Modeling the Effects of Pit Corner Geometry on Magnetic Flux Leakage Signals

Three-dimensional magnetic finite element analysis (FEA) has been used to simulate the effects of different pit corner geometries on magnetic flux leakage (MFL) signals. The pit corner geometries studied fall into three main categories: right angle, smooth triangular, and smooth round. These geometries are simulated using rectangular grooves and circular pits in steel plate. The axial and radial components of the MFL signal are obtained on the topside as well as the underside of the steel plate. Both the peak position and the peak height/depth of the MFL signal were found to be influenced by the sharpness of the pit corner. In general, the underside axial MFL peaks shifted toward the center of the pit, and their height increased with decreasing sharpness of the corner. For the underside radial MFL peaks, there was an appreciable peak shift; however, the change in peak height was insignificant. However, the peak height depends strongly on pit depth. The topside results were only slightly different from the underside. Despite some changes in MFL signal position and form, it was concluded that in practical inspection situations these changes would be relatively small and difficult to quantify.