| The pipeline structure is playing the vital role in the petroleum, the electric power, the chemical industry as well as the urban water supply system. In the five modes of transport, pipeline transport has a unique advantage of low cost, large volume, less land occupation and environmental pollution, etc. Today, most of oil and gas in the world are transported by pipeline; therefore, pipeline transport plays an important role in economic development, urban water supply and other aspects. However, because of increase of service time and environmental corrosion, improper use and other factors, cracks and other kinds of defects are gradually generated in pipeline structures. Once these defects cause leakage accident, it will not only bring life safety hazard, but also cause the pollution of environmental resources. Therefore, it is urgent for a regular safety check for the pipeline structure in the service. However, the conventional examination methods are unable to detect damages for the long distance and large rang pipeline structure, therefore, a new non-destructive inspection method called supersonic guided wave examination method based on PZT waves is developed and widely paid attention to.This dissertation researches on non-defective pipes, cracked pipes and filling pipes through the combining method of the theoretical analysis, numerical simulation and experimental verificationFirstly, the theoretical analysis of hollow circular tube based on wave method is performed, and the cylindrical and circumferential guided wave dispersion equations are derived. And the Matlab software is used to solve the guided wave dispersion equation. The desired size pipeline group velocity and phase velocity dispersion curves are plotted out. Through the analysis of the characteristics of guided wave in pipeline and variety of modal, the ultrasonic guided wave mode and the excitation frequency for the wave which is suitable for propagating in the pipeline are determined, to make smallest dispersion to reduce the complexity of the pipeline analysis of the echo signal. It provides a theoretical basis for the signal selection in the damage detection of the pipeline.Secondly, based on pulse echo method, a verification test of hollow steel pipe structure is performed. Through analysis of the excitation signal, the signal band becomes narrow with the increase of the signal cycle number, which is beneficial to control the signal frequency. But the signal has a long duration in the time domain, and waveforms are easy to superimpose. Therefore, a 7 cycle superimposed sinusoidal signal which is modulated by the Hanning window is used as the experimental excitation signal. Piezoelectric ceramic patches are applied as both signal emitting and receiving devices. A fast and accurate test system to detect both healthy pipes and pipes with corrosion damage is established. By using the experimental system, both of the undamaged pipes and the damaged one are detected to develop the performance.Finally, by using the finite element software ABAQUS, the numerical simulation is performed to analyze the undamaged and damaged pipe structures, respectively. The attenuation performance of the guided wave energy alone the pipe is developed. The influences for the radial direction depth and longitudinal length of the damage on the damage level are researched. The results show that the relationships between the damage level and the radial direction depth and longitudinal length of the damage are linear. The compare between the numerical simulation results and experimental ones is also studied and they match well which validates the veracity and practicability. |
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