Analysis of the Eccentric Problem of Wire Rope Magnetic Flux Leakage Testing

Magnetic flux leakage (MEL) technology is widely used for the inline inspection of wire rope made of ferromagnetic steel. In order to protect magnetic sensors and ensure the wire rope through the exciting device smoothly, the diameter aperture of exciting device was larger than the diameter of the wire rope. It causes wire rope deviate from the center of the exciting device (eccentric problem), leads to the problem which affect quantitative detection, such as the changed magnetizing condition, the lift-off (the distance between the Hall sensors and the surface of wire rope) and the angle of Hall sensors change. Through simulation analysis, we found that the magnetization state and angle factors have little influence on the detection signal, and changes of lift off is the main factor affecting the detection signal. From simulation analysis, A result equivalent relation between ideal state and eccentric state test is proposed in the thesis. By comparing the actual detection signals of same defect at different eccentric states, it is found that the eccentric state has an influence on the actual detection signal, it will affect the results of quantitative analysis of magnetic flux leakage detection.