Creep-Fatigue Life Properties and Its Life Prediction Method for Weldment of P91 Steel

In high chromium steel weldments used in major high-temperature components of thermal power plants, Type IV cracking is known to occur by accumulation of creep-fatigue damage. In this study, creep fatigue life data of P91 steel weldments were obtained by conducting strain-controlled creep fatigue tests. The inelastic finite element analysis was performed to clarify the stress distribution in P91 weldment/base metal under the creep-fatigue loading. Consequently, a highly accurate creep-fatigue life evaluation method considering the stress multiaxiality in the weldment was proposed based on the ductility exhaustion rule and nonlinear finite element analysis. As a result of this study, it was confirmed that Type IV cracks occur at the heat-affected zone (HAZ) in these creep fatigue tests, and the creep fatigue life of P91 weldment can be predicted within a factor of two by the modified ductility exhaustion method modified by the stress multiaxiality.