Experimental investigations of sensitivities for defect detection in pipes by guided waves were described. An efficient method of transduction with a reflector was used and its sensitivity was evaluated in comparison to that of conventional transduction without a reflector. An efficient transduction could be realized by placing the reflector at an appropriate axial position, which was briefly described in the paper. The experiments were carried out using a 60.5-mm-outer-diameter and 4-mm-thick aluminum pipe and a piezoelectric ring-shaped sensor system. It was confirmed that the sensitivity in the case with the reflector was more than twofold that in the case without the reflector. The detection limits and sensitivities in a noisy environment were compared between the transductions with and without the reflector.
This paper describes evaluation of obliquely stretching defect using guided waves propagating in pipes detections. Piezoelectric sensor ring having 16 sensor elements was used to generate and detect the T(0,1) mode guided waves. The inclination angles of the defects were set to be 0°, 20°, 40° and 60° to the axial direction of the pipes. In this paper, the signal amplitudes were shown as a function of the defect depth gradually increased in the experiments. The obtained results showed that the sensitivities of the defects were not so much different between the defects having 0°, 20°, 40° inclinations. Conversely, as for the 60° defect, sensitivity was a little bit poor and a unique phenomenon was observed comparing to the other defects.
Evaluations of axially increasing defects have been carried out with guided waves in 50A pipes. A piezoelectric ring shaped sensor was used to generate and detect the guided waves. Two types (rectangular and round) of defect shapes were evaluated in the experiments. Obtained amplitude was not monotonically increased but was fluctuated with the increase of axial length of the defect. The mechanism of this phenomenon minutely discussed.
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