systems connecting with the spray ponds, as well as them-
-- selves migrating to separate but connecting systems. (Exhibit.8, affi-davit).
- 29. In order to avoid such spreading of MIC, among other reasons, it is generally highly advisable as a first step in a treatment and control
-program to remove the microorganisms and corrosion through replacing the corroded materials or through chemical or mechanical cleaning.
Such replacement or cleaning activity should take care to remove both the microorganisms and all traces of corrosion in the under-deposit metal. (Exhibit 8.) Such treatment should also reflect awareness of the distinctions between the behavior and response to various treatment procedures of free-floating microorganism and tubercles. (Exhibit 6 at 64.) Biocides and other treatment methods which are effective against free-floating organisms may be ineffective against nodules.
'30. The potential for innoculating other plant systems with
! ' Gallionella or other MIC agents if the established concentration cells Il are untreated is further supported by the rapidity with which such
- microorganisms can establish themselves in a new environment.
roduce enormous numbers of individuals in a short They time p(generating-times of only 18-minutes are known), l thus allowing them under favorable circumstances to
" bloom" and quickly "take over" an environment.
(Exhibit 5 at 4; Exhibit 6 at 13.) Moreover, innoculation by MIC
- organisms can be difficult to detect, setting up the potential for safety situations which are recognized only when a system is called upon in emergency circumstances, as the NRC has recognized
4 The nature of aquatic fouling in piping systems is such that it may go unnoticed, or not severely degrade system performance , until the system is called upon to function following an incident. s
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" Abnormal Occurence: Blockage of Coolant Flow to Safety-Related Systems and Components," 47 Fed. Reg. 21654 (May 19, 1982). (The discussion-therein addresses both marine animal and MIC fouling.)
The safety significance of such circumstances is addressed:
'In a nuclear power plant, it is imperative that the heat generated by the nuclear reactor and the components of safety systems be dissipated into the environs. This process is usually performed by transferring the heat being generated to various cooling systems via heat j exchangers and then to a. heat sink such as a river, lake w or cooling tower. These processes are utilized during normal operations and subsequent to normal plant shutdowns j.. or. accidents. Failure to provide adequate cool'ing could result in severe
~
damage to the safety-related components or systems designed to safely shut down the-plant and to mitigate the consequences of a major occurence (such as loss of coolant accident, LOCA). Federal Register, op cit. (At PVNGS, the spray ponds function as the ultimate heat sink.)
- 31. Concern with MIC involves both the degredation of system struc-tural integrity or operating efficiency through pitting and leakage
-and fluid flow blockages. Gallionella can foul systems through the creation of tubercles which accumulate in pipes so as to plug them.
(Exhibit 5 at 6; Exhibit 6 at 17.) Gallionella may also establish itself in areas where protective coating has been applied through exploitation of " holidays" (discontinuities) in the coating, as may other MIC microorganisms: There has been a recent increase in the use of plastics, e.g., epoxy resins.. The application of such plastic coatings, however, suffers from the same general problems mentioned above; that is, imperfections provide sites where bacteria can establish themselves and influence or initiate corrosion. There is also the question of the permeability of plastic and other coatings to such substances as hydrogen sulfide, organic acids and various other corrosive chemicals. Therefore, these coatings, although removing the organism from direct contact with the metal may not, in reality, prevent corrosion due to the activities of microorganisms. (Exhibit-6 at'35.) Once intiated, the corrosion process can become almost auto-catalytic, even if the causative agent is removed or-killed, unlessLall corroded material is also cleaned or removed (Exhibit 8).
- 32. The foregoing establishes a dual safety concern created by the MIC situation at PVNGS: (1) whether the current levels of MIC.in the spray ponds so reduces the margin of safety as to constitute a signifi-cant safety question; and (2) the effect of spray pond MIC on the entirety of systems serviced by the spray pond, particularly the likeli-
hood ~that-operation will spread the MIC to other safety _ systems. .The Coalition alleges that the current levels of MIC. constitute a signifi-cant safety question, particularly for operation at higher power levels. j Perhaps an-even greater concern, however, is the additional risk of l
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malfunctions created by operation of the system and the transportation of MIC organisms, malfunctions which may go undetected until the systems ! are needed for safe operation. The existence of that risk is certain. It is, however, difficult-to quantify the extent of the risk'for numerous-4 reasons. .The variable nature and uncertain effect'of fluid flow rates
~
is~one such reason. Conditions of low fluid flow may be more favorable, f and conditions of stagnation or no flow during outages or cycling may be most conducive, to the attachment of MIC-related organisms. As the NRC has noted: ,
...[I]t has been observed that relatively rapid fluid. flow 3
tends to prevent attachment of organisms whereas low flow
- rates or stagnant conditions favor befouling and concentra-3 tion cell corrosion.
l (IE Information Notice No. 85-30 [SSINS No. 6835]: 'Microbiologically_ Induced Corrosion of Containment Service Water System, April 19, 1985, at'p. 2. Emphasis added.) This positive effect of rapid fluid flow is only a tendency, however, and may be mitigated against by several fac-tors. Even relatively brief periods of low or zero flow can provide an opportunity for microorganism attachment. Microorganisms are able to l: lodge themselves is small areas which are less subject to the effect , of flows, e.g., surface " holidays" (supra) or crevices and other small spaces in the system: . They [MIC organisms] are small (from.less-than:two-tenths to several hundred pm in length by up to two or three pm in width), a quality which allows them to penetrate crevices, etc., easily. L(Exhibit 5 at 4; Exhibit 6 at 13.) Significantly, APS recirculated the spray pond water regularly prior to. identification of-MIC, although it did not routinely operate the spray. nozzles. Once the bacteria have
- . set up in the form of nodules or tubercles protected by a slime film or
-ferric hydroxide excresences, the effectiveness of flushing is drasti-cally reduced. (See Booth, Exhibit 7 at 41.) Flushing may again have
'a positive effect once the MIC organism has pitted through the metal,
-as APS has~noted (" Evaluation," page 7). However, one then'has-to deal
'again with the free-floating organisms.~ Particularly if the diagnosed Gallionella~ concentration cells contain sulfate-reducing bacteria, the
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-bacteria may form spores which can lie dormant for extended periods
- of time in systems or components, germinating when conditions are .
y most-favorable. (See Pope, Exhibit 5 at 6; Exhibit 6 at 14.) The . [ . adaptability of MIC-related organisms has been noted by the NRC: They.have been known to tolerate a wide-range of tempera-tures-(-10.to 90*C), pH values of 0 to 10.5,-oxygen con-centrations from zero to almost 100 percent 0 and extreme , hydrostatic pressure. 4 (IE Information. Notice, op cit.) For all the foregoing reasons', the sole reliable. preventative to MIC contamination of other safety systems ! and additional incidences of spray pond MIC is removal of the tubercles.
- 33. Increasing.the concern over the potential for MIC infestation of other safety systems, MIC has been identified or possibly implicated J in the past:at PVNGS. APS identified MIC on the Unit 2 auxiliary feed-water pump in 1984. - (Final-Report DER 80-40, Exhibit 9.) However, APS' Final Report did not specify a causative agent. Bechtel Power. Corpora-tionthas considered the possible role of MIC in the corrosion of buried spray pond and other piping at PVNGS. (Exhibit 5, cover letter, January,
-1984.)- Following failure of the~Plasite lining in carbon steel piping connected to the spray ponds, " widespread rusting" was identified on the Unit 2 diesel generator jacket water and lube oil coolers. (Exhibit 10 at-1.) Although other hypotheses are also vaible, such rusting would-be '
compatible with Gallionella. In the Final Report on auxiliary feedwater pump. corrosion, APS stated:
- Whereas MIC bacteria probably exists.in other. safety-related systems at PVNGS, the conditions that existed in the auxiliary feedwater system are no more hospitable or inhospitable due to the startup flushing and testing.
+ (Exhibit 9 at p. 3.)
- 34. The foregoing establishes two concerns: . (1) APS must determine g whether MIC has-initiated or MIC-related organisms have established t
Lthemselves in other safety-related equipment, and (2) APS must establish that it.has or reliably will implement techniques adequate to monitor 4 for and control the potential for such spreading of MIC to' other systems l
- in the ' futu re. . The spray ponds function as the ultimate heat sink, for j safe 1 shutdown as well as for the emergency diesel generators. Failure
.to isolate the current MIC condition to the spray pond piping will sig-
- nificantly increase the probability or severity of accidents and increase
- the~1ikelihood of malfunction of other safety systems and-components at PVNGS.
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- 35. -APS' analysis of the status of other plant safety systems in this regard, as described in its April 3 " Evaluation," is based for the most part not on contemporary visual inspection and other direct surveillance, observatio.n and testing, but rather on review of prior inspections and operating performance. Given the rapidity with which Gallionella and other MIC-related organisms can establish themselves and initiate or influence corrosion and the capacity of MIC fouling of safety systems to go undetected absent specialized surveillance procedures, APS' analysis is inadequate.
- 36. APS' proposed monitoring program consists solely of monitoring spray pond pressure drop on a quarterly basis, and re-radiographing the previ-ously examined welds at the first refueling outage. Again, given the rapidity with which MIC intiation can occur, more frequent and extensive monitoring is indicated. The NRC (Federal Register, op cit. at 21656) has identified a range of techniques and commented upon them:
The Bulletin also asked licensees to describe their methods for preventing and detecting any future fouling at their plants. A combination of chlorination, heat treatment, flushing, backflushing and the installation of strainers --- were the preventative actions taken by most of the affected plants. Many of them routinely inspect the intake canal, the pump discharge strainers and the main condenser, cleaning them out as needed. Detection methods included surveillance programs comprised of visual inspections and measurements of flow, differential pressure, and temperature at various system locations. These actions by the licensees can be expected to have varying degrees of effectiveness depending on the fre-quency with which they are performed and the severity of the infestation present at and around the plant. In addition to other forms of surveillance, system water and metals should be monitored on a routine basis for the presence of MIC-related microor-ganisms, both to identify incipient problems and to monitor the effect-iveness of on-going treatment and control programs. Pope identifiies methodologies for such monitoring (Exhibit 6 at 66-69; Exhibit 8). A more intensive monitoring program than APS has proposed would aid in verifying the diagnosis of Gallionella as the causative agent. Ideally, APS should be required to obtain laboratory verification of its proposed treatment program in advance of implementation. This is important for two reasons: (1) the effectiveness of any treatment program depends upon the specific nature of the causative agent and the milieu in which the MIC is taking place, and (2) the presence of a given microorganism may mask the actual causative agent or agents, as discussed infra. .
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- 37. The mechanisms and role of Gallionella in MIC is not well-under-stood, according to Pope (Exhibit 6 at 17, 45). This increases the Eneed for a treatment, control and monitoring program that is conserva-tive on'the' side of safety. Gallionella is capable of direct oxidation,
_yet it may.also create a microenvironment in the underdeposits of its nodules in'which anerobic sulfate-reducing bacteria can initiate or
~ influence corrosion (Exhibit 6 at 12, 23, 40-44). Sulfate-reducing-bacteria, as well-as Gallionella and other iron bacteria, may be associ-ated withLpitting such as characterizes the instant case. (Exhibit 6 at 32.)
- 38. - As-a case in point, Gallionella is aerobic and directly oxidizes ferrous iron in solution-to_the ferric state and effects the precipita-tion of ferric hydroxides. (Exhibit 7 at 41; Exhibit 5 at 5-6; Exhibit 6'at'17, 30.) While stagnant water conditions may facilitate the estab-lishment of.Gallionella. infestation, aeration (such as APS proposes'at PVNGS) is recommended only for sulfate-reducing, anaerobic bacteria.
(Exhibit 7'at 52.) While aeration may increase the effectiveness of biocides in eliminating free-floating bacteria in the water, it.is likely to prove counter-productive against Gallionella in the tubercle-form. (Exhibit 6 at.44; Exhibit 8.) Oxygen can both cause Gallionella to
" bloom" more rapidly and increase the oxidation rate and hence the degreee of. corrosion. (Exhibit 8.) Inappropriate biocides can induce microorganisms to migrate to other systems as well, as noted supra.
Therefore,_ laboratory testing will prevent a misdirected treatment pro-gram from actually worsening the'MIC problem.
- 39. Oxidizers generally are resistant to a range of biocides (Exhibit
- 5 at 3-6; Exhibit 6 at 13-14, 34); and: Pope and coworkers and Costerton and coworkers and Characklis and coworkers have all pointed to the fact that-the usefulness of many biocides in the control of organisms in fouling mater-ial is much more limited than it is in the aqueous part of the system. The other problem with certain of the biocides is that
.they will simply shift the microbial population from a " normal aquatic community" or " normal cooling system" community to very
-specialized communities, i.e., those which form slime or those which are through some other mechanism, able to be more resis-tant to biocides.. This shift may cause a much more severe sliming'or corrosion problem than might be encountered with a mixed-microbial community.
(Exhibit 6 at-36-37.)-(Indeed, it is a valid hypothesis that the on-going treatment program at PVNGS has actually had this effect in relation to the current MIC situation.) Gallionella sets up a " differential aeration"
~
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, cell in which pH is altered (Exhibit 7 at 41). Eventual through-pitting i f may. allow / normal flushing to resume, as APS argues; but in the current s'ta t e , aeration cannot penetrate the Gallionella tubercle but can en-courage additional Gallionella MIC. Therefore, it is contra-indicated.
- 40. 'Do overcome the foregoing dif ficulties, ensure maximum effective-ness.of a proposed treatment program and prevent further infestation by
. the identified causative agent,-Pope recommends elimination of the
- causative microorganism or microorganisms and the sites of corrosion, followed by treatment (Exhibit 6 at 44). Biocide application and chemical control programs alone are not generally effective unless ac-companied by removal or cleansing of all corrosion (Exhibit 8). Booth also confirms that:
...a preliminary mechanical or chemical cleaning process may be essential before.the application of a microbial. inhibitor can become effective.
.(Exhibit 7 at 150.)
- 41. - The NRC has noted:
...[C] leaning and dry lay up, or periodic recirculation flushing, during extended outages to mitigate know [ sic]
biological activity would appear to be prudent alternatives. (IE Information Notice, op cit.) However, in choosing between cleaning and flushing, the distinctions made supra between aerobic and anaerobic bacteria, free-floating bacteria and tubercles, etc., must be borne in
. mind. In the current case, thorough mechanical or chemical cleaning to remove deposits and underdeposit corrosion, or replacement of the corroded materials (removing the deposits) are the prudent courses.
They are the. conservative courses, in the sense that they clearly will prevent the intiation of additional corrosion which can create both safety hazards by reducing the effectiveness of safety equipment and increased long-term economic costs. By contrast, APS has failed to meet'its burden of-proof that its proposed corrective actions will chave such positive effect and will not increase the probability of additional safety problems. Failure to take preventative actions that will avoid-such degredation of safety systems and components where
.possible, or postponement of such actions until damage is done, is not a prudent course that puts public safety first. Operating the system in its-present state,.which is likely to spread the MIC problem, is not prudent.- A more thorough inspection and analysis of the nature and extent of MIC at PVNGS and removal of-the causative agent and the
- corroded material is the prudent course that best serves the public interest. _
. _ . . _ - _ . . - . _ ._.-- _ -- - _ . - - . _ . . _ _ _ _ _ _ . _ _ - ~ . - . _ _ _ ,
18 -
^42. Given concern about the. ability of APS to' maintain ECWS. tempera-tures within design l criteria range and not reduce the margin of safety built into-the design criteria to unacceptable lavels, pipe replacement
[ and/or rewelding represents the optimally prudent solution to the need to remove the.Gallionella (or other microbial) infestation and under- ! lying corrosion. CONCLUDIONS.0F LAW i
- 43. 42 U.S.C. s2236(a) and 10 CFR 50.100 provide that a license or
- permit may be revoked, modified or suspended because of " conditions which'would warrant the Commission to refuse to grant a license on an
- original application..."
- 44. 42 U.S.C. @2236(a) and 10 CFR 50.100 also provide that a license or permit may be revoked, modified or suspended "for failure to construct i
or operate a facility in accordance with the terms of the construction permit or license..." , 45. (The existence of the uncorrected MIC problem, the potential effect on other safety systems and the defective evaluation and corrective i action proposals submitted by APS in.the instant case (supra), fulfill the conditions of the Atomic Energy Act and Chapter 10 of the Code of L Federal Regulations as set forth in paragraphs 43 and 44, supra, for-suspension of a license or permit. , . 46. As the discussion in paragraphs 7 through 18, supra, establishes, the-instant case meets the criteria for intiation of. formal hearings. It
~
should be pointed out that the relief requested (suspension of the license j and permits for PVNGS-1 and 2, respectively, pending hearings and rework of1the spray pond piping), is moderate and-should not require a delay in Unit-1. initial criticality of more than one to two months, which delay
.is not unreasonable to protect the public health and safety. If.the
- alternative relief suggested (deferral of a full-power decision until such time as these issues are addressed) alone were adopted, there would
' be no negative impact on PVNGS sheduling whatsoever, although the ability.
to prevent-spreading of the MIC would be reduced. RELIEF REQUESTED 47.. ' WHEREFORE, Petitioners pray that the Director, pursuant to 10 CFR
. 2.202(a),. Order the Arizona Public Service Company, et al., to show cause qas-to why Construction Permit No. 142 and License No. NPF-34 for PVNGS
. Projects 1 and 2, respectively, should not be suspended and a vote on full-power operation delayed, pending replacement of the corroded spray
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pond piping, re-inspection of other plant systems, and development of a revised corrective action program in light of the information dis-cussed above and any other relevant information; and
- 48. Initiate hearings on this issue, under 42 U.S.C. 2239(a).
Respectfully submitted,
. W MydnL. Scott COALITION FOR RESPONSIBLE
' ENERGY EDUCATION Dated.this 6 d -day of May, 1985. O
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AFFIDAVIT OF REPRESENTATION TO WHOM IT NAY CONCERN: Be notified that Myron L. Scott is Executive Director of the Coalition-for Responsible Energy Education and Arizonans for a Better Environment. The Executive Director, among his (her) other duties,is responsible for directing the activities of the litigation and research components of the Coalition for Responsible Energy Education and Arizonans for a Better Environment. The Executive' Director may, under the Charter and By-Laws of the Coalition and A.B.E., represent those organizations in all legal matters and interface with the attorneys representing or assisting the Coalition and A.B.E. in all legal proceedings. In particular, the Executive Director is authorized under the Charter and By-Laws and by vote of the Board of Directors to represent the Coalition for Responsible Energy Education in all proceedings before, petitions to and other matters before the U.S. Nuclear Regulatory Commission. Done this 5d day of N,7 , 1985. h, Barbara S. Bush President, Coalition for Responsible Energy Education and Arizonans for a Better Environment
.> M My[bn L. Scott Executive Director, CREE /ABE i
SUBSCRIBED ANS SWORN TO before me this j$44(dayofMay, 1985, by Barbara S. Bush and Myron L. Scott.
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$ Critics)a td'ck APS ' credibility gap' Meck said APS officials say there is no problem Hy KEITH BAGWEIA disintegrated, welds broke, pipes cracked and Progrew Staff Writer cooling water system problems were found. with salt drift and refuse to address it. When APS The U.S. Nuclear llegulatory Commission and Ahearn charged that the first news story about board chairman Keith Turley was confronted at Arizona Public Service Co. came under fire for the problems appeared July 30 and even though one meetng with the farmers, Meck said, he told "tutally lacking public credibility" Wednesday at APS officials had two extensive reports in front of - them that if anything happens to their crops they a meeting in Phoenix with the NRC's new them, they said damage was minor and there was , can sue the utility, the state's largest and a 29.1-regional administrator. only a "potentialdelay." percent shareholder in Palo Verde. APS also is Meeting with administrator Jack Martin were "Now, af ter being pushed to the wall, APS says Palo Verde construction director and will be local critics of the $4.3 billion Palo Verde Nuclear there will be at least a six-months delay - that plant operator.
Generating Station under construction 40 miles will cost consumers more for repairs and addl* Renz Jennings, a farmer and former legislator, west of Phoenis and reporters from Arizona tional financing. NRC's reactions to such things charged that APS officials wine and dine govern-newspapers, must be significantly stronger," he said. ment and other industry officials, make Martin said Ids backgrourid is in the NRC effort Jackle Meck, a formar Buckeye mayor and charitable contributions, use " propaganda scare to develop nuclear waste disposal capability, and member of the West Valley Agricultural Protec- tactics" and intimidate workers to keep them that he has limited knowledge of nuclear power tion Council that has intervened in the NRC pro. quiet about Palo Verde canstruction problems. plaat operations and even less knowledge of Palo cess leading toward a Palo Verde operating Jill Morrison of the Palo Verde Intervention Verde specifics. license, said APS never told area farmers of crop- Fund said NRC's credibility problems mostly are John Ahearn, state Residential Utility Con. damaging salt emissions from the plant's cooling due to its lacking on-site inspection of Palo Verde sumer Board chairman and a former state cor- towers and evaporation ponos and completely left construction. Iwration commissioner, said: "The operative them out of its Palo Verde environmental impact statement. . Martin said his agency lacks manpower and uurd here is credibiliy APS totally lacks it and . funds for more and better inspections and that its the problem has been tahanced by the NRC. The Yet, he said, the plant will e'mit "14,000 pounds , of salt into the air every day, just from the cooling authority over nuclear power plants is limited by words that come to my ndnd are miransigent, law to "the safety concerns that plants are built masIeadIng, noi fortheoming and towers." Such salt emissions, he said, are likely to right and operated correctly." misstatements." Detween miGMay and July 18, when APS con- damage extensively the 150,000 acres of crops He said, "'Ihe government will have to reflect dut,ted a " hot functional" test of Palo Verde's farmed by West Valley's 55 members, reducing on all this . . . we will need all your help we can nr:st reactor - then scheduled to begin operation significantly their $90 million to $100 million in an- get . . . credibility relys on some good will and in May 1984 - its cooling water pumps nuairevenues. faith on everyone's part." N
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h w @ m.: Doubts s are =s running N m rampant' %m.~P @. sn,M5MiGEMN_$M - am uQ as state's first nuclear plant a%L,.oRW"$.a8dMa m ySI ' prepares to produce energy N -_.s..
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sion's finding of 15 construction problems, including'.
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t i four "significant deficienc:es" for which the Arizons'
- i Public Service Co. may be fined; and allegations that
^~ records have been falsified and $1 million worth *; of P' tools buried.
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'$ i That's not the stuff to put area residents at ease about the first nuclear plant in the state.
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. .. s Assurances by APS that the 3,810-megawatt plant M7'.y ja. ,[n.cG5;&;:s.ggg% ... NT$, - will be safe and the prc,blems fixed apparently aren't kG.~ . .::%d soothing. ~
&ms n , 5. m N ws ... . _ <, Almost half of the 601 people surveyed for the t.@~lM9,,. " Report Card" are dissatisfied or very dissatisfied with
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.< . .n u w 'ZM T m e A the quality of the plant's construction. There are more
.. 9. ' * - ~ " - - than twice as many dissatisfled people as satisfied PeoPIe.
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. . . , percent are satisfied. The n -.t have no opinion.
l p .n e.Y ~i . C, . ,- : ~ '. % q;;;. ; ,- . Only one question on Palo Verde was asked: the level of satisfaction with the quality of construction at the
. apart. But they've got to get it into operatio, plant. .,
I before.w-.e know if it's safe or not . . . Every piec.- ._ _ __ - -.. - --.. - Ed Van Brunt, APS vice president in charge of the
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~4 ~ h .'t c~ A-f Isalo. Verde nuclear plant a ' mistake., .S.RP, A.PS:ailmit'~
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C Top managers blame political climite, miscalculations , myJoess syasos , eseseas assises misse should have twen builtinstead. nuclear plant today,"P6 ster eeld. Program officiele, seying the appeared b (auclear) technology DeMichele, contacted late Frl- was sound. & estimates were that
~" .h decwien to build the Pelo sweting was intended to be private, day, said that he agreed with costs would be hig
' has Verde Nuclear Generating Station ordered a reporter to leave the Pfister*e cornmente regarding the plant, and the f turned out to be a mistake, the session eher me identified himself controvessielplant.
. chief esecutive onicers of two in asking a question. reistively low, so the capital coste 1 Arinone utilities sold Friday. "As I recall," DeMichele'seid, i Pfister's statement wee made "what he (%ter) said wee that if for fuel and operating would pro-
' ' The essertion first was made by during V vide s ' bust ber' cost. Wt's b f
m Jack Pfister, Salt River Project Energy Day IAndership's 1985 he had the benefit of perfect 20-30 final cost es it goes off the ' em, ettended by hindsight, we would not have gone transminaion lines of the power 4 general aseneger,in Valley landership en address clase. lt leter wee Center. tome di people et the Valley Bank into it. That's absolutely correct. plant,"Nier said. - a=== dad by Mark DeMichele, pres- year, brings rara, in its sixth But his point la that we did gointo . "N bust.ber cost is very com-ident and ch*ef operating officer for munity leaderertopotentielcom-identif sad it and now we have to complete.it. petitive with cool, particularly with Arianne Public Service, . .s the retcheting:Ahet was going en discuss Valley problems and solu- It's . that simple."d'A.mid DeMiciale e .that in . with weather end. air-qu
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. APS la in charge of overseeing lions. . ..
Eter said that because of the reporting Eter's comesente,'m quire,mente for the coal-fired theconstructionof theplent. t* . In his address, Pfister said,"IfI. accident in 1979 et the Three Mile Republic had viola,ted a 7-year-old plants. And, fineDy,one of the very agreement betwesIn the newspaper attractave features of nuclear power Jack pneter knewnoinchance there's 1973I would whathave I know now, Island Pennsylvania, " nuclear nuclear-power power hee imente made plant in and Valley Leadership that coen-in the was that it h p.ir " in Pelo Verde.1 wish it fellen from gracein this country." ' tion's en the environonent.
*mber poiser ene issen kom wenn't'tlere." cimenes were not for attri -.
"Yes, there wee radioactive weste gece a3 #as couney " "No utiht executive in hie right fTi In his remerke, Pruter asid, .being_pyeduesd.in_the fuel cycle,_
. i. He added that a coal-fired plant, __piind, _ . . commit to e new, " Going back to the eerly 1970s,it, . )c
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Saturday, March 2,1935 Mistake d' '" " -""-=' . Continuedfrom AJ Reliability, a major issue with any power plant, was another but the res in the era felt that factor, he added. -
' Euld be re , t y didn *0thr, unite nee being sold by understand the political implica. ambustion hnunng, so we tions of technological problems,. would be the ninth or 10th unit of Pfister said this size and model to go on line, The SRP owns 23.1 and we thought we could,larn by the nuclear plant,50 mibreent west of of the technological evolution that downtown Phoenix. Arizona Public comm ebout.
Service Co. owns 29.1 percent; El Paso Electric Co. owns 15.8 percent; " Interestingly enough, those' ' Southern California Edison Co, other units were conceled, so Palo 15.8 percent; Public Service Cc6 of Verde is the first of this model to* New hierico,10.2 percent; and come on line,"Pfister uid. Southun California Public Power "But in 1973, when we made the Authority,5.91 percent. commitment,itlooked to us that we Unit I of h triple-reactor plant would be usmr an esperienced has completed fuel loading and is product rather than the state of.- i expected to be operating at 100 the. ort product that we find our. percent capacity by the last quarter selves with. , of this year. Unit 2 is espected to be *Well,SRP and APS had a lot of operational next year, with Unit 3 a competition as to who would be year later. _ project manager and operating . The 89.3. billion plant will be the agent for the Palo Vude plant. And biggest nuclest facility in the nation guess who lost? APS,"Pfister said. and the second largest in the world. APS got thejob. The lugest is just outside 14nin- Pfistu later mid, But with grad in the Soviet Union. . ,20 20 hindsight,ifonlyIhad known Pfistu said, "Anothu remon in 1973 what I know now, I never
'SRP and APS were intuated in. would have participated in Palo nuclear power was that in the Verde. There's just no doubt about period from 1960 to 1973, we were it. But I can't go back and make growing at a rate of 11 percent that decision. Palo Verde is there,
. annually. Our projections suggested its first unit is 100 percent com.
that growth would go on indefi. plete. We've spent over $4.5 billion
. nitely. - in the ground out there already. It~
"So we began an aggressive needs to be completed. I wish it
- campaign of additional coal fired wenn't there,I really do, but there's units. We were really concerned nothing I can do to push it away."
that perhaps we wouldn't meet the In answering a question from his load (demand) u it developed in audience, he stated that in hind. the area." sight, he would prefu "a large, That was the environment in cos!. fired generstmg station" in 1973 when APS and SRP made the Place of Palo Verde. jdecision to build three 1,270-mega.. Pnatt nuclear units, "Then the 0973) Arab oil em.' bargo esme and completely changed "Why did we make that deci- the dynamics in the electric-utihty sion? First of all, we had a water business "Pfister said. supply, and water is a key ingredi. ent in the generation of electricity. "We had thought before that One obvious water supply is the electricity price was inelastic. Peo. i ef0uent that comes from the 91st P e would contmue to use electricity Avenue sewage-treatment plant, no matter what the prece. %e found and SRP and APS felt that would that concept was in error. be an ideal water supply for a "Just like any other product in nuclear plant," Pfister said. society, electricity does have price "It was an excellent site out elasticity, and when prices go up, there, from the geological stand. demand begins to go down," the
- point. This area generally is a low SRP officialsaid.
i area for earthquakes." As a result of energy price "Another major reason for select. Increases due to the oil embargo ing Palo Verde was'the economics. Pfister said, "our customers started All the studies that APS and SRP using less, and we went from a load did at that time clearly demon. g owth of more than 11 percent to strated the choice was nuclear oneoflees than5 percent." power. It was far more economical "Until 1979, things were looking than cost. fired generation, and the rond, until the accident at Thru prices were for more predictable at hfile Island. That was, I believe, the that time than coal because of the turning point in environments 1" controversy, partic. of nuclear he said.power,"public acceptance
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A 16. - - - -
;- ~ THURSDAY; MARCH 28.1985~
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Editorials .. ' m
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a ,,nso. o w,. a..w m 4p>.n mewi Officials at the Palo..n.. Verde Nuclear? because.t he water not radioactive and 1 Generating Station and the U.S. Nuclear - simply would seep'badkinto the ponds.9] Regulatory Commission ~ seem to have a - i rather cavalier attitude about more defects ~"We "We're say it'si not plannin'g *'to'fix a non-problem."f
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that have been discovered 3 . at the f.acility. '-
.. The object of piping is to 'c"ontain and The latest problem involves leaking move liquid. No reputable Valley plumber welds in a backup cooling system, which could get away with leaving ~ leaks in an ' ~
may delay the scheduled May start-up of . installation. And this so-cafled S. . Unit 1. Eighty percent of the welds on non-problem - the latest'of many l stainless steel pipes in Units 1 and 2 are- . problems, some much more serious, has 1 pitting and corroding, according to occurre'd at a triple-reactor nuclear olant )
- Arizona Nuclear Power Pro lect officials. , whose latest cost estimate is $9.3 bl# ion. /
Some of the corroded welds according to .The non-problem may continue and ' ' l an NRC memo of March 11,have s
.! worsen, inasmuch as engineers suspect 1 developed leaks. Palo Verde officials ; -
that a microorganism is attacking pipe
, disclosed the corrosion problem in a welds. -
4-
' recent newsletter but made no mentiori of No problems, of whateve'r magnitude the leaks * ..
i can be tolerated at Palo Verde. It should . Brad Parker a spok'esman for the nuclear go on-line in as perfect a condition as I project, said tbe pipes might not need engineers and competent craftsmen can I
. replacing. - even if,they are leaking ~. ...- ..:.make it.. ...
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l l January 3, 1984 Arisona Nuclear Power Project '. P. O. Box Phoenir, 21666 Arizona - Mail Station 3003 85036 '
~.
Attention: Mr. Edwin E. Van Brunt, Jr. 4 AFS Vice President, ANFP Project Director -
Subject:
Arizona Nuclear Power Project - ' Bechtel Job 10407 Bechtel Action Items Regarding Corrosion Fiping Protection of Euried
- Filer E.16.05 Reference (A) Letter 3/AKPP-E-109836, Dece=ber 12, 1983V (B)
( Letter B/ANPP-E-40378, February 7,1979 - *
Dear Mr. Yao Brunt:
Our response to action items described in Conference Notes No [ Reference (A)] is summarized below. . CN-E-1405 1 Notes ites numbers.) (Ites numbers refer to Conference . Ites 3.1 We have verified that the proposed locations of additional anode beds, the location of the low level radwaste storage facilityre
, as shown on APS Drawing No. A0-A-RSS-A01, Revision.0, dated November 15
_ onsite_LI.1V_ 5tB~ ease _Jaci11ty-Flat-F22n) . - - _,1983, (Interin - Item 3 2 I i February 7, 1979, [Raference (5)].Three soils samples e er of were ana !- .eenacituents in the water extract sample. Ammonia was not listed as one of the In gaaeral, esmonia compounds esitive soil Tapidly as free in aerated soil to form nitrates and are uot retained ammonia. e in th ! corrosive to copper.) Also, (Free weammonia would notin high concentrations could be. br prodnets, in the soil saspies as the " farmland" that was used fexpect
.which hack. wasfillremoved en theprior
.aita.did to use as .aot or pipeline include the.f tree twa to. three . feet backfill.
(, \ i A cC,7. t
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' Mr. Edwin E. Vcn Brust , Jr. '
'Fago 2 ,
( . Januagy 3, 1984 . . Itan B.11 A list units three of allispipe isolating flanges installed, or to be installed enclosed. The list , for the - drawing of number and drawing coordinates to assist in the the flanges. physical loi cation Ites 3.14 We are not avere of~ aany ' lternate ' feasible methods available in th technology to verify in situ external pipe wall thickness of buri de current e piping. An inspection service is available (AMF Tuboscope of Houston) ces which u - a sognented through pipelinebef the pipeline " pig" which, with pressure from flowing fluid , travels og monitored. The " pig
- carries an electrosagnetic sensor pipe which surface. provides a magnetic flux over the entire 360* internal / externa Deviations in wall thickness, such as corrosion pits, can be recorded ing between internal for the andtotal externalinternalletternsi defects. thicknessdistinguish-without to pick up anor.altes where the depth of the defectThis device would not be able the disseter. Also, this device is not yet is greater than four times
( available on the market for pipes less than six inches in diameter. temporarily added to the piping systems to allow insertion and reSpecia the " pig
- from the piping. seval of Another service (Corrosion Logging Service, Lafayette, Louisiana) is measuring piping electrical resistivity to ground.available to che It would not be able to monitor together or the oneexternal above the coating other. protection of seversi pipes install ed close need to identify areas of defective costing on buried piping for future be determined by exesvation and visual inspection. yinspectio T Se belle've-tI[st7he~ current ~ _ _ _ _ -
highly corrosive areas in the soil will provide a basis for de the need for any additions 1 sonitoring or test nians. Hydrotesting can always be performed to verify adequacy of pipe wall thickness for excavat d areas where some surface corrosion may have occurred. e gf ( . 9-
r~ -.
' 'Mr. Ydvin E. Van Brunt, Jr. .
( Page 3 Janus'ry 3, 1984 -
~ ~
Item B.15 There chesteals areinnothe Bechtel soil. standards regardin5 limit of concentrations ous for vari - Civil / Structural engineering codes regarding such limits.Also, we hav standards refer to *ensincered" requirements and relate to physicalIndustry vide' - characteristics particle size, etc. of the soil, such as bearing pressure, compaction, den , Verde site, are acceptable for use in engineered backfills. Soils high Ites C.1 . Inclosed is a copy of a paper presented at the Nations 1 Association of Corrosion Engineers meeting in April, 1943. The
- state of the art" of -
aterobiological presented. influenced corrosion (MIC) of industrial alloys is The general conclusions of .the paper indicate that, although . ""
"MIC
, extent of several classes of alloys is well documented - - - - - data on the 1argelyofunevailable.'
the MIC probles relative to corrosion problems in general are .J (
-Action
.for the Palo Ites B.3 (cathodic Verde Projectproceetion schedule), and Iten B.10 (rationale in separate correspondence. cathodic protection design) will be addressed and Iten 8.13 (coat and. wrapAction Items 5.8 (isolating flange jumpers) balance of stainless steel piping) are in progress.
Please advise if additional information and/or clariflestion is required. Very truly yours, BECHTEL POVER COR80 RATION _ l _. __ _ ~ _, _
- - Oriinal 5:gned By bu.u .
W.T witscN
- v. n. Wilson Project bbnager Los Angeles Power Division RNC:1rw ... ,
Inclosurer (1) List of Piping Systess Isolating Flanges (1 page, & copies) (2) Microbiologically Influenced Corrosion of Industrial Alleys (RACE technical paper) (8 pages, & copies)
F e * * ( ' APER NUMBER L [ e
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' The International Corresten Forum Sponsored b the :i .: . .
Y - Notlanal Asseelation of Corresten Engineers - Anaheim Conventlan center, Anaheim, Calliernie ~ ' =
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- April 18 22, l183 '
MICR05101.0GICA1.1.Y IhT1,UE.NCED CORICSION OF INDUSTRIAI, AI. LO by . l David .T. 2 I Arland R. Johannes Duquette 3, Peter ,3 C. VaynerDaniel * [, H. Po Depart2 =ent of Biology and Tresh Water Institute,
. 3 Department of Materials Engineering. _.
Depart =ent of Chemical and Environnental Engineering Rensselaer Polytechnic Institute Troy, N.Y. 12181 , ABSTRACT A =ultidisciplinary group of scientists at Rensselaer Polytechnic Institute was asked by the Materials T chnology Institute of the Chemical Process Industries to survey the available literature on Microbiological Influenced ( Corrosion (MIC) and to repor their findings relative to the evidence for ' MIC of iron and mild steels, stainless steels, copper alloys, alu=.inu= and its aluminun alloys, nickel-chrome alloys, and titanium. Turther the group vas asked to report the state of the infornation relating to the mechanis (s) whereby MIC of each caterial occurs, methods of prevention and =ethods of detection in the laboratory and in the field. develop a list of priority areas for research. Finally, they were asked to except The nickel-chro=e group found evidence and titanium. in the literature for MIC of all alloy groups unknown. generally available. Protection from MIC and reliable methods of detecting it are no herein. Details and suggested research areas are discussed i l IhTRODUCTION The purpose of this paper is to present the findings of a multidisciplinary ! study grous constituted by the Materiala Technology Institute of the Che=1 cal Procesc cally influenr Industries ed corresten to evaluate OfIC).the state of the art with regard to r.icrobiologi-This group vas ashd to stud" the available licerature the question: and to vrite an interpretative doctnent which atte=pted to ansvar
'- MIC, of any kind, oc:urs in various metals andThe alloys?Is there suf ficient alloys of interest
- includ-d the r:ild steels,'stainlesa steels copper.alleya, e alu=inum and (
alu.inum alloys, nickel alloys and titanium. . , ( In cases where the ansver was l in the be evaluatedaffirmative withthe available regard to the infor=ation folleving: for each group of alloys was to e Pubne,% t',he p,e = g.,eg i.rge r g as w* e6D' CC' D =l " 9 Mass Cw'%er's t NAQ .g
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. a.
What are the physical _.and chemical conditions under ' ' ' ' which the MIC of a particular type of alloy occurs? b. Which type (s) of organisms are involved? c. What is the mechanism (s) whereby MIC occurs? d.
,e
{ What methods can be used to detect MIC in the laboratory? .
- e. '
wa _) What methods can be used in the field to detect MIC7 - f '. - What methods can be used to prevent MIC?
. g.
What research needs to be done?
- Finally, the group was asked to evaluate the general MIC' situation and make recommendations as to what research area (,s) should best advance receive thethe most attention understanding in prevalence, of the the near future in order to causes, detection and control of MIC.
GE!!IRAL REMARKS REGARDI?;G ~iE . LITERATURE USED: There is a good deal of literature on M!C. However much of it deals with reports of case histories, or observatiens incidental the physical, to the main study, with poor documentation regarding under which it eccurred.andchemical especially microbiological conditions It should be noted that usually the f ault of the observer since verv few qualifiedthis was notq environmental micr: biologists or corrosion experts have addressed the=sclves to the questions of MIC. Furthermore the.s techniques for derling with many of the organisms involved have been adapted primarily from the area of clinical microbiology and are, in many cases, not adequate for dealing with the a organisms involved in MIC, their isolation, growth, identifica:icn _o_r c an evalua:Len-of-their role (,s) in the
- l -ec~rrosion-precesstes-)r A sty.ifrcant portion of the literature -
was available only in foreign languages . Much of this literature was not used directly in writing the report since it was possible to establish an adequate case for MIC of most alloys from the available English language literature. It should be noted however that available, one in French there are at (1) and oneleast two excellent in Swedish (2). reviews There are also several English language review articles and books available which deal with MIC in a variety of ways. Reviews by Miller and Tiller (3) and Iverson (4) and Booth and i' Worsw=11.(5) especially helpful. and books.by McCoy.(6).and Postgate (7) were - A inrge percentage of the available literature deals with the area of corrosion of irens and steels by anaerchic, sulfate - reducing bacteria, and spana a long pe. icd of time in which many n
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(' different techniques were used. the area in which controversy still persists. the- most is known but also the aIt represents therefor Monal and titanium, received'the most attention e.g., herein. v F literature. Therefore the conclusions reachedn by the pre study on limited group data, forand these the dangers alloys should be recognized as being inherent, ased b - in such, realized. to evaluate the " state of the art" with regard y was to MIC and not to ' produce an exhaustive compendium of available literature . The rest of this article will be a summary of the findin gs of the each major study element. group. Finally, These are presented by alloy grouping for - group -regarding MIC research priorities are presentedthe general co . IXAMPLES OF MICRC3ICLCCICAL CCRRCSICN , a brief description of the cases to give the reader a 4 idea of what will be discussed below. gee.eral remarks regarding the characteristics of microorganisms as they relate to MIC. k
- 1. They are small, .
hundred micrometers(um) (fromin less than length bytwo-tenths up to twoto orseveral three um in width), penetrate crevices, etc., easily. a quality which allows them to 2. They may be motile which aids in migrating to more I favorable conditions conditions, e.g., or away from less favorable toxic materials. toward food sources or away from 3.
, _ _ They have specific receptors for certain che=icals which-all-owsntherto_ seek _ cut higher concentrations 3T'those substances which may represent It is very important especially c qanic to understand that nutrients, food sources.
nutrier.:s, supply in most are generally in short surfaces, including aquatic metals, environments; but that adsorb these materials, creating seek out areas of relative plenty. Organisms able to have a distinct advantage in suen environments.and
- 4. .
They -10.to leas: can withstand 99'C) pH, a wide rance ci temperatures, concentra:: ens (0 to almost(about .O .- 10.5) and . oxygen (atl (-
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- ( ' 10C% 02 atmospheres). -
'5.
They can grew in the fcrm of colonies which helps to cross-feed survival ofthe at least individu11s in the colony and make the .. some members of the " colony"
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' more likely under adverse conditions. 6. They produce enormous nu=h'ers of individuals in a short time (generation times of only 18 minutes are known), thus allowing them under favorable circumstances environment. to " bloom" and quickly "take over" an 7. by~ wind and water,The individuals can be widely and qui animals, aircraft, etc. and thus to reach more favorable environments is good 8. Many can quickly adapt to use a wide variety of i different food sources. For example Pseudemonas _ fluorescens can use well over 100 different compounds as sole sources of carbon and energy, including sugars, lipids, alcohols, phenols, etc. This give them tremendous advantages in aorganic acids, constantly changing environment. ' 9. Many can form
'(capsules or slime extracellular layers) polysaccharide materials are widely.
transfer, fluidrecognized movement, as causing problems in heatwhich, wher MIC can occur. and in creating sites where - organisms and debris (food),The slimes are sticky and trap _ ' resis:'the penetration of seme. toxicants (e.g., biocides) or other materials (corrosion inhibitors) source of the nutrients (the bulk fluid)and and the hold the c It also means thatsurface toward which these materials are diffusing to' lower concentrations of certain nutrients,the organisms since although in low concentratien, t; ey will be moving bv (not along with) always present to atthe cells and are therefore almost least a minimal level. The presence of the microbia_1 fi1= ultimately may lead to ~
--~'Eeat transfer,-macrofoultChirhicles. -etc) which can s al' o affect sites. fluid flow and. provide corrosion 10.
They temperatureproduce spores which are very resistant to hour), acids, (some even resist boiling for over 1 freezing, alcohols, disinfectants, drying, may:last and many other adverse conditions. These finding favorable conditions.for hundreds of years and then germin
- 11. ~
They are resistant
-disinfectants, etc.) by virtue of to many chemicals (antibiotics, '
' hair ability to
. degrade slime, . hem or by being inpenetrable to them (due to cell wall or cell me=trane characteristics).
be easily acquired by mutation or acquisition of k
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. ( ! plasmid exchange .(essentially between cells, by i.e., naturally occurring genetic the wild). 4 genetic engineering in . 12. Many species produce a wide variety of organic c s 'a id e.g., formic, accelerate corrosion of many types of metalssuccinic, w
- 13. .
Some species, produce mineral acids (e.g .,
. Thiobacillus are extremely thicoxidang, corrosive. which produces I 4 H SOc ) whi h 14.
Several bacteria metabolize NO corrosion inhibitor. Some (e.g.3, sometimes used as a reduce it to N 2 gas which leaves the system. Th, Pseudemonas ~ will do the same to NO3. Other organisms conver:ey to NOi. NO3 (Nitrosemonas) (N recaeter) oxidize NH to Noj, and 3 rs then othe 15. oxidize the Noi to No). Many acids. organisms form NH 3 drom the metabolism of amino . play 's copper a role in the corrosion of certain e.g. alloys. alloys,This 16. I ( They produce many enzymes, excreted outside the cell, and which act onsome of which may be ' substances outside the cells. One such, hydrogenase has been reported as important in the of the cathodic sites. en corros ' 17 Many organisms produce Co q and H2 as a result df their fermentative type or metabolism. Carbon dicxid e enhance such as corrosion. Hydrogen could depolariz stainless steel or may even cause t
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_ _ _ emb ri ttlemen.:. 18.
.Eny bacte ia (belonging to several geners) which nor= allysources energy use organic carbon can use H compounds as carbon and and C4 as their cerben source and live 2 gas as their energy source ,
chemoautetrephicall i carbon and energy).y (without organic sources of This could result is a depolarization of the cathodic sites on steels and' prerote corrosion. This is one of the pro
~
mechanisms whereby sulfate reducers (e.g. posed , Desulf: vibrio desulfuricans) obtain tha hydrocen ,- for sulfate r7 duction. It T i . this could promote cathodic depolari:stion andhas been sugge corrosion of the steels in anaerobic environments. ^ i 19. Some bac*eria can exidize or reduce metals or
jWy(Callionella. metallic ions directly. For example some Scheretilus).ox di e Fe.a to y..a. The
~ ferric compouncs precipitate in a sheath e under these deposits-with corrosion resultin Whether the removal of the_Fe*a directly affects the !
corrosion cl. ear,._however, of the metal that if or these not organisms is unclear."co- It is ! other such ions, accumulate" ferric or ferrous ions with chloride o Other organisms (e.g., aggressive mixtures could result. Pseudomonas spp from oil wells and bacteria from marine sediments) have been shown form. ferrous to reduce ferric iron to the more soluble It has been suqqested that this strips off the surface of mild steels, ferric ce= pounds which normally stabilize the Corrosion is thus accelerateleaving it reactive. . exidize or reduce manganese.d. Other bacteria can transformations listed above, This along with the iron . is the cause of considerable tubercle formation and subsequent fouling or occluding of pipes, and probably deposit associated corrosion by species such as the sulfate-reducing iron also transform bacteria. Many organisms which transform manganese. that It has been suggested some of these can reduce iron through the mediation of catalases and hydrogen peroxide. Yet other organisms are reported to metabolize chromium, possibly aiding in the corrosion of stainless steels. 20. They form synergistic or mutualistic co== unities with other bacteria, fungi, algae, plants and animals. The result tha: is that the co== unity can accomplish things
' 2 the individuals alone cannot perform, e.g.,
consume fungi certain 03 break down wood to organic acids and ( conditions which provides the food and anaerobic ry:i rd by n.s d f:v4h r.5, _g =q-gg---- ~ Th--(-itiec alsa ch...ge :neif scrurture, dominant , species, i etc. to meet changes in the external or internal protection for individuals, environments. The co== unity also provides e.g., or biocide sensitive organisms fromanaerobes biocides,from 02 otherwise subjected to these adverse (from the point s of view of the organism) factors. The co=munity
. therefora increases greatly the potential of microorganisms to accomplish many feats otherwise not possible, metals. among them the corrosion of many types of _
i'
-ECA32 FOR MIC CT IRCN AND MII.D STEE:.3
.Cerrosien under Anaerobi.- Conditions: . .
There is a large body of evidence that sulfa:e reducing
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(3acteria(SR3) and mild steels in anaerobic conditions (see references 3are an im 7 for detailed reviews of subject). This can occur in .
, 4, 5, underground are present einstallations where localized anaerobic conditions There are nu,mer.g., under a tubercle or under a thin biofilm. i freshwater and saline systems,ous reports of such occurrences from both genera and species of SRS's. involving a number of different The SR3',s, as a group, natural environments, including many types cf soils andare found in a great man sediments, oil and gas wells, fresh, brackish and salt waters, natural hot springs, I some insects and ruminants sulfur deposits, (sheep, cows, salt pans, guts of at least !
etc.) iron. aboutThey 5 to tolerate 9.5, temperatures from $5 to 75'Cand on corroding , hydrostatic precsures of ata wide range of osmotic ccnditions,a and pH range of ! do not grow under aerobic conditions least 1 x 105 kPa. They survive but i (7). The controversy in this area revolves around the mechanism and mild steels. (s) whereby the SR3's influence the corrosion of iren Tiller, 3; and Boeth, Several 5 groups of investigators (see Miller and that SR3's cause (or acc:elerate)for example) seem to currently believe hyd:: gen frc= cathodic sites, such corrosion by removing ( depolar::ation. resulting in cathodic
)ferm the bas:s for this proposed mechanism.The equati:ns (8) of Von Wol: ogen They are as follows:
4' Fe ' - ) 4 Fe*2 +8e-
- anodic reaction (1) 8 H 0- ) 8 H* + 8 CH- electrolytic dissociation 2
of water (2) 8 M* + 8'e* )8H cathodic reaction (3) So-a + 8_.E-
-- +S
- 2 L O -
carhbefe~~W#r Br ::::.ca (by SR3) Fe*2 , S- (4)
} Te5 corrosien product
(5) j1 Fe*2 + 6 OH-
) 3 Fe(CH)2 c rrosi n pr duct (6) lh 4 Fe
- S0-2 + 4 H,0 (f, 3 3 Fe(OH)2 + Fe5 + 2OH- )
overall reaction (7)
~~
Some workers (Booth et ai. 9) e were increased with increasing me'nh<A>riv :'ted that corrosion rates { dependent on the level of ferrout : ssy ratas and were medium. The most 't the surrounding produced to react w was h all the H 5 prcduced 2 and prevent theactive
- corrosion s
I
. L e
fermatien of a protective sulfide film. The role of the en:yme(s) hydrogenasets) which
. facilitate (s) the reactions: -
H2 ; 2H + J 2H* 2e*, whether frem SRB's or not, is not clear, since not all strains showing hydregenase activity cause corrosion, and the hydregenase levels were not always correlated with the rate of corresten (9).' Finally, Iversen (10), has reported that Desulfevibrio desulfuricans pr= duces a highly corrosive metamolle procu:: wh :h is the major factor responsible for anaerobic cerrosion of iren and mild steel by that crganism. The study grcup has concluded that: ' i. The evidence for cathodic depolarication is quite convincing
- 11. JThe
=les of hydrogenase and ferreus ien in solution are pocrly understeed iii.
The extent to which the vari =us mechanisms are cperative is dependent up:n enviren= ental c=nditiens e.g.,. levels of Fe*2, numbers and types of organisms present. iv. The metabelic produe: =echanism as prcpesed by
!versen (10) is intriguing but needs further i
documentation. . It was also c=ncluded that there are a variety of other mechanisms whereby varicus micrches could cause MIC of ir:n and
=11d steel under anaerebic conditiens, these include:
__, , _ , _ _ .,_ - - - ~ ~ - - - ~ " ~~'
- - -- 1. -- -The p.vu.ctiTM nr corresive mutacciac produ:ts such as organic or inorganic acids.
- 2. The f=rmation of icn cencentratzen cells.
'3. The production of ammenia.
4. ( 'The preventien by the very presence of the biefil=, ef cerres en inh: biters frc= reaching the areas of active cerresion. *
,~rr:sien under Aerebic Conditiers
- i t
The case of sulfuric acid produ::icn by Thi bacillus 1hi cxidzns fr== the ex:dation of elemental sulfur or recuced sulfur ::=p=unds is well established.
( The production of organic acids could have the same corrosive _ effects and could be produced by a wide variety of aerobic and facultatively anaerobic (lite with or without oxygen) cem= unities (e.g., tubercle organisms. The growth of variot.- microbes or microbial l organisms) of O and production of CO and/or their metabolic processesforming iron bacteria ( e . g. , consumption and assoc:a formktionofoxygenandionconcentrationcellsand 2 during respiration) result in the acidification of localized envircaments. form good conditions for the growth of SR3's.Indiree:1y, they also General metheds for sampling, detecting, enumerating and testing by Jope for et various al. (11).microorganisms involved in MIC are discussed fer SR3's, Specifically for the mild steels and i =n one veuld tes: by culture. microscopic (fluores:en antibody) or' bic:hemical te:hniques (identification of specific unique ccepeunds, see White, 12). Additionally one could tes: fcr the Jpresence of H 2s by chemical means. Tubercle forming organisms Q(e.g., b::: hem::al Callmeans. enella) may be identified by microsc pic or using routine tes: procedures (11). Acid producing organisms can be identified , ( Preventien cf MIC in mild steel and iren, like that of =estn other occurrence, alloys, rev=1ves primarily around trying to prevent the mierebes in.the grew:h and vicin :y metabolic of the metals. activities of MIC causing Many times this involves attempts to kill or inhibit the microbes using chemical means. t It sh=uld be stressed in this regard that many such chemicals water phase, but do a very good job of killing organisms in the bulk - are much less effe::ive in penetrating slime i (biofilms) and killing the organisms therein. The importance of g b:cfilm to the MIC processes should be apparent from the foregoing discussions. Therefore the understanding of the prc= esses whereby such film develop; their p cpe g eA _ _ _ _ __ e s pec i a H y,. i n r emrrd to 'm m r + 4 c - , i c n,-c_en: c r.; r 2 ;; a , ete: and the way in which they react with biocides and anti-cerr=sive chemicals is essential to the preventien of MIC of many types. ab=ut An=:her prevention meth=d is to cathodically pretect at
-0.95V (relative to a saturated Cu/CuSo, electrode). This has apparently been qu := successful. ,
' Coatings of a variety of types can be used, although their
- use
.. holidays. in many develop water side applicatiens is quite limited. Also, if in these. -
s :es and result in rapid Eney can beccme very active corrosien penetration. . ( A common method for prevent:ng anaerchic, SR3 related ~ ' cerrosion is to surround the pipe er other such stru::ure with materials which create an environ =en less permiss:ve of MIC. *
. m.
Such methods usually involve surrounding st with gravel or chalk to provide drainage and ructuresbetter or pipes
~
aeration. Research still needs to be done to:
. a .. develop si=ple or not the corr,osion seen is MIC related. reliable metho b.
MIC prcblem in industrial and other applicati . c. understand how biofilm fern and to develep better ways formatienof preventing is prevented, biofilms from forming. Since if prevented. several types of MIC can be d. work out the me hanisms whereby the SRS's premote understanding cures. should help lead to prevention or TEE CASE FOR MIC CF STAINLESS STEELS stainless steels wh::h inv=lves the ability ofrmmicr:be fi lms , within the withcrevice. crevices resulting, and to modify the envireneent the corrosien process.This may of ten take the form of accelerating pr:duMany ing CO, crqanisms create 0will as a result of censuming 07 and acid, beth cErr:sive to stainless steels. Many of these2 ccacentration ce are potentially corresive. organisms also produce organic acids under the manganous p;cuebly-c. m ;he Bacteria which icns to manganic oxidizes (e.g.,ferrousGa-- to ferric ions and/or,~ ~ ~ ~ c er M ~- E sti:n ei. ud m ce *-h. m : W :: r harge neutralizatien) in the region e.g., : rTs (to acheive chl= steels. ride solutions which are highly corr s:veresult in the ferm
- = stainless (see Ta:nall, This MIO 13 is of ten seen in the form of severe pitting and Kcbrin, 14). Pseud =menas spp. have in some cases been al:.hzuzh :he::assoc:,t:ed a:e::.fi: with corrosion of stainless steels ,
general bicfoulf.ng is ye:r:las, havend slime 1 rmation .1=d Clestridium. Flavebacter:umto be defined. Species of Aer: bacter. Desulf ::maculum nave Bacillus. Desulfovibrio end ass ==:atec w :n.ccrrosien depes:ts on sta:nless steel (J Gals 5t ecker pers nal cammunication and Ta:nall , 13). i ferman; a sli.te l=v. er, rroduceAs eentioned above it is qu:
. , bye certain that
! normally pahs:ve f:Im damaged by mechan: cal means or througha .
( halide attack go unrepa: red perhaps due to the consumption of s environment from reaching the interior of the crevice. oxy Another consequence of the oxygen depletion is the growth of the the SR3'son section inmild crevices steels. resulting in cerrosion as described in apparentAnother possible corrosion mechanism is through the of Fe*zfre.s ability of certain microbes to fix the redox potential and/or Mn*2/Mn** at the metal surface. They may j therefere polarise the surfaces of the metal to a potential at which Fe*3 or Mn** exists. The resultan: FeCl 3 and MnC14 selutiens are as discussed above, very aggressive to stainless steels are much like those for mild steel (see which research is needed, above). ste Areas in i fer ir=n and mild steels, n addition to those already described pass:ve films, include studies on the stability ei especially in the presence of organic acids. The , rcle ef Gallienella in the corrosion of stainless steels, should 1 he examine = :n =cre detail. The abilit { electrechemical cenditi ns seems espec:y of intriguing ally organismsand to fix pe ent: ally very imp =rtant. s'i I I, !.u.I CASI FOR MIC CF ALUMINUM A!O ALUMIIMM ALLCYS The study crcup has concluded that aluminum er :s alloys was demonstrated in almostaccelerated attack ef tes all of the thesesystems materials. in wh:ch microorganisms have been tested for MIC cf This has included almost all tests of the these materials. This may indicateabili :es of pure cultures of bacteria a susceptible to MIC. that aluminum is very . The best are those studied cases of MIC of alu=inum and its alloys involving fuel-water two phase systems in aluminum . a l l = y f u e l t a nk s . A t t a c k c an o c c u r u_n,d e r, a e r e.b: e e,r.ma e rs:. c.-- condit:cns acs unmy' r# ee 5 :::: - .
- pnase) and at ef the re d (water I the fuel-water interphase. Colonies or mars of the
! organisms can of ten be cbserved on the metal surf ace. In some buhtles were evolved. cases volcano-like tubercles have been observed frem which - include Crganic=s (15, 16)shown to be involved in MIC in these ceses i Bacter:a 4
,Funei .
Pseucemenas aerucinesa
- Aerecacter aerosenes Pen:e:11:um luteum . ". -
Clostridium scecies v.A st e r:211us-fisvus ( . Desulfov lo oesulfuritans
, 5;;ccria soecies M__i crececcus ceccle s F. rmecendrum hordei 5=naero::1us natans Cl ac=seerium species _ , , ~ - - . - - - - , . - - - - , , . . . . . , . . _ . - - . . ,..n- , . _ , ,, ,,_ .,.,_., - ,.-, ,_.-n,-- ,-,---- -- _ .--,., ---. - . _ , - - - - _ . , . . - - , ,
*=
Corrosion of aluminum alloys in single phase aqueous D systems has not b.een studied nearly so exhaustively. However Tiller ,and Booth (17) did show that several SRB cultures , accelerated the corrosion rate by 3-100 times the rate -found in sterile medium. acceleration Willingham and Quinby (18) showed a similar of weight
' systems.
'rather Corrosion in both these tests was of the pitting type than the generalized type observed with ir cultures. on in the same
' "five'pYiNarymechanismshav aluminum which support and its it; alloys occurs (e been preposed whereby MIC of 19). Each has research results seen in different environments.and each may play a role in the overall MIC These are:
(1) Depletion of natural inhibitors (2) Production of corrosive compounds
~ ~
(3~)~~ (4) Cathodic Creation of oxygen and/or ion concentration cells
~depolari:ation (5) Extracellular alloy constituents. en:y=e activity and metaboli:ation of 1
Identification in the laboratory and field may initially involve the ebservation of volcano-like tuber:les and/or pi :ing cultivatienassociated cerrosion and identification with microbial of the colonies organisms or =ats. Sampling, involved is ac::=plished by methods discussed above sectica above and 11). (see iron and mild steel Prevention of MIC of aluminum and aluminum alleys should invelve In addition, better handling procedures for fuels and fuel additives . effectively penetrate colonies,as discussed above, biocidal compounds to able developed. tubercios, and slimes must be the mechanisms involved.Research should concentrate on prevention and definiti l _ , .,_, _ . - - ~ - ~ - - - - ~~ GsE-FCEiMO-CE Gwr:.R ALbY3 than for steels or aluminum.The case for MIC of copper alloys is more poorly d This may be, in part, a reflection formed by cepper alloy corrosion to be lethaliftonot most,of the all, microorganisms (20). This is now known to be exampic Thiebseillus thicoxidans can withstand c=pper erroneous. For concentra:lons as high as 2% (21). l i I
. The study group has concluded that MIC of at least some ,
copper of :opper alloysalleys, does occur..In most reported cases of presumed MIC or :n=er=les ( see Grout pitting was observed under microbial colonies et al., 22; Bengough and May, 23;
- t 1
Rogers, corrosion in one test 24). The addition of nutrients accelerated such with 2 to 10 times the nor:al rate being . i 1
. . . . . - . . . ..-,...:.-... - _ . - - . . . ~ . - . - . . . - _ _ - . . , - --,
....,*:r 1
t
-. + ,
l
-... l
. j)
. observed corrosion than (24)purewhile mixed cultures appeared to cause more cultures (8). ere sev copperSeveral alloys.mechanisms have been proposed to explain M5C of m.
Through CO 2 , H25, the production of corrosive substances e g., NH3 , organic or inorganic acids. . b. Through the production,'tur microbes, (e.g. disulfide) which act of metabolites catalysts of corrosion reactions.as depolarizers or .
. c.
Through sulfur ce=the microbial metabolic transformation of pounds, and disulfides. anaerobically, producing mercaptans were not of ten associated with corrosion preblems heat (, begantransfer (during problems) which H25,whereas when decomposition processes pr:blems were observed. NH3 , CO2 are produced) corrosion. g
-pipe installati:ns,SR3's were shown to corrode copper alloys in underground L is pr:pesed : hat probably through the production of H,5. It on the surface of the metal, which is more neble than thethis o ordinary-film However, subsequen: fcund in the sulfide centaining environments breaks in the film would expose areas w.
pi:::nq or stress corrosion cracking might occur, with the here 1 sulfide film acting as the site of the cathodic reaction. Methods for the detection and isolation of organisms for suspected MIC of copper alloys follow the same general procedures as that outlined for MIC of iron ,and; sieels (see.,- ~--- ~ abeva) . _ca r-e--shou 1.1 ic -tahrkm ever to exclude apper cm the rni.ial isolation c=pper resistantmedia, strains unless of microbes. one is looking specifically for must include the development of new means of dispers
-and/or. preventing their formation.
Water treatment feasible, under certain circumstances.to remove sulfur compounds and maybe help, means . Researchof detection, needed again and involves the . development of.better prevention, I I. mechanisms whereby it occurs. as well as defining the T9E CASE FOR NICr.IL-CHROMIUM ALLOYS AND TITANIUM available No cases literature. couldAll betrials madereported for MICto ofdate theseindicate materials thatfrom the
saey aja resistant to the types of MIC fcmiliar to tha 3 ocientific cnd engineering communitics ct th2 prestnt timm. GENERAL CONCLUSIONS ! MIC of several different classes of alloys is well documented, defined. whereas the specific mechanisms for most are poorly least some. The sulfate reducing bacteria seem to be involved in at form of MIC of most of these alloys. It is also obvious that the formation of colonies, slimes, mats and . tubercles on the surface is a major fact contributing to MIC of most alloys, whether by production of oxygen and ion concentration cells, cathodic depolarization, acid production and concentration under the film, by halide accumulation, by direct metal transformation by the organisms or some other mechanism. It is also apparent that few good simple methods are available for the reliable confirmation of suspected MIC in the field. Methods for " curing" or preventing MIC, short of replacement with more resistant alloys seem largely unavailable. Data on the extent of the MIC problem relative to corrosion problems in general are largely unavailable. The areas for
" technological" andresearch needed f all into two main categories
" scientific". The former being those practical approaches prevent MIC. The required to identify, correct, and/or
- latter being a description of the specific
' mechanisms chemicals, etc.) involved and the to combat development of new means (alloys, MIC.
LITERATURE CITED
- 1. Chantereau, J.
Techniques1980. Corrosion Bacterienne et Documentation, 1980. 2nd ed. Paris:
- 2. Kucera, Vladimir. 1980. Microbiological Corrosion - A literature survey. Swedish Corrosion Institute, Stockholm.
- 3. Miller, J.D.A. and A.K. Tiller. 1970. In Microbial Aspects of Metallurgy (J.D.A. Miller, ed.) Elsevler, New York.
- 4. Iverson, W.P.
1974. Nielands, ed.) In Microbial Academic Iron Press, Metabolism. New York. (J.B.
- 5. Booth, G.H. and F. Wormvell. 1962. In First International Congress on Metallic Corrosion, London, Butterworth, London.
- 6. McCoy, J.W. 1980. Microbiology of Cooling Water. Chemical Pub. Co. New York.
- 7. Postgate, J.R. 1979. The Sulfate Reducing Bacteria.
Cambridge University Press. Cambridge.
- 8. Wolzogen Kuhr, C.A.H. Von and Van der Vlugt, L.S. 1934.
Water, Den Haag, 18, 147-165.
- 9. Boeth. G.H., F.M. Shinn, O.E. Wakerley. 1964. :n Comrier rendus du Cengres :nternal:enal de la Cerresion Marine et des Sallsrures, Cannes. Taris. C.R.E.C.
247/14 I l T. - - --
A 10. Iverson, W.P. 1982. 21st Annual Conference of % Metallurgists. p. 345. i 11. Pope, D.H. 1982. Natl. Assoc. Corr. Eng. Corrosion /82. Paper No. 23.
- /~
- 12. White, D. 1982. Natl. Assoc. Corr. Eng. Corrosion /82. Paper No. 55.
'I
- 13. Tatnall, R.E. 1981. Mater. Perf. 20, 41-51.
, 14. Kobrin, G. 1976. Mater. Perf. M , 38-43.
- 15. Churcl&ill, A.V. Matis. Prot. June (1963) p. 19.
.16. Hedrick, H.G. Matls. Prot. Jan. (1970) p. 27.
- 17. Tiller & Booth Corro. Sci. 8 p. 549 (1968).
I
- 18. Willingham & Quinby Dev. Ind. Microbiol. (1970) M p. 278.
- 19. Hedrick, Crum, Reynolds & Culver. Elec. Tech #3-4 (1967) p.
. 75.
- 20. Leidheiser, H., Jr. 1971. The Corrosion of Copper, Tin and Their Alloys. Wiley, New York.
- 21. Booth, G.H. and S.T. Mercer. 1962. Nature, Lond. 199: 622.
- 22. Grant, R., E. Bate, and W.H. Meyers. 1921. Inst. Eng.
Australia, Sidney Div. Paper No. 8.
- 23. Bengough, G.D. and R. May. 1924. J. Inst. Metals. M: 81.
- 24. Rogers, T.H. 1948. J. Instit. of Metals. 75: 19-38. ;
y.,e ' T,w ~4 -
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Fig. 2 - Open " gouging" a- i ien : "hi 4 . U l).'yd', f type corrosion of 304
. => .i i 1.! N;.. '
stainless steel flange. i- #5. O '. ! i '.' $ j ! - This occurred unger s1Ime
.- [b
. s u.
i.; s.i gA f;(::*. 9.. ya - >
. deposits harboring Desulfovibrio sulfate
, ',g' . , .g reducing bacteria.
l
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Fig. 1 - Rust colored vertical , {,]',, ' '
- streaks and pitting along weld i .,;, ,k i
l : ear in 304 stainless steel tank. h.
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MTl PUBLICATION NO.13 i
'MICROBIOLOGICALLY INFLUENCED CORROSION:
A STATE OFTHE ART REVIEW by Daniel H. Pope David Duquette Peter C. Wayner, Jr. O Arland H. Johannes Rensselaer Polytechnic Institute Troy, New York June,1984 Copyright C 1984
, by the Materials Technology Institute of the Chemical Process Industries, Inc.
, .. m .
,- q TABLE OF CONTENTS
~~/ FOREWORD V GLOSSARY . . v11
SUMMARY
. . . xi CHAPTER l-INTRODUCTION ,. 1 General Remarks regarding the Literature Used 1 Examples of Microbiological Corrosion . . 3 -
CHAPTER 2-CORROSION: EXPLANATIONS INVOLVING MICROORGANISMS . . . 6 Introduction . . 6 The Algae . . 6 The Fungi (yeasts and molds) . . 8 The Protozoans . . 10 The Bacteria . . . . 10 CHAPTER 3-THE CASE FOR MICROBIOLOGICALLY INFLUENCED CORROSION OF IRON AND STEEL . . ... . .. 21 f Introduction . . . . . .. 21 ~ Microorganisms involved in Microbiologically Influenced Corrosion of Mild Steel . . ... . 22 Physical and Chemical Conditions under which Microbiologically Influenced Corrosion of D Iron and Steel Occurs . ... 24 Mechanisms involved in Microbiologically 25
~
Influenced Corrosion of Iron and Mild Steel . Methods of Detecting Microbiologically Influenced Corrosion of Iron and Steelin the Laboratory . 30' Methods of Detecting Microbiologically Influenced f Corrosion of Iron and Steelin the Field . .. 32 Methods for Controlling Microbiologically Influenced Corrosion of Iron and Steel 34 Research needed in the Area of Microbiologically Influenced Corrosion of Iron and Steel . . 37 CHAPTER 4-THE CASE FOR MICROBIOLOGICALLY INFLUENCED CORROSION OF STAINLESS STEELS , . . 39 Introduction . .. . . 39 Microorganisms involved in Microbiologically Influenced Corrosion of Stainless Steels . . 40 Mechanisms involved in Microbiological 1y Influenced Corrosion of Stainless Steels . 42 Methods of Detecting Microbiological 1y Influenced Corrosion of Stainless Steels in the Laboratory and in the Field . . .. . . 44 Methods for Control of Microbiologically Influenced Corrosion of Stainless Steels 44 Research needed in the Area of Microbiologically Influenced Corrosion of Stainless Steels 45 111
,. st. . i-CHAPTER 5-THE CASE FOR MICROBIOLOGICALLY INFLUENCED CORROSION OF ALUMINUM ANDITS ALLOYS . . . 46 Introduction . . ... . 46 Corrosion in Two-Phase Fuel. Water Systems . . . 48 Corrosion in Single-Phase Aqueous Systems . .. 50 Mechanism (s) of Microbiologically Influenced Corrosionof Aluminum Alloys . ... . . .. 50 Identification of Microbiological 1y Influenced Corrosion of Aluminum . ... . . . 51 Prevention . . . . , . 52 Further Research . l. . . . . 52 CHAPTER 6-THE CASE FOR MICROBIOLOGICALLY INFLUENCED CORROSION OF COPPER AND COPPER ALLOYS. ... .... .. . . 54 a Methods of Detecting Bacteria involved in the Microbiological 1y Influenced Corrosion of Copper and Copper Alloys in the Laboratory . . . . . .. . 58 Methods for Detecting Microbiological 1y Influenced Corrosion of Copper and Copper Alloys in the Field . . . 59 Methods for Controlling Microbiologically Influenced Corrosion of Copper and Copper Alloys . . ... . . . .. 60 Research needed in the Area of Microbiologically Influenced Corrosion of Copper and Copper Alloys . .. 60 CHAPTER 7-THE CASE FOR MICROBIOLOGICALLY INFLUENCED CORROSION OF HIGH NICKEL ALLOYS ...... .. .. . ... . 62 CHAPTER 8-THE CASE FOR MICROBIOLOGICALLY INFLUENCED 0)
CORROSION OF TITANIUM . . . . . ..... . ...... ... . . 63 CHAPTER 9-GENERAL CONCLUSIONS AND SUGGESTED AREAS FOR RESEARCH . . ... . .. .. .... ..... ., . .. 64 Technological . . . .. .. . .. ...... . ... . . . 65 Scientific . . . . .. ..... . . . . .. . 65 APPENDIX-PROCEDURE FOR OBTAINING AND PRESERVING SAMPLES WHERE MICROBIOLOGICALLY INFLUENCED CORROSION (MIC)IS SUSPECTED AS BEING INVOLVED . . . .. . . 66 Observations in the Field . . . . .... . . .. 66 Preparing for Sampling ... . .. . . 66 Taking the Sample-General . . . . 67 Water Samples-Unpreserved . ... . 67 Water Sam:,les-Preserved . . . .. ... . . . . 68 Samples of Tubercles. Sediment, Etc.-Unpreserved . . .. . 68 Samples of Tubercies. Slimes, Etc.-Preserved .. . . 69 Sampling Kits Available . . . . . . . 69 REFERENCES. . . 70 iv ,
,- 1
. ~, o.
FOREWORD
]
w
- In recent years substantial interest in microbiologically influenced corrosion (MIC) has arisen in the chemical process industries. This is evident in the formation of various NACE CommittetJ, on-going programs within the Corrosion Control Engineering Joint Venture abroad and countless international symposia on the subject. While some enlightened individuals. Including Frank LaQue, formerly with INCO,.and Warren Iverson of NES, have been writing about the subject for decades, most materials and corrosion engineers remained oblivious to MIC.
Many of us were shocked out of our complacency in the 1970's when we began to see a puzzling parade of corrosion failures which were not explained by
" classic" corrosion mechanisms. MIC was identified as a probable cause. Case histories continue to mount but our understanding of, r.nd ability to control, MIC lags. Funding for basic research has been minimal because some in the corrosion
- community still maintain that MIC does not exist or is not a significant problem.
This project is an attempt to answer three questions: (1) Is MIC a valid phenomenon? {. (2) If so, is it a widespread problem in the CPI?
'e (3) ~ Does adequate technology already exist to combat it?
}a
- ~
This report answers yes, yes and no, respectively, and further emphasizes 'l the need for additional basic work. In response, the MTI is sponsoring the development by Dr. Pope and associates, of field ar/1 laboratory test kits to identify sulfate reducing bacteria. The method should be readily expandable to the detection of other species as well. It is expected that preliminary kits will be
.o available for use by member companies in the near future.
Finally, we wish to mention that Dr. Arthur J. Freedman was originally chairman of the Task Group. Aftei' he left Nalco to become an independent consultant, he was retained as a consultant to the Task Group, and did, in fact, provide much of the detailed liaison work to see this through. Our thanks for his continuing assistance. R. E. Tatnall ! 'g Chairman, Task Group No. 26 y Technical Advisory Council
. . ~ u. ~
SUMMARY
A mul:id:s plinary group of scientists at Rensselaer Polytechnic Institute vias asked by me Materials Technology Institute of the Chemical Process Industries. Inc.. to survey the available literature on Microbiologically Influenced Corros:on C.C and to report their findings relative to the evidence for MIC of iron and rr.Ci s: eels, stainless steels, copper alloys. aluminum and aluminum alloys. nicke'. chromium alloys, and titanium. Further, the group was asked to repor: the s:1:e of the information relating to the mechanism (s) whereby MIC of each :natent'. : curs, methods of prevention and methods of detection in the laboratory and '.n the field. Finally, they were asked to develop a list of priority areas for research. The grcup found evidence in the literature for MIC of all alloy groups except nickel chro:nmm and titanium. Detailed mechanisms for MIC are generally unknown. Protection from MIC and reliable methods of detecting it are not generally available. Details and suggested research areas are discussed herein. It is suggested mit development of methods for identifying corrosion as MIC and '
~
using these to ascertain the prevalence of MIC in chemical process industry environments is the technological research area requiring the most immediate attention. 50;entific studies designed to elucidate the specific mechanisms of MIC should alse re:eive a high priority.
"Y 9
Xi
1 CHAPTER 1 INTRODUCTION The purpose of this report is to present the findings of a multidisciplinary study group constituted by the Materials Technology Institute of the Chemical Process Industries, Inc., to evaluate the state of the art with regard to microbiological 1y influenced corrosion (MIC). This group was asked to study the available literature and to write an interpretative document which attempted to answer the question: Is there sufficient evidence in the literature to conclude that MIC. of any kind, occurs in various metals and alloys? The metals of interest included the mild steels, stainless steels, copper alloys, aluminum and aluminum alloys, nickel alloys and titanium. In cases where the answer was in the affirmative, the available information for each group of alloys was to be evaluated with regard to the following: (1) What are the physical and chemical conditions under which the MIC of a particular type of alloy occurs? (2) Which type (s) of organisms are involved? (3) What is the mechanism (s) whereby MIC occurs? (4) What methods can be used to detect MIC in the laboratory? (S) What methods can be used in the field to detect MIC? (6) What methods can be used to prevent MIC? (7) What research needs to be done? Finally, the group was asked to evaluate the general MIC situation and make recommendations as to what research area (s) should receive the most attention in the near future in order to best advance the understanding of the prevalence, causes, detection and control of MIC. General Remarks regarding the Literature Used There is a good deal of literature on MIC. However much of it deals with reports of case histories, or cbservations incidental to the main study, with poor documentation regarding the physical, chemical and especially microbiological conditions under which it occurred. It should be noted however that:
^
f11 In the cases reperted in the literature and deaP .": : thir nudy. this "t.. ;h!," r.ot t..: nult of the observer :; .:. ; c.. - n .. the case
*)
't hat the observerts) were r.ot trained in environmental microbiology and corrosion, i.e., there was not an interdisciplinary approach to the case study.
(2) In many cases the techniques used in the study were adapted primarily from the area of clinical microbiology and are inadequate for MIC investigations. (3) Some cases of MIC may have been successfully identified and dealt with by qualified persons in various industries, e.g., the water treatment industry, but reports regarding these are generally unavailable and could not therefore be dealt with herein. . A significant portion of the literature was available only in foreign languages. Much of this literature was not used directly in writing the report r-since it was possible to establish an adequate case for MIC of most alloys from the available English language literature. It should be noted however that there are at ,! least two excellent reviews available, one in French'll* and one in Swedish.(2)
~ Also several English language review articles and books are available which deal with MIC in a variety of ways. Reviews by Miller and Tiller,* IversonW and Booth and Wormwell t s) and books by McCoy* and Postgate(7) were especially helpful.
A large percentage of the available literaturs deals with the area of corrosion of irons and steels by anaerobic, sulfate-reducing bacteria, and spans a long period of time in which many different techniques were used. It represents i therefore not only the area about which the most is known but also the area where most controversy still persists. For those reasons this area has received the most attention herein. For other alloys, e.g., Monel and titanium, there is very , little available in the open literature. Therefore the conclusions reached by the present study group for these alloys should be recognized as being based on limited data, and the dangers inherent in such, realized. Finally, it should be stressed that the purpose of the study was to evaluate the " state of the art" with regard to MIC and not to produce an exhaustive compendium of available e literature.
- References appear on page 70. .
.. ,-a?,a.
- . _ . . a 2. . . .. .,
The rest of this report consists of a chapter on the ways in which microbes can influence corrosion and chapters presenting the case for MIC for each alloy group. Alloys are grouped according to major element. The general conclusions of the study group regarding MIC and needed research priorities are presented in - the last chapter. Finally, an outline of procedures for sampling where MIC is suspected is presented in the Appendix. , Examples of Microbiological Corrosion Two examples of MIC are shown in Figures 1 and 2 along with a brief description of the cases to give the reader a better idea of what will be discussed in the following chapters. p 4
1 1
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I i Figure 1 l i Rust colored vertical streaks t nd pitting along weld seam in 304 stainless steel tank. * (Reprinted with permission: ! G. Kobrin, Materials Performance,1@, July 1976, p 42.) l.
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Figure 2 Open " gouging" type corrosion of 304 stainless steel flange. This occurred under slime deposits harboring Desulfovibrio sulfate reducing bacteria. (Reprinted with permission: R. E. Tatna11. Materials Performance,2Q, September 1981, p 34.)
e - .;. ; -
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" ~
CHAPTER 2
, CORROSION: EXPLANATIONS INVOLVING MICROORGANISMS i-Introduction .
The intent of writing this chapter is to present a brief description of l mi::roorganisms and the way in' which their structure and function may relate to' f I
- the corrosion of metals. Details'of mechanisms or proposed mechanisms for '
[ specific organisms or materials'will be found, for the most part, in various research reports published elsewhere. Microorganisms are generally thought of as those organisms witich are too small to be clearly perceived using only the unaided human eye. The major divi-sions of this microbial world are protists and monera. The protists are the algae,
- fung 1'and protozoa. These are all eukaryotic (have true nuclei) and have certain ether characteristics in common. The monera are the bacteria and blue-green .'
bacteria (formerly classified as blue green algae) both of which are procaryotic f' (have no true nucleus) and share certain other common properties. _ yi.. The Algae
~
The algae are eukaryotic, photosynthetic organisms, relatively large, l-sometimes motile and usually colored. They include the green and yellow algae and the dinoflagellates and diatoms all of which are unicellular, although many . form filaments or colonies. The algae also include the red and brown algae which are plant like (kelp, etc.) and do not concern us much in the present connection. ,, The algae, as a group, can tolerate conditions of very high to very low light . ! intensity, some even growing slowly (and nonphotosynthetically) in the dark. f. 4 They can grow over a pH range of about 5.5 to 9.0, although rare strains may tolerate a wider range. The temperature range for survival is from much less than 0'. C (32' F) to somewhat over 40' C (104' F) while the range for good growth is , t
' from about 10' to 35' C (50' to 95* F). Many marine strains are of course forced f. -
to grow only at temperatures less than 5* to 10' C (41' to 50' F) since they occur t f in permanently cold water, e.g., arctic. Since they produce oxygen when exposed ! l m.e r w-- eup =' re tw y +w=e---+w- g%=-w,,y,m--, ,,orv gr W ,*
c- . 7-to' light, algal cells are usually in a relatively oxygenated envircnment. They do
'not, however, like environments where both high 0, and low CO, levels are found (such as in algal blooms) and may die under these conditions. They tolerate a
_ wide range of salinities, from distilled water to saturated brine. The algae generally have simple nutritional requirements; light, water, air and a' few inorganic nutrients of which phosphorus for fresh water and nitrogen for marine organisms are usually limiting to growth. Where the limiting nutrient is supplied in excess, rapid growth of large amounts of algae (a " bloom") may result. Inorganic trace elements, Fe, Mn, Mg, etc., are required in very small amounts. Some strains also require vitamins or other organic factors in trace
- amounts. The algae (along with the blue-green bacteria, see below) are widely recognized as agents which can cause severe fouling problems (slim?, reduction in heat transfer rate, plugging of tubes, etc.). These fouling problems w hether caused by algae, fungt or bacteria can also be the source of many problems related to corrosion, since they can lead to the formation of concentration cells
, involving 02,'various ions, etc., due to the fact that the diffusion of these .
- h- materials through a biofilm will usually be at a different rate than to the bare surface of the metalitself. Alternatively, the biofilm community may actively concentrate such materials within itself, transport them through the biofilm to the surface or exclude them from the film altogether. Each of these could
, theoretically lead to the rapid development of concentration cells in and/or around the biofilm. Also important is the fact that these films can prevent the diffusion of certain blocides and of corrosion inhibitors to the surface of the metal.
. Algae must be considered as important to MIC in yet another general way; that is, they along with higher plants are primary producers of the food necessary to support the growth of bacteria and fungi in the biosphere. Therefore if the system under consideration is lighted and/or downstream of algae, or points where manufacturing plant products are being discharged (pulp mills, etc.), this will affect the ability of bacteria, etc., to cause MIC at the site of 4 -
interest. This is of course an indirect, but nevertheless important role for algae, and indeed plants in general, in MIC.
. 8-Specific metabolic activities by which algae might cause MIC might include ,
the production of gaseous oxygen and the production of corrosive chemicals.
' In the light, algae, like the blue-green bacteria and higher plants, produce 02 - -
during photosynthesis. The 0, so produced can accumulate within the biofilm to quite high concentrations and result in a much larger difference in 0 concentrations between these sites and adjacent sites not covered by algae. This 02 could also depolarize the corrosion reacti on, leading to increased corrosion rates. It should be noted that this condition will reverse itself at night since algae - consume Oz (respire) in the dark. Many algae also excrete organic acids which can accumulate to relatively high concentrations in films and cause corrosion by creating localized areas of :, 4 . low pH, thereby removing the passivating or protecting layer of corrosion products. ; i' I The Fungi (yeasts and molds) The yeasts are unicellular, generally reproduce by budding (although some divide by fission) and are relatively large. They appear to be of minimal importance in the context of corrosion of metals, as they are rarely found in large numbers in most aquatic systems. Their roles in the deterioration of wooden vat , t materials, etc., should be considered elsewhere. l-The molds are a very diverse group of microbes which may be filamentous (e.g., bread molds, Figure 3) or colonial. They are non-photosynthetic and require 0, and organic compounds for growth. They are nutritionally diverse, using a wide variety of compounds including wood as food sources. They produce an enormous variety of end products from alcohols and organic acids to antibiotics. The pH range for growth is about 2 to 8 with the optimum around 6 for most species. Temperature ranges for growth are from about O' to 60' C (32' to 140' F), although most only grow in the range of about 10' to 35' C (SO' to 95* F). The molds reproduce by cellular division, fragmentation (falling apart into , individual cells which can start new colonies), asexual spore formation and many by sexual means. The spores are generally very tolerant of desiccation and ,
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[\ :. )q rei.3 N:p A M-Figure 3 Asexual and sexual reproduction in the common black bread mold Rhizopus. The mold consists of branched hyphae, including thizoids, which anchor the mycelium, stolons which run above ground; and sporangiophores. At maturity, the fragile wall of the sporangium disintegrates, releasing the asexual spores, which are carried away by air currents. Under suitable conditions of warmth and moisture, the spores germinate, giving rise to new masses of hyphae. Sexual reproduction occurs when two hyphae from different mating strains come together, forming gametangia, which fuse to form a thick walled, resistant zygote, commonly called a zygospore. After a period of dormancy, the zygote undergoes meiosis and germinates, producing a new sporangium. (Reprinted with permission: Helena Curtis, Biology, 2nd Ed., Worth Publisher, Inc., New York, NY,1975, p 322.)
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~ '
I I somewhat more resistant to certain chemicals than are the vegetative cells. They , may remain viable but dormant for many years until favorable conditions are encountered. They can also be transported in water, wind, etc., for long distances. Fungi are important as they can form large masses of filaments which may
. trap other material. This can quickly cause a worsening of fouling problems with the resultant effect on corrosion that fouling may entail (see algae, above). ,
As with the algae, fungi produce many potentially aggressive metabolic by products, especially the organic acids (established as a cause of corrosion of l: aluminum aircraft fuel tanks). Their role in the establishment of 02 concentration cells would however be related to their consumption of 03 rather than its
~
production (as would be the case with the algae). They also break down complex polymers, like those found in wood with the concomitant release of various by products which may serve as nutrients for organisms more directly involved in corrosion processes. Thus they are very important in systems containing wood or wood products. The Protozoans I These are eukaryotic and may be amoebold, flagellated or ciliated. There have been no reports of the involvement of protozoa in the corrosion of metals. As predators on bacteria and algae, they may have a potential role to play in preventing corrosion caused by these organisms. It is of interest to note that some pathogenic species have been found in thermal effluents from heat exchangers. The Bacteria A generalized diagram of a bacterial cell is shown in Figure 4. They may be spherical, rod shaped, filamentous, helical or colonial. Most reproduce by dividing the cell in half, a process known as binary fission. They are generally small, usually about 0.2 to 5 micrometers (pm) wide by 1 to 10 m in length, although , some filaments may be several hundred um in length. The cells are generally colorless when viewed as individuals (except for the blue-green bacteria, the green , and purple sulfur bacteria and the purple non sulfur bacteria which are red to purple in color)
.- --- -_ , _ _ L ._ _ - - - _ - - -
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> (Reprinted with permission:
, J. Mandelstam and K. McQuillen, Biochemistry of Bacterial Growth,2nd Ed., Halsted Press, New York, NY,1973, p 64.) t a I i
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BacteNa may live at relatively cold temperatures (the psychrophiles, from , less than O' to about 25' C (32' to 74* F)], at moderate temperatures [the mesophiles, from about 15' to 45' C (59' to 113' F)], at relatively high temperatures [the thermophiles, from about 45* to 75 C (113' to 167* F)) or at' extremely high temperatures (the extreme thermophiles, from about 75' to 99 + ' C (167' to 210 + ' F)]. Bacteria, as a group, can grow over the pH range from about O to 12. They can be obligately aerobic (require 0, to survive and grow), microaerophilic (require low O, concentrations), facultative anaerobes (prefer aerobic conditions i I but will live under anaerobic conditions), or obligate anaerobes (will grow only i under conditions where 0, is absent). It should be emphasized that some of the r latter organisms may survive aerobic conditions for quite a while. Also note that, for a microorganism, anaerobic conditions may be quite easily found in what are thought to be generally aerobic environments. Often these anaerobic microenvironments are in, or under, films, in particles of debris, inside crevices, etc. As a group, the bacteria may use almost any available organic carbon molecules, from simple alcohols or sugars to phenols to wood or various other complex polymers as food (heterotrophs) or they may fix CO, (autotrophs) as do ; plants. The heterotrophs may use a wide variety of (almost any) organic molecules ! as energy sources. The autotrophs may oxidize reduced inorganic compounds, elements or ions (e.g., NH, or NO, , CH., H,, S*, Fe*8, Mn*8, etc.), most as sources of energy. A few may use light as a source of energy. These organisms may use organic molecules for carbon (food) sources (the photoheterotrophs) or CO, as a carbon source (the photoautotrophic blue green bacteria). The nutritional requirements of these organisms, therefore range from very simple (blue-green bacteria) to very complex (such as the obligate parasites which require a hving ; host of a specific type). Most fall in between these extremes and require a limited number of organic molecules, moderate temperatures, moist environments and near neutral pH. i I . t L
i - t, i 1 13
- l. The bacteria have many unique properties, some of which may be important*
in tlie corrosion process: 3 (1) They are small, (from less than two-tenths to several hundred m in length by up to two or three m in width), a quality which allows them to penetrate crevices, etc., easily.
! (2) They may be motile which aids in migrating to more favorable i conditions or away from less favorable conditions, e.g., toward food sources or away from toxic materials.
(3) They have specific receptors for certain chemicals which allows them to seek out higher concentrations of those substances which may
- g. -
represent food sources. It is very important to understand that nutrients, especially organic nutrients, are generally in short supply in most aquatic environments; but that surfaces, including metals, adsorb these materials, creating areas of relative plenty. Organisms able to seek out and establish themselves at these sites will have a i distinct advantage in such environments. (4) They can withstand a wide range of temperatures [at least -10' to 99* C (14' to 210' F)], pH (about 0 - 10.5), and oxygen concentrations (O to almost 100% 0, atmospheres). (S) They may utilize 0,, NO,, CO,, SO. and perhaps other compounds as the , final electron acceptor in their respiratory metabolism. The reaction j products, H,0, NO, , N,, CH., H,S can be important in many ways. ,; Especially important here is H,S since it is known to be involved in the l corrosion of many metals (see following chapters). (6) They can grow in the form of cell aggregates (" colonies") which helps f to cross feed the individuals in the colony and make the survival of at least some members of the " colony" more likely under adverse conditions. (7) They produce enormous numbers of individuals in a short time I, (generation times of only 18 minutes are known), thus allowing them under favorable circumstances to " bloom" and quickly "take over" an environment. h u.' o 1
,q; 2 4 1 3~ , + 4' - i (8).. The individuals can be widely and quickly dispersed by wind, water, animals, aircraft, etc., and thus the potential for some of the cells in
- the population to reach more favorable environments is good.
(9) L Many can quickly adapt to use a wide variety of different food sources
~
. For example, Pseudomonts fluorescens can use well over 100 different j compounds as sole sources of carbon and energy, including sugars, Ih ~ lipids, alcohols, phenols, organic acids, etc. This capability gives them
+
tremendous advantages in a constantly changing environment. I (10) Many can form extracellular polysaccharide materials (capsules or slime layers) which, where accumulated, are widely recognized as
+
causing problems in heat transfer, fluid movement and isi creating
- i
. sites where MIC can occur. The slimes are sticky and trap organisms o '[ -
. and debris (food), resist the penetration of some toxicants (e.g.,
, blocides) or other materials (corrosion inhibitors) and hold the cells ]_ between the source of the nutrients (the bulk fluid) and the surface toward which these materials are diffusing. It also means that the .
~*
3 ' organisms may be able to adapt te lower concentrations of certain -
.. nutrients, since although in low concentrations, they will be moving
?: 3 (not along with) the cells and are therefore almost always present to l, at least a minimal level. The presence of the microbial film ultimately
'~
j may lead to macrofouling (barnacles, etc.) which can also affect heat transfer, fluid flow and provide corrosion sites.
- (11) They produce spores which are resistant to temperature (some even
, resist boiling for over 1 hour), acids, alcohols, disinfectants, drying.
l - freezing and many other adverse conditions. The spores may last for [ ,
. hundreds of years and then germinate on finding favorable conditions.
d N (12) They are resistant to many chemicals (antibiotics, disinfectants, etc.) m -
.- by virtue of their ability to degrade them or by being inpenetrable to them (due to slime, cell-wall or cell membrane characteristics). It is . also important to note that such resistance may be easily acquired by mutation or acquisition of a plasmid (essentially by naturally-4: occurring tjenetic exchange between cells, i.e., genetic engineering in l
i the wild). 4 I , m 7
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E lS- I O . (13) Many species produce a wide variety of organic acids e.g., formic,
* :I succinic, which may initiate or accelerate corrosion of many types of metals. b 4 (14) Some species produce mineral acids (e.g., Thiobacillus thiooxidans,
{ which produces H,SO.) which are extremely corrosive. (IS) Several bacteria metabolize NOi, sometimes used as a corrosion inhibitor. Some (e.g., Pseudomonas spp.) reduce it to N, gas which - leaves the system. They will do the same to NOi. Other organisms convert NOc to NOi. Several types of soil and water organisms - (Nitrosomonas) oxidize NH, to NOi, and then others (Nitrobacter) oxidize the NOc to NOr. f (16) Many organisms form NH, from the metabolism of amino acids. NH, c6nverts to ammonium ion in aqueous solution and may play a role in f j the corrosion of certain alloys, e.g., copper alloys. hj
] (17) They produce many enzymes, some of which may be excreted by the
). cell, and which then act on substances outside the cells. One such enzyme, hydrogenase, has been reported as important in the corrosion -
of iron and steels, presumably due to depolarization of the cathodic r x: sites. - (18) Many organisms produce CO, and H, as a result of their fermentative type of metabolism. Carbon dioxide in solution becomes carbonic acid - and could thereby enhance corrosion. - (19) Many bacteria (belonging to several genera) which normally use [ organic carbon compounds as carbon and energy sources can use H, ' gas as their energy source and CO, as their carbon source and live chemoautotrophically (without organic sources of carbon and energy). _ By living in this manner, they could cause depolarization cf the " cathodic sites on steels and promote corrosion. This is one of the - proposed mechanisms whereby sulfate reducers (e.g., Desulfovibrio lj desulfuricans, see Figure S) obtain their hydrogen for sulfate { reduction. It has been suggested that, in so doing, they could promote ; I cathodic depolarization and corrosion of steels in anaerobic
- I>
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(6000X) Figure 5 Electron micrograph of Benghazi strain of Desulfovibrio af. Gold-shadew-cast. (Reprinted with permission: Marcel Dekker, Inc. H. L. Ehrlich. Geomicrobiology, Marcel Dekker, Inc., New York, NY,1981, p 263.) l l 1 I _m rrii, g. ., pg . -**-M= ==M 6* - * * * - '
F i l 17-
- f. i20) Some bacteria can oxidize or reduce metals or metallic tons directly.
- For example some species (Gallionella, Figure 6 and Sphaerotilus, j Figure 7) oxidize Fe to Fe. These ferric compounds then precipitate in a sheath around the cells, and can accumulate as tubercles in pipes and plug them. Concentration cells are easily formed under such I deposits with corrosion resulting. Whether the removal of the Fe
directly affects the corrosion of the metal or not is unclear. Other organisms (e.g., Pseudomonas spp. from oil wells and bacteria from marine sediments) have been shown to reduce ferric iron to the more soluble ferrous form. It has been suggested that this bacterial action strips off the ferric compounds which normally stabilize the surface of mild steels, leaving it reactive. Corrosion is thus accelerated. Other
! bacteria can oxidize or reduce manganese which, along with the iron i transformations listed above, is the cause of considerable tubercle formation and subsequent fouling or occluding of pipes, and probably deposit-associated corrosion by species such as the sulfate-reducing bacteria. Many organisms which transform iron also transform manganese. It has been suggested that some of these organisms can reduce iron through the mediation of hydrogen peroxide and catalases (enzymes capable of breaking down hydrogen peroxide into oxygen and water). Yet other organisms are reported to mediate changes in the oxidation state of chromium, possibly aiding in the corrosion of nsinless steels.
[ (21) They form synergistic or mutualistic communities with other bacteria, i
; fungi, algae, plants and animals. Such communities can accomplish ! things that the individuals alone cannot perform, e.g., certain fungi i break down wood to organic acids and consume 0, which provides the i
N food and anaerobic conditions required by Desulfovibrio app. These communities also change their structure, dominant species, etc., to l meet changes in the external or internal environments. The community also provides protection for individuals, (e.g., anaerobes d B w 4 {:. s
4 18-
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Figure 6 Gallionella. Note the small bell attached laterally at the tip , of each of the twisted stalks. l (Reprinted with permis,sion: Marcel Dekker Inc. l H. L. Ehrlich, Geomicrobiology, Marcel Dekker, Inc., New York, NY,1981, p 180.) 6 l t i i l
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Figure 7 Sphaerotilus species. a sheathed bacterium. (Phase contrast photomicrograph courtesy: J. T. Staley and J. P. Dalmasso.)
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l f, rom oxygen or biocide-sensitive organisms from biocides) which would otherwise be subjected to adverse (from the point of view of the organism) factors. The community therefore increases greatly the [ potential of microorganisms to accomplish many feats otherwise not possible, among them the corrosion of many types of metals. It should be emphasized here that the community is a primary reason why pure-culture-laboratory tests often do not adequately reflect the real world situation. The results of such laboratory screening types of tests should not be extrapolated to field conditions without adequate tests and follow-up in real world operating situations. Ideally, more laboratories will begin to consider films, communities, debris and MIC, etc., when designing test systems for blocides or corrosion inhibitors. It should be noted that there are many people operatmg in industrial settings (e.g., the water treatment industry) who are undoubtedly aware of the above problems and apparently deal with them effectively. Reports of their activities are however not generally available. e i i
* * . . . , y t.
g~ 9 . CHAPTER 3 THE CASE FOR MICROBIOLOGICALLY INFLUENCED CORROSION OF IRON AND STEEL Introduction The role of microorganisms in corrosion of iron and steel has been the subject of numerous articles and a number of excellent review articles on this topic are currently available, including those by Iverson M) and Miller and Tiller.f33 In addition there are a number of books available which have much useful information relating to the subject of corrosion in general and to the question of the role of microorganisms in mineral cycling and in the corrosion of metals.
, These include books by McCoy,(e) Neilands,(a) Postgate,(73 Fenchel and Blackburn,5) Ehrlich(10) and Weinberg.(lli Recognition that microbes play a role in the corrosion of metals buried in , the ground or immersed in water occurred as early as the late 19th century.
Gainest12) early in the 20th century, was one of the first to suggest that iron bacteria and sulfur bacteria might be responsible for the corrosion of ferrous metals buried in soil. Von Wolzogen Kuhr and Van der Vulgtfl3) were among the j first to attempt to provide a mechanism to explain the corrosion of metals in soils ! due to the action of sulfate-reducing bacteria. The concept of MIC of iron and steel is intimately linked with the development of an understanding of sulfate reducing a bacteria, their physiology, biochemistry and ecology. This is not to imply that the sulfate-reducing bacteria are the only bacteria involved in MIC of iron and steel; however, it has certainly been the most widely observed instance of MIC in these materials and is the one which has received the most detailed attention in terms of the number of cases observed in the field, the number of field trials attempted to define conditions under which it occurred, and the number of laboratory j experiments which have been done to determine the mechanisms whereby it
,; occurs.
There has been a recent upsurge in the number of reports of various types of n y MIC involving iron and steel, and in the level of interest in the topic shown by ,+ h i
,.m. '
t 22-members of especially the chemical process, petroleum and water treatment , industries.(14'18) The remainder of this chapter is an attempt to briefly describe the current state of the information on microbiological involvement in the corrosion of iron 4 and steel, excluding the stainless steels which are covered in a separate chapter. Microorganisms involved in Microbiological 1y ; Influenced Corrosion of Mild Steel l i The best known group of organisms involved in the corrosion of iron and steel are the sulfate-reducing bacteria. These fall currently into three genera (a genus may contain one or more species of organisms which are very much alike) Desulfovibrio, Desulfotomaculum and Desulfomonas. The species of organisms in ' the genus Desulfovibrio are the best linown, probably because they are the easiest I to isolate, are mesophilic (grow at temperatures of about 10' to 40' C (50' to l 104* F)] and are perhaps the most wide spread. The organisms in this genus can be terrestrial, fresh water or marine (require sodium) and do not form spores. They are, like all of the other sulfate reducing bacteria, anaerobic. Earlier names for this genus were Spirillum, Sporovibrio, Microspira and Vibrio. The organism about which most is known is Desulfovibrio desulfuricans. . Desulfotomaculum strains can be mesophilie or thermophilic (have the ability to grow at elevated temperatures). The best known of these is probably Desulfotomaculum nigrificans, an organism which is reported in much of the literature as Clostridium nigrifircans. All of the Desulfotomaculum species form l spores, which are dormant forms of the organisms resistant to many harsh environments. The Desulfomonas appear to be quite similar to the Desulfovibrio. An excellent source for more information on the sulfate-reducing bacteria is the book by Postgate.m e The other microorganisms which are mentioned most commonly with regard to their role in the corrosion of iron and steel are the bacteria in the genus
?
Thiobacillus. These organisms have the ability to oxidize reduced forms of sulfur , with the subsequent production of sulfuric acid. The mechanism (s) whereby this ' l- ! acid produces corrosion is well established in the general corrosion literature and involves the destab111: anon of ctherwise protective corrosion product films. (
. .. m t.
23-The case for corrosion of iron and steel by the bacterium Thiobacillus
- ferrooxidans is straightforward. This organism oxidizes ferrous iron to ferric iron to obtain energy.
i The other major group of organisms which have been reported as important in the corrosion of iron or steel are the so-called iron bacteria. This group includes the organisms in the genera Gallionella, Leptothrix, Sphaerotilus, Crenothrix, Clonothrix and Lieskeella.(lo) Those most commonly reported in connection with the formation of raised " growths" on the surface in iron water pipes and water mains, and as possible agents of MIC in various industrial situations have been Sphaerotilus and Gallionella. The role of these microorganisms in MIC seems to involve their presence in (their formation of?) deposits or tubercles, under which various types of corrosion can occur. These . organisms and mechanisms are discussed in more detail below. Recently another group of organisms has been identified as important in the corrosion of mild steel. These are the Pseudomonas or Pseudomonas-like organisms which have been reported as having the ability to reduce ferric to ferrous iron.(18-22) These organisms have been found in various freshwater and marine environments and appear, in many cases, to be the organisms which ordinarily use oxygen or nitrate as final acceptors of electrons in their respiratory metabolism, but which can in the absence of these substances turn to ferric iron as an alternative electron acceptor for respiratory activity. It has been reported (19-21) that a ferric-iron-reducing Pseudomonas strain isolated from crude oil has the ability to depolarize anodic sites and also to remove a protective amorphous coating from the surface of mild steel, thereby exposing bare metal to the environment and increasing corrosion rates. There have also been several reports of the importance of other aerobic and facultatively anaerobic organisms (like to grow in aerated conditions but will grow under anaerobic conditions) in the corrosion of ferrous metals. Several of ; these, including Escherichia coli, Bacillus megaterium, Serratia marcescens and Salmonella typhimurium have all been reported to promote the oxidation of iron.(23)It has been suggested by some investigators that this is due to the ability ( ,, of these organisms to produce organic acids as metabolic end-products. Other b
, .. o.. .
i-I' investigatots t2o report that the enzyme, hydrogenase, possessed by some of these , organisms is responsible, perhaps by removal of hydrogen, thus causing depolarization of cathodic sites. This is discussed further below. Physical and Chemical Conditions under which Microbiologically Influenced Corrosion of Iron and Steel Occurs The temperature range within which MIC can occur in iron and steel is broad. The temperature can vary from approximately freezing (at such low ; temperatures most metabolic processes, e.g., organic acid production, can occur a although quite slowly) to 45* to 75' C (113' to 167* F) at which thermophilic organisms, such as Desulfotomaculum, can be active. The availability of oxygen determines in large part the kinds of metabolic activities which can' be performed. In strictly anaerobic conditions such reactions as sulfate reduction, nitrate reduction, ferric iron reduction and production of organic acids by a variety of microorganisms will occur quite readily. In aerobic environments the production of sulfuric acid by Thiobacillus and the oxidation of ferrous iron will occur. Some forms of MIC will therefore probably occur over a wide range of O, concentrations, i.e., zero to almost saturation. The pH range in which MIC of these materials can occur is also very broad. It ranges from approximately zero, in the cases where acid tolerant organisms like the Thiobacilli are involved, to neutral or slightly alkaline conditions, where a great variety of organisms can grow, up to about pH 10.5 where some organisms (e.g., Nitrobacter) can grow. The various bacteria which are potentially involved in the corrosion of iron , and steel can tolerate a wide variety of other conditions. For example, salinities may range from approximately zero, i.e., distilled water, to saturated brines. ! Some microorganisms can tolerate high concentrations of materials, e.g., biocides l' and copper ions, which are very toxic to a great many other microorganisms. These microorganisms will therefore represent possibilities for corrosion of iron and steel under a variety of extreme conditions. For a more general discussion of the mechanisms of resistance in microorganisms, see the introductory chapter en microorganisms and also references 25 and 26. 1
.- - .. . - - . -- - -. I
It should also be remembered (see Chapter 2, Corrosion: Explanations *
-Involving Microorganisms) that bacteria as a group use a great variety of organic compounds (e.g., cellulose, alcohols, acids, etc.) as carbon and energy sources, while others use light or reduced inorganic compounds (Fe, NO , CH.) as energy sources, with CO2 or organic compounds serving as the carbon source.
Again, it should be noted that many cases of MIC are probably associated with biofouling material (biofilms, slime). Fluid flow patterns are therefore important considerations since, for example, where fluid velocity prevents the formation of a film of the required thickness to achieve MIC, no MIC of that (those) type (s) will be seen. In other cases where the film is " protecting" the surface, removal of a portion may expose active sites. Mechanisms involved in Microbiological 1y Influenced Corrosion of Iron and Mild Steel Corrosion under Anaerobic Conditions. Certainly the best documented case
,.i for MIC is that for mild steel and iron under anaerobic conditions by sulfate reducing bacteria (SRB). There is an enormous amount of literature on this subject and the reader is encouraged to read much more of the detail than can be presented here, e.g., the reviews by Iverson(4) and Miller and Tiller
- and for an understanding of the ecology, physiology and biochemistry of the SRB, a relatively recent work by Postgate.m j There seems to be little doubt from the numbers of case histories presented
' and the literature reporting the corrosion of pipes in underground locations, that the SRB are involved in corrosion processes. The major point of dispute is the specific mechanism (s) whereby this corrosion occurs. The main items of contention seem to revolve around the following:
(1) The failure of laboratory experiments to reproduce the rates of corrosion observed in the field; (2) The role of hydrogenases (enzymes capable of performing the following t, i reactions, H2 = 2H = 2H' + 2e-), in the process; (3) The ro19 of SRB and oth6r organisms in cathodic depolarization; { { '.h. h 4 I
; . . . - " Lt.
I 26-(4) hhe' influence of iron concentrations in the solution on the corrosion . rate; and (5) The role of the organisms in the formation and production of a protective sulfide film. o The following equations are those originally proposed by Von Wolzogen Kuhr and Van der Vulgt(* to explain the mechanism of cathodic depolarization: 4 Fe-4 Fe*2 + 8 e- anodic reaction (1) 8 H20-8 H' + 8 OH- dissociaton of water (2) 8 H' + 8 e - 8 H cathodic reaction (3) SO. 2 + 8 H-S 8 + 4 H 0 cathodic depolarization (by SRB) - (4) ;
- Fe*8 + S-2-FeS corrosion product (5) 3 Fe*8 + 6 OH -3 Fe(OH) corrosion product (6) 4 Fe + SO. 2 + 4 H,0-3 Fe(OH), + FeS + 2 OH- overall reaction (7)
Mara and Williams (2n reported a direct linear relationship between weight loss by cast iron and five different steels during corrosion by hydrogenase-positive (produce the enzyme hydrogenase) SRB's, and the carbon content of the - alloys. Further the rate of weight loss was reported as increasing in iron-poor media. The latter result suggested to the authors that the corrosion rate would be proportional to the number of available cathodic sites on the surface of the metal. Ashton et al.,t28) using the facultatively anaerobic Escherichia coli, found that corrosion of six different iron-carbo"n alloys in anaerobic environments was attributable to the activities of the bacteria, but not related to the amount of , nitrate reduced nor to the carbon content of the alloys. They did report that the f corrosion rate was reduced by the formation of a protective Fe,0, film. King et al.(29) reported that a protective FeS (Mackinawite, FeS ..) film ~ +' formed on ferrous metals frcm the reactions of HaS produced by SRB's with the iron. The rate of breakdown of the film was reported to be proportional to the concentration of iron in solution, as was the rate of corrosion after film breakdown. Film breakdown was associated with the conversion of FeS,.. (Mackinawite) to hexagonal Fe3S. (Symthite) and Fe .,S (Pyrrhotite) and not to cubic Fe,S. (Greigite). I k
.' : ,..-"t.
27-Booth et al.(303 showed that the corrosion rates of mild steels were increased . with in' creased metabolic rates of the SRB's in the test system. Further, the corrosion rates were dependent on the nature of the sulfide film on the surface, most rapid corrosion occurring when sufficient ferrous iron was precent in the medium to react with all of the H,S produced by the SRD's and thus to inhibit the formation of the protective iron sulfide film on the me;,a1 surface. Finally, they reported no good correlation between the hydrogenase activity of a given strain and the rates of corrosion. This result is in contrast with that reported by Booth and Wormwell,(24) who found a linear relationship between the rate of corrosion and hydrogenase activity of the strains employed. Salvarezza and Videla f313 reported that introduction of steels into sea water containing SRB's resulted in a change in pitting and corrosion potentials to more active values, but that similar results could be obtained with artificial sea water , with added sulfide ions or SRB's. They also concluded that the breakdown in passivity was due directly to the metabolic production of H S by these SRB's and that it occurred most easily under anaerobic conditions. Gaylarde and Johnson,(s2) on the other hand, reported that the direct adsorption of SRB's on metal surfaces allowed the production and maintenance of thicker, sulfide-rich precipitates than that which formed when the medium was also allowed to interact with the metal surface. The deposits associated with SRB's were hard to remove, in contrast to the " fine" deposits found in the absence of SRB-metal surface interactions. They suggested that the role of HaS itself is minimal and that it is either cathodic depolarization or the production of high molecular-weight metabolic products which may be responsible. Miller and Tiller in their 1970 review article (3I state that "the available evidence suggests that factors controlling anaerobic microbiological corrosion are: (a) the utilization of hydrogen by sulfate reducing bacteria (and possibly by other j microbes that possess a suitable enzyme system); (b) cathodic depolarization by precipitated ferrous sulfide; (c) the prevention of formation of protective sulfide t films in the presence of excess ferrous ions; (d) anodic stimulation by the sulfide ions; and/or perhaps (e) the formation of local concentration cells." They further stated that (a) and (b) above were most important and were perhaps interrelated to some extent, in a way that was not fully understood. Postgate, in his 1979
. ~ 2 .. j book on the SRB's (7) has concluded that anaerobic corrosion of cast iron is ,
brought about by SRB's and has three main characteristics: (1) It is restricted to anaerobic environments such as clay or waterlogged soils. (2) The corroded metal tends to be pitted rather than evenly corroded, 1 indicating that corrosion is not self-stifling. L ' (3) If the alloy is cast iron, it should-at the point of corrosion-show a graphitic structure, i.e., the metallic iron at the site is entirely removed but the graphite skeleton of the pipe often retains its original form. Postgate further concludes that: (1) The mechanism of anaerobic corrosion by sulfate-reducing bacteria was once controversial but is now largely understood and agreed upon. (2) Hydrogen sulfide is in itself corrosive. (3) The corrosion of metals by sulfide-producing bacteria other than SRB's has been recorded. (4) The distinctive feature of corrosion by Desulfovibrio and Desulfotomaculum is cathodic depolarization. He further states that "in underground corrosion the sulfate-reducing bacteria can remove the hydrogen film through their enzyme hydrogenase with the formation of both iron hydroxides and iron sulfide in the corrosion product." There is considerable evidence that corrosion of ferrous metals occurs by mechanisms in addition to cathodic depolarization. Postgate(7) mentions several of these. They can be summarized briefly as: direct attack on iron by HaS, with or without the formation of oxygen concentration or ion concentration cells, due to the presence of bacteria in or under tubercles or by actually forming the tubercles themselves. In addition, solid ferrous sulfide has been reported as being corrosive to iron and steel.(33) The extent to which a particular corrosive reaction or set of ; reactions dominates in a given location or environment depends on a variety of ! I ' factors. 7'hese will include: , (1) The nature of the alloy surface; (2) The presence or absence of dissolved iron in the medium, or the a presence of organic matter capable of chelating iron or other metals in the surrounding water: f-i s
.3 i
(3) The nature of the strain (s) of bacteria itself, since some tend to form a . film on the metal and some do not; (4) Whether the iron sulfide itself forms a film which can under some circumstances be protective; and (5) Whether other ions such as sodium, chloride, nitrate, nitrite or phosphate are present. Iverson, in a report
- and also in a talk at a Canadian Institute of Mining and Metallurgy meeting in Toronto," presented evidence that it is the formation of a highly corrosive (and as yet unidentified) metabolle product by Desulfovibrio desulfuricans which is the actual cause of corrosion of iron and steel in anaerobic conditions, and further that the cathodic depolarization theory for such corrosion
. could not account for the observed corrosion rates.
Therefore it can be seen'that there are a large number of organisms and mechanisms involved (or possibly involved) in the corrosion of steel and iron under anaerobic conditions. The general mechanisms whereby corrosion involving the production of organic acids, mineral acids, ammonia and so forth occurs, as well as mechanisms involving the production of oxygen or ion concentration cells are not discussed in detail here as they have been discussed in some detail in previous chapters. However, it appears that these general classes of MIC mechanisms can occur on iron or steel quite readily under anaerobic or aerobic conditions and may involve a great many different types of microorganisms. Finally, it should be stressed that in environments generally thought to be aerobic, a great number of microenvironments can exist which are anaerobic, or which are at times anaerobic due to fluctuating conditions within the overall system. It is important to realize that in these microenvironments many of the same types of corrosion which are recognized to occur in grossly anaerobic . conditions will also occur. Microbiologically Influenced Corrosion of Iron and Steel in Aerobic Conditions. One mechanism in aerobic environments whereby microorganisms may cause corrosion of iron and steelis the case of Thiobacillus which, through its oxidation of sulfur compounds, produces acidic environments. The local pH around these organisms may be very low and the surrounding
\
f
~
. -m.s material ma'y disintegrate quite rapidly. Likewise the production of organic acids ,
by a variety of different organisms will corrode iron and steel materials in much the same way. It might be noted in this connection that some organisms are known which break down some of the types of coatings used on iron and steel pipe and that the breakdown products of these coatings may provide substrates to 5 acid producers, ultimately resulting in the corrosion of the materials underneath.- It might be noted also that holidays (breaks) in these coatings provide excellent starting points for the growth of microorganisms and/or anaerobic environments in what are otherwise generally considered to be aerobic conditions. l Other mechanisms whereby MIC occurs in the aerobic environments are the ' general cases of microbial growths and deposits on materials creating oxygen or , ion concentration cells, which can result in corrosion explained by classical corrosion; theory. These can lead to the corrosion of the materials either under the growth or around the perimeter of the growth. A good example of this is seen in the involvement of the iron bacteria which produce extensive ferric hydroxide deposits termed tubercles, especially inside of iron water pipes. Associated with these deposits are often very extensive areas of corrosion. ) Methods of Detecting Microbiologically Influenced Corrosion of Iron and Steel in the Laboratory The methods generally available for' detecting MIC of iron and steel in the laboratory are related to the attempts to isolate or otherwise identify specific organisms involved in the corrosion processes. The most obvious are the culture of the SRB's, Thiobacilli, and the iron bacteria. Any standard reference giving microbiological methods will outline methods for the culture, or attempted culture, of each of these types of organisms. The culture of other microorganisms capable of producing organic acids or producing sufficient biological growth in slimes, to allow for the development of oxygen concentration cells, ion concentration cells and the like is a fairly straightforward matter. These methods o can also be found in standard reference volumes. 6 s 6 - s: w --
~
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Another approach is to attempt to identify, through various microscopic . means, the types of microorganisms involved in the suspected MIC. The iron i bacteria can often be identified by simply observing the material under the light microscope. An example of such an organism is shown in Figure 6. The general value of the light or phase microscope in a "first cut" determination of whether one has an MIC problem or not cannot be overestimated. This simple technique allows a rapid determination of the general types of microorganisms present and the general magnitude of the populations. One can also, with some experience, identify many of the microorganisms by simply observing them under the microscope or with the help of simple staining procedures. Further one can get an idea from the appearance of the materials in the specimen as to what is happening in the areas suspected of having MIC. There are a variety of chemical and biochemical means for attempting to ascertain whether microorganisms are present or to ascertain what specific microorganisms are present. These techniques might take the form of trying to identify specific chemical species, that is, the presence of HaS, H,SO., organic acid.s, etc. Alternatively, one can look for specific molecules which identify various microorganisms. This may take the form of identifying lipids which are . characteristic of fungi, algae or bacteria or by the identification of lipids specific for sulfate-reducing or other bacteria. A good discussion of the latter biochemical methods is to be found in the article by White.(35) Another useful technique is the fluorescent antibody procedure. In this procedure antibodies directed against a specific organism, e.g., a particular sulfate-reducing bacterium, are produced in rabbits or other animals, and purified and chemically linked to a fluorescent dye. A suspected MIC specimen is then removed, placed on a microscope slide, stained with the reagent containing the fluorescently labeled antibody to the SRB, processed and viewed under a fluorescence microscope. The numbers of organisms reacting with the antibody can then readily be enumerated. For a further discussion of many of the above culture and microscopic techniques, the reader is directed to an article by Pope et al.(3* It is impossible to identify, beforehand, which technique (s) should or could be used either in the laboratory or in the field to give the most information. e
. . .- u.
l 32-All have their advantages and disadvantages and all should be tried (the simplest . first, perhaps) until the investigator is satisfied with the evidence. Also a little experience and thought about the chemical and physical conditions should alert the investigator to the possible types of microbes to be found, and therefore help him to choose a method (s). k I Methods of Detecting Microbiological 1y Influenced Corrosion of Iron and Steel in the Field An important point to make in connection with the detection of MIC of iron and steel in the field is that very careful observations of the suspected sample of MIC and the physical and chemical conditions in and surrounding these samples must be made and recorded. It is especially important to note: ,' (1) Whether there is blistering or tuberculation and the patterns thereof; (2) The appearance of the metal (bright?, black?) underneath in tubercles; (3) . The color of the fouling and/or corrosion product; (4) The presence or absence of the H2S odor in the general environment (soil, water) or from the corrosion product upon adding a few drops of HC1; (5) The general conditions of water (chemistry); and (6) The types of materials in use. If it is suspected that the MIC is due to Desulfovibrio or other SRB's, it is important to attempt to establish that there are in fact anaerobic conditions surrounding the MIC area. It would also be important to establish whether H,S or FeS were present in the area. Additional useful tests are to determine general bacterial populations by viable plate counts, whether there were SRB's or other l anaerobic bacteria present or whether there were strict aerobes present, each of these being important indic'ators as to the conditions in the area. It would also be
- important to note whether the corroded metal was generally corroded or whether it was pitted, since the latter condition could be indictative of SRB related
! corrosion. j If one suspects that the MIC is related to the Thiobacilli, then it would be important to determine whether sulfur is present in the environment and in what i l t
- r. .. . ..
IL'n , k - l l x _, forms, i.e., as elemental sulfur, as H S or HaSO., These determinations can be 2 made by straightforward chemical methods. Also important is an attempt to culture the Thiobacilli. This can be done by methods as outlined in any general microbiological-methods reference work. In addition the pH should be measured,
) '
since a low pH would be one indication of the presence of Thiobacilli. Finally the ! l conditions should be aerobic, so a determination of the level of oxygen would be l important. Electrodes, chemical analysis or redox dyes can be used depending on the conditions. If it is suspected that MIC is related to the production of organic acids by one or more bacterial types, then one should measure, if possible, the pH in the local environment surrounding the corroded area (a contact pH electrode is useful for this), take samples for analysis for organic acids, and attempt to culture as many of the bacteria as possible from the samples using ordinary culture techniques. An additional procedure which is often helpful is to collect some corrosion product, moculate it into a growth medium containing one or more fermentable carbon sources (e.g., glucose) and use a pH indicator to determine whether the potential MIC microbial community can in fact produce acids as a result of their metabolism. The MIC environment could be anything from aerobic to anaerobic and still contain organisms whose metabolism produces organic acid by-products, so although this procedure is not indicative of specific types of organisms ceing present it is still quite useful. It would also be wise to measure the oxygen levels at the site, if possible. If MIC is suspected as being related to the formation of tubercles then of course one would want to observe the MIC for the presence of tubercles. One or more should be removed and the area underneath observed for bright areas indicating active corrosion. The presence of H S and/or metal sulfides or blackening of areas under the tubercles would indicate the presence of SRB's. It would be important to analyze the tubercle material and surrounding material for the presence of iron bacteria or other bacteria which may be responsible for the formation of the tubercle. Microscopic analysis to demonstrate the presence of the I tren t acar:a may be the most fruitful and direct way. Culture techniques. as mentienn above. for the general types of bacteria present in the tubercles should be use'. Chemical analysis to show an association of organic acids or inorganic
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acids with tub'ercles would also be suggestive of the presence of bacteria capable
. of causing MIC, and one should therefore try to analyze for these if possible.
- Methods for Controlling Microbiologically Influenced Corrosion of Iron and Steel Although a variety of approaches are currently in use to try to combat corrosion, none of them seems to have been designed specifically to prevent the occurrence or activities of organisms involved in MIC. Most biocides seem to have
' been designed more to prevent the growth of the organisms and the associated problems of sliming and heat transfer loss than to prevent corrosion by them. It should be noted however that control of slime will prevent many types of MIC.
In general the methods of preventing or retarding corrosion can be lumped into two major oategories: (1) using noncorrodible materials and (2) using corrodible materials with some other kind of condition (s) being imposed. Using noncorrodible materials certainly is an excellent solution provided that the
. materials are obtainable in the form that is required, not prohibitively expensive ,
for the use required, and have the qualities necessary to be resistant to any other
~
conditions besides the possible MIC in the environments being used. In many instances it is simply not economically feasible to use materials such as titanium or nickel. base alloys, which might be more resistant to the types of MIC seen than are iron or steel. The second alternative, that is, using corrodible materials will require, if used in an aggressive environment, the application of additional measures to counteract the effects of MIC. These countermeasures fall into four groups which are discussed in the following paragraphs. One approach is through modification of the environment. This involves the l
' modification of the localized environment around the iron or metal structure or
- pipe such as to create a local environment which will be less likely to support j MIC. An example of this type of approach is the procedure of surrounding pipes in otherwise anaerobic soils with gravel or chalk to provide drainage and better aeration of the soils. Another example would be to modify the pH of the surrounding environment to prevent certain organisms from growing or performing certain types of metabolic activities. This might be done, for example, by adding carbonate-type rods to in ground installations to prevent acid accumulation.
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l: A second method is the application of protective coatings. These coatings . gI 't usually fall into the categories of coal-tar-base materials, asphaltic bitumen-based ~!' materials, concrete, zinc, lead or plastics. Romanoff(37) reported that the coal-tar and asphaltic coatmgs have been quite successfulin protecting underground steel structures and pipes. Spellertsa) found that cement coatings applied over steel .T were quite effective. Wagner (39) reported that polyethylene sleeving applied over .I cast iron pipe was effective in preventing corrosion. Dittmer MO) however, reported greater weight losses in specimens of polyethylene-coated iron than in controls when both were exposed to SRB's. It should be noted however that the application of various types'of coatings
. to iron and steel (especially in the absence of cathodic protection) brings another
.I' whole set of MIC problems to the fore. Some of these coatings may be laid over reinforcements containing cellulosic materials which if attacked by microorganisms can produce organic acids and therefore decompose not only h parts of the coating itself but cause extensive corrosion of the underlying metal. t The application of coatings often leaves holidays (discontinuities) in the protective coatings which constitute areas where microorganisms can enter and form microcolonies very rapidly and result in very rapid corrosion at these localized sites. Cathodic protection may solve most of these cases (see below). Zinc coating of steel pipes has been reported as preventing corrosion for extended periods of time. However, there are several cases where zine coated metals have shown MIC. Coatings with other types of metal should be effective under certain conditions. However, again, imperfections or cracks in the coating are localities where very rapid MIC can occur. There has been a recent increase in the use of plastics, e.g., epoxy resins. The application of such plastic coatings, however, suffers from the same general problems mentioned above; that is, imperfections provide sites where bacteria can establish themselves and influence
- or initiate corrosion. There is also the question of the permeability of plastic and other coatings to such substances as hydrogen sulfide, organic acids and various other corrosive chemicals. Therefore, these coatings although removing the lp organism from direct contact with the metal may not, in reality, prevent
( corrosion due to the activities of microorganisms. c
t The third method is cathodic protection. Cathodic protection and the principles underlying its application to combat MIC are discussed in a very thorough way by Miller and Tiller in their review article.'3) These authors concluded that cathodic protection either alone or in combination with protective coatings seems to be a quite effective means of controlling the corrosion of iron or steel by the SRB's under anaerobic conditions. Booth and Tiller (41) did note, however, that effective protection by cathodic means requires the potential to be increased in the active direction to about -0.95 volt instead of the usual-0.85 volt (versus a saturated copper / copper sulfate electrode). Since these potentials cause the development of very alkaline conditions, pH may be the mechanism whereby protection is afforded. However, high alkalinity may cause other problems, e.g., cracking. . The fourth method is through the use of microbialinhibitors. The use of various inhibitors to stop the occurrence, growth or metabolic activities of a variety of microorganisms is a well established practice. There are a wide variety of these biocides in use today including oxidizing compounds such as chlorine or hypochlorite, ozone and chlorine dioxide; various organic biocides such as the organotins, quaternary ammonium compounds, dibromonitrilopropionamides (DBNPA), isothiazolins and a variety of others. Many of these blocides are very effective in the control of organisms when they are suspended in an aqueous medium; that is, when they are occurring as single cells or as small clumps of cells in the medium. The control therefore of organisms in the water itself is usually a reasonably simple task compared with the resi problem which is control of the organisms in the biological films on the surface of the materials. The latter situation is much more difficult to deal with, the concentration of blocide required to effect killing or control of the organisms under this situation often being many times the concentration necessary to kill the organisms in an r aqueous phase. Pope and coworkers (42* and Costerton and coworkers (45) and Characklis and coworkers (46) have all pointed to the fact that the usefulness of many biocides in the control of organisms in fouling material is much more limited than it is in the aqueous part of the system. The other problem with certain of the blocides is that they will simply shift the microbial population from a " normal aquatic community" or " normal cooling system" community to very i
. . u , c.
-3 7-specialized communities, i.e., those which form slime or those which are through some other mechanism, able to be more resistant to the biocides. This shift may ultimately cause a much more severe sliming or corrosion problem than might be encounterel with a mixed microbial community. Certain organisms such as the Pseudomonas-type organisms are noted for their ability to form slime and for their resistance to a great variety of chemicals. In fact, they are able to break down and use as foodstuffs some of the blocides which are ordinarily used to kill other organisms. One partial solution to this problem, currently in wide use, is to switch blocides to prevent build-up of " biocide-resistant" types of organisms.
Research needed in the Area of Microbiological 1y Influenced Corrosion of Iron and Steel It is clear that microorganisms can play an important role (s) in initiating and/or accelerating corrosion of all steels. However, the specific mechanisms of attachment and/or enhancement are still not clearly understood. For example, L after considerable study the exact mechanism whereby SRB's cause corrosion of iron and steel is still open to question. The question of whether other organisms which produce HiS but which are not sulfate reducers can produce the same sort of symptoms needs to be studied. Very little research has been done on the matter of how. organic acids cause corrosion. The relative problems represented by different organic acids must be addressed. The role (s) of other materials such as ammonia, nitrite, nitrate, etc., which are very common metabolic intermediates from a variety of microbes, needs to be further elucidated. Certainly the recent discussions relating to the ability of certain microorganisms, including certain of the Pseudomonas spp., to actively reduce ferric to ferrous iron needs to be intensively investigated to determine the importance of this capability in the corrosion of iron and steel under a variety of conditions. Finally, we feel that it is extremely important that a group of investigators be given an opportunity to investigate cases in a variety of industrial situations where MIC is suspected. This group would need to examine the situation from microbiological, metallurgical, I environmental and process points of view and to do thorough work-ups relative to the microbiology and chemistry of the water and MIC products, electron
. ~u.
il
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. h t; microscopy and other types of metallurgical analysis all of which should be designed to confirm whether these are cases of MIC or not.
The area in which research might do the most toward helping to estimate the magnitude of the MIC problem and ultimately lead to the best chance for understanding and controlling it is the area of developing rapid methods for identifying MIC and the organisms involved, in the field. Such methods might certainly take the form of sampling kits for microbiological or chemical analyses i or the use of the fluorescent antibody techniques. In addition, on-line detection methods, somewhat similar to the " bug-pots" in use at DuPont,847) might be used. g Electrochemical methods (linear polarization) might be developed to assess l whether MIC is occurring under the conditions in the plant being studied. I Much more research needs to be done under controlled laboratory conditions, using biochemical, molecular, genetic and genetic engineering techniques to define the exact role of microorganisms in the various types of microbiological corrosion processes. Finally, the ultimate goal of being able to prevent MIC must be addressed. One of the most important areas in this regard is the development of methods, be they chemical or otherwise, to prevent the sorption of organics and/or attachment of organisms to the metal surface, since most cases of MIC can be prevented if these processes can be controlled. Also in this regard, we must find ways to disassociate preformed biological films from the surfaces of metals, since clean surfaces will under most conditions offer much less opportunity for MIC. A prioritized list for research needs relative to MIC of iron and steel is essentially the same as for MIC in general. That list is given in the last chapter: General Conclusions and Research Needs.
- . . _ . . __..m _.. _ _ . _ =_ . . _ . , .-
1 I r* . i CHAPTER 4 THE CASE FOR MICROBIOLOGICALLY INFLUENCED CORRO8 ION OF STAINLESS STEELS Introduction Stainless steels are iron-chromium alloys in which 12 to 30 weight percent chromium is added to iron to impart corrosion resistance. In general they are resistant to oxidizing media unless such media contain significant a, mounts of halide, (particularly chloride) lons. However, they are not particularly resistant to reducing environments. Since for aqueous solutions, dissolved oxygen is often the oxidant which induces passivation, areas of alloy surfaces in contact with an environment which is depleted in oxygen and also in contact with passivated surfaces often show abnormally high corrosion rates. Thus, crevices where oxidant availability is generally low, are particularly prone to corrosion. Additionally, if crevices become acidified, for example by the incursion of halides, corrosion rates in the crevices may be increased considerably. Metallurgically, the stainless steels are usually divided into four categories: austenitic, ferritic, martensitic and duplex. The most common alloys used in
; chemical process applications are the austenitic alloys. These alloys contain 12 to 25% chromium and 8 to 35% nickel. The addition of nickel stabilizes a face-centered-cubic crystal structurs which improves ductility and workability.
Common alloys in this family are Types 304 stainless steel (18 Cr - 8 N1), 316 stainless steel (with approximately 2% Mo added to improve resistance to i chloride lon),304L and 316L (very-low carbon grades of 304 and 316, respectively) and the less frequently used 317 stainless steel (approximately 3 to 4% Mo). Modern melting techniques allow high purity ferritic alloys consisting of Fe, 11 to 30% Cr, and O to 4% Mo, to be produced. Some of these alloys show good resistance to pitting corrosion, stress-corrosion cracking and general corrosion in l oxidizing environments. However, considerable research remains to be performed
. before they are generally accepted as replacements for austenitic alloys.
t
g, The third class of alloys, the martensitic stainless steels, are generally used for applications where high strength and moderate corrosion resistance are required, e.g., steam turbine blades, aircraft compressor blades and cutlery. There are no references to MIC of these alloys and it is unlikely that they would generally be used in chemical process environments which contain significant numbers of bacteria. The fourth class of alloys, the duplex steels are phase mixtures of ferrite and austenite. They have recently become available as wrought materials (sheet, plate and pipe). They show good resistance to intergranular stress-corrosion cracking and localized corrosion with improved strength when compared to either single-phase austenitic or ferritic steels. Additional duplex structures have traditionally been utilized in weldments for normally austenitic structures to inhibit many of the problems of tearing which sometimes occur in single phase alloys upon cooling after welding. Microorganisms involved in Microbiological 1y Influenced Corrosion of Stainless Steels 3 Microbiologically influenced corrosion of stainless steels, particularly of the 300 series, has been reported by a number of authors.neA8-52)It should be noted, , liowever, that several investigators have reported observing little or no attack on these alloys in experiments where MIC was specifically studied and where mild j steel was shown to be corroded.* SSI Perhaps the area of largest controversy vis-a-vis stainless steels relates to the involvement of MIC in crevice corrosion; the question is whether it is simply a classical crevice corrosion problem with the biomaterials being involved in the screening of oxidants, or whether there is a true accelerative effect by these biological elements on the corrosion rates. Reports of accelerated corrosion of stainless steels associated with microorganisms began to appear in the early 1970's. Many of these reports did not detail the specific types of organisms involved in MIC, but rather, only indicated that bacteria or some other organisms could be identified as causal to i the corrosion problems. Of the microbes identified with corrosion of stainless
- steel, aerobic iron- and manganese-oxidizing bacteria were associated with pitting I e
( . d l
]
- l in 304 and 316 stainless steels.(16,48)In these cases it was believed that the bacteria oxidized ferrous (Fe*8) and manganous (Mn*8) ions to ferric (Fe*8) and manganic (Mn") ions which when combined with ambient chlorides, resulted in pitting. In the cases reported, virtually all of the pitting was associated with weld seams.(16) However, it should be noted that, in this case, preferential corrosion of the ferrite phase was observed, suggesting a more complicated explanation. The preferential corrosion of delta-ferrite in duplex weldments has been reported in at least two other independent studies. In a NASA study, corrosion of 321 stainless steel (Fe - 18 Cr - 8 N1 T1) was reported to have been attributed to ,
microorganisms derived from human feces or from bath water inoculated with bouillon.(sa) However, while a variety of organisms were isolated, no direct causal relationship between individual bacterial species and corrosion was identified. There are few reported observations of sulfate-reducing bacteria (SRB's) involved with the corrosion of stainless steels. Only two cases of extensive corrosion in CPI environments involving 304 and 303 have been reported. However, several reports of similar cases are available from other industries (e.g., pulp and paper). Corrosion was observed on carbon steel, stainless stcels and galvanized steel in the same system.(16,48) Both SRB's and Sphaerotilus were identified. The results suggested that corrosion of the stainless steel may have occurred due to oxygen and or acid concentration cells created by sludge buildup. In this case then, the action of the bacteria may have been to create an occluded cell geometry rather than to intrinsically corrode the alloy. In a recent report, Pseudomonas Sphaerotilus and Desulfovibrio were shown to be associated with slime which covered corroded areas on stainless steel.(48)It was suggested that the slime formers set up anaerobic conditions in which the metabolic products of Desulfovibrio accumulated and acted to destroy the passive film. In a second study cited in the same reference, corroded areas of a 304 stainless steel pump impeller were covered with slime deposits which contained Pseudomonas, Aerobacter, Flavobacterium and/or Bacillus types of - bacteria. Desulfovibrio, Desulfotomaculum and/or Clostridium species were identified as occurring in or under the slime. Gallionella was also identified as
. causing corrosion at welds in 304 stainless steel in yet another case study cited in . the same reference (J. G. Stoecker, personal communication, R. E. Tatnall).
. ]
1 It should be noted, however, that other studies have indicated no effect of the SRB's, in the absence of slime, on corrosion of stainless steels.(51.53) i Mechanisms involved in Microbiologically Influenced Corrosion of Stainless Steels Stainless steels and other " passive" alloys rely on a thin (virtually transparent) surface film to provide resistance to corrosion. This film requires oxidizing conditions for stability, both to initiate passivity and to repair subsequent chemical or mechanical damage to the film. It is for this reason that b stainless steels are particularly susceptible to crevice corrosion. The passive film , is set up by reduction of oxygen in solution according to the reactions: Me-Me" + 2e- (1) 1/2 O2 + H 0 + 2e -2OH- (2) 1 Me" + 2OH -Me (OH), (probably precipitated film) (3) Alternatively, some investigators believe that oxygen alone, reacting with the ; alloy surface, is sufficient to induce passivity. In either case, oxygen is generally required to initiate the film and, if the film is damaged, to repair it. In non-halide environments film repair is usually not a problem since crevices, being essentially stagnant areas, do not create conditions where the passive film is damaged. However, when mechanical action, such as fretting, occurs in the crevice, high s corrosion rates may be observed. An additional problem is presented by the halides which, when present, can chemically damage the passive film. If insufficient oxygen is available to reform the film, corrosion may be initiated. Even if the nominal bulk chloride concentration is extremely low, the chloride concentration in the crevice may increase considerably due to continued metal dissolution. Since in this process, no oxygen is available to produce hydroxide ion, dissolved metal ions will react with available hydroxide, and a charge imbalance of Me" and H* ions will arise. Chloride ions which are more mobile (due to concentration gradients) than hydroxide ions will diffuse into the crevice, and will react with the metalion and water according to the reaction: Me"+ 2Cl + 2H 0-Me(OH) + 2H' + 2Cl-4
fu . ,
\
4 f I 43 [p,. - This halide acid envircamer. , further destroys passive films resulting in
~
6
. high corrosion rates in the crev.ce.
It is tempting to assoc: ate all MIC of stainless steels with simple crevice
,e mechanisms, where slime prod 1.cers are simply effective creators of crevions. i.e.,
between the slime and the metal surface. However, there is evidence that the l _
, microbes create a further accelerative effect which omtalyzes the corrosion l N reactions to a greater degree than is explained solely by the mechanism of a j simple crevice. For example the following scenario has been proposed
- for
, situations where sulfate.reducir.g bacteria are present in aqueous solutions:
t (1) Slime formers attach .o the metal surface and multiply especially in a t regions of low fluid ve'.ocity, such as at joints and at other stagnant areas. (2) As the deposit grows. it traps particles from the water. These include many aerobic bacteria. including the iron bacteria, which subsequently 7 oonsume oxygen. creating the anaerobic conditions required for
.. classical crevice corrosion. Thus, the bacteria at this stage accelerate i
the rate of oxygen depletion and the formation of the crevice. (3) Any SRB's present may grow and concentrate in the anaerobic zones . and will attack the ferrous alloy in much the same manner as they .j
. _t- ! would attack mild steels (see Chapter 3).
Another possibility by which microbes may accelerate localized corrosion processes of stainless steels is suggested by the presenon of metal I ; concentrating / oxidizing microtes. These bacteria apparently fix the Fe**/Fe" or
' ~ '
Mn*'/Mn** redox potential at the metal surface. Accordingly, they may polarize l the surface of the metal to a potential which exceeds the critical breakdown potential and/or accumulate chlorides in the crevice region. The latter situation )
*~ would be expected to arise if the migration of chloride ions into the crevios is
, driven by the requirement to neutralize the increased charge created by the higher oxidation state of the metal ion. Thus the crevice environment is, in l(. reality, a FeCl, or MnC1. solution, both of which are known to be highly damaging to the normally protective passive film. This would be analogous to the conditions
, ~ employed in localized corrosion tests in which inorganic FeC1,/FeC1, combinations are used to accelerate (and to assess) the pitting resistance of stainless steels.
I 9
It should be stated that few mechanistic studies of MIC of stainless steels have been conducted, and the specific processes by which bacteria may increase 1 corrosion rates are still open to question. t Methods of Detecting Microbiological 1y Influenced Corra son of Stainless Steels in the Laboratory and in the Field I The bacteria suspected of involvement in corrosion of stainless steels are essentially those associated with corrosion of mild steels. (In the absence of passivity, stainless steels behave essentially like mild steels). Accordingly, the methods of detection are outlined in the chapter of this report related to mild i steels and in the Appendix. Methods for Control of Microbiologically l Influenced Corrosion of Stainless Steels Controlling MIC of stainless steels can be accomplished by the obvious techniques of either eliminating the bacteria, eliminating the sites where crevices , may occur, or by coating surfaces with alloys which are more resistant to localized corrosion. The first of these can theoretically be effected by appropriate biocide additions, but this has proven to be difficult if not impossible to accomplish in actual operating coriditions. In theory it is also possible for some blocides to encourage attachment of some organisms, thereby promoting fouling and perhaps subsequent MIC. Additionally, there are presently no uniformly accepted guidelines which can be used to determine appropriate blocide levels to prevent MIC. With regard to geometric effects, the elimination of gaskets, joints, stagnant areas, etc., is often not possible in engineering design. However, when possible, surfaces should be smoothed to help discourage bacterial attachment. Finally, overlaying or lining with higher chromium or higher nickel alloys may prove to be an effective method for controlling MIC if crevices are inevitable. Several other suggestions for controlling MIC are contained in the general article on the fundamentals of MIC by Tatnall.(se) 4 l 1
)
45-Research needed in the Area of Microbiological 1y Influenced Corrosion of Stainless Steels The research areas described in the section of this report dealing with iron and steel certainly apply to the stainless steels. In addition, however, the stability of passive flims should be examined, particularly in the presence of organic acids such as those often produced by microbes. It has been reported, for instance, that the resistance of stainless steels to localized corrosion is very much reduce'd when organic solvents are present.(87) The specific role of microbes such as Gallionella must be assessed. For example, in the section entitled Proposed Mechanisms, it was suggested that the Fe**/Fe*8 and/or Mn**/Mn** redox potentials might directly affect the corrosion potential of an alloy and possibly lead to enhanced chloride levels. Thus the ability of microbes to fix electrochemical conditions needs to be addressed. Mechanistic studies aimed at understanding the specifics of MIC might be one of the most fruitful, ultimately leading to control of corrosion of nominally " corrosion resistant" alloys. e L l f l e 0 0 e-
c-
= ,
i 1 _, 53- l
. .e \
o- . TUBERCLE l/ 4A1(OH)3
*/
' ~
lt:0, + 3H,0 + 6e,, ,64 0H)~ 4'Al**e 6(OH)/s. 6e + 3H,0 + 1%On c#'* / %e anode 4A1 Figure 9 - Diagram of oxygen concentration cell formed by tubercle.(64)
. (Reprinted with permission:
'The publisher, The Electrochemical Society, Inc., Pennington, NJ.)
.O .
e
i' 61 CHAPTER 9 GENERAL CONCLUSIONS AND SUGGESTED AREAS FOR RESEARCH It is the opinion of the study group that MIC of several different classes of alloys is well documented in the literature whereas the specific mechanisms for most are poorly defined. The sulfate-reducing bacteria seem to be involved in at least some form of MIC of most of these alloys. It is also clear that the formation of colonies, slimes, mats and tubercles on surfaces is a major contribution to MIC of most alloys. (It should be noted here that a decided effort to inform field engineers of the differences between free-floating and attached organisms and the problems caused by each should be made.) Enhanced corrosion under these formations may occur by production of oxygen and ion concentration cells, cathodic depolarization, acidification, halide accumulation or by direct metal /lon transformation by the organisms, etc. It is also apparent that few good simple methods are available for the reliable confirmation of suspected MIC in the field. In the literature available for review, reports of methods for the prevention of MIC (short of replacement with more resistant alloys) are largely unavailable. This probably does not adequately reflect the situation since presumably many cases of MIC are successfully treated by chemical water treatment methods with the results never published. It is hoped that ways wfill be found for reports on i such " success stories" to be published in the open literature. Data on the extent l of the MIC problem relative to general corrosion problems also are largely unavailable. For example, there may be many cases of accelerated corrosion, due to contributions from MIC, which have been improperly diagnosed due to ignorance of the possibility of the problem. , a The areas in which research is needed fall into two main categories
" technological" and " scientific." The former are those practical approaches i required to identify, mitigate and/or prevent MIC. The latter consists of a ;
description of the specific mechanisms involved and the development of new '
; means (alloys, chemicals, etc.) to combat MIC. (Note that specific recommendations for each alloy type are given at the ends of the chapters dealing with alloy systems.)
4 1 I
j 65-A prioritized list is as follows: f{ A. Technological [ 1. Develop reliable, simple (and hopefully inexpensive) means for detecting MIC in the field. In situ probes, test kits, etc., should be developed.
- 2. Develop quantitative or sem1 quantitative estimate of the extent of the problem using the methods made available above.
- 3. Develop adequate antifouling and slime dispersing agents.
B. Scientific
- 1. Investigate SRB's in greater detail as they are obviously very important to MIC of many metals.
, 2. Study the role of organic acids, particularly those produced by microbes. in the corrosion of various alloys.
- 3. Determine the ability of microbes to fix electrochemical potential parameters, e.g., on metal or alloy surfaces.
- 4. Perform biochemical / genetic studies of the microbes involved in
$ MIC.
y v i S. Investigate the possibility of biological solutions to MIC k problems, for example, enzyme treatments, use of bacteriovores, etc. . It should be emphasized that, while somewhat arbitrary priorities have been assigned in these lists, it is, at best, difficult to assign specific priorities. Rather,
- tha priorities assigned in the " Technological Research Areas" should be considered as evolutionary with Item 1 being required before Item 3 can be addressed. Similarly, the " Scientific Research Areas" are often specific to certain metal / environment couples and should probably be treated rather independently.
l e (0 .
- .. a
V Jl t APPENDIX 0 PROCEDURE FOR OBTAINING AND PRESERVING SAMPLES WHERE MICROBIOLOGICALLY INFLUENCED CORROSION (MIC) 18 8USPECTED AS BEING INVOLVED i A. Observations in the Field
- 1. It'is very important that the conditions to which a sample is normally exposed be accurately recorded in order to obtain the maximum amount of information from the sample analyses. At a minimum, data should be obtained for:
- a. Temperature or temperature range in the system
- b. pH of the system f
- c. Type of material (s) in the system, e.g.,304 stainless heat i exchanger
- d. Type of water being used, e.g., fresh, brackish, marine
- e. Operating conditions including shut downs, cleanings and other unusual events
- f. Chemical treatment used, if any I
- g. Water or process chemistry
- 2. Almost any other observations which can be made will be useful, e.g.,
conductivity, turbidity, suspended solids, organic loads, " downstream from a pulp mill," etc. ." B. Preparing for Sampling
- 1. Try to set up for sampling before the need arises, i.e., be prepared to ,
take advantage of unexpected sampling opportunities as they arise.
- 2. Try to let the laboratory staff doing the analyses know as far in j advance as possible that samples will be sent, how many, what type, etc.
- 3. If microbiological analyses are to be done, have available shipping containers, ice and arrangements for immediate transport of the sample to the laboratory. Getting the sample to the laboratory as soon as possible is critical, within 12-24 hours is a must (see D below). .
t
' 1 4-
~
- .. . s. ..
l w a
~
- 67
- 4. If it is decided that the samples will probably not be analyzed within
- 12 24 hours then it is suggested that the samples be killed and 3
processed for light and electron microscopy and chemical analyses (see D below). S. The best procedure is to combine the above and send both live and
^
preserved samples. C. Taking the Sample-General
. 1. Samples of water, or scrapings from the area, nodules, tubercles or k sections of material containing suspected MIC should be taken as soon as possible after disturbing the " normal operating conditions."
- 2. Samples should be taken in, or put into clean, sterile, glass or plastic containers.
- 3. Water samples are best taken from a " flowing stream" situation with
? minimum disturbance to the other components of the system, i.e.,
sediment or slime. Water samples are most useful when accompanied j by other evidence of MIC, e.g., tubercles. l
- 4. Scraping of some samples (tubercles, slime, etc.) is best done with sterile utensils, e.g., spatulas or spoons. Simply dipping in alcohol and burning off the excess will sterilize them. Swabbing is best done with i
sterile cotton swabs or gauze squares. ) D. Water Samples-Unpreserved
- 1. These are useful for microbiological, microscopic and chemical analyses.
I 2. Samples must be placed in a sterile container, capped, refrigerated and put on ice (not dry ice) and delivered or shipped to the laboratory as 1 ( soon as possible. Analysis in the laboratory should begin no more than 12-24 hours after collection. Samples must be kept cold (O' to 4* C) until analysis is complete. s I l l c. I
- ; *S i
1 b I . E. Water Samples-Preserved .. j
- 1. These are useful for optical and electron microscopic analyses and I i
for some chemical analyses. .
- 2. For routine analyses, preservation with approximately 2% i formaldehyde is generally satisfactory. Add 1 part commercial formalin to approximately 20 parts of water sample. The formalin should be neutralized (to pH 7.0) with KOH or NaOH before use.
For electron microscopy: 3. Add 1 volume of a 4% paraformaldehyde - S% glutaraldehyde fixative solution (see below) to 1 volume of sample, put on ice and ship to laboratory as soon as possible. ' Prepare the fixative solution as follows:
- a. Take appropriate precautions to avoid getting on skin or inhaling
- b. Dissolve 4g paraformaldehyde in 25 ml distilled water
- c. Heat solution while stirring
- d. Cool to room temperature
- e. Add 10 ml 50% glutaraldehyde solution
- f. Bring final volume to 100 ml with filtered buffered water Prepare buffered water as follows: i NaH 3PO. 6.41 g Na:HPO.
- 7H2O 4.31 g Distilled-deionized water 100 ml Filter through 0.2 pm or 0.22 pm membrane filter into sterile container, seal and refrigerate until use.
F. Samples of Tubercles, Sediment, Etc.-Unpreserved
- 1. These should be as undisturbed as possible and kept so during transit.
- 2. Guidelines for use of sterile sampling utensils, vessels, refrigeration and rapid analyses (see above) should be followed.
- 3. Be certain that the samples do not dry out before analysis. Place in moist container or, if appropriate, cover with water from the site.
l i 4
2 L - G. Samples of Tubercles, 811mes, Etc.-Preserved
- 1. Routine analyses: Bring the solution covering the specimen to 2% final concentration formalin (see E above).
- 2. Electron microscopy: Add samples to a 2% paraformaldehyde -
2,5% glutaraldehyde solution (see E-3 above).
'il. Sampling Kits Available
- 1. Kits for all types of sampling can be made available on a cost reimbursable basis. One such source of kits is Dr. D. Pope, (S18) 270-6757.
A G
---;_-~_.,___~,_~--7~_-~-~~~ -
'*"'"'"'^#'"'"
j M & B Monographs CE/l
' CE/2 SOLVENT TREAThfENT OF COAL W S Wise G'eneral Editor:J Gordon Cook, PliD, FRIC h
CE/3 Tirs FLuinisEn ConsusTion or COAL 0 D G Skinner I CE[I CARBONISATION OF COAL x . J Gil> son and D II Gregory , I.U , CE/5 Tur. Pa:NCIPI.Es OF GAS EXTRACT ON s P Paul and W S Wise M, 1 C r O b 1 0 l O E 1 C a l l O Other Chemical Engineering Titles availaisle TL/CE/l nonon CarrOS On A G Massey and J Kane G H Booth, MA, PhD (Cantab.);
,,,, ,,,,,,;,,,, ,, , ,;,,, ,,g n,,, gi,i,,,
BSc (Lond.) I
! i
~8 8
I Mills & Boon Limited *?y london '- k 4
, (
--NO. 4 *We(M.*
~~ _ : - - - ~ i" - e e- m -- - - - -
I l First published in Great Britain 1971 CONTENTS
. by h1 ills & Boon Limited,17-19 Foley Street, London WI A IDR page
. List of Plates . 7
, C hiills & Boon Limited 1971 '
List of Figures 9 8 i
! ISBN 0.263.51584.2 1. NTRODoCTiON II j il , Nomenclature- 11 ' l! All rights reserved. No part of this publication 3: may be reproduced, stored in a retrieval system, 2. MICRO-ORGANISMS OF IMPORTANCE IN CORROSION 13 d or transmitted in any form or by any means, Sulphur-oxidising bacteria 14
- electronic, mechanical, photocopying, recording Sulphate-reducing bacteria
, , 16 or otherwise, without the' prior permission of l Mills & Boon Limited. 3. BACTERIAL CORROSION IN THE PREsENCr' OF OXYCEN . 2I
. Corrosion of concrete 22 Corrosion ofiron and other metals 23
- 4. BACTERIA 1. CORROslON IN THE ABSENCE OF OXYGEN 27 Iron and steel 27 Non-ferrous metals 40
; ; 5. CORRosidN DUE TO DIFFERENTIA 1. AERATION l stTUATIONs SET UP BY BACTERIA 4I
- l .
Tubercles 41 I [ 6. PROGNOsts OF AGGRESSIVENESS OF solLs TOWARDs l BURIED METALS 44
, Assessment of soil aggressiveness 45
; I.*
- 7. PREVENTION oF MiCROB AL CORROSION 50 Inhibitors of microbial action 50 s). Metalmlite removal Oxygen 52 52
, pli 52 Protective cestings 53 Cathodic protection 54 Natural protection 55 Printed by photo-lithography and Reading List 5ft made in Great liritain at the Pitman Press, Bath 5
_ _ . _ _ _ _ _ _____s
- 4
.}~
. ' LIST OF PLATES . -
I Electron micrographs of Asulfeci&rie =lgaris b.
, (Hildenborough)-usual form. By courtesy of a the National Physical Laboratory. . Crown -
l copyright. 17~ 3-8 I II Spirilloid form of a mesophilic asalfeui&rie.
. l Crown copyright. I8
[ III Acid corrosion of building stone. By courtesy of :( J. Pochon and C.Jaton. 23 .( i i . IV Corrosion of historical monuments by sulphur-
- I oxides in Cambodia. By courtesy ofJ. Pochon e and C.Jaton. 24 -
8 V i ' Cast. iron pipes from anaerobic soils. By courtesy of the National Physical Laboratory. Crown lS{ h t copyright. 27 , VI Perforation of water pipe (cast-iron) by j' 5 . sulphate. reducers. Crown copyright. 28 1-i n .
; VII Apparatus for the study of the polarisation of . ; -
{ i steel in bacterial cultures. By courtesy of the , I I National Physical Laboratory. Crown copyright. 30 , i ! VIII The measurement of bacterial corrosion in : l continuous culture. By courtesy of the National j ' Physical Laboratory. Crown copyright. 35 IX Steci specimens used for polarisation experi- l' ments. (a) unused, (b) exposed to sulphate- ; reducers, (c) as in (b) but with an excess of , ferrous iron in the medium. By courtesy of the a
},
t National Physical Laboratory. Crown copyright. 36 5
, X Bare steel specimens exposed to River Thames i for 5 years. Note combination of corrosion and
- i fouling. By courtesy of the National Physical '
l Laboratory. Crown copyright. 13 i ' i I 7 a : . g ! i g .
, . - . . - . . . . - . . . . 0
- . ~ . . . . . . . . . . . - . - * - - - *
~
tescacesotocacAL ComecesON
;. t l'
XI Field testing of soil for resistivity and redox- LIST OF FIGURES potential. 47
- t. I XII Well preserved metal objects recovered from 1. The sulphur cycle in nature. ';
l .~ , 13 Hungate, York. By courtesy of the Department of the Environment. Crown copyright. j 56 2. Anodic and cathodic polarisation curves for mild . steel at 30*C. 31 p: t J 3. Anodic and cathodic polarisation curves for mild 4
;! steel at 30*C. 32 h.
ll Ik
- e. 4. Relation between hydrogenase activity and corro- ld i fl sion rate in batch cultures of sulphate-reducing I bacteria. 34 I
- n -
]
- 5. Cathodic polarisation curves for mild steel in i
, i l,
g e
static sterile suspensions of FeS in 1 per cent ,t [* Nacl at 25*C. 37
!l il
- 6. Redox probe.
<t 48 ,',
l i - go li
. u.l ' :
,\
. l .' ' .;
i
* ,I,'
ll : l'h ;
.s ,
,o 6 9 .
l j .- , 3 i
, If i '
, :! 4 4 I , 8 . t i i;
. - - . . . . . . . . . . . _ I
L
; minooucwm - .
. I t
- 1. Introduction L.
s. 8 Microbial intrusion into' the field of corrosion does not
' -involve any new form orcorrosion process. Corrosion can E. be defined as an electrochemical process Whereby part of C 1 the surface of the corroding substrate is oxidised and
- 6 transferred from the solid state into solution, accompanied ' !!!
by the simultaneous reduction of some component of the
-3 corrosive environment. This definition remains valid lk.
id ' ll ( whether microbiological influences are at work or not. I There are essentially two ways in which microbes are f , involved in corrosion processes. Firstly, by virtue of their 3 : ,, growth and metabolism, they can introduce into an
}* otherwise innocuous system, chemical entitics such as acids, alkalis, sulphides and other aggressive ions which will render the environment corrosive. Secondly, microbes l' l may enter dirull.y into one or more of the electrochemical j - l $
, j reactions at the surface of the substrate, thereby initiating ;!! i; or accelerating an electrode reaction already potentially j j!I
, present. Alternatively, the presence of the organism and l f ,
t
. its entry into the cIcctrode reaction may provide a d ;
t differert pathway for a familiar process. If these points arc l ab j I ; borne constantly in mind, much of the " mystique" that p# ; has bedevilled this subject for many years will disappear. i ! j
, NOMENCLATURE ?
! P
' 9
; Confusion may arise over the nomenclature of micro. e
,1 organisms. A micromrganism is classified and named j according to its known characteristics and physiological i 1
and biochemical behaviour. All too frequently,in the light p 6 of new knowledge,-it becomes necessary to reclassify a ' ' ' particular organism. This has often happened to organisms involved in corrosion, and the same organism may bc
; encountered in the literaturceunder a variety of names.
l I f 8.
,p ... ... ... . ........
_ _ _ _ _ _ - - - -w
344CROR3OlJDGICAL CORROG80N
- The sulphate-reducing bacteria, for example, which include the most important and most frequently-
- 2. Micro-Organisms of- . , .
encountered bacteria in the corrosion field, may be found under the name of Spirillum, Microspsra, Vibno, Sporovibno, ImnOrtanCC r in Corrosion Desulfovibrio, Clostridium and Desulfotomaculum. E
' Micro organisms covering a wide range of genera and In this account, names used are those in general use at the :L species are encountered in corrosion problems, but the time of writing; in referring to earlier literature,' the most familiar and important ones have one feature in !h nomenclature used therein is changed to that now current.
common; sulphur and/or its compounds play a vital part in their metabolism and they are intimately concerned if4 with the sulphur cycle in nature. .
- t The natural sulphur cycle is illustrated in simplified form in Fig.1. The upper part of the main cycle is relevant to ; ' the understanding of microbial corrosion, together with the "short. circuit" in which sulphate may be reduced to .
sulphide without going through the organic sulphur I, . compounds. !'J;e
$ik
.\
I SULPHUR e Oxidation I Oxidation 'd .
-bacterio I -bacterio Y j
Reduction I f -bacterlo j. *
/
/ Reduction-bacterio l HYDROGEN SULPHIDE SULPHATES i .
Degradotion i!
-onimals and l Synthesis ,
bacterio plants '
~
t ORGANIC SULPHUR COMPOUNOS Fig.1 The sulphur cycle in nature. ,
! 13 12 i
f 4
un omoimecas.(_ -
' meno.omumma ca mean=s m um.mm -
4 The portion of the main cycle concerned is the province of ' as its main energy. producing reaction. The ' oxidation
.[.E the sadidur.exiduins Aecteria; the short-circuit is that of the ; does set involve tetrathionate as an intermediate,'and in "
selfr": " -!q 6erserie. this way it differs from the other two. n. deeperus will y' t 4 also oxidise elementary sulphur to sulphate but will not i- t SULPHUR.OXIDISING BACTERIA I oxidise sulphide. The oxidation will begin at a pH ofabout ' 7 8 and a fully-grown culture will reach a pH of around The oxidation of sulphur, thiosulphate, sulphite and 3
- 45. i.
g several polythionates to sulphate, with the simultaneous , i 8 production of strong acid, is carried out by a group of H. rescretirares will oxidise thiosulphate with tetrathionate
} bacteria of the genus Die &arillas; three species, n.
~
as intermediate; it will also oxidisc sulphur and sulphide. j #Aieperas, n. die.exideas, and the graphically. named H. The optimum pH for the growth of the organism. is I d rearrrtiverus, find a place in corrosion phenomena. They between 4 and 2, but slow growth may continue to an l ' l- are all stubby, rod-shaped bacteria, measuring 0 5 p by ' ultimate pH of about 1. :
; l 0 to.3 O p; they are aerobic _(requiring the presence of , I l oxygen for growth) and obligately autotrophic, meaning n. die.exidans will produce even stronger acid, reaching al !
F that they synthesise all their complex organic compoimds : pH of 0 6 or less, and it will continue to live in a more acid g
} (proteins, carbohydrates, etc.) from inorganic starting medium than any other organism yet reported.
I Nf materials, and are unable ia make use oforganic materials ! . M-c as foodstuffs. Cell carbon is derived from carbon dioxide, All three organisms are widely distributed in nature, being , 0 l nitrogen from ammonium compounds, etc. found in muds, soils and water. l :11 These bacteria are all actively motile, bein'g propelled by a DETECTION TEST O single polar flagellum when in young culture, but they A simple test is recommended by Staikey' for detecting I! i may lose their motility with age. They do not form spores. 3 the presence of these bacteria in suspect material, using a They exist as single cells and do not tend to form chains or mineral salt medium of the following composition: h! aggregates. 3 y/ , (Ni1.),SO. 3g i The net energy gain resulting from the oxidation of K H,PO. 3g reduced sulphur compounds provides energy for the C 0 Sg < ,. synthetic processes of the grow, m g orgamsm. The optimum 9 g FeSO 0 01 g j temperature for growth is 25-30*C; the orgamsms Distill'ed water i dm* p exhibit some growth over the range 10-37'C and are {!
. killed at about 55-60*C. . This medium is dispensed conveniently in 100 cm8 3 quantities in 250 cm' Ehrlenmeyer flasks. About I g of j Differences between the three important species may be I clementary sulphur is sprinkled on the surface of tin- i summarised as follows: contents of each flask, and the flasks are closed with loose plugs of non-absorbent cotton wool. The flasks are
- n. dieparas oxidiscs thiosulphate to sulphate and sulphur sterilised by steaming for one hour on each of three 14 .
l'e i 4 1
. . . . - . - . _ . . . - . - . . . . _ . . . . . .*.~. . .. .
uncmo..otooicas. commonon ! MICMO-OMHAWSMS OF WPuu TAWF. m mM!OHON -
; s i-successive days, taking care that the sulphur remains '
, .e c c.- -
floating on the surface of the liquid. (If the sulphur sinks,
, _ , ' ,(. 1. , -" ^ 'i'% 'iy- c i ..
the efficiency of the medium is greatly reduced.) The pH of the medium is adjusted with sterile hydrochloric acid or k,[{! y ( '
'- %p; y E s caustic soda to a suitable value (7 5 for Th. thioparus or 5 0 for the others) and a flask is inoculated with about I g or vy h-bg.p,g a
vef I cm* of the material to be tested. The flask is then in- < . M;, - ! cubated in air at 30*C and the pil measured at intervals .C (?<l[W@M. Mb
- i
! over a period of 4 days to 2 weeks. An abrupt drop in the ' h- .
1 plI of the medium indicates growth of thiobacilli and their N8T ' w i:' .*
' MTd. .M
$ 3 8 '. .-
9; N I j i presence in the inoculum. r, q .'P.f.t J
*M ' ; .4D r.7. A h.:
1.l.8 - [
-- ; ;i -
pk,Q SULPIIATE. REDUCING BACTERIA
# I '
j 5,b **' fp ,; 4.: F w - n . .- 1, M, JI ~ ' The reduction of sulphates to sulphides is effected by i *g I f .,.{.j@(',1.,1,,f. ,, { sulphate-reducing bacteria of the genera Desulforibrio and '- Desulfotomaculum. l Og]:
& . '.., :l4' y,:i:. i.4 '.'h T . ' . . -
The genus Desulfocibrio comprises five species, four of hf-h . f.h [p.g9 &L-:,g '* h I ? which influence corrosion. All are curved rods (they may Y@W'IP*'h ' '.
'j occasionally appear straight), sometimes sigmoid or [p;.y71 *. - '
' C iP spirilloid (Plates I, II). All are obligate anaerobes, i.e. r$MM'D-#?- - j '
!3)
I
! they will not grow in the presence ofeven traces ofoxygen.
They grow well at temperatures between 25 and 44*C, and f.DJ M
,)
at pil values betv een about 5 5 and 9 (optimum pII 7 2 . thyf,Ny).*?p (f.Nk,,y ?+^,,g'[
+- ih' approx). rd4#,pe 'h?q{[. .: ;($p -
i
* ')
t ' ,, l The three species D. vulgaris, D. desulfuricans and D. Plate I Electron micrograph of " Desulfovibrio vulgaris" !; salexigens are all about 0 5-l 0p by 3 0-5 0 p in size r (Hildenborough)-usual form. By courtesy of the National l l { and are actively motile, bem_ g propelled by a s_mgle I i Physical Laboratory. Crown copyright. ll t polar flagellum. D. salexigens has an absolute require-l ment for about 2 5 per cent sodium chloride, but the ei other two species can be trained to grow in either fresh ' or salt water conditions. The species D. africanus is larger, j are known to be involved in corrosion. These organisms a sigmoid rod 0-5 p by 5-10 ;it is rapidly motile, with a are also obhgate anaerobes; they are straight or curved l polar flagellum at each end. rods, usually smgle but sometimes m pairs or short chams. They produce terminal or subterminal spores, accom- ; The genus Desulfatomaculum compri-s the spore-forming panied by slight swelling of the cells; they are motile, sulphate-reducers; it contains three species, two of which using peritrichous flagella to give a " twisting and
- 16 . 17 i ,
J. ._ ........ .. ..
~- _- ,- - ,
-.. .......a...o. ;
a neuOo-oRoAN snes or enerORTAN(7 BN cORMORION { , l. t' i
- tumbling" motion which is easily distinguished from Browman movement. t, the oxidation of elementary hydrogen. The latter property !
governs, at least partially, the involvement of these !. *
- bacteria in corrosion phenomena. '
l' ! . g--,J ',' g . The vigorous growth of sulphate-reducers demands L 4 .w . ,
. ' reducing conditions more rigorous than can be obtained
@,$;g[g
~- simply by the exclusion of oxygen, and a redox-potential "
, ,,,. g,b4 . .# of around -100 mV (normal hydrogen scale) is necessary i j gy' *O - if the bacteria are to thrive. In the absence ofinterfering [!! y , ' $, ,, influences, however, even a marginal growth will produce !!
.,lid' s .; '
{ ~ " ~~ 7 .' s. 4 sufIicient hydrogen sulphide to reduce the redox-potential to a more favourable value, so that growth once begun
'il .
{ g
.#'.- g *w*
T .
- s. e '
C tends to accelerate. DETECTION TEST [ There is again a simple te.*t available for the detection of I . sulphate-reducers. In this case, the medium (due to i i Baars'8") consists of: . l .
- Plate II Spirilloidform of a mesophilic "Desulfocibrio". Crown KII,PO, 05g l*
copynght. . Nil,Cl Ig f. i CaSO. Ig ' Dim. nigrifwans, formerly classified as Clostridium nignficans, MgSO* 2g Sog;ug,'711 lactate0 35g
; measures about 0-3-0-5 by 3-0-6 0 . It is thermophilic.
tap water (A i with an optimum growth temperature of 55'C. Growth 1dm8
, r*
I occurs even at 65-70*C, and the organism can be trained in grow at 30-37'C. Dtm. orientis, I 5 by 50 ' is a I' The medium is sterilised by autoclaving and the pil I ' adj.usted to 7 to 7 5. About I g of the suspect maten.a l is mesophile w. h optimum growth between 30 and 37'C it l . . ! and an upper limit of 42*C. p aced in a stente screw. capped bottle of about 10 cm 3 4 i I ; capacity, and the bottle ,s filled to the bnm w,th i i the The pil range of Desulfotomaculum is similar to that of *** * ** "** ^ ***" *** Y*' '*"'
"'"'"'E i ** * "
.Desulforibria. All the sulphate-reducers are heterotrophic' (f' * *"" 'l**"EE#' b*
is screwed home so that air is not trapped inside the te. t, icy require an orgame source of carbon. Energy for ' growth is supplied by the reduction ofsulphate to sulphide. bottle. (For liquid sampics, double. strength medium is j *
! All the sulphate-reducers can effect this reduction at the '#'***" ' "" E #9 " * ' * ' " .' "" #
) expenw of the . corresponding oxidation of organic sample. For sampics of a marm.""#' .e origm, the med.ium :
'l*"fd be supplemented with 2 5 per cent sodium i
i material; many of them can also effect it at the expense of . , chloride.) I.
, 19 , l I ) '
N8 ' - -
neN:Rossos.ocaCA1. MamOEBON BACTERIAB. CORROS80N IN THE PRFSENCO OF OXVs;F N The boede is incubated at so c (55 c ror diermophiles). . Presence of the bactena as andacated by blackening of the
- 3. Bacterial Corrosion in the .
medium aue to the p,oduction of fer,ous suiphide. 2 or s days .meubatson as often sufficient for heavily-contaminated - Presence of Oxvwen /O samples; up to 21 days should be allowed before negative I results are affirmed. An absolute minimum of time should clapse between sampling the suspect material and closing Corrosion due to the activity of micro-organisms in the culture bottle; this prevents undue oxidation by aerobic conditions is invariably the result of the production J. exposure to air and inhibition of any sulphate-reducing organisms present. of a corrosive metabolite. Usually this is an acid, either 4l
, mineral or organic. lt ,
The sulphate-reducers are widely distributed in naturg; A wide range of organisms may be concerned in corrosion , using efficient technique, they can be isolated from most of this type, but thiobacilli, the sulphur-oxidising bacteria, soils. They occur also in natural and polluted fresh and salt are by far the commonest and most important. Situations - water, in hot springs, in oil wells, in temperate and in in which the bacteria have been unequivocally in- ,. ,. tropical environments; they have been found (inc.luding criminated are comparatively rare, but it seems. probable 3l the thermophilic types) even in the Antarctic permafrost. that this is often due to inadequate diagnosis of the , y cause. , 4
!h When corrosion occurs in an environment containing a '5 substantial amount of sulphuric acid, and there is no i immediately-obvious explanation ofits origin, thiobacilli I i should be suspected. The presence of the organism may be !
confirmed using the simple test already described, and an , l' investigation of the circumstances of the corrosion will ' ) usually reveal the source of sulphur. C'
'l' .
A typical example of this type of corrosion was ex-perienced on a housing estate in South London, where gas I pipes laid in a peaty soil were perforated by corrosion in little over a year. It was found that the soil had a pil of ;j about 2, and a sample stored in the laboratory for about a b ;; week continued to become more acid, reaching eventually ! !- t a pil of 0-6. Thiobacilli were shown to be active in the [ soil, and the source orsulphur was traced to the diffusion of hydrogen sulphide from a lower level; sulphate reduction was occurring in a layer of anaerobic clay, due to the action of sulphate-reducing bacteria. 20 21 I l
-+,,-- , ,... _... .. . .. _,..._,,
j un uimsosamarAL cuottiinHsM I BACMMIAl. (DNRosloN IN TuK PRFSENCE OF oXYt:FN
's V 2
i CORROSION OF CONCRETl; Other examples of this type of corrosion have caused the Ili ; r j There are several species of sulphur-oxidising bacteria collapse of massive concrete cooling towers. There are p'
) with difTerent optimum ranges, and it is possible for very many cases of corrosion of building stone (Plate III), and the archaeological treasures of Angkor Vat, the ancient T-4 low pII values to develop from conditions of near. ' .,
ncurrality (or even alkalinity) by successive dominance of temples of Cambodia (Plate IV) are in great danger from the same cause. Ahhough the phenomenon is com-h, ! the various types. Most metals suscrptihic to acid attack paratively unusual, its results can he spectacular. !! . may be affected, but some of the most impressive examples
- of corrosion by this mechanism have involveti concrete. - ' . ., r;. ,
y L ) i An example of concrete corrosion, investigated by ns.4' * ~._ ' lg;'l Parker'22' in Australia involved concrete pipes carrying "+' sewage; it demonstrated both chemical and micro- ,
*J' ' ..
bioh>gical. processes at work. The pipes were not com- 6
"
- l pletely filled, and the concrete surface in contact with the
- 7
, 'L y
) air above the liquid was exposed to the combined action of I : i gl carbon dioxide and hydrogen sulphide in condensate , ,
- j;. -,]. *i' from the slightly warm and fermenting sewage. The carbon dioxide gradually reduced the pil from its .
i *
. . . - 2 - g. ,s .
S r e d.c. , b,, ,j e
-?-
!,L , -
.l original value of about 12 5 to around 8 5; the hydrogen -"~~ {.p.
i sulphide was partially oxidised by the air to ;i mixture of I .,,- ' c
._ L ' :-~ - #
-Wit shQs ] ,,
. __ - 27 l thiusulphate and polythionates, which further reduced the ' y ?. "
t
'U M tf. rig'F pil to about 7 5. l
~,
K7%=r-~
. g .; r3. *
* / l In the early stages of the oxidation, while the pII was still , ,
. -- L;, t*
around 10, a wide variety of organisms slowly oxidised
'[
thiosulphate and polythionates to polythionates and 4f 'N
.R N N ,t 1
sulphate. When the pli had fallen below 9, Thiobacillus , ) thioparus began ta show significant activity, forming l Plate nAmrosion of building stone. By courtesy ofJ. Pochon cicmentary sulphur, the pli continuing to fall to about 5. f l l and C. Jaton.
- A
- this stage, Th. concretivorus and Th. thio-exidans took over, t
,8
] oxidising the sulphur to sulphuric acid; this resulted in a CORROSION OF IRON AND OTilER METALS 1 rapid fall in pil to around I, causing the concrete to i ! disintegrate. ,, !. The iron-oxidising organism, Ferrobacillus ferro-oxidans, , { . e another autotroph, is often found in association with l !,'i it is interesting to note that the almost unique conditions thiohacilli, commonly in the vicinity of pyritic deposits, ' l in a concrete sewer pipe are precisely those that favour e.g. in mines. The organism derives energy for its meta-j , development of these particularly destructive organisms. i bolism from the reaction Fe + - Fe'+ + e. 2 1' 1 *2
? . '
] 23 1 g I , e } .
eeM'atomIOREN38 CAL (INEROBION DAf t FEBAl. (NKRUMION IN TBIF PEFSFMt3 np OxynFM often ofgreat value and great beauty, have been destroyed
$. , ,, , , ; by the action of these bacteria; the phenomenon is ,e Y-}
described as " fossil disease". N p,.
-l. . On the credit side, the activities of sulphur-oxidising F . '! bacteria have been put to constructive use. They have
?.
', +
, been used to accelerate the natural Icaching oflow-grade ores in the recovery of copper and uranium, and a y, f, ,i - ,'
? / . considerable research effort is being made to improve the : 1 k .,3 .
( efliciency of the process. h'i 13g
- k e ,. } e 3 For many years, an unusual form ofcorrosion oflead cable
*E1,$-)>g.3 p.~,v , ,fg ~~
sheathing in underground situations was known as y
. J \ . " phenol corrosion". It was believed to be caused by
[ .y , .
. 4' 'c
( ., ,y,' 'f phenols in the tar-impregnated wrapping materials used g { D g s .s._-
; ! as a protective for the lead, and much conflicting evidence accumulated on the corrosivity of phenolic compounds t
i
") Q". zi,-}.k [ J.'-h ". ,5 towards lead. Eventually, Coles and co-workers"* 8 showed that the real cause of the corrosion was the
'l ib
, s presence of organic acids oflow molecular weight; these ;'j Qb - .
s. were produced by bacterial and/or fungal decomposition i i
'6 4gM. . 4I ". . . v ;. ;% >-
of cellulosic material in the wrapping material itself or in '
'E i the soil. The use of cellulosic wrapping materials, such as s
- 3 hessian, as reinforcing insert for protective coatings is thus
, , . 5- {l to be deplored. . .
,e Plate IVCorrosion ofhistorical monuments by sulphur-oxidisers in Cambodia. By courtesy ofJ. Pochen and C. Jaton.
Examples oi organic-acid corrosion of iron, copper and aluminium associated with fungal growth have been l reported. Allen et al.'8" have described the corrosion of p The ferric iron produced in this way will oxidisc sulphur steel in a sugar-beet factory, caused by Imtobacillus. compounds to sulphuric acid. About a million tons of s sulphuric acid are contributed annually to the drainage ' A potentially serious situation can arise by the develop-area of the Ohio River as a result of oxidation by this ment of acidity and consequent corrosion in aluminium l organism of the pyrite in the mines of Western Pennsyl- fuel tanks on aircraft. A wide variety oforganisms has been vania. Severe corrosion of pumping and other mining isolated from this unusual environment. Acrobic organisms machinery results from action of this sort. Problems have include the fimgus Cladosporium resinas; organic acids arisen even in museums, where mineralogical and secreted by the organism have been blamed for this type of palaeontological specimens based on a pyrite matrix, corrosion. The bacterium, Pseudomonas aeruginosa, an 24 25 8, N- - - . . . . . . -
-ee .mpmeg - .mam- o e=pmenweg. M --
l - - - co o o SACTFStEAl, CORROSION IN TIIE Alt 3FNf'F. OF OXYGFN e occasional human pathogen, may also make a significant i, . contribution; Blanchard and Goucher"** have isolated a high-molecular. weight corrosive substance of unknown 4* Bacterial dorrosion in . composition from laboratory cultures. the Absence of Oxu~en /5 : Although most examples of bacterial corrosion in the acrobic environment can be identified as acid corrosion, IRON AND STEEL there are instances of the production of alkali, especially ammonia. This was reported by Bengough and Afay88in . r. l43 y 1924. Afore recently, workers in France'888 have demon- a , ' 1 .. strated the accelerated corrosion of copper in the
!.',....
- 1Nt laboratory by cultures of Flambacterium hydrophilium; no '
proven cases are known from the field. {. ' a;
. -g 4
1 I!, i i
,js j -
lu ; i
- s ~ :.j, .
l n' u . lI,i-6f-i ; :
' D-i *
.~
- l e '
.a . o=
( . ll -
" .Y,'{.'. -
l ,
}j$!} .?Y i !.
~
'e Plate V Cast-iron pipesfrom anaerobic soils. By courtesy of the National Physical Laboratory. Crown copyright.
hiost instances of seriom corrmion involving micro-organisms in the absence of oxygen (anaerobic conditions) concern iron and steel. Elcrirochemical comiderations 26 27 ? _..a. 7
**0CROG0sM.DC8 CAL (Ilah0SO90 antagensts>M IMJF 360 SMtf F'ONTIAL A8LM19fsN St8 ff43*lDNS se ila ge reanisni in canned foods. It has an optimum-growth temperature of 55 C and an ability to survice at 5. Corrosion due to .
very much higher tempesatures (c. 80*C). It exists in both
~
positive and negative hydrogenase strains. Differential Acration The pos. .itive strains of Dem. nigrificans behave .in the same - Situations set un I' bvf Bacteria way as their mesophilic counterparts. They are seldom - encountered in problems of corrosion in soil, rivers or the sea, but they appear frequently in corrosion of central- Consumption of oxygen in the course of metabolism is a heating installations, heat exchangers and cooling systems y feature common to all types of aerobic micro-organism. If .y og. crating at elevated temperatures. *
- microbial action is localised in the neighbourhood of a 8 3
structure liable to corrosion (e.g. a pipeline) a " differential NON. FERROUS METALS aeration" cell may be set up between those giarts of the g g ;
. structure where the oxygen supply has been depleted and Much of the emphasis in any consideration of corrosion (
problems is placed upon the corrosion ofiron and steel. In those parts where micro-organisms are not active, and the lsl a 4, supply ofoxygen remains unaltered. The oxygen-depleted recent years, however, it has become apparent that regions will be anodic to the rest, and will become centres aluminium and its alloys are equally susceptible to for the loss of metal. Tomashov and Mikhailovsky'8" j ,l microbiological corrosion. This is of particular concern to consider that "long.line currents" set up in pipelines by
- l. i the aircraft industry, where cases of corrosion and failure such a mechanism account for much pipeline corrosion. h*
of aircraft fuel tanks have been ascribed to,the action of sulphate-reducing organisms (often in association with 3[ TUBERCLES " other micro-organisms). {
. i Aerobic iron bacteria, such as Callionella ferruginea, l Exampics of the corrosion of copper, zine and lead have oxidise ferrous iron in solution to the ferric state and effect 8e also been described from time to time. In these cases, the t '
the precipitation of ferric hydroxides. These organisms are
- cffect may be a " secondary" one, caused by hydrogen common inhabitants of springs and brooks, and may find sulphide. A low redox. potential emironment is a good $
their way into water pipes. Precipitated ferric hydroxides { indication of corrosivity and of suitability for sulphate. can build up on the internalsurface of a pipe to form hard l reducing bacterial growth. It might be anticipated also ) excrescences known as " tubercles", which are firmly that metals such as copper, zinc and lead would exert a adherent to the metal surface.
- I toxic cIfect on the bacteria. '
. A tubercle shields the surface of the pipe from contact with .
The corrosion rates of non-ferrous metals under reducing oxygen dissolved in the water, and the surface at the base soil conditions measured by Denison and RomanofP8" are
.abstantial, and cannot be dismissed out of hand.
'., of the tubercle becomes anodic to those parts of the internal surface of the pipe which are not covered by the deposit. Similar tuberculation phenomena have been described in which other types ofirori-oxidising bacteria, ,
40 - 41 4 e
**.m** mea.* -r 6 - - - - r------ -. _ _ _ - - _ -
, , ,,, p ,
- - , _ _ _ _ _ __e
l ans. 4ateemass44as33CAS COR300EOc6 43Dethtut04DN IM rp. tot BHPFF.St Po g l40. %D IE % 8ItDN SilUA B BIDMS c.g. IsprotArix and CremotArix have been involved.'*" The relatively small area of anodic surfacg in these circum- /* g stances results in intense localisation of the coirosion, and v, ' ' _. ., / E ?- water pipes are readily perforated. 4 f .
- The problem is often intensified by the fact that the anaerobic region at the base of the tubercle provides a ',
suitable habitat for sulphate-reducing micro-organisms; (they proliferate in this region and add their own con-a- n Y tribution to the total corrosion. When a tubercle is .
., _ Qi
- chipped away, the area in contact with the metalis often
- 6 rich in sulphide, and active vibrios can be isolated. The d .*
l [~ , ,
- 1-5-2 5 per cent sulphide and 1,000 cells,Igram reported by
- 0 '
i llutlin'8"is typical. g { , l
- {! j!
There are many other examples of sulphate-reducers #.
- taking advantage of the anaerobiosis created by the growth 1
j of acrobes. Well documented examples are given by
}',3 I verson,i2" in which sulphate-reducers were found in j association with Pseudomonas arruginosa and the fungus
;j Cladosporium, the whole system being inst,rumental in
< p bringing about corrosion of aluminium.
j 63 lL
. [,. ,7 - .<-. ,$$
1 Sulphate-reducers are found beneath barnacles attached, 8
- o. .E ,e g -2.5 'Ny j for exampic, to the hulls of ships, where they find an N D
,. sy b anaerobic micro-climate similar to that provided by a tubercle. Other forms of marine fouling can yield similar II. ? - g/ I f l
! fconditions. Complex situations prevail at the surface of metal exposed to the waters of an industrialised estuary. 2.
- g., !, ,
j 4j licre, corrosion can be caused by water ofvarying salinity and oxygenation; sulphate-reducers may be active, 8 f generally at times of anaerobiosis and in localised situ- } ations beneath marine attachments and accretions of j ' 1 corrosion product. The formation and retention of accre- ~ { tions is influenced by movement and turbulence and it is i Plate X Bare steel spuimens exposed to River Thames for 5 \ often difli' cult to assess the importance of microbiological Jears. Note cornbination ofcorrosion andfouling. By courtesy ofthe ) s factors in the overall corrosion pattern (Plate X). I Xational Physical I.aboratorr. Crmen copyright,
. l
{ d i i n 1 i l t
- . - - .. - - - -.. : ~ . .
~
. u . , _ w. -- 4
,gy,m ,o, o, ,,:,o,,,, m,,,,,
t^ d; j .p.
- 7. Prevention of Microbial I
-(s) It must be. rcliabic fbr the or Consi,ic,al,ie ,peci,ici,y i, i,,,,iv I, ;ganism concerned.
nd i, i, impo,,a,,, .
.. that the causative organism is properly identified. -
.f (b) The inhibitor must retain its inhibitory properties in -
There is no universal panacea for the prevention of y the conditions prevailing, i.e. it must not he deactivatal by any other substance likely to be present. It must be stabic corrosion by micro-organisms, and the problem is usually ' approached more from the " corrosion" than from the at the operating temperature of the relevant system and it 4
" microbiological" viewpoint. must be a substance for which the organism cannot 5 develop a tolerance. (The development of strains resistant I, to disinfection is well known, particularly in the malical :
I .limination F of the causative organisms is seldom practi. p field, where pathogenic organisms with an acquirni ! cabic, except in closed systems, e.g. cooling systems and resistance to antibiotics have become a serious probicm.) tanks; even then, precautions must be taken to minimise .I 2' the risk of reinfection. A controlling additive must .I (c) The inhibitor must not itscir display any corrosive ~T
, pcnctrate to au parts of the system. ' Bacterial action, particularly when anaerobes are conecrned, is often action towards the system in which it is to be used.
f. concentrated in re-entrant crevices and stagnant corners 7 of a closed system;it is commonly associated w,ith deposits. Dilliculties of various types may be encountered in using
- h "A prebminary mechanical or chemical cIcaning procesls inhibitors against micro-organisms. The spore. forming 'r may be essential before the application of a m,icrobiaji thermophilic sulphate-reducer Deselfefomaculum nigryicans, k, for example can be controlled (bacteriostasis) by 0 25 Q inhibitor can become effective. [ ppm of chlorhexidine gluconate; the mesophi!- Ihselfe. 3
;3 ei&rie emigaris requires 2 5 ppm, D. deselfericans 10-25 ppm, INiilillTORS OF MICROBIAL ACTION and the obligate halophile D. salexigens will often tolerate ].
I I,000 ppm. Inhibitors of microbial action are of two types. On the one hand, there are the " biocides". which actually kill the organisms; on the other hand, there are the "biostats" Afost of the sulphate. reducers are inhibited by 20,50 ppm [e of cupric ions, but this would not be tolerable (and that maintain the organisms in a state of inactivity or would not be maintained) in protecting a structure based i
"non-growth". The distinction between these two classes on ferrous metals. The thiobacilli (sulphur.oxidisers), on 8 may be only a matter orconcentration ; a substance may be the ofher hand, will thrive in media containing up to bacteriostatic at one concentration and bacteriocidal at a 20,000 ppm of copper.
higher one. An cificient bacteriostat, however, may never become bacteriocidal.
- , Chromates are good inhibitors of sulphate-reducers and are also good corrosion inhibitors, but they are toxic and An inhibitor for corrosion. producing organisms must tend .to be dermatitic, rendering them undesirable in possess the following properties: many applications.
Inn
- 51
--_ - 1 . .. . #
- _ . . . _ . =- ~ _ - , ,_ __ _ ._ _ _ _ _ . __. . -
wermosmosca n s coenossose
' emmmwm or asecenniu. remummew In rilbet, every canc resguiscs inulividual cimsideratiosa it' -
activity and growtle are ahnost completely suppressed. biological controlis to be used as the protective measure. Laboratory experiments 'may be useful in predicting the Acidic conditions are undesirable from .the corrosion '. point of view,:but the maintenance of mildly-alkaline possible effectiveness of ' microbial inhibitors, but . conditions can be helpful in the ' protection ofiron and
. laboratory results cannot necessarily be extrapolated a . steel (such conditions can be dangerous in the case 'of directly into field conditions. Field trials are an essential I, supplement. metals that readily form complex anions). This tecimique has been used with some success by~ employing a lime or hlETABOLITE REMOVAL "
chalk backfill in a trench. There are other methods of 4 i
.providing high pH values in the immediate vicinity of. ])
Sometimes, it is poss.ble to control bactenal action by i
- buried metals (see page 55). .i d a ..
removal from the system of an essential metabolite. I Elimination of sources of sulphur, for example, will stop . PROTECTIVE COATINGS .{ the production of sulphuric acid by thiobacilli. In the , lc '
- complex ' system described earlier. . thiobacilli obtained - The commonest metliod of protecting metals against
- . their sulphur via hydrogen sulphide from fermenting corrosion is the use of protective coatings, i.e. the inter- ' %'
, j; i sewage; this might have been prevented by aeration of the '
Position of an (ideally) impenetrable physical barrier ! sewage during its passage through the concrete pipe. f between the metal and the corrosive environment. A wide 7 Unfortunately, the damage has oRen been done beyond range ofcoatings is availabic, and the most suitable for use i repair before it is realised that the problem exists. .k in any given situation must be selected with due regard to :- l , the physical, chemical and biological characteristics of. OXYGEN. - that environment. {; . J j So far as the sulphate-reducers are concerned, the l cheapest and most efhcient inhibitor is air or oxygen, Thading should w iMfM@@A a @ which is used to establish aerobiosas. Forced aeration of l Sometimes forgotten. Kulman'888 has reported on extensive te . 6 stagnant water has been used to control corrosion in tanks testmg orcoatmgs m. tended for underground use, and has t (and, mcidentally, to banish; offensive odours); the sh m m to k s g h m M h a h ' - 6
- - drainage of water-logged sou.s to improve aeration has rganisms. Neoprene, asbestos, icit, petroleum wax 'and .
! been used to control corrosion of buned pipes. The laym, g salt msdMpWI @pMW& j ! of pipehnes with a surround ofgravel has proved effective, in soil. %dv nidd a dh Wa m 1 but care is necessary to ensure that such treatment pudady & to ad hig W m 4 , providcc a dram and not a sump. In the latter event,- .- ethylene or polyvinyl chloride, heavy coherent coatings conditions may be worsened. - bMohMewdeAN4wam mechanical reinforcement by inert materials such as glass 1 Pgg , 1 . fibre, give good results and are relatively cheap to apply. o
=,
f+ Extremer of pH miiy be used for controlling sulphate-It is important that ti cre sliuld be a gooil physical bond 4
, +
rethicers. Guuiddhe approximate pli range of 5 5-9, between a coating and the surface it is designed to protect. f . . 52 3 4 51 1 < y l L 3
. .. .. _. _... -n -
. n. .
" ' - _ .. .+ . . , . . , ~ -- ~
e - " ~ >~
,.,, A - _ Y : s f 2, .
av m mm. unu.=ia 6.=:anow .
~ .
.n -
jj ,) / < [foisture bescath a' poorly-bonded coati'ng may contain 3J - llaboratory experiments using pure cultures of the bacteria - +' an assortmeD. of micro-organisms, and conditions for the by Booth et eL"85
.M
establishment of anaerobiosis are excellent. By the same ; token, the coating should be free-Irem fMects, pinholes s
, The use of cathodic protection gives 'a Innus in so far as
- ;and mechanical damage sustained after its application;it e restriction of the action of the sulphate-reducers is
, si.ould have low absorptive capacity for water, and the { concerned, since its application results in the development outer surface should be free from protuberant reinforcing g of alkaline conditions in the immediate vicinity of the material liable to.sedi any " wicking" action. surface. This has an inhibitory effect on the bacteria.
ir ,, 7 j CATHODIC /I'ROTECTION ' In order to reduce current drain from the protected f~ j , i -
' system to an economic level, v.athode protection is applied Thwietically, the techm<.que of cathodic protection of - wherever possible in combination with a good protective metals should be foolproof. Corrosion of the vulnerable i h ;, sd a % & fmcie of & Wic -
- , ; g -
surface is-rendered impossibic, as all awxlic, areas are , ; climinated by making the entire structure into tlac ' -; j cathode of an electrochemical cell. The achievement of t NATURAL PROTECTION lp } this state of affairs is a technology in itself. 1 In 1950, in the course of archaeological excavations in ( York, a number of extremely well-preserved iron objects b Two techniques of cathodic protection are commonly 4 employed: (1) the " sacrificial" method, in which the dating from the Roman occupation were unearti ed from C structure to be protected is electrically bonded to anodes soil in which microbial corrosion would have been
! of a more electronegative nature which are corroded expected to have been very severe indeed (Plate XII). The same phenomenon has been observed in many other cases, f
.r preferentially, and (2) the " impressed current" method, i wherchy a direct current is passed into the protected and some museums-notably the Guildhall Afuseum in I
l l the City of London-have impressive exhibits of archaco-l surface, thmugh the corrosive environment, fro:n anodes 8 of a remotely-situated inert or scrap metal matenal by logical specimens preserved in this way. The soils in which means of a direct-current generator. these specimens are found are usually water-logged black ' clays and silts containing, in addition to the well-preserved iron, quantities of bones, Icather and wood.
- in normal circumstances, protection of stect is achieved I For a long time, it was considered that preservation was when its potential is depressed to -0 850 volts (referred to the Cu/CuSO. electrode).. Practical experience has shown -
due to the inhibition of the sulphate-reducing bacteria, .*
' abundant in the soils, by traces of tannins emanating from that, in the presence of active sulphate-reducers and/or the leather and wood. Experiments showed, however, that sulphides, it is necessary to depress the potential by a l tannins were not inhibitory to the bacteria unicss the
- further 0-100 volts, i.e. to 950 volts (Cu/CuSO.) to l concentration was sulliciently high to shift the pH below a achieve the desired protection. This extra requirement is value of about G. The "non-aggressive soils concerned I predictable from the thermodynamic considerations of were always around pII 7 and contained only traces of i
llorvath and co-workers"Uamt is further substantiated by tannins. i i
! st .
55 5
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Mee:sessetwasisolcp.a. txastrosaure PalEVENTION OF teICROntAL (xn2Rutanes i The preserved objects are covered with a thin, compact and strongly-adherent black film, often carrying a light- - blue bloom. Analysis showed this coating to be largely of
' the basic ferrous phosphate, vivianite (3FeO.P3 30.
8110). 2 Polarisation test on the objects revealed intense
, anodic inhibition of the escape of ferrous ions into solution.
The general condition of the objects and the absence of any detectable quantities either of oxide or sulphide , suggests that there had not been any appreciable corrosion 3 in either aerobic or anaerobic circumstances before the t vivianite coating was laid down; it can be inferred that this occurred soon after the time of burial. ['
. , 8 We have no knowledge of the mechanism of formation of 2
., ; I this highly efficient " natural" protective coating, nor
~ . j i'
'i I
whether its equivalent could be produced artificially. The ; conditions in which it arises are clearly very difTerent from i c. ..- v
.]
j) those in which industrial phosphate coatings are applied . { and from those to which iron articles are normally exposed 1
>{ in use. There is clearly scope for much useful work on @
9
,4: I thisintimidatingly complex system; the results could be of
.. ~ ,rA a
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immense economic imprance, l' e W T. - ti
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Plate XII Wellpreserved metal objects ruoveredfrom flungate, l York. By courtesy of the Department of the Environment. Crown ; copyright. l i M
- 57 4
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sewmoseonnueCAR. OpetseOEGON . ggggg,g,,g g ggy l READING LIST 11. G. H. Booth aml A. K. Tiller, "Polarisation studies of mild steel in cultures of sulphate-reducing bacteria", .- l Treas. Faraday Soc., 1960, 56, 1689-96; 1 % 2, 58, i 110-115; 1962, 58, 2510-6.
- 12. G. II. Booth and F. Wormwell, "Corresion of mild CORROSION (General) steel by sulphate. reducing bacteria: clTect ofdilTerent strains of organism",1st lat. Congr. metall. Cerres.1961, I. L. L. Shreier,. (Ed.), " Corrosion" 2 vol. Newnes, Butterworth, London 1962.
London 1963. 13. G. H. Booth and 'A. K. Tiller, " Catholic character- 4
- 2. U. R. Evans, " Corrosion and oxidation of metals", istics of mild steel in cultures of sulphate-reducing Arnold, London 1960. !
bacteria", Cerros. &i.,1968, B, 583-600.
- 3. J. A. Costello,- "The corrosion of metals by micro-
!{
- 14. G. II. Booth et al., " Criteria of soil aggressiveness organisms : a literatu re survey", Internet. Biedeterieration i Bull.,1%9, 6,101-118. !
towards buried metals", Brit. Corrot. J.,1967, 2, 104-118.
- 4. A. IL Walters andJ.J. Elphick, (Eds.), "Biodeterior- . 15. G. H. Hooth L Elford and D.S. Walcricy,"Corros:on ation of materials", Elsevier, Iondon 1968. of mild steil by sulphate-reducing bacteria-an -
alternative mechanism",Rrit.Corros.J., 1968,3,212-4. 3
- 16. E. L Coles and R. L Davies, "The protection of
- MICRO-ORGANISMS cable sheathing: the ' phenol-corrosion' of lead", "
CArm. A d., 1956, 39, 1030-1035. ~
- 5. W. Vishniac and M. Santer, "The thiobacilli", Bact. 17. J. Ilorvath and M. Solti,"Beitrag zum hicchanismus --
Rev.,1957, 21,195-213. der anaeroben mikrobiologischen Korrosion der 7
- 6. L L. Campbell and J. R. Postgate, "Classincation of Metails im Boden", Werkst. Kerros., 1959, 10, 624- -
the spore-forming sulphate-reducing bacteria", Bact. 630. ; Rev.,1965, 29, 359-363. 18. J. Horvath and M. Novak," Potential /pil equilibrium i-
- 7. J. R. Postgate and L. L. Campbell, " Classification of diagrams in some Fe-S-IIs0 ternary systems and their l Desulfovierie species, the non-sporulating sulphate- interpretation from the point of view of metallic
- reducing bacteria", Bact. Rea., 1966, 31, 732-738. corrosion", Corros. &i.,1964, f,159-78.
- 8. R. L. Starkey, "The general physiology of the 19. W. P. Iverson, " Corrosion of iron and formation of '
sulphate-reducing bacteria in relation to corrosion", iron phosphide by Desulforierie desulfuricans", Nature, o Producers Afoothly, 1958, 22(9), 12-16. 1968, 217, 1265-7. d
- 20. W. P. Iverson,"Apossihic role forsulphate-reducers m MISCELLANEOUS the corrosion of aluminum alloys", ElutrwArm.
- Tuhmol., 1967, 5, 77-9.
- 21. T. P. Iloar and T. W. Farrer,"The anodic character-
- 9. M. E. Adams and T. W. Farrer, "The influence of istics ofmild stect in dilute aqueous soil electrolytes",
ferrous iron on bacterial corrosion", J. appl. CArm., Corros. &i.,1961, I, 49-61. 1953,;3, 117-120. l
- 22. F. E. Kulman, "Microbioh>gical deterioration of
- 10. G. C. Blanchard and C. R. Goucher, " Aluminum - buried pipe and cabic", Corrosion,1958, H, 213-222.
corrosion processes in microbial cultures", Elutrochen. Tuhmol., 1 % 7, 5, 79-83. 23. C. D. Parker,"The corrosion of concrete", Austral.J. Esp. Biol. Aled. &i., 1915, 23, 81-98. 58 -
,,9
- l. .
o ~ ~~ _ , _ .e - -
. u,. m.m. ,m a.. . m r2 ==. . a r i
- 24. J. R. . Postgate, "DilTerential media for sulphur 41. W. II. J. Vernon, "Comervation of Natur.il bacteria", J. Sci. Food Agric., 1959, 12, 669-674. Rewurces",1956, p.121 (london, inst. Civ. Engrs.). .
- 25. M. Romanoff, " Underground corrosion", Nat. Bureau 42. W. T. Smith, " Analysis of the merits ofsoil corrosion ofStandards, Circular 579, Washington D.C.1957. survey work for the Amarillo-Denver line", Westers
- 26. R. L Starkey and K. M. Wight," Anaerobic corrosion Cas,1931, (Feb.), p. 30.
ofiron in soil", Am. Car Ass., New York 1945. 8
- 43. R. F. Stratrull, Cerrosies, 1961, 62, 943.
- 27. N. D. Tomashov and Y. N. Mikhailovsky, "Corro. I sivity of soil", Cerresien, 1959, 15, 77-82. i
' 28. C. A. H. von Wolzogen Kohr'and L S. van der t i Vlugt, "The graphitisation of cast. iron as an electro.
- I .,
biological process in anaerobic soils", IVater (den ' IImag),1934,18,147. , ;
- 29. R. L. Starkey, " Isolation of bacteria which oxidise thiosulphate", Soil Sci., 1935, 39, 197.
- 30. J. K Baars, "Over sulfaatreductie door bacterien", 3 s
Thesis,1930, Meinea, Delft, Holland. :
- 31. L A. Allen et al., " Microbiological problems in sugar ! i manufacture", J. Soc. CArm. I=d., 1948, 67, 70. :
- 32. G. D. Bengough and R. May,J. last. Metals,1924, '
39(2), 199. *
- 33. J. Brisou and Y. de R. de la Roy, Traa. Centri Reck. -
Etud. Oceanogr., 1 % 5, 6, 373. '
- 34. J. R. Postgate, "Recent advances in- the study of -
, sulphate-reducing bacteria", Bact. Rev., 1965,29,425.
7* 35. T. P. Hoar and C. D. Stockbridge, Electrochem. Acta, 1960, 3, 94. ., 36. G. II. Booth, L Elford and D. S. Wakerley," Polar- , ization of mild steel in the p*resence of hydrogen bacteria and methane bacteria , Brit.Cerros.f.,1968, 3, 68. 37.1. A. Denison and M. Romanoff, " Soil corrosion I studies", J. Res. Nat. Bur Stds.,1950, ff,259. '
- 38. V. V. Kutzetsov and L B. Verzhbitskaya, MiAro-biologiya, 1961, 30(3), 511. ,
- 39. K. R. Butlin, M. E. Adams and M. Thomas, .
" Sulphate-reducing bacteria and internal corrosion of ferrous pipes conveying water", Nature, 1943, 163,
- 26. .
- 40. K. R. Butlin and W. II.J. Vernon, " Underground -
corrosion-its causes and prevention",J. Inst. Water Engrs.,1949, 3, 627. 60 . 61
*~ < ~ - - . . = - ~ ~ . - e n - ~ ~ - e. . .. ,. m
4 h Euca8 ~L Memorandum: Telephone Conversation, April 19, 1985 (1:30 P.M. M.S.T.) Between: Daniel H. Pope, Rensselaer Polytechnic Institute, Troy, N.Y. and Myron L. Scott (affiant), C.R.E.E., Tempe, Arizona. Prof.' Pope's qualifications include authorship of Microbiolonically Influenced Corrosion of Industrial Alloys A State of the Art Rev:.ew published by Materials Technology Institute, Columbus, Ohio, consultation for' numerous contractors including Bechtel Power Corporation, and a contract with EPRI for a general text on MIC in nuclear power plants. Pope stated that he is only generally familiar with the current MIC situation at Palo Verde, but could offer generic comments. Pope identified five " concerns" in any alleged case of MIC:
- 1. Correct diagnosis of causative agent. Gallionella and MIC generally "over-diagnosed." Several other organisms could produce same or similar physical characteristics as gallionella. Mere presence of a microorganism insufficient to establish its role as causative agent.
Others could be present. Indeed, gallionella nodules can provide a habitat for' sulphate-reducing bacteria. Relatively few labs and technicians are qualified to accurately identify gallionella.
- 2. Accurate identification of causative agent essential to effective treatment. Treatment and monitoring must be specific to the verified causative agent. Improper identification can result in counterproductive action. . Treatment that is effective for some bacteria might cause gallionella or other organisms to flourish.
- 3. Diagnosis and treatment efficacy should be verified experimentally.
1To confirm-identification of causative agent and to verify effectiveness of proposed treatment program, the treatment should be tested experimental-ly-on samples in the laboratory before field application.
- 4. Corrosion must be removed. "Whenever possible, as the first step, we must rid ourselves of the nodules and all underlying corrosion." Other--
wise, treatment is likely to be ineffective and corrosion can sgread. When it is impossible to physically remove all corroded areas, I recom-mend thormgh chemical cleaning, followed by treatment to keep it sterile." ' It is not enough to kill the bacteria. Corrosion in the under-deposits must also be removed or corrosion process can continue "almost auto-catalytically." l
- 5. Absolute followup monitoring on a frecuent and regular basis.
The correct monitoring technique is organism-specific. In response to questions, Pope confirmed that gallionella could be transported through transfer of water or nodule materials to other systems. . Verified that gallionella (and other MIC agents) could potentially be spread to "other, separate systems which are connected to the spray ponds" by piping, etc. Would recommend inspection and monitoring of other systems in all probability. Pope asked nature of ANPP proposed core &ctive adti6H which was read to him. "Why should you aerate if the causative agent is tallionella: Gallionella is aerobic; it requires oxygen." Aeration might ma ce sense
-for sulphate-reducers, but not for aerobic, iron-oxidizing gallionella.
When informed that ANPP proposed using spray nozzle circulation to reduce stagnation which led to MIC, Pope commented: "That may well be. But once it is established, oxygen will cause the gallionella to flourish."
"We have found few methods of treatment to be truly ef fective. Organic 1
l l
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m:morandum: Papa, 2. 5 biocides are generally not effective." Chlorine in the form of chloride can be counterproduc.tive, can cause some problems with stainless steel. Ozone treatment is "phenomenally successful, but should be preceded by cleaning out the corrosion." Cleaning (corrosion removal) and ozone are generally recommendable. The foregoing is accurate to the best of my recollection and belief, and has been reviewed by Mr. Pope. , Done this 351L day of AAnw.M96 Myr[L. Scott SUBSCRIBED AND SWORN TO before me by Myron L. Scott this
'd b day of April, 1985.
' 2(l) brS' My Commission Expires:
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~b Memorandum: . Tele-con, April Between: Daniel H. Pope; Myron 30,L. 1985 (8:30 Scott A.M.,)M.S.T.) (affiant Prof. Pope stressed that he was unfamiliar with the specifics of the PVNGS situation. Therefore, all his comments were general in nature, and based upon his statements in published work and statements at professional conferences. However, " based on what data there is in that (ANPP: " Evaluation of Spray Pond Weld Corrosion at PVNGS," April 3, 1985), there are some questions I have":
- 1. Who identified the causative agent as gallionella? Metallur-gist was consulted, on Pope's personal knowledge. Metallurgist is
-qualified to analyse metal characteristics, and those characteristics could.be compatible with gallionella. However, the same corrosion characterstics could be compatible with sememl other bacteria. Only a microbiologist specializing in the MIC field is qualified to make a positive diagnosis of the causative agent.
- 2. (Page 2) The " enormous number" of indications cited for the Unit 2 North spray pond not necessarily consistent with numbers for other ponds. Although not a statistical analyst, working knowledge of characteristics in field suggests such statistical exptrapolation prone to errors. Intervening variables likely to. affect such calcula-tions include site of each pond, flow rate differentials, etc.
- 3. (Page 5) Methodology for determining thermal-impact appears methodologically sound and utilizes apparently conservative assumptions.
However, the analysis is premised upon one critical assumption: APS
" assumes there will be no further incidences. .That there will be no increase in the number and size of the indications. That is something that can only-be established over time, through regular metallurgical and microbiological monitoring."
The only other way to assure no further incidence is to make sure your treatment program has killed all the bugs and~ stopped the processes. Then you could still have metallurgical processes which could cause the corroision to worsen. Generally, we must rid ourselves of both the microorganisms and the corrosion." Confirmed that replacement or cleaning is the indicated first step 1 where feasible. Specific recommendations would tend'to be site-specific. l Frequently, biocidal treatment is ineffective unless preceded by. cleaning. I APS " Evaluation" acknowledges by indicating (page 2) " pits are expected '
-to continue to grow" at unpredictable rate. i Flushing could spread microorganisms to other isolated systems. j Or microorganisms could migrate if not removed.
Chlorine has limited effectiveness against nodules. In an experi-ment reported to the National Disinfection Conference, Pope cultured small'nallionella nodules on 304L stainless steel in five days using
' Troy c:.ty tap water. Nodule film was very thin, but some growth had occurred. Then treated with 3 parts-per-million and 10 parts-per-mil-l" exceptionally 3 ppm chlorine had no effect.
lion chlorine. thin 10 ppm penetrated the film" in three days. Further experimental work needed, but this experiment demonstrates that nodule film is resistent-to chlorine to a measurable degree. Absent cleaning, second best treatment program involves use of ozone. : Ozone also is environmentally benign (doesn't produce'THMs, etc.), ; appears to create fewer materials problems, and is demonstrably more effective in-penetrating film and re-passivitizing stainless steel. l
'l g-
- 2-However, more experimental work required.
The foregoing is accurate and complete to the best of my knowledge and belief. Done.this J d day of Asy j g rs'. m m
, My n L. Scott SUBSCRIBED AND SWORN TO before me by Myron L. Scott this ,Y day of M (xtJ 1985. '
(
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Notary Public My Commission Expires: O?t7d cGA? /92% ( '
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- ANPP-31489-TDS/TRB ^
1 1 U. S. Nuclear Regulatory Ccnaission ' Region V 1450 Maria 14.r.e - Suite 210 c'd-fa.?
. Walnut Creek, California 94596-5368 gag Attention: Mr. D. F. Kirsh, Acting Director NO Division cf Reactor Safety and Projecta
~
Subject:
Final Rep:,rt - DER 84-40 A 50.55(e) Reportable Ccadition Relating To Unit 2 Auxiliary Feedvater Punp Has Corrosion. File: 84-019-026; D.4.33.2 Refe:ence: A'; Telephone Conversation between J. Ball and T. Bradish on June 5, 1994 B) ANFP-29867, dated June 29, 1984 (Interin Report) C) A:!PP-30566, dated September 19, 1984 (Time Extension) D) ANFP-30930, dated October 23, 1984 (Time Extension)
Dear Sir:
Attached is our final written report of the deficiency referenced above, which has been deter:sined to be Not Reportable under the requirenents of 10CFR50.55(e). Very truly yours,
. CLt.A. S Uli E. E. Van Brunt, Jr.
APS Vice President Nuclear Production ANPP Project Director EEVB/TRB/nj Attachment ces See Pade Two E412310!G1 d 4;p.r, PDR ADOCK C50003?? ff. d
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/. ./* FINAL rrPCPI - DER 84-40 D .'I"!:L"Y E' All'ATIJN 50.55(e) ARIZC"'. FL*3LI" ST.* CI COMPANT (A?S) PVNGS UNIT 2 I. Des:ription of Deficiency The resciution of DER 83-66 required rework of all auxiliary f eedwater ptap impeller assemblies. Upon inspection by Bechtel Engineering at the Supplier's (Bingham-Willamette Co.) f acility for rework as described in DER No. 83-66, it was noted that the impeller assemblies for Auxiliary Feedwnter Pumps 2-M-AFA-P01 (turbine driven? and 2-M-AFB-P01 (motor driven) had areas of corrosion with the turbine-driven pu=p having the greatest concentration. Analysis of the deposits indicated the presence of bacteria associated with "Microbiologically Influenced Corrosion" cr MIC. Examication of the pump cases for these pumps also showed evidence of corrosion. Nonconformance Reports (NCRs) MC-2229 and 2230 were initiated to docu=ent the condition for the pump cases. The corrosion on the pump rotating assemblies had been noted upon receipt of the assenblics at the supplier's shop. A separate inspection plan (Engineericg log numbers M021-230 and 300) and Purchase Order Revision to P.O. 10407-13-NM-021 were initiated to determine the extent of corrosion on the rotating assemblies, and to determine if the assemblies' safety function had been adversely affected. Evalcation A. Background : Microbiological 1y influenced corrosion is defined as the deterioration of a metal by corrosion processes which occur directly or indirectly as a result of the activity of living I organisms. ' Microorganisms that influence corrosion are found in soils, in natural waters such as well water, in oil wells, in silty river bottoms, in municipal sewage systems, and in numerous industrial environments. These living bacteria can be carried into a systec in dust or sand. There are various types of microorganisms that influence corrosion; some are anaerobic and others aerobic. The mechanisms whereby they influence corrosion vary with the type c. microorganism and the type of material involved. The details of some of the mechanisms of MIC are not ccapletely understood. Microbiological 1y influenced corrosion requires both moisture an nutrients to occur. It occurs in a pH range of 0 to 10.5 and only where the velocity is below 3 ft/sec. It can result from water being lef t in systems af ter hydrostatic test. Natural waters, particularly well waters, and soil, including airborne dust aci sant contain several classes of cieroorganisms that thrive in er environments and greatly accelerate metal estrosica. A
I,.., o n V' Finc1 net. ort PCR 64-40 Page Two-These bacteria, as with any living organism, require certain conditions for growth, including nutrients. Open cooling systems, such as cooling tevers, have almost unlimited nutrient sources f rom the air and dead organisms af ter chlorination. In systems which carry demineralized water, only trcces of nutrients
. are present af ter flushing has removed the dirt debris from the construction process. Therefore, those safety-related cystems at IVNOS which carry demineralized water in unlined pipe do not have the most favorable conditions for MIC.
~
B. Inspection of Auxiliary'Feedwater Pumps and Piping:
, , In order to determine the extent of damage f rom the ef fects of MIC in the auxiliary feedwater system and provide a basis for further. inspection and repair, if necessary, NCRs MC-2229 and 2230 were interim dispositioned as follows:
- 1. Inspect with radiographs the areas in the auxiliary feedwat, system piping which could be sensitive to MIC.
2 ' Inspect the pump casings using dye penetrant examination an grinding to base metal. The impact of MIC on the rotating elements was evaluated by Bingham"Willamette Co. in accordance with the inspection plan referenced above. The inspect ' 4 program per NCRs MC-2229 and -2230 showed no extensive corrosion of the pump casings from the observed corrosion. In addition, radiographs of weld metal, known to be
- particularly susceptible to NIC, showed no evidence of corrosion. Samples of water f rom the pump casings showed traces i of MIC bacteria.
The pump rotating assemblies were examined by Bingham-Willamette Co. Any surface corrosion was removed by a sand-water slurry, and the components were dye penetrant examined. Defects were noted and ground out to base metal. An evaluation of the conditions found showed that the ability of the rotating elements to perform their safety function was not adversely affected. f
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Tital Report DER 81-40 Fage Three l l The turbine-driven pump had by f ar the greatest concentration of corrosion. This is attributed in part to the fact that che pump was never operated (ncn-availability of steam) and to an inadvertent condition which happened during startup flushing of the syntes. Both the suction and discharge lines f rom this pump were separately flushed with the pump isolated f rom this activity; however, as discovered later, some water had leaked into the pump and was left to stand in excess of six months. The pump was not drained af ter system flush because startup had no knowledge of this seepage. The pump had been approximately half full as indicated by the water line and existence of corrosion on only the lower portions of the pump casings. i During the Unit 1 auxiliary feedwater pu=p impeller assembly rework described in DER 83-66, 'his condition was not observed because these assea"ies had nst been exposed to a long period of. standing water. The Unit 3 auxiliary feedvater pumps have not yet been exposed to water at PVNGS. i C. Root Cause: , The root cause of the condition was the undetected retention of flushing water in the feedwater pu=p casings af ter the startup flushing operation of the feedwater system. This stagnant water contained sufficient microorganisms, and nutrients, to initiate and sustain a microbiological influenced corrosion precasa. II. Analysis of Safety Implications Evaluations of the rotating elements by Bingham-Willamette Co. and of 6 the pump easings by Bechtel Material and Quality Services have determined that the existence of MIC did not adversely affect the capability of the auxiliary feedwater system to perform its safety-related function. The auxiliary feedwater system use. domineraliaed water. Although conditions for bacterial growth existed, no corrosion had occurred. If left undetected, additional use of the system would have eliminated the conditions for growth. Whereas MIC bacteria probably exists in other saf ety-related systens at PVNGS the conditions that existed in the auxiliary feedwater
-system are no more hosnicable or inhospitable due to the startup
-flushing and testing.
. . _ . - _ _ _ _ _ . . - , _ _ _ . - _ - . . . _ _ . _ . _ _ _ - _ - . _ , _ _ , _ . _ , _ _ _ . ~ . . , _ . , . .__
b .
,; . Ts.
i -h Tincl .5:epert D:R 85-40 l'agt Tcur Based or. the above, this condition is evaluated as not reportable under the requirements of 10CFR50.55(e) or 10CFR Part 21 since if left uncorrected would not rcpresent a safety-significant conditics. III. Cerrective Action This problem is isolated to the Unit 2 anziliary feedwater pumps. In accordance with the final dispositions of NCRs MC-2229 and - HC-2230,'the Unit > pump cases were cleaned of corrosion. All parts of the Unit 2 rotating assemblies will either be cleaned or replaced at the vendor's facility. The PVNGS Startup Manager has been requested to assure that flushing procedures ensure adequate system cleanliness and to notify PVhCS chemistry whenever there exists the possibility that any safety-related system could be lef t in a wet, untreated condition for a period in excess of one week. PVNGS chenistry will assure that proper operating and lay-up water chemistries are maintaned to einimize the potential for microbiological and other forms of Corrosion. The PVNGS Operations Managers have been requer,ted to review applicable operating procedures to assure that for shut down periods in excess of one week measures will be implemented to ensure that proper operating and lay-up water chemistries are maintained in safety-related systems to minimize the potential for microbiological and other forms of corrosion. r i l l e 9 e
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EN merr 10 [ V - SSINS No.: 6835 IN 85-24 UNITED STATES NUCLEAR REGULATORY COMISSION OFFICE OF INSPECTION AND ENFORCEHENT WASHINGTON, D.C. 20555 March 26, 1985 IE INFORMATION NOTICE NO. 85-24: FAILURES OF PROTECTIVE C0ATINGS IN PIPES AND HEAT EXCHANGERS Addressees: All nuclear power reactor facilities holding an operating license (0L) or construction permit (CP). -
Purpose:
This.information notice is provided to alert recipients of a potentially significant problem pertaining to the selection and application of protectiv'e coatings for_ safety-related use, especially painting interior surfaces of pipes and tubing._ It is expected that recipients will review the information for applicability to their facilities and consider actions, if appropriate, to preclude a similar problem occurring at their facilities. However, suggestions contained in this.information notice do not constitute NRC requirements; therefore, no specific action or written response is required. . Description of Circumstances: 1.- Spray Pond Piping While making minor repairs to the spray pond piping system in 1982, Palo Verde Nuclear Generation Station Unit 1 personnel discovered delamination and peeling of the interior epoxy lining in three 24-inch-diameter 90' elbows. Examination of the remainder of the piping system showed similar lining failures in other elbows, such as 3-inch blisters that contained solvent, poor adhesion, soft film, and excessive film thickness. The spray pond is the ultimate heat sink for the Palo Verde Station. During a shutdown _where the ultimate heat sink was needed, separation of the epoxy
- lining from the elbows could potentially cause a flow restriction in the
. piping system.
- The epoxy coating specified was Plasite 7122-H, a product of Wisconsin Protective Coatings Company. This material is formulated to be applied by -
mechanical spraying equipment in layers 2-1/2 to 4 mils. thick with sufficient time allowed for each layer to cure. The use of mechanical spray equipment provides a uniform and controlled coating film thickness. The straight sections of the piping system were coated in this manner. The multilayer mechanical deposition and curing of 12-15 mils of coating in the straight - sections of pipe took 7 days, and no discrepancies similar to those in the elbows were found. . 8503220444 b _ _ ___,_ _.___.__.__,..-_.._ _ _ ___ _ . __ . _ _ _ _
IN 85-24
, March 26, 1985 Page 2 of 3 However, the elbows were coated in two layers using a hand-held gun. The lining was uneven with the coating up to 25 mils thick. Coating took only l 3 days in December of 1980; this reduction in curing time can be critical, I especially in the' winter when chemical curing and solvent evaporation tends to be retarded. In addition, the elbowst were capped after the final coating application and there was insufficient air necessary for curing.
A hand-held gun was used to spray the coating because of the shape of the elbow. There are other methods of applying epoxy coatings that are more controllable and use less solvent. Electrostatic spray uses less epoxy and solvent for the same coating thickness. Electrodeposition in a water solution provides the most uniform coating and does not use solvents. The fluidized bed method will provide the thickest epoxy deposit. Whatever application method is selected, epoxies are thermosetting materials and are normally cured by oven baking or infrared heating. Heating reduces curing time from several~ days to several hours. - The elbows were repaired by removing the deficient lining, preparing the surface by grit blasting, and recoating with Plasite 9009-IT. The repairs
- were acceptable and a final report was issued in January 1984.
I 2. Diesel Generator Heat Exchangers While operating train A of the spray pond piping system in May 1984, Palo Verde Nuclear Generation Station ~ Unit 2 personnel discovered an accumulation of epoxy material. The jacket water cooler, air after-coolers, and lube oil coolers of all the train A and train B diesel generator heat exchangers had extensive failure of the epoxy coating and resulted in complete blockage of the governor oil coolers. The failures of the epoxy coating included severe blistering, moisture entrapment between layers of the coating, delamination, peeling, and widespread rusting. The epoxy coating specified was Plasite 7155-H. It is. formulated _to be deposited in thin layers using mechanical spraying equipment. An evaluation of the deficiencies showed the presence of cutting oils on l the heat exchanger surface before the coating was applied. It is a basic
)
requirement to have a dry, oil-free surface before applying coatings. In : addition, the. surface was too smooth for the epoxy cocting to adhere. Epoxy coatings are applied directly to the metal without a primer and it , is necessary to slightly roughen the metal surface. Finally, the heat exchangers were sealed after spraying and there was insufficient air to '
-complete the curing process. Repairs were successfully made with Plasite
- 9009-IT and a final report was issued in September 1984.
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IN 85-24 March 26, 1985 Page 3 of 3 It should be noted'that this information notice is not intended to imply that Plasite materials produced by Wisconsin Protective Coatings Company are unacceptable. Other applications using appropriately selected materials and application techniques have been successful. No specific action or written response is required by this information noti a Administrator of the appropriate regional office or this o Yi-obn', Director 70 ward Divisio f Emergency Preparedness and E ineering Response Office f Inspection and Enforcement P. Cortland, IE Technical
Contact:
(301) 492-4175 List of Recently Issued IE Information Notices
Attachment:
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