Research on transducer and frequency of ultrasonic guided waves in urban pipe inspection

Guided ultrasonic wave is a new non-destructive pipe inspection technology for its rapid, long distance inspection. It can be used to inspect urban pipes, for example, residential drinking water pipe, natural gas pipe, heating pipe, sewage pipe. Most urban pipes are underground pipes and difficult to access using other conventional NDT methods. The inspection distance, that is, the traveling range of guided wave is dependent on propagation characteristics of ultrasonic guided waves. In this paper, longitudinal wave L(0, 2), which was used as the excited guided wave and L(0, 1), which should be suppressed during the experiment were both discussed. Furthermore, effects of transducers number and transducer ring spacing on characteristics of excited signals were investigated. Factor that may affect the selection of experimental frequency was studied and optimum frequency of guided wave for pipe with different thickness and diameter was recommended. In the end, an experiment was performed on a 40 meter long heating pipe in the residential area of Bohai Oil Company, Tianjin city, China. And the experimental results showed good agreement with the theoretical analysis.