Research On Multiple Crack Pipeline Monitoring By Using PZT-based Ultrasonic Guided Waves

In the five modes of transport, Pipeline transport has a unique advantage, low cost, large volume, less land occupation and environmental pollution, etc. Today most of the world’s oil and gas are transported by pipeline, therefore pipeline transport play an important role in economic development, urban water supply and other aspects. However, because of environmental corrosion, improper use and other factors, result that in the course of pipe cause corrosion, cracks and other kinds of defects. Once these defects cause leakage accident, not only brought to life safety hazard, but also causes pollution of environmental resources. This shows pipeline structural damage detection is essential. Because of the limitations of traditional methods, based on piezoelectric ceramic ultrasonic guided wave detection technology has been widespread concern in the field of non-destructive testing.This text researches on non-defective pipes, cracked pipes and filling pipes through the theoretical analysis, numerical simulation and experimental verification of combining methods. First, Wave theory of hollow circular tube are deduced, reach that cylindrical waveguide and guided circumferential wave dispersion equation, and then filling the pipeline longitudinal ultrasonic guided wave modal dispersion equation are deduced. And we use Matlab software to solve the guided wave dispersion equation. We draw out desired size pipeline group velocity and phase velocity dispersion curves. Analyzing the characteristics of guided wave in pipeline and variety of modal, Make sure that ultrasonic guided wave mode and the excitation frequency which propagate in the pipeline. To make smallest dispersion to reduce Pipeline analysis of the complexity of the echo signal. It provides a theoretical basis for the detection of the pipeline signal selected.Second, according to the pulse-echo method use Ansys software to do numerical simulation for lossless pipelines, including one circumferential crack pipes, including bi-weekly to crack pipes and filling pipes. Giving the guided wave propagation process in the pipeline, and to do the analysis for that guided waves spread in lossless pipes, cracked pipes, hollow pipes and filling pipes, and to do the analysis for the pipe damage impact of crack parameters in double crack pipes. The result shows that the degree of pipeline damage has a substantially linear change with crack length, width and depth.Finally, to do verification testing of pipeline structural damage, through analysis of the excitation signal, the signal cycle number is large, narrow band is conducive to the control signal frequency, but in the time domain signal has a long duration, waveforms are easy to superimpose. So we use 10 cycles superimposed sinusoidal signal which is modulated by the Hanning window as a superposition of the experimental excitation signal. We use piezoelectric smart materials as the excitation signal and receiving devices. We establish a fast and accurate test system to detect lossless pipes, cracked pipes, fluid-filled pipes respectively. And to verify the results of numerical simulation, tests showed good agreement between those two, Thereby we verify the accuracy of numerical simulation methods.