Research On Nondestructive Testing Method Of Buried Pipeline Based On Ultrasonic Guided Wave

As the main method of long-distance transportation of oil and gas,the health of pipelines directly affects the safety of oil and gas transportation.In the daily oil and gas transportation process,the pipeline is corroded by internal liquid impurities and the external environment,and defects of varying degrees are prone to appear.Therefore,in order to ensure the safety of oil and gas transportation and avoid safety accidents and economic losses caused by oil and gas leakage,it is of great significance to study a non-destructive testing method for buried pipelines.In this paper,the method of guided wave detection of buried pipeline defects is researched.Firstly,the wave equation and dispersion equation of the guided wave propagating in the pipeline are derived,and the dispersion curve is drawn.According to the dispersion curve,the T(0,1)mode without dispersion and the L(0,2)mode with the characteristics of fast speed and easy to distinguish from other modes can be selected as guided waves for detecting buried pipelines.According to the influence factors of the conversion efficiency of the electromagnetic ultrasonic transducer,the structure of the T(0,1)mode transducer is optimized,and then the L(0,2)mode electromagnetic ultrasonic transducer is designed based on the Lorentz force mechanism.The excitation process of the L(0,2)modal transducer was simulated by the finite element simulation software,and the correctness of the design was verified.Finally,different parameters are selected in the three aspects of excitation frequency,coil turns,and the size of permanent magnets to simulate respectively to explore the factors that affect the excitation of guided waves.According to the simulation results,select appropriate parameters to make the transducer used in the experiment.Aiming at the problem that when guided waves propagate in buried pipelines,the type of medium,medium pressure and water content around the pipeline may affect the propagation of guided waves,which in turn affects the detection of pipeline defects,this paper studies the changing law of the guided wave amplitude when the soil pressure increases through experiments.The pipes were buried in sand and soil,and experiments were carried out in dry and wet conditions.By applying different pressures to the soil,the changes in the amplitude of the guided waves were recorded,and the law of amplitude changes was analyzed.The study found that whether it is in sand or in soil,with the increase of soil pressure,the reduction in the amplitude of guided waves in the L(0,2)mode is about 20% smaller than that in the T(0,1)mode,so the L(0,2)modal guided wave is selected to detect long-distance buried pipelines.Finally,a pipeline defect location method combining wavelet energy density and damage index is designed.And according to the defect location method and the propagation characteristics of the L(0,2)mode guided wave,the structure of the receiving transducer is improved.Then,the feasibility of the defect location method was verified through finite element model and experiment.The results show that the defect location error of this method is within 1%,which can well meet the defect location requirements in buried pipelines.