Research On Axial Defects In Petroleum Pipeline By Ultrasonic Guided Wave Testing Technology

Pipelines have been widely used in oil, chemical and other industries. In the process of manufacturing, installation, service and so on, various kinds of defects which will bring potential safety hazard to the pipeline transport system can be created. Hence how to conduct the nondestructive testing on pipelines in service quickly and efficiently always concerns people. Ultrasonic guided wave detection is getting more and more attention for its simple operation, high efficiency, wide detection range and other advantages. The current pipeline guided wave testing studies mainly focus on the circumferential and through-wall axial defects in straight pipes, the mode conversion of guided waves in the "straight-curved-straight" pipeline and so on. However, there is little research on the part-through defects in curved pipeline. Against this background, the project of "Ultrasonic Automatic Testing on Large-diameter Roasted Bend Pipes" is executed. By studying on the part-through axial defects in curved pipeline, this project aims at guiding the petroleum pipeline’s actual detection.According to the dispersion characteristics of guided waves in the studied pipes, this paper chooses T(0,1) mode guided wave to detect the straight and curved pipes with specific sizes. And the propagation process of T(0,1) mode guided wave in pipe is simulated by the transient dynamic module of ANSYS. Then the accuracy of the model is verified by experimental tests. The results include:(1) With the increase of the defect’s axial length, the defect echo gradually divides into two wave packets. At this time, the front-edge and back-edge signals’reflection coefficients should be studied respectively.(2) When the defect’s axial length is under1.5wavelengths and increases as a single variable, the overall reflection coefficient of the defect echo changes periodically. When the defect’s axial length is more than1.5wavelengths and increases as a single variable, the reflection coefficient of the front-edge signal almost remains the same, but the reflection coefficient of the back-edge signal changes periodically.(3) When the defect’s depth increases as a single variable, the reflection coefficient of the front-edge signal increases linearly. However, by putting the50%wall thickness as the turning point, the reflection coefficient of the back-edge signal increases linearly in two different slopes.(4) When the defect’s circumferential width increases as a single variable, the reflection coefficient of the front-edge signal increases linearly, but the reflection coefficient of the back-edge signal first increases and then decreases in the form of a quadratic curve. According to the results of the study, the method of determining the axial defect size is put forward, which has important engineering significance and practical value.