The Modal Analysis And Defect Detection Of Ultrasonic Guided Wave In Curved Pipes

In recent years,with the advantages of long propagation distance,speediness,small attenuation and high efficiency,ultrasonic guided wave can be used to detect pipeline information of the section testing without coasting peeling off at high temperature. Therefore the research of engineering is becoming an important direction of pipeline inspection technology research and development. Using ANSYS, the simulation research of transmission characteristics and detect of crack defects in noth straight and curved pipes by L(0,2) guided waves.According to the dispersion properties and the modal transformation phenomenon of ultrasonic guided waves,the longitudinal mode L(0,2) is selected as defects detection mode in pipes.First of all, to analyze the propagation characteristics of ultrasonic guided wave: the L(0,2) guided wave propagation of visual simulation in straight pipes and curved pipes,while the guided wave through the pipe bending part,modal transformations phenomenon happened;When the curved pipes material property change, the L(0,2) guided wave transmission coefficient changes;From its transmission coefficient curve can be found that the excitation frequency during(80 ~ 95 k Hz),L(0,2) guided wave transmission coefficient is relatively high, theoretically more suitable for detecting defects in pipe bending.Second,crack defects of different sizes in straight and bend pipes for numerical simulation research:Find the same size of the straight pipe crack defect echo signal better than bend crack defect echo signal, specification pipe bending part will hinder the guided wave propagation;With the increase of crack defect size, the reflected wave signal enhancement. When material property change,to do the simulation, the results from numerical simulation, the echo of crack defects found signal strength and end reflection echo signal strength has changed, some even appear the phenomenon of modal transformation.Finally, to simulate the crack defects of the pipeline in 20°C、100°C、300°C and 500°C,found that higher temperatures will lead to guided wave velocity smaller,and the modal transformation phenomenon happened.L(0, 2) based on the numerical simulation research of guided wave in straight and 90 ° bend some propagation characteristics of some data and detect crack defects, for pipeline detection provides important theoretical basis for engineering application.