超声导波管道检测中伪缺陷信号识别及消除方法

A method of recognition and elimination to the pseudo defect signals by ultrasonic guided wave NDT for pipes

单端激励与接收方式的超声导波管道检测信号,经过管道中缺陷处和管道端头时会产生多次来回反射和透射,直到信号功率流耗尽为止,这种多次来回反射和透射过程导致了超声导波伪缺陷信号的出现,而伪缺陷信号的存在严重影响了对管道检测中缺陷数量和位置的判别.针对伪缺陷信号识别难点问题,绘制超声导波在管道中传播路径示意图,归纳总结出超声导波检测伪缺陷信号出现的位置特征规律,即:第1个反射周期检测信号中不会出现伪缺陷信号或其信号幅值很小可忽略,较大幅值的伪缺陷信号从第2个反射周期检测信号开始出现并与真实缺陷信号关于该周期内检测信号的时域中点对称,并采用数值模拟方法和实验检测验证了该规律的正确性.依据伪缺陷信号出现的特征规律,对超声导波管道检测信号中缺陷波包信号进行识别和提取,并利用匹配追踪方法和数值比对赋值法对伪缺陷信号进行消除.研究结果表明:提出的超声导波管道检测伪缺陷识别及其消除方法行之有效,实现了超声导波检测缺陷信号去伪成真目的,解决了超声导波检测信号识别难点问题,极大促进了超声导波无损检测技术的工程应用.

The detected signals using ultrasonic guided wave non-destructive testing （NDT） for pipes with the method of excited and received to one end of pipe, which run with come-and-go many times of reflection and transmission between the two ends of pipe and the defect location in pipe until its energy dissipation over. The multiple reflection and transmission process lead to the appearance of the pseudo defect signals which seriously affect the judgement of the defect numbers and its locations in pipes. Aiming at the difficulty problem of the pseudo defect signal identification, the sketch map of the propagation path of ultrasonic guided wave in pipeline is drawn. The position characteristic of the pseudo defect signal is summarized. Namely： the pseudo defect signal does not appear in the first reflection cycle of the detected signals or its amplitude of the signal is negligible; meanwhile, the larger amplitude of the pseudo defect signal appear from the the second reflection cycle of the detected signals, and which is symmetric with the real defect signal about the time domain midpoint of the signal period in the second reflection cycle. The correctness of this characteristic law is verified by using numerical simulation and experimental results. According to the characteristic law of the pseudo defect signal, the defect wave packet signals in the ultrasonic guided wave detected signals were identified and extracted, and the matching pursuit method and the numerical comparison assignment method were used to eliminate the pseudo defect signal. The conclusion are shown that the proposed method of the pseudo defect signal recognition and elimination in the ultrasonic guided wave NDT for pipes is practical and effective, which achieves the goal of discarding the false and retain the true detected signals, and solve the the detected signals recognition difficulty problem in ultrasonic guided wave NDT for pipes, and also greatly promotes the application of the ultrasonic guided wave NDT technology.