Research On Quantitative Evaluation Of Complex Defect In Pipeline Based On Ultrasonic Guided Waves

Pipelines are crucial infrastructure in oil,gas and urban water industries.Due to poor working conditions and environment,a variety of defects may occur in the in-service pipelines,bringing safety risks and accidents,and resulting in economic losses and casualties.Therefore,it is urgent to emphasize the detection and evaluation of pipeline defect.Ultrasonic guided waves technique has been widely used in the field of nondestructive testing in recent years because of its long detection distance,wide range and high efficiency.However,due to the geometrical irregularity of actual pipeline defect,the reflection echo of defect generated by guided wave detection is very complex.Therefore,this technique can’t be used to realize the fine measurement or quantitative evaluation of pipeline defects currently.In this thesis,the interaction process between ultrasonic guided waves and complex defect in pipeline was studied through a lot of simulation and experimental work,and the scattering characteristics of ultrasonic guided waves at complex defect in pipeline were analyzed.The quantitative evaluation strategies of pipeline complex defect were proposed which were constructed based on edge reflection and chirp excitation respectively.The work is expected to provide a support for comprehensive quantitative detection of pipeline defect.In order to ensure the accuracy and efficiency of modeling and simulation,it is necessary to set appropriate simulation parameters in the process of finite element numerical analysis.In this thesis,according to the time-space characteristics of ultrasonic guided waves,an optimization scheme for the simulation process of pipeline based on guided waves was proposed.The simulation results were comprehensively analyzed by constructing multiple modeling simulation quantitative evaluation criteria to achieve the optimal simulation parameters to improve simulation precision and calculation efficiency of simulation,which provides a theoretical support for researching ultrasonic guided waves with simulation method.In order to detect and evaluate pipeline defect by using guided waves effectively,it must to establish an understanding of the complex interaction process between ultrasonic guided waves and pipeline defect.In this thesis,the approximate model of pipeline corrosion defect in practice was established and the corresponding relationships between complex defect and parameters of guided wave echo were further studied.The results showed that the reflection echo of complex defect was mainly composed of reflection components at the front edge and back edge of defect,and the reflected energies of two edges were mainly related to the radial depth and circumferential width of defect.On this basis,a quantitative evaluation strategy of pipeline defect based on edge reflection was proposed and verified.In order to improve detection and evaluation efficiency of pipeline based on ultrasonic guided waves,the multi-mode characteristics of ultrasonic guided waves and the sensitivity of different modes to different defect features can be considered in inspection.Aiming at the problem of detection and evaluation of complex pipeline defect,the work in this thesis proposed a defect evaluation method based on broadband chirp excitation.That is,a wide frequency chirp signal was used to excite multiple guided wave modes,so as to obtain the reflection echo containing a large amount of defect feature informations.The evaluation criteria were further constructed,and the reflection echoes were processed by principal component analysis to realize the extraction of defect feature parameters.Examples for verification were given at last.