ACFM（Alternating Current Field Measurement,交流电磁场检测)技术是通过测量磁场的变化探测裂纹并测定裂纹尺寸的一种无损检测方法。近几年来，国内海洋工程行业引进了ACFM设备进行水下结构件检测工作。介绍了利用U31型检测设备对水下铁磁构件实施ACFM检测的试验情况，对检测中得到的显示图谱进行了分析，总结了不同的相关显示和非相关显示的图谱特征，并编制了一个用于检测缺陷判定的工艺流程，用于实际检测时帮助识别缺陷。

ACFM, which means Alternating current field measurement, is a NDT technique which detects cracks and determines the size of the cracks by measuring the change in the magnetic field. In recent years, ACFM equipment was introduced to the domestic marine engineering industries for underwater structure inspection. The paper described test cases where ACFM inspection by U31-type testing equipment was implemented for underwater ferromagnetic structures. The detected spectrums obtained were analyzed; the spectrum features of the different related display and non-display were summarized. At the same time, a defect determination process was prepared for the actual test to help identify defects.