Investigation into the prediction of creep crack growth rate in P91 steel under multi-axial stress state

P91 steel components are often subjected to multi-axial stress states during service, which can lead to creep damage and crack propagation, thereby reducing their operational lifetime. By employing the Wen-Tu multi-axial creep ductility factor, the relationship between ductility and creep crack behavior in P91 steel is analyzed to determine the strain under multi-axial stress states. A creep damage model based on ductility exhaustion is established to evaluate damage accumulation. The GE-EPRI method is used to compute fracture mechanics parameters, and a power-law creep model incorporating a threshold stress is applied to characterize the multi-axial stress field. Through the definition of constraint parameters and the development of a predictive model, the creep crack growth rate is estimated. Experimental results indicate that, under identical conditions, the crack growth rate in notched specimens of P91 steel under triaxial stress is higher than that in smooth specimens. Compared with existing approaches, the model proposed in this paper demonstrates improved agreement between predicted creep crack growth behavior and experimental data, leading to significantly enhanced accuracy in predicting the service life of P91 steel under complex stress states. This methodology offers a more reliable basis for safety assessment and remaining life prediction of P91 steel components.