Research On Pipeline Stress Detection Method Based On Remanence Technology

Oil and natural gas are important energy sources of national energy reserves.Pipeline transportation is one of the main transportation methods of oil and gas energy.It is convenient and fast,does not occupy ground space and has high safety.The total mileage of long-distance oil and gas pipelines in China has exceeded 122.3 kilometers and is still growing.Because oil and gas energy are flammable and explosive,there are potential safety hazards,so the management of pipeline safety is particularly important.In the process of long-term operation,the pipeline is subjected to the action of external load,resulting in stress.When the external load increases,the pipe gradually changes from elastic deformation to plastic deformation,and finally even fatigue failure leads to safety accidents such as burst.Effective detection of pipeline stress can not only prevent accidents,but also prevent resource waste caused by energy leakage,which is of great significance to ensure pipeline safety.As an emerging technology,pipeline stress detection method based on remanence technology has been recognized by the industry in the world.It has the advantages of sensitive stress signal,convenient operation and early stress state diagnosis.Based on the magnetic and mechanical properties of ferromagnetic materials,and based on the J-A(Jiles-Atheron)coupling model,the model is optimized and improved.The hysteresis loop of ferromagnetic materials under stress is analyzed and calculated.The residual magnetic induction intensity under different stress is compared,and the variation law of residual magnetism is obtained.Based on the improved J-A coupling model,the mechanical and magnetic simulation of Q235 pipe is carried out,and the distribution law of magnetic signal under stress state is analyzed.Taking the pipe without defects and the pipe with through defects as the experimental objects,the residual magnetism detection experimental platform and the residual magnetism measurement experimental platform based on hysteresis are designed.The distribution characteristics of the residual magnetic induction intensity signal of the pipe under different stress and excitation intensity are analyzed,and the detection ability of the residual magnetism to the pipe defects is studied.The results show that the residual magnetic induction intensity signal of flawless pipe under stress state increases briefly in the low stress stage with the increase of stress,and decreases linearly with the increase of stress;The remanence at the defect of the defective pipe is consistent with that of the non-defective pipe specimen.The remanence increases briefly in the low stress stage,and decreases linearly with the continuous increase of stress;When the excitation magnetic field is large,the radial component and axial component of the residual magnetic signal have peaks at the defect,and the residual magnetic signal is obvious.Before magnetization to saturation,the changes of radial and axial components of remanence signal increase with the increase of magnetization,and the changes tend to be stable after magnetization to saturation.