NRC Welding Residual Stress Validation Program International Round Robin Program and Findings

Rathbun, H.J.; Fredette, L. F.; Scott, Paul; Csontos, A.; Rudland, D.

doi:10.1115/pvp2011-57642

Cited by 27 publications

(38 citation statements)

References 6 publications

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“…The most recent project included an international round-robin study involving many organizations' participation in simulating and measuring the weld residual stresses developed in a series of mock-ups representing real nuclear piping components [2,3,4,5]. The welding simulation results from the round-robin participants correlated well with each other, and with detailed measurements using various techniques.…”

Section: Introductionmentioning

confidence: 74%

Welding Simulation Used in the Design of Metallic Armor Systems

Fredette

Beach

2014

AMR

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Welding steel armor reduces the armor material's protection capability. Several industrial and military welding standards exist for welding armor materials with the primary focus on joint strength rather than ballistic integrity.The Heat Affected Zone (HAZ) created by the welding process introduces vulnerabilities in the protection system. The process and designs that we have demonstrated include mitigation features that eliminate the ballistic degradation and provide uniform protection across all armor materials.In this study we used finite element simulation of the welding process to perform trade studies evaluating welded joint designs, and to show how the designs could be altered to both optimize armor performance and reduce welding heat input. Beneficial effects of reduced heat input, and the corresponding reduction in welding-induced residual stresses, created an overall reduction in distortion in the assembly and improvement of the armor performance.The simulated welding process included the creation of the heat affected zone and the development of residual stresses in the structure. ABAQUS finite element software was used for the simulation with the aid of an extensive material property database created over the wide range of welding temperatures.The finite element simulation predictions were validated and verified with excellent results by metallography and micro-hardness measurements. Live-fire ballistic tests were used as the final proof of measurable design improvements. Finite element welding simulation was shown to be an effective tool for improving upon standard welded armor designs, and above all in improving human safety.

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Section: Introductionmentioning

confidence: 74%

Welding Simulation Used in the Design of Metallic Armor Systems

Fredette

Beach

2014

AMR

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“…As discussed in a paper on this topic presented at the ASME 2011 Pressure Vessel and Piping (PVP) Conference, the second phase of this program consisted of an analytical international round-robin for validation of predicted WRSs in a prototypical PWR PZR surge-nozzle geometry (Rathbun et al 2011). The results from the round robin were validated through comparison of predicted residual stress fields with a variety of physical measurements performed on the mockup.…”

Section: Welding Residual Stress Finite Element Analysis Validation Smentioning

confidence: 99%

Assessment of the Mechanical Stress Improvement Process for Mitigating Primary Water Stress Corrosion Cracking in Nickel Alloy Butt Welds in Piping Systems Approved for Leak-Before-Break

Sullivan¹,

Anderson²

2013

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Executive SummaryIn recent years, operating experience has shown that Alloy 82/182/600 materials used in reactor coolant system (RCS) pressure boundaries of pressurized water reactors (PWRs) are susceptible to primary water stress corrosion cracking (PWSCC). Cracking can initiate at the inside surface of these materials, in part, because of tensile residual stresses introduced by welding. These materials are present in piping systems that were approved by the U.S. Nuclear Regulatory Commission (NRC) for leakbefore-break (LBB) before PWSCC was found in RCS dissimilar metal butt welds. The identification of PWSCC led to concerns regarding the potential effect of this degradation on existing LBB analyses.In response to these concerns, the NRC Office of Nuclear Regulatory Research initiated a program entitled, "PWSCC in Leak-Before-Break Systems," and a follow-on program entitled, "Degradation in Extremely Low Probability of Rupture (xLPR) Systems." Under these programs, Pacific Northwest National Laboratory (PNNL) is assessing the various strategies being used by industry to manage potential or existing PWSCC in susceptible welds in piping systems approved for LBB.The commercial nuclear power industry has implemented strategies to manage potential or existing PWSCC at Alloy 82/182 dissimilar metal welds (DMW) in PWRs. One general strategy consists of management by a combination of mitigation plus inspection, where several mitigation techniques have been used by industry. The other general strategy is to manage potential PWSCC by inspection alone.At the request of the NRC, the American Society of Mechanical Engineers (ASME) took actions to develop improvements to the existing Code requirements to address the potential for PWSCC in Class 1 PWR piping butt welds fabricated with Alloy 82/182 weld materials. The ASME developed Code Case N-770, "Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated with UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities, Section XI, Division 1." It was realized that the Code Case needed to be revised to address specific examinations such as welds with a design life of less than 10 years and post-weld preservice surface examinations. In general, the revised Code Case (N-770-1) has requirements for inspection of unmitigated as well as mitigated Alloy 82/182 RCS butt welds. As such, specific inspection requirements for welds mitigated by the Mechanical Stress Improvement Process (MSIP®), (a) the subject of this technical letter report (TLR), are contained in the Code Case. The NRC incorporated ASME Code Case N-770-1 by reference into §50.55a (76 FR 36232, p. 36278) in June 2011.This TLR provides an assessment of MSIP as a mitigation strategy and includes an assessment of the MSIP-related inspection requirements of Code Case N-770-1, as conditioned in §50.55a.Depending upon the weld geometry, fabrication practices, and the presence of a nearby safe end-topipe weld, Al...

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“…As discussed in a paper on this topic presented at the ASME 2011 Pressure Vessel and Piping Conference (PVP), the second phase of this program consisted of an analytical international round robin for validation of predicted WRSs in a prototypical PZR surge nozzle geometry (Rathbun et al 2011). The results from the round robin were validated through comparison of predicted residual stress fields with a variety of physical measurements performed on the mockup.…”

Section: Welding Residual Stress Finite Element Analysis Validation Smentioning

confidence: 99%

“…Hence, the suite of WRS measurements described above was taken before and after completion of the safe end-tostainless steel weld. Only DHD/iDHD results were presented and discussed in Rathbun's PVP paper (Rathbun et al 2011). The XRD and IHD results are to be presented in a future publication.…”

Section: Welding Residual Stress Finite Element Analysis Validation Smentioning

confidence: 99%

“…Although the average measurements and individual FE analysis results differ in places by significant stress levels, given the overall scatter in the results, to a reasonable approximation, they do occupy the same distribution. Rathbun et al (2011) discuss factors to which the stress results from the Phase 2 study were sensitive.…”

Section: Welding Residual Stress Finite Element Analysis Validation Smentioning

confidence: 99%

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Assessment of Weld Overlays for Mitigating Primary Water Stress Corrosion Cracking at Nickel Alloy Butt Welds in Piping Systems Approved for Leak-Before-Break

Sullivan¹,

Anderson²

2012

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SummaryIn recent years, operating experience (OE) has shown that Alloy 82/182/600 materials used in reactor coolant system (RCS) pressure boundaries of pressurized water reactors (PWRs) are susceptible to primary water stress corrosion cracking (PWSCC). Cracking can initiate at the inside surface of these materials, in part, because of tensile residual stresses introduced by welding. These materials are present in piping systems that were approved by the NRC for leak-before-break (LBB) analyses before PWSCC was found in RCS dissimilar metal butt welds. The identification of PWSCC led to concerns regarding the potential effect of this degradation on existing LBB analyses.In response to these concerns, RES initiated a program entitled, "PWSCC in Leak-Before-Break Systems," and a follow-on program entitled, "Degradation in Extremely Low Probability of Rupture (xLPR) Systems." Under these programs, Pacific Northwest National Laboratory (PNNL) is assessing the various strategies being used by industry to manage potential or existing PWSCC in susceptible welds in piping systems approved for LBB.The commercial nuclear power industry has implemented strategies to manage PWSCC at Alloy 82/182 dissimilar metal welds (DMW) in PWRs. One general strategy consists of management by a combination of mitigation plus inspection, where several mitigation techniques have been used by industry. The other general strategy is to manage potential PWSCC by inspection alone.At the request of the NRC, ASME developed Code Case N-770-1, which provides inspection requirements to address PWSCC in Class 1 butt welds containing Alloy 82/182. Code Case N-770-1 has requirements for inspection of unmitigated as well as mitigated Alloy 82/182 RCS butt welds. As such, specific inspection requirements for welds mitigated by weld overlays (WOLs), the subject of this TLR, are contained in the Code Case. The NRC incorporated ASME Code Case N-770-1 by reference into §50.55a (76 FR 36232, p. 36278) in June 2011.This TLR provides an assessment of weld overlays as a mitigation strategy, and includes an assessment of the WOL-related inspection requirements of Code Case N-770-1, as conditioned in §50.55a.There are two types of weld overlays-full structural weld overlays (FSWOLs), which have a minimum thickness of one-third the pipe wall thickness, and optimized weld overlays (OWOLs), which have different design requirements and result in less applied weld overlay metal. Depending upon the weld geometry, fabrication practices, and the presence of a nearby safe end-to-pipe weld, Alloy 82/182 piping butt welds may have tensile residual axial and hoop stresses within a zone near the inside surface of the weld. This tensile zone contributes to the susceptibility of Alloy 82/182 to PWSCC. Weld overlays convert tensile residual stresses in inner diameter regions of these welds, to zones of compressive residual stresses, or substantially reduced tensile residual stresses.In performing this assessment, PNNL considered operating experience with weld overlays and a numb...

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NRC Welding Residual Stress Validation Program International Round Robin Program and Findings

Cited by 27 publications

References 6 publications

Welding Simulation Used in the Design of Metallic Armor Systems

Welding Simulation Used in the Design of Metallic Armor Systems

Assessment of the Mechanical Stress Improvement Process for Mitigating Primary Water Stress Corrosion Cracking in Nickel Alloy Butt Welds in Piping Systems Approved for Leak-Before-Break

Assessment of Weld Overlays for Mitigating Primary Water Stress Corrosion Cracking at Nickel Alloy Butt Welds in Piping Systems Approved for Leak-Before-Break

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