Physical Compensation Approach for Feature Enhancement of High-Speed MFL Signals via Magnetic Field Polarization

Magnetic flux leakage (MFL) testing has been widely used to evaluate pipe integrity due to its high detection efficiency. However, motion-induced eddy currents (MIECs) occur in a steel pipe because of the relative movement between pipelines and magnets, resulting in diminished pipe magnetization and a distorted signal shape. Current approaches treat MIECs as a new excitation source or utilize compensation algorithms to eliminate the effect of MIECs, but they require collaborative environments and Big Data training. In this article, a physical compensation method that uses the polarization angle of magnets is proposed to address the issue. First, the generation, propagation, and distribution of MIECs in the pipe are analyzed to elucidate the action mechanism of MIECs on MFL signals. Second, a controllable magnetization method is utilized to achieve continuous saturation magnetization of the pipe. Third, an obliquely incident magnetic field is injected into the pipe to reduce the asymmetric of MIECs. Finally, an experimental pipe is applied to intuitively illustrate the velocity compensation effect. Results evidenced the capability to accurately detect defects in the range of 0–3 m/s. The ease of the proposed method has a bright future for high-speed MFL evaluation in the service of the pipe.