ML20213C976
| ML20213C976 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 10/17/1986 |
| From: | Cofie N, Froehlich C, Yoshida D NUTECH ENGINEERS, INC. |
| To: | |
| Shared Package | |
| ML20213C932 | List: |
| References | |
| XCP-40-101-R, XCP-40-101-R00, NUDOCS 8611100377 | |
| Download: ML20213C976 (15) | |
Text
NUTECH CONTROLLED COPY XCP-40-101 Revision 0 October 1986 CPLO40.0101 TECHNICAL JUSTIFICATION FOR CONTINUED OPERATION OF BRUNSWICK UNIT 1 WITH THE SUMMER 1985 WELD OVERLAYS Prepared for:
Carolina Power-and Light Company Prepared by:
NUTECH Engineers San Jose, California l Prepared by: Reviewed and Approved by:
N. G. Cofie C. H. Froehlich, P.E.
Project Engineer Engineering Manager r
]
! Issued by:
Y Date: OGS W D. K. Yodida, P.E.
Project Manager mm sh 8611100377 861031 I IW LU PDR ADOCK 05000352 *
- G PDR
REVISION CONTROL SHEET TITLE: Technical Justification DOCUhlENT FILE NUMBER: CPLO40.0101 for Continued Operation of Brunswick Unit 1 with the Summer 1985 Weld overlays N. G. Cofie/ Principal Consultant MdC.
N AME / TITLE INITIALS C. H. Froehlich, P.E./ Staff Encineer NAME/ TITLE INITIALS NAME / TITLE INITIALS NAME / TITLE INITIALS AFFECTED DOC PREPARED ACCURACY CRITERIA REMARKS PAGEls) REV SY I DATE CHECK 8Y / OATE CHECK SY / DATE i-iv 0 #4C '*/'7/96 CNf lo/s7/g4 OW8 to/#1/t6 Initial Issue l'** *
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TABLE OF CONTENTS Page LIST OF TABLES iv
1.0 BACKGROUND
1 2.0 COMPLIANCE WITH REGULATORY REQUIREMENTS 1 3.0 TECHNICAL ISSUES 3 3.1 Weld Metal IGSCC Resistance 3 3.2 Residual Stress Benefits 4 3.3 Long-Term Performance of Weld Overlay Repairs 5 3.4 Weld Metal Toughness 5 3.5 Non-Destructive Examination 6 4.0
SUMMARY
AND CONCLUSION 6
5.0 REFERENCES
10
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LIST OF TABLES Number Title Page 1 . Brunswick Unit 1 Flaw Dispo~sition/ Weld 8 Overlay Design Data 2 Thickness of Standard Weld Overlays for 9 1985 Circumferential Flawad Welds e
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XCP-40-101 Revision 0 iv gg
l.0 BACKGROUND In response to industry-wide concerns with intergranular stress corrosion cracking (IGSCC) in BWR stainless steel piping, Brunswick Unit I has been subjected to extensive inservice inspection since Spring 1983. As a result of these inspections, thirty-two (32) welds in the recircu-lation system were found to have indications that re-quired weld overlay repair. These indications are.in Type 304 stainless steel material. A summary of flaw characteristics and designed and as-built dimensions of the weld overlays for all the affected welds is shown in Table 1. This table also identifies the outage during which the repair was made.
During the upcoming Unit 1 outage (Winter 1987 RFS),
Carolina Power and Light Company (CP&L) plans to upgrade the weld overlay repairs from Spring 1983 through Fall 1984 to " standard" weld overlays. CP&L plans to operate Brunswick Unit 1 for one additional 18 month fuel cycle without upgrading and reinspecting twenty-one (21) of the twenty-two (22) Summer 1985 weld overlays which have operated for only one fuel cycle. This report provides technical justification for continued operation of Brunswick Unit 1 for an additional 18 month fuel cycle without up' grade or inspection of twenty-one (21) weld overlays applied during the Summer 1985.
2.0 COMPLIANCE WITH REGULATORY REQUIREMENTS The Summer 1985 weld overlays were designed to the requirements of ASME Code,Section XI (Referen~a 1) and Generic Letter 84-11 (Reference 2). The weld overlays were designed assuming flaws were through-wall for their measured length. Welds containing axial flaws required XCP-40-101 1 Revision 0 4
nutgch
only leakage barriers. These leakage barriers consisted of two layers of weld overlay material not including the first layer.. Circumferential flaws in the 12-inch pipes were overlay repaired in accordance with Reference 1.
The overlay designs restored the safety margin required in Section IWB-3640 of the ASME Code (Reference 1). The welding process used during the repair of these welds is the gas tungsten arc welding process (GTAW) with Type 308L filler material.
Draft NUREG-0313, Revision 2 (Reference 3) provides the NRC's staff position regarding design and application of weld overlays as a repair for IGSCC. Three types of weld overlay designs,are* identified in Reference 3, standard, designed and limited service. Standard weld overlays are designed assuming that the original pipe was cracked completely through the wall over its entire circumference. Since this was not the-design basis for the overlays under consideration, these overlays can be classified as designed or limited service. Weldments with a total length of circumferential cracking less than 10% of the circumference, with no more than four axial cracks, are considered appropriate for repair by designed overlay.
In order to account for possible low toughness of the original butt weld as required by Reference 3, the Summer 1985 weld overlays for circumferentially cracked pipes were evaluated per Table IWB-3641-1 (Reference 1) assuming a 100% through-original pipe wall by 360* flaw (standard weld overlay repair design criteria). The design thicknesses associated with these evaluations are shown in Table 2. As can be seen from this table, the design thickness for the full structural weld overlays for these welds did not change significantly from that XCP-40-101 2 Revision 0 nutp_qh 1
l of the designed overlays. This is due to the relatively -
small stress ratio ~s at these welds. These new design thicknesses are much smaller than the as-built thicknesses.
In addition, the overlays with small axial flaws under -
consideration have a minimum of two layers of weld metal after the surface has passed penetrant inspection (PT) -
as required by Reference 3. No credit was taken for this first layer even though it contained a minimum of 7.5 FN after passing PT. Therefore, the Summer 1985 weld overlay repaired welds at Brunswick Unit 1 meet the design criteria set forth in the draft NUREG (Reference 3).
1 In accordance with Generic Letter 84-11, inspection of an overlay repaired weld is required only when the weld has a circumferential crack longer than 10% of circum-ference. By this criterion, Weld No. 12-BR-J3 should be reinspected during the upcoming Winter 1987 outage. It is planned that this weld will be inspected.
3.0 TECHNICAL ISSUES ,
The following technical issues are discussed to further support the basis for continued operation of Brunswick Unit I without reinspection of 21 of the 22 existing weld overlay repairs performed'in Summer 1985.
3.1 Weld Metal IGSCC Resistance
- Various studies have shown that if the microduplex structure of the Type 308L weld metal used for the weld overlay has a low carbon content and a high ferrite content, it will consistently arrest propagating IGSC XCP-40-101 3 Revision 0 nutp_qJJ
cracks even under severe loading and environmental conditions (References 4 and 5). The weld overlay
. material specification used for the Summer 1985 welds
^
required that the undiluted alloy contain a maximum of 0.02 wt% carbon and a minimum ferrite content of 8 FN. This carbon and ferrite combination provides assur-ance of high resistance to IGSCC. Because of possible weld metal / base metal dilution'during application of the initial first layer of weld overlay material, it is important to assure that adequate ferrite levels are maintained in this initial layer. Ferrite measurements taken on the first layer of the Summer 1985 weld over-lays showed ferrite levels of at least 7.5 FN.
3.2 Residual Stress Benefits Analytical studies performed by NUTECH (Reference 6) have shown that thermo-plastic behavior and shrinkages associated with weld overlay repairs produce beneficial compressive residual stresses through a major portion of the~ original pipe inner wall thereby arresting the growth of pre-existing flaws. These analytical predic-tions have been confirmed by experimental studies performed on laboratory specimens as well as pipes removed from plants (References 6, 7, 8 and 9). These studies have provided adequate assurance that in addi-l' tion to being resistant to IGSC crack propagation, weld overlays also arrest the growth of IGSC cracks in the original pipe. The design and fabrication of the weld
- - overlays at Brunswick Unit 1 are consistent with
- accepted industry methodology and guidelines. There-fore, the presence of beneficial residual stresses is assured, which should arrest the growth of pre-existing cracks.
4 XCP-40-101 4 Revision 0 r1 Lite.I.1
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. 2 3.3 Long-Term Pert'orma ce' of Weld Overlay Repairs i
Several programs are in progress to evaluate the long-term service performance of weld overlay repairs. These ,
programs consist of accelerated IGSCC and structural 3 integrity tests. In one of the accelerated IGSCC tests initiated under EPRI sponsorship (References 4 5 and 10), flawed 4-inch and 12-inch stainless steel pipe welds were exposed to environments more severe than BWR service conditions. The effectiveness of the weld overlay in.the arrest of a through-wall flaw was demonstrated after.6000 hours0.0694 days <br />1.667 hours <br />0.00992 weeks <br />0.00228 months <br /> of accelerated testing. .
After accounting for test acceleration factors, a minimum plant service life of at least 7. fuel cycles (about11 hears) for overlay repaired pipe was projected.'
g Ongoing structural integrity tests being conducted at
! Battelle Columbus Laboratories have shown the ability of weld overlay to provide very effective repairs for IGSC i cracks. In tests.on 6-inch diameter, schedule 120 weld overlayed pipes with circumferential flaws (Reference 11), it was discovered that under bending loads in a BWR environment (550 0P and 1100* psi), the' pipe was perman-ently deformed on either side of the veld overlay while the integrity of the weld overlay was maintained. These preliminary results give support to the long-term effec-tiveness of weld overlay repair joints to withstand loads greater than those' associated with BWR operating 3 4 f conditions.
s T 3.4 Weld Metal Touchness
\
The overlay repairs for the Summer 1985 weld overleys were performed using a gas-shielded (GTAW) welding XCP-40-101 5 Revision 0 nut.ec..h.
_ w - - - -
s process, which has demonstrated toughness of at least
. equal to.that of the original pipe material. In order to account for possible low toughness of the original butt weld, the weld ove~rlays for circumferential flaws were evaluated assuming the flaws to be through-original pipe wall by 360* (standard weld overlays) which
, ~d comp'ies l with Reference 3. The as-built thicknesses were more than adequate to meet the standard weld overlay requirements, thereby eliminating the original
,, butt weld. low fracture toughness concerns.
3.5 Non-Destructive Examination
'\ .
During the Summer 1985 outage, the overlays were in-1 spected using.non-destructive examination. A liquid penetrant examination was performed on the first weld overlay layer and the completed weld overlay.
Volumetric examination was also performed on the completed weld overlay per ASME Section XI (Reference 1) and existing circumferential pipe weld by the ultrasonic examination technique in accordance with the EPRI interim report in Reference 8.
I; I5 4.0
SUMMARY
AND CONCLUSION t 4 I .
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J The Summer 1985 weld overlays were designed to meet the
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regulatory requirements in References l-and 2. Further-l more, they also meet proposed regulations set forth in Reference 3.
i The weld' metal and welding process used during the fabrication of the overlays assures adequate ferrite levels to prevent IGSC crack growth into the weld overlay.- Favorable residual stresses from the overlay is on nutp_qh
~
application arrest any further crack growth in the original pipe.
Because of the welding process used during weld overlay fabrication, the fracture toughness of the weld overlay material is at least equal to that of the base metal.
EPRI sponsored studies have shown a projected service life of at least seven fuel cycles for overlaid repaired welds. In addition, non-destructive examination has advanced to the stage that volumetric examination of the overla~y and part of'the original pipe wall can be performed to assure that pre-existing cracks are not propagating.
t In conclusion, the twenty-one Summer 1985 weld overlays are effective IGSCC repairs which have restored the original design basis of the piping system. .These repairs meet the existing regulatory requirements.
Based on the short service of the 1985 weld overlays (one fuel cycle) and on the discussions presented in this report, operation of Brunswick Unit 1 for an additional 18 month fuel cycle.without reinspection of-these twenty-one Summer 1985 weld overlays'is justified.
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XCP-40-101 7 Revision 0 nutggh l
Table 1 BRUNSWICK UNIT 1 FLAW DISPOSITION / WELD OVERLAY DESIGN DATA Description of Design As-Built Wald No. Outage Maximum Indication t,;n(in.) Le ng th ( in . ) t,gn(in.) Length (19.)
17-AR-E2 Axial 1004 0.35 5.00 0.45 5.84 12-BR-H4 Spring 83 Axial 100% 0.20 3.00 0.40 .3.25 28-A-15LU-0 Axial 114 x 0.5* 0.30 6.00 0.47 6.03 28-A-14 Fall 83 Circa 20% x 23' O.42 5.00 0.46 5.18 28-8-8 Cires 30% x 8" 0.42 5.00 0.46 5.33 1-RR-4A10-A Circa 100% x 2.0** 0.125 >1.0 0.409 1.73 12-AR-A4A- Circa 19% x 1.6" 0.19 >1.5 0.351 2.51 12-AR-82A Fall 84 Cice: 204 x 2' O.19 3.0 0.205 3.45 12-AR-84A Circ; 45% x l' O.19 >1.5 0.262 2.20 12-8R-F4A Circa 23% x 0.5" 0.19 >1.5 0.290 2.62 Circa 9% x 4.0*
12-AR-A2 Axial 0.4* 2 layers 3.0 0.303 3.45 12-AR-A3 Cire '354 x 1.75* 0.25 3.0 0.419 3.19 12-AR-83 Axial 0.5" 2 layers 3.0 0.398 3.43 12-AR-C2 Circa 50% x 0.6* 0.26 3.0 0.435 3.64 12-AR-C3 Axial: 0.4" 2 layers 3.0 0.435 3.04 12-AR-D2 Axial 0.6" 2 layers 3.0 0.296 3.17 12-AR-03 Axial 0.38" 2 layers 3.0 0.317 3.08 12-AR-D4 Circa 35% x 2.0" 0.22 2.12 0.404- 2.22 12-AR-E3 Axial 0.4' 2 layers 3.0 0.373 3.06 12-BR-F2 Summer 85 Axial: 0.75" 2 layers 3.0 0.328 3.45 12-BR-G2 circa 254 x 1.12* 0.22 3.0 0.418 3.29 12-BR-G3 Axial 0.8* 2 layers 3.0 0.468 3.05 12-BR-G4 Axial 0.5" 2 layers 2.10 0.205 2.92 12-BR-H2 Axial 0.4" 2 layers 3.0 0.280 3.48 12-BR-H3 Axial: 0.5* 2 layers 3.0 0.465 3.18 12-BR-J2 Axials 0.6* 2 layers 3.0 0.290 3.10 12-BR-J3 Circs 60% x 4* 0.23 3.0 0.447 3.12 12-BR-K2 Axial 0.7"* 2 layers 3.0 0.410 3.11 12-BR-K3 Axial: 0.75* 2 layers 3.0 0.320 3.25 12-BR-K4 Arial, 0.4" 2 layers 2.05 0.213 2.42 4
28-A4 . Axial, 0.6" 2 layers 3.2 0.140 3.52 28-84 Axial, 25% x 0.6" 2 layers 3.0 0.163 3.72 Assumed Value XCP-40-101 8
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. l Table 2 ,
THICKNESSES OF STANDARD WELD OVERLAYS FOR SUMMER 1985-CIRCUMFERENTIAL FLAWED WELDS (1) (2) (3) (4)
Weld t p Stress t fs t
ab No. Ratio 12-AR-A3 0.75" 0.376 0.270" 0'.419" 12-AR-C2 0.77" 0.361 0.270" 0.435" 12-AR-D4 0.66" 0.400 0.250" 0.404" 12-BR-G2 0.65" 0.332 0.230" 0.418" s
12-BR-J3 0.67" 0.333 0.240" 0.447" (1) t p
= original' pipe wall thickness
-(2) Stress.tatio is based on original pipe thickness plus design overlay thickness (3) tfs = design thickness for standard weld overlay (4.) tab = as-built thickness 4
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XCP-40-101 9 Revision 0 i
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5.0 REFERENCES
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- 1) ASME Boiler and Pressure Vessel Code,Section XI, 1983 Edition with Addenda through Winter 1984, Paragraph IWB-3640, " Acceptance Criteria for s
Austenitic Stainless Steel ~ Piping."
- 2) NRC Generic Letter 84-11 " Inspection.of BWR Stainless Steel Piping," April 19, 1984, including Attachments 1 and 2.
- 3) Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping," NUREG-0313, Revision 2 (Draft),
May'1986.
- 4) " Assessment of Remedies for Degraded Piping - First Semi-annual Progress Report," November 1983 -July 1984, Prepared by General Electric Co. , Document No. NEDC-30712-1, September 1984.
- 5) " Assessment of Remedies for Degraded Piping -
Second Semiannual Progress Report," August 1984 -
August 1985, Prepared by General Electric Co.,
Document No. NEDC-30712-2, August 1985.
- 6) Kulat, S. D., Pitcairn, D. R. and Sobon, L. J', .
" Experimental Verification of Analytically Determined. Weld Overlay Residual Stress Distribution," Transactions, 8th International Conference on Structural Mechanics in Reactor Technology, Volume D, Paper No. D2/1, Brussels,
<, Belgium, August 19 - 23, 1985.
.; 7) Shack, W. J., " Measured Residual Stresses in.
Overlay Pipe Weldments Removed from Service,"
i- Transactions, 8th International Conference on l Structural Mechanics in Reactor Technology, Volume D, Paper No. D2/5', Brussels, Belgium, August 19 -
23, 1985.
- 9) " Continued Service Justification for Weld Overlay
~
Repairs," BWR Owner's Group'Ad Hoc Committee, May 23, 1984.
XCP-40-101 10 Revision 0 @f
- 10) Gilman, J. D., " Overview of Weld Overlay for Repair of Corrosion Cracking in Stainless Steel Piping Welds." Proceedin'gs, Conference on Maintenance Welding in Nuclear Power Plants /III, American ~
Welding Society, Nov. 6, 1985, Knoxville, Tennessee.
- 11) " Degraded Piping Program, Phase 2 - Semi-annual Report, April 1985 - Sept. 1985," NUREG/CR-4082, Vol. 3, Prepared by Battelle Columbus Laboratories,
, September 1985.
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