The role of initial cracks on creep crack growth and fracture mode of thick-walled pressurized pipe weldments

The creep crack growth (CCG) behavior and loading mode coupled with the initial small cracks distributed within the weldments play critical roles in the failure mode of thick-walled welded pipe at elevated temperature, which has not been revealed yet. In order to achieve this, a P91 welded pipe was selected as an example by considering the localized material inhomogeneity and geometry discontinuity of the weldment at 650 °C. In addition, the Liu-Murakami creep damage model was adopted and applied to the finite element (FE) analyses of P91 welded pipe with varied pre-defined initial small cracks within the weldment. The effects of pre-cracks lengths, locations, as well as loading modes (i.e., maximum end-load and closed end-load) were comprehensively and systematically evaluated, leading to the establishment of the fracture envelops for thick-walled welded pipe at elevated temperature. The key findings of this work are capable to provide a guidance for on-site health monitoring, maintenance, and remaining life assessment of in-service thick-walled welded pipe used in power plant at elevated temperature.