Abstract
In the last decade, data has changed the perception of Alloy 690 and its weld metals from materials that are immune from stress corrosion cracking (SCC) to materials that can exhibit low growth rates under good circumstances, but have vulnerabilities that can increase the growth rates by 1000X. The primary vulnerabilities evaluated relate to microstructural homogeneity and cold work. With sufficiently high cold work, roughly above 20%, dramatically higher crack growth rates are observed. This appears applicable to most, if not all, heats and forms of Alloy 690. This paper summarized on-going work that presents data on the effect of cold work and the orientation of the crack plane in relation to cold work. Various heats of Alloy 690 have been studied, ranging from plates to control rod drive mechanism (CRDM) housings. This paper summarizes extensive testing on Alloy 152 and 52 weld metals, which consistently show very low growth rates apart from one case where 20% additional strain was applied to the weld metal. Other studies in progress have characterized various welds and heat affected zones, and are beginning to evaluate conditions of greater concern, i.e., related to weld repairs and welds with re-fuse layers, both of which increase the residual strain levels.
