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.