Devt of Tube Repair Techniques for HR Steam Generators

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Development of Tube Repair Techniques forHeat Recovery Steam Generators

Supporting Stress Analyses, Code Interpretation, and Internal Tube Repair

1010512

Effective December 6, 2006, 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 of this publication, this report is subject to only

copyright protection and does not require any license agreement from EPRI. This notice

supersedes the export control restrictions and any proprietary licensed material notices

embedded in the document prior to publication.



EPRI Project ManagerD. Gandy

ELECTRIC POWER RESEARCH INSTITUTE3420 Hillview Avenue, Palo Alto, California 94304-1395 ▪ PO Box 10412, Palo Alto, California 94303-0813 ▪ USA

800.313.3774 ▪ 650.855.2121 ▪ [email protected] ▪ www.epri.com

Development of Tube RepairTechniques for Heat Recovery

Steam GeneratorsSupporting Stress Analyses, Code Interpretation,and Internal Tube Repair

1010512

Technical Update, March 2006



DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I)WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, ORSIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESSFOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON ORINTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUALPROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'SCIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER(INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVEHAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOURSELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD,PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT.

ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

Electric Power Research Institute (EPRI)

Structural Integrity Associates

NOTEFor further information about EPRI, call the EPRI Customer Assistance Center at (800) 313-3774 oremail [email protected]

Electric Power Research Institute and EPRI are registered service marks of the Electric PowerResearch Institute, Inc.

Copyright © 2006 Electric Power Research Institute, Inc. All rights reserved.



CITATIONS

This report was prepared by

Electric Power Research Institute (EPRI)NDE Center1300 W.T. Harris Blvd.Charlotte, NC 28262

Principal Investigator

D. Gandy

Structural Integrity Associates3500 Massillon RdSuite 420Uniontown, OH 44685

Principal InvestigatorsE. JonesM. Berasi

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Development of Tube Repair Techniques for Heat Recovery Steam Generators: Supporting

Stress Analyses, Code Interpretation, and Internal Tube Repair. EPRI, Palo Alto, CA: 2006.1010512.

iii



PRODUCT DESCRIPTION

This report describes the results of two strategies for repair of heat recovery steam generators.The first few sections of this report provide supporting information for the tube-to-headerattachment repair described in EPRI report 1010441. The remainder of the report describes anew repair strategy that is to get underway in early 2006 that looks to address tube repair fromthe inside diameter of a tube.

Results and FindingsThe methodology and results of a finite element stress analyses performed on four configurationsof Heat Recovery Steam Generator (HRSG) header-to-tube attachments is described herein.These analyses were performed to compare stress levels in the original method of attachment tothose resulting from 3 alternative repair options designed to remove service-related cracking orother defects in the attachment weld. The repair options evaluated included two partialpenetration welds and one full penetration weld. Stresses due to internal pressure and externaltube bending loads were evaluated. For the two types of analysis completed in this study(internal pressure and unit bending moment), the original configuration generally showed higherstress levels than those found in the repair options. The full penetration repair weld option hadthe lowest stress levels.

Challenges and ObjectivesThis analysis (and the complete EPRI study on this matter) is important to all HRSG plantoperators as headers in these units have shown a propensity for failure at the header-to-tubeattachment weld during service. Furthermore, limited access typically associated with theseheaders generally precludes the use of traditional weld repairs made from the external surface of the header. As a result, EPRI has developed an innovative repair method performed from theinside of the header. The stress analysis of this report was subsequently important to demonstratethat this repair weld geometry would not introduce operating stresses greater than those of theoriginal geometry.

Applications, Values, and Use

This analysis is one part of the ongoing EPRI study into repair options for HRSG header-to-tubeweld.

v



EPRI PerspectiveThis report provides the supporting stress analysis data for performing HRSG attachment repairsfrom the inside diameter of a header. Utilizing this information, along with the repair approachdocumented in EPRI Report 1010441, EPRI approached the National Board in early 2006 andgained acceptance of the new HRSG header-to-tube weld repair approach. With this in hand,

utilities can now utilize the new repair approach to significantly reduce repair time when header-to-tube attachment cracking is identified. Furthermore, unnecessary removal and subsequentrepair of undamaged tubes to gain access to the damaged attachment area can be eliminatedaltogether.

ApproachUsing ANSYS 9.0 finite element software, a separate model for four different weldconfigurations was created and boundary conditions to simulate internal pressure and bendingmoment loads were applied. The results of this analysis were then presented to the NationalBoard, along with a discussion of the overall header-to-tube attachment repair approach. Basedon information, an “Interpretation” was provided by the National Board which enables utilities to

now utilized the repair technology.

KeywordsHRSG headerStress analysisStub tube attachmentfull penetrationPartial penetration

vi



CONTENTS

1 INTRODUCTION ....................................................................................................................1-1 2 DESIGN INPUTS....................................................................................................................2-1

Geometry ..............................................................................................................................2-1 Material Properties ................................................................................................................2-5 Loads ....................................................................................................................................2-5

Internal Pressure Boundary Conditions............................................................................2-5 Bending Moment Boundary Conditions ............................................................................2-5

3 RESULTS ...............................................................................................................................3-1 Internal Pressure Application Results ...................................................................................3-1 Bending Moment Application Results....................................................................................3-1 Conclusions and Recommendations.....................................................................................3-3

4 NATIONAL BOARD INTERPRETATION 04-15 ....................................................................4-5

5 INTERNAL TUBE REPAIR ....................................................................................................5-7 A APPENDIX............................................................................................................................ A-1

Original Configuration Pressure Run Images....................................................................... A-1 Partial Penetration (0.225” Weld Depth) Pressure Run Images......................................... A-13 Partial Penetration (0.243” Weld Depth) Pressure Run Images......................................... A-25 Full Penetration Pressure Run Images .............................................................................. A-37

B APPENDIX............................................................................................................................ B-1 Original Configuration Bending Moment Analysis Images ................................................... B-1 Partial Penetration (0.225” Weld Depth) Bending Moment Analysis Images..................... B-15 Partial Penetration (0.243” Weld Depth) Bending Moment Analysis Images..................... B-29 Full Penetration Bending Moment Analysis Images........................................................... B-43

vii



LIST OF FIGURES

Figure 2-1 Original Configuration 2-D Geometry (Side View)....................................................2-2 Figure 2-2 Partial Penetration (0.243” Weld Depth) 2-D Geometry (Side View)........................2-3 Figure 2-3 Partial Penetration (0.225” Weld Depth) 2-D Geometry (Side View)........................2-4 Figure 2-4 View of Applied Pressure Loads...............................................................................2-6 Figure 2-5 View of Applied Forces for Bending Moment Analysis .............................................2-7 Figure 4-1 Interpretation 04-15 Part RD-2060 Utilizing a Flush Patch to Gain Access

Window in Pressure Retaining Items. ......................................................................4-6 Figure A-1 Header Hoop Stress................................................................................................ A-1 Figure A-2 Header Hoop Stress................................................................................................ A-2 Figure A-3 Header Hoop Stress................................................................................................ A-3 Figure A-4 Header Axial Stress ................................................................................................ A-4 Figure A-5 Header Axial Stress ................................................................................................ A-5 Figure A-6 Header Axial Stress ................................................................................................ A-6 Figure A-7 1

stPrincipal Stress................................................................................................... A-7

Figure A-8 1st

Principal Stress................................................................................................... A-8 Figure A-9 1

stPrincipal Stress................................................................................................... A-9

Figure A-10 Stress Intensity.................................................................................................... A-10 Figure A-11 Stress Intensity.................................................................................................... A-11 Figure A-12 Stress Intensity.................................................................................................... A-12 Figure A-13 Header Hoop Stress............................................................................................ A-13 Figure A-14 Header Hoop Stress............................................................................................ A-14 Figure A-15 Header Hoop Stress............................................................................................ A-15 Figure A-16 Header Axial Stress ............................................................................................ A-16 Figure A-17 Header Axial Stress ............................................................................................ A-17 Figure A-18 Header Axial Stress ............................................................................................ A-18 Figure A-19 1

st

Principal Stress............................................................................................... A-19 Figure A-20 1

stPrincipal Stress............................................................................................... A-20

Figure A-21 1st

Principal Stress............................................................................................... A-21 Figure A-22 Stress Intensity.................................................................................................... A-22 Figure A-23 Stress Intensity.................................................................................................... A-23 Figure A-24 Stress Intensity.................................................................................................... A-24 Figure A-25 Header Hoop Stress............................................................................................ A-25

ix



Figure A-26 Header Hoop Stress............................................................................................ A-26 Figure A-27 Header Hoop Stress............................................................................................ A-27 Figure A-28 Header Axial Stress ............................................................................................ A-28 Figure A-29 Header Axial Stress ............................................................................................ A-29 Figure A-30 Header Axial Stress ............................................................................................ A-30 Figure A-31 1


Figure A-32 1st



Figure A-34 Stress Intensity.................................................................................................... A-34 Figure A-35 Stress Intensity.................................................................................................... A-35 Figure A-36 Stress Intensity.................................................................................................... A-36 Figure A-37 Header Hoop Stress............................................................................................ A-37 Figure A-38 Header Hoop Stress............................................................................................ A-38 Figure A-39 Header Hoop Stress............................................................................................ A-39 Figure A-40 Header Axial Stress ............................................................................................ A-40 Figure A-41 Header Axial Stress ............................................................................................ A-41 Figure A-42 Header Axial Stress ............................................................................................ A-42 Figure A-43 1


Figure A-44 1st



Figure A-46 Stress Intensity.................................................................................................... A-46 Figure A-47 Stress Intensity.................................................................................................... A-47 Figure A-48 Stress Intensity.................................................................................................... A-48 Figure B-1 Header Hoop Stress................................................................................................ B-1 Figure B-2 Header Hoop Stress................................................................................................ B-2 Figure B-3 Header Hoop Stress................................................................................................ B-3 Figure B-4 1

stPrincipal Stress................................................................................................... B-4

Figure B-5 1st

Principal Stress................................................................................................... B-5 Figure B-6 1

stPrincipal Stress................................................................................................... B-6

Figure B-7 Stress Intensity........................................................................................................ B-7 Figure B-8 Stress Intensity........................................................................................................ B-8 Figure B-9 Stress Intensity........................................................................................................ B-9 Figure B-10 Tube Axial Stress ................................................................................................ B-10 Figure B-11 Tube Axial Stress ................................................................................................ B-11 Figure B-12 Tube Axial Stress ................................................................................................ B-12 Figure B-13 Tube Axial Stress ................................................................................................ B-13 Figure B-14 Tube Hoop Stress ............................................................................................... B-14 Figure B-15 Header Hoop Stress............................................................................................ B-15 Figure B-16 Header Hoop Stress............................................................................................ B-16 x



Figure B-17 Header Hoop Stres ............................................................................................. B-17 Figure B-18 1

stPrincipal Stress............................................................................................... B-18

Figure B-19 1st

Principal Stress............................................................................................... B-19 Figure B-20 1


Figure B-21 Stress Intensity.................................................................................................... B-21 Figure B-22 Stress Intensity.................................................................................................... B-22 Figure B-23 Stress Intensity.................................................................................................... B-23 Figure B-24 Tube Axial Stress ................................................................................................ B-24 Figure B-25 Tube Axial Stress ................................................................................................ B-25 Figure B-26 Tube Axial Stress ................................................................................................ B-26 Figure B-27 Tube Axial Stress ................................................................................................ B-27 Figure B-28 Tube Hoop Stress ............................................................................................... B-28 Figure B-29 Header Hoop Stress............................................................................................ B-29 Figure B-30 Header Hoop Stress............................................................................................ B-30 Figure B-31 Header Hoop Stress............................................................................................ B-31 Figure B-32 1


Figure B-33 1st

Principal Stress............................................................................................... B-33 Figure B-34 1


Figure B-35 Stress Intensity.................................................................................................... B-35 Figure B-36 Stress Intensity.................................................................................................... B-36 Figure B-37 Stress Intensity.................................................................................................... B-37 Figure B-38 Tube Axial Stress ................................................................................................ B-38 Figure B-39 Tube Axial Stress ................................................................................................ B-39 Figure B-40 Tube Axial Stress ................................................................................................ B-40 Figure B-41 Tube Axial Stress ................................................................................................ B-41 Figure B-42 Tube Hoop Stress ............................................................................................... B-42 Figure B-43 Header Hoop Stress............................................................................................ B-43 Figure B-44 Header Hoop Stress............................................................................................ B-44 Figure B-45 Header Hoop Stress............................................................................................ B-45 Figure B-46 1

STPrincipal Stress.............................................................................................. B-46

Figure B-47 1ST

Principal Stress.............................................................................................. B-47 Figure B-48 1

STPrincipal Stress.............................................................................................. B-48

Figure B-49 Stress Intensity.................................................................................................... B-49 Figure B-50 Stress Intensity.................................................................................................... B-50 Figure B-51 Stress Intensity.................................................................................................... B-51 Figure B-52 Tube Axial Stress ................................................................................................ B-52 Figure B-53 Tube Axial Stress ................................................................................................ B-53 Figure B-54 Tube Axial Stress ................................................................................................ B-54

xi



xii



LIST OF TABLES

Table 2-1 Material Properties for P91 Material at 1000ºF..........................................................2-5 Table 3-1 Maximum and Minimum Stresses for Internal Pressure Analysis..............................3-2 Table 3-2 Maximum and Minimum Stresses for Bending Moment Analysis..............................3-3

xiii



1 INTRODUCTION

Plant owners have been experiencing failures in HRSG units where the tubes attach to theheader. EPRI has been conducting research for different repair options at this attachment pointincluding the use of a stub tube insert. Because this proposed fix will result in a much differentgeometry, stress analysis of the repair options was required to determine the resulting operatingstresses relative to those existing in the original weld joint geometry. Finite element (FE) stressanalysis was subsequently performed for one selected original header-to-tube weld jointgeometry, and for three proposed repair configurations. The results of the analysis should show if significant additional stressing occurs in the repair methods.

In order to compare the three different attachment configurations, two separate load conditionsare analyzed. The first condition is internal pressure in the header. The second condition is anexternal tube bending moment that results from temperature differences that typically existbetween adjacent tube legs entering the header. A specific bending moment was not determinedfor the evaluated header geometry. However, an equivalent unit bending moment was applied toeach model to show the response of each configuration to this loading.

1-1



2-1

2 DESIGN INPUTS

Geometry

Four separate FE models were evaluated for this investigation, representing the original tube-to-header weld configuration, one full penetration weld repair, and two alternative partialpenetration repairs. Figures 2-1 through 2-3 show 2-dimensional sketches of each geometry.Note that the two partial penetration configurations differ only with respect to the depth of theweld and corresponding depth of the un-fused area in the weld joint. It is also noted that because

of the curvature of the header, the weld depth was held constant around the circumference of thetube. For the full penetration configuration, the weld depth is considered to be the full thicknessof the header.

The FE models for the pressure runs depict one-fourth of a tube cross-section and one-half of theheader cross-section for one row of tubes. The models are restricted in the necessary planes sothat further modeling of symmetrical sides of the header/tube is not necessary to apply thepressure loads and retrieve accurate results. For the bending moment analysis, however, it wasnecessary to mirror copy the model to create a full header cross-section and half cross-section of a tube. This change was necessary to correctly apply the forces that mimic a bending moment.



Design Inputs

Figure 2-1Original Configuration 2-D Geometry (Side View)

2-2



Design Inputs

Figure 2-2Partial Penetration (0.243” Weld Depth) 2-D Geometry (Side View)

2-3



Design Inputs

Figure 2-3Partial Penetration (0.225” Weld Depth) 2-D Geometry (Side View)

2-4



Design Inputs

Material Properties

The material specified by EPRI for all three configurations is P91 (9Cr-Mo). The temperaturewas given as 1000ºF for the evaluated header. The material properties for P91 at 1000ºF are

shown in Table 2-1.

Table 2-1Material Properties for P91 Material at 1000ºF

Property Value Unit

Elastic Modulus 25.4E+06 Psi

Secant Coefficient ofThermal Expansion

6.90E-06 in/in/ oF

Poisson's Ratio 0.3

Density 0.277 lb/in3

Loads

Internal Pressure Boundary Conditions

The pressure stress run was made using an internal pressure of 1800 psi. This pressure wasapplied to the inner diameter of the tube and header. It should be noted that this pressure wasalso applied to all faces of the lack of weld fusion gap in the original configuration. Along withthe internal pressure, an equivalent blow-off pressure was applied to the end of the tube andheader cross-section opposite of the tube. Figure 2-4 shows the applied pressures for the originalconfiguration.

Bending Moment Boundary Conditions

To simulate the effects of a bending moment, a force in the y-direction (tube axial direction) wasplaced on each node of the tube end face. The total sum of the absolute value of the nodal forceswas 1000 in-lbs. It should be noted that one half of the modeled tube face was assigned positiveforces and the other half was assigned equal but opposite forces to create a bending moment.

Because no actual value was calculated for the magnitude of this moment, a unit value wasassumed. This allows for easy comparison between the four configurations. Figure 2-5 shows theapplied boundary condition for the bending moment run.

2-5



Design Inputs

Figure 2-4

View of Applied Pressure Loads

2-6



Design Inputs

Figure 2-5

View of Applied Forces for Bending Moment Analysis

2-7



3 RESULTS

Internal Pressure Application Results

A comparison of maximum and minimum stress values due to internal pressure application foreach configuration can be seen in Table 3-1. Due to the geometry of the original design, it hasthe highest header hoop, header axial, and 1

stprincipal stresses. It also has the highest stress

intensity. All of these maximums for the original configuration are located at the end of the gapbetween the tube and header. Because this gap or lack of fusion is located so that it directly sees

internal pressure (as opposed to the repair welds which have a gap on the outer diameter of theheader), it makes sense that the pressure effects will cause high stress concentrations in thislocation. The actual stress concentration effect may be higher than that indicated in the FE resultsas this is dependent on mesh refinement of the FE model.

The three repair configurations tested in this analysis show similar results for the pressureapplication. The full penetration repair option does have slightly lower stress values than the twopartial repair configurations. Even though it doesn’t directly see the effects of internal pressure,the lack of fusion created in the two partial penetration configurations does create enough of aconcentration that its stresses are 2 to 17% higher than the full penetration design. Images thatshow the results of the internal pressure analysis for each configuration are available inAppendix A.

Bending Moment Application Results

The 1000 in-lbs bending moment maximum and minimum stress values and location of maximum stress are located in Table 3-2. As seen in this table, the stress values for the originalconfiguration and partial penetration designs are very similar. The location of maximum stressfor the original configuration is located at the top of the weld where it meets the tube outerdiameter. For the partial penetration designs, the location is in the gap or lack of weld fusionarea. This is to be expected because of the geometry of the weld and therefore the location of thelack of fusion. Similar to what is noted above for the pressure load, the actual stress

concentration effect at this gap may not be completely captured in the FE results.

The full penetration configuration shows significantly less stress than the original or repairdesigns. The stress intensity at the maximum location is over 40% less than the other optionsanalyzed. This can be understood by realizing that the only stress riser is the sharp cornerbetween the OD of the tube and the OD of the header. Since there is no lack of weld fusionassociated with the full penetration geometry, this stress concentration is not present in thisdesign Also, the original design has only the thickness of the original tube (0.180”) at thelocation of highest stress as compared to the thickness of the stub tube (0.437”) for the full

3-1



Results

penetration option. Images that show the results of the bending moment analysis for eachconfiguration are available in Appendix B.

Table 3-1Maximum and Minimum Stresses for Internal Pressure Analysis

Pressure Stress RunStress Comparison Header

Attachment Welds Maximum(ksi)

Minimum(ksi)

Location

Header σhoop

49.2 -4.7 Weld Root at Tube OD (Gap End)

Header σaxial

45.6 -8.8 Weld Root at Tube OD (Gap End)

Principal σ 58.5 1.4 Weld Root at Tube OD (Gap End)

OriginalConfiguration

σINTENSITY

53.6 3.7 Weld Root at Tube OD (Gap End)

Header σhoop

43.3 -5.6 Tube ID at Header ID

Header σaxial

19.0 -2.5 Gap End

Principal σ 46.6 0.0 Gap End

PartialPenetrationRepair

(0.225" WeldDepth)

σINTENSITY

48.5 0.4 Gap End

Header σhoop


Header σaxial

19.1 -3.1 Gap End

Principal σ 44.9 0.0 Gap End

PartialPenetration

Repair(0.243" Weld

Depth)σ

INTENSITY46.0 0.4 Gap End

Header σhoop


Header σaxial

15.9 -1.8 Intersection Header/Tube

Principal σ 42.5 0.1 Tube ID at Header ID

FullPenetration

Repair

σINTENSITY

43.7 0.4 Tube ID at Header ID

3-2



Results

Table 3-2Maximum and Minimum Stresses for Bending Moment Analysis

Bending Moment RunStress Comparison Header

Attachment Welds Maximum

(ksi)

Minimum

(ksi)

Location (Max)

Header σhoop 11.5 -11.5 Top of Weld (Tube OD)

Tube σaxial 13.5 -13.5 Top of Weld (Tube OD)

Principal σ 17.4 -2.2 Top of Weld (Tube OD)

OriginalConfiguration

σINTENSITY 16.5 0.0 Top of Weld (Tube OD)

Header σhoop 9.7 -9.7 Gap End

Tube σaxial 16.4 -16.4 Gap End

Principal σ 17.3 -4.2 Gap End

PartialPenetration

Repair

(0.225" WeldDepth)σINTENSITY 17.6 0.0 Gap End

Header σhoop 10.2 -10.2 Gap End

Tube σaxial 16.5 -16.5 Gap End

Principal σ 17.4 -4.4 Gap End

PartialPenetration

Repair (0.243" Weld

Depth)σINTENSITY 17.5 0.0 Gap End

Header σhoop 9.4 -9.4 Intersection Header/Tube

Tube σaxial 7.4 -7.4 Intersection Header/Tube

Principal σ 10.6 -1.6 Intersection Header/Tube

Full

PenetrationRepair

σINTENSITY 9.6 0.0 Intersection Header/Tube

Conclusions and Recommendations

The results of the internal pressure and bending moment runs show similar results. For both,most of the applicable stresses are highest in the original configuration and lowest in the fullpenetration configuration. This is expected as the original configuration has a smaller tubethickness than the stub tube attachment used in the repair options and also a stress concentrationassociated with the lack of fusion on the internal surface.

The especially high stresses seen in the original configuration during the internal pressureanalysis give some potential insight into the failures seen by HRSG operators. The lack of fusionseems to create a significant stress concentration at the end of this gap and therefore could resultin fatigue type cracking. The bending moment application showed no significantly higherstresses for this configuration over the two partial penetration designs, however.

3-3



Results

3-4

For the repair configurations in the pressure run, it should be noted that all three have verysimilar stress values. The full penetration design has the lowest stresses but the values are notsignificantly different that the two partial penetration options. In the bending moment analysis,however, the full penetration repair does show over 40% less first principal stress and stressintensity than the other three.

After comparing the results of both the internal pressure and bending moment analyses for eachconfiguration, evidence has been established that the replacement of the original header-to-tubeattachment weld with any of the three repair options would reduce stresses for the two conditionsanalyzed in this project. The full penetration option, because it has no lack of fusion, has thelowest stress values of any of the configurations.



National Board Interpretation 04-15

4 NATIONAL BOARD INTERPRETATION 04-15

Following completion of a header-to-tube repair device described in EPRI Report 1010441,many member utilities asked that we work with ASME Boiler & Pressure Vessel Code and/orthe National Board to make sure the new technology could be readily applied. Severaldiscussions were held with ASME Section I members during the 4

thquarter of 2005. It was

recommended that we further discuss the approach with members of the National Board, sincethe new approach is considered at repair instead of new construction.

National Board members were contacted in November 2005. The primary issue of discussion

concentrated on whether the ID repair weld configuration was addressed by one of theconfigurations shown in ASME Section I PW-16. EPRI was asked to provide both an overviewof the technology and supporting information (stress analysis data as reported earlier in thisreport) to NBIC in December. Subsequently, EPRI staff attended the January 2006 NBICmeeting to request an “Interpretation” on utilizing the new technology. The Interpretation 04-15was titled: “Part RD-2060 Utilizing a Flush Patch to Gain Access Window in Pressure RetainingItems.” The official documentation for this is shown in Figure 4-1.

With the Interpretation in hand, utilities should now be able to use the header-to-tube repairtechnology to address attachment cracking in the future.

4-5



National Board Interpretation 04-15

Figure 4-1

Interpretation 04-15 Part RD-2060 Utilizing a Flush Patch to Gain Access Windowin Pressure Retaining Items.

4-6



Internal Tube Repair

5

INTERNAL TUBE REPAIR

Repair techniques for address two different types of HRSG repairs have been developed andreported in EPRI report 1010441. The techniques include repairs for tube-to-tube applicationsand for tube-to-header attachments. EPRI is continuing development in 2006 and has plans todevelop an internal repair method for HRSG tubing. In December 2005, a request for proposalwas sent out to 10 repair vendors/OEMs to initiate the process for developing the internal tuberepair device. Proposals are expected by February 2006, and work should hopefully get

underway by April 2006. The RFP is provided below:

Request For ProposalInternal Repair For HRSG & Boiler Tubing

Purpose of Work

In recent years, flow accelerated corrosion (FAC) has become a significant problem for heatrecovery steam generator (HRSG) tubing particularly at bends or locations where turbulence hasincreased. Damage can occur anywhere along the tube length and with time can result in tubeleakage or blowout. Such failures are costly not only in terms of repair, but also in terms of lostavailability of the plant.

EPRI is currently developing inspection technologies that will enable power producers toexamine tubes at various locations along the tube length. Assuming FAC damage can be locatedusing this technology, an effective method to perform the repair is needed. The purpose of thisRequest for Proposal is to solicit proposals for the development of an Internal Welding RepairDevice (IWRD) for HRSG and Boiler tubing which can be inserted from one end of the tube,transferred along the tube positioned at the exact location of the damage, and used to perform an

ID weld buildup at that location.

Statement of Work

The Internal Welding Repair Device should make use of the gas tungsten arc welding (GTAW),gas metal arc welding (GMAW) or laser beam welding (LBW) process and should be capable of performing a weld buildup at a location along an HRSG tube or a boiler tube. The device should

5-7




be capable of insertion from within a header tube bore location allowing it to be pushed (fromlower header) or dropped (from upper header) to the repair location. Access to the bore regioncan be accomplished by removal of an access port (hole) 180 degrees opposite the bore region of the header.

Transfer along the tube inner diameter from below will require a certain rigidity (enabling thedevice to be pushed) or crawler capability to access the precise location of the repair. The IWRDshould be capable of insertion and repair within tube diameters ranging from a 1.0” to 2.5” ID.Additionally, the repair device should be capable of navigating a bend angle of 25 degrees suchas that shown in Figure 1. The tube-to-tube center spacing is 4.0 inches.

Figure 1. Example header configuration showing a tube bend angle of 25 degrees. Thetube-to-tube spacing is 4.0 inches.

The IWRD and welding system selected for the use should include:

o A power supplyo Automatic voltage control (AVC), if required. If GTAW is used, the bidder should

propose the minimum diameter capability that can incorporate AVC, vision system, self centering device, etc.

o A remote wire feed assembly or wire feed capabilities that can complete a single repairlocations without re-insertion or wire reload

o A weld head capable of operating in the 2G and 5G weld positions.

5-8




o A video probe vision system that provides real-time monitoring of the weld puddle.o A clamping device to center the IWRD at the precise repair location

The RFP should address the following questions:

o How will the tube ID be cleaned/machined/ground prior to welding?o How will the wire be fed to push it over a distance of 50-100ft?o What happens if the tungsten sticks during welding (GTAW process only)? What

additional tooling would be required for rework if the tungsten should stick?o What diameter of wire will be used for the IWRD process?o What video probe vision system will be incorporated into the IWRD system.o How will the final surface be prepared to minimize flow disruptions within the tube

which often lead to a second failure? A detailed specification stipulating surfaceroughness and buildup (reinforcement) will be required in final system.

HRSG Tube Specifications

o Tube ID – 1.0” to 3.0” IDo Tube thickness > 0.125”To Distance IWRD must be inserted into tube to perform repairs:

o If push/pull system, 0-50fto If push only, 0-100fto If pull only, 0-100ft.

o Bend Angle (around dog leg) is 25 degrees—See Figure 1.o Tube spacing (center-to-center) is 4.0 inches.

Period of Performance

The period of performance will be April 2006 to December 2007. Several individualdemonstrations of the IWRD systems capabilities will be required at specified intervals as shownin the Schedule below.

Schedule & Demonstration

EPRI will perform metallography and radiography to assess performance of the selectedcontractor’s ability to meet the following schedule and welding demonstrations.

o Contractor will demonstrate ID tube welding capability on a 1” and 3” diameter tube at adistance of 5 feet from insertion of IWRD on a straight tube. (December 2006)

o Contractor will demonstrate ID tube welding capability on a 1”and 3” diameter tube at adistance of 50 feet from insertion of IWRD (April 2007)

o Contractor will demonstrate ID tube welding capability on a 1” and 3” diameter tube witha radius as shown in Figure 1 at a distance of 50 feet from insertion of IWRD (August2007)

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o Contractor will demonstrate ID tube welding capability on a 1” and 3” diameter tube witha radius as shown in Figure 1 at a distance of 50 feet from insertion of IRD (December2007)

Successful demonstration of each of the above will be considered when the contractor meets bothmetallography and radiography requirements.

Cost Information

Cost-sharing of the IRWD development is encouraged. The proposal should include potentialcost-sharing arrangements that apply to the bidder. Cost sharing will be considered for licensingagreements. EPRI will reward one contract; subcontracting is allowed, although the bidder willbe responsible for subcontracted work.

EPRI Project Manager

David Gandy

Commercialization Plan

The bidder is to propose a commercialization plan.

Evaluation Criteria

See Attachment 1.

List of Invitees

a) Arc Machines, Incb) Polyseude-Astro Arcc) Liburidi-Dimetricsd) Encompass Machines, Ince) Magnatechf) Aggressive Equipmentg) Welding Services, Inc.

h) PCI Energyi) Areva j) GE Services

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A APPENDIX

Original Configuration Pressure Run Images

Figure A-1Header Hoop Stress

A-1



Appendix


A-2



Appendix


A-3



Appendix

Figure A-4

Header Axial Stress

A-4



Appendix

Figure A-5Header Axial Stress

A-5



Appendix


A-6



Appendix

Figure A-71

stPrincipal Stress

A-7



Appendix

Figure A-81

stPrincipal Stress

A-8



Appendix

Figure A-91

stPrincipal Stress

A-9



Appendix

Figure A-10Stress Intensity

A-10



Appendix


A-11



Appendix


A-12



Appendix

Partial Penetration (0.225” Weld Depth) Pressure Run Images


A-13



Appendix


A-14



Appendix


A-15



Appendix


A-16



Appendix


A-17



Appendix


A-18



Appendix

Figure A-191

stPrincipal Stress

A-19



Appendix

Figure A-201

stPrincipal Stress

A-20



Appendix

Figure A-211

stPrincipal Stress

A-21



Appendix


A-22



Appendix


A-23



Appendix


A-24



Appendix

Partial Penetration (0.243” Weld Depth) Pressure Run Images


A-25



Appendix


A-26



Appendix


A-27



Appendix


A-28



Appendix


A-29



Appendix


A-30



Appendix

Figure A-311

stPrincipal Stress

A-31



Appendix

Figure A-321

stPrincipal Stress

A-32



Appendix

Figure A-331

stPrincipal Stress

A-33



Appendix


A-34



Appendix


A-35



Appendix


A-36



Appendix

Full Penetration Pressure Run Images


A-37



Appendix


A-38



Appendix


A-39



Appendix


A-40



Appendix


A-41



Appendix


A-42



Appendix

Figure A-431

stPrincipal Stress

A-43



Appendix

Figure A-441

stPrincipal Stress

A-44



Appendix

Figure A-451

stPrincipal Stress

A-45



Appendix


A-46



Appendix


A-47



Appendix


A-48



B APPENDIX

Original Configuration Bending Moment Analysis Images

Figure B-1Header Hoop Stress

B-1



Appendix


B-2




B-3



Appendix

Figure B-41

stPrincipal Stress

B-4



Figure B-51

stPrincipal Stress

B-5



Appendix

Figure B-61

stPrincipal Stress

B-6



Figure B-7Stress Intensity

B-7



Appendix


B-8




B-9



Appendix

Figure B-10Tube Axial Stress

B-10




B-11



Appendix


B-12




B-13



Appendix

Figure B-14Tube Hoop Stress

B-14



Partial Penetration (0.225” Weld Depth) Bending Moment Analysis Images


B-15



Appendix


B-16



Figure B-17Header Hoop Stres

B-17



Appendix

Figure B-181

stPrincipal Stress

B-18



Figure B-191

stPrincipal Stress

B-19



Appendix

Figure B-201

stPrincipal Stress

B-20




B-21



Appendix


B-22




B-23



Appendix


B-24




B-25



Appendix


B-26




B-27



Appendix


B-28



Partial Penetration (0.243” Weld Depth) Bending Moment Analysis Images


B-29



Appendix


B-30




B-31



Appendix

Figure B-321

stPrincipal Stress

B-32



Figure B-331

stPrincipal Stress

B-33



Appendix

Figure B-341

stPrincipal Stress

B-34




B-35



Appendix


B-36




B-37



Appendix


B-38




B-39



Appendix


B-40




B-41



Appendix


B-42



Full Penetration Bending Moment Analysis Images


B-43



Appendix


B-44




B-45



Appendix

Figure B-461

STPrincipal Stress

B-46



Figure B-471

STPrincipal Stress

B-47



Appendix

Figure B-481

STPrincipal Stress

B-48




B-49




B-51



Appendix


B-52




B-53



Appendix


B-54



Export Control Restrictions

Access to and use of EPRI Intellectual Property is

granted with the specific understanding and

requirement that responsibility for ensuring full

compliance with all applicable U.S. and foreign export

laws and regulations is being undertaken by you and

your company. This includes an obligation to ensurethat any individual receiving access hereunder who is

not a U.S. citizen or permanent U.S. resident is

permitted access under applicable U.S. and foreign

export laws and regulations. In the event you are

uncertain whether you or your company may lawfully

obtain access to this EPRI Intellectual Property, you

acknowledge that it is your obligation to consult with

your company’s legal counsel to determine whether

this access is lawful. Although EPRI may make

available on a case-by-case basis an informal

assessment of the applicable U.S. export classification

for specific EPRI Intellectual Property, you and your

company acknowledge that this assessment is solely

for informational purposes and not for reliance

purposes. You and your company acknowledge that it

is still the obligation of you and your company to make

your own assessment of the applicable U.S. export

classification and ensure compliance accordingly. You

and your company understand and acknowledge your

obligations to make a prompt report to EPRI and the

appropriate authorities regarding any access to or use

of EPRI Intellectual Property hereunder that may be in

violation of applicable U.S. or foreign export laws or

regulations.

The Electric Power Research Institute (EPRI)

The Electric Power Research Institute (EPRI), with

major locations in Palo Alto, California, and Charlotte,

North Carolina, was established in 1973 as an

independent, nonprofit center for public interest energy

and environmental research. EPRI brings together

members, participants, the Institute’s scientists andengineers, and other leading experts to work

collaboratively on solutions to the challenges of electric

power. These solutions span nearly every area of

electricity generation, delivery, and use, including

health, safety, and environment. EPRI’s members

represent over 90% of the electricity generated in the

United States. International participation represents

nearly 15% of EPRI’s total research, development, and

demonstration program.

Together…Shaping the Future of Electricity

Devt of Tube Repair Techniques for HR Steam Generators

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