Primary Water Stress Corrosion Cracking of High-Chromium Nickel-Base Welds – 2018 (NUREG/CR-7276)

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Publication Information

Manuscript Completed: October 2018
Date Published: April 2023

Prepared by:
B. Alexandreanu, Y. Chen, and K. Natesan

Argonne National Laboratory
Argonne, IL 60439

M. Audrain, NRC Project Manager

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

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Abstract

Nickel-base Alloy 690 and the associated weld Alloys 52 and 152 are typically used for nozzle penetrations in replacement heads for pressurized water reactor (PWR) vessels, because of their increased resistance to stress corrosion cracking (SCC) relative to Alloys 600, 82, and 182. The report presents the results of a confirmatory research program conducted with the purpose of evaluating the susceptibility of Nickel-base Alloy 52/152 and variant welds to stress corrosion cracking (SCC). Several areas have been of particular interest: heat to heat variability, the effect of welding parameters, and the effect of cold work on SCC CGR response. An Alloy 152 weld heat (WC04F6) used in the production of two early weldments by ANL Central Shops was found to be particularly susceptible to IG SCC. This data set was found to have an average SCC CGR approximately 17x lower than the disposition curve for Alloy 182. SCC CGR testing of an Alloy 152 mock-up produced by MHI for the Kewaunee reactor was found to occasionally result in elevated levels of IG fracture, especially at high stress intensity factors. The SCC CGR for this latter weldment were not as high as those measured for the ANL-produced welds. A systematic study on the effect of welding parameters on the SCC CGR response was conducted on three weldments produced by ANL Central Shops with the same Alloy 152 heat code and in the same geometry. The welding parameters tested do not seem to affect the SCC CGR response. In addition, testing also involved an Alloy 52M weld produced at EPRI with high heat input. Although this weld was also found also appears to be resistant, concern remains with susceptibility to SCC at high stress intensity where one SCC CGR measurement was as high as those measured in the early ANL-produced Alloy 152 weldments. The effect of cold-work was evaluated on an Alloy 52 weld in both as-welded and 20% cold-forged (CF) conditions, and all the SCC CGRs were found to be very small. Overall, it was found that the Alloy 52/152 SCC CGR disposition curve proposed in MRP-386 [13] bounds hardly any data presented in this report. The likely explanation lies with the fact that the MRP-386 curve [13] relies on a database of which 60% of the data were obtained at 350-360°C, and to which an unproven dependence on temperature was applied, resulting in an artificially low curve. By contrast, the ANL data were obtained at 320°C, hence, they did not need to be adjusted for temperature.