Abstract: According to Lenz’s Law, eddy current effect essentially occurs when relative movement happens between steel pipe and axial magnetizing coil in magnetic flux leakage(MFL) testing. The eddy current magnetic field and the magnetizing field magnetize the pipe together, eventually affecting consistency of the MFL signals. The aim is to analyze the affection on the pipe magnetization by eddy-current effect. Firstly, the eddy current distribution equation in the pipe is established based on the Lenz’s Law, and moreover the eddy current magnetic field is obtained. Then, the eddy current magnetizing affections on the pipe head, pipe body and pipe tail are analyzed respectively. The direction of the eddy current in the pipe head is opposite to the one of the magnetizing current, which brings about the reduction of magnetization status. However, the eddy current in the pipe tail and the magnetizing current have the same direction, resulting in the increase of the magnetization. For the pipe body, the eddy current has no affection on the magnetization. The finite element simulation was applied to analyze the relationship between the eddy current intensity and the pipe moving speed and the affection of the eddy current on the magnetization of the whole pipe, which supplies the reference of the uniform evaluation for the steel pipe.

Key words: Consistency, Eddy current effect, Magnetic flux leakage testing at hi-speed, Magnetization, Steel pipe