Research On Pipeline Stress Detection Method Based On Magnetic Anisotropy Technology

Pipeline is one of the main transportation methods of oil and gas.Its laying method is shallow and the transportation medium has flammable and explosive characteristics.Therefore,effectively guaranteeing the safety of pipeline structure is one of the most concerned issues in the pipeline industry.The causes of pipeline failure are mostly caused by local stress concentration,microscopic defects and cracks.After the stress concentration occurs on the pipe wall,it will yield or even break.Under repeated stress,the pipe wall will produce fatigue cracks.In a corrosive environment,the pipe wall will produce stress corrosion cracks,which will cause further damage to the pipe wall.Therefore,detecting the stress condition of the pipeline is an effective method to avoid the failure of the pipeline.In this paper,the pipeline is used as the research object,and the magnetic anisotropy is used to detect the stress state of the pipeline.The principle of this technology is that when the ferromagnetic material is stressed,the magnetic permeability in different directions will be significantly different.The difference between the magnetic susceptibility in the direction of hard magnetization and the mathematical relationship between stress and magnetic susceptibility yields the equivalent stress on the wall of the pipe,and determines whether it has yield failure according to the third strength criterion of stress.By studying the reasons for the magnetic anisotropy of ferromagnetic materials,it is believed that it is mainly affected by the magnetocrystalline anisotropy and stress energy.According to the principle of minimum energy,the mechanism of stress-induced magnetic anisotropy is studied.Through the analysis of the stress state of the pipeline,it is considered that the radial stress of the pipe wall is much smaller than the hoop stress and axial stress,which can be equivalent to the biaxial stress state.According to the law of conservation of energy,combined with the stress distribution of the pipe wall,a mathematical model between the susceptibility and the stress of the pipe wall is established.A mathematical model between the output voltage and the susceptibility of the magnetic anisotropy probe is established according to Ohm's law of magnetic circuit.Experimental results show that under the condition that the magnetization of the external magnetic field is 300A/m,Q235 steel exhibits the highest magnetic susceptibility,the stress will rotate the magnetization direction inside the tube wall,and form the easy and difficult magnetization directions.Anisotropy detection method can effectively detect the angle of the extension line where the main stress direction of the pipe wall is located,the error is within 16°.This method can qualitatively measure the equivalent stress of the pipe wall,and is sensitive to stress changes,and can effectively detect the position of the stress concentration area of the pipe wall.