Primary Water Stress Corrosion Cracking of High-Chromium, Nickel-Base Welds Near Dissimilar Metal Weld Interfaces (NUREG/CR-7226)

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Publication Information

Manuscript Completed: February 2016
Date Published: January 2018

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

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

The report summarizes the results of a testing program to evaluate the stress corrosion cracking (SCC) susceptibility at or near the interface between Alloy 52 and 152 weld metals and other weld or base metals. Alloys 52 and 152 are high-chromium weld metals used in reactor pressure vessel head penetration nozzles and as overlays, inlays, or onlays for dissimilar metal piping welds. Alloys 52 and 152 typically show very low SCC growth rates in laboratory testing and are not known to have cracked in service. Nevertheless questions remain as to whether the localized dilution of chromium content or the presence of microstructural features near the interface with the low-chromium weld metals Alloy 82 and 182, as in the case of a weld overlay (WOL), or with steel, as in the case of a head penetration nozzle, could affect the SCC response. For this study, SCC growth rates were measured on a WOL mockup with Alloy 52M (a compositional variant of Alloy 52) on Alloy 182 and on a butt weld mockup with Alloy 152 joined to low-alloy steel (LAS). For the WOL mockup, tests were performed in which the crack growth direction was either from Alloy 182 directly into Alloy 52M or along their interface. In the butt weld mockup, measurements were made in the first layer of weld butter beads, within about 1 mm of the interface with LAS. The tests on both mockups resulted in crack growth rates in Alloy 52M and 152 that are higher than have been previously reported for the weld metals, even though the dendrites were not favorably oriented for cracking. In the WOL mockup, crack branching along the interface was observed when the cracking direction was perpendicular to the interface. In the butt weld mockup, material compositional analyses taken along the crack path indicated that locations with the highest measured crack growth rates did not necessarily correlate with the lowest chromium content. This suggests that microstructural factors, in addition to the chromium content, could affect the SCC susceptibility near the interface.