Study On Pipeline Defects Detection By Ultrasonic Guided Waves

Pipeline transportation business plays a much important role in the economy construction and national defence industry. Keeping pipeline safety and preventing pipeline accidents is an important work to the pipeline industry and safety management bureau. If pipeline leakage happens, lots of money would lost, more seriously it maybe causes casualty. Pipeline defects detection is a main work of safety inspection for oil or gas pipeline. Conventional inspection methods always take time and take a lot of trouble, meanwhile ultrasonic guided waves techniqhe has good command of efficiency and it can inspects the whole wall thickness of pipe. Therefore, as an NDT method, ultrasonic guided wave technique is paid more attention in pipeline long-rapid testing and plant integrity management area.In this paper, industry pipeline defects NDT using ultrasonic guided waves was carried out theoretically and experimentally. Firstly, some main studies and progresses in this field were reviewed, and the relative theoretical basis was introduced. Secondly, the theories of guided wave in hollow circular cylinder were deduced in details. The characteristic equation of cylindrical guided wave was obtained and the corresponding dispersion curves were calculated. And three cylindrical guided wave modes in hollow circular cylinder were analyzed, including longitude, torsional and flexural mode. Then excitation method in hollow cylinder was given and also the usual testing modes L(0,2) and T(0,1) excitation. The propagation characteristics in cylinders were analyzed, including attenuation and reflection. On the basis of theoretical analysis, pipeline defects detection experiments using guided wave testing instrument was done, and the results are greatly agreed with the theoretical analysis. Finally, the L(0,2) mode and T(0,1) mode testing results were analyzed, it indicates that the longitude mode and torsional mode detected all of the welds and the prefab defects, and the positions were localized; guided wave is more sensitive to circumferential defects; comparing the results of the two modes, we know the waveforms of the former were obviously complicated than the latter's, that indicates longitude guided wave calls for more accurate axisymmetric excitation signals.