A comparative study between magnetic field distortion and magnetic flux leakage techniques for surface defect shape reconstruction in steel plates

Abstract Both magnetic flux leakage (MFL) and magnetic field distortion (MFD) techniques are promising methods for surface defect detection in ferromagnetic components. The two techniques are based on different physical principles. However, their defect sizing and shape reconstruction abilities are seldom comparatively explored. In this study, finite element simulations and experiments were performed to achieve magnetic scanning imaging of a defective plate with both MFD and MFL techniques. First, the curves of voltage extracted from the lines crossing the center of cylindrical-hole defect (CHD) were used to evaluate the performance of several feature parameters in sizing the diameter and the depth of CHD. Second, the profiles of the normalized magnetic scanning imaging results were analyzed with a threshold plane to evaluate the abilities of MFD and MFL on reconstructing the shape of 8-shaped and cross-type through wall defects. Under the condition that the Hall device for measuring both the normal component of MFL and MFD has same lift-off distance as 1 mm, the MFD technique showed the advantages in defect shape reconstruction at the cost of available detection depth as compared with MFL techniques.