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Crack Growth Rate Testing Of Alloy 82 In BWR Environments

The nickel base weld metal Alloy 82 is used in various applications in boiling water reactors (BWRs). Applications that are vital from a safety point of view are e.g., welds between core shroud support legs and the reactor pressure vessel (RPV), and feedwater nozzle to safe end welds. Laboratory testing and service history have shown that Alloy 82 is susceptible to stress corrosion cracking (SCC) in BWR environments. However, in comparison with Alloy 182, fewer failure cases have been reported, which could be related to the higher Cr content in Alloy 82 (~ 15 vs. ~ 20 %). It is also possible that the higher frequency of SCC in Alloy 182 is related to the wider use of this weld metal, and the larger surface area exposed to reactor water. Given the lower frequency of failures in Alloy 82, the database regarding SCC in BWR environments is much larger for Alloy 182.

Product Number: ED22-17295-SG
Author: Johan Stjärnsäter, Katsuhiko Kumagai
Publication Date: 2022
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The nickel base weld metal Alloy 82 is used in safety related applications in boiling water reactors (BWRs). Laboratory testing and service history have shown that Alloy 82 is susceptible to stress corrosion cracking (SCC) in BWR environments. However, in comparison with Alloy 182, the susceptibility to cracking appears to be lower, possibly an effect of the higher Cr content in Alloy 82. Disposition curves for Alloy 82 are needed to demonstrate the higher resistance vs. Alloy 182 in BWR normal water chemistry (NWC) and hydrogen water chemistry (HWC). To generate data to support the development of disposition curves for Alloy 82, crack growth rate (CGR) testing was carried out in NWC and HWC at stress intensity factors (K) in the range 30 to 40 MPa√m, and at very high K (>80 MPa√m). Sulfate was added during part of the tests to enhance the extent of intergranular cracking. A total of ten compact tension (CT) specimens of three welds (MIG and TIG), in as welded or post weld heat treated (PWHT) conditions, and of different sizes (0.5TCT, 1TCT 1.5TCT), were tested. Post weld heat treatment resulted in lower CGRs compared to the as welded condition. In addition, HWC was effective in mitigating cracking, especially in the PWHT condition, and the factor of improvement relative to NWC ranged from 2 to 15. No effect of the specimen size was observed. The paper discusses the effects of K, corrosion potential, sulfate, and specimen size on the crack growth rate.

The nickel base weld metal Alloy 82 is used in safety related applications in boiling water reactors (BWRs). Laboratory testing and service history have shown that Alloy 82 is susceptible to stress corrosion cracking (SCC) in BWR environments. However, in comparison with Alloy 182, the susceptibility to cracking appears to be lower, possibly an effect of the higher Cr content in Alloy 82. Disposition curves for Alloy 82 are needed to demonstrate the higher resistance vs. Alloy 182 in BWR normal water chemistry (NWC) and hydrogen water chemistry (HWC). To generate data to support the development of disposition curves for Alloy 82, crack growth rate (CGR) testing was carried out in NWC and HWC at stress intensity factors (K) in the range 30 to 40 MPa√m, and at very high K (>80 MPa√m). Sulfate was added during part of the tests to enhance the extent of intergranular cracking. A total of ten compact tension (CT) specimens of three welds (MIG and TIG), in as welded or post weld heat treated (PWHT) conditions, and of different sizes (0.5TCT, 1TCT 1.5TCT), were tested. Post weld heat treatment resulted in lower CGRs compared to the as welded condition. In addition, HWC was effective in mitigating cracking, especially in the PWHT condition, and the factor of improvement relative to NWC ranged from 2 to 15. No effect of the specimen size was observed. The paper discusses the effects of K, corrosion potential, sulfate, and specimen size on the crack growth rate.