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Title: Mitigation of Tensile Weld Stresses in Alloy 22 Using Laser Peening

Abstract

The goal of the Yucca Mountain Project (YMP) is safe permanent disposal of high-level nuclear waste. One of the many technical challenges to this plan is the design of the Engineered Barrier System (EBS) including the waste package that will contain the radioactive waste. One potential failure mode of the waste package is stress corrosion cracking (SCC), which occurs when three criteria simultaneously exist. These criteria are a potentially corrosive environment, a material susceptible to SCC, and the presence of tensile residual stresses at the surface of the material. While many design decisions have been made to attempt to minimize the occurrence of the first two conditions, it is necessary to control the third condition, the presence of tensile residual stresses. These stresses occur as a result of a variety of manufacturing techniques, including welding. While most of the residual stresses due to the welding of the waste package can be mitigated through solution heat-treating, the final closure weld, which occurs after the radioactive waste has been placed in the waste package, must be treated to eliminate the presence of tensile residual stress near the surface. Laser peening is a commercially proven technology that has been shown to create compressivemore » residual stress in both unstressed materials, as well as materials containing tensile surface residual stresses generated by welding. Lawrence Livermore National Laboratory (LLNL) has developed the laser peening process and the associated hardware for use by the YMP. Upon completion of the testing and engineering phases, LLNL will transfer the laser peening technology to U.S. industry and assist DOE in developing vendors to supply production units to be installed at the YMP facilities. The overall testing effort is divided into-two phases. Phase I of this project consisted of a study into the effectiveness of laser peening in generating compressive stress in small Alloy 22 base metal coupons and converting tensile stress in Alloy 22 welds into compressive residual stress. Particular emphasis was placed on optimization of process parameters to achieve compressive residual stress at greater depths than has currently been demonstrated. The process parameters studied included the laser irradiance (power per area), the laser pulse duration, the number of peening layers, the effect of the ablative layer (described below), and the effect of part thickness. Additionally, the effect of two process parameters, the number of peening layers and the effect of the ablative layer, was evaluated by measuring general corrosion resistance of peened and unpeened Alloy 22 coupons with an electrochemical polarization method. This initial effort ($95,000) was started in August 22, 2002 and completed on September 30, 2002. Phase 11 ($70,000) of this project was started on September 14, 2002. Using the parameters determined from the initial phase (and listed in Appendix A), five welded flat plate specimens (three plates, 3/8 inch thick and two plates, 1 inch thick) were laser peened at LLNL. These peened plates, identified as Stress Mitigation Welded Specimens, were shipped to qualified YMP suppliers (Chalk River Neutron Diffraction facility, and Lambda Research Inc.) for residual stress measurements. This report summarizes technical achievements made in Phase I. It is evident from this work that laser peening is a mature technology for YMP to effectively mitigate the potential for stress corrosion cracking in Alloy 22 welds.« less

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
15003132
Report Number(s):
UCRL-ID-151055
TRN: US0402450
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 27 Nov 2002
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AVAILABILITY; CALCITE; ALLOYS; CORROSION RESISTANCE; LASERS; LAWRENCE LIVERMORE NATIONAL LABORATORY; MITIGATION; NEUTRON DIFFRACTION; RADIOACTIVE WASTES; RESIDUAL STRESSES; SHOT PEENING; STRESS CORROSION; STRESSES; YUCCA MOUNTAIN

Citation Formats

Chen, H L, Evans, K J, Hackel, L A, Rankin, J E, Yamamoto, R M, Demma, A G, Dewald, A T, Lee, M J, and Hill, M R. Mitigation of Tensile Weld Stresses in Alloy 22 Using Laser Peening. United States: N. p., 2002. Web. doi:10.2172/15003132.
Chen, H L, Evans, K J, Hackel, L A, Rankin, J E, Yamamoto, R M, Demma, A G, Dewald, A T, Lee, M J, & Hill, M R. Mitigation of Tensile Weld Stresses in Alloy 22 Using Laser Peening. United States. https://doi.org/10.2172/15003132
Chen, H L, Evans, K J, Hackel, L A, Rankin, J E, Yamamoto, R M, Demma, A G, Dewald, A T, Lee, M J, and Hill, M R. 2002. "Mitigation of Tensile Weld Stresses in Alloy 22 Using Laser Peening". United States. https://doi.org/10.2172/15003132. https://www.osti.gov/servlets/purl/15003132.
@article{osti_15003132,
title = {Mitigation of Tensile Weld Stresses in Alloy 22 Using Laser Peening},
author = {Chen, H L and Evans, K J and Hackel, L A and Rankin, J E and Yamamoto, R M and Demma, A G and Dewald, A T and Lee, M J and Hill, M R},
abstractNote = {The goal of the Yucca Mountain Project (YMP) is safe permanent disposal of high-level nuclear waste. One of the many technical challenges to this plan is the design of the Engineered Barrier System (EBS) including the waste package that will contain the radioactive waste. One potential failure mode of the waste package is stress corrosion cracking (SCC), which occurs when three criteria simultaneously exist. These criteria are a potentially corrosive environment, a material susceptible to SCC, and the presence of tensile residual stresses at the surface of the material. While many design decisions have been made to attempt to minimize the occurrence of the first two conditions, it is necessary to control the third condition, the presence of tensile residual stresses. These stresses occur as a result of a variety of manufacturing techniques, including welding. While most of the residual stresses due to the welding of the waste package can be mitigated through solution heat-treating, the final closure weld, which occurs after the radioactive waste has been placed in the waste package, must be treated to eliminate the presence of tensile residual stress near the surface. Laser peening is a commercially proven technology that has been shown to create compressive residual stress in both unstressed materials, as well as materials containing tensile surface residual stresses generated by welding. Lawrence Livermore National Laboratory (LLNL) has developed the laser peening process and the associated hardware for use by the YMP. Upon completion of the testing and engineering phases, LLNL will transfer the laser peening technology to U.S. industry and assist DOE in developing vendors to supply production units to be installed at the YMP facilities. The overall testing effort is divided into-two phases. Phase I of this project consisted of a study into the effectiveness of laser peening in generating compressive stress in small Alloy 22 base metal coupons and converting tensile stress in Alloy 22 welds into compressive residual stress. Particular emphasis was placed on optimization of process parameters to achieve compressive residual stress at greater depths than has currently been demonstrated. The process parameters studied included the laser irradiance (power per area), the laser pulse duration, the number of peening layers, the effect of the ablative layer (described below), and the effect of part thickness. Additionally, the effect of two process parameters, the number of peening layers and the effect of the ablative layer, was evaluated by measuring general corrosion resistance of peened and unpeened Alloy 22 coupons with an electrochemical polarization method. This initial effort ($95,000) was started in August 22, 2002 and completed on September 30, 2002. Phase 11 ($70,000) of this project was started on September 14, 2002. Using the parameters determined from the initial phase (and listed in Appendix A), five welded flat plate specimens (three plates, 3/8 inch thick and two plates, 1 inch thick) were laser peened at LLNL. These peened plates, identified as Stress Mitigation Welded Specimens, were shipped to qualified YMP suppliers (Chalk River Neutron Diffraction facility, and Lambda Research Inc.) for residual stress measurements. This report summarizes technical achievements made in Phase I. It is evident from this work that laser peening is a mature technology for YMP to effectively mitigate the potential for stress corrosion cracking in Alloy 22 welds.},
doi = {10.2172/15003132},
url = {https://www.osti.gov/biblio/15003132}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Nov 27 00:00:00 EST 2002},
month = {Wed Nov 27 00:00:00 EST 2002}
}