Imaging and analysis of closed stress corrosion cracks in Ni-based alloy weld metal using subharmonic phased array

Closed stress corrosion cracks (SCCs) in Ni-based alloy weld metal (NBAWM) lead to a problem of underestimation or overlook in ultrasonic inspection, resulting in catastrophic accidents such as radiation leaks. For application of new inspection methods to solve this problem, and for training/education of inspection, fabrication of realistic of realistic closed SCC specimens is required, through it takes many years. Here we propose a two-step process to form closed SCCs in NBAWM in relatively short time of several months. This method first forms an open SCC by accelerated chemical methods and then close it by a short time immersion in high temperature pressurized water (HTPW). The crack closure was verified by subharmonic phased array for crack evaluation (SPACE), capable of measuring closed SCC. In addition, we developed an FDTD (finite difference time domain) method with damped double node (DDN) model of closed crack for 2D simulation of subharmonic generation. (author)