| As an important national strategic energy source,oil and natural gas have a wide range of application fields.They occupy an extremely important position in the national economy.Due to the different geographical environment and uneven distribution of oil and gas resources,the transportation method of oil and gas is mainly pipeline transportation.With the increase of operation years,pipelines will produce various defects,thus making the safe operation of pipelines face a great test.Therefore,it is important to carry out periodic inspection of oil and gas pipelines.Based on the internal magnetic flux leakage detection technology,this thesis conducts research on the identification and quantification of pipeline defects.In this thesis,the pipe with an outer diameter of 406 mm and a wall thickness of 7 mm in the actual inspection engineering case is taken as the research object,and a pipeline magnetic flux leakage internal detection model and a pipeline defect model are established based on Ansys Maxwell 16.0 electromagnetic simulation software.Firstly,the magnetization ability of the internal detection model to the pipeline is checked,and the results show that the pipeline can reach the magnetization intensity required for detection.Then,in order to optimize the extraction path of the magnetic flux leakage signal in the model,this study analyzed the influence of the lift-off value on the leakage magnetic signal,and found that the magnetic induction intensity decreases rapidly with the increase of the lift-off value,the smaller the lift-off value,the higher the detection accuracy,and the lift-off value was selected as 1 mm after comprehensive consideration.By establishing cylindrical defects with different sizes,the influence of defect depth and defect diameter on the leakage magnetic field signal is analyzed.For the problem of less research on pipeline girth weld defects,this thesis establishes two types of weld defect models for incomplete penetration and undercut,the corresponding relationship between defects and leakage magnetic field signals was obtained,and the quantification equation of defects was established.For incomplete penetration defects,the peak value of the axial component and the peak value of the radial component of the magnetic induction intensity can be used as the characteristic quantity to quantify the incomplete penetration depth;for undercut defects,the peak value of the axial component of the magnetic induction intensity and the peak-valley value of the radial component Can be used as a feature quantity to quantify the undercut depth.In order to verify the accuracy of the finite element analysis results,a pipeline magnetic flux leakage detection device was designed and built under laboratory conditions.The hardware part of the device includes a magnetization unit,a signal acquisition unit and a computer.At the same time,the magnetic flux leakage detection software is developed by using C language to facilitate the analysis of the collected magnetic field leakage signals.After the entire testing device was built,the incomplete penetration defect test plate and the undercut defect test plate were manufactured by means of CNC machining.Firstly,four repeated acquisitions were made on the leakage magnetic field signal of the defect with a depth of 1.40 mm,so as to verify the stability of the device.Subsequently,tensile tests were conducted on incomplete penetration defects and undercut defects.The experimental results show that the experimental results of the incomplete penetration defects and undercut defects are in good agreement with the numerical calculation results.The signal change pattern is consistent and the signal magnitude is similar,thus verifying the reasonableness and correctness of the finite element model of magnetic leak detection of pipe defects.This proves that the analysis results of the finite element model in this thesis can effectively identify and quantify the pipeline defects. |
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