Evaluation of wall thinning defect in magnetic material based on PECT method under magnetic saturation

One of the major safety issues in nuclear power plants is pipe wall thinning where the pipe is mainly of magnetic material. Due to the large magnetic relative permeability of piping and the skin depth effect, the conventional PECT method is difficult for detecting the opposite side wall thinning. In this study, a pulsed eddy current testing (PECT) method under magnetic saturation was proposed and validated through numerical simulations and experiments. First, the mechanism of how magnetic saturation can increase the skin depth was studied through numerical simulation with help of COMSOL Multiphysics software. Second, the detection sensitivity of magnetic field signal and voltage signal for wall thinning defect of specimens with various magnetic permeability was investigated through numerical simulation. Finally, the experiments of magnetic saturation PECT were conducted, and the feasibility and superiority of the proposed magnetic saturation PECT method were demonstrated.