A new type of magnetising and magnetic flux leakage inspection system for the non-destructive testing of pit defects on the surface of a steel sheet

A new type of magnetising and magnetic flux leakage (MFL) inspection system is designed, in which an ARM microprocessor-based measuring circuit and a novel magnetising device developed by the authors are combined to detect the magnetic field around a pit defect in a steel sheet. Based on a series of careful detection experiments, the spatial distributions of the three-dimensional (3D) MFL components of some typical artificial defects are described and observation, comparison, feature extraction and analyses are then carried out. The results show that the 3D components of the MFL field produced by the newly proposed magnetising device present some distinctive properties compared to those made by the traditional magnetising device. They involve rich information that exhibits close correlations to the morphology and critical parameters of the pit defects on the near side of the steel sheet, demonstrating the feasibility, effectiveness and reliability of the newly proposed inspection system, as well as laying a good foundation for the testing, evaluation or reconstruction and inversion of the pit defect.