Research On Detection Technology Of Inner Wall Defects Of Electromagnetic Eddy Current Oil And Gas Gathering And Transportation Pipeline

As an important national infrastructure,oil and gas gathering and transportation pipelines play an irreplaceable role in the transportation of oil and natural gas.In order to prevent problems before they happen and ensure the safety of oil and gas transportation,it is necessary to timely and effectively investigate hidden dangers in pipelines.Aiming at the practical application requirements of oil and gas gathering pipeline defect detection,based on the related theoretical research of electromagnetic eddy current nondestructive testing technology,this thesis introduces the tunnel magnetoresistance sensor and excitation coil to form an eddy current detection probe,and develops an electromagnetic eddy current nondestructive testing system,which uses sine wave excitation.In this way,the effective detection of the defects of the low-carbon steel plate specimens is realized,and a solid foundation is laid for the subsequent quantitative detection of the defects of the oil and gas gathering and transportation pipeline.This thesis mainly conducts research from the following four aspects:a)Theoretical research on electromagnetic eddy current testingAccording to the classical electromagnetic field theory,the impedance analysis method is used to further study the principle of electromagnetic eddy current detection.At the same time,research and analysis on how the skin effect and penetration depth affect the depth and sensitivity of defect detection are done.Through theoretical calculation and analysis of eddy current density,it provides theoretical support for the design of specifications such as the diameter of the detection probe.b)Hardware design of electromagnetic eddy current detection systemIn the hardware circuit of the system,an excitation signal source is designed using direct digital frequency synthesis technology to provide a sine wave excitation signal for the detection probe.Considering that the output of the detection sensor is a weak signal,in addition to the selection of low-noise amplifier filtering processing,an application scheme of quadrature vector type lock-in amplifier in this system is proposed.c)Software design of electromagnetic eddy current testing systemIn the system software design,the frequency of the excitation signal source is adjusted by the MSP430 single-chip microcomputer,and the working status of the system is displayed,and the digital phase-sensitive detection algorithm is realized based on the hardware logic of FPGA.Finally,the defect-related signals are sent to the host computer platform through the serial port for data processing.d)Experimental research on defects in electromagnetic eddy current detectionThe system joint experimental test results show that the electromagnetic eddy current inspection system can effectively detect the defects on the low-carbon steel plate specimens,and can realize the defect detection with a diameter of 2mm.At the same time,the thesis expanded the research of electromagnetic eddy current defect detection,and analyzed and compared the detection performance of defects of different depths and diameters.