Research On Surface Defect Detection System Of Steel Plate Based On Eddy Current Technology

In recent years,China's steel production is growing,the annual output in 2016 reached 1.138 billion tons.Steel is widely used in all areas of national production.With the increase in the use of oil and natural gas,the demand for steel in oil and gas pipelines has increased year by year.Pipeline surface quality is one of the important criteria for the inspection of pipeline qualified,the pipeline in the manufacture and use of the process may produce bubbles,cracks,corrosion and other defects,a direct impact on the safe operation of oil and gas pipelines,resulting in unnecessary economic losses,so the pipeline surface quality testing is critical.In this paper,a method of pipeline detection using eddy current effect and eddy current testing technology as an important method of nondestructive testing are proposed.With the advantages of high sensitivity and fast response speed of specimen surface defects,Has been widely used in non-destructive testing of oil and gas pipelines.In order to solve the problem of defects in the inner wall of the pipeline,this paper takes the steel plate as the research object,simulates the pipeline wall defects,uses the bridge type eddy current detection technology to realize the pipeline wall defect detection and recognition,optimizes the eddy current detection sensor,uses the bridge eddy current sensor,detection accuracy.The equivalent model of eddy current testing sensor and defective steel plate and defect is established by using COMSOL simulation software.The finite element simulation technique is used to analyze the key factors affecting the magnetic induction and induced current density distribution in the steel plate.By changing the sensor size,the excitation frequency and the distance between the sensing plate and the steel plate are measured,and the variation law of the magnetic induction and induced current density of the steel plate is obtained.According to the simulation results,the eddy current detection sensor is optimized and the eddy current detection system is fabricated.The detection system mainly includes excitation source circuit,amplifier circuit,bridge eddy current sensor circuit,differential amplifier circuit and effective value detection circuit.The detection of the output signal of the eddy current detection device is carried out by detecting the different defect types on the surface of the steel plate and changing the extraction value of the eddy current detection sensor.The problem of the identification of the inner wall of the pipeline is realized by using the equivalent contrast method with the standard defect signal.The eddy current testing system was used to detect the pitting corrosion,crack defects and surface crack defects on the surface of the steel plate,and the output signal of the sensor was tested at different values.The experimental results show that the higher the excitation frequency is,the lower the depth of the vortex is,and when the excitation frequency is the same,the amplitude of the detection signal increases obviously with the increase of the depth of the pitting or crack.The system can distinguish the minimum diameter of 2mm,depth 1mm defect signal,in the detection of the sensor lift-off value of 4mm is still able to clearly detect the surface defects,can achieve the defect signal non-contact measurement.