Creep-fatigue damage and life prediction in P92 alloy by focused ultrasound measurements

Abstract

In the present study, the characteristics of creep damage in P92 alloy were investigated via nondestructive evaluation. Generally, as the hold time of a static load increases, the degradation of the material becomes more severe along with a reduction of service life. Therefore, in power plants, the reduction of creep-fatigue strength and the creep-fatigue life of high pressure vessels at high temperatures, such as steam pipes, become very important. To evaluate the effect of damage, backscattering ultrasound signals were analyzed from creep-fatigue specimens, where both static and cyclic loads had been applied simultaneously. The testing temperature trapezoidal creep-fatigue loading wave shapes with hold times ranging from 0 s to 1000 s at the maximum load were employed. The results obtained from bulk waves of focused ultrasound were compared and analyzed with the experimental parameters. The relationships between these parameters, the RMS level of backscattering signals, and the area fraction of the cavity in the creep-fatigue damage zone were investigated to evaluate the lifetime of the damaged specimens.