Examination of inspecting method of opposite side defect in steel plate using AC and DC magnetic field

Abstract

In the inspection of the steel wall of the tank in the petrochemical plant etc., it is necessary to detect the opposite side defect from the surface of the steel wall. In this paper, the electromagnetic inspection method using alternating (ac) and static (dc) magnetic field is proposed. And, this m ethod is investigated by verification experiment and 3-D nonlinear finite-element method (FEM) taking account of hysteresis (minor loop) and eddy current. It is shown that the detection of 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.