Incident angle selection for the guided wave inspection of pipe defects

The work reported here is focused on the experiments conducted for a choice of incident angle in ultrasonic guided wave inspection of blind pipe. Of hundreds of test point possibilities from the dispersion curves, some points are much better than others from a detection point of view. Reasons are based on wave structure across the thickness of the pipe, which changes drastically as you move along each individual mode on a dispersion curve. Incident angle is related to phase velocity via Snell's law. The phase velocity dispersion curves on pipes were tested at different frequencies and incident angles. Different machined defects on pipes were detected by shifting the incident angle of the transducer and then scanning frequency. The incident angle for the most effective detection of different defects in pipes was found from the test results.