RS-23-058, Submittal of Sixth Inservice Inspection Interval Relief Request I6R-11 Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges

Submittal of Sixth Inservice Inspection Interval Relief Request I6R-11 Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges

ML23114A378
Person / Time
Site:	Quad Cities
Issue date:	04/24/2023
From:	Simpson P Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
RS-23-058
Download: ML23114A378 (1)

Text

Constellation~

April 24, 2023 RS-23-058 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Quad Cities Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-30 NRC Docket No. 50-265 4300 Winfield Road Warrenville, IL 60555 630 657 2000 Office 10 CFR 50.55a(z)(1)

Subject:

Submittal of Sixth lnservice Inspection Interval Relief Request I6R-11 Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges In accordance with 10 CFR 50.55a, "Codes and standards," paragraph (z)(1 ), Constellation Energy Generation (CEG), LLC requests U.S. Nuclear Regulatory Commission (NRC) exigent approval of the attached relief request I6R-11, Revision 0, for repair(s) of the reactor pressure vessel head to shell flanges at Quad Cities Nuclear Power Station (QCNPS),

Unit 2. CEG has determined that the proposed alternatives provide an acceptable level of quality and safety as required by 10 CFR 50.55a(z)(1 ).

These proposed alternatives, contained in Attachment 1, apply to maintenance outage Q2M30 for the sixth 10-year lnservice Inspection (ISi) interval. The sixth 10-year ISi interval for QCNPS, Unit 2 began on April 2, 2023, and will conclude on April 1, 2033. The sixth interval complies with the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, 2017 Edition.

QCNPS, Unit 2 has been tracking unidentified leakage in the drywell and has planned a maintenance outage to repair the leak. This leakage is assumed to be coming from the mating surfaces of the reactor pressure vessel head and shell flanges due to steam cutting of the flange via a failure with the vessel flange O-ring. The planned weld repair(s) involves using Ambient Temperature Temper Bead (ATTB) welding in accordance with the requirements of ASME Code Case N-638-10. As an alternative to performing the required nondestructive examinations at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the completion of the third tempering layer, CEG proposes performing the nondestructive examinations after completion of the repair(s). CEG is also requesting an alternative to the requirement to perform a volumetric examination of the welded region(s) as described in Attachment 1.

CEG requests authorization of this request by May 12, 2023 in support of maintenance outage Q2M30.

U.S. Nuclear Regulatory Commission April 24, 2023 Page 2 There are no regulatory commitments contained within this letter. Should you have any questions concerning this letter, please contact Ms. Rebecca L. Steinman at 630-657-2831.

Respectfully, Patrick R. Simpson Sr. Manager Licensing Constellation Energy Generation, LLC Attachments:

1 10 CFR 50.55a Relief Request I6R-11, Revision 0 2

White Paper: Ambient Temperature Temper Bead-Elimination of 48-Hour Hold Time from N-888 When using Austenitic Filler Material cc:

Regional Administrator - NRC Region Ill NRC Senior Resident Inspector - Quad Cities Nuclear Power Station 10 CFR 50.55a Request Number I6R-11, Revision 0 Page 1 of 5 Proposed Alternatives for a Temper Bead Weld Repair of the Mating Surfaces of the Reactor Pressure Vessel Head and Shell Flanges In Accordance with 10 CFR 50.55a(z)(1),

"Alternate Provides Acceptable Level of Quality and Safety"

1.

ASME Code Components Affected Code Class:

1

Reference:

Code Case N-638-10 Examination Category:

N/A Item Number:

N/A

==

Description:==

Mating Surfaces Between Reactor Pressure Vessel (RPV) Head and Shell Flanges Materials:

Flanges - SA-336 RPV Head and Shell - SA-302 GR. B Weld Metal - Alloy 82 filler material Drawing Numbers:

151824 - Closure Head Assembly 151826 - Lower Head Assembly 151832 - Shell Flange Details

2.

Applicable Code Edition and Addenda

The code of record for the sixth 10-year Inservice Inspection (ISI) Program interval at Quad Cities Nuclear Power Station (QCNPS) is the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code),Section XI, 2017 Edition. The sixth 10-year interval is effective from April 2, 2023, through April 1, 2033.

The code of construction for the RPV is the ASME Code,Section III, 1965 Edition through Summer 1965 Addenda.

3.

Applicable Code Requirement

QCNPS implements ASME Code Case N-638-10 within the stations sixth interval ISI Program.

Code Case N-638-10 is approved in Regulatory Guide (RG) 1.147, Revision 20, Table 1. This Code Case is an approved alternative to Section XI IWA-4400 to use an automatic or machine gas tungsten arc welding (GTAW) temper bead technique to repair certain materials.

The proposed repair(s) will be performed by using Ambient Temperature Temper Bead (ATTB) welding in accordance with ASME Code Case N-638-10. Paragraph 4(a)(2), of Code Case N-638-10 requires the final NDE be performed 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the completion of the third tempering layer. Technical justification has been developed to allow non-destructive examination (NDE) methods to be performed after completion of the weld repair, without waiting for the 48-hour hold time. Technical justification for eliminating the 48-hour hold time is located in.

In accordance with Code Case N-638-10, Paragraph 4(a)(2), examination of the welded region shall include both volumetric and surface examination methods.

10 CFR 50.55a Request Number I6R-11, Revision 0 Page 2 of 5

4.

Reason for Request

Unidentified leakage into the drywell at a current rate of approximately 3.3 gal/minute has been detected in the QCNPS Unit 2 drywell floor drains. As a result, CEG has decided to perform a maintenance outage to locate and repair the leakage. The site has not yet performed primary containment entry to positively confirm the source of the leakage but based on analysis of primary containment temperature and leakage monitoring system data, it is postulated that the O-rings which seal the RPV head to shell flange may have failed with the potential for steam cutting of the adjacent surface(s). This relief request is being submitted as a contingency repair plan prior to entering the maintenance outage, in anticipation that this is the source of the leakage. A mold of the affected areas will be taken to determine the area(s) and depth of repair necessary. Repair options will be chosen based upon the discovery and sizing of the affected area(s).

Constellation Energy Generation, LLC (CEG) proposes to perform emergent weld repair(s) at QCNPS Unit 2 using ATTB welding. The affected area(s) needing repair will be mechanically prepared to support the necessary welding. Welding will be performed using the machine GTAW process with Alloy 82 filler material. After the completion of each layer, a surface exam will be performed in accordance with the rules of ASME Section III. CEG is requesting the use of progressive surface exams as an alternative to the requirement of N-638-10 to perform a volumetric examination of the welded region.

The NRC has approved N-638-10 to allow ATTB welding with austenitic filler materials within 1/8" of or on ferritic materials without the requirement for preheat or post-weld heat treatment. The current version of this Code Case requires that the completed weld be at ambient temperature for at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> prior to NDE. Technical justification for austenitic filler materials has been developed to allow NDE methods to be performed after completion of the weld repair, without waiting for the 48-hour hold time.

5.

Proposed Alternative and Basis for Use Proposed Alternative Pursuant to 10 CFR 50.55a(z)(1), CEG proposes alternatives to Code Case N-638-10. An alternative is proposed to the requirement of N-638-10, Paragraph 4(a)(2), that requires a 48-hour hold time prior to performing NDE. CEG intends to perform weld repair(s) with austenitic filler material in accordance with the ATTB welding technique of Code Case N-638-10, with two exceptions. As an alternative to performing the required NDE at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the completed weld has reached ambient temperature, CEG proposes to perform the NDE methods after completion of the weld repair(s). Additionally, CEG proposes to perform progressive surface examinations in lieu of the required volumetric examination in Code Case N-638-10. The bases for these alternatives are provided below.

CEG plans to apply weld repair(s) of the RPV head and shell flanges by using austenitic Alloy 82 filler material over the repair area(s). Each weld repair will be a minimum of 3 layers per the temper bead rules in Code Case N-638-10. The ATTB technique of ASME Section XI Code Case N-638-10 has been approved by the NRC in RG 1.147.

10 CFR 50.55a Request Number I6R-11, Revision 0 Page 3 of 5 Basis for Elimination of the Ambient 48-Hour Hold Time Removal of the 48-hour hold is consistent with the requirements of ASME Code Case N-888-1 and is supported by the white paper that was developed for the proposed change to that Code Case. Although this ASME Code Case is not approved in RG 1.147, it has been approved by the ASME Section XI Standards Committee. Attachment 2 provides the white paper supporting elimination of the 48-hour hold in Code Case N-888-1. Since Case N-888 is the culmination of temper bead code cases that have been produced over the years, combining requirements from N-638, N-839, and Appendix I in cases such as N-740 and N-754, etc., the justification is also applicable to the planned use of Code Case N-638-10 at QCNPS Unit 2.

Basis for Performing Surface Examination In lieu of Volumetric Examination As an alternative to the final volumetric inspection, CEG proposes to perform progressive surface exams with the Liquid Dye Penetrant Examination (PT) process on the repair area(s). A minimum of three weld layers will be applied for each repair. PT examination will be performed on 100% of each layers surface. Each layer will satisfy the PT acceptance criteria for welds of Section III, NB-5300. The adjacent base material will satisfy the surface examination acceptance criteria for base material of Section III, NB-2500. All NDE examinations will be performed with qualified examiners and a procedure qualified in accordance with ASME Section XI.

The ASME Code,Section III, NB-5300 liquid dye penetrant (PT) acceptance criteria are considered acceptable in this application for the following reasons. The 3/16" dimension for rounded PT indication is the dimension of the liquid dye that has escaped the surface indication, not the actual through wall dimension of the surface breaking indication. Each weld layer is approximately 0.07" thick. Weld fabrication defects would not be expected to be more than one weld layer deep based upon the welding application process. The installation of each repair uses a developed and refined approach to address weldability issues with Alloy 82. The installation vendor is using optimized welding procedures in combination with interlayer grinding and a proprietary shielding gas system to minimize weldability concerns.

The original code requirement for the RPV was ASME Section Ill Division 1, 1965 Edition through Summer 1965 Addenda. Later editions of this code allow for progressive surface examination for temper bead repairs to partial penetration welds, in lieu of volumetric examination, if meaningful results cannot be obtained (an example is provided in Reference 8.3). This provides a precedent for the suitability of progressive surface exams in lieu of volumetric exams. As shown in the simplified flange configuration drawing provided below, it is not feasible to perform volumetric inspections (e.g.; UT and RT) due to the thickness, geometry, and orientation of the reactor vessel flanges.

6.

Conclusion 10 CFR 50.55a Request Number I6R-11, Revision 0 Page 4 of 5 Figure 1 Simplified Flange Configuration The temper bead technique is an effective tool for performing repairs on carbon and low alloy steel (P-No. 1 and P-No. 3) materials. Code Case N-638-10 provisions allow for ambient temperature temper bead welding with no post weld heat treatment. However, the 48-hour hold prior to performing the final weld acceptance NDE has remained a Code Case requirement. summarizes the technical basis to eliminate the 48-hour delay for examining temper bead welding when using austenitic filler materials. The data and testing performed shows that when austenitic weld metal is used the level of diffusible hydrogen content in the ferritic base metal heat affected area (HAZ) is too low to promote hydrogen-induced cracking (HIC).

Therefore, the 48-hour hold requirement in Code Case N-638-10 is not necessary to prevent HIC.

The precedents listed in Section 7 of this relief request provide a basis for concluding that the elimination of the 48-hour hold prior to performing NOE and the use of progressive liquid penetrant examination for the QCNPS weld repair(s) provides reasonable assurance of structural integrity.

Duration of Proposed Alternative These alternatives are proposed for use during the weld repair(s) expected to be performed on the RPV head and shell flanges during the Unit 2 forced maintenance outage Q2M30.

7.

Precedent The following relief request was previously approved to eliminate the 48-hour hold time specified in Code Case N-638-10:

Letter from David Gudger (Constellation Energy Generation, LLC) to U.S. NRC, "Submittal of Emergency Relief Request ISR-11 Concerning the Installation of a Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld (32-WD-208)," dated March 24, 2023, ADAMS Accession No. ML23083B991.

10 CFR 50.55a Request Number I6R-11, Revision 0 Page 5 of 5 o Verbal NRC authorization was issued on March 31, 2023 (ADAMS Accession No. ML23090A130).

The following relief request was previously approved to perform progressive surface exams in lieu of volumetric examinations:

Letter from Dianne Strand (NextEra Energy) to U.S. NRC, Relief Request 4RA-22-001, Proposed Alternative in Accordance with 10 CFR 50.55a(z)(2), dated February 24, 2023, ADAMS Accession No. ML23055A289.

o The corresponding Safety Evaluation was issued on March 23, 2023 (ADAMS Accession No. ML23073A156).

8.

References 8.1 ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components,"

2017 Edition.

8.2 ASME Code Case N-638-10, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1, dated May 6, 2019.

8.3 ASME Section Ill, Rules for Construction of Nuclear Facility Components Division 1, Article NB-4622.11(d)(3) 1998 Edition, No Addenda.

ATTACHMENT 2 Ambient Temperature Temper Bead-Elimination of 48-Hour Hold Time from N-888 When using Austenitic Filler Material White Paper 1.0 Introduction and Background In welding, the presence of hydrogen in the weld metal or heat affected zone (HAZ) can cause hydrogen-induced cracking (HIC) occurring phenomena that occurs after the weldment has cooled to at or near room temperature. HIC is largely dependent upon three main factors, diffusible hydrogen, residual stress and susceptible microstructure. There are many theories on the mechanism for HIC, however, it is well understood that HIC requires simultaneous presence of a threshold level of hydrogen, a susceptible brittle microstructure and tensile stress. Additionally, the temperature must be in the range of 32 to 212°F (0 to 100°C). Elimination of just one of these four contributing factors will prevent HIC. [1]

Two early overlay (WOL) repairs involving temper bead welding were applied to two core spray nozzle-to-safe end joints at the Vermont Yankee boiling water reactor (BWR) in 1986 to mitigate intergranular stress corrosion cracking [2]. To avoid post weld heat treatment, temper bead was deployed when installing the repair overlay on the low alloy steel SA-508 Class 2 (P-No. 3 Group 3) reactor pressure vessel nozzle. This early application of temper bead welding required elevated preheat and a post weld hydrogen bake.

As the industry experienced an increased need for temper bead welding the requirement for preheating and post weld bake made temper bead welding complicated. EPRI responded to the industry concern and conducted studies that demonstrated that repair to low alloy steel pressure vessel components could be made without the need for preheat or post weld bake [3,4]. As a result of these studies the preheat and post weld bake requirements were not included in Case N-638 for ambient temperature temper bead welding with machine GTAW.

Deployment of the ambient temperature temper bead technique has been highly successful for many years with no evidence of HIC detected by nondestructive examination (NDE). During the past twenty years, many temper bead weld overlay repairs were successfully performed on BWRs and PWRs using ambient temperature temper bead technique, as illustrated in Table 1. The operating experience shows that with hundreds of ambient temperature temper bead applications, there has not been a single reported occurrence of hydrogen induced cracking.

Case N-888 is the culmination of temper bead code cases that have been produced over the years, combining requirements from N-638, N-839, and Appendix I in cases such as N-740 and N-754, etc. Case N-888 applies to temper bead of P-No. 1 or P-No. 3 materials and their associated welds or welds joining P-No. 8 or P-No. 43 materials to P-No. 1 or P-No 3 materials. Additionally, Case N-888 provides provisions to allow for ambient temperature preheat with no post weld bake.

However, the post weld 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold at ambient temperature has remained as a requirement in N-888. This 48-hour delay between welding completion and cooling to ambient temperature and the final nondestructive examination (NDE) of the fully welded component is intended to assure detection of delayed hydrogen cracking that is known to occur up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the weldment is at ambient temperature.

Page 2 of 11 The post weld 48-hour delay following cooling to ambient temperature has resulted in a considerable cost burden to utilities. As there are significant economic advantages associated with eliminating the 48-hour hold time and immediately performing NDE following the completed weld, it is important to determine the technical advantages and disadvantages of making such a change.

2.0 Objective The objective of this white paper is to provide technical justification to eliminate the 48-hour delay when using austenitic filler materials in the temper bead welding process for P-No. 1 and P-No. 3 ferritic materials. The industry and regulatory technical concerns related to this change are examined and the technical bases for changing the requirements for the 48-hour delay are presented. Discussion from white paper for Ambient Temperature Temperbead Weld Overlay Gas Tungsten Arc Welding by Hermann and Associates [9] are included in this white paper.

If adopted, it is expected that the change in the 48-hour delay requirement will become part of a revision to the current ASME Section XI Case N-888 that currently allows for ambient temperature temper bead repairs but requires 48-hour delay after the initial three temper bead layers prior to final NDE.

3.0 Technical Issues Related to the 48 Hour Delay The reasons for performing the final NDE after the 48-hour delay is the recognition that alloy steels can become susceptible to HIC. There are two primary weld cracking mechanisms of concern for low alloy steels during cooling or after reaching ambient temperature. These are cold cracking of high restraint geometries (weld shrinkage-induced) and hydrogen induced cracking (HIC), often referred to as hydrogen delayed cracking. Cold cracking occurs immediately as the weldment cools to ambient temperature. In contrast, HIC can occur immediately during cooling to ambient temperature or up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after reaching ambient temperature. Cold cracking that occurs with high restraint weldments would therefore be detected by NDE performed immediately after the weldment is complete.

EPRI studies [4] have indicated that cold cracking occurs under conditions of high geometrical restraint especially where low toughness HAZs are potentially present.

Restraint mechanisms can occur either hot (resulting in intergranular or interdendritic cracking), or cold (resulting in transgranular cracking of material having marginal toughness). Cold cracking occurs immediately as the weld deposit cools to ambient temperature. Proper joint design, appropriate welding procedures and bead sequences, are practical solutions that avoid critical cold cracking conditions. This form of cracking is addressed effectively by the ASME code guidance including welding procedure qualification testing and by in-process and or post-weld inspections.

The other form of cracking at ambient temperature, which is the focus of this white paper, is HIC.

This cracking mechanism manifests itself as intergranular cracking of prior austenite grain boundaries and in contrast to cold cracking generally occurs during welding, but also up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after cooling to ambient temperature. It is produced by the action of internal tensile stresses acting on low toughness HAZs (generally characterized by inadequate tempering of weld related transformation products). The most widely accepted theory suggests that the internal stresses will be produced from localized buildup of monatomic hydrogen. Monatomic hydrogen can be entrapped during weld solidification, and will tend to migrate, over time, to prior austenite grain boundaries or other microstructure defect locations. As concentrations build, the monatomic hydrogen will recombine to form molecular hydrogen, thus generating highly localized internal stresses at these internal defect locations. Monatomic hydrogen is produced when moisture or hydrocarbons interact with the welding arc and molten weld pool.

Date 2002 2002 2002 2002 2002 2002 2002 2002 2003 2003 2003 2003 2003 2003 2003 2003 2004 2004 2004 2004 2004 2004 2005 2005 2005 2005 2005 2005 2005 2005 2005 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2006 2007 2007 2007 2007 2007 2008 2008 2008 2008 2009 2009 Page 3 of 11 Table 1: Successfully Implemented Repairs Completed Using Temper Bead Technique from 2002-2021 Plant Component (Qty.)

Oconee1 Mid-Wall RVH Repair (15)

ANO' Mid-Wall RVH Repair (6)

Oyster Creek' Recirculation outlet nozzle (1)

Peach Bottom Units 2 & 32 Core spray, recirculation outlet, and CRD retum nozzles Calvert Cliff2 Healer Sleeve Repairs (Pads) (~50)

Oconee1 Mid-Wall RVH Repair (2)

Davis-a ess e 1 Mid-Wall RVH Repair (5)

Millstone' Mid-Wall RVH Repair (3)

Palo Verde 12 Heater Sleeve Repairs -Pads (36)

Pilgrim2 Core spray nozzle and CRD return nozzle TMI Unit 1' Hot leg and Surge line nozzle Ringhals1 112 Nozzle with Stru ctural Pad (2)

Crystal River' 1/2 Nozzle with Stru ctural Pad (3)

South Texas' 1 /2 Nozzle with Stru ctural Pad (2)

Millstone' Mid-Wall RVH Repair (8)

St. Lucie1 Mid-Wall RVH Repair (2)

Palo Verde 22 Heater Sleeve Repairs -Pads (34)

Susquehanna Unit 1' Recirculation inlet and outlet nozzles Hope Creek1 SWOL (1)

Palisades1 Mid-Wall RVH Repair (2)

Point Beach' Mid-Wall RVH Repair (1)

ANO' Mid-Wall RVH Repair (1)

Palo Verde 32 36 Healer Sleeve Repairs - Pads (36)

AN02 Mid Wall heater sleeve repair Waterford2 Mid Wall heater sleeve repair Calvert Cliffs Unit 2' Hot Leg Drain and Cold Leg Letdown Nozzles DC Cook Unit 12 Pressurizer Safety Nozzle TPC Kuosheng2 N1 Nozzle SONGS 32 Heater Sleeve Repairs -Pads (~29)

Three Mile lsland1 SWOL (1)

St. Lucie1 Mid-Wall RVH Repair (3)

SONGS 22 Healer Sleeve Repairs -Pads (~30)

Davis Besse" Hot and Cold Leg SONGS 22 Pressurizer Nozzles (6)

Millstone 32 Pressurizer Nozzles (6)

SONGS 32 Pressurizer Nozzles (6)

Oconee 1' Pressurizer Nozzles (6)

Beaver Valley 22 Pressurizer Nozzles (6)

Byron 23 Pressurizer Nozzles (6)

Wolf Creek3 Pressurizer Nozzles (6)

McGuire2 Pressurizer Nozzles (6)

DC Cook1 SWOL (4)

Gallaway3 Pressurizer Nozzles (6)

St. Lucie' SWOL (4)

Crystal River*

SWOL (4)

Three Mile lsland1 SWOL (4)

North Anna' SWOL (4)

Prairie Island' SWOL (1)

Diablo Ganyon1 SWOL (6)

Diablo canyon*

SWOL (4)

Seabrook' SWOL (4)

Three Mile Island' SWOL (1)

Three Mile lsland1 Full Nozzle with Structural Pad (1)

Date 2009 2009 2010 2010 2010 2010 2011 2011 2011 2011 2011 2011 2011 2012 2012 Page 4 of 11 Plant Crystal River 1 Palisades1 Oconee*

Krsko 1 Tiha nge1 Davis-8 ess e 1 Hatch" Talen Energy CorporationA Monticello' Tllree Mile Island" Doel Tiha nge' St. Lucie1 North Anna4 Palo Verde' Component (Qty.)

SWOL (1)

Mid-Wall RVH Repair (2)

U3 Letdown WOL (1)

SWOL (5)

SWOL(1)

Mid-Wall RVH Repair (24)

Nozzle WOL (1)

N5 core spray nozzles Emergent WOL (1)

TMI PZR Spray Nozzle (1)

SWOL (1)

SWOL (1) 112 Nozzle with structural Pad (30)

SG Nozzle WOLS (3)

Small Bore CL Nozzles WOL 2012 Grand Gulf' Reactor Vessel Nozzle Contouring and N6 Weld Ove rlay 2012 Doel1 2012 Calvert Cliffs 1 2012 Quad Cities' 2012 Harris Nuclear Plant 1 2013 Fartey4 2013 Oconee*

2013 Hope Creek*

2013 Tllree Mile lsland 1 2013 Palo Verde' 2013 Harris Nuclear Plant' 2015 Harris Nuclear Plant1 2015 Hatch4 2015 Millstone*

2015 Hatch' 2016 Harris Nuclear Plant' 2017 F itzpatric.k4 2017 Limerick' 2018 Waterford' 2018 Palisades1 2018 Doel1 2018 Harris Nuclear Plant1 2018 Brunswick' 2020 Peach Bottom 1 2020 Palisades1 202 1 Oconee*

202 1 AN0-2 1 N otes:

f e.1{ erience ovidedb Opera 1llg p

pr y Steve McCracken Travis Olson (Framatome)

(1) Fran:iatome (2) Unknovm (3) PCI (4) AZZ Specialty Welding SWOL(1)

Mid-Wall Przr Heater Repair (119) 112 Nozzle with Structural Pad (1)

Mid-Wall RVH Repair (4)

Unit 2 FAC Pipe Replacement and WOL Hot/Cold Leg Small Bore Alloy 600 Emergent N5A WOL SWOL(1) 112 Nozzle with Structural Pad (1)

Mid-Wall RVH Repair (2)

Mid-Wall RVH Repair (3)

N4AWOL 2" Drain WOL Recirc (N2) WOL Mid-Wall RVH Repair (4)

RHR WOL 1/2 Nozzle with Structural Pad (1)

Emergent Drain Nozzle WOLs (2)

Mid-Wall RVH Repair (3)

Mid-Wall RVH Repair (16)

Mid-Wall RVH Repair (1)

SWOL (2) 112 Nozzle with Structural Pad (1 )

Mid-Wall RVH Repair (2)

Complex nozzle pads on RCS piping Mid-Wall RVH Repair (1)

(EPRI), Darren Barborak (EP RI, formerl with AZ y

Z), and The concerns with and driving factors that cause hydrogen induced cracking have been identified.

These issues are fundamental welding and heat treatment issues related to temper bead welding, requiring a technical resolution prior to modification of the current ASME Code Cases N-888 by the ASME Code and the technical community. Specific concerns relate to the following issues:

-Microstructure

-Sources for Hydrogen Introduction

-Diffusivity and Solubility of Hydrogen In the following discussion of this white paper each of these factors is briefly described to provide insight into the impact and proper management of these factors that cause HIC.

Page 5 of 11 4.0 Discussion of Technical Issues Related to the 48 Hour Delay Microstructure:

C-Mn and low alloy steels can have a range of weld microstructures which is dependent upon both specific composition of the steel and the welding process/parameters used. Generally, untempered martensitic and untempered bainitic microstructures are the most susceptible to hydrogen cracking.

These microstructures are produced when rapid cooling occurs from the dynamic upper critical (Ac3) transformation temperature [1]. Generally, a critical hardness level necessary to promote hydrogen cracking is on the order of Rc 35 for materials with high hydrogen and Rc 45 for low level of hydrogen. Maintaining hardness levels below these thresholds generally avoids hydrogen cracking [1].

EPRI has examined in detail the effects of welding on the hardening of low alloy steels. The microstructure evaluations and hardness measurements discussed in EPRI reports [4, 5, 6] have described the effects of temper bead welding on the toughness and hardness of P-No. 3 materials.

The research results have illustrated that the microstructure in the low alloy steel (P-No. 3) beneath the temper bead WOL in the weld HAZ consists of a structure that is tempered martensite or tempered bainite and has maximum hardness at a distance of 2 to 3 mm (80 to 120 mils) beneath the surface of the order of 280 to 300 KHN (28 to 30 Rc) or lower. The research outlines that the microstructure resulting from temper bead welding is highly resistant to HIC. Additionally, hardness would not be a concern provided there are adequate hydrogen controls are in place.

Furthermore, materials having face-centered-cubic (FCC) crystal structures such as austenitic stainless steels (300 series) and nickel base alloys such as Inconel are not susceptible to hydrogen induced cracking. The reason is that FCC atomic structures have ample unit cell volume space to accommodate atomic (diffusible) hydrogen. It is noted that the diffusion of hydrogen at a given temperature is slightly higher in body-centered-cubic (BCC) materials, ferritic steels, than it is in FCC austenitic materials. The FCC crystal structure has increased capacity to strain significantly without cracking (ductility) providing acceptable levels of toughness capable of resisting HIC. The inherent ability to deform and accommodate diffusible hydrogen are the reasons austenitic stainless steel and nickel base coated electrodes do not have low hydrogen designators that are found for ferritic weld materials [6]. Since the ferritic HAZ is in a tempered condition and an FCC filler material is used, a susceptible microstructure susceptible to HIC is highly unlikely.

Presence/sources of Hydrogen:

Hydrogen can be introduced into the weld from several sources. These include 1) hydrogen in the original base material, 2) moisture in electrode coatings and fluxes, 3) organic contaminants (grease or oils), 4) hydrogen in the shielding gas and 5) humidity in the atmosphere.

The reduction of diffusible hydrogen in temper bead and non-temper bead weldments begins with implementing low hydrogen weld practices. These practices originate with Federal requirements that nuclear utilities control special processes such as welding and design and fabricate components to various codes and standards. These requirements, when followed, will effectively eliminate the contamination, and minimize the environment pathways.

Cleanliness of surfaces to be welded are mandated by Code and subsequently implemented via adherence to sound welding programs. The controls and requirements for cleanliness of the welded surface at nuclear utilities significantly reduce the likelihood of hydrogen entering the weld from surface contamination. Furthermore, repair and replacement applications typically deal with components that have been at operating temperatures above 390ºF (200ºC) for many years and any hydrogen present in the base material would have diffused from the steel and escaped to the Page 6 of 11 atmosphere. Thus, surface contaminants and the base materials are not expected to be a significant source of diffusible hydrogen.

For SMAW, main pathway for diffusible hydrogen to enter the weldment will be the electrode coating. Welding programs primarily maintain low moisture in electrode coatings through procurement via an approved supplier, controlled storage conditions, and conservative exposure durations. The conservative exposure duration and coatings that resist moisture uptake minimize the amount of additional moisture in the coated electrode taking into consideration that moisture uptake is a function of time, temperature, and relative humidity. Extensive testing by the EPRI Welding and Repair Technology Center shows there is an extremely low probability of HIC with H4 and H4R electrodes. EPRI performed diffusible hydrogen analysis per AWS A4.3 via gas chromatography on thirteen commercially available electrodes. Electrodes with AWS E7018, E8018 and E9018 from multiple vendors exposed at 27°C at 80% relative humidity (HR) for exposure times from 0 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Many of the electrodes did not have R moisture resistant coating.

Figure 1 shows EPRI diffusible hydrogen test results for the thirteen lots of low hydrogen electrodes. All H4R electrodes exhibited < 16ml/100g of diffusible hydrogen at 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of exposure. Figure 3 shows that new electrodes without exposure have < 2ml/100g diffusible hydrogen. Only one of the electrodes tested at the extremely aggressive 27°C and 80% Relative Humidity (HR) 72-hour exposure had diffusible hydrogen > 4 ml/100g. This demonstrates that exposure limits in the field of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or less is adequate to assure electrodes maintain the H4R limit. Ferritic electrodes were verified to have less than 4ml/100g diffusible hydrogen [6]. Testing verifies that ambient temperature is acceptable, post weld hydrogen bakeout is not needed, and a 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold at ambient temperature prior to performing final NDE is unnecessary and diffusible hydrogen levels will be below any susceptibility threshold that supports HIC.

For GTAW, EPRI performed studies investigating the diffusion of hydrogen into low alloy pressure vessel steels [4]. Due to the little information published at the time, EPRI decided to generate experimental data that would provide information on the levels of diffusible hydrogen associated with GTAW welding. The experimentation included individual sets of diffusible hydrogen tests as follows:

1. determination of diffusible hydrogen levels for the GTAW process under severe welding and environmental conditions simulating (or exceeding) repair welding conditions which may be expected in a nuclear plant.

2. measurement of diffusible hydrogen levels for various shieling gas dew point temperatures

3. examination of diffusible hydrogen levels for modern off-the-shelf filler wires Discussion of these items can be found in the EPRI documents and will not be reiterated in this report. The results demonstrate that introducing hydrogen is unlikely with the GTAW process. The typical hydrogen content for the GTAW process is less than 1.0mL/100g. Therefore, hydrogen cracking is extremely unlikely.

18 16 tiii 14 0

0....

-12 E -

~ 10 QI) 0...

"'O 8

c QI

'.j5 6

.2 0

4 2

0 Page 7 of 11

__ L __ 2 __ J ___ L __ L __ l __ J __ J j

Region Considered "Low Hydrogen" Code Case N-839 Exposure Limits 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />s-E70XX and 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />s-E80XX/E90XX I t,.

~.

a Q

+

wwwwwwwwwwwwwwwwwwwwwwww 0

10 20

(\\ Vendor A E7018 C Vendor B E7018-H4R

+ Vendor E E8018-C3H4

• Vendor D E9018-B3H4R e Vendor C E9018-B3 30 40 so Exposure Time (hr)

.l Vendor A E7018 X Vendor C E7018-R

- vendor C E8018-C3H4

• Vendor F E9018-B3H4R 60 70 O Vendor B E7018-H4R Vendor D E8018-C3H4 X VendorC E8018-NMH4 Vendor C E9018-B3H4R Figure 1.

Results of EPRI diffusible hydrogen testing at 27°C 80%

Relative Humidity (HR) for zero to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of exposure [6]

0) 0 0

6

..---E

~5 Q.)

0) 0 "O 4 I

Q.) 3

.0

• c:;;

~ 2 i:5 "O

Q.)

..... 1

(/)

ro Q.)

~ 0 A

B C

Vendor 80°F-80%RH 11110 hours 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />

~

72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> D

Figure 2.

Graph showing slight increase of diffusible hydrogen after exposure of 24 and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> [6]

80 Page 8 of 11 Diffusivity and Solubility of Hydrogen Diffusivity and solubility of hydrogen in ferritic, martensitic, and austenitic steels is an important factor to consider. Materials having face-centered-cubic (FCC) crystal structures such as austenitic stainless steels (300 series) and nickel base Inconels generally are not considered to be susceptible to hydrogen delayed cracking as discussed in the microstructure section, above. Additionally, due to the temperatures expected during the welding of the temper bead layers, and during the welding of any non-temper bead layers, the temperature should be sufficient for the hydrogen to diffuse out of the HAZ, either escaping the structure or diffusing into the austenite, where it can be held in much greater quantities. The diffusion rate is clearly from the ferrite to the austenite and whatever hydrogen remains will reside in the austenite, which has little to no propensity to hydrogen related cracking.

Use of fully austenitic weld metal on ferritic base material is a technique that has been used for decades to install welds on ferritic base materials with high potential of HIC. Austenitic filler materials are used in applications where preheat or post weld bake out is not possible because hydrogen (H+) has high solubility, Figure 3, and low diffusivity, Figure 4, in austenite relative to other phases and acts as a trap for hydrogen to prevent HIC. Figure 3 show the solubility of hydrogen in -Fe and -Fe. Note that -Fe is at the saturation limit at ~4ml/100g of hydrogen.

At temperatures above ~1700° C the solubility of hydrogen in austenite (-Fe) is nearly five times that of ferrite (-Fe). The benefit regarding HIC is the hydrogen stays in the austenite and is not available to promote HIC. Figure 4 shows the overall difference in hydrogen diffusion between ferritic and austenitic materials. The diffusion of hydrogen in ferritic material is orders of magnitude greater compared to austenite. Again, the obvious advantage regarding HIC prevention is the hydrogen is slow to diffuse out of the austenitic material. When comparing how hydrogen behaves in ferritic versus austenitic weldments the hydrogen stays within the austenitic material whereas in ferritic welds, it tends to diffuse into the base material.

For a weld made with ferritic electrodes, the H+ is absorbed in the molten weld puddle and as the weld solidifies, it transforms from austenite to ferrite and the H+ is rejected and diffuses into the HAZ of the base material. When the HAZ transforms from austenite to martensite, the H+

becomes trapped in the brittle microstructure and causes cracking, Figure 5. However, with an austenitic electrode, H+ is absorbed in the molten weld puddle and there is no solid state transformation in the solidified weld metal so the H+ stays in the austenitic weld material.

No diffusion of the H+ into the brittle martensite, thus avoiding the possibility of HIC, Figure 6. Schematics in Figure 5 and Figure 6 are adapted from Lippold and Granjon as shown in draft chapters 2 & 4 for Temper Bead Welding Process in Operating NPPs, International Atomic Energy Agency, [1, 8].

10--3 J

10-4

'u Q)

(/)

N E 10..s

(.)

._j C

(l)

~ 10-6 (l) 8 C

-~ 10-7

i::

'6

~ 10-8 Q) 0 10-9 Page 9 of 11 I/

J I

(

10 v,.....

_,,/

/~

/

V

,A

/'

J '\\

f

= \\ Ferritic = ~~

-materials_?,'.

//-

r,

I I

I I

FL J

Fl \\

Austenitic materials 1 oo 200 3004og0ioo Temperature, °C Figure 3 Hydrogen solubility in ferritic and austenitic materials as a function of temperature 25 Liquid Fe Cll 0

20 0,...

E 15

.a

J 0

10 CJ)

C Q)

Cll 0

5

-0 >

I 0

500 1000 1500 2000 Temperature (°C)

Figure 4 Diffusion Coefficient of hydrogen in ferritic and austenitic materials as a function of temperature Page 10 of 11 martensite (M) austenite (y-Fe)

Figure 5 Hydrogen movement with ferritic electrodes [8]

martensite (M) austenite (y-Fe)

Figure 6 Hydrogen movement with austenitic electrodes [8]

Page 11 of 11 5.0 Conclusion The temper bead technique has become an increasingly effective tool for performing repairs on carbon and low alloy steel (P-No. 1 and P-No. 3) materials. Case N-888 provisions allow for ambient temperature temper bead welding with no post weld bake. However, the 48-hour hold at ambient temperature prior to performing the final weld acceptance NDE has remained a requirement. This white paper summarizes the technical basis to eliminate the 48-hour delay for temper bead welding when using austenitic filler materials. The data and testing by EPRI and other researchers show that when austenitic weld metal is used the level of diffusible hydrogen content in the ferritic base metal HAZ is too low to promote HIC. The 48-hour hold requirement in Case N-888 can therefore be removed.

Lastly, field experience applying austenitic filler materials to hundreds of dissimilar metal weld overlays using the ambient temperature temper bead procedures has never experienced hydrogen delayed cracking nor would it be expected. The reason is simply that the final diffusible hydrogen content is low - well below any threshold level that would be required for hydrogen induced cracking. Table 1 outlines the last 20 years of temper bead weld repairs in the nuclear industry with no reported occurrence of HIC when using austenitic weld metal.

References

1. Welding metallurgy and Weldability, 2015, chapter 5, Hydrogen Induced Cracking - John Lippold

2. Inconel Weld-Overlay Repair for Low-Alloy Steel Nozzle to Safe-End Joint, EPRI Palo Alto, CA: 1991. NP-7085-D.

3. ASME Case N-638, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Techniques,Section XI Division 1, September 24, 1999.

4. Ambient Temperature Preheat for Machine GTAW Temperbead Applications, EPRI Palo Alto, 1998. GC-111050.

5. Temperbead Welding Repair of Low Alloy Pressure Vessel Steels: Guidelines, EPRI Palo Alto, CA: 1993. TR-103354. 1993.

6. Welding and Repair Technology Center: Shielded Metal Arc Temper Bead Welding, EPRI Palo Alto, CA: 2015. 3002005536.

7. 2021 ASME Boiler & Pressure Vessel Code,Section XI Rules for Inservice Inspection of Nuclear Power Plant Components, Division 1.

8. S.L. McCracken and N. Mohr, Draft Chapters 2 and 4 prepared for: Temper Bead Welding Process in Operating NPPs, International Atomic Energy Agency, Vienna, 2022.

9. Repair and Replacement Applications Center: Temperbead Welding Applications 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding, EPRI, Palo Alto, CA: 2006.1013558.