Experiment and Numerical Simulation of Ultrasonic Guided Wave Propagation in Bent Pipe

摘要

Elbows have been widely used in the process industry, whose structure integrity is extremely important for the safety production. This paper aims to inspect the axial crack-like defects in 90°elbows using T (0, 1) mode which has the constant group velocity. The elbow with a crack in the extrados and middle area is firstly studied by guided wave experiment. The propagation of guided wave in the bent pipe is then simulated by using finite element method. The results show that the rates of T (0, 1) mode passing through elbow correlate strongly with the excitation frequency. Less mode conversion is generated at the frequency of 38 kHz when passing through the elbow, while most of energy converted into F (1, 2) mode at the frequency of 75 kHz. The crack in different areas of the elbow can affect the rates of mode conversion. The crack in the middle of the elbow inhibits mode conversion which increases the detection sensitivity at the frequency of 38 kHz, while the crack in the extrados of elbow causes more mode conversion.