Research On Pipeline Stress Detection Method Based On Magnetoelasticity

With the rapid growth of China’s economic output and the rapid improvement of production capacity,the structure of long-distance oil and gas pipelines is widely used in oil and natural gas long-distance transportation projects,and plays an important role in my country’s industrial infrastructure construction and social and economic development.Longdistance oil and gas pipelines are often built in areas prone to geological disasters such as landslides and earthquakes.Additional stress on the pipeline caused by geological problems such as slope creep and soil settlement will lead to pipeline displacement and deformation,and local pipe body bending strain will cause damage to the pipeline.Therefore,it is necessary to regularly test the stress state of pipelines in areas prone to geological disasters to avoid pipeline failure.The magneto-elastic stress detection technology has the advantages of not easily affected by the environment,strong identification ability,fast measurement speed,and no radiation danger.It has good research value and application prospects in pipeline stress detection.Aiming at the problems of pipeline deformation and buckling caused by the difficulty in measuring the bending stress of oil and gas pipelines,this paper proposes a pipeline bending stress detection method based on the magnetoelastic effect.In the process of deflection,the magnetic domain wall will be deflected and displaced,and the internal energy of the magnetic domain will change continuously during the deflection process,which will cause the change of the magnetic permeability or the magnetic resistance of the ferromagnetic material.According to the magnetic domain of ferromagnetic material and the thermodynamic equilibrium theory in the magnetic domain,the generation mechanism of the magneto-elastic effect is studied,the stress on the pipeline is studied by stress analysis of the buried pipeline,and the stress distribution inside the material under the bending action is studied.,using Q235 steel plate commonly used in pipelines as the experimental object,the three-point bending experiment was carried out on the Q235 steel plate to simulate the stress distribution of the pipeline wall in the bending state,and the research on the change of the impedance with the stress during the bending process of the Q235 steel plate under different conditions was carried out.The experimental results under different excitation frequencies and current intensities are compared,and the equivalent stress of each part of the steel plate under different external forces is calculated by means of finite element analysis,and the corresponding situation of equivalent stress and impedance under different external forces is explored.According to the different force modes,the detection results of the magnetic properties of the upper and lower surfaces of the steel plate in the bending state are respectively studied,and the stress in different ranges is measured.The results show that the surface impedance of the steel plate has an obvious downward trend with the increase of stress.The impedance and stress have an approximately linear corresponding relationship within a certain stress range.The change of impedance with stress can still be detected within the range,and the experimental results and theoretical analysis are in good agreement.