ML20137A887
| ML20137A887 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 01/10/1986 |
| From: | Gallo J COMMONWEALTH EDISON CO., ISHAM, LINCOLN & BEALE |
| To: | Callihan A, Cole R, Grossman H Atomic Safety and Licensing Board Panel |
| References | |
| CON-#186-737 OL, NUDOCS 8601140575 | |
| Download: ML20137A887 (46) | |
Text
ISHAM, LINCOLN & BEALE.
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January 10g,j8) g 00CMLI!NG & SEftviu 8 RANCH Herbert Grossman, Esq., Chairman Dr. Richard F. Cole Administrative Law Judge Administrative Law Judge Atomic Safety and Licensing Atomic Safety and Licensing Board Board U.S. Nuclear Regulatory U.S. Nuclear Regulatory
. Commission.
Commission Washington, D.C.
20555 Washington, D.C.
20555 Dr. A. Dixon callihan Administrative Law Judge 102 Oak Lane Oak Ridge,'TN 37830 Re In the Matter.of Commonwealth Edison Company (Braidwood Station, Units 1 and 2, Docket Nos. 50-456 and 50-457) 61, Gentlemen:
I am enclosing Commonwealth Edison's final report on the Corroded Pipe issue.
This report, entitled " Engineering Evaluation of the Pipe Corrosion Problem Identified in CECO NRC
- 633," addresses concerns raised by the NRC Staff in I&E inspec-tion report 84-17 with respect to the use of.some 337,500 feet of safety-related pipe.
The report is relevant to item ll.C. of Intervenors Rorem, et al. quality assurance contention.
Sincerely, h
M Joseph Gallo One.of the Attorneys for Commonwealth Edison Company JG/mg cc Service List Enclosure M
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O Commonwealth Edison Braidwood Station-Units 1 and 2 j
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Engineering Evaluation of the l
Pipe Corrosion Problem l
Identified in CECO NCR #633 t
l Docket Nos. 50-456 and 50-457 i
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l January 1986
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Contents Page d
1-1 I.
Executive Summary ll-1 II.
History 111-1 111.
Conservative Evaluation Engineering IV-1 IV.
Confirmatory Testing l
V-l' V.
Additional Assessments 1
VI-l VI.
Conclusions Vil-1 Vll.
References I
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Executive Summary I-!
This report documents the conclusions reached by Commonwealth Edison Company (CECc) with respect to the corroded pipe problem identified in Nonconformance Report (NCR) 633, Revision 1. These conclusions are basec on engineering evaluations and studies performed by Sargent &
Lundy (S&L) and a consultant. CECO has evaluated S&L's conclusions and the bases for them and has determined that these conclusions provide an adequate basis for dispositioning NCR 633. Tuis report is intended to serve as the basis for the final report for closure of 10 CFR 50.55(e) 34-10 and also to serve as the basis for closure of item 2 in the Notice of Violation issued in connection with NRC Staf f Inspection Report 34-17.
NCR 633, Revision 1, identifies certain nonconforming hea ts of small bore (2-inch,1-1/2-inch,1-inch, 3/'4-inch, and 1/2-incn) carbon steel pipind. (A " heat" refers to a batch of steel produced in the primary melt of the steeltnaking process. A heat number is uniquely assigned to each batc1 of steel.) The hea ts identified in NCR 633, Resision I, haec areas below the wall thickness required by the insterial specification to which the pipe was fabricated, AS\\tE SA-106 Grade B. (This material specification is identical to AST\\1 A-lG6, and the two are hereaf ter used interchange-ably.) This wall thickness is the nominal w211 thickness of the pipe minus a 12-1/2% manufacturer's tolerance to account for manuf acturin;; variability.
The pipe found not to satisfy that material spe "fi" Hon was believed to !se af fected by one or (nore of tne following conditions:
s
e I-2 Corrosion resulting from unprotected outdoor e
storage e Surface defects Potentially excessive chemical cleaning e
This failure to uniformly meet the minimum wall thickness requirement of the material specification for a single heat was reported by CECO to the NRC, as required by 10 CFR 50.55(c). It was reported orally on June 21, l934, and by letter on July 20,1934, and was designated lleport 34-10 for tracking purposes. On September 18, 1934, the notification was expanded to cover other heats and sizes of pipe.
The observed defects gave rise to two concerns regarding the adequacy of the pipe installed in safety-related systems. First, reduced wall thickness could potentially result in the piping not complying with the design requirements of the ASME code. Second, chernical residue on tertain chemically cleaned pipe could induce further degradation of the material. Sargent & Lundy and CECO pintly developed a program to address both concerns and to provide an engineerind disposition for NCll 63). The program consisted of a very conservative engineering ovaluation, the results of which were confirmed by two additional measureu a material testing program and a statistically bas,'d wall thickness measurement sarnpling pr0 gram.
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The fact that pipe wall thickness does not' meet the i
minimum required by the material specification does not j
mean that the pipe is unacceptable under the ASME code.
The code is met if the code allowable stresses are not exceeded when the actual wall thickness and the design loads are used in the analysis. -
In order to assess the corroded pipe, CECO personnel chose approximately l000 feet of the affected pipe which appeared to exhibit the worst discrepancies in terms of pitting and other surface defects, measured the extent of -
the defects, and sent this data to S&L for further evaluation. Sargent & Lundy was asked to perform studies to determine whether the affected pipe continued to meet the minimum wall thicknesses required by the ASME code to accommodate the stresses resulting from the applicable pressure and mechanicalloading. This evaluation 1
I established that even with the application of conservatise stress increase f actors to take account of reduced wall thicknesses f rom pitting and localized thinning, all the piping met the ASME code allowable stresses with the I
l exception of six pipe segments. ; As a prudent measure, even though the evaluation was very conservative, those six
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segments were removed and replaced with new pipe.
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l Subsequent measurements performed on these six segments j
conf trmed that they were acceptable because they would, in i
f act have met all code stress allowables.
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l In addition, it was subsequently observed that additional margin relative to ASME code allowable stresses could be obtained by replacing the next four mest highly stressed pipe segments. Therefore, again as a prudent measure, these four pipe segments were also~ removed and l
replaced by new pipe, even though they met the acceptance l
criteria established by the conservative initial evaluation.
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l Thus, the l0 most highly stressed segments where the f
af fected pipe could have been used have been removed fro'm the plant and replaced with new pipe. This action ensures that the af fected pipe will not be in service at locations of high calculated stress.
Samples of the af fected pipe ' vere then tested by _a consultant to confirm the conservative nature of the I
engineering evaluation. The testing also confirmed the i
assumption, implicit in the eva;uation, that the material properties of the af fected pipe were typical of those expected in ASTM A-l06 piping materials. Testing included provisions to determine the ef fects of corrosion on the chemical, mechanical, and metallurgical properties of this pipe. Testing also included provisions.to determine whether corrosion-inducing chemicals were still present, and whether such chemicals could have an adverse effect on the pipe during its normal operating life. These tests demonstrated that the samples met of exceeded att applicable requirements and that no degradation in service I.
. life or performance should occur.
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l-5 A confirmatory study was performed, based on actual l
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wall thickness measurements of a statistically based sample of the af fected pipe insta!!ed in Unit I and common systems l
and that remaining in storage in order to confirm that the piping met the cede a!!owable stress levels. These evaluations confirm that at any location where the affected pipe was used in Unit I and common systems, the pipe still
' meets ASME code allowable stress levels. An engineering judgment was made that this evaluation applies equally to af fected pipe installed in Unit 2.
On the basis of CECO's evaluation of S&L's studies, all l
the af fected piping which has been installed will be allowed l
to remain. However, as a further prudent measure, CECO 1
will not install the remaining af fected pipe in safety-related
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History Il-1 4
The piping affected by NCR 633, Revision 1, was ordered by CECO on December 3,1976, when CECO placed a purchase order for various sizes and schedules of SA 106 Grade B carbon steel small-bore piping (2 inches and under). The pipe was manufactured by Gulf States Tube
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i Corporation to the ASME SA l'06 material specification, certified as such, and shipped to the Braidwood site. As part of this order, the site received a total of approximately l
l 341,000 feet of ASME Section !!!, Class 2 safety-related pipe on various dates from August 1977 to early 1973.
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At that time, construction activities at the Braidwood l
site had not progressed to the point where smatt-bore pipe I
would be installed. The pipe was stored outdoors on open racks, uncovered and uncapped.
In 1981 construction had proceeded to the point where installation of the small-bore piping was initiated. By that time, rust and corrosion had formed on the inside and outside surfaces of the pipe from exposure to the elements, and it was decided to clean the pipe by immersion in a chemical bath before using it.
Two purchase orders, Nos. 254379 and 730091, were
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issued by CECO to the H. H. Howard Company ~. The purchase orders required that the chemical cleaning proces,s follow designated steps. The methods of cleaning were standard commercial methods, and it was believed by CECO that they would not adversely affect the pipe. As a result,-
CECO believed the cleaning process itself was non-safet -
related and accordingly issued the purchase orders to H. H ' Heward, a non-safety-related vendor. AccordingS.,
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H. H. Howard was not required to have an approved QA program. In a letter to Braidwood Project Construction, H. H. Howard documented the chemical cleaning methods that would be used. This list of methods was forwarded to S&L for review prior to approval by CECO. A Field Change-Request allowing the cleaning was then approved. In order ~
to maintain required material heat traceability,' each piece
- of pipe to be chemically cleaned was mechanically marked
- with a heat code identification.
As depicted on Exhibit 1, of the approximately 341,000 feet of pipe' originally received, about 268,000 feet were -
available for installation in safety-related piping systems.
The remaining 73,000 feet of piping are 3/8-inch diameter pipe, and no safety-related systems in the plant require use of this size pipe. Not all of the pipe received at the site in the original shipment was chemically cleaned. Of the approximately 268,000 feet of pipe available for installation in safety-related applications, about 203,000 feet were chemically cleaned by H. H. Howard Company. In addition to this 203,000 feet, approximately 3,000 feet of the 3/8-i_nch pipe were also chemically cleaned. Based on as-built drawing review, of the 268,000 feet of pipe available for installation, a maximum of about 13,000 feet was' installed in safety-related applications in Unit I and common systems. A computerized status report indicates that an -
estimated 3,000 feet were installed i,n safety-related applications in Unit 2. Approximately 70,000 feet remain in 4
Quantity Breakdown of Pipe Under the Scope Exhibit 1 of CECO NCR 633, Rev.1 341.000 feet Original shipment i
If 73.000 feet 5.-inch 268.000 feet pipe not used in available for safety-related safety-related use application i
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l l 65.000 feet l
l 203.000 feet l
l 3.000 feet l
l 70.000 feet l
l P:pe not chemscally l l Pipe chemically l
1.-inch pipe g
l 5.-6nch pipe not cleaned chemically cleaned g chemically cleaned g
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l l cleaned L________;
L ___T___ _I L __ _7 ____1 l_____-
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_ __ _t_ _ _ _ q 206.000 feet l
l Total amount of l pipe chemically l cleaned I
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u 13.000 feet 182.000 feet Safety-related Non-safety related installation 70.000 feet 3.000 feet installation in Unit 1 (temporary services.
Pipe on hold Fafety related and common construction gas in storage installation in Unit 2 systems (includes systems (includes ASME Sect 6on illand systems scaffoldmg.
ASME Section lit and Class H) cutouts, and scrap)
Class H)
Note: Numbers on this chart are approsimate.
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i storage, and the remaining-132,000 feet have been used for plant temporary construction systems, scaf folding, and non-
-J safety-related piping applications.
The pipe that had been chemically cleaned was returned from H. H. Howard between late 1981 and the middle of 1982. Upon return,'the pipe was received and documented on CECO Material Receiving Reports, and a i
receipt inspection was performed.. Dimensional checks were not performed as part of these inspections. The pipe was -
inspected for proper cleaning and for handling or shipping damage. Quality documentation was not required from H. H. Howard with the shipments. After receipt, the pipe was stored indoors in a warehouse and the ends were l
l capped.
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In December 1933, while performing dye penetrant i
tests on small-bore piping welds, Philips, Getschow Company (PGCo) observed axial surf ace indications on some installed 2-inch pipe from material heat nurnber KD6751.
PGCo issued an NCR and dispositioned it internally by undertaking to determine locations in which pipe from this heat was installed. This matter was brought to the attention of CECO Project Construction in late April 1984.
CECO instructed PGCo to investigate further and issue reports. Upon further investigation it was observed that some pipe from this heat of material was pitted and
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-corroded.~ PGCo measured wall thicknesses of the pitted
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- and corroded pipe, both installed and in storage. Samples of pipe from heat KD6751 were discovered to be deficient, in that'they did not meet material specification requirements for minimt.m wall thickness.
As a result of these reviews, a 10 CFR 30.55(e) notification was issued to the NRC on June 21,~1934. On
. June' 28, CECO NCR 633 was issued to document the!
problem. All 2 inch schedule 30 pipe with heat number KD6751 was placed on hold. Further measurements were performed on other samples (! stored pipe, and it was -
determined that carbon steel small-bore pipe from other heats and in other sizes from the origmal 341,000 foot shipment had similar problems. CECO issued Revision I to NCR 633, expanding the scope of the recognized problem, and similarly expanded the scope of the 10 CFR 50.55(e) notification.
In August 1984, CECO put a hold on all the pipe from the original shipment that had not yet been installed; this amounted to approximately 70,000 feet of pipe. CECO developed a program to determine.whether the pipe installed in safety-related systems was adequate. The tasks performed by PGCo as a part of this program were controlled and documented in accordarce with the PGCo quality assurance program. Certain detailed activities were performed as prescribed by approved PGCo Procedures
-PGC P-52.
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-Part of this program involved a PGCo engineering i d i
. department review of the as-built isometr c raw ngs to determine all locations in Unit I and common systems where this size and type of pipe could have been used.. It was assumed that in any location on the drawing where suspects pipe could have been used,' it was in fact used. By.
this method it was determined that a maximum of 13,000
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feet of the pipe in' question had been installed in Unit I and common safety-related systems. Because as-build isometric drawings were not yet available for Unit 2, PGCo based its estimate on a computerized status report that identified the small-bore carbon steel pipe installed in Unit 2 prior to-August 1984. By this method it was determined that '
approximately 3,000 feet had been installed in Unit 2.
Samples of the affected pipe in storage selected by CECO engineers were sent to CECO's System Materials Analysis Department (SMAD). A metallurgical analysis.
performed by SMAD (summarized in Ref. 2) showed that the
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material was typical of A-106 Grade B carbon steel,' but that a combination of pitting'and localized thinning had resulted in wall thicknesses at certain localized locations of.
less than that required by the ASTM A-106 material specifi-cation. Minimum wall thickness under the material specification is defined as the nominal wall thickness -
specified in ANSI B36.lC minus the ASTM A-106' allowed
-manufacturer's tolerance of 12-1/2%.
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F in addition, contractor personnel under the direction of
- CECO performed detailed pit depth measurements and wall.
thickness measurements on other samples of the piping in storage using a pit depth gauge and a digital thickness meter. Pit depth measurements were made on both the ID
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and OD surfaces of split sections of pipe. These measurements were taken at locations which appeared to the inspectors to be the worst or deepest pits in the given segment of pipe. The sample consisted of 272 segments representing over 1000 feet of pipe which were considered 1-by CECO engineers to be the most af fected by pitting and l
corrosion. Out of 544 pit measurements on the 272 samples, the deepest pit found was 0.033-inch deep, while awraging the " worst" pit from each segment resulted in a depth of approximately 0.0l! inch.
The results of these measurements were forwarded to S&L. Sargent & Lundy was requested to investigate the problem, to help develop a program to determine whether i
the installed piping still met ASME code requirements and could perform its intended design function.
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Conserv tiva Engineering Ev luation III-I_
On the basis of the above pit depth measurements, S&L performed a highly conservative engineering evaluation to determine whether the affected pipe met all ASME code
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allowable stress levels.' CECO had concluded that the selection of the 1000 feet of corroded pipe from storage, which was based on engineering judgment, was representative of the worst corrosion that would be found in the pipe installed in Unit 1, Unit 2, and common systems.
Based on these measurements, the S&L engineering evaluation made conservative assumptions regarding pitting and wall thinning. (The statistical based sample performed subsequently confirmed that the selection based on engineering judgement was representative and did result in an appropriately conservative evaluation.)
It was judged that the engineering evaluation would be applicable both to the chemically cleaned and the corroded uncleaned pipe. This was later confirmed by Dr. Steven Danyluk, a corrosion expert, who exarnined specimens of the corroded pipe and the pipe which was corroded and chemically cleaned, as well as specimens of new pipe. Dr.
Danyluk concluded that there was no relevant dif ference in
. the corrosion behavior of the three categories of pipe (Ref.9).
Pipe with a wall thickness that does not meet the=
material specification is not necessarily unacceptable under the ASME code. The wall thickness requirements of the niaterial specification are intentionally quite censervative.
- The code contains equations to be used in determining the minimum wall thickness required to meet the piping design pressure. ( ASME code, section Ill, subsections NC and ND,
111-2 paragraphs NC/N3 3641', equations (3) and (4)). In selecting a schedule of pipe, the designer adds various allowances (bend allowance', manuf acturer's tolerances, etc.) to this minimum wall to determine the actual wall thickness required at the specified designed pressure. He then selects piping with the next highest commercially available nominal wall for that application. This was the procedure followed by S&L in selecting and specifying the small-bore piping to be installed at Braidwood. This procedure for selecting the nominal wall assures that the actual wa!! thickness less the manufacturer's tolerance will conservatively accommodate the design pressure. The installation of piping with wall thickness less than ncminal wall minus manufacturer's tolerance, however, is acceptable under the code, pravided that the code design equations are still satisfied.
Sargent & Lundy analyzed the ability of the af fected pipe to withstand the design prersure. A comparison was made between the minimum wall for pressu:e loads calculated using the applicable code equations and the wall remaining af ter subtracting the maximum pit depth, the maximum mill tolerance, and the maximum bend allowance (for bends with radii equivalent to three pipe diameters)'
from the B36.10 r.ominal wall. This comparison showed that the' associated pipe sizes in the potential pressure applications where this piping could have been used would still meet the minimum i'all requirements for pressure.
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1 In addition to withstanding the internal design pressure,'-
pipmg must be adequate to meet external;y applied design loads. The piping stress analysis is required by the ASME code to be performed for dead weight, thermal, and seismic loads as applicable, using the nominal wall thickness, by application of ASME code subsection NC/ND 3652, equations (3), (9),' (10) and (!!).
Therefore, af ter establishing conformance with the code rninimum wa!! pressure requirements, S&L performed studies to conservatively evaluate the adequacy of the corroded pipe to withstand the applic.?ble stresses resulting f rom operating pressures and mechanical loads. Since inf ormation on the density and the' distribution of the pits was not available, conservative ass'umptions were made about the stress increases attributable _ to such pits.
Sargent & Lundy determined the increased stress -
concentration by developing specific stress increase factors for each size and schedule of' piping to account for notch ef fects and section inodulus reduction postulated to occar as a result of the reported pitting and localized thinning.
-("Section modulus" is a nanerical representation of the strength of a cornponent in bending which varies with the geo netrical propertie', of the cross-sectional ~ area of the com ponent.)'
The notch ef fect component of the stres: increase f actor was based on the mathem.itical model shown in Exhibit 2 in which it was assumed that the 0.033-inch
" worst" pit existed on both the OD and ID of the pipe at the_-
Exhibit 2 N
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same axial location. This is a very conservative assumption i d h
. because the actual cbserved pitting was random n ept and location around the circumference of the pipe, and only one pit measured 0.033-inch deep. Therefore, the probability of two pits of the maximum depth occurring exactly opposite one another on tl.e ID and OD at the pipe and at the same longitudinal locat.on is very low.
The reduction in section modulus was them calculated assuming that the worst pit (0.033-inch) wall reduction was not localized, but rather was represented as a uniform wall thickness reduction around the circumference of the pipe.
In order to maximize the reduction in section modulus, this 0.033-inch wall thinning was assumed to occur entirely on the OD of the pipe as shown in Exhibit 3. Applying this-reduction to the outside diameter is conservative in that it results in the greatest reduction of the available section modulus.
The assumptions relative to the notch etfect calculations are conservative in light of the methods recommended to reduce stress concentration ef fects contained in standard mechanical design textbooks (e.g.,
Phelan, Fundamental of Mechanical Design, McGraw-Hill, New York; l970, figures -7 and 6-8 on pages 113 and 114':
6 Shipley, Mechanical Engineering Design,-McGraw-Hill, New Yerk.1972, figures 6-) and 6-6 on pages 224 and 225).
These texts indicate that the stress concentration ef fects of -
a groove can be decreased by making additional grooves onz either side of the ' groove in question. These multiple
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A Exhibit 3 Asdornec Waii Thickness PecLc' an A See Section Exnibit 4 j
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as P.iatne at cal f.iocei 'or Tneoreticai 5e ction 'siocatus Ar.1uct.cn iShacec area rep'; sorts area of assumec metat loss i u-f, 44 JO
Ill-7 grooves of random depth reduce the stress concentration ef fect by decreasing the sharpness of bend of the " stress flow" Lines in the member, in a similar manner, multiple pits on the surface of a pipe will tend to tnitigate the stress concentration effects of any given single pit. (The conservatism of the analysis was later corroborated by the f atigue testing performed by Taussig Associates, Inc.
(Ref. 6), as discussed in section IV of this report.)
The assumptions made concerning the section modulus reduction were also conservative. Exhibit 4 reeresents a typtcal cross-section of corroded pipe as found during the wall thicknen xampling performed af ter the initial studies were completed. It can be seen from the figure that the reduction in section modulus due to the corrosion is negligible. Thus, the assumption of uniform rnetal los; based on the worst single point pit rreasurement to a wry conservative assumption.
For t: e3e studies, then, two very conservative assumptiens regarding increased stresse3 were applied sitnultar!eously. The worst case riotch ef fect stren mcrease f actor was combined with the reduced section inodulus stress :ncrease factor to determine a " theoretical" oserall 3 tress increase factor. These conservatively estimated stresses were then applied to ASME section Ill, code subsections NC and ND, NC/ND 3652, equatier..3),(9),(10) and (11) to determine the adequacy of the piping unc'er the rnaxunum stress increa3e which cou!d be expec*ed. Two separate evaluations were then perforrned.
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In initially designing the pipe, S&L had em.oyed two r
dif ferent inethods of analysis. Sargent & Lundy desi ned d
the inajority of the pipe using conscreatise dirnplified design rules that it had deteloped and that it regularly uses. (In this report such pipe will be referred to as the " simplified design pipe." In certain applications, however, where the pipe connectec; to large-bore pipe or where it would experience local loads not provided for in the simplified design rules, the pipe was designed with the assistance of cc:nputer analysis. (In this report such pipe will be referred to as the " computer analyzed pipe.")
In perforrning this stress evaluation, separate cialuations were perforined for the siinplified design piping f or C! ass B, C (safety-related ASME class 2 and 3 piping) and H (safety-related instr; nentation piping) applications and for the computer analyzed piping for Class B, C and D app!; cations. Using the conser/ative stress increase factor calculated by S&L for each size and schedule of pipe, all locations where the pipe could have been instal!ed in Unit I and com:non systems were esaluated.
5 argent & Lundy simplified design rules used a stress intensification factor throughout the original analysis.' This factor represents a conser/ati/e approach to piping design and is utilized to reduce the need for mose costly detailed computer analysis. Therefore, simplified design pipe will not be potentially cierstressed unless the theoretical cierall stress increase factor exceeds the stress intensification factor used in the original design. The stu i>
III-10 considered all pipe in the plant which was designed by the si nplified rules anJ showed that no piping exceeded the original factor. Therefore, all piping analyzed by the si nplified method is acceptable and mee ts the AS\\1E code aliswable stresses.
Computer analyzed small bore piping was then eeatuated, assu:ning that the stresses were increased by the theoretical o<erall stress increase factor calculated previously. The results of this evaluation (Ref. 5) showed that out of the approximately 33,000 node points in 324 subsystems (which included all Unit I and Common cc:nputer-analyzed piping), all nodes except for six met the code allowable stress levels when the conservatively-deriecd stress increase factor is uniformly applied to the applicable ca:culated stresses. (A node point is a
- aathe natical representation of a specific physical location in the analytical model of a piping system used to define the point at which stresses are calcu!ated.) If it could Se termined, as it !ater was, that no stress increase factor due to aatch ef fect was necessary, and that the actual wall thickness reduction was not as great as assumed, then these six codes would also meet AS\\1E code allowable stress iciels. Nonetheless, as a prudent measure, since all the testin6 and wall tSickness sarnpling was not yet complete, tSe six nodes were identified and cut out of the plant, and new pipe was instal:cd in their ? ace. It was later l
confirrned on the basis of the wall thickness sampling program and specific wa!! Inickness measurements or, these
111-1 1 six nodes, that they did in fact meet all code allowable stresses and would haec been acceptable had they remained in place, in addition, in order to restore additional desige margin relati/e to the As\\1E code allowable stresses, and to assure tha t the conser/a ti/e initial evaluation would de fi.11tely bound any potential unforeseen variations in later tests and e /aluations, the piping associated with the next four inost highly stressed nodes of the computer analyzed piping was reeno/ed fra:n the plant and replaced with new pipe.
Based on the results of this very conservative engineering evaluation, S&L concluded that, with the initia!
six nodes cut out, all of tne pipe installed in Unit I and
- ommon sjstems met all applicable A51tE code require-nents and was capaLile of fulfilling its intended design function. As descri'oed more fully below, S&L inade an engineering judgement that this conclusion applied equally ta the pipe instai:ed in Unit 2.
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IV.
Testing IV-1 5 argent & Lundy esta'oiis:Ted a testing prograin to coafirin the conser<atis.n of the engineering e tafuation.
The testing was also designed to confirm the assumption, itnplicit in the eialuation, that the material properties of the af fec ted pipe are typical of those expected in \\ST\\1 A-106 piping materials. Finally, the testing was designed to address the additional concern that chemical residue lef t from cleaning might induce f arther corrosion in the pipe.
Sargent & Lund) selected Taussig Associates, thc., an independent testing laboratory, to perform the tests.
Three categories of tests were performed by Taussig Associates according to the require nents set f orth in 51L Consultant Specification 121, "\\le tallurgical Testing Ser/ ices." These categories were:
Fatigue Testing e
Fatigue testing was performed on 11 sampics of pipe to confirin that the notch ef fect component of the stress increase factor selected by S&L us conscr ea ti /e.
o Other Confirmatory Testing Six additional tests were perfor ned to confirm that the,;eneral physical and che nical propert.es of piping material were within acceptable !!mits.
These were:
Tensile Testing (9 sainp;es)
Chemical Analy sts (9 samples) m
IV-2 o
Burst Testing (2 samples)
Bend Testing (9 samples)
Macro-Etch Examination (10 samples)
Metallographic Examination (19 samples).
Testing for Chemical Residue e
Three tests were designed to determine whether potentially corrosive residue remained on the piping ma'erial from cbemical cleaning.
Depos'.t Analysis (OD Surf ace Deposits)(10 samples) by X-Ray Flourescence Ptt Res: cue Anal) sis (OD and ID Pits)(10 samples) 03 Energy Dispersion X-Ray (fiDX)
Restcual Chemica! Acidity (pH) Testing (three samples)
The piping samples seiected by CECO engmeers for testing were chosen so as to be representative of the rarg.-
of sizes and schedules of the heats af fected by ints corrosion problem. The specimens selected by CECO were tho3e which were judged to exhibit significant pitting and corrossen. Samples of new otpe were also sen to be tested in order to establish a herchmark or a "contro;" sample fer each test performed.
I
IV-3 The results of this testing program are contained in Taussig Associates, Inc. Report No. 60493-2, da ted OS-27-S5 (Ref. 6). While the tes:s showed some minor dif ferences between the corroded and new pipe samples, the corroded pipe was confirmed to have the same typical properties of, and to meet the AST.\\1 material specification requirements for A-106 Grade B pipe.
1.
Fatigue Testing The fatigue tests were designed to confirm the conservatism of the assumption made regarding the notch etfect stress increase factor in S&L's engineering evaluation. The tests consisted of the application of eery large mechanical loads (much beyond those Ictels expected darng normal services of the pipe) in alternately opposing directions to determine the number of stress cycles that can Se accommodated by the pipe. These tests establish a fatigue life (number of stress cycles) for the type of pipe involeed. The AS\\1E code addresses the fatigue life for the classes of pipe in question by requirin6 the application of certain stress intensification factors to certain confijarations of piping. The stress intensification factors used in tne AS\\1E code are based on testing performed by
\\larkl (Re f.10).
Fatigue life of a particular component is significant!>
reduced by the presence of deep, narrow defects (notches).
This so called " notch ef fect" results in a localized stress concentration and serves as a mechanism for more rapid u
IV-4 O
f ailure of the component. The reason for perforrning the fatigue tests was to determine whether the pits in the af fected pipe did result in this notch ef fect reduction in fatigue life and, if so, to determine whether the theoretical notch ef fect component of the stress increase factor calculated by S&L was adequately conservative.
Fatigue testing was performed on i/2-inch and 2-inch schedule 30 pipe sizes in order to bound the ef fect of the corrosion on the various sizes in question. The test was patterned af ter Marki s original fatigue tests which form the basis of the stress intensification factors used by the ASME code.
The samples selected for this fatigue testing were cnosen from pieces significantly af fected by corrosion and ottting. Markt's tests were limited to only one size of pipe (4-inch standard wall) and the results have since been extrapolated by the industry to cover other pipe sizes and schedules. In view of Markl's tests, the sample size selected for this testing program was judged to be adequate to obtain meaningful engineermg results because ' heir purpose was to ver.fy that the range of values obtained were similar to those ootained by Markt. One variation from the Markl test meth'odology should be noted. A four-point bend was performed, rather than the cantilever beam bend utilized by the Marki method.
IV-5 This four point bend approach subjects a greater volume of pipe to the maximum moment, and thus is rnere conservative than the Markt test, which induced the maximum moment only at a single point. This can be seen by reviewing Exhibit 5. Because the four-point bend would distribute the maximum moment over a larger area of pipe, it provides increased assurance that the severely pitted areas on the pipe specimen are subjected to the maximum applied mon.?nt, thus yielding rehable results.
The results of these fatigue tests are shown plotted as 5-N fatigue curves in Taussig's report as Figures 1 and 2.
Superimposed on these curves are Markl's reference curves labeled "Not Clamped," wh;ch corresponds to a stress intensification factor of i = 0.64, and a second reference curse labeled " clamped " which corresponds to a stress intensification factor of i : l.0. By inspection of these curses, it can be seen that all of the test data points plot above the i : 1.0 reference line, which means that the actual stress intensification of the pipe samples in les> than 1.0. 'A hile minor dif ferences exist between the ct.rses Ier tne "new" and " corroded" pipes, all curves f a!! w ithm or above the bounds predicted by Markt for straight pipe sections. This means that the assumption of a stress intensification factor of i = 1.0 for all straight sections of corroded pipe is a valid anc conservative assumption. It also establishes the conservatism in the initial evaluation, which utilized stress increase f actors greater than 1.0, anc elimmates the need to mclude the notch ef fect cornponent of tne stress increase factor in sequent evaluations.
Exhibit 5 Cantilever Beam Bending (used in Markl's original tests)
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2.
Other Confirmatory Tests A variety of tests was performed to confirm that the general physical and chemical properties of the piping material were within acceptable limits. This had been implicitly assumed by the engineering evaluation, because the evaluation was based on typical ASTM A-106 Grade B material properties. These tests serified this assumption, and therefore the tests support the conclusions reached based upon that evaluation.
Tensile tests were done on pipe samples which included the pitted ID and OD surf aces. The test results showed that the tensile strength, yield s*rength and elongatton values rnet or exceeded the requ:rements for A-lC6 Grade B pipmg produc ts.
The themical anal)sts tests showed that the corroded pipe contained no significant amounts of contaminants or unusual ailoying elements and that the saniples were m conformance with the chemical requirements of ASTM A -l C6.
Both new and corroded pipe samples were nba ctec :o h.drostatte burst tests. Again there were m:nor Otf ferences between the test results; however, these variatiens are typical fer experimental data 3catter. A!!
san p!es exceeded the AS TM mtntrnum burst pressu e, by,i f actor O! 3.5 or greater.
IV-8 Gend tests were performed to ierify ductility during the bend forining process. The test sainples were bent over dies which had a much sharper radius (equivalent to 5 pipe diameters or less) than that required by ASTM A-106 (12 pipe diameters for standard bends and S pipe diameters for close bends)in order to assure conservative test results and to be consistent with the bend radius normally used by the piping contractor. The bent pipes were then visually esa:nined by a qualified Level !!! Visual Examiner. These test samples met the bend test acceptance requirernents of ASTM A-106 as no indications or other defects were noted on the nine pipe samples.
Macro-etch testing was performed on samples of the corroded pipe. Visaal examination of the samples revealed no evidence of inherent defects or weld seams. Though no requirements are specified by A-106 for Macro-etch Testin3, the samples obscried were confirmed to be typical for A-106 type materials.
Metal!agrap;.ic examinations were performed on !O sa nples of the corroded pipe. The samples exhioited micro-structures which are typical of low carbon steel products such as.\\-106. The pitting on the ID and OD surfaces was obsereed to be broad and shallow. Surf ace imperfections which are shallow and rounded have a fower stress concentration ef fcct than that associated with sharp notches and grooves. None of the samples displayed c eidence of other unacceptable surf ace conditions sa:h as intergranular or grain boundary attack, stress corrosion L
I IV-9 cracking, or indications of embrittlement. While A-106 has no specific requirements for this type of examination, the
- results were confirmed to be typical of A-106 type inaterials with the exception of the visible surface pitting.
i 3.
Chemical Residue Tests A series of tests was performed to determine whether chemical residues from the cleaning process might be present on the pipe and might cause or accelerate further l
corroston. As noted above, the chemical analysis showed l
that no significant contaminants were present and that the samples were in conformance with the chemical requirements of A-106. These tests confirmed an assumption inherent in the S&L engineering evaluation, which did'not account for the potential of future chemical ettack.
A surface deposit anaksis was perfortned by the x-ray flourescence test method as a part of the corrosive residue evaluation. No measurable amounts of chlorine or sulfur, possible corrosive agents, were identified. Other trace e!ements which were identified by these analyses would not be expected to either cause or accelerate corrosion.
An energy dispersion x-ray (EDX) analysis was also performed on the residue in the pitted areas and the results were found to be in good correlation with the surf ace deposit analysis. The most commen trace elements were f ound to be alununum, sulphur, and silicon. None of these represent any threat :o the life of the pipe.
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The outer surface of the piping'was checked for corrosive chemical residue by adding deionized water to the outside surface of the pipe and checking the resultant pH.
The acidity of the water was checked af ter letting the.-
water stand for several minutes. No measurable change in-
- the pH of the deionized water was noted.' This test
. indicated.that the sulphur and chlorine on the pipe surface are not in suf ficient quan' tit'y or are not adequately chemically active to cause significant amounts of sulphuric j
or hydrocholoric acids to be formed when exposed to water. Therefore, this test indicated that-there were no detrimental chemical residues remaining on the pipe surface, and the piping was not under chemical attack.
u Dr. Steven Danyluk.~ a corrosion expert, examined specimens of tile corroded pipe and the pipe which was corroded and chemically cleaned, as well as specimens of new pipe. Dr. Dany!uk concluded that there was no relevant difference in the corrosion behavior of the three categories
' of pipe. (Ref. 9.)
4.
Conclusion Based on the test results, it was concluded by; Taussig -
- that,'while the corrosion has caused some variation in proper-1 ties of.the piping. materials when corApared with new pipe. '
l the samples all met or exceeded the requirements and
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expected values for the specified materials. Taussig expect.1 -
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- no degradation in service perfor mance or lifetime beyond
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'what would be expected for uncorroded A-106 materials.
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.\\s indicated abote, the Taussig testing confirmed the conclusions of the S&L engineering evaluation in three ways. First, it confirmed that the notch ef fect stress increase factor used in the evaluation was extremely conseriative and that in f act no notch ef fect stress increase factor was necessary for a valid and conservati>c stress analysis of the af fected pipe. Second, the testing confirmed S&L's assumption that the material properties of the af fected pipe were typical of those expected in ASTil
\\-106 Grade B piping rnaterials. Third, the testing and Dr. Danyluk's cialuation confirmed S&L's assu nption that no sigTificant chemical residues fro:n the cicaning process were present on the pipe which might cause or accelerate further corrosion.
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. Additional Assessments.
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In order:to provide an additional assessment of the acceptability of the af fected pipe and to further confirm -
the engineering evaluation, a random sampling program for both installed and uninstalled pipe was established. The program was designed to confirm,'on a statistical basis, that cthe wall thinning observed would no't result in pipe cross--
sections with inadequate strength. The population for this
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statistical sampling was considered to b'e " pieces" of small-b' ore pipe. For the_ installed pipe,'a piece was defined as a section of pipe between connections, usually welded. For
- uninstalled pipe, a piece was detined as a section egeal-to
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the average length of an installed piece, approximately 3 feet. There were 4,586 such installed pieces of pipe in Unit I and common systems, and 24.137 equivalent stored -
pieces, for a total population of 23,723 pieces. These pieces were each unique y identified by assigning sequential l
numbers for purposes of random selection for exanimation.
For purposes of satisfying a 95% confidence /99% reliability criterion,300 samples from the above population. were examined for wa!! thickness. The 300 randomly selected -
pieces were identified in.a letter dated Apri! 4, l935.- f rorn
.5&L to CECO..
Samples were cut and obtained fron) both field-installed a_nd storage locations and were uniquely. identified -
.throughout the' measurement process. J PGCo was '
respensible _for obtaining and measuring the:desi.;nated.
s4mpe in accordance with PGCo Procedure PGCP-32.' Each piece ivas subdivided in'to 6-inch song sections and or.e end
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of-each '6-inch section was measured for wall thickness with
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a point micrometer at eight points equally spaced arxnd2 the circumference. -Dne additienal nieaErement w k takeh a
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between each of the eight points'at a location where
. localized thinning was apparent.. All measurements were.
performed.by qualified and certified PCCo quality control-
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inspection personnel using calibrated inspection equipment. The CECO Quality Assurance Department
. performed audits and surveillances uf the above activities-to assure compliance with the requirements of procedure PGC P-52.
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The previously discussed fatigue testing confirmed that no stress intensification did in fact occur at the pit -
-locations. Therefores there was actually no need to apply tne notch ef fect stress increase factor, as was done in the engineering evaluation. The piping from the wall thickness-sampling program could be evaluated based soleiv on the reduction in section modulus resulting from the pits and -
localized thinning. Thus, all the af fected piping could now be evaluated us.ng the code design allowable without.
imposing a stress factor to account for th'e notch ef fect.
Sargent & Lundy developed conservative criterta fer
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evaluating the. wall thickness measurements. If the measured wall thickness of the pipe met.-the industry standard tolerances of nominal thickness minus the manufacturer's tolerance of 12-1/2%, the piping required no -
further evaluation'because it ' as within-the standard limits w
established for new piping. If the measured wall thickness of the pipe did not meet the industry standard tolerance.
the pipe was evaluated by applying the worst case reduction in wall thickness measured for pipe of that size in.the 2
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u statistically based sample' to the most highly stressed node for that size pipe, excluding cut-outs. in a;l cases, the-measured wall ti ekness resulted in larger section moduli -
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. and cross-sectional area than tnose used in the engineering ~
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- evaluation.
The pipe thickness data based on these actual field -
measurements was transmitted from CECO to S&L.' The measurements were thhn evaluated b'y S&L. The 300 samples.taken. represent 28,112 wa!! thickness measurements.- Only S2 of the samples contained one or more locations (for a total of 497 locations out of the' 23.112 points measured) where the measured wall thickness c
was below the nominal wall thickness minus the 12-1/2%
manuf acturer's tolerance allowed by ASTM A-106.
Therefore,218 samples were within standard industry tolerances and required no further evaluation. The.
remaining 32 samples were then evaluated against ASME t
code allowable stresses and were found to be acceptable.
t The wall thickness measurements taken on this f
statistical saniple conf trmed the? conclusions of the S&L~.
1 engineering evaluation.. The measurements confirmed that for each size and schedule of pipe, the measured available wall res21ted in a section modulus and cross-sectional area -
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greater than that used in the engineering evaluation.' In
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additton, Inc. measurements confirmed that the available..
. wall was in all cases suf ficient to enable the pipe to meet '
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s all A'SME code allowable stresses.
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T hen both the notch effect and section modulus stress increase factors are considered for the engineering evaluation with the 10 cutouts removed, all pipe meets the ASME code allow;able stresses. In addition, when the worst =
case section modulus reduction from any size pipe from the wall. thickness sample program is combined with the most.
nighly stressed node from any size pipe remaining af ter the
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.10 cutouts were removed, the ASME code allo'wable. stresses
-were met even in this " worst / worst" case.
As previously~ indicated, a quantity of the af fected pipe has been installed in Unit 2. At the time the hol:f was.
placed on further installation of the affected pipe,. virtually no safety-related small-bore piping stress analyses had been done on Unit 2. As a result, the methodology used in'the engineering evaluation (i.e.,' stress increase factor applied to calculated str,ess) could not be directly. applied-to the Unit 2 piping because calculated stresses were not available -
for comparison. Therefore, although the engineering evaluation.does not specifically address the pipe installed in.
Unit 2, the results obtained and the concluuons reached can still be applied to the Unit 2 pipe with high confidence for the fo!!owing reasons.
The majority of the Unit 2 piping will be subject to the simplified analysis approach which has been shown'to be generically acceptable when evaluated against.the -
engmeering evaluation acceptance criterion. In' addition..
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.the design and installation approach being utilized on Unit.2 -
is*to duplicate the Unit I design and installation ~where -
possible. Thus, in.the majority of cases, the Unit I results will be directly applicable to Unit 2.
lt should also be noted that'even though the wall-thickness sampling program did not specifically include any potentially af fected pipe;from Unit 2 as part of the sample population, the results obtained are still appl _icable to
- Unit 2. First, there is no reason to believe that the piping that may have been installed in Unit 2 is any different from that installed in Unit 1..The dnit 2 piping has been subjected to the same conditions of cleaning and storage as the Unit 1 pipe. In addition, the wall thickness samp!ing program did draw many of its samples from the piping in -
storage. This is the same. location where the Unit 2 piping would have been stored. Therefore, CECO believe; the statistically based sampling results should apply equally to Unit 2 and to Unit 1.
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- Conclusions -
VI-l-
.t The engineering evaluation concluded that with the exception of the six previously discussed computer analyzed I
node points (cut-outs), all pipe installations would meet
' ASME code allowable stress limits notwithstanding the use
- of corroded pipe.- The confirmatory testing and wall
- thickness sampling program indicate' that all pipe locations (including the~six cut-outs) would meet the ASME code s
-allowable stress limits and that the methodology used in the engineering evaluation was very conservative. The maximum stress which can occur at any_ location where this -
pipe has been or could have been used was shown to be less than the code allowable design stress.
l-
. In addition, based on the evaluations, testing, and wall i
thickness sampling performed,'it has been demonstrated that, while some minor degradation of mechanical properties has occurred due to corrosion, the corroded pipe still has adequate strength to perform its intended design i
function in the same manner as new pipe. Chemical tests I
have indicated no surface residue which would tend to cause additional corrosion in.the future, beyond what would be expected due to norrnal service. The service conditions to
.which this piping is subjected and the mdoor environment in I
which the majority of the piping is installed are normal pow:er plant applications and are neither highly corrmive l'
nor highly corrosion-inducing. Therefor _e, considering~ the
- design margin available in the pipi.ng, andlthe vast amount of experience of using carbon steel pipmg m similar applications, this pipe is expected to perform in the same manner as new p:pe d6 ring its service life. Therefore. the Ir
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safetv-related piping which has been installed will be allowed to remain installed. However, as a further prudent measure, the existing quantities of uninstalled corroded pipe will not be installed in safety-related applications.
y VII.
R f:rences Vil-1 1.
" Stress Intensification Factors for 1/4. to 2-inch Schedule 30 Pitted and Corroded Pice," EMD-049664, 10-01-34 2.
" System Materials Analysis Department Report on Seamless Carbon Steel Pipe at Braidwood Station,"
M-2525-84, 03-20-84.
3.
" Stress Check of 1/2-and 3/4-Inch Schedule 50 Pickled Pipe," EMD-049655, Il-16-84, Addendum A, 09-13-85.
4 DlT-BR-PMDF-0025-0,10-05-S4, and DIT-BR-PMDF-0025-I, 09-03-85.
5.
" Evaluation of the Corrosion Problem Applicable to Small Bore Carbon Steel Piping Subsystems," EMD-351333. 07-10-35, Addendt m A,0S-06-S$; Addendum B.
08-28-35; Addendum C, 09-17-35.
6.
" Metallurgical Testing of Pipe Samples Per Consultant Spec.fication No. (2l," Taussig Associates, Inc., Report No. 60493-2, 03-27-3 5.
7.
" Acceptance Criteria fer Corroded P:pe 4 all Thickness Measurements," EMD-0 54 207, 59-0 3-8 5.
S.
" Evaluation of % a!! Inickness Measurement Samples for Corroded Pipe." EMD-0:4246, 09-l3-35.
f.
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VII-2 I
)
9.
Letter from Dr. Steven Danyluk to C. Berger of Taussig
- Associates, Inc., dated 11-26-35, transmitting his report dated November 1935.
i
- 10. ASME Transactions,1952, pp. 402-413.
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