ML16351A248

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Code Case N-513-3 Evaluation of High Pressure Service Water Piping Thinning
ML16351A248
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Site: Cooper Entergy icon.png
Issue date: 12/14/2016
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Structural Integrity Associates
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Office of Nuclear Reactor Regulation
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Enclosure 7 .a RR5-02, Page 5 of 22 Attachment 8.1 ER2016-053, Page 1 of 17 lJ Structural Integrity Associates, Inc.* File No.: 1601004.301 Project No.: 1601004 CALCULATION PACKAGE Quality Program Type: 0 Nuclear D Commercial PROJECT NAME:

Cooper High Pressure RHRSW Thinning Evaluation CONTRACT NO.:

4200002842 CLIENT: PLANT:

Nebraska Public Power District Cooper Nuclear Station CALCULATION TITLE:

Code Case N-513-3 Evaluation of High Pressure Service Water Piping Thinning Project Manager Preparer(s) &

Document Affected Revision Description Approval Checker(s)

Revision Pages Signature & Date Signatures & Date 0 1 - 12 Initial Issue

~ ~

A-1 -A-5 Eric J. Houston Eric J. Houston EJH 12/12/16 EJH 12/12/16

~

Chris S. Lohse CSL 12/12/16 Page 1of12 F0306-0IR2

Enclosure 7.a Attachment 8.1 e

RR5-02, Page 6 of 22 ER2016-053, Page 2of17 Structural Integrity Associates, Inc.

Table of Contents 1.0 OBJECTIVE .................................................................................................................. 3 2.0 METHODOLOGY ........................................................................................................ 3 3.0 DESIGN INPUTS .......................................................................................................... 4 4.0 ASSUMPTIONS ............................................................................................................ 5 5.0 CALCULATIONS ......................................................................................................... 5 5.1 Applied Loads .................................................................................................... 6 5.1.1 Hoop Stress ........................................................................................................ 6 5.1.2 Axial Stresses ................................................. :................................................... 6 5.2 Stress Intensity Factor Calculations ................................................................... 7 5.3 -Critical Fracture Toughness Determination ....................................................... 8 6.0 RESULTS OF ANALYSIS ........................................................................................... 8

7.0 CONCLUSION

S ........................................................................................................... 9

8.0 REFERENCES

............................................................................................................ 10 APPENDIX A SIPE FILES ......................................... :........................................................ A-1 List of Tables Table 1: Applied Moment Loads ................................................................... ......................... 11 Table 2: Load Combinations for Circumferential Flaw Analyses .......................................... 11 Table 3: Axial and Circumferential Structural Factors ........................................................... 11 Table 4: Allowable Through-Wall Flaw Lengths (based on tadj = 0.300") ............................. l l List of Figures Figure l. Transition Temperature Master Curve .................................................................... 12 File No.: 1601004.301 Page 2of12 Revision: 0 F0306-0IR2

Enclosure 7.a RR5-02, Page 7 of 22 Attachment 8.1 ER2016-053, Page 3of17 SJ Structural Integrity Associates, Inc.

1.0 OBJECTIVE Multiple thinned locations were recently discovered in the Residual Heat Removal Service Water (RHRSW) system at Cooper Nuclear Station. The thinned locations are near TE 390B in drawing 2851-3 (work order 5121085) [1, 2] and downstream of SW H92 in drawing 2851-7 [3, 4]. The 18-inch carbon steel line is safety related Class 3 piping. The thinned locations have been removed from service and ultrasonic testing has been conducted [5, 6]. The objective of this calculation is to demonstrate structural stability in accordance with ASME Code,Section XI, Code Case N-513-3 [7] to support a Relief Request.

2.0 METHODOLOGY The flaw evaluation is based on the criteria prescribed in ASME Code Case N-513-3. This Code Case provides rules for determining the allowable flaw size, including through-wall flaws, for moderate energy Class 2 or Class 3 piping. N-513-3 is conditionally accepted by the Nuclear Regulatory Commission (NRC) in the most recent Regulatory Guide 1.147 [8]. Because the scope of N-513-3 is limited to moderate energy systems, and the subject piping is considered high energy (maximum operating pressure greater than 275 psig), this calculation provides the technical justification for an NRC submittal seeking relief from the moderate energy limitation. All other provisions or requirements in N-513-3 are to be satisfied.

The Code Case 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 observed thinning is conservatively characterized as through-wall thinning for the purposes of structural evaluation. The conservatively characterized non-planar, through-wall flaw evaluation herein is conducted using the Structural Integrity Pipe Evaluation (SIPE) 3.1 software [9]. SIPE is a web-based evaluation tool that performs the flaw evaluation procedure described in Code Case N-513-3.

SIPE 3.1 was developed under the SI Nuclear Quality Assurance Program and is approved for use on safety related systems.

Allowable through-wall flaw sizes in the axial and circumferential direction are calculated and are shown to bound the observed flaws. The measured wall thickness values in the pipe section containing the flaws are bounded by a thinner analyzed thickness (i.e., the wall thickness surrounding the thinned locations is assumed to be uniformly thinned to the analyzed thickness, tactj). This conservatively ignores the load carrying capacity of the pipe wall that is greater than tact}

Code Case N-513-3 evaluation criteria rely on the methods given in ASME Section XI, Appendix C

[IO]. Linear Elastic Fracture Mechanics (LEFM) criteria are conservatively employed as described in Article C-7000 (N-513-3 3.2(d) allows the use of N-513-3 3.1 (c)). Equations for through-wall stress intensity factor parameters Fm, Fb and Fare given in Appendix I of the Code Case. Allowable flaw lengths are determined by SIPE iteratively through comparison of the calculated stress intensity factors to a critical fracture toughness defined in C-7200 of Section XI, Appendix C. The critical fracture toughness is based on material toughness given in Article C-8000 of Section XI, Appendix C.

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3.0 DESIGN INPUTS The following design inputs are used in the flaw evaluation:

1. Nominal pipe outside diameter= 18 inches [11, sheet 9; 12, sheet 10]
2. Nominal pipe thickness= 0.437 inch [11, sheet 9; 12, sheet 10]
3. Code of Construction= USAS Power Piping, B3 l.1 1967 Edition [11, PDF p. 9, Section E; 12, PDF p. 10, Section E]
4. Pipe material= A 106 Grade B [11, sheet 9; 12, sheet 1O]
5. Code minimum tensile strength, Su= 60 ksi [13, Table A-2]
6. Elastic modulus at hot condition, E = 27,880 ksi [12, sheet 1O]
7. Design pressure= 490 psig [11, sheet 9; 12, sheet 1O]
8. Design temperature= 145°F [11, sheet 9; 12, sheet 10]

The allowable stress is taken from a newer edition of B3 I .1, as justified by [14], and is 17.1 ksi [15, Table A-1].

The moment loadings applied to the piping are obtained from the stress reports and are shown in Table

1. Nodes 130, 135, 140, and 1051 are applicable to the 2851-3 inspection location [16] and Nodes 640 to 645 are applicable to the 2851-7 inspection location [17]. Node 1051 is bounding for all locations and is used in the analysis. The load combinations for each service level are shown in Table 2 for the circumferential flaw analyses.

The average reported wall thickness in the straight section of piping (rows 13 through 18) for the 2851-3 inspection report [2] is 0.41 inch. The average reported wall thickness for the 2851-7 inspection report

[4] is 0.35 inch. The evaluated wall thickness, tactj, is taken at a smaller thickness of0.300 inch. This conservatively assumes that the entire wall thickness surrounding the flaws is uniformly thinned to the valued of tact} A corrosion allowance is not considered in the analysis because the flaws have been removed from service. The location with the largest extent of thinning in either inspection report is 1.5 inches at the 16 location in the 2851-7 inspection report. The report does not indicate if this dimension is the axial or circumferential extent. The conservatively characterized flaw evaluated herein assumes a through-wall flaw of 1.5 inches in both the axial and circumferential extent. This easily bounds all of the observed part-wall flaws in the two inspection reports. Assuming a through-wall flaw means it will be treated as a planar defect rather than wall thinning, which is conservative.

Ductile crack initiation has been shown to occur at significantly lower temperatures than the 200°F limit for upper shelf specified in the 2007 Edition of Section XI [10, C-8321 and C-8322].

Reference [ 18] demonstrates that for ferritic piping commonly used in the nuclear industry, the upper shelf transition temperature is a function of pipe wall thickness (due to constraint effects) and crack direction (through-wall propagation vs. axial or circumferential propagation of a through-wall flaw),

and that ductile crack initiation and growth can occur at temperatures much lower than 32°F.

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Several materials were evaluated in Reference [ 18], including A 106 Grade B. Figure 1 shows the transition temperature for several crack geometries and material thicknesses for A106 Grade 8.

Figure 1 has been incorporated into Appendix C in the 2013 Edition as Table C-8321-2 [19].

The upper shelf transition temperature for pipe with a wall thickness of 0.300 inch is interpolated from Table C-8321-2 [19] as 23°F for a through-wall flaw. Therefore, the lower bound fracture toughness, lie, used in the evaluation is based on Section XI, Appendix C, Table C-8321-1 and Table C-8322-1 [ l O] for ferritic material at the upper shelf temperature. A value of 300 in-Jb/in2 is used in the analysis for both circumferential and axial flaws.

4.0 ASSUMPTIONS The following assumptions are used in this calculation:

l. Poisson's ratio is assumed to be 0.3, which is a typical value for carbon steel.
2. A value of 35 ksi is assumed for the material yield strength and is a required input into the SIPE software. However, yield strength is not utilized in the Linear Elastic Fracture Mechanics (LEFM) evaluation. Therefore, this assumption has no impact on the results.

5.0 CALCULATIONS An evaluation of the 831.l stress limits was conducted using inputs discussed in Section 3.0. The minimum required uniform wall thickness, tmin, is based on the pressure hoop stress and is 0.255 inch (the axial stress based minimum required wall thickness is less).

Code Case N-513-3 requires that the wall thickness between adjacent flaws exceed tmin for a distance of the greater of:

2.5~Rfnom OR 2Lm.avg (1) where:

R mean pipe radius, in tnom nominal pipe wall thickness, in Lm,avg = average extent of flaws below tmin for adjacent thinned areas, in If the requirements of Equation l are not satisfied, the flaws must be evaluated as a single flaw. The required separation distance is 4.9 inches for 2.5~Rtnom . Conservatively taking Lm,avg as the maximum extent of thinning (l.5 inches per Section 3.0), the separation requirement is 3 inches. Therefore, 4.9 inches is the required separation distance.

The two locations below tmin in the 2851-3 inspection report [2] are at E 13 and E 18. The grid size is 6 inches and these locations are separated by more than one grid. Therefore, the E 13 and E 18 locations meet the separation requirements. There are four locations (H2, 13, I4, and 16) below tmin in the 2851-7 File No.: 1601004.301 Page 5of12 Revision: 0 F0306-0IR2

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ER2016-053, Page 6of17 inspection report [4]. The grid size is also 6 inches, meaning locations 14 and 16 meet the separation requirements. The location ofH2 is described as "8.25" from clamp, 50.0" from TDC clockwise with flow" while I3 is described as "13.5" from clamp, 58" from TDC clockwise with flow." The distance from clamp measurement is the relative axial position while the measurement from TDC is the relative circumferential position. Taking only the circumferential measurement, H2 and I3 are separated by 8 inches. Therefore, H2 and 13 meet the separation requirements. I3 and 14 are in adjacent grid locations.

13 is listed as 13 .5" from the clamp while 14 is listed as 21.5" from the clamp. This puts 8 inches between the locations, so they also meet the separation requirements.

All of the flaws are separated by more than 4.9 inches and may be evaluated as independent flaws.

5.1 Applied Loads Axial and circumferential (i.e., hoop) stresses are calculated by SIPE from pressure and the moment loads in Table I for Node 135. The evaluated wall thickness, tadj = 0.300 inch, is used to determine the section properties.

5.1.1 HoopStress For the allowable axial flaw length, the hoop stress, O"h, due to internal pressure is calculated by SIPE as

[7, Equation 2]:

(2) where:

p internal pressure, psig Do outside diameter, in tadj evaluated wall thickness, in 5.1.2 Axial Stresses For the allowable circumferential flaw length, the axial stress due to pressure, deadweight and seismic loading is calculated by SIPE. The axial membrane stress due to pressure, crm, is taken as half of the hoop stress:

(3)

Axial bending stress, crb, due to deadweight and seismic moments is calculated as:

ab =0.75iM (4) z File No.: 1601004.301 Page 6of12 Revision: 0 F0306-0IIU

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(5) where:

stress intensification factor, unitless 1.0 for straight pipe M applied bending moment, in-lbs Z section modulus, in3 Di inside diameter (based on Do and tadj), in Note that the quantity 0.75i shall not be less than 1.0.

Axial bending stress due to thermal expansion, cre, is calculated as:

M a.=-z (6) 5.2 Stress Intensity Factor Calculations For the allowable flaw lengths using the LEFM approach, the stress intensity factor, Kr, is calculated by SIPE using the equations in Article C-7000 as prescribed by N-513-3. The stress intensity factor for an axial flaw is:

(7)

(8) where:

SFm = structural factor for membrane stress (see Table 3)

F = stress intensity factor parameter for through-wall axial flaw under hoop stress (given in Appendix I ofN-513-3) a flaw depth (half flaw length for through-wall flaw per Appendix I ofN-513-3)

Q flaw shape parameter (unity per Appendix I of N-513-3)

Krr Kr from weld residual stresses at flaw location (taken as zero as all flaw locations are in base metal)

The stress intensity factor for a circumferential flaw is:

K, =Kim +Krb +K,, (9)

K,m =SF,,,Fmam J'i:i (10)

K,b = [SF;, ab+ a.] F;, J'i:i (11) where:

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Fm stress intensity factor parameter for through-wall circumferential flaw under membrane stress (given in Appendix I of N-513-3)

SFb structural factor for bending stress (see Table 3)

Fb stress intensity factor parameter for through-wall circumferential flaw under bending stress (given in Appendix I ofN-513-3)

Note that the stress intensity factor parameters are a function of flaw length.

Table 2 shows the specific load combinations considered herein for the allowable circumferential flaw calculations. Since the load combination for Service Level C and D are equivalent, the more limiting flaw length associated with the Service Level C structural factors are presented.

Only the hoop stress influences the allowable axial flaw length which is a function of pressure and primary bending stress.

5.3 Critical Fracture Toughness Determination The static fracture toughness for crack initiation under plane strain conditions, K1c, is calculated by SIPE using the equations in Article C-7000 as prescribed by N-513-3.

(12)

E'=~2 (13) l-v where:

J1c material toughness, in-lb/in2 E Elastic modulus, ksi v Poisson's ratio Based on the design input listed above, Kie is calculated as= 95.9 ksi-in° 5

  • The allowable flaw lengths are determined iteratively by increasing flaw length until the stress intensity factor is equal to the static fracture toughness. This iterative process is carried out internally by SIPE.

6.0 RESULTS OF ANALYSIS Table 4 shows the allowable axial and circumferential through-wall flaw lengths. The most limiting allowable flaw length is 2.2 inches in the axial direction and 3.9 inches in the circumferential direction.

The conservatively characterized through-wall flaw is 1.5 inches in the axial and circumferential directions. The allowable flaw size is larger than the conservatively characterized flaw, which satisfies the structural evaluation of Code Case N-513-3. The SIPE input and output files are shown in Appendix A.

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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 [7, Equation 9]. For an equivalent diameter, dactj, of l.5 inches, the required average thickness, tc,avg, is 0.09 inch. The inspection data in References [2, 4]

shows that the minimum measured thickness is 0.127 inch. Thus, this Code Case requirement is met.

7.0 CONCLUSION

S Multiple thinned locations were recently discovered in the Residual Heat Removal Service Water (RHRSW) system and have been removed from service. All flaws meet the N-513-3 separation requirements and are evaluated independently. The evaluation in accordance with ASME Code,Section XI, Code Case N-513-3 shows that the allowable through-wall flaw lengths bound the conservatively characterized flaws. Although Code Case N-513-3 is not applicable to systems with pressure exceeding 275 psig, the results of this calculation demonstrating structural integrity may be used as technical justification in a reliefrequest.

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8.0 REFERENCES

1. NPPD Drawing ONL16_W05121085_MrkDwg_2851-3.pdf, SI File No. 1601004.205.
2. GE Hitachi Ultrasonic Thickness Measurement Report No. SW-E-3-2851-3, 9/15/2016, SI File No. 1601004.203.
3. NPPD Drawing ONL16_W05120799_MrkDwg_2851-7.pdf, SI File No. 1601004.205.
4. GE Hitachi Ultrasonic Thickness Measurement Report No. SW-Z4-285 l-7, 9/13/2016, SI File No. 1601004.203.
5. NPPD Inspection Report No. UTM-2016-011, SI File No. 1601004.203.
6. NPPD Inspection Report No. UTM-2016-010, SI File No. 1601004.203.
7. ASME Boiler and Pressure Vessel Code, Code Case N-513-3, "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping,Section XI, Division 1," January 26, 2009.
8. Regulatory Guide 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division l ," Revision 17, U. S. Nuclear Regulatory Commission, August 2014.
9. SIPE, Structural Integrity Pipe Evaluation, Version 3.1, February 18, 2015.
10. ASME Boiler and Pressure Vessel Code,Section XI, 2007 Edition with Addenda through 2008.
11. NPPD Calculation No. NEDC 89-1318, Revision 4, "Review of EAS Calculation No. 150 P-SW-13," SI File No. 1601004.201.
12. NPPD Calculation No. NEDC 89-1316, Revision 3, "Review ofEAS Calculation No. 150 P-SW-15," SI File No. 1601004.201.
13. USAS Power Piping, B31.1.0 1967 Edition.
14. SI Report No. 1601004.401, Revision A DRAFT, "Technical Basis for Increased Allowable Design Stress."
15. ASME Code for Pressure Piping, B3 l, "Power Piping," B31.1-2004 with 2005 Addenda.
16. NPPD Calculation No. NEDC 89-1318, Revision 4, Nodal Drawing 2851-3, SI File No.

1601004.201.

17. NPPD Calculation No. NEDC 89-1316, Revision 3, Nodal Drawing 2851-7, SI File No.

1601004.201.

18. Wilkowski, G. M., Rudland, D., Walterman, R., "Predicting the Brittle-to-Ductile Fracture Initiation Transition Temperature for Surface-Cracked Pipe from Charpy Data," Pressure Vessel and Piping Division Conference, July 17-21, 2005, Denver, CO, PVP2005-71199.
19. ASME Boiler and Pressure Vessel Code,Section XI, 2013 Edition.

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ER2016-053, Page 11 of 17 Table 1: Applied Moment Loads Node SRSS Moment (in-lbs)

DW OBE SSE TH 640 29,655 90,836 162,177 7,463 645 86,786 96,812 168,502 6,382 130 1 14,989 95,982 162,404 2,871 135 1 16, 151 251,520 424,350 6,485 140 1 34,443 258,110 433,360 6,273 1051 1* 2 85,347 299,265 500, 190 6,627 Notes:

I. SAM Condition 2 is the bounding TH loading.

2. Node 1051 is the bounding nodal loads and is used in the evaluation.

Table 2: Load Combinations for Circumferential Flaw Analyses Load Combination Service Level P+DW+TH A P+DW+OBE+TH B P+DW+SSE+TH CID Table 3: Axial and Circumferential Structural Factors Service Level Membrane Stress, SFm Bending Stress, SFb A 2.7 2.3 B 2.4 2.0 c 1.8 1.6 D 1.3 1.4 Note: Structural Factors from [10, C-2621 and C-2622]

Table 4: Allowable Through-Wall Flaw Lengths (based on ta11j = 0.300")

Service Allowable Axial Flaw Allowable Circumferential Level Length (in) Flaw Length (in)

A 2.2 5.0 B 2.5 3.9 CID 3.4 4.3 File No.: 1601004.301 Page 11 of 12 Revision: 0 F0306-0!R2

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150

--...- TWC FPTT 0 100 Ductile initiation, stable ductile creek growth and dynamic duclile crack growth TWCFITT all*.750 I

alt=.500 i

I all* .375 1! alt* .250 50 alt=.187 E

GI alt*.156 I-c: -+- alt=.125 0

= 0 Ductile initiation,

'iii c: slable dudile crack I! growth , and brlUe I-u nstable crack

~ -50 propagation

I u

I!

u.

Brit tle lnillatbn an d britl le crack growth

-150 +-~~~~-'-~~~~+-~~~~-t-~~~~-t-~~~~...;-~~~~+-~~~~

0 10 20 30 40 50 60 70 Material Thickness, mm Figure 1. Transition Temperature Master Curve Note: Figure fro m Reference [ 18]

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