Nondestructive inspection of in-service pipelines by guided ultrasonic waves

Ultrasonic techniques for inspection of pipelines are investigated, using them as channels for guided ultrasonic waves. The current standard method for pipe inspection requires sending a rotating probe inside the pipe and measuring the wall thickness by pulse-echo technique. The inside wall of the pipe should therefore be accessible, clean, and smooth. These requirements limit the applicability of this method. The inconvenience of the above method can be removed by the guided wave technique that uses the pipe itself as a waveguide. In the guided wave technique the waves are not reflected from the inside surface of the pipe and they do not have the restrictions mentioned above. It is well known that dispersion of ultrasonic guided waves occurs in the wall of the pipe. As the waves propagate along the length of the pipe, different modes travel at different speeds. Selection of an appropriate mode for the transmitted waves is used to detect various flows in the pipelines. These flaws include wall thinning, pitting by corrosion, or cracks. High-frequency ultrasonic transducers in the range of 10 to 20 MHz are used for this purpose. Theoretical results are discussed and compared with the experimental findings on the ultrasonic nondestructive in-service pipe inspections.