Researches Of Inspecting Crack Defect In Bent Pipe Using Ultrasonic Guided Waves

Guided wave as a long-range, accurate and efficient detection method has received a lot of attention in recent years. Elbows have been widely used in the industrial piping systems, studying guided wave propagation characteristics in elbow can help to improve the accuracy of detecting pipeline once. This paper aims to investigate the bent pipes by experiments and simulations.In order to explore the influence of elbow to mode conversion, the piezoelectric transducers were evenly pasted on the end of the pipe so as to excite axisymmetric mode L(0,2) and T(0,1). The detection of circumferential cracks of different areas in elbow pipes were investigated in experiments and simulations using the guided waves in mode of L(0,2). The effect of elbow to guided wave inspection was researched by comparing the result of straight pipe inspection, and the effect of defect location on guided wave detection sensitivity was discussed. Then, double elbow pipes were divided into Z-shaped pipe, U-shaped pipe and space Z-shaped pipe based on different combinations of two 90°elbows. The cracks in and beyond the second elbow were investigated. The results show that when the guided wave is propagating across the elbow, the guided wave energies move from the intrados of the elbow to extrados of the elbow, which lead to different detection sensitivity in elbows. Double elbow structures have an impact on the guided wave distribution of the second elbow and the ability to pass through the elbow. Piping system also have a lot of axial crack defects, so the axial crack defect in 90°elbow using the mode T(0,1) is investigated in this paper. The results show that most of guided waves are converted into F(1,2) mode at a relatively higher excitation frequency. The cracks in elbows can also affect the rate of mode conversion. The paper provides a certain theoretical foundation and project application value on guided waves inspection.