Research On Defect Detection Of Oil And Gas Gathering And Transportation Pipelines Based On Far-field Eddy Current Technology

The environment of oil and gas pipeline is special.On the one hand,the conveying medium of the pipeline has strong corrosiveness.On the other hand,the factors such as soil,rain also affect the pipe wall.In this environment for a long time,the pipeline is prone to various corrosion phenomena,forming defects such as perforation,grooves,and large area thinning.In order to solve the problem of corrosion and ensure the safe operation of oil and gas gathering pipelines,the remote field eddy current technology is applied to carry out the research of corrosion defects detection.Far field eddy current technology defect detection in pipelines.It has strong adaptability to environment and can detect the whole pipe wall without coupling agent.It has higher sensitivity than magnetic flux leakage detection.The remote field eddy current detection probe excites the magnetic field in the pipe,and part of the magnetic field energy will penetrate the tube wall twice to reach the remote field area,the receiving coil placed in the remote field area picks up the magnetic field signal to analyze the wall defect information.Based on the analysis of the far-field eddy current technology and the mathematical model of pipeline defect detection,the simulation experiment is carried out by using the finite element simulation software COMSOL.The remote field eddy current pipeline defect detection system is built,and the pipeline artificial injury detection experiment is carried out.First of all,the finite element simulation model is established by COMSOL based on far field eddy current pipeline defect detection principle and mathematical model.Then,the magnetic field distribution in the pipeline,the axial and radial components in the pipe,the magnetic field distribution under the circumferential axisymmetric groove defect,the relationship between the defect depth and the magnetic field signal,and the signal relationship between the inner and outer wall defects are simulated.Finally,the simulation of magnetic field distribution pipe and magnetic Valley is consistent with the node detection principle and mathematical model,proving the feasibility of the simulation.Compared the axial component Bz of the magnetic field is more suitable for defect detection than the radial component Br.The axial component Bz of the magnetic field is further studied and find out the accurate distribution of the far field in the pipeline.The change of magnetic line of force near the defect is simulated for the defect of all circumferential axisymetric grooves.The magnetic field signal under the depth of defect is studied and there is an approximate proportional relationship between them.The defects in the inner wall of the pipe and in the outer wall of the pipe is defected respectively.The result of sensitivity is the same.Aiming at the problem that the length of far-field eddy current probe is too long,the design of the probe is optimized and simulated.In the near-field area,the magnetic shielding disk is added.It is found that the shielding plate made of high permeability material is more effective than the conductive material made in advance in the far-field area.A remote field eddy current defect detection system is built,which mainly includes excitation signal generation and power amplification part,detection probe,signal differential amplification,phase sensitive detection and signal display part.The detection probe is introduced in detail:Three receiving coils are designed to get the best one.The receiving coils all use a double loop differential form,which can effectively weaken the partial noise signal.According to the simulation results,the near field shielding device set at a certain position of distance excitation coil can shorten the length of the probe.Based on the results of the simulation experiment and the remote field eddy current testing system,several test experiments of artificial injuries are carried out.In view of three kinds of receiving coil,the contrast test of defect detection ability is carried out and the best one is obtained.Three representative defects are analyzed.It shows that the defects of the circumferential extension are most easily to be detected and the defects in the axial extension are most difficult to be detected.The relationship between defect depth and detection signal is analyzed.The experimental data shows that the defect depth is approximately exponentially related to the voltage amplitude of the detection signal and is approximately proportional to the voltage phase.The quantitative research on the depth of defect can be realized.To solve the problem that the sensitivity of the probe is not high enough,the probe's structure is Improved.The sensitivity of the probe has been improved,but further analysis is needed.At present,the domestic far field eddy current technology is mainly used to detect small and thin wall pipes,such as heat exchanger.The application in the oil and gas gathering pipeline is not mature enough.In this paper,a part of far-field eddy current defect detection experiments are carried out based on the outer diameter and wall thickness of ferromagnetic pipes,which are 108mm and 5mm respectively.The data can provide some references for remote field eddy current pipeline inspection.