EAC Crack Initiation in Ni-Based Alloy Dissimilar Metal Welds in Doped Steam

EAC susceptibilities of Alloy 600 and 690 and their weld metals with and without weld defects such as hot cracks were studied in pure and doped hydrogenated steam at 400oC on four-point bend (0.35- 1.1% strain) and U-bend specimens (5% strain). Contrary to the expectations, no EAC initiation from existing weld defects was observed. As expected, Alloy 600 and its weld metals Alloys 82 and 182 were much more prone to EAC initiation than Alloy 690 and its weld metals Alloys 52 and 152. Oxide structures remain the same in doped and pure steam, although the doped environment has an impact on the EAC initiation time and oxidation rate. Because of the similar oxide structures, the EAC mechanism is assumed to be the same in the studied environments. The application of doped steam testing as accelerating testing method for environmentally assisted cracking of nickel-based alloys is discussed