Affiliations: [a] School of Manufacturing Science and Engineering, Sichuan University, Chengdu, Sichuan, China | [b] School of Mechanical Science & Engineering, Huazhong University of Science and Technology, Wuhan, Hubei, China
Correspondence:
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Corresponding author: Hui Fang, School of Manufacturing Science and Engineering, Sichuan University, Chengdu, Sichuan, China. Tel.: +86 13551233880; E-mail:jfh@scu.edu.cn
Abstract: Eddy current effect essentially occurs when relative
movement happens between steel pipe and axial magnetization coil in Hi-speed
MFL (magnetic flux leakage) testing. Based on the forming mechanism of
eddy-current, the eddy-current magnetic field distributions in different
parts were obtained, and it was found that the eddy-current magnetic field
and the original magnetizing field in pipe tail have the same direction,
resulting in the increase of the magnetization intensity; however, the
direction of the eddy-current magnetic field is opposite to the one of the
original magnetizing field in pipe head, which brings about the reduction of
magnetization intensity; and that the eddy-current magnetic field in pipe
body nearly has no influence on the magnetization. Due to the different
magnetization intensity in different parts of the steel pipe, sensitivity
difference is formed, lowering the accuracy of MFL testing. Further, the
elimination method for sensitivity difference by building extending magnetic
pole was proposed. Lastly, the relevant experiments for steel pipe were
conducted to verify the influence of the eddy-current magnetic field and the
effectiveness of elimination method.
Keywords: MFL (Magnetic flux leakage), steel pipe, eddy-current magnetic field, sensitivity difference, extending magnetic pole
