Accurate differentiation of whether the defect position is located on the inside or outside surface is necessary in the low-frequency electromagnetic detection technique (LFET) on oil and gas pipelines. We design a set of composite probe arrays that consisted of inductive magnetic coils (LFET coils) and eddy current testing (ECT) coils to accomplish comprehensive inspection, meanwhile, the theoretical calculation and analysis of the mutual interference mechanism between LFET and ECT coils were mainly implemented. Experimental result demonstrates that the ECT coils can effectively minimize the low-frequency magnetic field interference and allow low-frequency excitation coil setting parameters to be adjusted in a wide range (760 V Hz of voltage–frequency product in this experiment) to identify the inside defects above 1 mm depth while nothing found to detect outside defects. This circumstance enables the identification of the inside defect of 4 mm wide and 1 mm deep (10% wall thic...

中文翻译：

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低频电磁检测技术中基于附加涡流识别油气管道内外缺陷的有效方法

在油气管道上的低频电磁检测技术（LFET）中，必须准确地区分缺陷位置是位于内表面还是位于外表面。我们设计了一组由感应磁线圈（LFET线圈）和涡流测试（ECT）线圈组成的复合探头阵列，以进行全面检查，同时，对LFET和ECT线圈之间相互干扰机理的理论计算和分析主要是已实施。实验结果表明，ECT线圈可以有效地减小低频磁场干扰，并允许在宽范围内调整低频励磁线圈的设置参数（本实验中电压-频率乘积为760 V Hz）以识别内部深度超过1毫米的缺陷，而没有发现任何外部缺陷。这种情况下，可以识别出4毫米宽和1毫米深的内部缺陷（壁厚10％）。