The Effect of Motion-Induced Eddy Current on High-Speed Magnetic Flux Leakage (MFL) Inspection for Thick-Wall Steel Pipe

The magnetic flux leakage (MFL) inspection technology is widely used in pipeline industry to detect defects to ensure pipeline safety. During the high-speed inspection, a relative motion occurred between the pipeline inspection gauge (PIG) and the steel pipe wall will generate motion-induced eddy current (MIEC). There is a lack of research on analyzing the effect of MIEC on high-speed MFL inspection for thick-wall steel pipe. In this article, a three-dimensional (3D) finite-element method (FEM) simulations are conducted with an inspection speed range of 0 m/s to 8 m/s and a wall thickness range of 8 mm to 15 mm. Simulation results show that both high-speed inspection and thick-wall thickness will decrease the magnetization of steel pipe. It is observed that, at the speed of 8 m/s and the thickness of 15 mm, the magnetic field strength is lower than 2 kA/m and the steel pipe exits from the magnetic saturation zone, which causes the severe distortion of three-axis MFL signals, and the signal-to-noise ratio (SNR) is lower than 6 dB. A high-speed PIG is developed here for experiments to measure the three-axis MFL signals. The characteristics of simulated and measured MFL signals are found to be quite consistent.