The Research Of Non-destructive Testing For Defects In Pipes Using Ultrasonic Guided Waves

At present, the ultrasonic guided wave has been paid more and more attention with its wide detection range, ease of implementation and low cost as a new non-destructive testing technology. It is not only a means to change the point by point detection way but also a solution to solve the problemof coating layer.By analyzing the dispersion characteristic, the L(0,2) mode guided wave has been selected as the excited mode to detect defects in pipes. Crack defects and hole defects in both straight pipes and bends have been simulated with the software ANSYS. The results have shown that the ultrasonic guided may identify the axial position of defects in straight pipes accurately and identify the probable extent of damage by the reflection coefficient. However, the energy of the guided waves is decayed severely locating defects in bent pipes. The time reversal method has been used to overcome the problems of weak reflected signals and low detection accuracy. It is shown that the time reversal method can effectively improve the sensitivity and accuracy by the principle of energy focusing in time-space.The defects in pipes have been detected with experiment. The results have shown that there havs been same linear relationship between the simulation result and the experiment result. The simulation problems have been furtherly corrected with comparation to the experiment results which has layed the foundation of the practical application of the ultrasonic guided wave.