ML113530092
| ML113530092 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 04/30/2011 |
| From: | Nuclear Energy Institute |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| Shared Package | |
| ML113530062 | List: |
| References | |
| RAS 21566, 50-247-LR, 50-286-LR, ASLBP 07-858-03-LR-BD01 | |
| Download: ML113530092 (20) | |
Text
NYS000169 Submitted: December 16, 2011 April 2011 Industry Guidance for the Development of lnspeEtion Plans for Buried Piping Prepared by: Buried Pipg":lGf~rity Task Force Fi~~~~
<~prr1:2011 IPEC PA OAG0023179
April 2011 TABLE OF CONTENTS 1.0 Preface ................................................................................................................. 4 2.0 Purpose ................................................................................................................ 4 3.0 Background ......................................................................................................... 4 4.0 Terms and Definitions.............................................................................. 6 5.0 Buried Piping Reasonable Assurance Flow Chart-Description ...... .
6.0 References .........................................................................................
April 2011 1.0 Preface This document provides industry guidance for the determination of reasonable assurance for structural and/or leakage integrity for buried piping. The criteria and guidelines presented in this document were developed as a consistent basis for establishment of what is necessary to provide "reasonable assurance of integrity".
2.0 Purpose The purpose of this document is to provide a technically based approach f:pr** .
development of inspection plans that establish reasonable assurance of st~~tutal and/or leakage integrity of buried piping through the application of the p@sults of both indirect inspections and direct examinations. The approach is prc::>§r~m~~tically founded in the precepts established in the "Recommendations for an EffeCt~¥~ Program to Control the Degradation of Buried and Underground Piping aa~tTari.ks (EPRI 1016456, Revision 1) and utility site specific program documents. T~j§ ijg~ument is intended to establish reasonable assurance for scoped buried piping ~~~t~ms; optimizing the inspection scope, while not requiring 100% inspection:
- 3.0 Background Reasonable assurance is an industry met~gd~ldgy used to achieve increased confidence in the capability of a structure, §yst~fh or component (SSG) to perform its intended function. Reasonable assut:~fl~~ dbes not equate to absolute assurance or confidence. Rather, reasonable assuf:~nce collects appropriate data/insights/information to ~~::~~port the establishment of increased confidence.
Situations may occur where~yffieient data cannot be easily collected; in these cases, the available data may b~$bpplemented with additional insights to bolster a technical foundation of reaSO!l~Qf~>§~§urance. If available information (even with supplemental insights) is insuffi~~~nt.Ib ~upport a conclusion of reasonable assurance, then additional actions must.~.~ tak~rrto achieve reasonable assurance. Ultimately, the establishment of reasonabl~ *.~s~urance is the obligation of the owner. This guideline provides insights to achiev~ fbn$1stency among industry users to identify what actions are generally neces~?~.t~>establish reasonable assurance for structural and/or leakage integrity for b4[l~d pl~i~g.
Reasonable assurance of integrity in buried piping systems containing licensed material or non-licensed material is obtained when activities such as an engineering evaluation (including a Fitness-for-Service assessment), indirect inspections of underground components, direct examination and remediation (if necessary), are performed. Such a combination of activities will provide a high level of confidence that the structural and leak integrity of the buried piping systems, will be managed and effectively maintained.
April 2011 A reasonable assurance of integrity process is based on defining systems that are in scope, risk ranking these systems, and then identifying a sample of locations in these systems for inspections. It relies on engineering analyses, expert judgment, operating experience, and groundwater protection program data to determine what regions of the buried pipes are vulnerable to degradation and adequately characterizing the vulnerability so that, if necessary, appropriate corrective actions may be taken. This process is based on risk identification and inspection sampling intended to greatly reduce the potential for unacceptable leakage or failures in the most susceptible systems.
Engineering evaluation is an important part of the "reasonable assurance ~'Jgrity" process. The engineering evaluation will consider but not limited to ite~s such as high consequence and/or likelihood areas, previous inspection resultS,;fqbrl~~lion practices, material type, backfill, coating, soil condition, water levels, water~~.as6il chemistry, cathodic protection, operational history, industry operating e~~riente, site operating experience and groundwater protection program data. Thi~,~galneering evaluation will identify the risk of potential leakage, the most probable lp~~Ubns, and/or areas of likely susceptibility. The evaluation will also identify the ppteAtial consequences that could result if a leak occurred. With this information, ag ip;~ection plan can be developed and implemented that provides information regardig~tb;;*~ondition of the structure, system or component. The inspections can be indice~t]h that they will provide information on the condition of the pipe remotely- from §[~~nd'level or from an exposed section of pipe that is distant or remote from th~~i~'f&cation of interest. Inspections include a direct examination of the pipe wall an~.*a visual inspection of the outer surface coating to determine coating integrity . .Qk.ect examination can also be achieved using an in-line vehicle (or Pipeline lnspectid~',GaGge "PIG") deployed with demonstrated direct examination equipment 'tapable of detecting degradation that is possible at the location of interest large enough to challenge structural or leakage integrity if present.
The specific j;~~ctions and examinations that are performed will be based on the type of degrad§:tib6~bserved or expected, the susceptibility of the pipe to leakage, the consequ~Q6e~ of a leak, and the location of the pipe. The scheduling of re-inspection agd<F:e:~~~~ination is also dependent on the engineering determination of susceptibility, corl~~quences, and the results of the initial inspection or examination.
April 2011 4.0 Terms and Definitions 4.1. Adverse Inspection Findings - Indications from inspections that require immediate repairs or repairs within one cycle.
4.2. Baseline Inspections - Inspection of new or replaced pipe or compog~nts that have not previously been involved in plant operations.
4.3. Corrosion Rate (CR) is the rate of corrosion occurring over a <~~;;~~d period of time.
4.4. Direct Examination -A Nondestructive Evaluation (NQE~;~amination where the NDE sensor(s) is in immediate contact with Qr in<~o~e proximity to the section of the component being examined. Resl{Jt§:provide some degree of quantitative measurement of wall thickness c9r <di~continuity size. Direct examinations can be performed from .lll~. frlterior or exterior surface.
Detection and characterization capabilitiesw~ry by NDE method as well as by specific NDE technique. Examples of:[XJIDEmethods include ultrasonics, eddy current, radiography, visual and ){Bfi~hs electromagnetic techniques. Visual examinations need to be supp}e~~flted with NDE or engineering judgment that addresses the conditiqg>c:>fth;~~pi~e wall.
4.5. Fitness-for-Service (FFS;r>~ i: a technical evaluation of direct examination data to determine a~eptable flaw size, degradation rate, remaining life, and the time to the neXIjp~pection or repair/replacement/mitigation.
4.6. Highest §<y~~~~~;~l: Locations are the highest likelihood and consequence risk ra&~ed li~es, segments or zones as defined in the buried piping sus~eptibiUtyanalysis and risk ranking database.
4.7. Jrfdl);~t Inspection - Survey techniques used to assess the likelihood of
. d~g~adation without having direct access to the section of the component being examined. These inspections typically measure surrounding conditions that may be indicative of corrosion or damage. Results are typically qualitative and less accurate than direct examinations. Examples of indirect inspection methods include over-the-line surveys and for the purpose of this document, long range guided wave.
4.8. Initial Inspection - The inspection of pipe or components that have been in service but have not been previously inspected.
April 2011 4.9. Inspection Program - A systematic evaluation of in-scope components using various techniques (e.g., ultrasonic testing (UT), radiographic testing (RT),
visual testing (VT), leak testing (LT), eddy current testing (ET)).
4.10. Lg- is the total length of piping associated with a group of lines.
4.11. L indirect - is the total length of pipe associated with a group of pipe lines that have been indirectly inspected.
4.12. Line Grouping- is a process that may be used to optimize inspehti§~$cope and schedule duration. Lines/segments/zones are grouped ba§~Q o~ various attributes, such as but not limited to process fluid, pipe mjaterial,> coatings,
~at:::
depth, age, soil/backfill, etc.
4.13. Next Scheduled Inspection (NSI) - is the until another inspection of the pipe line group is required.
4.14. Opportunistic Inspection - An inspectior~brtormed when buried or underground components are exposed ori~x~avated due to another activity providing an opportunity to inspect apdddtument the results for a program 4.15. :~:::n::gment - Portions ?,;s:: piping systems that are grouped together for risk ranking p~f:phs~~ based on similarities such as installation, manufacture, or environmental conditions. Some risk ranking methods may use other terms to piping segments, such as zones.
4.16. Post Asses~m,~t an assessment of all indirect and direct examination results iiJdtl@in~ a FFS evaluation that will determine the projected structural and leak~geJntegrity of a pipe.
4.17. R!>'ll~in'; Life (RL) is defined as the time period until the pipe wall ttJi~hess is no longer acceptable.
- ~~sua I Inspections involve direct observation by inspectors or by the use of remote visual inspection devices.
April 2011 Figure 5-1 Buried Piping Inspection Reasonable Assurance (RA) Flow Chart 8
April 2011 Figure 5-2 Buried Piping Inspection Reasonable Assurance (RA) Flow Chart
- :~::.:-:**:.>:-!>:*
- ~-
- :::':~:::~-:- :
.-;~,~<< '"ci'~.;~ .'*,
.;.:~ ~N::::!'+/-C!:::~:s*~cti:~ ****~-*~*'"'S-----P'
~~::;.:. :;::;,:;::! - - - - - - - - + l
.;..,.~,..;t.,*:..,..,::,>;:*,,***~*:f' i-'
- ..,'*, *. ~""~*::. :: :' .; - l:.:::::::.:::::::~J
.T.
. J f:~~ll *:=*~
0~
r*
........... .t. ...........
- !
- :-:'!~~::-:"c
- .:::::~~*
April 2011 5.0 Buried Piping Inspection RA Flow Chart-Description 5.1 Buried Piping Program Susceptibility Analysis and Risk Ranking
- 1. Susceptibility Analysis and Risk Ranking are used to determine the overall likelihood and consequence of a line, segment or zone failure.
- 2. This evaluation is based on detailed site specific information and provides a risk assessment of all piping within the program scope. ./<> .
- 3. The following potential exclusions from the program scope maY be considered in the susceptibility and risk ranking process. Th.~ ba.~i;fbr the exclusion should be documented:
- a. Segments or zones constructed of materials not sysceptible to the associated ID and OD degradation mechanism.s> lik~ titanium and super austenitic stainless (e.g., AL6XN or 254 8~6;:)
- b. Segments or zones of materials fully bae~f:illed<Dsing controlled low strength material (flowable backfill) in acgg~9~nce with NACE SP0169-2007, unless the pipe is susceptible tol~>a~g~adation.
- c. Piping sections that are hydrostatie:~.~~~ t~sted in accordance with 49 CFR 195 subpart E on an to exceed 5 years.
5.2 Create Line Groupings
- 1. The purpose for the grou~if)g ~~~fnes is to be able to extrapolate inspection results from one or more e~~~inations to the rest of the group, optimizing the number of excavations.
- 2. Separate segmen~~ b{.;z:ones by process fluid (e.g., Tritiated, Service Water,
& Oil lines woul9.6@:1~~uped separately; Corrosive vs. non-corrosive fluid, for instance chemftijlleed would be grouped separately from condensate and separat~tyff~rtltritiated circulating water piping)
- 3. Further*~~pJ~ate or create groups of lines with similar physical attributes by thef~!Jowi~g order of importance :
Material (e.g., Carbon Steel, Stainless Steel, Plastic, Fiberglass, and Aluminum would be grouped separately)
Coating type/age
- i. ID coating, type/age ii. OD coating, type/age
- c. Line depth (the basis for this grouping is the effect of live loads, and overburden):
April 2011 ii. > 1Oft below grade
- d. Pipe Age (e.g., Inspections on newer lines should not be used to justify reasonable assurance on older lines).
- e. Location in similar soil conditions (e.g., Lines in close proximity to one another in the same underground path/fill trench, backfill)
- f. Cathodic protection availability and operating history
- g. Operating Conditions
- i. Temperature (e.g., lines that undergo temperature changes and/or are >100F would grouped with ambient temperature lines).
ii. Operating frequency, and continuous vs.
infrequent/outage only)
- h. Pipe joining methods (e.g., §~bk~t vs butt welds or threaded connections & could be a g~o;!'deration for the adequacy of the external coating applicatiggJ. **
- 4. It is not required to separate or4£'?~ new groups for each category listed in 5.2.3 above.
- 5. Each segment or zone be included in a Line Group.
- 6. Documentation is required to support the basis for each line grouping.
- 7. Inspections wouldbe~erformed on the highest susceptible locations in each group.
5.3 lndire¢fl~~~~ction
- 1. lhQir;~~><i~spections, when feasible, are the best approach for determining
~umber and location of direct examinations that are required.
Indirect inspections are not required and the owner can go straight to direct examinations.
- 3. Indirect Inspection Selection is based on the highest susceptible locations in a line group.
- 4. Review each of the Indirect Inspection techniques per station or industry examination guidelines for determining applicable or optimum methods for each grouping or individual segments/zones.
April 2011
- 5. Review historical cathodic protection survey data and segment or zone location accessibility in order to refine the inspection selection areas.
- 6. Review the Groundwater Protection Program data.
- 7. Indirect inspection measurements should be referenced to precise geographic locations and documented so that inspection results c~ll pe used for excavation and direct examinations. Indications from.i~s:g~tlfins should be aligned with other results, drawings and structure~,.
- 8. Verification of the indirect inspections should be done~sing the direct examination results. At least one direct examinati.0n ~e performed in each high risk line grouping.
5.4 Classify Indirect Inspection Results
- 1. Criteria for classifying indirect inspecti6h results must be established.
- 2. The criteria for classifying the ~~~rity of indications should take into account the indirect inspecti~h t~chniques used and the conditions surrounding the pipe segiT)~ht~<'6e following general classifications may be used:
- Severe - indication~ h~~in~ the highest likelihood of active corrosion activity;
- Moderate jQd~sible pipeline corrosion activity; or
- Minor- t~¢:1~West likelihood of active corrosion activity.
- 3. The C~Ra~ilifr'and accuracy of the inspection method used must be con~id~;~d.'as part of the engineering evaluation.
5.5 Dir~~:;~ination Initial Sample Size
- \
- :::: ',>'
c*1~ When indirect inspections (for example a combination of Guided Wave and Above Ground Coating Surveys), covered greater than 50% of total (group) length including the highest susceptibility locations and where no severe indication (Section 5.4) is identified; one direct examination of the highest susceptible location to confirm the indirect inspection results would be required for each high risk line grouping, irrespective of the total line length. If an acceptable direct examination was achieved (i.e., Post Examination Assessment), then reasonable assurance could be demonstrated.
April 2011
- 2. When indirect inspections covered less than 50% of total length of a pipe group and where no severe indication is identified:
- a. For those High Risk Ranked lines that are safety related or contain Licensed Material or are known to be contaminated, that have pipe groups with total lengths of piping less than approximately 500' (ft),
then one direct examination of the highest susceptible location, with acceptable results, may be sufficient to demonstrate reasqtjable assurance. In selecting the location of the direct ~~aJUjil?:l~fibn, consideration can be given to the accessibility q{ e~~rlifhation locations.
§:>
- b. For those High Risk Ranked lines that are ~afE;lty ~~fated or contain Licensed Material or are known to be contarll'iD'~t~d, that have pipe groups with total lengths of piping great~f:. thah approximately 500' (ft), but less than 2500' (ft), two direct.~~~minations of the highest susceptible locations, with accept~BI~.results, may be sufficient to demonstrate reasonable assur§riba~ In selecting the location of the direct examination, conside~~t£pry can be given to the accessibility of examination locations . .. /* NNN
- c. For those High Risk*'~~' ;ines that are safety related or contain Licensed Material ~Ill~~ known to be contaminated, that have pipe groups with totall~ngths of piping greater than approximately 2500' (ft), three direct examinations of the highest susceptible locations, with a~~;~table results, may be sufficient to demonstrate reasof{abl~ assurance. In selecting the location of the direct
~xa~irl§tion, consideration can be given to the accessibility of
. . . . . . . e~~rllination locations.
For those lines that are High Risk Ranked and are not safety related, do not contain Licensed Material or are not known to be contaminated that have pipe groups with total lengths less than approximately 500 ft, one direct examination of the highest susceptible location, with acceptable results, may be sufficient to demonstrate reasonable assurance. In selecting the location of the direct examination, consideration can be given to the accessibility of examination locations.
- e. For those lines that are High Risk Ranked and are not safety related, do not contain Licensed Material or are not known to be contaminated that have pipe groups with total lengths greater than 13 IPEC PA OAG0023190
April 2011 approximately 500 ft, two direct examinations of the highest susceptible locations, with acceptable results, may be sufficient to demonstrate reasonable assurance. In selecting the location of the direct examination, consideration can be given to the accessibility of examination locations ..
- f. For those lines that are Medium and Low Risk Ranked, a monitoring plan should be established and direct examinplions performed on an opportunistic basis to determine <(e~~fiable assurance.
- 3. For indirect inspections that indicate severe levels of ~rrosion activity, categorize locations for direct examination and pro~ee:~>f~ <§ection 5.6.
- 4. For indirect inspections that indicate mod<\fll!;in;/ minor levels of corrosion activity the direct examination or~x~wlhations in section 5.5.2 would be focused on the highest area of indi6ated degradation.
- 5. Where indirect inspections that evp'~~,~:all thickness are performed at the most susceptible location§>jh>~> group, and the results of such inspections indicate NO or MI~QR likelihood of corrosion activity, then confirmation of the indirect\:irl~p~ction results may be obtained from a direct examination of ?T:'l~tJ::l~~ indirect inspection location in the same group (where the sam~> inspection technique was used). This can be allowed eccessibility issues exist for conducting a direct examination.
Using tbefi~Li~ below to illustrate this concept; a guided wave shot is tak~pf~~~6avation 1 showing only "minor" indications at "B" and "D".
[;:.. di~@~t~xam is performed that validates these results, and the remaining iff&: ..Js acceptable. A second set of guided wave shots is taken through a f~alf penetration (highest susceptible location), showing minor indications at "A" and "C". The pipe condition and indications at "A" and "C" would be considered validated by the direct examination completed in Excavation 1 with an acceptable remaining life. A second excavation would not be required to validate indications "A" and "C". To provide additional assurance of pipe integrity for all of these indications; one or more of the monitoring activities listed in section 5.8-3 should be periodically performed.
April 2011
',',\!""*
5.6 Direct Examination Selection The objective of direct examination is to asse~~the extent of corrosion activity for line segments selected for examination<ba~ed on the risk assessment and indirect inspections, when performed, when no significant degradation is found from a direct examination there~?ihing service life and next scheduled inspection should be calculated usi6g}h~ guidance in the following sections.
- 1. Indirect inspections re1!Jllt~f~.::: be used in determining the priority of direct examinations. BJ(9w is an example of criteria used for prioritizing direct examinatiqiJs based on the severity of indications from the indirect
- .s::~:r:: (~:::ons
~e~ti~g~ncies Initiate Direct for Mitigating Action for:
Examination Plan with Severe indications in close proximity Severe indications in a region with multiple moderate indications Isolated severe indications in a high risk region or area Indications known to be actively corroding Moderate indications in a region of high risk, prior leaks or severe corrosion
- b. Moderate Indications- Scheduled Action Required
- i. Isolated severe indication in a low risk region ii. Groups of moderate indications iii. Groups of minor indications in a medium risk region iv. Groups of minor indications in close proximity 15 IPEC PA OAG0023192
April 2011
- c. Minor Indications- Monitor
- i. All remaining indication scenarios
- 2. If no Indirect Inspections were performed for a group, then selection of the direct examination locations is based on the highest susceptible location of each line group considering location accessibility. Review historical cathodic protection survey data or other relevant parameters to refi~~>!re direct examination area.
- 3. Direct examinations resulting from excavations should coatings inspections by a person trained and experienced in ~eating condition assessment.
- 4. At least one Direct Examination is required fora~ch igh Risk Line Group in order to establish reasonable assurance ~~Group.
- 5. A Direct Examination at an individual exea~ation will assess a minimum 10 feet length of pipe, if feasible. is more than 1 pipeline in an excavation, each pipeline that an examination accounts for a separate direct examination.
5.7 Inspection Sample Expa~~nsiderations
- .* ./
When a pipe segmenJ or zohe has degradation detected by direct examination that Eif:xd~~os the acceptance criteria in section 5.8 and 5.9:
- 1. DetermineJ~¢':~~e~t of the corrosion by mapping the axial and transverse lengthS*@rlij cjepths of the corroded area.
R.e~i~~*.t~e indirect inspection results for the affected segment or zone 5
2.
~hp determine if additional excavation is required to perform direct
<e~c:lmination of other areas with severe or moderate indications.
Determine any segments or zones that share the same corrosion susceptibility characteristics and schedule additional direct examinations.
The timing of the additional examinations should be based on the severity of the degradation identified and should be commensurate with the consequence of a leak or loss of function.
- 4. Scope expansion must be sufficient to provide confidence that the extent of condition reasonably bounds the degradation.
- 5. Document the findings and actions in the appropriate corrective action program.
April 2011 5.8 Post Examination Assessment The purpose of the post assessment process is to define the inspection interval (time to Next Scheduled Inspection or NSI), assess the effectiveness of the program, and then feed the results back to the pre-assessment step to revise the risk ranking of buried pipe segments or zones as a continuous improvement process. The cumulative goal of the evaluations for a piping >
group is to complete a post assessment; including a fitness for se~yic~><
evaluation, that determines the remaining life and next schedul~d i~sp~Ction interval to provide quantitative reasonable assurance for that g~dijg,<. /
§:>
- 1. The assessment of the examination results shot1lq >5: >made using a Fitness-for-Service (FFS) assessment. Any degr~~~ffo:~ found during a direct examination should be appropriately dod~went~d.
- 2. The FFS evaluation performed will apply ,!,~~. segments, or zones in the group.
- a. When direct wall thickness m~~~~;~~ent meets tmin & tmeas is >87.5%
of tnom no FFS evaluatio!7il~ '<<', ~/
r~quired, unless active degradation is identified.
- b. When direct wall thi¥~=~s measurement meets tmin & tmeas is <87 .5%
of tnom: , , ,. ,'>>,
- i. Perf~(~an FFS ii. E'[aly?fe cause of degradation (consider all variables-backfill,
,,>>,,,,.*~~~tlhgs, installation, etc.)
. iii. Etaluate the extent of degradation (localized verses global) i~:>/ Evaluate the need for scope expansion When direct wall thickness measurement does NOT meet tmin:
- i. Evaluate cause and extent of degradation
- Inspection scope expansion (See section 5.7)
- Determine the Extent of Condition
- Repair degraded areas
- Evaluate potential mitigation strategies
- Enter into the corrective action program
- 3. Monitoring activities should be considered as part of the reasonable assurance programmatic or compensatory actions. Examples for the 17 IPEC PA OAG0023194
April 2011 justification of the scheduling/deferral of reasonable assurance direct examinations are:
- Increased Ground Water Initiative related well monitoring frequency
- Enhanced Cathodic Protection and/or Area Potential Earth Current (APEC) Surveys
- Soil Analysis
- Coating Scans
- Flow/pressure testing
- Guided Wave inspections
- Corrosion Probes
- Leak Testing (Acoustic monitoring, etc.)
5.9 1
- e::r:::e:i::e(F::~ ::1:::::: proces~ft~ provide guidelines for evaluating wall thickness degradation it} ~~fety and non-safety related components. Engineering should use tp~~~guidelines, or other applicable methodologies, when establishing tbe adceptance criteria or refining the acceptance criteria when warranted~ ~he projected life of the component, based on these calculations, is.t~ b:? used to establish the interval between examinations. An engineering f~~tfnidal evaluation is required for any deferral of the next scheduled exa~l~a~ibrl>past the remaining life date.
a) Corrosion Rate It is re~~i"that for buried piping, most degradation mechanisms areJ!l!ptll~ear with time. Any corrosion rate calculated from one ift~pe¢tion is likely to have a large inaccuracy and could be either
}> coris~rvative (for inactive degradation mechanisms) or non-
<eonservative (for recently activated mechanisms). Whenever possible, external corrosion rates should be determined by directly comparing measured wall thickness changes over a known time interval.
Therefore, it is recommended to perform at least two inspections before a more accurate corrosion rate can be established.
When previous pipe wall thickness measurements or other data are not available, default corrosion or pitting rate may be used to determine re-inspection intervals. NACE recommends a default pitting rate of 16 mils/year. NACE further indicates that the default corrosion rate may be reduced by 24% (from the default 16 mils/year), provided that the Cathodic Protection (CP) levels of the pipeline segments being 18 IPEC PA OAG0023195
April 2011 evaluated have had at least 40 mV of polarization, considering the voltage drop, for a significant fraction of the time since installation. If the evaluated line can potentially be subjected to an internal corrosion process, such as Flow Accelerated Corrosion (FAG),
Erosion/Corrosion (E/C) or Microbiologic Influenced Corrosion (MIG),
effects of internal wall loss should also be considered.
For components with multiple examinations the corrosion rate more refined, as outlined in equation 1 below:
CR =(timemw'1- timemw) x SF I time .................. :*bfr~ation 1 Where:
CR = Corrosion rate, also referred timemeas1 = tmeas at 1st examinab~.n timemeas2 = tmeas at 2nd or>$~b~~quent examination at mea~b:~~~~lue same location tmeas = The minimum SF = Safety Factor (r:e~g!J,mend at least 10%) = 1.10 time = The length a~>tlme between the (timemeas1 and timemeas2) examination~<~~@~rs) b) Remaining Life (RL~~~~ti:
For the ex~~ihation of a buried pipe component, the remaining life (RL) m'!Y~~d~lculated as per Equation 2 below:
0
~A~ ~l:~,- lm;o) I CR ...........................................Equation 2
- *
- yv~:r~:
tmeas = The minimum measured value from the 1st examination tmin = The minimum acceptable wall thickness for the current inspection required to meet Code requirements.
CR = Corrosion Rate (mils/year). Whenever possible external corrosion rates should be calculated from direct comparison of changes in wall thickness over time. However, for the initial examination the time period of active corrosion is unknown. In the absence of a known period of time from the initiation of corrosion, a default corrosion rate (CR) of 16 mils/year may be used.
April 2011 If the evaluated line can be subjected to FAG, E/G, and/or MIG, then the effects of internal wall loss should be considered.
- 3. Time to Next Scheduled Inspection (NSI)
When tmeas is found to be less than or equal to 50% of tnom, the re-examination interval should be taken as one-half the remaining life (RL) calculated in Equation 2. The examination interval may be increas~~>if it can be determined that the corrosion mechanism is inactive, for: ex~mpl~ a coating repair has been applied. When corrosion is less th~n SD.~o>bf tnom (i.e. tmeas is greater than 0.5 tnom), the re-inspection interval <Ma.¥be taken as 75% of RL, as summarized below:
tmeas > 0.5 X tnom: .................. Equation 4
- 4. Mitigation or Engineering Technical q:.valuation a) A determination should ~~~;~~:>to either mitigate directly or to perform additional engi~~~(ing technical evaluation/analysis if the remaining life dq~s rf~tsLpport the period of time until the pipe will be available for t~ehext>examination (e.g., refueling outage).
b) If more>t~~n a single line is in the group, the lines with no examination tlata need to be evaluated based on the examinations perfo~TF~~ *for determination of condition. Additional examination
.~~~>p&*required based on this evaluation.
A<~e~ermination should be made to repair, replace or implement compensatory actions.
All engineering evaluations should be performed and documented as required by station procedures.
April 2011 6.0 References
- 1. "Recommendations for an Effective Program to Control the Degradation of Buried and Underground Piping and Tanks 1021175 (EPRI 1016456, Revision 1)
- 2. Radiological SSG Groundwater Initiative Risk Evaluation Criteria
- 3. A.P. Moser "Buried Pipe Design", McGraw Hill, 2nd Edition (Tabl.~
Loads").
- 4.Section XI, Div. 1 Class 2 and 3 Metallic Piping Buried in a Ba~k:~Jited Trench, Inquiry, Draft "What Rules may be used to evaluate Class 2 9D~glass 3 metallic piping buried in a back-filled trench subjected to metal ~~~S.Q,O the internal and external surfaces of the pipe or fitting"
- 5. ASME B&PV Code,Section XI
- 6. ASME B&PC Code, Section Ill
- 7. ASME B31.1, "Power Piping"
- 8. ASME Standard B31.3, "Process Piping/~>
- 9. ASME B31-G, "Manual for Deterrpi~~~~ the Remaining Strength of Corroded Pipelines" 10.American Petroleum lnstitute(:API)Standard 510 Pressure Vessel Inspection Code: "Maintenance lm;pection;>Rating, Repair, and Alteration" 11.API Standard 570 Pi~;~,~~f:rispection Code: "In-service Inspection, Rating, Repair, and Alteration of F'~pi~g.Systems"
- 12. API StandardSi~; *. ~*~~nk Inspection, Repair, and Reconstruction" 13.ASME Cod~~a~e N-597-1, "Requirements for Analytical Evaluation of Pipe Wall Thinni~§1:1~.,Se~tion XI Div. 1.
14.AS.M~~O~e Case N-513, "Evaluation Criteria for temporary Acceptance of Flaws JrtMdBerate Energy Class 2 or 3 Piping",Section XI, Div. 1.
- ~I 579-2/ASME FFS-2, "Fitness-For-Service"
. NACE Standard Practice SP0169-2007, Control of External Corrosion on Underground or Submerged Metallic Piping Systems, 2007.
17.NACE International Standard Recommended Practice, RP0502, Item No. 21097, "Pipeline External Corrosion Direct Assessment Methodology".