Numerical Electromagnetic Simulation for High Resolution Eddy-current Testing Method

Abstract

The applicability and feasibility of eddy current detection method for the measurement of wall thinning and surface crack of steel structure have been practically confirmed by field and laboratory experiments. Recently, we could roughly understand where and how large the defects are by this method. However, it is difficult to estimate the exact size and shape of them. For more accurate inspections, there has been a growing demand to quantitatively evaluate the defects. Therefore, we have developed a numerical simulator to consider whether we could develop the high accuracy eddy current method. Eddy current method uses the information of excitation and induced magnetic field. In order to calculate the induced magnetic field, we used a 2.5 dimensional finite-difference frequency domain technique (2.5D-FDFD) to solve Maxwell's equations numerically. In this technique, we assumed the two-dimensional structure and the three-dimensional electromagnetic field. We used two-layer structure consisting of seawater and steel plate containing defects. To estimate characteristic of the induced magnetic field, we simulated for a variety of defects and compared what effect appear. As a result, we could confirm the effect of surface defects of steel plate on receiving magnetic field intensity. The induced magnetic field intensity increases near the edge of the defects and decays above the defects. The larger depth and width of the defects are, the more attenuate the magnetic field intensity becomes. Our simulation results indicated that we could obtain the response of magnetic field intensity whose detectable scale of defects is no smaller than mm order.