Research On Pipeline Stress Detection Method Based On Strong And Weak Magnetic Coupling Technology

Pipeline transportation is the preferred channel to connect oil and gas important energy and market users.During the service period,the main facilities buried in the ground for a long time will be affected by soil corrosion and medium pressure factors,resulting in the formation of defective areas and pipe body rupture and explosion.Therefore,the safety of oil and gas pipeline directly determines the national energy transformation and development plan.At present,the effective solution recognized by the international pipeline testing industry is to conduct nondestructive testing on the stress concentration and defect corrosion area of the pipeline.Magnetic testing technology is widely used because it can meet the requirements of in-service testing of pipelines.How to identify the stress concentration in pipeline defects is the focus of NDT industry.For traditional pipeline magnetic flux leakage can’t identify the defect and the weak magnetic field detection problem of stress signal,subject weak magnetic coupling technology testing method is proposed,by studying the theory of magnetic coupling force,in the traditional J-A nail(Jiles-Atheron)model based on optimization coefficient and add stress demagnetization factor,ferromagnetic materials defect force magnetic relationship optimization model is set up,The initial magnetization curves and hysteresis loops of ferromagnetic materials under different stresses were obtained by solving them,and the variation rule of magnetic induction intensity with external magnetic field under stress was analyzed to obtain the optimal magnetic field intensity.Based on the improved J-A force-magnetic model,mechanical simulation and forcemagnetic coupling simulation were carried out for Q235 steel material,and the variation law of stress and magnetic induction intensity signal in defect location was analyzed.The experimental platform of strong and weak magnetic properties was designed to study the initial magnetization curve and hysteresis loop variation of pipe steel specimens under different stresses.An experimental platform for detecting the stress of strong and weak magnetic defects was designed to analyze the distribution of magnetic induction intensity signals of pipe steel specimens with defects and stress concentration under different stresses and different applied magnetic fields,and the linear relationship between strong and weak magnetic detection signals and stress was obtained.The results show that the influence of stress on magnetic induction intensity increases first and then decreases with the increase of excitation field intensity.When the excitation intensity reaches saturation,the influence of stress cannot be recognized in the composite signal.In the process of excitation,the magnetic signal has a maximum ratio of stress signal,and the magnetic field intensity corresponding to the maximum value is fixed and will not change with the change of stress.The stress concentration of the pipe with defects occurs at the defects,and the magnetic induction intensity at the defects increases compared with the magnetic induction intensity at the non-defects.The extreme value of magnetic induction intensity at the defect of pipe is different from that at the defect of pipe without stress.The magnetic induction intensity at the defect increases linearly with the increase of stress.The stress of pipe defect can be identified according to the signal value of magnetic induction intensity.