Research On Pipe Ultrasonic Guided Wave Imaging Testing Based On Angular Spectrum Propagation

Pipeline has a widely application in the transportation of inflammable and explosive materials, such as natural gas, oil, etc. So the security detection for pipe can not be ignored. Ultrasonic guided wave testing technology has many advantages, such as longer inspection distance and higher efficiency, so it's very suitable for the inspection of huge mileage pipeline. But the results of guided wave testing are abstract, people can not get the defect information directly. If the pipe can be imaging tested by guided wave technology, then the testing results can be displayed visually by the image, and the workers can also be understood and mastered the testing technology more easily, so that the application of guided wave testing technology in pipeline will be faster and better.This paper proposed a method of pipe guided wave imaging testing. This method was based on the theory of ultrasonic guided wave, and combined with the sound field imaging theory which is based on angular spectrum propagation. And by numerical simulation and experiment, the imaging testing for the pipe carried out successfully, using the obtained images studied the defects' localization and size. The main work and conclusions of this paper include:1) The ultrasonic guided wave theory and the angular spectrum propagation sound field imaging theory was illustrated. According to the characteristics of guided wave testing, a theoretical model of pipe guided wave imaging which was based on the angular spectrum propagation principle was established, and the imaging algorithm was also designed.2) Using the finite element analysis software ANSYS established the analysis model of pipe guided wave imaging testing, the imaging effect of different guided wave modes, excitation signals, sensor arrangements and effective frequency band “BE” were studied. The results show that the smaller guided wave dispersion and the shorter wavelength, the better axial resolution of the imaging; the more sensors which were circumferential uniform layout, the less affect caused by the interference mode for the imaging; existed a certain value of the effective frequency band “BE”, when reached it, the images could get the same effect as the full band. According to the above conclusions, using the T(0,1) mode, 5 cycles hanning window sine signal, 40 motivate nodes, 35-115 k Hz effective frequency band “BE” under the 75 kHz excitation frequency done the imaging testing successfully.3) Using the imaging algorithm obtained the angular spectrum of guided waves and the data of imaging, studied the wave mode conversion and the imaging testing of the defect size circumferential and axial changes pipes. For the research of mode conversion, found that the larger circumferential defect size, the greater proportion of flexural mode guided waves in the pipe; but for the axial defect, the proportion of flexural mode guided waves in the pipe were basically unchanged; and also found that no matter how the defects change, the modes convert form T(0,1) in the pipe were basically the same, including the F(1,2), F(2,2), F(3,2), F(4,2) and some other modes. For the research of imaging testing, found that the locations of defects and pipe characteristics could obtain accurately from the testing images, the circumferential positioning accuracy could up to ±5°, the axial positioning accuracy could up to ±12mm; for the defect which circumferential size were larger than the wavelength of the guided wave, using the 3/4 circumferential amplitude width could detect its circumferential size.4) The imaging experimental system was established; and the experimental verification study of the pipe guided wave imaging method was carried out. The research shows that the guided wave imaging method could be used to detect the actual pipe, detection images accurately reflected the position information of defects and pipeline characteristics, the axial positioning accuracy of circumferential defects could up to ±8mm; according to the conclusions of numerical simulation study, the quantitative experimental study of circumferential defects was also done.In this paper, the imaging testing of the pipe was carried out by using the ultrasonic guided wave, through numerical simulation and experimental research, the correctness of the pipe guided wave imaging method which was based on angular spectrum propagation was proved, the research work provided the bases of theory and engineering application for the pipe guided wave imaging testing.