基于脉冲激励的远场涡流检测机理及缺陷定量评估技术

Inspection Principle and Defect Quantitative Estimation of Pulsed Remote Field Eddy Current Technique

脉冲激励信号包含非常丰富的频谱成分,以脉冲激励代替传统的正弦激励为克服远场涡流技术的不足提供了新的解决途径。在分析了脉冲激励下远场涡流检测机理的基础上,仿真分析了激励线圈和管道周围磁场和涡流的分布,得到了检测线圈处于不同场区时瞬态检测信号的变化规律,确定了远场区的范围。并从检测信号中提取了过零时间作为缺陷定量的特征量。最后,采用实验的方法验证了脉冲激励下的远场涡流技术对管道中轴向裂纹缺陷长度和深度的定量检测能力,实验结果表明该技术可以很好的实现对缺陷的定量评估。

Remote field eddy current （RFEC） technique has been widely used for the inspection of ferro- magnetic pipes and it＇s not restricted by the skin-depth effect. However, the technique under the sinusoidal excitation needs a long probe and a high power dissipation, which restricts the application of RFEC in real inspection. The pulse exciting signal has the advantages of rich frequency components, the disadvantages of the traditional RFEC can be overcome by using pulse excitation instead of sinusoidal excitation. On the basis of analyzing the principle of pulsed RFEC, the distributions of the magnetic field and eddy current a- round the pipeline and exciting coil are simulated and analyzed, the changing rule of transient state detec- ting signals in different field regions is studied and obtained with finite element simulation method, then,the remote field region is confirmed. The zero-crossing time and negative peak value are extracted as the eigenvectors for defect quantification. Finally, the performances of quantifying the axial defect length and depth by the pulsed RFEC are verified by performing an experiment, the result shows that this technique can be used to realize the quantitative estimation of the defect.