Double Coil Compensation Method for Reducing Distortion of High-Speed MFL Signals
Jinhai Liu, Hang Xu, Lin Jiang, Huaguang Zhang, Jiarui Liu · IEEE Transactions on Instrumentation and Measurement · 2025
The magnetic flux leakage (MFL) testing is widely used in the health evaluation of oil pipelines due to its nondestructive and efficient characteristics. However, motion-induced eddy currents (MIECs), which will cause distortion of the high-speed MFL signals, are generated in pipelines due to the relative motion with magnets. The distortion signals will reduce the accuracy of defect evaluation. In terms of the above issues, a double coil compensation method is proposed. First, the causes, distribution positions, and diffusion characteristics of MIECs are determined through the theoretical analysis to clarify the reasons for the distortion of high-speed MFL signals. Second, given the asymmetric distribution characteristics of MIECs, an asymmetric structure is proposed to capture MIECs at the defects and the magnetic poles, which cause distortion of high-speed MFL signals. Third, based on the double coil groups, an active–passive strategy is proposed to distinguish pipeline surface and back defects, which ensures the integrity of defect evaluation and enhances the reliability of pipeline repair. Finally, the compensation performance and distinguishing capacity of the proposed method are verified by simulated and experimental analysis. The results show that compensated signals approximate the static MFL signals and have satisfactory performances of defect size quantification.