| Pipeline transportation plays an important role in the petrochemical industry.The quality inspection of pipeline is a necessary means to ensure the safety of transportation.Therefore,the nondestructive testing technology of pipeline has always been a hot spot of research.The traditional ultrasonic detection technology is single point detection,which is difficult to detect long distance pipelines.Using electromagnetic acoustic guided wave technique to detect pipeline cracks can solve this problem.The line detection is not only time-saving and efficient than single-point detection,but also has the advantages of non-contact detection,working at high temperature and detection distances up to tens of meters.The transducer is the basis and key to the detection of the pipeline to use the electromagnetic acoustic guided wave.The longitudinal guided wave transducer has high detection sensitivity to the circumferential defects of the pipeline and has good detection effect in the low frequency range.The design of longitudinal guided wave transducer based on the magnetostrictive mechanism and set up a complete detection system of pipeline defect are of great value in promoting the popularization and application of electromagnetic acoustic guided wave pipeline defect detection technology.In this paper,the excitation guided wave process of the EMAT based on magnetostrictive mechanism is studied theoretically.On this basis,a transducer based on the magnetostrictive mechanism for pipeline detection was designed and manufactured,and a complete experimental detection system platform was set up.The related experimental research was conducted on the designed transducer and pipeline defect detection system.The main contents of the thesis are as follows:(1)The research background and significance of the application of electromagnetic ultrasonic guided wave technology to pipeline detection are discussed,and its research situation is briefly introduced.The current research status of ultrasonic guided wave nondestructive testing technology on magnetostrictive mechanism at home and abroad is summarized,and presented the research content and research route of this paper.(2)The mechanism of the magnetostrictive effect is introduced,the principle of magnetostrictive guided wave technique applied to pipeline crack detection is analyzed.Based on the theoretical work of the predecessors,the theory of guided wave in the circular pipe is derived in detail,and the dispersion equation in the circular pipe is obtained.The dispersion equation of the guided wave is numerically calculated for the dispersion curve,and the guided wave mode and the excitation mode for detecting the crack of the pipe are determined,and the method for exciting the L(0,2)mode ultrasonic guided wave in the circular pipe is given.(3)The structure of the transducer based on the magnetostrictive mechanism is designed.The influence of the magnetic circuit structure on the bias magnetic field intensity and distribution uniformity of the transducer is studied.Based on this,the bias magnetic field and the excitation coil structure and parameters of the transducer are designed.The impedance matching design of the transducer is completed,and the transducer is produced.(4)A complete experimental platfrorm of electromagnetic ultrasonic guided wave pipeline defect detection system based on magnetostrictive mechanism is set up,and the experimental research is carried out.The performance test of the designed transducer is carried out,and the experimental research on the signal attenuation is carried out with the numerical simulation analysis of the guided wave propagation.Finally,the detection experiment is carried out on the pipeline with cracks.The test results show that the EMAT based on the magnetostrictive mechanism designed in this paper can effectively excite the L(0,2)mode longitudinal guided wave.The designed detection system can realize the nondestructive testing of pipelines with circumferential crack defects. |
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