INVESTIGATION OF HYDROGEN ATTACK IN 2.25Cr-1Mo STEELS WITH A HIGH-TRIAXIALITY VOID GROWTH MODEL

Abstract-A model is presented to estimate the lifetime under hydrogen attack (HA) conditions. The first ingredient is the Odette-Vagarali model to calculate the equilibrium methane pressure as a function of hydrogen pressure, temperature, and type and composition of the carbides and the alloy. The second ingredient is a model for the growth to coalescence of methane-filled grain boundary cavities, possibly under the presence of (applied or residual) macroscopic stresses. This model is based on recent detailed numerical studies of the growth of voids under simultaneous grain boundary diffusion and creep of the grain material. A new, accurate analytical approximate void growth relation valid for high stress triaxialities is adapted for application to HA. The model is used to perform a study of HA, including a computation of Nelson curves, in 2.25Cr-1Mo steels with different types of carbides and for various applied stress states. Finally, the results of the model are presented in a concise, non-dimensional form that reveals the key parameters that determine HA life times. 1