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

Abstract

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.