Velocity effect in defect detection for ferrite metals by electromagnetic NDT

Nondestructive Testing (NDT) for moving ferrite metal component is a challenging topic because of the magnetic fields generated by the motion induced eddy current (MIEC) and ferrite magnetization in sample. The magnetic fields distribution inside the moving ferrite metal are more complicated. Therefore, an accurate and efficient NDT technique for monitoring the health condition of metal component with the high-speed is an urgent problem. In order to investigate the influence of velocity effect on defect detection of ferrite metal components, a numerical simulation model of the electromagnetic NDT system by using Finite element method was established, and the relationship between the detection signal and velocity considering the different defect depths and widths are deeply analyzed. The results show that with the increase of the speed, the MIEC is stronger and the dragging effect is more obvious, which are the new phenomenon for the moving sample compared with the static sample. Furthermore, the defect width and depth can be reflected by the magnetic flux density, and the strength of the magnetic flux density increases with the increase of the speed, which is advantageous to the localization and characterization of the defect. The findings in this paper are helpful and beneficial to propose a new NDT method for the defect detection in the moving ferrite metals, such as rail tracks and pipelines.