assessment of socket weld integrity in pipings (2)

8/16/2019 Assessment of Socket Weld Integrity in Pipings (2)

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Code Acceptance of Overlay Repair of Socket WeldFailures

Technical Assessment

1003165

Effective October 22, 2009, this report has been made publicly available in accordance with Section 734.3(b)(3)and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result ofthis publication, this report is subject to only copyright protection and does not require any license agreementfrom EPRI. This notice supersedes the export control restrictions and any proprietary licensed material noticesembedded in the document prior to publication


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Code Acceptance of Overlay Repair of Socket Weld Failures

1003165

Technical Assessment, December 2001

EPRI Project Manager

Greg Frederick

RRAC Coordinator

Mike Sullivan, PG&E

EPRI-RRAC 1300 W.T. Harris Blvd., Charlotte, NC 28262 • PO Box 217097, Charlotte, NC 28221 • USA704.547.6100 • [email protected] • www.epri.com


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DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OFWORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI).NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANYPERSON ACTING ON BEHALF OF ANY OF THEM:

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ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

EPRIPacific Gas & Electric

NOTICE: THIS REPORT CONTAINS PROPRIETARY INFORMATION THAT IS THE INTELLECTUALPROPERTY OF EPRI, ACCORDINGLY, IT IS AVAILABLE ONLY UNDER LICENSE FROM

EPRI AND MAY NOT BE REPRODUCED OR DISCLOSED, WHOLLY OR IN PART, BY ANY

LICENSEE TO ANY OTHER PERSON OR ORGANIZATION.

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ORDERING INFORMATION

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Electric Power Research Institute and EPRI are registered service marks of the Electric Power Research Institute, Inc.EPRI. ELECTRIFY THE WORLD is a service mark of the Electric Power Research Institute, Inc.

Copyright © 2001 Electric Power Research Institute, Inc. All rights reserved.


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iii

CITATIONS

This document was prepared by

EPRI, Repair and Replacement Application Center

1300 W.T. Harris Blvd.Charlotte, NC 28262

Principal InvestigatorG. Frederick

Pacific Gas & Electric

3400 Crow Canyon Rd.San Ramon, CA 94583-1308

Principal InvestigatorMike Sullivan

This document describes research sponsored by EPRI, Repair and Replacement ApplicationCenter.

The publication is a corporate document that should be cited in the literature in the followingmanner:

Code Acceptance of Overlay Repair of Socket Weld Failures, EPRI-RRAC, Charlotte, NC: 2001.1003165.


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EPRI Proprietary Licensed Material

v

SUMMARYFailures of small bore piping connections (2-inch and smaller) continue to occur frequently atnuclear power plants in the United States, resulting in degraded plant systems and unscheduled

plant downtime. Fatigue-related failures are generally detected as small cracks or leaks but, in

many cases, the leak locations are not isolable from the primary reactor coolant system, resultingin extended outages. Outages associated with fatigue failures have resulted in shut downs aslong as 7 days with lost revenue costs exceeding $300K per day.

To reduce costs associated with these common failures of small bore piping and fittings, EPRIhas conducted several studies to improve socket weld design, fabrication practices and repairapplications to address high cycle fatigue. One of the options evaluated was an overlay repair of the leaking connections which was intended to extend the life of a failed connection and allowreplacement to be scheduled during a routine outage. Preliminary results indicating that sealwelding and overlay weld repairs can provide a fatigue life equal to the original 1:1 code weldgeometry. As a result, Code Case N-XXX, Alternative Rules for Repair of Class 1,2, and 3

Socket Welded Connections was drafted to support the on-line repair of leaking socket weldedconnections.

The goal of this program is to support the Code Case to permit the use of this repair technologyfor on-line repairs of leaking socket welds in operating nuclear plants, including high cycle

fatigue and MIC. To validate the repair technology a series of mockup configurationsrepresentative of plant components will be tested. The mockup configurations will include arange of socket weld pipe diameters, materials and initial failure modes to substantiate the repairapproach. The purpose of the test matrix is to provide experimental confirmation that an overlayrepair would allow the socket weld to remain in service or allow replacement at a scheduledoutage.

An ASME task group has been established to review the Code Case and test matrix. The latestrevision of the Code Case, test matrix and preliminary results are included in this progress report.The final report with all test results, conclusions and ‘Position Paper’ will be completed in theearly 2002.


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vi


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vii

CONTENTS

1 INTRODUCTION.....................................................................................1-1

2 TEST PROGRAM ...................................................................................2-1Test Matrix.............................................................................................................. 2-1

Test Procedures..................................................................................................... 2-2

Shaker Table Assembly .................................................................................... 2-3

3 TEST RESULTS .....................................................................................3-1

A APPENDIX: CODE CASE..................................................................... A-1


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viii


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1-1

1INTRODUCTION

Failures of small bore piping connections (2-inch and smaller) continue to occur frequently atnuclear power plants in the United States, resulting in degraded plant systems and unscheduledplant downtime. Fatigue-related failures are generally detected as small cracks or leaks but, inmany cases, the leak locations are not isolable from the primary reactor coolant system, resultingin extended outages. Outages associated with fatigue failures have resulted in shut downs aslong as 7 days with lost revenue costs exceeding $300K per day.

To reduce costs associated with these common failures of small bore piping and fittings, EPRIhas conducted several studies to improve socket weld design, fabrication practices and repairapplications to address high cycle fatigue. One of the options evaluated was an overlay repair of the leaking connections which was intended to extend the life of a failed connection and allow

replacement to be scheduled during a routine outage. Preliminary results indicating that sealwelding and overlay weld repairs can provide a fatigue life equal to the original 1:1 code weldgeometry. As a result, Code Case N-XXX, Alternative Rules for Repair of Class 1,2, and 3Socket Welded Connections was drafted to support the on-line repair of leaking socket weldedconnections.

The goal of this program is to support the Code Case to permit the use of this repair technology

for on-line repairs of leaking socket welds in operating nuclear plants, including high cyclefatigue and MIC. To validate the repair technology a series of mockup configurationsrepresentative of plant components will be tested. The mockup configurations will include arange of socket weld pipe diameters, materials and initial failure modes to substantiate the repair

approach. The purpose of the test matrix is to provide experimental confirmation that an overlayrepair would allow the socket weld to remain in service or allow replacement at a scheduledoutage.

An ASME task group has been established to review the Code Case and test matrix. The latestrevision of the Code Case, test matrix and preliminary results are included in this progress report.The final report with all test results, conclusions and ‘Position Paper’ will be completed in theearly 2002. The test procedures and test matrix are documented in Section 2, PreliminaryResults are documented in Section 3 and the draft Code Case is included in Appendix A. Thefinal report with all test results, conclusions and ‘Position Paper’ will be completed in the early2002.


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2-1

2TEST PROGRAM

The test program is divided into two sections; 1) Test Matrix and 2)Test Procedures.

Test Matrix

A test matrix was outlined by the ASME task group formed to support the Code Case on overlayweld repair. The test matrix was to include a range of pipe sizes, materials and failure modes toassure the repair technology would cover most failures in a power plant. The group elected to

test common nominal pipe sizes (3/4-inch (1.91 cm) and 2-inch (5.08 cm) NPS) and typicalmaterials (stainless steel and carbon steel).

A test matrix consisted of standard equal leg (1:1) socket welds fabricated from Schedule 80piping and standard pipe to pipe couplers. Loading amplitudes were selected based on fatiguedata from prior socket weld fatigue tests, and desired failure modes (toe and root failure modes).The final test matrix is shown in Table 2-1.

Table 2-1. Proposed Test Matrix for Socket Weld Overlay Code Case

Test Specimens and Stress Conditions

Base Material Size Original Crack

Location

Stress Range Number of

Specimens

High 3

2” Toe Low 3

High 32” Root

Low 3

High 2¾” Toe

Low 2

High 2

Stainless Steel

¾” RootLow 2

High 3

2 Toe Low 3

High 3

Carbon Steel

2 RootLow 3


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2-2

Test Procedures

The high cycle fatigue testing of socket welds has been developed over the past few years atPG&E to accommodate typical socket weld configurations. The testing method is displacementcontrolled, peak-to-peak, with the specimens vertically cantilevered on a shaker table as seen in

Figure 2-1. Each set of socket weld specimens is bolted to the shaker table and shaken

simultaneously near their resonant frequencies to produce the desired stress amplitudes andcycles per Table 2-1. A typical caniliver specimen is shown in Figure 2-2.

The test matrix consisted of standard equal leg (1:1) socket welds fabricated from common pipesizes and diameters. The specimens are processed on the Shaker Table Assembly until they fail.The socket weld connections are processed at various stress ranges to promote through-wall toeand root crack failures. The failed specimens are seal welded and overlay repaired in accordance

with the proposed Code Case (Appendix A). The leaks will be peened, with water in the pipe atpressure, to allow a seal weld to be applied. Most of the specimens will be overlay repairedwhile the pipe is filled with water and pressurized. Select specimens will be repaired withoutwater backing. The weld overlay will be applied in accordance to the dimensions illustrated in

the Code Case.

The overlay design governed by the Code Case applies a sufficient reinforcement to cover thepossibility of either a toe or a root failure. The overlay design adds 0.77tn (tn = pipe wallthickness) to the weld throat across the entire profile, from the pipe side toe to the fitting side toe.The thickness is measured from the seal weld and not the existing toe. The weld is applied byshielded metal arc welding (SMAW) to simulate the most likely welding process that would beused for in-line repair in a power plant.

The overlaid specimens are again processed on the Shaker Table Assembly until failure or untilthe specimen exceeds the original number of cycles to failure (run-out). The repaired specimenswill be tested at a high stress range (failure in 107

cycles).

Figure 2-1. Shaker Table Assembly


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2-3

(6.5-in.)

( 1 4 .2 5 -i n. )

Test Weld

Figure 2-2. Test Specimen Details

Shaker Table Assembly

Different load amplitudes can be applied to different samples in the same test by fine-tuning the

specimen natural frequencies relative to the shaker table excitation frequency. The shaker tabletypically operates at 100-110 Hz and the test specimens had natural frequencies that were

nominally 4-8 Hz lower than the excitation frequency. By adding or subtracting small masses,such as nuts and washers, the frequencies of the test specimens were moved enough off resonance to adjust each individual response acceleration.

The specimen are instrumented with an accelerometer and a pressure gauge, and are monitoredcontinuously during testing. The specimens were pressurized with air to a moderate pressure of approximately 50 psig (344.75 kPa). Failure of a specimen is indicated when depressurizationoccurres, the specimen are removed from the table at the next convenient test stoppage point, andthe testing is resumed with the remaining specimens.

Figure 2-3 illustrates the actual test apparatus with all monitroing equipment attached. The tubesand wires are leads for the strain gages and pressure transducers, which were relayed to the testcontrol computer (right side of figure). The desired stress level for each test specimen wasprecalculated as a top mass acceleration and was adjusted to produce a particular failure modes(toe or root failure). The shaker table amplitude was computer-controlled to achieve a presetaccelerometer amplitude on one of the mounted samples. The accelerometer amplitude isrecorded for all samples and is used to determine the tested stress amplitude for each specimen.


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2-4

Figure 2-3. Test Apparatus with test control computer on right)


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3-1

3TEST RESULTS

A number of the overlay test specimens from the test matrix shown in Table 2-1 were tested inaccordance to the test procdures in Section 2. The status of the test matrix is documented inTable 3-1 and the preliminary results are shown in Figure 3-1 for 2-in. stainless steel, Figure 3-2for 2-inch carbon steel and Figure 3-3 for ¾-inch stainless steel. At this time, additional toefailures are needed to complete the original test matrix.

Further evaluation of the test specimens will be conducted once the entire test matrix has beencompleted. Each specimen will be compared to the original fatigue life and metallographicallyevaluated to determine failure mode (i.e. crack initiation site and crack extension). Results willdetermine if the weld overlay repair process was successful in restoring or improving the originalfatigue strength of the specimen.

At the completion of the entire test matrix and failure analyses a final report with all test results,conclusions and ‘Position Paper’ will be completed. The expected completion date is March2002. The position paper will be presented to the ASME task group for review at that time.

Table 3-1 Socket Weld Test Matrix Status

Base Material Size Original CrackLocation

Stress Range Number ofSpecimens

Completed

Stainless Steel 2” Toe High 3 2Low 3 0

2” Root High 3 2Low 3 5

¾” Toe High 2 1Low 2 2

¾” Root High 2 3Low 2 2

Carbon Steel 2 Toe High 3 0Low 3 0

2 Root High 3 2Low 3 4


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3-2

2" Stainless Steel Socket Welded Specimens

1000

10000

100000

100000 1000000 10000000 10000

# of cycles

S t r e s s A m p l i t u d e ( p s i )

Weld Overlays are solid symbols; Original c racked socket welds are open symbols

2

3tr

2r>

6rr

3

5rt6

88rr9rr9

6r>

1

7rr

75 4

4r>

1tt

Figure 3-1. Preliminary Results of 2-inch Stainless Steel Test Specimens


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3-3

2" Carbon Steel Higuchi Curve with our Test Results

1000

10000

100000

100000 1000000 10000000 100000000

# of Cycles

S t r e

s s A m p l i t u d e ( p s i )

Weld Overlays are solid symbols; Original cracked socket welds are open symbols

6rt

9r>

95rr

5

8r>

11r>

4r>

Figure 3-2. Preliminary Results of 2-inch Carbon Steel Test Specimens


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3-4

3/4" Stainless Steel Higuchi Curve with our Test Results

1000

10000

100000

100000 1000000 10000000

Weld Overlays are solid symbols; Original cracked socket weld are open

3

7t>1rt

1

7

46

5

4tr

Figure 3-3. Preliminary Results of 3/4-inch Stainless Steel Test Specimens


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A-1

A APPENDIX: CODE CASE


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A-2


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A-3

Case N-XXX

Alternative Rules for Repair of Class 1, 2, and 3

Socket Welded Connections

Section XI, Division 1

Inquiry: Under the rules of IWA-4611,

structural integrity of componentscontaining unacceptable defects may be

restored by defect removal and repair. Asan alternative to defect removal and repair

of a cracked or leaking socket weld wherethe failure is predominantly a result of

vibration fatigue, is it permissible to restorethe structural integrity by installation of

weld reinforcement (weld overlay) on theoutside surface of the pipe, weld, and

fitting?

Reply: It is the opinion of the Committee

that, in lieu of the requirements of IWA-

4611, the structural integrity of a cracked or

leaking socket weld in Class 1, 2 and 3, NPS

2 and smaller piping may be restored by

deposition of weld reinforcement (weld

overlay) on the outside surface of the pipe,

weld and fitting, provided the requirementsof this case are met:

1.0 General Requirements

(a) The repair shall be performed in

accordance with a Repair ReplacementProgram

1satisfying the requirements of

IWA-4150 in the Edition and Addenda of Section XI applicable to the plant in-service

inspection program, or later Edition andAddenda of Section XI. The references used

in this Case refer to the 2001 Edition of

Section XI. For use with other Editions and

1 When applying this Case to Editions and

Addenda later than the 1989 Edition,

reference to Repair Program shall be read asRepair Plan.

Addenda, refer to Table 1 for applicable

references.(b) Use of this Code Case is limited toClass 1, 2, or 3 NPS 2 and smaller socketwelded connections with base material of P-

Number 1 Group 1, P-Number 1 Group 2, orP-Number 8.

(c) Reinforcement weld metal (structuraland seal layers) shall be deposited in

accordance with a welding procedurespecification qualified in accordance with

IWA-4440.

(d) The repair shall be acceptable forservice for one refueling cycle if no action istaken to determine the cause of the vibration

and to reduce it to acceptable levels. Therepair shall be acceptable for the remaining

life of the piping system if corrective actionis taken to reduce vibration to acceptable

levels. When the time to failure of theoriginal socket weld was less than one fuel

cycle, then corrective action to reduce thevibration to acceptable levels must be taken.

(e) This case can only be applied onceper socket weld. A socket weld may not be

reinforced more than one time.(f) All other applicable requirements of

IWA-4000, IWB-4000, IWC-4000, or IWD-4000 shall be met.

2.0 Evaluation

(a) Determine that the socket weldfailure mechanism is predominantly a result

of vibration fatigue. This determination, asa minimum, should be based on review of

the design, operating history, and the visualinspection of the failed socket weld.

Metallurgical analysis of the flaw surface forfailure determination is not required.


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A-4

(b) Verify that pipe base material

adjacent to the socket weld requiring repairmeets design minimum wall thickness.

(c) Evaluate the effect of water backingon the repair

3.0 Design

(a) The intent of the design is to restorethe integrity of the welded connection such

that the fatigue life is at least equal to that of a new standard socket weld. The source of

the vibration that failed the original socketweld will also eventually fail the overlaid

socket weld unless measures are taken to

identify and mitigate the vibration. Theowner shall consider this in the suitabilityevaluation required by IWA-4160.

(b) The completed weld reinforcementrepair shall meet the dimensional

requirements specified in Figure l. Theminimum reinforcement dimensions also

apply when the fatigue crack is located inthe base metal adjacent to the toe of the

socket weld. The minimum reinforcementdimensions shall be measured from the

location of the crack furthest from the weldtoe.

(c) The filler metal for structuralreinforcement of P-No. 1 materials shall be

AWS Class E70XX-X or ER70S-X. Fillermetal for structural reinforcement of P-No. 8

materials shall be AWS Class E3XX-XX orER3XX. The filler metal for the seal weld

may be any filler metal permitted by aqualified welding procedure specification.

(d) Evaluate all relevant applied loads inthe system.

(e) C2 and K2 (reference NB-3680) or i(reference NC-3673) values for the repaired

socket weld shall be the same as for astandard socket weld.

(f) For Class 1 piping, evaluate theeffect of the increased mass of the

reinforced weld on thermal stress.

4.0 Procedure

(a) Prior to repair, visually examine the

socket weld to determine the location andapproximate extent of cracking.

(b) Seal the crack by depositing one ormore weld beads directly over the crack.

Peening may be used in combination withwelding to seal the crack.

(c) VT-1 examine the seal weld,remaining socket weld and adjacent base

material that will be reinforced. Visualexamination shall be performed with a

minimum 8X magnification and shall verify

that the leakage has been stopped and thesurface is dry and suitable for structuralreinforcement

(d) Deposit two or more structuralreinforcement layers around the entire

circumference of the fitting, weld, and pipe.The minimum required deposit length, throat

and leg dimensions shall be in accordancewith Figure 1. The throat and leg

dimensions shall not include the seal layer(s)deposited in accordance with 4(b) above.

The weld surface need not be ground; an as-welded surface is acceptable.

5.0 Examination and Testing

(a) Examination of the final structural

reinforcement weld shall be performed inaccordance with (1) or (2) below:

(1) The completed structural

reinforcement weld shall be examined inaccordance with the Construction Code

identified in the Repair/ Replacement Plan.

Type of examination and coverage shall be

the same as that specified for a standardsocket weld.


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A-5

(2) When the system operating

temperature exceeds the temperature at

which a specified surface examination can

be performed, a VT-1 examination may be

performed as an alternative. This VT-1

examination shall be performed with aminimum of 8X magnification. Visual

indications shall be evaluated using the

surface examination acceptance criteria of

the Construction Code specified in theRepair/Replacement Plan

(b) Following completion of all repair

activities, the affected restraints, supports,

and snubbers shall be VT-3 visually

examined to determine that designtolerances are met.

(c) A system leakage test shall beperformed in accordance with IWA 5213.

6.0 Documentation

Use of this code case shall be documentedon an NIS-2 form.


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A-6

TABLE 1

References for Alternative Editions and Addenda of Section XI

1995 Addenda through 2001Edition

1991 Addenda through1995 Edition

1988 Addenda through1990 Addenda

1983 Winter Addendathrough 1987 Addenda

1981 Winter Addendathrough 1983 Summer

Addenda4110 Scope 4110 4110 & 7110 4110 & 7110 4110 &7110

4120 Applicability 4120 (91A-92E) 4111(92A to 95E)

7400 7400 7400

4150 R/R Program and Plan 4140 & 4170 4120 & 4130 & 7130 4130 & 41207130 added W85A

4130

4160 Verification of Acceptability

4150 7220 & 4130 7220 & 4130 7220 & 4130

4180 Documentation 4910 4800 &7520 4700 & 7520 4700 & 7520

4400 Welding, Brazing, Defect

Removal and Installation

4200 & 4300 through

93A & 4170

4120, 4200,4300 & 4400

and IWB-4200 88A to

89A

4120, 4200,4300 & 4400

IWB-4200

4120, 4200 & 4300

IWB-4200

4500 Examination and Test 4700 &4800 4600 & 4700 4400 & 4500 4400 & 4500

4530 Preservice Inspection and

Testing

4820 4600 & 7530 4500 & 7530 4500 & 7530

4540 Pressure Testing 4700 4700 4400 4400

4600 Alternative WeldingMethods

4500 4500 IWB-4300 IWB-4300


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tn

0.77 tn

Seal weld

Rootcrack

r

Seal weld 0.77 tn

0.77 tn

0.77 tnToecrack

Seal weld

Seal weld

r

tn

Figure 1. Socket Weld Reinforcement Dimensions. The right side of the figures shows the designdimensions while the left side shows the as-welded appearance. The final surface of the overlaymay be left in the as-welded condition

Toe Crack

Root Crack

As Welded

Appearance

Design Dimensions


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EPRI creates science and technology

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are registered service marks of the Electric Power ResearchInstitute, Inc. EPRI. ELECTRIFY THE WORLD is a service

mark of the Electric Power Research Institute, Inc.

1003165

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EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

assessment of socket weld integrity in pipings (2)

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