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应用远场涡流检测技术检测导电管材,无论是铁磁的还是非铁磁的,正为人们广泛认识。这项技术用的是较简单的内部传感器,其中有一个激励源和一个置于远场空间的检测器。使用这项技术,可以以同样的灵敏度检测管壁内外表面的凹坑、裂缝和壁厚整体减薄。再者,如果将激励源和检测器信号间的相位滞后作为检测量,那么壁厚正比于相位滞后,而且提离效应很小。检测器区域的场以穿透式两次穿过管壁,而且那种直观的直接耦合在管内被大大削弱。人们熟知的涡流技术对凹坑和裂缝的检测能力已被扩展到能检测整个管壁,涡流信号与壁厚有线性的关系。对于钢,使用的频率范围是20～200Hz。图1为一具有代表性的远场涡流探头,它有一个螺管线圈式激励源和检测器。检测器可以是感应径向场式也可以是感应轴向场式,通常放在远场区域,距离激励源两至三倍的管径处。
The application of far-field eddy current testing technology to detect conductive pipe, whether ferromagnetic or non-ferromagnetic, is widely recognized. This technique uses a simpler internal sensor with an excitation source and a detector placed in the far field. Using this technique, pitting, cracks and wall thickness reduction on the inside and outside surfaces of the pipe wall can be detected with the same sensitivity. Furthermore, if the phase lag between excitation source and detector signal is used as the detection volume, the wall thickness is proportional to the phase lag and the lift-off effect is small. The field of the detector area penetrates through the tube wall twice, and the intuitive direct coupling is greatly impaired in the tube. The well-known eddy current detection of pits and cracks has been extended to detect the entire tube wall, the relationship between the eddy current signal and the wall thickness. For steel, the frequency range used is 20 ~ 200Hz. Figure 1 shows a representative far field eddy current probe, which has a solenoid coil excitation source and detector. The detector can be either inductive radial or inductive axial, usually in the far-field region, two to three times the diameter of the excitation source.