| Oil and gas pipeline is one of the necessary transport in petroleum, chemical, thermal,water, etc. As the oil and gas pipelines, pipelines in gas station, as well as open-air pipelinesexposed in air all the time. External corrosion in pipeline and electrolyte perennial erosion inthe pipeline result in defect in pipeline. Exposed pipelines without repair cause accidentsfrequently. People must detect the extent of the damage and the region of the destructionbefore the repture of the pipelines, detect the defects or replace pipelines timely to ensure thesafety of oil and gas pipelines. Electromagnetic ultrasonic detect technology gets people’sattention with thus advantages: without coupling, without stripping, tests quickly, propagatesdistantly, operates easily.In this paper, we research the electromagnetic ultrasonic testing technology. Researchderivated the multi-equations theoretically: electromagnetic, mechanical field and sound field.Research studied the working mechanism of electromagnetic acoustic transducers respectivelythrough mathematical modeling: mechanism of the lorentz force, mechanism of magneticforce, mechanism of magnetostrictive force. In order to research the propagationcharacteristics of ultrasonic guided wave in pipe, the paper studied the multi-modal anddisperaion of ultrasonic guided wave in propagation by the basis of elastodynamics. The papercalculated the dispersion equations of waveguide and drew the dispersion curves. The paperresearched the propagation characteristics of axial ultrasonic guided and circumferentialguided wave. By contrast, we confirm the structure of CL-EMAT for long-range detection.COMSOL finite element simulation proved the accuracy of theoretical studies. Testsconfirmed the advantages of Lamb wave in long distance detection of pipeline. The paperestablished mathematical model of ultrasonic directional field, and we verified the correctnessof the mathematical model by matlab. The paper simulated of the actual sound field byCOMSOL finite element simulation and got sound directional parameters of sound field.Experiment verificated distribution of the acoustic beam, confirmed the relationship betweenthe half spread angle and the echo signal.Study got parameters of different mechanisms of electromagnetic acoustic transducer,derived dispersion equation, plot dispersion curves. Research selected the structure of CL-EMAT and got the parameters which fit the long distance detection. The paper designedpermanent magnet and the coil of electromagnetic acoustic transducer. Compared withconventional electromagnetic acoustic transducer, the designed transducer improves theefficiency significantly. The paper proved the relationship between half spread angle ofacoustic and1/5maximum of echo signal, which determined the range of acoustic radiation.By the research sound field transducer structure and acoustic radiation, the paper realized thepurposes of long distance detection. |
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