LIC-14-0109, Evaluation of a Through-Wall Leak in a Raw Water Elbow in Support of Relief Request
| ML14231B310 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 08/19/2014 |
| From: | Dean E Omaha Public Power District |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LIC-14-0109 | |
| Download: ML14231B310 (25) | |
Text
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iJppu Omaha Public Power District 444 South 1 efh Street Mall Omaha, NE 68102-2247 LlC-14-0109 August 19, 2014 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Fort Calhoun Station, Unit No.1 Renewed Facility Operating License No. DPR-40 NRC Docket No. 50-285 10 CFR 50.55a
Subject:
Evaluation of a Through-Wall Leak in a Raw Water Elbow in Support of Relief Request RR-14
Reference:
- 1. Letter from OPPD (L. P. Cortopassi) to NRC (Document Control Desk), Fort Calhoun Station Relief Request RR-14, Proposed Alternative, Request for Relief for Temporary Acceptance of a Pin Hole Leak in Raw Water (RW)
System 20-inch Elbow Located in Room 19 of Auxiliary Building, dated August 15, 2014 (LlC-14-01 06)
In Reference 1, the Omaha Public Power District (OPPD) submitted a request for relief (RR-1 4) for a proposed alternative for Fort Calhoun Station, Unit NO.1. Attached is the evaluation of a through-wall leak in a raw water elbow, which has undergone owner-acceptance review by OPPD and supports the conclusion of the relief request.
There are no regulatory commitments contained in this submittal.
If you have any questions concerning this submittal, please contact Mr. Bill R. Hansher at (402) 533-6894.
EDD/KGM/brh
Attachment:
Evaluation of a Through-Wall Leak in a Raw Water Elbow Employment with Equal Opportunity
LlC-14-0109 Attachment Page 1 Evaluation of a Through-Wall Leak in a Raw Water Elbow File No.: 1401013.301
PED-QP-3.1 Calculation Coversheet Calculation Number: FC08390 OA Category: [X] COE [ ] Non-COE [
Calculation
Title:
] LCOE Evaluation of a Through Wall Leak in a Raw Water Page No.: i Total Pages:
- 2-3 Short Term Calc: [X] Yes Page 1 of 2 Rev. 13
[ ] No Elbow Vendor Calc. No.: 1401013.301 Associated Project::
Software Tracking No.: N/A Responsible Dept No.: 356 (from PED-MEI-23, if applicable)
Owner Assignment (by Dept Head): N/A (Required only if there are affected documents to be changed)
OPPD Engineer Assignment (by Dept Head): Chris Hooker (Required only for verification of vendor/contractor calculations)
Verification of Vendor/Contractor Calc. assumptions, inputs and conclusions complete:
OPPD Engineer: ~. ~
Employee 10:
/~1/~
Date: <J/;VI'f APPROVALS - SIGNATURE AND DATE Confirmation (Multiple preparers shall identify section prepared per PED-QP-3, Required?
Section 4.2.)
Supersedes Rev.
Preparer(s)
Reviewer(s) Employee Required for Responsible Yes No No.
10 CQE Department Calc No.
Independent Head Reviewer(s) 0 See cover page of vendor calculation for Owl-uJ~
N/A X
preparer, reviewer, and approver.
~ \\ \\1\\1"\\
PED-QP-3.1 Calculation Coversheet Page 2 of 2 Rev. 13
/calculation Number: FC08390 I Page No.: ii Applicable System(s)/Tag Number(s)
Raw Water EA's and/or Calculations Used as input in this Calculation EA95-012, Rev. 3 FC06553, Rev. 1 FC01013, Rev. 0 External Organization Distribution (Groups affected by this calculation)
Name and Location Copy Sent (-/)
Name and Location Copy Sent (-/)
PRODUCTION ENGINEERING DIVISION QUALITY PROCEDURE FORM CALCULATION REVISION SHEET PED-QP-3.2 R6 Calculation No.: FC08390 I Page No.: iii r-----~---------------------------------------~----------------
Rev. #
Description/Reason for Change o
Original Issue EAG Reviewed 9 A
(
ej;c,/;1 riil
-Toafe-
PED-QP-3.8 Calculation Affected Documents Calculation No.:
Page No.:
Page 1 of 2 Rev. 8 FC08390 Rev. 0 iv The Calculation Preparer is to identify documents affected by this Calculation. Markups are to be provided in an Attachment to the Calculation except those noted with an *.
Changes not involving procedures should follow the associated change process. The preparer is to indicate below how the Calculation is to be processed by Document Control.
Not Required, Calculation supports EC No.
or is used to support EA-FC-this form can be signed off by the Calculation Preparer.
Calculation "As Built" follows direction given for modifications.
EC, FLC, Preapproved NRC commitment change, or Condition Report need identified. Calculation is closed on receipt of the completed PED-QP-3.8 form.
Change to a DBD, USAR, etc., without a change to plant procedures identified.
Calculation is "As Built" on receipt of the completed PED-QP-3.8 form.
Change to a DBD, USAR, etc., and plant procedures (no hardware) identified.
Calculation is "As Built" on receipt of the completed PED-QP-3.8 form.
X No document changes or other changes are required. Calculation "As Built" on receipt of the completed PED-QP-3.8 form.
NOTE: Markups are to include any inputs or assumptions which define plant configuration and/or operating practices that must be implemented to make the results of the Calculation valid. The Calculation may provide the basis for a 10 CFR 50.59 and/or 10 CFR 72.48 analysis or substantiate a 10 CFR 50.59 and/or 10 CFR 72.48 analysis.
Affected Documents Document Number Procedure Change Document Type (N/A = not applicable)
No., FLC No., etc.
Emergency Operating N/A Procedure*
Abnormal Operating N/A Procedure*
Annunciator Response N/A Procedure Technical Data Book N/A Surveillance Test Procedure N/A Calibration Procedure N/A Operating Procedure N/A Maintenance Procedure N/A PM Procedure N/A PED Procedure N/A EP/EPIP/RERP*
N/A Operating Instructions N/A System Training Manuals N/A Technical Specification*
N/A
PED-QP-3.8 Page 2 of 2 Calculation Affected Documents Rev. 8 Calculation No.:
FC08390 Rev. 0 Page No.:
v Affected Documents Document Number Procedure Change Document Type (N/A = not applicable)
No., FLC No., etc.
USAR N/A Licensing Commitments N/A Standing Order N/A Security Procedures
- N/A (Safeguards )*
Security Plan (Safeguards)
N/A CQE List N/A Vendor Manual Changes N/A Design Basis Documents N/A Equipment Database N/A Oil Spill Prevention, Control and Countermeasure (SPCC)
N/A Plan EEQ Manual N/A ERFCS Computer Point N/A Manual SE-PM-EX-0600 N/A Updated Fire Hazard Analysis N/A EPIX N/A Electrical Load Distribution N/A Listing (ELDL)
Station Equipment Labeling N/A Engineering Analysis N/A Calculations N/A Drawing Number N/A Drawing Number N/A Other N/A Completed by Owner (if Plant Procedure Changes Required or N/A):
N/A Employee ID:
Date:
Completed by Preparer: Chris Hooker Employee ID: 13818 Date: 8/18/14
PED-QP-3.10 Owner Acceptance Review Checklist for External Vendor/Contractor Calculations EC No.:
N/A EAG Reviewed C
gl'
~~:-:-....;.....,;;;;..-.--
Calculation No.:
FC08390 Rev.:
Page 1 of 1 Rev. 0 o
Page No.:
VI Yes No N/A
- 1.
Are the assumptions reasonable and have sufficient rationale?
X
- 2.
Are assumptions compatible with the way the plant is operated and with X
the licensing basis?
- 3.
Are design inputs/attributes correct for the calculation being performed and referenced to appropriate Design Basis and Licensing Basis X
Documents?
- 4.
Do the design inputs/attributes reflect the way the plant is operated?
X
- 5.
Are Engineering Judgments, if any, clearly documented and justified?
X
- 6.
Do the results and conclusions satisfy the purpose and objective of the X
design analysis?
- 7.
Is the Calculation prepared in a clear and understandable manner such that it will allow revision or review in the future without assistance from X
the preparer and uses reference documents or standards available to OPPD?
- 8.
Have any limitations on the use of the results been identified and X
transmitted to the appropriate organizations?
Reviewer: ~
f/~
Employee 10: /3ttlr Date: f?l1/f~
Print/Sign: Ch7S 4.-,.j, '"
Comments: A 50.59 review will not be completed for this calculation. Procedure PED-QP-3, Rev.
39, Calculation Preparation, Review and Approval indicates that the appropriate 50.59 review shall be included in the calculation package if the calculation is not being performed in support of a hardware configuration change to the facility. For this calculation, the appropriate review is no review for the following two reasons. First of all, this is not a design calculation; it is performed to determine operability of Raw Water piping from a structural integrity standpoint. Normally this calculation would be included as part of an operability evaluation and a 50.59 review would not be required for the calculation itself, only the required compensatory measures. Secondly, the code case used in this calculation required a relief request from the NRC. The ASME N-513-4 code case has not been generally accepted by the NRC which required a relief request to use it for determining operability of the Raw Water elbow. The purpose of a 50.59 review is to determine if prior NRC approval is required. In this case NRC verbal approval has already been granted (see attached), therefore a 50.59 review is not required.
Additionally assumption number 2 in the calculation was verified. The flaw and subsequent leak were found in the middle of the elbow and is not near (within 5 inches) of any welds.
/Lw. 0 HOOKER, CHRISTOPHER T From:
Sent:
To:
Subject:
Origi na I Message-----
SIMPKIN, TERRENCE W Monday, August 18, 2014 12:59 PM HOOKER, CHRISTOPHER T FW: Verbal Authorization RR-14 From: Lyon, Fred [1]
Sent: Friday, August IS, 2014 10:06 PM To: SIMPKIN, TERRENCE W; HANSHER, BILL R Cc: EDWARDS, MICHAEL L; Oesterle, Eric; Alley, David; Tsao, John; Hay, Michael
Subject:
Verbal Authorization RR-14 VERBAL AUTHORIZATION FOR RELIEF REQUEST RR-14 TEMPORARY NON-CODE REPAIR OF RAW WATER PIPING FORT CALHOUN STATION, UNIT 1 August IS, 2014 By letter dated August IS, 2014, Omaha Public Power District (the licensee) requested relief from the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, IWD-3120(b),
at at Fort Calhoun Station, Unit 1.
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) sO.SSa(a)(3)(ii), the licensee submitted Relief Request RR-14 and proposed to use an alternative methodology to ASME Code Case N-S13-3 to disposition a pin hole leak in lieu of performing a repair on the leaking elbow ofthe raw water system piping immediately.
The licensee states that it will perform daily walkdown and measurement of the leakage to confirm that the analysis supported by the ultrasonic testing remains valid. The licensee calculated an allowable axial through wall flaw size of 4 inches and allowable circumferential through wall flaw size of 10 inches. The leaking flaw is of pin hole size. There is a substantial margin between the pin hole flaw size and the allowable flaw size. The NRC staff finds that the probability of pipe failure would be unlikely.
The NRC finds that the licensee has provided a adequate justification that Relief Request RR-14 will provide a reasonable assurance of the structural integrity ofthe subject raw water piping.
The NRC staff determines that the proposed alternative provides a reasonable assurance of structural integrity of the subject raw water piping. The NRC staff finds that complying with IWA-4000 ofthe ASME Code,Section XI, would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR SO.S5a(a)(3)(ii). Therefore, on August IS, 2014, Eric Oesterle, Acting Chief, NRRjDORL/LPL4-1, and David A"ey, Chief, NRR/ DEjEPNB, verbally authorize the use of Relief Request RR-14 at Fort Calhoun Station, Unit 1 until September 5, 2014, or when the leakage flaw size exceeds the allowable flaw size discussed above, whichever occurs first.
All other requirements in ASME Code,Section XI, for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
This verbal authorization does not preclude the NRC staff from asking additional clarification questions regarding the Relief Request while preparing the subsequent written safety evaluation.
DOCUMENT REVIEW FORM Document(s) Reviewed:
FC08390, Rev. 0 Date Reviewed:
8/18/2014 No.
Reviewer Section or Ref.
Comment I would like to remove the assumption regarding the long radius 1
C. Hooker Assumptions, page 4 and 5 elbow and add it to the inputs section. This assumption was verifed by a field walkdown and will bt added to rev. of the Design Input Transmittal (DIT).
What is the basis for using Takahashi's SIFs instead of the code values? Is this acceptable per the code and code case? If so, 2
C. Hooker Technical Approach, page 3 where is this stated? More basis needs to be provided as to why this is acceptable to use with the code and code case. If sufficient basis cannot be provided the code SIFs should be used.
3 C. Hooker 4
C. Hooker 5
C. Hooker 6
C. Hooker 7
C. Hooker 8
C. Hooker 9
C. Hooker 10 C. Hooker 11 C. Hooker 12 C. Hooker 13 C. Hooker 14 C. Hooker 15 C. Hooker 16 C. Hooker 17 C. Hooker 18 C. Hooker 19 C. Hooker 20 C. Hooker Page 1 of 1 Project:
Date Resolved:
Resolution Acceptance Will remove assumption after receiving revised DIT.
Y The third sentence in the last paragraph of pg. 3 explains that "the Code Case allows for alternate stress intensity factor parameters to be used." To make this more clear, we will add an additional sentence as y
follows: "... 1.5 to 80.5 [5]. The Code Case states that alternative solutions for Fm and Fb may be used when Rtt is greater than 20 [1, Appendix 1-2].
Takahashi has proposed... "
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CALCULATION PACKAGE PROJECT NAME:
Ft Calhoun Evaluation of Leaking Elbow CONTRACT NO.:
165134 Release 10 CLIENT:
PLANT:
File No.: 1401013.301 Project No.: 1401013 Quality Program: [8J Nuclear 0 Commercial Omaha Public Power District F0l1 Calhoun Station CALCULATION TITLE:
Evaluation ofa Through-WaH Leak in a Raw Water Elbow Document Revision o
Affected Pages 1 - 12 Al - A-3 Revision Description Initial Issue Project Manager Approval Si~nature & Date L,~-1/:1=-
Eric 1. Houston 811912014 Preparer(s) &
Checker-(s)
Signatures & Date Preparer:
dr;ZtJJw 1Jv~
Matthew C. Walter 8/19/2014 Checker:
/'
y-, /.
Brad P. Dawson 8/19/2014 Page I of 12 HJ306*01R 1
StrucluTallntegrity Associates, lnc.qt' Table of Contents 1.0 INTRODlJ('TION......................................................................................................... 3 2.0 TECHNICAL APPROACH.................................................,........................................ 3 3.0 DESIGN INPUTS AND ASSUMPTIONS...................................................................4 4.0 CALClJLATIONS......................................................................................................... 5 4.1 Applied Loads.................................................................................................... 5 4.1.1 Hoop Stress........................................................................................................ 5 4.1.2 Axial Stresses..................................................................................................... 6 4.2 Stress Intensity Factor Calculations................................................................... 6 4.3 Critical Fracture Toughness Dctc1l11inatioll....................................................... 7 5.0 RESlJLTS...................................................................................................................... 8 6.0 CONCLlJSIONS........................................................................................................... 8 7.0 REFEREN(~ES.............................................................................................................. 9 APPENDIX A CODE CASE N-513-4 PROCEDl RES FOR ELBOW FLAW EVALUATION............................................................................................ A-I List of Tables Table 1: Applied Moment Loading for Bounding Moments [7]............................................ 10 Table 2: JIC Values for AI06 Gr. B Carbon Steel from NRC's Pipe Fracture Database [8].. 11 Table 3: Axial and Circumferential Structural Factors [3]..................................................... 12 Table 4: Load Combinations for Circumferential Flaw Analyses.......................................... 12 Table 5: Pressure Blowout Check........................................................................................... 12 File No.: 1401013.301 Revision: 0 Page 2 of 12 F0306-01 R I
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1.0 INTRODUCTION
Fort Calhoun Station has identified a pinhole leak in a 20-inch elbow in the raw water system. The system is safety related, and therefore requires an evaluation to demonstrate operability. The objective of this calculation is to detelmine the allowable through-wall flaw lengths in accordance with an upcoming revision of ASME Code Case N-S13-3 [1].
2.0 TECHNICAL APPROACH The flaw evaluation herein is based on the criteria prescribed in an upcoming revision of ASME Code Case N-S13-3. This Code Case allows for the temporary acceptance of through-wall flaws in moderate energy Class 2 or Class 3 piping. N-S13-3 has been conditionally accepted by the NRC with the stipulation that, "The repair or replacement activity temporarily defelTed under the provisions of this Code Case shall be perfOlmed during the next scheduled outage," and is published in the latest revision of Regulatory Guide 1.147 [2]. N-S13-3 allows non-planar, through-wall flaws to be characterized and evaluated as planar (i.e.,
crack-like), through-wall flaws in the axial and circumferential directions.
The evaluation criteria provided in N-S13-3 are only for straight pipe since the technical approach relies on ASME Section Xl, Appendix C [3] methods. A new revision of the Code Case (N-S13-4) includes mles for the evaluation of piping components such as elbows, branch tees and reducers. Flaws in these components may be evaluated as if in straight pipe provided the stresses used in the evaluation are adjusted to account for geometric differences. For elbows, hoop stress is adjusted by considering flaw location and through-wall bending that results from elbow ovalization due to in-plane or out-of-plane bending moment. For axial stresses, the stress scaling follows the same approach given in ASME Section III, ND-3600 [4] design by rule using stress indices and stress intensification factors for the adjustment. Details are provided in N-SI3-4 for detern1ining these adjusted stresses.
N-S13-4 has been approved by ASME and is pending publication. It is recognized in ASME committee that the technical approach is very conservative. Simple treatment of piping component flaw evaluation using hand calculations was an important objective in the development of the approach recognizing the trade-off being conservative results. N-S13-4 allows for alternative methods to calculate the stresses llsed in the analysis to reduce conservatism. N-S13-4 has not been generically reviewed by the NRC.
As stated above, Code Case N-513-3 evaluation criteria rely on the methods given in ASME Section XI, Appendix C. Linear Elastic Fracture Mechanics (LEFM) criteria are conservatively employed as desclibed in Al1icle C -7000. Equations for through-wall stress intensity factor parameters Fnh Fb and F are given in the appendix to the Code Case, although the Code Case allows for alternate stress intensity factor parameters to be used. For circumferential through-wall flaws, the Code Case stress intensity factor parameters are valid over a range of mean pipe radius to thickness (Rm/t) ratios from S to 20 and become increasingly conservative for Rm/t>20. The Code Case states that alternative solutions for Fm and Fb may be used when RJt is greater than 20 [1, Appendix 1-2]. Takahashi has proposed alternate stress intensity factor parameters, which are valid over the range of I.S to 80.S [5]. Since the Rn,lt ratios in the present analysis are greater than 20, the Takahashi parameters are appropriate to use. Therefore, for the circumferential through-File No.: 1401013.301 Revision: 0 Page 3 of 12 F0306-01 RI
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wall analysis, the Takahashi stress intensity factor parameters are used in place of the Code Case stress intensity factor parameters. Axial through-wall flaws are evaluated using the stress intensity factor parameter from the Code Case, Appendix 1. Allowable flaw lengths are detemlined through iteration comparing calculated stress intensity factors to a critical fracture toughness defined in C -7200 of Section XI, Appendix C.
Details of the Code Case N-513-4 evaluation procedure for elbows are given in Appendix A.
3.0 DESIGN INPUTS AND ASSUMPTIONS The piping design Code ofConstmction is USAS B31.7, 1968 Draft Edition [6] as specified in Reference
[7].
The elbow material is ASME A234 WPB [7] carbon steel. For the analysis, Al 06 Gr. B carbon steel is judged to have equivalent matelial properties. The nominal composition of the two materials is essentially the same and the: minimum yield and tensile strengths are the same for both materials.
The following design inputs are used in this calculation:
- 1. Outside diameter = 20 inches [7]
- 2. Nominal wall thickness = 0.375 inch (based on standard pipe size) [7]
- 3. Elbow bend radius = 30 inches [7]
- 4. Maximum normal operating pressure = 54 psig [7]
- 5. Design temperature = 500°F [7]
- 6. Maximum operating temperature = 200°F [7]
- 7. Material stress allowable = 15 ksi [6]
- 8. Young's modulus = 26,400 ksi [6]
- 9. NDE inspection results [7]
The moment loadings applied to the piping are obtained from the design input transmittal [7] for element CIS. The bounding moments are shown in Table 1.
Determination of the fracture toughness, 11(", used in the evaluation is based on Section XI, Appendix C, C-8320 [3], which specifies that 'reasonable lower bound fracture toughness data' may be used to determine the allowable stress intensity factor, KIc. The NRC's Pipe Fracture Encyclopedia [8] contains numerous CVN test results for Al 06 Gr. B carbon steel at low temperature, which are reproduced in Table 2. The minimum reported value of 293 in-Ib/in2 is used in the analysis.
The following assumptions are used in this calculation:
- 1. Poisson's ratio is assumed to be 0.3.
- 2. The leak is remote from a weld, so the residual stress is assumed to be negligible.
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- 3. A cOlTosion allowance is not considered (the ongoing inspection requircments in Code Case N-513-3 address the possibility of flaw growth during the temporary acceptance period).
4.0 CA LCULATIO~ S The applied stresses and resulting stress intensity factors are evaluated for a surrounding wall thickness of 0.225 inches.
4.1 Applied Loads Axial and circumfercntial (i.e., hoop) stresses are calculated from the moment loads in Table 1 and the maximum operating pressure. The sUlTounding wall thickness, tadj, is used to determine the section prope11ies. The nominal wall thickness, toom, is Llsed to calculate the flexibility characteristic 'h' in accordance with the guidance ofN-513-4 (see Appendix A).
4.1.1 Hoop Stress For the allowable axial flaw length, the hoop stress. O'h, due to intemal pressure ancl elbow ovalization from the axial moments may be detennined from Equation 9 ofN-513-4 (see Appendix A):
where:
p== intemal maximum operating pressure, psig Do== outside diameter, in tadj== sUlTounding (adjacent) wall thickness, in Rbcnd== elbow bend radius Ro== outside radius, in
¢== circumferential angle from elbow flank (see Figure 7 in Appendix A) h== flexibility characteristic== tntHll*Rbend/(R mcani [6, section D-402]
tnom== nominal wall thickness== 0.375 in (Section 3.0)
Rmeao== elbow mean radius, in Mb== plimary bending moment, in-lbs I== moment ofine11ia, in4.
(1)
Note that the first term of Equation 1 accounts for the hoop stress due to internal pressure and includes a scaling factor to account for the circumferential location of the flaw (assuming uniform thickness, pressure based hoop stress is a maximum at the elbow intrados, while a minimum at the elbow extrados). At the flank, the pressure based hoop stress is equal to that of straight pipe. For the analysis herein, it is conservative to set ¢== 1.5ft since this maximizes the hoop stress.
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The second tenn of Equation 1 accounts for the through-wall bending stress resulting from the axial moments acting to ovalize the elbow. The basis for this factor comes from Reference [9].
Finally, N-513-4 limits the lise of Equation I for h 2: 0.1. For this elbow. h is greater than 0.1.
4.1.2 Axial Stresses For the allowable circumferential flaw length, the axial stress due to pressure, deadweight and seismic loading is presented below. For axial membrane stress due to pressure, (in" Equation 10 ofN-513-4 is used:
(j
_ B (PDo )
11/
- 12t (2) where:
8 I is an ASME Section III primary stress index for intemal pressure (N-513-4 sets this value to 0.5).
For axial bending stress, Gb, due to deadweight and seismic moments, Equation 11 ofN-SI3-4 may be used:
(3) where:
8 2 is an ASME Section III ptimary stress index for moment loading (from Figure ND-36 73.2(b )-1 of Reference [4], B2 = 1.30/h2 \\
For axial bending stress, Ge, due to thennal expansion, Equation 12 of N-S13-4 may be used:
a =1 _0_'
.(RM.)
l' J
(4) where:
i = stress intensification factor Me = resultant thermal expansion moment, in-Ibs.
4.2 Stress Intensity Factor Calculations For LEFM analysis, the stress intensity factor, K" for an axial flaw is taken from Article C-7000 [3] as prescribed by N-SI3-3 and is given below:
where:
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SFm = structural factor for membrane stress (see Table 3)
F = through-wall stress intensity factor parameter for an axial Haw under hoop stress (given in Appendix IofN-513-3)
(Jh = hoop stress, ksi a = flaw depth (taken as half flaw length for through-wall flaw per Appendix I ofN-513-3), in Q = flaw shape parameter (unity per Appendix IofN-513-3)
K lr = KI from residual stresses at flaw location (assumed negligible)
Only the hoop stress influences the allowable axial flaw length, which is a function of pressure and primary bending stress.
For LEFM analysis, the stress intensity factor, KI, for a circumferential flavy' is taken from Article (' -7000
[3] as prescribed by N-513-3 and is given below:
where:
Kim = (SFm)Fm(Jm(na)O.5 Fm = through-wall stress intensity factor parameter for a circumferential flaw under membrane stress [5]
(Jm = membrane stress, ksi KIt) = [(SFb)(Jb + (Je]Fb(na)O.5 SFb = structural factor for bending stress (see Table 3)
(Jb = bending stress, ksi (Je = thelmal stress, ksi Fb = through-wall stress intensity factor parameter for a circumferential flaw under bending stress [5]
K lr = KI from residual stresses at flaw location (assumed negligible)
Note that the through-wall flaw stress intensity factor parameters are a function of flaw length.
Table 4 shows the specific load combinations considered herein for the allowable circumferential flaw calculations.
4.3 Critical Fracture Toughness Determination For LEFM analysis, the static fracture toughness for crack initiation under plane strain conditions, KJc, is taken from Article C -7000 [3] as prescribed by N-513-3 and is given below:
where:
K =
lie = material toughness, in-lblin1 E' = E/(l-v2)
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E = Young's modulus, ksi v = Poisson' s ratio.
Based on the design input listed above, KJc = 92.2 ksi-ino 5. The allowable flaw lengths are determined iteratively by increasing flaw length until the stress intensity factor is equal to the static fl:acture toughness.
5.0 RESULTS Based on inputs in Section 3.0, moments in Table 1 and using equations ti'om Section 4.0, the allowable through-wall naw in the axial direction is 4 inches. The allowable through-wall naw in the circumferential direction is 10 inches. These flaw lengths are for a 0.225 inch sUlTounding wall thickness. Based on the inspection data given in Reference (7], the analyzed thickness and flaw lengths easily bound the observed thinning. Thus, the acceptance cliteria of Code Case N-513-4 are met.
Code Case N-513-3, Paragraph 3.2( d) requires that the remaining ligament average thickness over the degraded area be sufficient to resist pressure blowout [1, Equation 9]. Table 5 shows the required average thickness, tc.avg, as a function of the equivalent diameter of the circular region, dudj, for which the wall thickness is less than tadj. Based on the inspection data given in Reference [7], the values in Table 5 easily bound the observed thinning. Thus, the Code Case requirement is met.
Note that the through-wall flaw evaluations and the pressure blowout evaluation are separate analyses.
6.0 CONCLUSION
S 1'011 Calhoun Station has identified a pinhole leak in a 20-inch elbow in the raw water system. Allowable through-wall naw lengths have been calculated in accordance with an upcoming revision of ASME Code Case N-513-3 (designated N-513-4) for the elbow identified with node point CI5. N-513-4 has been approved by ASME and is pending publication. It is recognized in ASME committee that the technical approach is very conservative. Simple treatment of piping component naw evaluation using hand calculations was an important objective in the development of the approach recognizing the trade-off being conservative results. N-513-4 has not been generically reviewed by the NRC.
The allowable through-wall flaw in the axial direction is 4 inches. The allowable through-wall flaw in the circumferential direction is 10 inches. These flaw lengths are for a 0.225 inch sUlTounding waH thickness.
Table 5 shows the requirements to resist pressure blowout.
The observed pinhole leak naw is easily bounded by the results of the analysis; thus, the acceptance criteria of Code Case N-513-4 are met. The system should be considered operable but degraded.
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7.0 REFERENCES
I. ASME Code Case N-513-3, "Evaluation Critelia for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section Xl, Division 1," Cases of ASME Boiler and Pressure Vessel Code, January 26, 2009.
- 2. Regulatory Guide 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," Revision 16, Nuclear Regulatory Commission, October, 2010.
- 3. ASME Boiler and Pressure Vessel Code,Section XI, Appendix C, 2004 Edition.
- 4. ASME Boiler and Pressure Vessel Code,Section III, 2004 Edition.
- 5. Y. Takahashi, "Evaluation of Leak-Before-Break Assessment Methodology for Pipes With a Circumferential Through-Wall Crack. Part I: Stress Intensity Factor and Limit Load Solutions,"
Intemational Joumal of Pressure Vessels and Piping, 79, 2002, pp. 385-392, SI File No.
0801508.204.
- 6. USAS B31. 7 "Nuclear Power Piping," 1968 Draft Edition.
- 7. OPPD Design Input Transmittal NED-14-108, Revision 1, "Design lnfonnation Transmittal for Evaluation of the Raw Water Through-wall Leak (CR 2014-10078)," SI File No 1401013.201.
- 8. Pipe Fracture Encyclopedia, US Nuclear Regulatory Commission, Volume 1, 1997.
- 9. Moore, S.E., and Rodabaugh, E.C., "Background for Changes in the 1981 Edition of the ASME Nuclear Power Plant Components Code for Controlling Primary Loads in Piping Systems," Journal of Pressure Vessel Technology, Volume 104, pp. 351 - 361, November 1982.
File No.: 1401013.301 Revision: 0 Page 9 of 12 F0306*()) R)
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Noles:
Table 1: Applied Moment Loading for Bounding Moments (7]
[in-Ibs]
[in-Ibs]
lin-Ibs]
lin-Ibs]
22,320 38,647 22,812 36,937 I. Square Root Sum of the Squares (SRSS) is used to calculate moments from Reference [7].
- 2. Moments are from the bounding location on the elbow, \\vhich is at node 113.
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Table 2: J1c Values for AI06 Gr. B Carbon Steel from NRC's Pipe Fracture Database 18]
File No.: 1401013.301 Revision: 0 A106 Grade B Database Reference 2
2 16 16 16 16 22 22 22 22 22 22 22 23 23 23 23 24 24 24 25 25 25 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 Temperature ("G) 24 24 25 25 25 25 24 20 20 23 20 20 20 52 23 23 23 23 23 57 23 23 57 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 Temperature (OF)
JIG (kJ/m')
75 97 75 336 77 81 77 418 77 270 77 193 75 224 68 112 68 117 73 214 68 167 68 223 68 108 126 116 73 103 73 105 73 93 73 76 73 82 135 51 73 77 73 70 135 62 68 235 68 219 68 255 68 281 68 281 68 335 68 421 68 385 68 175 68 172 68 178 68 214 68 275 68 133 68 140 68 174 68 111 68 190 68 71 68 110 68 104 68 104 68 97 68 89 68 88 68 267 JIG (Ib-in/in' )
KIG (ksi-in )
552 133 1919 249 464 122 2386 277 1542 223 1104 189 1278 203 641 144 668 147 1223 199 954 175 1271 202 617 141 663 146 590 138 600 139 528 131 431 118 4!2!!
123 293 97 439 119 400 114 356 107 1342 208 1251 201 1456 217 1605 228 1605 228 1913 248 2404 279 2198 266 999 180 982 178 1016 181 1222 199 1570 225 759 157 799 161 994 179 634 143 1085 187 405 114 628 142 594 138 594 138 554 134 508 128 502 127 1525 222 Page 11 of 12 F0306-01 R I
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Table 3: Axial and Circumferential Structural Factors (3)
Service Level Membrane Stress, SPm Bending Stress, S Fb File No.: 1401013.301 Revision: 0 A
2.7 2.3 B
2.4 2.0 C
1.8 1.6 D
1.3 1.4 Table 4: Load Combinations for Cit-cumferential Flaw Analyses d Combination Service Level P+OW+TH A
W+TH+OBE B
DW+TH+SSE C/O Table 5: Pressure Blowout Check dadj [in]
tc,a\\'g (in) 0.25 0.01 0.75 0.02 1.25 0.03 1.75 0.04 2.25 0.05 2.75 0.06 3.25 0.07 3.75 0.08 4.25 0.09 4.75 0.10 5.25 0.11
/Uv,()
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Appendix A CODE CASE N-S13-4 PROCEDURES FOR ELBOW FLAW EVALUA nON File No.: 1401013.301 Revision: 0 Page A-I of A-3 F0306-01RI
Siruciuralinlegrity Associates, Inc....
File No.: 1401013.30)
Revision: 0 3.3 Through-wall Fl'H' ~ in Elhow~ and Benr Pipe Thn)\\l~I; -'\\'Hll tbw" ill
- Ib() \\\\' ~ nue! be]}t pipt' lIlay be c,'nluHkd usin¥ Iho'.oil,)i:e1r pipe plOct'rlures giveu ill.< 1
(,r 3.2(d) J.'w\\*id ~,.1 th~ slre.,<t's tb ed in tht "valuatioll nrt' adjusred as de,,:nbed [>",)(1\\\\' iCo :1.:c,)\\Ul! for The geollierr:;
differellce"... \\ Ii<'llwr", il!trho(!; Illay be nsed to ca!o::lIlaie the.streS$e.~,us t'.d in e ~;:llll\\ui(on. _ -- __ -
The hoop.In:',.
Co, _ for elbow rllld helll pipe el'Riuatil>1I.hall he:
where RoC',;
= d bol\\' 01 o,"1lf pIpe bend radius
¢
= c irc\\tlll!~'r"'nrial.Hl~1e defined ill Figure -
h
= ti<:' :\\ ihihl~ cil.u-*ll"leri,ric.
- \\fb
-= H,:;.ulrarll pi illl