In order to get a thorough comprehension on how the eddy current affects the MFL signal in high speed testing, distribution of eddy current and the magnetic field generated by it are first analysed theoretically. Then, the magnetization statuses of the pipe in static and motional situations are investigated by finite element simulation. Finally the external and internal defect signals are extracted in both static and motional cases. The results show that, in high speed testing, the magnetic field is strengthened at the outer surface and weakened at the inner surface, which increases the external defect signal but decreases internal defect signal.
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