Axial Excitation In The Pipeline Magnetic Flux Leakage Testing Research Of Magnetic Saturation

With the economic development of country, the length of oil pipeline and gas pipeline iscontinually increasing. With the increasing of the buried pipeline, there will be more corrosionand deformation which will cause an enormous negative influence during its operation. Inorder to find the corrosion and deformation as soon as possible, it is necessary to improve thedetection methods and its accuracy. Magnetic flux leakage testing is an effective way in thedefect detection of oil pipeline and gas pipeline. Using electromagnetic field or permanentmagnet magnetic field to excite line will bring an obviously effective detection, but themagnetization equipment volume is relatively large and the steel tube is hard to demagnetizeafter magnetization. For oil pipeline and gas pipeline, the excitation part of pipeline magneticflux leakage can’t be used simultaneously with the inspection and testing part in some specialcases, there will be lots of difficulty in magnetic flux leakage signal detection.Contrapose the influence of inside pipeline magnetic flux leakage testing magneticsaturation degree on the pipes and pipeline remanence problem, this paper has researched andpresented a method of using remanent magnetism effect to detect pipeline defect size. Basedon the pipeline magnetic flux leakage detection technology and the magnetization method ofthe magnetic flux leakage testing, to research the axial excitation test method of permanentmagnets and the DC axial excitation coil detection method, to study the detection of defectmagnetic flux leakage signal in reducing magnetic saturation, to optimize the detectorexcitation unit volume, to discover the method of using the residual magnetism effect to detectpipeline defect signal and determine the defect size. Using finite element simulation analysissoftware Comsol and establishing pipe three dimensional leakage magnetic field simulationmodel. Through the analysis of the simulation model and checking the defect axial and radialcomponent of the magnetic induction intensity, to acquire the influence of different magneticsaturation degree on the defect of magnetic induction intensity. In the meantime, withestablishing a DC excitation coil pipe three dimensional simulation model and spiralpermanent magnet excitation pipe three dimensional simulation model, to acquire the optimalcurrent parameters in the pipeline magnetized to saturation state and the leakage magneticfield simulation analysis results on the different pipeline defect which is excited by annular permanent magnet and spiral permanent magnet. To study pipeline residual magnetism effectdetection principle and pipe material residual magnetism parameters, with establishing anexperimental platform, magnetizing the two different thickness pipeline to saturation by usingDC excitation coil produce magnetic remanence effect after different current pipeline,conducting the outside pipeline magnetic flux leakage testing, while the detector passing thepipeline there will be residual magnetism produced, and using hall element to detect the defectresidual magnetism signal.Comsol simulation analysis to obtain the effects of different degrees of saturationmagnetic flux density of defects, obtain optimal saturation magnetization pipeline to currentparameters; Remanence principle experiment, the signal detection method and residualmagnetism factors were demonstrated to verify the feasibility of using residual magnetismeffect pipeline defect detection methods, analyzes the relationship between the residualmagnetization remanence signal derived signal and pipeline defects, and the impact ofdifferent excitation currents of remanence effects.