Stress Corrosion Cracking in Nickel-Base Alloys 690 and 152 Weld in Simulated PWR Environment - 2009 (NUREG/CR-7137)

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Publication Information

Manuscript Completed: June 2012
Date Published: June 2012

Prepared by:
B. Alexandreanu, Y. Yang, Y. Chen, and W. J. Shack

Argonne National Laboratory
Argonne, IL 60439

Darrell Dunn/Appajosula Rao, NRC Project Managers

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

Alloys 600 and 182 are used as structural materials in pressurized water reactors (PWRs) and have been found to undergo stress corrosion cracking (SCC). Alloys 690 and 152 are the replacement materials of choice for Alloys 600 and 182, respectively. The primary objective of this work is to determine the crack growth rates (CGRs) in a simulated PWR water environment for the replacement alloys. This is an ongoing effort, and the report presents the initial investigations on Alloys 690 and 152 weld. A second objective was to obtain tensile data for these alloys for a wide temperature range, from operating to extreme conditions. To meet the objectives, testing conducted at ANL included Alloy 690 in the asreceived condition and cold-rolled by 26%, as well as a laboratory-prepared Alloy 152 double-J weld in the as-welded condition. For the SCC CGR measurements, the specimens were pre-cracked under cyclic loading in a primary water environment, and the cyclic CGRs were monitored to determine the transition from the fatigue transgranular fracture mode to the intergranular SCC fracture mode. The cyclic CGRs of the cold-rolled Alloy 690 showed significant environmental enhancement compared with the asreceived alloy. Compared to Alloy 600, the as-received Alloy 690 proved to be more resistant to SCC in the simulated PWR environment at 320°C (608°F), with sec CGRs of 10^-12 m/s. However, the sec CGRs for the cold-rolled alloy were an order of magnitude higher, about 10^-11 m/s, at comparable stress intensity factors in the range of 22 to 32 MPa·m^1/2 (20 to 29 ksi·in.^1/2). This finding is consistent with results obtained by industry on similar cold-worked alloys. A possible explanation for the relatively high CGRs in the cold-worked material is the presence of cracked grain boundary carbides, a feature that was observed for all cold-worked alloys displaying relatively high CGRs. The environmental enhancement of cyclic CGRs for Alloy 152 was minimal; nevertheless, the transition from transgranular to intergranular cracking was successful. Weld samples tested from a single heat of Alloy 152 exhibited SCC CGR rates of 10^-11 m/s in the simulated PWR environment at 320°C (608°F), which was only about an order of magnitude lower than typical for Alloy 182. The report also presents tensile property data for Alloy 690 and Alloy 152 welds in the temperature range of 25-870°C (81-1598°F). These data meet the minimum requirements of ASME SB-167, and are in excellent agreement with data on similar alloys.