Quantification of creep cavitation damage around a crack in a stainless steel pressure vessel

In this paper, metallographic sectioning and non-destructive small angle neutron scattering (SANS) are used to map the level of creep cavitation around a surface breaking crack in a stainless steel pressure vessel. The cracking developed during 65,000 h service at an operating temperature of around 525 °C and was promoted by the accumulation of creep strain resulting from relaxation of tensile residual stresses associated with a nozzle attachment weld. The distribution and evolution of the cavities is discussed in terms of existing models of creep cavitation failure based on a ductility exhaustion model in which the corresponding multi-axial creep ductility, expressed as the von Mises strain at failure, is a function of the strain rate and stress state. An empirical approach has been adopted for describing the effects of stress state on ductility, which takes into account cavity nucleation as well as cavity growth by creep deformation, and is similar to local approach models for ductile crack growth. Crack initiation is conceded when the creep damage parameter Dc≥1. The measured creep cavitation results are found to be in reasonable accordance with such a model