Investigations on the lifetime behaviour of a P23 pipe under fatigue loading

The performance of girth welds on new P23 low chromium steel pipes under cyclic loading at 450°C was investigated. The loading conditions were chosen to be representative for bore crack initiation and growth observed in main steam lines fabricated of 0.5Cr0.5Mo0.25V (CrMoV) steel. The microstructure of the base material and weldments was analysed. A lifetime model, initially set up for the prediction of thermo-cyclic loading, is used to predict the isothermal component behaviour. It is based on a Chaboche-type deformation model and the DTMF crack growth mode. The failure mechanism of two component tests was compared to the model assumptions and the component lifetimes and failure locations are compared to the model preditions.