Crack initiation resistance characterization of weld by small-punch test in boiling water reactor environment

Crack initiation resistance tests of a type 316L stainless steel weld were performed in high temperature and high pressure water. Small-punch test specimens were used under trapezoidal loading. This survey showed that there are two crack initiation modes in such conditions. The crack initiation at the slip line was promoted by a gradient in term of oxide film composition and in term of local environment (water chemistry). The crack initiation at inclusions was promoted by a local dissolution creating geometric default. The heat affected zone specimen presented the highest probability of initiation with the highest probability to have the longest crack according to the Poisson distribution. These phenomena were attributed to the residual stress that enhanced: (1) a deformation at the micro scale very irregular promoting an instability of the oxide film; (2) the diffusion of Fe producing the formation Fe ₃O ₄ associated with α-Fe ₂O _3..