小径管脉冲远场涡流检测研究

Study on Inspection for Small Diameter Tubes Using Pulsed Remote Field Eddy Current Method

小径管如热交换器管等在工业中应用广泛,不少使用情况下需要定期检测。远场涡流技术是检测小径管缺陷的有效技术之一,在此基础上,脉冲远场涡流检测技术结合了脉冲涡流的频谱丰富性和远场涡流技术同时检测内外管壁缺陷的特点。应用脉冲远场涡流检测技术对小径管进行检测,并对该技术中差分式探头和绝对式探头的检测特点进行系统详细的研究。设计一种新型差分式探头,其接收部分由两个差分连接的检测线圈组成。差分结构中的一个检测线圈用作绝对式线圈,其检测信号采用一个信号采集通道处理,同时两个线圈的差分信号则采用另一个信号采集通道处理。通过数值仿真分析了检测原理,并对腐蚀、孔状和裂纹三种类型管道试件缺陷进行了系列检测研究。试验结果表明探头中的差分线圈对裂纹类、孔类缺陷具有很好的检测灵敏度,远优于绝对式线圈的检测能力,但对检测渐变腐蚀类缺陷不敏感;同时探头中的绝对式线圈对渐变腐蚀具有很好的检测灵敏度。绝对式线圈检测信号中存在着明显的伪峰信号,但差分式线圈则能够有效抑制伪峰信号。所设计的应用双通道处理方法的探头可同时有效检测三种类型的缺陷,并且脉冲涡流检测所具有的缺陷深度定位特征也仍然有效。

Small diameter tubes such as heat exchanger tubes are widely used in industry, and usually require regular inspection in many services. Remote field eddy current testing(RFEC) is one of the effective nondestructive testing methods to detect defects in small diameter tubes, Pulsed remote field eddy current(PRFEC) method combines the rich spectrum of pulsed eddy current with the characteristic of RFEC to detect inner and outer defects simultaneously. PRFEC method is used to detect small diameter tubes, the detection characteristics of the differential probe and the absolute probe in this technology are systematically studied. A novel differential probe is designed with two receiving coils connected in differential mode. One receiving coil of the differential probe is used as absolute coil and its signals are processed with one signal channel. The differential signals from two receiving coils are processed with another signal channel. The detection principle is analyzed through numerical simulations, and three types of defects, corrosion, hole and crack are tested in experiments. The experimental results show that the designed differential probe has a high detection sensitivity for cracks and holes, which is much higher than the absolute coil, but wide defects are detected by the absolute coil. Signals of the absolute coil have obvious spurious peaks, but the spurious peak can be restrained by the differential probe. Three kinds of defects can be effectively detected using designed probe with dual-channel signal reception method, and the defect depth characteristic of pulsed eddy current testing is still valid.