| Ferromagnetic Oil and natural gas account for 56% of the global primary energy.The oil and gas pipeline transportation industry is an important industry in China's national economy and social development.With the rapid development of pipeline construction,pipeline safety maintenance is the core issue to ensure its normal operation.Stress is an important parameter in the safety maintenance and risk assessment of long-distance oil and gas pipelines.During the normal operation of the pipeline,stress concentration areas on the ferromagnetic metal components may cause macroscopic volume defects or mechanical damage on the surface.buried significant safety hazards in normal operation.Internal detection of pipelines is the most effective means of pipeline safety inspection recognized by the international pipeline industry.As a new stress detection technology,metal magnetic memory detection method is based on the principle of detecting the weak magnetic signal on the surface of the stress concentration area of ferromagnetic metal components in geomagnetic environment to determine the stress damage area and the degree of stress damage of components.Metal magnetic memory testing method is a non-destructive stress testing method,which has the advantages of being sensitive to stress concentration,no need for coupling agent,fast detection speed,support for non-contact dynamic online detection,and no need for destructive treatment of ferromagnetic metal components.What's more,this technology has good application prospects in the field of detection in oil and gas pipelines.At the same time,it has been widely used in the engineering practice of stress detection.However,the mechanism of the magnetic memory phenomenon is the bottleneck of this technology.Most of the existing magnetic memory detection theories are a summary of the experimental phenomenon,which can only explain part of the magnetomechanical relationship.There is no unified conclusion on the relationship.This paper takes the internal stress detection of long-distance oil and gas pipelines as the project engineering background,and focuses on the mechanism research of metal magnetic memory detection technology.The paper links the microscopic magnetic properties with the macroscopic mechanical properties,establishes a mathematical coupling model of the whole process of metal magnetic memory,and expounds the mechanism of the whole process of magnetomechanical changes in the detection process of metal magnetic memory.In this paper,the magnetomechanical characteristics of the undoped micro-magnetomechanical model were analyzed by changing the uniaxial external load.With the background of X80 steel commonly used in long-distance oil and gas pipeline applications,the influence of common elements in X80 steel as doping elements on the microscopic magnetomechanical model of are analyzed.The magnetomechanical characteristics of the micro-magnetomechanical model under different doping are analyzed under uniaxial load.By calculating the microscopic magnetic properties of different models under tensile stress and compressive stress separately,the calculated magnetomechanical change trend and the magnetomechanical change in the macro experiment both exhibit two inflection points of magnetomechanical signals.In ferromagnetic metal components,due to the effect of solid strength,the phase change mechanism of uniaxial external load and uniaxial strain is different.In this paper,the magnetomechanical characteristics of microscopic models are analyzed by the uniaxial strain of ferromagnetic components.By loading the undoped micromagnetic mechanical model under different uniaxial strains and the magnetic mechanical model doped with common elements in different X80 steels,the stress-strain curves and basic mechanical properties of different doped micro-magnetic mechanical models are calculated,and the effects of different doped elements on mechanical properties are analyzed;At the same time,the microscopic magnetic properties and magnetomechanical relationships of different doping magnetomechanical models are calculated.The calculation results and the change trend of the magnetomechanics under uniaxial external load both show two inflection points of magnetomechanical signals.In this paper,based on the long-distance oil and gas pipeline test platform,the magnetic mechanical steel plate tensile test,pipeline crushing experiment and magnetic mechanical pipeline hydraulic blasting experiment are designed under different loading methods.Through real-time monitoring of stress changes and magnetic memory signal changes during loading,the stress-strain curves of pipelines under different loading methods are analyzed,and the changing characteristics of magnetic memory signals under different loading methods and different stress stages are studied.The research results and the change trend of the relationship between micro-magnetism and mechanics show two inflection points of magneto-mechanical signals under different stress stages.In this paper,by establishing a micro-magnetomechanical coupling model of ferromagnetic metal components,the micro-magnetic properties and mechanical properties are calculated under two loading modes of uniaxial external load and uniaxial strain.The change trends of magnetomechanics are very similar,both of which show two inflection points of magnetic signal changes.Through a series of macro experiments,it is proved that the calculation results of the micro magnetomechanical model can provide the possibility of predicting the trend of magnetic memory signals with stress changes in macro engineering practice.Metal magnetic memory detection technology provides reference and theoretical basis for magnetomechanical analysis and comprehensive stress assessment in the application of long-distance oil and gas pipeline stress internal inspection engineering,and promotes the application of metal magnetic memory detection technology in pipelines,railways,pressure vessels,chemical industry,aviation and other fields Engineering practical application. |
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