Magnetic Permeability Perturbation Testing Based on Pulse Magnetization for Buried Defect in Ferromagnetic Material

Magnetic permeability perturbation testing (MPPT) based on dc magnetization is effective for deep-buried defect detection. However, ferromagnetic materials with large thicknesses require larger magnetization devices, which hinders the lightweight design of in-service inspection equipment. This article proposes an MPPT based on pulse magnetization (PMPPT) for buried defects. Under the influence of pulse magnetization, information about the internal defects is mainly transferred to the surface layer of the material through the magnetic permeability perturbation (MPP) and then detected by sensors. The MPP within the material under pulsed magnetization is analyzed, and the feasibility of this method is verified by simulations and experiments. Experimental results demonstrate the effective detection of defects located at a depth of 1 mm on the backside of a specimen with a thickness of 12 mm. Furthermore, the effects of pulse magnetization parameters, including frequency, duty cycle, and amplitude, on the detected signals are investigated. The results indicate that increasing the pulse current amplitude enhances the detection signal, while a lower pulse square wave frequency is more effective for thicker samples. By adjusting the amplitude and duty cycle of the pulse current, the detection signal can be improved compared to dc magnetization. PMPPT can contribute to reducing the weight of in-service inspection equipment and holds significant potential for engineering applications.