Ultrasonic guided waves are routinely incorporated by industries for pipeline testing. Both guided wave energy tuning upon excitation and signal interpretation upon reception are important for discontinuity detection in pipes. Active phased array systems for long-range pipe inspection are available. Choosing active phased array or synthetic focusing is often necessary for improved testing speed, as well as overall penetration power. In this paper, two synthetic focusing techniques were utilized for
discontinuity detection in a pipe. One synthetic focusing technique used time delays, while the other technique utilized a mode extraction and backpropagation scheme. Synthetic focusing techniques use either axisymmetric loading or partial loadings to generate guided waves and receive the waves by individual segments. Synthetic focusing is achieved by data analysis of the received signals, so it is faster to carry out a total focal scan for a pipeline by employing a synthetic focusing technique than by using the active focusing technique. This study shows that the time delay synthetic focusing technique yielded more accurate results for discontinuity detection and localization in a 101.6 mm steel pipe with four channels, while the back-propagation technique gave better discontinuity imaging results of a 203.2 mm steel pipe with eight channels. Both methods are useful.
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