A Simplified Lift-Off Correction for Three Components of the Magnetic Flux Leakage Signal for Defect Detection

Abstract

Magnetic flux leakage (MFL) testing is widely used to detect and estimate defect in ferromagnetic materials. The lift-off of sensors caused the weakening of the detected signal inevitably. Therefore, it is necessary to correct lift-off for the detected MFL signal. In this article, we analyze the approximate negative exponential relationship between the three components of MFL signal of the defect and the lift-off based on magnetic dipole analytical method and establish a simplified numerical calculation model of MFL signal based on the lift-off. A lift-off correction method is also proposed to revise the three components of the MFL signal at a suitable range of lift-off efficiently. In this method, an exponential function compensation is introduced and only the lift-off correction value is concerned. The validity of the correction method is verified by the 3-D MFL testing experiment for the ferromagnetic pipeline defects. The results demonstrate that the corrected MFL signals match the experimental signals well.