Thermal–mechanical fatigue behaviour of P92 T-piece and Y-piece pipe

This paper presents a study on thermal–mechanical fatigue (TMF) behavior of P92 T-piece and Y-piece pipe at the most critical working fluctuations. Pressure and temperature in isothermal, in-phase (IP) and out-of-phase (OP) loading conditions were taken into account. Cyclic plasticity model considering the effect of temperature was used, in which both kinematic hardening variable and isotropic hardening variable are included. All the parameters used in the simulation were obtained from low cycle fatigue (LCF) tests at different temperatures. These parameters have been validated through the comparison of experimental data with the simulated data. Then, finite-element models (FEM) of P92 T-piece and Y-piece pipe were developed to investigate the location of the most critical region at typical thermal-mechanical loading. Simulated results reveal that the most dangerous position occurs at the region where the inner surface of horizontal pipe and branch pipe crossed for both T-piece and Y-piece pipe which is irrelevant to the types of loading. IP loading is the most serious working condition for both T-piece and Y-piece pipe. Comparing with T-piece pipe, Y-piece pipe at IP loading is the most dangerous condition.