Detection Technology In Magnetic Flux Leakage Method On The Pipeline Of 300mm In Diameter

Pipelines play an important role in the medium transmission of petrochemical industry,and the wall defect will affect their normal work,cause a series of production accidents as well.Magnetic flux leakage testing technique can detect the on-line pipelines extensively,and evaluate the corrosion extent to ensure the security under the normal operation conditions.This article is based on the basic principle of magnetic flux leakage testing technique,and takes the pipeline of 300 mm in diameter as the specific object to research the outer wall inspection technology.Based on the analysis of pipeline magnetic flux leakage testing with the finite element theory,the finite element simulation software is used to establish the model in the outer wall of pipeline,and to solve the leakage magnetic field distribution.Change the size and characteristics of the defects model on the tube wall,and extract the magnetic flux density data of the leakage magnetic field around the defect,and then analyze the influence on the leakage magnetic field from different parameters.Results show that,for cylindrical defects,the magnetic flux density peak increases at first then decreases along with the increasing of the diameter,and increases persistently with the increasing of the depth;for pipe wall circumferential crack defects,three-dimensional distribution of the magnetic flux density is compatible to the trend and the distribution of the cracks.In addition,the leakage magnetic field around the defects group is analyzed,and the influence of sensor height is compared,so as to get the best effect of signal acquisition during the detection.After the analysis of simulation results,the system for the detection of pipeline defects is assembled,then take pipes of 300 mm in diameter under laboratory conditions,and prefabricate cylindrical defects of different diameter with the same depth,and that of different depth with the same diameter,and crack defects of different depth with the same width,to carry out the magnetic flux leakage detection.Then process the results of experimental data that collected.The 3d data waveform and the signal acquisition data curve from the channels that directly above the defects are utilized to analyze the distribution law of the leakage magnetic field,and finally discovered the same law of leakage magnetic field distribution with the results gotten from the finite element simulation;Besides,the defects on the inner wall of the pipe section are found out,which verifies the effectiveness of the outer wall detection device for the detection of the defects on inner surface.On the basis of summary for the formers work,an outer wall automatic detection device is designed,which driven by a motor and can change the direction as wished.