Primary Water Stress Corrosion Cracking of High-Chromium Nickel-Base Welds at or Near Interfaces – 2020 (NUREG/CR-7277, ANL-23/19)

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Manuscript Completed: July 2020
Date Published: April 2023

Prepared by:
B. Alexandreanu and Y. Chen

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, repairs of existing components as well as for designs of advanced nuclear reactors of the 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 690 and 52/152 and variant welds to stress corrosion cracking (SCC). Several areas that have been of particular interest are: Alloy 690 HAZ, Alloy 52/152 weldments in 1^st layer butter configurations as well as weld overlays, and Alloy 52/152 weldments with repairs. The SCC CGR data generated in this program was discussed in the framework provided by the industry-proposed disposition curves for Alloys 600 [13], 182 [14], and 690, 52/152 [1]. Two Alloy 690 HAZ on CRDM tubing were investigated in the program Despite the fact that some of the data were included in the database for the disposition curve [1], the resulting MRP-386 curve bounds only 23% of the Alloy 690 HAZ CGR data generated in this program. When the fracture mode becomes 50% IG, proportion of bound data points falls to zero. The analysis presented in the report suggests that the 25^th Percentile Alloy 600 curve [13] is a better descriptor of the Alloy 690 HAZ data. The SCC susceptibility of first layer Alloy 52/152 and variant welds have been investigated, and the substrate seems to be paying a role. For example, 1^st layer Alloy 52/152 weldments deposited on Alloy 182 or LAS appear more susceptible than those deposited on SS with one exception, an Alloy 152M weld butter deposited on Alloy 308L. However, when SCC occurred, SCC CGRs almost as high as the EPRI MRP-115 disposition curves for Alloys 82/182 [14] were measured for both 1^st layer Alloy 52M deposited on Alloy 182 and the interface between the two weldments. Likewise, for Alloy 52/152 deposited on LAS, SCC CGRs as high as a factor 2 less than the EPRI MRP-115 disposition curve [14] were measured. Overall, it was found that the MRP-386 curve [1] only bounds 6% of the data points obtained in Alloy 52/152 in a first layer configuration. The effectiveness of an Alloy 52M Weld Overlay (WOL) to mitigate SCC growth was evaluated for three WOLs by distinct manufacturers. In an ANL-produced WOL, direct transmission of IG SCC into the Alloy 52M WOL occurred over approximately 40% of the crack front. For a KAPL-produced WOL, the transmission of IG SCC across the interface was 100% and extended for 2 mm, approximately for two Alloy 52M beads. In contrast with the KAPL-produced WOL, in the case of an EWI-produced WOL, IG SCC transmission across the interface in two tests was minimal. The effect of weld repairs on the SCC response was for two weldments: a 20% repair and a 20 and 40% double repair. Both specimens tested from the 20% repair weld were found to be resistant. By contrast, both specimens tested from the double repair weld were found to be susceptible, with the MRP-386 [1] bounding no SCC CGR data resulting from this weldment. However, there was not sufficient evidence to determine conclusively whether the outcomes were in any way influenced by the repairs.