Natural crack growth analyses for circumferential and axial PWSCC defects in dissimilar metal welds

The natural crack growth analysis (sometimes referred to as advanced finite element analysis (AFEA)) methodology has been developed by the US NRC and the nuclear industry to evaluate the natural crack growth due to primary water stress corrosion cracking (PWSCC) in nickel-based alloy materials. The natural crack growth (or AFEA) methodology allows the progression of a planar crack subjected to typical stress corrosion cracking (SCC)-type growth laws by calculating stress intensity factors at every nodal point along the crack front and incrementally advancing the crack front in a more natural manner. This paper describes the step-by-step procedure enhancements that have been made to the existing AFEA methodology. A significant enhancement was the feature to evaluate axial crack growth, where the crack was contained within the susceptible material. This methodology was validated by performing an AFEA evaluation for the axial crack that was found in the V.C. Summer hot-leg dissimilar metal weld (DMW). Other enhancements to the AFEA methodology include: feature to handle nonidealized circumferential through-wall cracks, mapping of weld residual stress for crack growth, and determination of limiting crack size using elastic-plastic J-integral analysis that included secondary stress (weld residual stress and thermal transient stress) effects. © 2012 American Society of Mechanical Engineers.