Magnetic Flux Leakage Testing of Reverse Side Wall-Thinning by Using Very Low Strength Magnetization

This study focused on the very low-field region of the initial magnetization curve and developed a method to inspect and evaluate reverse side wall-thinning on a ferromagnetic test object by using very low strength magnetized magnetic flux leakage testing. The principle of the method was derived based on the magnetic circuit theory, and a parameter named as differential magnetic-leaking reluctivity was found to be a linear function of the remaining thickness of a ferromagnetic steel plate with thinning on the reverse side. This approach was verified by electromagnetic numerical simulation, and highly sensitive magneto-impedance sensor utilized measurements. Preliminary measurements demonstrated that it is possible to measure and estimate the thicknesses of ferromagnetic plates using very low-level magnetized magnetic flux leakage testing, suggesting the applicability of using this approach to inspect and evaluate over a sufficiently large area reverse side thinning.