Modeling the creep damage effect on the creep crack growth behavior of rotor steel

Abstract

AbstractTo evaluate the fracture life of steam turbine HP-IP rotors more accurately, an understanding of the creep damage effect on creep cracking performance of service-exposed rotor steel, and a proper creep crack growth (CCG) model considering the creep damage effect, is essential. In the present work comparative CCG tests were carried out on virgin and rotor steel that had been in service for 16 years, to examine the differences in creep crack microstructure and CCG rate between these two specimen types. Test results showed that the CCG rate of service-exposed steel is accelerated by creep damage due to metallurgical deterioration. Based on the CCG model derived by Webster, an improved CCG model is proposed by replacing the constant exponent with a creep-damage-related variable. To validate the improved model, a comparison of da/dt vs. C* between experiment data and the CCG models was conducted. The predictive result of the improved model is in better agreement with the experiment results than the classical CCG and Webster models for the service-exposed rotor steel. With decrement of C* value within the improved CCG model, the remaining life of HP-IP rotors may be predicted more accurately.