Study On Magnetization Characteristics Of Oil And Gas Pipeline And Online Demagnetization Technology

Magnetic flux leakage detection is a common method for periodic pipeline inspection.Magnetic flux leakage detection and other factors will cause a certain amount of remanence in the pipeline,which will cause arc blow phenomenon during the docking of new and old pipelines,thus affecting the quality of welding.The traditional methods of demagnetization are mostly off-line,and are not suitable for demagnetization of in-service pipelines.The use of welder cables to reversely cancel the interface magnetic field does not substantially solve the magnetic problems of the pipeline.Therefore,it is necessary to study the magnetization characteristics of the pipeline and the online demagnetization technology.This paper mainly studies the magnetization characteristics of pipelines after magnetic flux leakage detection and the on-line demagnetization prototype of pipelines.Combined with the principle of magnetic flux leakage detection,a Maxwell-based pipeline magnetization model was established.The leakage magnetic field components around the defects with different defects and different intensity excitation sources are simulated,and the relationship between the defect parameters and the magnetic field strength and the leakage magnetic field components is obtained.A magetic flux leakage detection system is designed and experimental verification is carried out.Based on the hysteresis curve of repeated magnetization,an online demagnetization prototype based on permanent magnet was designed and manufactured.On this basis,the response surface method is applied to optimize the main parameters of the prototype.Finally,a test bench is set up to verify the effectiveness of the demagnetization prototype.The experimental study of magnetization and online demagnetization prototype shows that the designed leakage magnetic detection experimental system can clearly identify the pipeline defect size.The larger the pipe defect,the stronger the externalexcitation source and the larger the leakage magnetic field component are.After one operation,the prototype can reduce the polarity of the magnetic field of the pipeline by40%?46%,achieving a better demagnetization effect,which lays a foundation for the design of the online demagnetization prototype of the long-distance oil and gas pipeline.