Evaluation of nondestructive inspecting method of surface and opposite side defect in steel plate using large static and minute alternating magnetic field

Abstract

In the inspection of the steel wall or bottom steel plate inside the tank in the petrochemical plant etc., it is necessary to detect the opposite side defect from the surface of the steel plate. In this paper, the electromagnetic nondestructive inspection method using large static and minute alternating magnetic field is proposed. And, this proposed inspection method is investigated by verification experiment and 3-D nonlinear finite-element method (FEM) taking account of hysteresis (minor loop) and eddy current in steel. It is shown that the detection of both surface and opposite side defect is possible by the differential permeability of minor loop of which the position on the hysteresis loop is affected by the existence of defect.