Welding Issues, Code Applications, Irr Weld

18 – Welding Issues and Code Applications

Steve McCracken EPRI Welding & Repair Technology Center

Commission Materials Programs Technical Information Exchange Public Meeting

May 24, 2017 Rockville, MD

. Welding Issues – Nickel-base Filler Metal Weldability Testing – Development of 52M Filler Metal Alternative – Irradiated Material Welding Solutions . Code Applications – Code Rules for Welding on Irradiated Material – Repair by Carbon Fiber Reinforcement – N-871 – Excavate and Weld Repair for SCC Mitigation – N-847 – Branch Connection Weld Metal Buildup for SCC Mitigation – N-853 – Pad Reinforcement Repair of Atmospheric Storage Tanks – N-865

Nickel-base Filler Metal Weldability Testing

Steve McCracken EPRI WRTC

© 2017 Electric Power Research Institute, Inc. All rights reserved. High-Cr Ni-Base Filler Metal Weldability Testing • Weldability testing at OSU ‒ Cast pin tear test (CPTT) ‒ Strain-to-fracture (STF) ‒ Transvarestraint (TVT) ‒ Characterization studies ‒ Solidification temperature range (modeling & SS-DTA) • 82, 52, 52M, 52i, 52MSS, Transvarestraint Test SN690Nb, 52M-Ta-Mo Cast Pin Tear Test • Fundamental study of ductility-dip and hot cracking mechanisms • Crack healing by liquid back filling • Effect of SS dilution on hot cracking resistance

Gleeble Strain-to-Fracture Test 4 © 2017 Electric Power Research Institute, Inc. All rights reserved. 52M Hot Cracking on Stainless Steel Base Material • Nine high-Cr Ni-base weld metal specifications • Twenty-two stainless steel base materials with varying Si, S, and P compositions • Crack no-crack plots show influence of Si, S and P • Guidelines presented to minimize hot cracking ‒ Composition control ‒ Dilution control ‒ Bead placement control ‒ Buffer layer control

5 © 2017 Electric Power Research Institute, Inc. All rights reserved. High-Cr Ni-Base Filler Metal Screening Test • Industry Need: Field deployable test to screen 52M heats and 52M variants • Approach: Narrow groove high restraint geometry design (EPRI & IHI) to promote DDC with validation by computer modeling • Next Step: Investigate single bead approach with GTAW parameters (weave, sync-pulse, etc.) that may promote DDC

6 © 2017 Electric Power Research Institute, Inc. All rights reserved. WRTC Reports on 52M Weldability Issues • WRTC: Measures to Minimize 52M Hot Cracking on Stainless Steel Base Materials – Update Report 3002003140, December 2014

• WRTC: Screening Test for High- Chromium Nickel-Base Weld Metals – Preliminary Studies Report 3002005527, September 2015

• WRTC: Weldability Testing of High- Chromium Nickel-Base Weld Metals – Resistance to Solidification Cracking Report 3002007909, December 2016

Development of 52M Filler Metal Alternative

Steve McCracken EPRI WRTC

. Fundamental research performed to understand cracking mechanisms and weldability problems with 52M . Development of alloy composition for new filler metal – Model welding behavior and mechanical properties of target compositions – Validate modeled behavior with button melting experiments . Manufacture weld wire for target composition – Kobe Steel selected to manufacture target weld wires – Perform laboratory weldability testing . Assess weldability and perform validation NDE of new filler metal – Assess process parameters for GTAW and GMAW – Make large scale mockups for weldability and NDE – Perform mechanical, corrosion, & crack growth rate testing – Assess feasibility of alternative advanced welding processes (laser welding, magnetic stir, hybrid, etc.)

9 © 2017 Electric Power Research Institute, Inc. All rights reserved. 52M-Hf and 52M-Ta Experimental Alloys Selected Table 1: Target Composition Al B C Co Cr Cu Fe Mn Mo Nb 0.01 < 0.001 0.035 <0.01 30 0.03 8 0.6 (note 1) 0.5 Ni P S Si Ta Ti Zr Hf N ― Rem < 0.01 < 0.001 0.2 <0.01 0.2 < 0.01 (note 1) < 0.008 ― Note 1: Vary Hf-Mo and Ta-Mo as shown in Table 2a and 2b respectively

Table 2a: Range of Hf and Mo . Matrix of compositions in Tables 2a and 2b used to Heat # Hf Mo optimize final target composition with best 1 0.25 <0.03 2 0.25 3.9 resistance to ductility-dip cracking (DDC) and 3 <0.001 <0.03 solidification cracking 4 <0.001 3.9 Table 2b: Range of Ta and Mo – CPTT showed 52M-Hf & 52M-Hf-Mo wires had poor Heat # Ta Mo resistance to solidification cracking 5 3.8 <0.03 – CPTT showed 52M-Ta & 52M-Ta-Mo wires had improved 6 3.8 3.9 resistance to solidification cracking 7 <0.005 <0.03 8 <0.005 3.9 – STF showed 52M-Ta-Mo had improved resistance to DDC

. 52M-Hf and 52M-Hf-Mo variants are complete . 52M-Ta and 52M-Ta-Mo variants are complete . All variants at WRTC in Charlotte

• Weldability observations – oxide, wetting, etc. • Dual GTAW wire feed system used to build weld specimens of varying composition ‒ 52M-Ta, 52M-Ta-Mo wires mixed to study influence Transvarestraint of composition on weldability • Weldability testing at OSU ‒ Cast pin tear test (CPTT), Strain-to-fracture (STF) test, transvarestraint (TVT), Gleeble hot ductility and material characterization studies Dual Wire Feeder

Strain-to-Fracture Test Specimen Oxide Observations Cast Pin Tear Test

• Complete ‒ Computational modeling and DOE studies of solidification behavior ‒ Button melting and weldability experiments ‒ Manufacture of target 52M-Hf, 52M-Hf-Mo, 52M-Ta & 52M-Ta-Mo wires ‒ Cast pin tear testing (CPTT) of 52M-Hf & 52M-Hf-Mo wires ‒ Strain-to-fracture (STF) testing of 52M-Ta & 52M-Ta-Mo variants ‒ CPTT dilution testing of 52M-Ta variants with CF8A ‒ Characterization of 52M-Ta & 52M-Ta-Mo wires • In Progress ‒ Hot ductility testing and transvarestraint testing ‒ Procurement of 40 kg lot of 52M-Ta-Mo welding wire (delivery 4th quarter 2017) • Near Future ‒ Test with various welding processes and joint configurations (1st quarter 2018) ‒ Mechanical testing (tensile, bends, etc.) • N + 1 ‒ Full scale mockup for CGR testing (cold wire GTAW process)

Irradiated Material Welding Solutions

Jon Tatman EPRI WRTC

© 2017 Electric Power Research Institute, Inc. All rights reserved. Laser Welding Techniques for Repair of Irradiated Material . Improved heat input estimation techniques to establish definitive helium induced cracking threshold . Development of optimal laser welding parameters for expected materials and repair configurations (groove, fillet, overlay) – Stainless steel parameter development completed in 2014 – Parameter development for nickel-base material planned in 2017 . FEA modeling performed to validate irradiated SS parameter development . Low Heat Input Laser Beam Welding for Repair of Irradiated 10

Reactor Components - EPRI WRTC Report 3002003146 *

1 * *

* * * *

Effective Heat Input Heat Effective Input (KJ/cm) * *

0.1

JOG-GTAW-BM - No Cracking JOG-GTAW-BM - Cracking JNES-GTAW-BM - No Cracking JNES-GTAW-BM - Cracking JNES-GTAW-WM - No Cracking JNES-GTAW-WM - Cracking LBW-BM - No Cracking LBW-BM - Cracking LBW-WM - No Cracking LBW-WM - Cracking LBW - Remelt Trials - No Cracking LBW - Remelt Trials - Cracking JNES-GTAW-WM - GBD LBW-BM - GBD LBW - Remelt Trials - GBD * - Denotes single pass result 0.01 0.1 1 10 100 Helium Concentration (appm)

. Prototype of field-deployable auxiliary beam stress improved (ABSI) laser weld head has been developed . Weld head design is tailored for underwater welding applications . Designed to perform “dry- underwater” weld operations . Fabrication of initial prototype is complete, will be tested in underwater chamber to confirm operability . Initial testing will be reported in 2017

. New effective heat input and dilution equations are in development . Equations have been validated for GTAW and LBW processes – GTAW validation: 2013 Tech Report – 3002000412 – LBW validation: 2015 Tech Update – 3002005531 . Initial trials have begun to determine effects of weld parameters and chemical composition on critical efficiency values of austenitic stainless steel material

Code Rules for Welding on Irradiated Materials

Steve McCracken and Jon Tatman EPRI WRTC Wayne Lunceford EPRI BWRVIP

© 2017 Electric Power Research Institute, Inc. All rights reserved. Background – Weldability of Irradiated Material . Helium generated by neutron transmutation reactions can result in formation of helium-induced cracks when welded . It is appropriate to provide guidance for consideration of irradiation effects with the objective of preventing helium-induced cracking

Morishima, Y., JNM, 2004

Nakata, K., Env. Deg., 1998 Asano, K., JNM, 1999

. Observed cracking of BWR reactor internals resulted in EPRI Boiling Water Reactor Vessel and Internals Project (BWRVIP) program developing guidance for welding on irradiated materials – Initial guidance published as BWRVIP-97 in 2001 – BWRVIP-97-A approved by NRC in 2011 . Additional data obtained by EPRI in 2006 from studies performed in Japan and documented in BWRVIP-151, “Technical Basis for Revision to BWRVIP-97 Welding Guidelines” . Subsequent to approval of BWRVIP-97, effort undertaken by EPRI Materials Reliability Program (MRP) to develop guidance for U.S. designed PWRs and by BWRVIP to update the guidance for U.S. designed BWRs in BWRVIP-97-A based on these new data – MRP-379, Materials Reliability Program: Irradiated Materials Welding Guideline (published in 2014) – BWRVIP-97 Revision 1, Guidelines for Performing Weld Repairs to Irradiated BWR Internals (published in 2015)

. Criteria contained in ASME Section XI related to welding on irradiated materials includes the following variations: – predicted neutron fluence of 1017 neutrons per square centimeter – thermal neutron (E < 0.5 eV) fluence of 1 x 1017 neutrons per cm2 – if repair area is subject to a significant fast neutron fluence greater than 1019 nvt E ≥ 1 MeV – 0.1 APPM measured or calculated helium content generated through irradiation – the neutron fluence in the repair areas shall be taken into account when establishing the weld metal composition limits – consideration shall be given to the effects of irradiation on the properties of material, including weld material for applications in the core belt line region of the reactor vessel. Special material requirements in the Design Specification shall also apply to the test assembly materials for these applications

. Current rules in Section XI are inconsistent and should be comprehensively revised . ASME action initiated in 2010 to review rules and evaluation appropriate criterion (see ASME Rec. No. 10-1842) . The use of neutron fluence as the primary criterion is not optimal – Fast neutron fluence not relevant to evaluating helium generation assessing weldability – Thermal fluence is only one of several parameters affecting weldability, other important parameters are boron content, material type / grade, heat input . Desirable to define weldability guidance in terms other than neutron fluence . Guidance provided in BWRVIP-97 Rev. 1 and MRP-379 can be used as a basis for proposed changes to Section XI . Various approaches may be taken and dialogue between EPRI, industry/Code committees, and NRC is appropriate

. Both MRP-379 and BWRVIP-97R1 include identical weldability threshold plots for Type 304 and Type 316 stainless steels . Weldability is based on He concentration and weld heat input . Improvements from BWRVIP-97-A include: – Additional JNES data – Data plotted in terms of effective heat input instead of theoretical heat input. – Allows data from both GTAW and LBW to be included on a single plot. – Consideration of additional heat input from multiple remelt passes . At He concentrations < 0.1 appm, both Type 304 and 316 stainless steel are weldable without consideration of irradiation effects . Insufficient data to develop similar threshold plots for either nickel-base alloys or low-alloy steels – Data available for nickel-base alloys does not indicate a dramatic difference in weldability from stainless steel – Available low-alloy steel data suggest weldability at least as good as stainless steels

. Japanese GTAW and LBW studies1,2 on irradiated low alloy steel did not indicate significant susceptibility to helium-induced cracking – Increased porosity was noted in the LAS weld metal along the fusion boundary (weld process issue), however sound welds were achievable on irradiated LAS material – No evidence of helium-induced cracking or grain boundary deterioration even at significant helium concentrations . Toughness reduction is the more important concern for welding on low-alloy steels . Very few locations for which welded repairs may be needed for irradiated ferritic materials – Materials have performed well in service to date – Absent cracking in adjacent stainless steel or nickel-base alloys, welding on irradiated low- alloy steel is unlikely – Limited number of relevant locations (i.e., BWR riser brace attachment welds, PWR core support / core stop lugs)

1. K. Kazuhiko, et al., Repair Welding of Irradiated Reactor Vessel Steel by Low Heat Input GTAW and LBW, Materials Science Forum Vols. 539-543 (2007), pp 3912-3919. 2. FY2003 Safe Maintenance/Repair Welding Techniques for Nuclear Plant Irradiated Material (WIM), June 2004, Japan Nuclear Energy Safety Organization.

. Both MRP-379 and BWRVIP-97R1 include parametric helium generation studies for example reactor configurations – Based on benchmarked fluence models and including thermal neutron energy groups – Conservative upper end estimates of initial boron content (20 to 50 wppm B) – Parametric assessment of impact of service life (thru 80-yr operation) . PWRs – Westinghouse reactor evaluation documented in MRP-319 Rev. 1 – Combustion Engineering reactor evaluation documented in MRP-346 – B&W reactor evaluation documented in MRP-399 . BWRs – Updated analysis using BWR/4 reactor (same reactor type used to develop generic weldability boundaries in BWRVIP-97-A) – Used RAMA code with addition of thermal energy groups . Results used to define zones of weldability

26 © 2017 Electric Power Research Institute, Inc. All rights reserved. Example Helium Generation Map Comparison (B&W Reactor, MRP-399) . Parametric analyses – 1 wppm to 75 wppm B – 4 different cases, assuming 40 and 60 EFPY and two fuel management scenarios . Results indicate a steep helium generation gradient above and below the core . Relatively little movement of the 0.1 appm He generation line axially above / below the core at higher B concentrations and longer service times . Large portions of the RPV above and below the core remain weldable regardless of service life or initial boron Low Fluence Case High Fluence Case 40-Yr Service Life 60-Yr Service Life content 10 wppm B 75 wppm B

27 © 2017 Electric Power Research Institute, Inc. All rights reserved. Weldability Categorization (Applicable for BWRs & PWRs) . Based on observations from both weldability studies and helium mapping, four weldability categories defined: 1. He > 10 appm Limited weldability data exist, although it appears that 304SS may be weldable by LBW 2. 0.1 appm < He ≤ 10 appm Weldable with appropriate evaluation of helium content and application of heat input controls 3. 0.01 appm < He ≤ 0.1 appm 0.1 appm is below the lowest He concentration found to induce helium-induced cracking by conventional welding. If the location is determined to have a He concentration ≤ 0.1 appm, welding can be performed without consideration of irradiation effects. 4. He ≤ 0.01 appm In regions of the reactor system where generic bounding evaluations show He concentration < 0.01 appm, welding can be performed without the need for a component-specific He calculation. Available data indicate that the conservative inputs to the generic evaluations performed and the additional margin factor of 10 adequately address variations in reactor design.

. There are substantial data that can be applied to characterize the weldability of austenitic materials in BWRs and PWRs . Analysis indicates that many RPV and reactor internals locations can and should be generically dispositioned as not affected by irradiation effects . Neutron fluence is not a useful criterion for determining when irradiation effects must be considered – Fast neutron fluence values not relevant to assessing weldability – Most plants have not performed thermal fluence calculations and cannot either generate such calculations or perform helium measurements in short outage timeframes – Thermal fluence is only one of several parameters affecting weldability, other important parameters are boron content, material type / grade, heat input

. Initial boron concentration and reactor operating time have “relatively” small influence on the weldable zones above and below the core . Substantial gradient in estimated helium generation, even when using upper end initial boron content assumptions – RPV nozzle to safe end welds clearly remain weldable – RPV upper and lower head penetrations clearly remain weldable – Most internals components located in regions significantly above / below the core will be weldable, even after 80 years of service . Most BWR components located in the annulus region will be weldable, even after 80 years of service

30 © 2017 Electric Power Research Institute, Inc. All rights reserved. EPRI Recommendations for ASME Code Changes . For code cases primarily applicable to RPV nozzle DM welds or upper / lower head penetrations – Remove existing criteria related to fluence – Add a statement that the code case is not applicable to repair of reactor internals . For code cases that may be applied to reactor internals – Remove existing criteria related to fluence – Add criteria based on helium concentration – Include language allowing generic disposition of components located significantly above / below the core (< 0.01 appm He based on generic evaluation) . For locations near the core, owners can apply the guidance in BWRVIP-97 Rev. 1 or MRP-379 . Material applicability should be specified consistent with materials addressed in the existing research

. Presentation, January 2016 “Welding on Neutron Irradiated Austenitic and Ferritic Materials” NRC public meeting (ML16008A081) . Presentation, August 2016, EPRI International BWR and PWR Materials Conference in Chicago, IL . PVP2016-64007 Paper, “Applications of Welding to Repair Irradiated Reactor Internals” . MRP-379, Materials Reliability Program: Irradiated Materials Welding Guideline (published in 2014) . BWRVIP-97 Revision 1, Guidelines for Performing Weld Repairs to Irradiated BWR Internals (published in 2015) . ASME Record No. 10-1842, “Research appropriate use of Fluence/He Concentration for Ni Alloys & Low Alloy Steels”

Repair by Carbon Fiber Reinforcement Composite Code Case N-871

Steve McCracken EPRI WRTC Jim O’Sullivan, Procon1 Key Contributor to N-871

© 2017 Electric Power Research Institute, Inc. All rights reserved. Repair by Carbon Fiber Reinforced Composite (CRFC) . N-871, Repair of Buried Class 2 and 3 Piping Using Carbon Fiber Reinforced Polymer Composite (Record # 12-1478) . Full-circumferential interior application of carbon fiber laminate (CFRP repair system) designed to replace degraded portions of buried metallic piping . Limited to buried piping with maximum design temperature ≤ 200⁰F . Provides requirements for design, qualification, installation, acceptance, examination and

Degraded Pipe

CFRP Repair

Terminal Ends

Interior CFRP repair designed to replace degraded portions of metallic piping

Excavate and Weld Repair (EWR) for SCC Mitigation Code Case N-847

Steve McCracken and Jon Tatman EPRI WRTC

Mechanical Stress Improvement Process Weld Overlay (MSIP) (N-504-4, N-740-2, N-754, App. Q)

Inside Diameter Inlay Inside Diameter Onlay (N-766) (N-766)

. PWR Configuration – Dissimilar metal weld (DMW) joining low alloy steel to austenitic safe-end or piping – PWSCC susceptible Alloy 82/182 weld metal

EWR for Dissimilar Metal Weld . BWR Configuration – Similar metal weld (SMW) joining stainless-to-stainless piping – IGSCC susceptible sensitized stainless steel base material heat- affected-zone (HAZ)

EWR for Similar Metal Weld

. Excavation extends less than 360º of Partial circumference Arc EWR . Weldment not fully mitigated . SCC reduced to acceptable size . Provides timely option when emergent ISI examination reveals rejectable SCC indication . Provides time for deployment of more permanent repair . Circumferential overlap is critical design parameter which likely will define partial arc EWR design life . Consideration to deploy partial arc EWR with Cross-Section of Partial Arc EWR SMAW temper bead (code case N-839)

. Residual Stress Evaluation – Main purpose was to compare and validate FEA residual stress simulations with residual stress measurements • Modeling performed by Structural Integrity Associates (see PVP2016-63815) • Measurements performed by Hill Engineering (see PVP2016-63197) ‒ Demonstrate temper bead in EWR cavity . UT Demonstration ‒ EWR partial arc mockup fabricated to demonstrate UT examination capability ‒ Proof of concept UT demonstrations completed ‒ Full scale mockup with a 50% and 75% thickness partial arc excavations in-process ‒ Includes implanted weld flaws • Intended for Appendix VIII qualification

40 © 2017 Electric Power Research Institute, Inc. All rights reserved. FEA Model vs. Measured Residual Stress for Partial Arc EWR . General agreement in shape of stress field . Measured residual stress trends lower in magnitude

FE Measured

. N-847, Excavate and Weld Repair for SCC Mitigation – Board Approved 24 Oct 2016 (Record # 10-1845) – N-847 provides rules for EWR design, analysis, installation, and post repair acceptance examination

. N-770-5, ISI Requirements for PWSCC Mitigation and Repair – Board Approved 07 Nov 2016 ( Record # 14-2233) – N-770-5 provides rules for EWR PSI/ISI and extent and frequency of examination

42 © 2017 Electric Power Research Institute, Inc. All rights reserved. N-847 Bases Documents and References . EPRI Reports – Report 3002007901, Jun 2016, WRTC: Technical Basis and Residual Stress Studies to Support the Excavate and Weld Repair (EWR) Methodology for Mitigation of SCC in ASME Class 1 Butt Welds – Report 3002005518, Sept 2015, WRTC: Excavate and Weld Repair Demonstration Mockup Results – Preliminary Report – Report 1021012, Dec 2010, Topical Report: Application of the Excavate and Weld Repair Process for Repair and Mitigation of Alloy 182 and 82 in PWRs . 2016 NRC Document – NRC Technical Letter Report (ML16257A523), Weld Residual Stress Analysis of Excavate and Weld Repair Mockup . 2016 PVP Conference – PVP2016-63769, Technical Basis for Code Case N-847 – Excavate and Weld Repair (EWR) – PVP2016-63815, 3D Residual Stress Simulation of an Excavate and Weld Repair Mockup – PVP2016-63197, Residual Stress Mapping for an Excavate and Weld Repair Mockup . 2017 PVP Conference – PVP2017-66173, Crack Growth Evaluation of Remnant Cracks Underneath an Excavate and Weld Repair

Branch Connection Weld Metal Buildup for SCC Mitigation Code Case N-853

Steve McCracken EPRI WRTC Dave Waskey & Steve Hunter, Areva Key Contributors to N-853

© 2017 Electric Power Research Institute, Inc. All rights reserved. PWSCC Susceptible Alloy 600 Branch Connections . NRC issued Regulatory Issue Summary (RIS) 15-10 ‒ Request for ASME Code to review ISI requirements for Alloy 600 branch connections ‒ Contingency weld repair design needed for Palisades and B&W Plants ‒ PWROG Projects PA-MSC-1283 and 1294 established

PWSCC Resistant Weld RCS HL Class 1 Run Pipe Metal Buildup and Cladding

PWSCC Resistant Existing PWSCC Attachment J-Weld Susceptible Weld

Existing PWSCC Susceptible Nozzle

PWSCC Resistant Replacement Nozzle

1) Remove existing nozzle 2) Apply structural weld metal buildup 3) Contour, PT & UT buildup 4) Install new Alloy 690 nozzle

. RCS hot leg elbow configuration . Fixture designed to represent field conditions . Simulated 42” – 44” OD pipe . Coupon insert of carbon steel (SA-516)

As-Welded Pad As-Ground Pad

. 52M weld metal buildup – Liquid penetrant (PT) examination – Ultrasonic (UT) examination – Cross section macro evaluation – Cross section PT examination . J-groove machining . Installation of new Alloy 690 nozzle

. Status of N-853 – Board Approved 27 Jun 2016 (Record # 15-360) . N-853 provides rules for design, analysis, installation, post repair examination and PSI/ISI requirements for the branch connection weld metal buildup (BCWMB) . Areva performed a full scale demonstration mockup – The BCWMB was ‒ PVP2016-63902 – Technical Basis for Code Case N-853 – nondestructively examined A600 Branch Connection Weld Repair for SCC Mitigation and metallurgically evaluated Dave Waskey (AREVA), Steve McCracken (EPRI)

Pad Reinforcement Repair of Atmospheric Storage Tanks Code Case N-865

Steve McCracken EPRI WRTC Ed Gerlach, Gerlach Engineering Key Contributor to N-865

. Status of N-865 – SC XI Letter Ballot May 2017 Record # 15-2235 Ballot # 16-3541RC1 . N-865 provides rules for design, analysis, installation, examination and post repair inspection requirements . Based closely on provisions in N-789-2 for pad repair of Class 2 and 3 moderate energy piping for raw water service and ASME PCC-2 repair of pressure equipment and piping Structural and Pressure Pad Repairs