High-resolution pipeline in-line inspection based on non-equilibrium sensing with uneven electromagnetic distribution

High-resolution eddy current in-pipe inspection faces a critical trade-off between sensitivity and resolution. In particular, the uneven magnetic field will result in inconsistent responses from the receiving array elements to decrease the sensitivity of defect, complicating the defect identification and evaluation. To address this issue, this study develops a non-equilibrium sensing mode of enhancing electromagnetic field adjustments to balance the induction field due to an uneven distribution. Specifically, it builds upon differential eddy current probes by adaptively constructing Gaussian compensate distributed hollow-core copper coils with varied structural parameters, forming a receiving array that enhances the probe's discriminative ability as well as maintaining sensitivity. To strengthen the induced eddy current, the excitation coil is relocated from above the receiving coil to the same plane as the receiving coil array. This adjustment mitigates the sensitivity reduction caused by the resolution enhancement. A theoretical equivalent circuit model of the proposed method is established. Both simulation and experiments on vary defects in pipeline have been conducted to validate the reliability and efficiency of the proposed system. Furthermore, the defect's location relative to the probe and its estimated size can be preliminarily determined based on the presence and amplitude of the detection signal from the receiving coil array.