ML20080C290

Rev 2 to Flaw Evaluation & Repair Plan

ML20080C290
Person / Time
Site:	Quad Cities
Issue date:	01/31/1984
From:	Buchholz R, Gustin H NUTECH ENGINEERS, INC.
To:
Shared Package
ML20080C268	List: ML20080C262 ML20080C280 ML20080C290 ML20080C309
References
COM-75-001, COM-75-001-R02, COM-75-1, COM-75-1-R2, COM075.0200, COM75.0200, NUDOCS 8402080040
Download: ML20080C290 (19)

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Attachment 3 COM-75-001 Revision 2 January 1984 i C OM 07 5. 0200 FLAW EVALUATION AND REPAIR PLAN QUAD CITIES UNIT 2 FALL 1983 OUTAGES Prepared for:

Commonwealth Edison Company Ch icag o , Illinois Prepared by:

NUTECH Engineers, Inc.

San Jose, California Prepared by: Reviewed by:

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H. H. Buch holz H. L. Gustin, P.E.

Project Director Technical Leader 8402080040 840127 gDRADDCK 05000265 PDR

REVISION CONTROL SHEET TITLE; Flaw Evaluation and DOCUMENT FILS NUMBER: COM075.0200 Repair Plan Fall 1983 Outage Quad Cities Unit 2 R. H. Buchholz/proiec t Director 13 $

N AME / TITLE I INITI ALS H. L. Gustin / Technical Leader NAME / TITLE INITI A LS N AME/ TITLE INirt A LS N AME / TITLE iNiTr A Ls N AME i 71TLE iN Ti As.s A *

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Flaw Evaluation and Document File Repair Plan - Number: COM075.0200 Fall 1983 Outage Quad Cities Unit 2-Affected Document Page Revision # Change / Reason 1 2 Removed reference to Dresden 3. A separate Dresden-only report will be prepared.

2: 2 Added reference.to ACRS letter which recom-mends additional repair design requirements.

3 2 Added logic g for flaws with circumferential' extent >l20 - consistent with ACRS letter.

4 2 No change. Original Rev. O and Rev. 1.

5 Revised crack growth law to be consistent with correlation presented in December 7, 1983 ACRS meeting.

6 2 Added. sentence to indicate that evaluation approach has been updated to current practices.

7 2 No change. Original Rev. O and Rev. 1. ,

8. 2' No change. Original Rev. O and Rev. 1.

9 2 No change. Original Rev. O and Rev. 1.

10 2 Added e) to incorporate requirement fog flaws with circumferential extent >l20 .

11 '2 Removed reference for supplementary tearing

-modulus calculation - not required to demon-strate structural adequacy.

12 2 Added c) to incorporate requirement fog flaws with circumferential extent >120 .

Removed reference to "each plant" since separate report will be prepared for Dresden 3.

13- 2 No change. Original Rev. O and Rev. 1.

14' 2 Added Reference 2 and revised reference numbers.

15 2 Revised reference numbers.

Page 2 of 2

TABLE OF CONTENTS Page LIST-OF FIGURES 11

1.0 INTRODUCTION

1 2.0 EVALUATION CRITERIA 4 2.1 Strength Evaluation 4 2.2 Fatigue Evaluation 4 2.3 Fracture Mechanics Evaluation 5

3. 0 - EVALUATION METHODOLOGY 7 3.1 Code Stress Analysis 7 3.2 Fracture Mechanics Evaluation 7 3.3 Ef fect on Repaired Piping Systems 8 4.0 WELD OVERLAY DESIGN & ANALYSES PROCEDURE 9 4.1 Input Pa rame ters 9 4.2 held Overlay Design 9 4.3 Flaw Evaluation and Repair Analyses 10 4.3.1 Weld Overlay 11 4.3.2 Flawed Pipe Analysis 11 4.3.3 IHSI Evaluation 12 4.4 Docume n tat ion 12 5.0

SUMMARY

13

6.0 REFERENCES

14 l

l LIST OF FIGURES r-Number Title Page 1 Typical Flaw Disposition Sequence 3 COM-75 001 ii Revision 2 i

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1.0 INTRODUC TION 1

.This report summarizes the flaw evaluation and repair plan, including the weld overlay design and analysis t

methodology being used for the af fected stainless steel piping systems at Commonwealth Edison Company's Quad Cities Nuclear Power Station Unit 2 during the Fall 1983 outage. This~ plan addresses ultrasonic examination results which are believed to be indicative of intergranular stress corrosion cracking (IGSCC) in the vicinity of some of the welds on the concerned systems. .

Each flaw indication is evaluated to determine whether a repair is necessary. No te , for small flaws, a repair may not be necessary. Figure 1 shows the disposition sequence for a typical flaw. Since Quad Cities Unit 2 is also implementing IHSI during the current outage, IHSI is performed on welds with flaws that are deemed to be candidates to be lef t "as-is", whenever practical.

Based on the pos t-IHSI UT examination, a decision is made either to leave the flaw "as-is" or to perform a weld ove rlay repair.

COM 0 01 1 Revision 2 1

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For flaws that are repaired by weld overlay, the overlay thickness (which is a function of flaw depth, flaw length, and applied stresses) is sufficient to provide full IWB-3640 margin. The purpose of each overlay is to arrest any further propagation of cracking and to restore original safety margins to the weld. Analysis of flaw indications to date demonstrate that weld overlays do in fact arrest crack growth completely.

The flaw evaluation and repair criteria meet the intent of the guidelines set forth by the NRC in recently issued SECY-83-2 67C, dated November 7, 1983 (Reference 1). They also incorporate the recommendations contained in the ACRS letter, dated Decenber 19, 1983, commenting on the NRC staff requirements for reinspection and repair of cracked BWR piping (Reference 2).- The detailed evaluation criteria and the design / analysis approach are discussed in Sections 2.0, 3.0, and 4.0.

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WELDS POR IMSI puw MTMW INCICATION INEPGCTIONI l

l I CIRCUMPERENTIAL AXIAL PLAW PLAW IS LENGTH PERPORM ANALY$l$

LESS THAN FOR M W 120' OVERLAY DEssGN YES NO I I DEPTH DEPTM gyp.jggy LESS THAN LARGER THAN WELD OVERLAY

%t' %t' PERPORM ANALY$15 IS TO DESIGN NO gggg WELD OVERLAY P'UCA8LE YES IMPLEMENT WELD OVERLAY j  % PERPORM IM$1 PER PORM POST 4MS4 E XAMIN ATION

+ APPROXIMATE MEASURED FLAW DEPTH l

AS PERCENTAGE OF PtPE WALL THICKNESS.

PERPORM PLAnto THE ALLOWA8LE DEPTH DEPENDS ON THE PIPE ANALYS13 FLAW LENGTH AND APPLIED STRESS.

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(USING APPLICA8LE RESIOUAL STRESS ACOM84.01 l

PATTERN)

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LEAV4 CESIGN AS .S WELD OVERLAY I

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REIN 5PECT l $USSEQUENT OUTAGES l

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TYPICAL FLAW DISPOSITION SEQUENCE l

coM-75-001 1 Revision 2 3 l

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2.0 EVALUATION METHODOLOGY This section describes the criteria that are applied to evaluate the acceptability of the weld overlay repairs or flawed pipe analyses. The intent of the design crite.ia described below is to demonstrate equivalent margins of safety for the strength and fatigue considerations in the ASME Code,Section III design

. rules. In addition, because of the IGSCC conditions that led to the need for repairs, IGSCC resistant materials have been selected for the weld overlay repairs.- Criteria are also provided below for fracture mechanics evaluation of the repairs.

2,1- Strength Evaluation Adequacy of the strength of the weld overlay repairs with respect to applied mechanical loads is demonstrated with an ASME Boiler and Pressure Vessel Code Section III, Class 1 (Reference 4) analysis for each repair.

l 2.2 Fatigue Evalu a tion The stress values obtained from the above strength evaluation are combined with thermal and other secondary stress conditions to demonstrate adequate f atigue a

COM-75-001 4 Revision 2

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resistance for the design life of each repair in accordance with the requirements of Reference 4.

2.3 Fracture Mechanics Evaluation A conservative method is used to demonstrate the adequacy of the weld overlay repair. All relevant UT indications are assumed to be twice the confirmed crack depth. The intermittent flaws are assumed to be continuous for these evaluations. The weld overlay is then designed such that the requirements of Reference 3 are satisfied.

IGSCC growth depends on the total steady-state stress.

The major contributor to steady-state stress is weld residual stress. The residual stresses due to the original butt weld plus those due to the weld overlay are determined by analysis.

The conservative upper-bound crack growth law (Reference

6) for these analyses is pa = 1. 697 x 10-8 y2.53 dt 1

COM - 7 5-001 5 Revision 2

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where, da = differential crack size dt = differential time I

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K = . applied stress intensity f actor 4 ,

Crack. growth as a function of time is calculated assuming an intinitely long crack using the NUTECH computer program NUTORAK.

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t This eva16ation r/,pproach has been used previously and s

has .been reviewe'd and accepted by the NRC for Dresden

- Un it . 2, Ha tch Un it 2,' Ve rmont Ya nkee, and Brun swick s

- Units 1'& 2. -As appropriate, specific aspects in the

.i' evaluation process' have been updated to reflect current practicbs,.i.e., revised' crack growth law.

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3.0 EVALUATION METHODOLOGY The evalua tion of a flaw or a weld overlay repair consists of a code stress analysis per Section III (Reference 4 ) and a fracture mechanics evaluation per Section XI (References 3 and 5). The effect of the repair on piping system is also evaluated.

1 3.1 Code Stress Analysis i

A finite element model of the repaired region is developed using the ANSYS computer program. The stresses in the overlaid pipe (weld region) due to design pressure and applied moments are calculated using the finite element model.

The weld overlay thermal model is taken to be axisym-metric. The exterior boundary is assumed to be insulated. The maximum thermal stresses for use in the fatigue analysis are calculated in accordance with i

l Reference 4.

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l j 3.2 Fracture Mechanics Evaluation i

The allowable crack depth is calculated based on t

Reference 3. Crack growth due to f atigue is determined i

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based on the analyses described ,in Section 3.1. Crack growth due - to' IGSCC is eval'uated -based on Ref erence 3, the applied stresses, and empirical crack growth data.

It~is noted th'at for nost flaws -where weld overlay repair is applied, the change in the residual-stress

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. pattern is sufficient to prevent further crack growth.

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', Weld-overlay repair causes a small amount of radial and s.g 4

axial shrinkage,underneath the overlay. The effect of

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( g the' observed weld shrinkage bn t' he af fected piping

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'syAtems will be' evaluated using the NUTECH computer 2, .

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4.0 WELD OVERLAY DESIGN & ANAL YS IS PROC EDUR E This section describes the manner in which the flaw evaluation including weld overlay design and analyses is carried out.

4.1 Input Parameters f

The ~ following parameters are used as input to the flaw evaluation:

a. -Flaw characteriza tion based on UT inspection,

b. Piping system stresses at welds from existing stress reports, and

c. Geometry and pipe wall thickness.

4.2 Weld overlay De sig n The following steps are involved in design of a weld overlay:

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a. Applied stresses and flaw length are used to de t.e rmine the allowable (IWB-3640) flaw size as a fraction of thickness (a/t) ,

b. The ratio of twice the measured flaw r i. ze to the allowable flaw size is used to determine the COM-75-001 9 Revision 2

overlay thickness required to meet IWB-3640 criteria,

c. It is demonstrated ' that the required overlay produces a residual stress pattern which arrests f ur ther crack growth, and d.- It will also be demonstrated that the overlay by itself is sufficient to meet IWB-3640 requirements for a through-wall or near through-wall flaw,

e. For flaws with ef fectively continuous crack indications for a circumferential extent greater than 120*, the overlay design is based upon assuming the depth to be through-wall (per Re ference 2 ) .

4.3 Flaw Evaluation and Repair Analyses The repair may consist of IHSI and/or weld overlay as applicable. For small - flaws, the flawed pipe evaluation may demonstrate that no repairs are needed. The analyses performed to demonstrate the adequacy of these repairs / resolutions are described in Sections 4.3.1, i 4.3.2, and 4.3.3.

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4 . 3.1. Weld overlay Analysis of weld overlay repair is performed in the following steps:

a. Finite element analysis of the repaired geometry is used as input to an ASME Code,Section III, Class 1 stress analysis of :the repaired geometry,

b. Weld residual stress analysis of repairs of part-wall flaws is performed ,

c. Crack growth analysis using results from the finite element stress analysis and the residual stress analyses is performed to demonstrate that structural integrity of the repaired weld will not be degraded by further crack growth. These analyses generally show complete arrest of IGSCC c rack propagation.

4.3.2 Flawed Pipe Analysis For certain flaw indications, crack growth analyses as discussed in Section 2. 3 are performed to justify continued operation wi thou t repair (with or without IHSI). These analyses consider the ef fect of the residual stress pattern to inhibit growth.

COM- 75-001 11

. Revision 2

4.3.3 IHSI Evalua tions For . flaws that. have ' been treated by IHSI, a crack growth analysis is performed using a post-IHSI residual stress pattern (Reference 7 ) and comparing the measured flaw depth with an ' allowable flaw depth based on 2/3 of the IWB-3 640_ source equa tion value s. The flaw is considered acceptable without repair-other than IHSI if:

a. No crack growth results in the post-IHSI con f ig ura tion,

b. The requirenents of IWB-3640 are met with the remaining pipe wall (allowable flaw depth based on 2/3 IWB-3 640 source equation) ,

c. The circumferential extent of flaw indications

< 120*.

4.4 Documenta tion The results of all of the above analyses will be documented in a certified Design Report.

COM-75-001 12 Revision 2

5.0

SUMMARY

The evaluation of the flaw and repairs to the stainless steel piping systems is performed conservatively to provide assurance that the resulting stress levels are acceptable for all design conditions. The stress levels are assessed. from the standpoint of load capacity of the components, fatigue, and the resistance to crack growth.

Me e ting the acceptance criteria utilized for the analyses will demonstrate that:

1. There is no loss of design safety margin over that provided by the ASME Code,Section III, for Class 1 piping.

2. Dur ing the design lifetime of each repair, the observed cracks will not grow to the point where the above safety margins would be exceeded.

In fact, for the flaws evaluated to date, the selected repair method, (weld overlay or IHSI) has been demonstrated to arrest IGSCC crack growth completely.

COM 0 01 13 Revision 2

4 6.' 0 REFERENC ES

1. NRC Policy Issue SECY-83-2 67C dated November 7, 1983 from W. J. Dircks to the Commissioners, " Staff Requirements for Reinspection of BWR Piping and Repair of Cracked Piping ."

1

2. ACRS letter from J.J. Ray to Nunzio J. Padlid ino ,

"ACRS Comments on the NRC Staff Requirements for Reinspection of BWR Piping and Repair of Cracked Piping ," dated December 19, 1983.

3. ASME Boiler and Pressure Vessel Code,Section XI, Paragraph IWB-364 0, " Acceptance Criteria for Austenitic Steel Piping," (Approved by main committee for incorporation into Section XI in 1983).

4. ASME Boiler and Pressure Vessel Code,Section III, Subsection NB, 1980 Edition.

5. ASME Boiler and Pressure Vessel Code,Section XI, 1980 Edition with Addenda through Winter 1981.

COM -7 5-001 14 Revision 2

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6. EPRI Repo rt NP-2 4 23-LD, " Stress Corrosion Cracking of Type-304 Stainless Steel in High Purity Water:

A Compilation of Crack Growth Rates," June 1982.

7. EPRI Report NP-2662-LD, " Computational Res idual Stress Analysis for Induction Heating of Welded BWR Pipes," December 198 2.

COM 0 01 15 Revision 2