Research On Pipeline Stress Detection Technology Based On The Coercive Force Of Ferromagnetic Materials

Ferromagnetic materials have been widely used as raw materials for oil and gas transportation pipelines due to their excellent mechanical properties.In order to ensure the sufficient energy supply in China,the scale of oil and gas transportation pipeline network is gradually increasing,and the construction speed is accelerating.The pipeline will inevitably be affected by soil erosion and geological changes during the operation of deep underground,so that the pipeline will have stress concentration areas.Long-term stress concentration will cause local deformation and even metal failure of oil and gas pipelines,resulting in pipeline fracture and oil or gas pipeline leakage accidents.Therefore,regular inspection and maintenance of active pipelines is an important way to reduce pipeline safety accidents caused by stress.Aiming at the pipeline stress problem that needs to be solved urgently,this thesis proposes a pipeline stress detection technology based on the coercivity of ferromagnetic materials.This method can indirectly reflect the stress of the pipeline by measuring the coercivity,which is of great significance to solve the safe operation of oil and gas pipelines in practical engineering.In this thesis,the classification and magnetic properties of magnetic materials are introduced.The magnetic theoretical basis of ferromagnetic materials is studied from the microscopic point of view,including magnetic domain structure,magnetization mechanism and hysteresis phenomenon caused by domain wall movement and magnetic moment rotation,the hindering effect of stress on the magnetization process of ferromagnetic materials is analyzed,and the theoretical quantitative relationship between stress and coercivity is obtained.On this basis,a stress detection system based on coercivity is designed.The system uses the U-shaped yoke laminated by silicon steel sheet as the probe.The finite element simulation software is used to simulate the excitation and induction signals of the device,and the optimal excitation parameters are sought for the design of the detection system.In the construction of the system platform,the detection system includes two parts : hardware circuit and software design,the low-frequency sinusoidal excitation signal is used to magnetize the test piece after power amplification,so that a closed alternating magnetic field is formed between the probe and the specimen,and the induced voltage signal is collected.The induction signal generates a zero-crossing pulse through the zero detection circuit,and the zero-crossing pulse is used as a sign of the coercivity acquisition time,at this time,the main controller of the lower computer transmits the collected excitation signal to the LabVIEW of the upper computer after analogto-digital conversion,calculates the coercivity value according to the formula and displays it through the front panel.Through the experiment of the stress detection system based on the coercivity of ferromagnetic materials,exploring the trend of coercive force changes in ferromagnetic materials under different stresses.Experiments show that when the magnetic field direction is parallel to the tensile direction,the coercivity of the specimen in the elastic stage does not change significantly with the stress,and there is an increasing trend in general.The coercivity of the specimen under plastic deformation is proportional to the stress and increases with the increase of stress.When the magnetic field direction is perpendicular to the tension direction,the coercivity always has a good positive linear relationship with the stress.