Examination of Thickness Evaluation of Steel Plate Using DC Bias Magnetic Field by 3-D FEM Analysis Considering Minor Loop Magnetic Characteristics

A thickness evaluation of steel plates and large-diameter steel pipes in various plant structures is considered important for plant safety. In this article, an electromagnetic inspection method that can evaluate this thickness using a pulsed magnetic field is investigated. When a steady square-wave pulse magnetic field with dc bias is applied from the surface of the steel plate, the relationship between the leakage flux on the steel plate and the plate thickness is investigated. The inspection principle is evaluated by an electromagnetic field analysis considering eddy current and minor loop magnetic property of the steel plate and verification experiments. In addition, it is also confirmed that the calculation results considering the hysteresis curve in the steel plate are more useful than those considering only the initial magnetization curve.