The Study On Testing Mechanism And Application For Stress Damage Of Oil And Gas Pipeline Base On Magnetic Memory

Oil and gas pipeline with high efficiency,low cost and safe and reliable advantages,is an important way of energy transport.At present,the world has built more than 2.5 million kilometers of oil and gas pipelines,and this data is still growing every year.The oil and gas pipeline transportation has become an important industry related to national economic and social development in China which has vast territory and uneven distribution of oil and gas resources.As the pipeline with the characteristic of high energy and high pressure,flammable and explosive,toxic and harmful,continuous operation,chain length,environmental complexity,the pipeline safety management is very important.Oil and gas pipelines made by the steel material has good strength,hardness,plasticity and toughness and other mechanical properties and good ferromagnetic properties,so their destruction will experience the process from stress concentration to the material yield and then plastic deformation and then to the damage.In the course of construction and service,the pipeline will be subject to a variety of stress.When there are defects or other quality problems,it will produce local stress concentration,cause large local stress,and even lead to plastic deformation or pipeline damage.Therefore,stress concentration is an important factor threatened pipeline safety,and plastic deformation damage caused by stress concentration is considered to be an early damage to the material.The effective detection of pipeline stress and plastic deformation can predict the occurrence of harm,and can be used as a basis for evaluating the concentration of pipeline stress,which is of great significance to ensure the safety of pipeline.As a kind of stress detection method,magnetic memory detection method has been recognized by the industry,it has the advantages of simple equipment,convenient operation,large-scale non-destructive testing on-line and early judgment of equipment danger.However,there is no uniform conclusion about the formation mechanism and characteristics of magnetic memory signal,and it can not clearly detect the signal characteristics under various conditions.At the same time,because of the weak magnetic memory signal also affects the effectiveness of the experimental research method has higher requirements,many experimental methods have certain limitations,the real situation can not effectively explain the phenomenon,which leads to the effectiveness of the method in some engineering application has been questioned.The magnetic properties of the ferromagnetic material are derived from the atomic magnetic moments,which are fundamentally determined by the motion and interaction states of the microelectronic system.Based on the theory of quantum mechanics,this paper establishes the theoretical model of magneto-magnetic coupling magnetic memory effect of ferromagnetic material based on density functional theory.The first-principles are used to study the magnetic memory signal characteristics of ferromagnetic system in the process of magnetic coupling,the magnetic memory signal characteristics and detection mechanism of stress damage are studied in depth.The theoretical results were validated by stretching and pipe compression experiments.The engineering application of magnetic memory detection technology for pipeline stress damage is carried out.The feasibility and effectiveness of engineering application are studied.The mechanical and magnetic properties of ferromagnetic materials were studied in this paper,and the microcosmic mechanism of the formation of stress damage and the microscopic origin of magnetic properties are analyzed.Based on the microelectronic density distribution function of the system,the model of the force-magnetic effect of ferromagnetic material force is established by the quantum mechanics density functional theory.The band structure,electron density of states and atomic magnetic moment of two kinds of ferromagnetic systems under different stress were calculated by the first-principles simulation software CASTEP.The theoretical results show that with the increase of the external stress,the band structures of ferromagnetic materials move away from the direction of the Fermi level in the uniaxial tension and three-way tensile stress,the number of electrons near the Fermi level decreases,the peak value of the electron spin state decreases gradually,and the degree of interaction between the electron spin weakens.The local distribution of orbital electron distribution shows that the magnetic properties of the ferromagnetic system are weakened under stress.The variation of the magnetic memory signal of the ferromagnetic system is quantitatively analyzed by the calculation of the atomic magnetic moment.The magnetic memory signal decreases with the increase of the stress,and there is a linear correspondence between the stress and the magnetic signal.When the material occurs plastic deformation,the magnetic memory signal mutation,signal change characteristics change.The magnetic memory signal of the plastic deformation magnetic system is smaller than that of the normal ferromagnetic system with the change of the stress,which indicates that the degree of magnetic coupling is weakened after the plastic deformation.In this paper,tensile samples and long-distance experimental pipelines without artificial defects and shape effects are designed,and the experimental platform of material stretching and pipe compression are established.The magnetic memory signals of the ferromagnetic materials under uniaxial tension and three-direction stress are studied experimentally,and the relationship between the stress and the magnetic memory signals of the ferromagnetic materials is obtained.The change characteristics of the magnetic memory signal are analyzed when the ferromagnetic material is changed from elastic deformation to plastic deformation under stress.The experimental results show that the ferromagnetic material will produce magnetic memory signal under the action of geomagnetism and stress.The magnetic induction intensity decreases with the increase of stress.When the material yields,the magnetic memory signal changes abruptly,The degree of magnetic coupling of the material decreases,and the magnetic memory signal becomes slow with the change trend.The experimental results are consistent with the theoretical results and the correctness of the experimental study is validated.In this paper,the engineering application of magnetic memory technology for testing stress damage of oil and gas pipeline is studied in the application background of the magnetic memory stress testing of ?1219 gas pipeline.The secondary stress testing method under the difference pipeline running pressure is put forward,and the test results are analyzed and evaluated.The detected hazard point is verified by actual evaluate testing.The results show that the application of magnetic memory technology for testing stress damage of oil and gas pipeline is feasible and effective.