Electromagnetic Inspection for Detecting Defect of Underground Part of Road Sign Pillar

Since the steel pipe of a road sign pillar is built for years on the ground, the underground part of its steel pipe may be corroded. In recent years, the accident from which the road sign pillar falls down has increased owing to the corrosion in the underground part of its steel pipe. In this paper, the nondestructive inspection method for detecting the defect in the underground part of its steel pipe using the alternating magnetic field by low exciting frequency is proposed. In this method, both the distance from the electromagnetic sensor to the defect and the depth of the defect are presumed. The usefulness of this proposal inspection method is shown from both the 3-D nonlinear electromagnetic finite-element method analysis and the experimental verification.