ABSTRACT In high-speed magnetic flux leakage (MFL) testing, the tested workpieces pass rapidly through magnetizers. Thus, the magnetization time for workpieces is short. Because of the eddy current effect, the magnetic field inside the workpieces cannot instantly reach equilibrium, and if the magnetizing time is insufficient for the field to reach equilibrium, the MFL signals will be changed because of incomplete magnetization. In this article, the magnetization time lag caused by eddy currents and the influence of this lag on high-speed MFL testing is investigated. The time required for magnetic field to reach equilibrium in specimens, including steel bars and pipes, is obtained by theoretical calculations, finite element simulations, and experiments. The results indicate that the time required for a magnetic field inside a specimen to reach equilibrium is in the range of 50–100 ms. Using conventional magnetizers, the defect signals at testing speed of 10 m/s change because the workpiece reaches the detection zone before the magnetic field inside reaches the stable state. A simple solution is to increase the axial length of the magnetizing coil. After this procedure, signals obtained at 0.1 m/s and 10 m/s are almost identical.

中文翻译：

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涡流引起的磁化时滞及其对高速MFL测试的影响

摘要 在高速漏磁（MFL）测试中，被测工件快速通过磁化器。因此，工件的磁化时间很短。由于涡流效应，工件内部的磁场不能瞬间达到平衡，如果磁化时间不足以使磁场达到平衡，MFL信号会因磁化不完全而改变。在本文中，研究了涡流引起的磁化时间滞后以及这种滞后对高速 MFL 测试的影响。磁场在试样（包括钢筋和管道）中达到平衡所需的时间是通过理论计算、有限元模拟和实验获得的。结果表明，样品内部的磁场达到平衡所需的时间在 50-100 ms 的范围内。使用常规磁化器时，由于工件在内部磁场达到稳定状态之前到达检测区域，因此在10 m/s的检测速度下缺陷信号发生了变化。一个简单的解决方案是增加磁化线圈的轴向长度。在此过程之后，在 0.1 m/s 和 10 m/s 获得的信号几乎相同。