Serious Concerns and Actions for Mitigating Future Degradation in Modern Steam Generators

Abstract

This review discusses both corrosion-related degradation that can occur in the future in modern steam generators and what actions should be taken to predict and minimize such degradation. This review considers the full set of tubing materials now being used: Alloys 600MA, 600TT, 690TT, 800NG, and Type 321 stainless steels. It appears that the Alloys 690TT and 800 give the best performance in vertical SGs and that the Type 321SS gives adequate lifetimes for the horizontal steam generators. Predicting future modes of degradation for long life plants is emphasized with respect to the expected longer lives of SGs, higher performance, and less inspection. A method for predicting degradation after long times is described. Special attention is given to the effects of lead- and sulfur-related SCC together with the tendencies of such species to accumulate in the deposits of heat transfer crevices. A set of damage scenarios is given, and high priority tasks that should be considered are identified.