Evaluation Of Creep Damage Of Steam Turbine Heat Resistant Material Based On Nonlinear Ultrasonic Longitude Wave Technique

Ultra supercritical steam turbine which is operated at high temperature and high stress for long periods usually face the threat of creep damage. Therefore, it is very important to perform quick and effective testing for structure health monitor during creep damage. Recent studies have shown that the damage of material has a close relationship with the nonlinear ultrasonic wave which attracted much research interests. The present paper has performed an in-depth analysis on the evaluation of the creep damaged specimens using nonlinear longitude wave. The main researches and results were as followings:(1) Evaluation of creep damage of steam turbine screw material In783 using nonlinear ultrasonic wave. Results show that the nonlinear ultrasonic parameters of longitudinal wave increase with the increasing of creep strain. Based on the observation of microstructure, nonlinear parameter increases due to the increasing of dislocation density and the growth of precipitates. The hardness of the creep In783 specimens was also measured which exhibited the same trend as the variation of the nonlinear parameter. It can be inferred that, to a certain extent, the results of nonlinear longitude wave could be used to characterize the change state of the mechanical property in material. A theoretical computation was performed by the dislocation-precipitate model, the results show that the computation results from the analytical model displays a good agreement with the experimental data.(2) Evaluation of creep damage of steam turbine rotor steel FB2 using nonlinear ultrasonic wave. Results show that the nonlinear ultrasonic parameters of longitudinal wave increase with the increasing of creep strain. Based on the observation of microstructure, nonlinear parameter increases due to the increasing of dislocation density, the variation of the nonlinear parameter has relationship with the creep damage regime. Furthermore, the relationship between steady creep strain rate and nonlinear parameter was established.