The influence of cyclic hydrogenated and oxygenated high temperature water on corrosion and stress corrosion cracking in Alloy 690

This study investigated the corrosion and stress corrosion cracking behavior of Alloy 690 in high temperature water under cyclic dissolved hydrogen and dissolved oxygen. Immersion and slow strain rate tensile tests were employed. Immersion results show that a duplex oxide structure forms, consisting of outer spinel layer and compact Cr-rich inner layer. Notably, prior DH exposure significantly accelerates subsequent oxidation in the DO stage. SCC susceptibility was found to be most severe in the DH-DO environment. This indicates that permeated H during the DH environment promotes SCC nucleation and propagation after exposure to DO. Optimizing primary water chemistry by maintaining moderate DH levels is essential for extending the service life of critical reactor components.