Eddy Current Internal Inspection Technology Of Pipeline Based On Cross Magnetic Field

Pipelines are fundamental infrastructure in modern industry and daily life,but they suffer from defects such as corrosion,cracks,and fatigue during long-term service,leading to pipeline leaks and damage.Therefore,regular inspection and maintenance of pipelines are necessary.Pipeline inspection techniques include magnetic flux leakage(MFL),ultrasonic testing(UT),eddy current testing(ECT),etc.Among them,MFL is applied to large-scale long-distance pipelines,while ECT is suitable for internal inspection of small-diameter pipeline because of its small detector size,high penetration,and sensitivity.However,ECT is affected by skin effect and can only detect surface and near-surface defects on the pipe wall.This thesis proposes a pipeline eddy current internal inspection technique based on cross magnetic field to overcome the limitation of eddy current detection technology for small-diameter buried pipelines in detecting defects in the deep and outside wall of pipelines.Combining the principles of planar eddy current and remote field eddy current for pipeline internal inspection,a magnetic field that propagates vertically to the pipe wall and along the pipeline is simultaneously excited inside the pipe to detect defects on both the inner and outer walls of the pipe.By building finite element simulations and setting up an experimental platform for validation,a pipeline internal detector is designed for detecting various types of pipelines.The main research work is summarized as follows:(1)Based on the principles of planar eddy current and far-field eddy current,a pipeline eddy current internal inspection technique based on cross magnetic field is proposed for detecting defects on both the inner and outer walls of the pipeline.The simulation model for cross magnetic field pipeline detection is constructed and verified using COMSOL software,and an experimental platform is set up to determine the sensing architecture,excitation voltage,and excitation frequency,as well as to verify the detection capability of defects on the inner and outer walls of a half-pipe.(2)A pipeline eddy current internal detector based on cross magnetic field is designed,and an integrated detection system is set up,including signal excitation module,signal acquisition module,data storage module,etc.The mechanical structure is also fabricated,and the detection capability is improved by optimizing the sensing architecture,including magnetic pole ring and shielding sheet,excitation coil and detection coil distance.(3)The internal detector is used to detect a pipeline with full outer wall defects,a pipeline with small outer wall defects,and a simulated field pipeline.The voltage sensitivity,phase sensitivity,and minimum resolution of the pipeline eddy current internal detector based on cross magnetic field for detecting defects on both the inner and outer walls of the pipeline are calculated and analyzed,and compared with the pipeline internal detector that uses only a single detection magnetic field.