2016 Volume 57 Issue 3 Pages 397-403
Guided wave testing offers an efficient screening method for thinning of pipe walls because of its long inspection range and its ability to inspect pipes with limited access. However, the existence of an elbow in pipes makes the interpretation of echo signals difficult. The present study investigates the sensitivity of defect detection when guided wave testing is applied to detect a defect at a pipe elbow. To examine the defect sensitivity when a defect exists at different locations on an elbow, an artificial defect was produced at one of 12 different locations on the outer surface of the elbow of each aluminum alloy piping specimen. The defect signals were observed as the defect depth was gradually increased at each defect location to obtain the defect sensitivity. The transmitted guided wave frequency was in turn set to 30 kHz, 40 kHz, and 50 kHz. At 30 kHz, high sensitivity values were obtained at the intrados of the elbows, whereas at 40 kHz and 50 kHz, high sensitivity values were obtained at their extrados. This paper also shows the results of computer simulations that used the same configuration as that used in the experiments to analyze the propagation behavior of guided waves passing through the elbow. In addition to the experimental results, the simulation results indicate that the defect-sensitive locations are controlled by the guided wave frequency. Thus, proper selection of the excitation frequency for guided wave testing enables efficient defect detection at pipe elbows.
