基于脉冲远场涡流的管道缺陷外检测与定量评估

Outside inspection and quantitative evaluation of pipe defects based on pulsed remote field eddy currents

远场涡流技术用于金属管道检测时,由于对内、外壁缺陷具有相同的灵敏度,而难以有效区分缺陷位置。针对压力管线在役检测需求,提出了一种基于脉冲远场涡流的管道外检测方法,并实现了内、外管壁缺陷的深度定量和位置区分。首先根据远场涡流效应的磁场传播特点,对比分析了将传感器置于管内和管外时的检测原理;随后采用有限元仿真方法,优选了激励脉冲的重复频率和占空比等参数;然后,研究了内、外壁缺陷对磁场的扰动作用及其响应信号特征,分析了信号的峰值和过零时间与缺陷深度及位置的对应关系;最后,在实验室构建了脉冲远场涡流系统,对预制有内、外壁缺陷的碳钢管道进行了检测验证。结果表明,检测信号的峰值随管壁缺陷深度的增加单调增大,可用于缺陷的深度定量;内壁缺陷的过零时间总是大于相同深度外壁缺陷的过零时间,这一特征可用于管壁缺陷位置的识别。

The remote field eddy current(RFEC)technique is widely applied for defect inspection in the wall of metallic pipes.However,it is difficult to identify the defect’s specific location because this technique has the same sensitivity to inner diameter(ID)and outer diameter(OD)defects.To meet the demand of in-service inspection for pressure piping,this paper presents an outside inspection method based on pulsed remote field eddy current(PRFEC)for pipe defects and makes a contribution on depth quantification and location identification of ID and OD defects.First,based on the characteristic of magnetic field propagation,the principles of inside and outside RFEC inspection were compared and analyzed.Afterwards,the repetitive frequency and duty cycle of the excitation pulse were optimized by using finite element simulation.Then,the magnetic perturbations caused by ID and OD defects and their response signals were studied,and meanwhile the correlations of signal peak and time of zero-crossing(TZC)with the defect depth and location were revealed.Finally,a PRFEC system was set up and experiments were carried out on a carbon steel pipe with prefabricated ID and OD defects.The results show that:i)the peak value of defect signal increases monotonically as the defect depth increases,which can be used to quantify defect depth;ii)the signals’TZCs of ID defects are always greater than those of OD defects with the same depths,and therefore,by using this feature,the defect location can be identified.