Long-Term Crack Initiation Behavior of Cold-Worked Alloy 690 in PWR Primary Water

摘要

High-Cr, Ni-base Alloy 690 is considered resistant to stress corrosion crack (SCC) initiation because a protective oxide layer readily forms above grain boundaries (GB) intersecting the surface when exposed to high-temperature water due to their high Cr content. However, recent laboratory studies revealed an alternate mechanism of crack initiation in highly cold-worked (CW) Alloy 690 through formation and growth of GB cavities induced by creep. This paper summarizes the latest results of the ongoing long-term crack initiation test performed on CW Alloy 690 at constant load in 360°C PWR primary water to investigate the effect of starting microstructure, cold work level, and applied stress on GB cavity formation and crack initiation. Periodic examinations performed on tested specimens are providing key information to understand possible degradation mechanism in these SCC resistant materials over long-term exposure and facilitating the prediction of their service life in LWRs.