Effects of initial crack positions and load levels on creep failure behavior in P92 steel welded joint

The finite element method based on ductility exhaustion damage model coupled with the stress-regime dependent creep constitutive model was used to investigate creep failure behavior at different load levels for six initial cracks at different positions in P92 welded joints. The stress states and creep damage around cracks, creep crack growth (CCG) paths and rates and rupture life have been calculated and analyzed, and the creep failure and life assessments for welded joints were discussed. The results show that for some cracks with specific positions in the welded joint, load level causes the change of CCG path due to the stress-regime dependent creep constitutive. At low load level, the significant mismatch effect in creep properties promotes the initiation and propagation of second cracks in soft materials near interfaces, and the creep rupture life is mainly determined by the incubation time of the second cracks. This result is confirmed by similar experimental observations in the literature, and the mechanism was analyzed. For the initial crack positions with a second crack, if the extrapolation of CCG rate from higher load levels is used in creep life assessment of a welded joint at lower load levels, the non-conservative (unsafe) results will be produced. In creep failure analyses and life assessments of welded joints, the effects of initial crack positions and load levels should be fully considered.