Environmental fatigue analysis of a U seal in pressure vessel under simulated LWR operation

Abstract

U seal components are widely used in light water reactor (LWR) plant for the purpose of sealing and connecting vessels and piping. Due to remarkable environmental effects, the environmental fatigue analysis is of crucial important for assessing the life of U seal in LWR applications. The environmental effects are incorporated by multiplying the cumulative fatigue usages (CUF) with an environmental factor (Fen), which is a complex function of many variables such as dissolved oxygen (DO) content, strain rate, temperature. The Fen-factor is found to be greater than 2 at the root of lower U seal branch, which indicates that environmental effects can significantly reduce the fatigue life of the components. Since the fatigue is related and initiated by high local stresses and temperature transient, an elastic–plastic finite element (FE) calculations are carried out. The environmentally assisted fatigue life assessments were performed by implementation of Fen-factor in FE calculation. The results of the case studies suggested that there were a sharp increase in calculated fatigue usage with Fen-factor, and the monitoring data were in consistent with the predicted environmental fatigue usage.