Simulation And Experimental Study Of Low Frequency Electromagnetic Detection Technology For Metal Materials

Metal materials are widely used in pressure equipment such as boilers,pressure vessels and pressure pipes,and are often used as key parts of pressure structures.In recent years,with the continuous rise of industry,pressure equipment plays an increasingly important role in the fields of petroleum,chemical industry,aerospace and energy.Corrosion is the main cause of failure(leakage,explosion)of pressure equipment,and it is of great significance to timely discover various material damage and other defects in the use of pressure equipment,so as to prevent the fracture failure of pressure structural parts and the occurrence of major malignant accidents.The low-frequency electromagnetic detection technology makes the detected object to be magnetized by alternating current by energizing the soft magnetic core,which has the advantages of large penetration depth and high detection sensitivity,and is suitable for the detection of pressure structure parts.Taking steel plate and pipeline as the research object,this paper studies the low-frequency electromagnetic method of different types of defects of steel plate and pipeline by means of finite element simulation analysis and experiment.Based on the principle of low-frequency electromagnetic detection,a three-dimensional finite element simulation model of metal plate components is established to obtain the electromagnetic characteristics of metal plate components,analyze the distribution characteristics of low-frequency electromagnetic field,and optimize the structure of low-frequency electromagnetic sensor.The simulation model of metal plate member with crack defect was established,and the factors affecting the detection sensitivity of low frequency electromagnetic sensor were analyzed from the angles of excitation frequency and coil parameters.The corresponding relationship between the flaw size,the buried depth and the detection signal is obtained by simulation,which can be used to guide the quantitative detection of cracks.The simulation results show that the low frequency electromagnetic sensor has high detection sensitivity and detection depth for the defects of steel plate members.Combined with the simulation and test results of high accuracy multi-channel low-frequency electromagnetic detection sensor is developed,the experimental study on influencing factors of probe detection sensitivity,and optimize the incentive core sizes and coil parameters,improve the detection sensitivity of the sensor,found that when incentive core shape for C,incentive core winding layer 2(390)coils,detecting coil diameter is 3mm,height is 4mm,the ability to recognize the best of defects.Design of different materials,different types of defect detection test block,low frequency electromagnetic sensor sensitivity test,developed low frequency electromagnetic sensor can achieve the 12 mm buried depth of 9.6mm of 304 stainless steel and 12 mm buried depth of 8mm of 20# carbon steel defect effective detection.The production of sheet metal testing sample,set the low frequency electromagnetic detection system and to carry out the test,to determine the high permeability material best detection frequency of 5Hz,low permeability material optimum detection is 100 ? 300 Hz frequency,crack depth of different length and different depth of the corrosion defect detection,get the influence law of different kinds of defects of the detection signal.The test results show that when the defect type is groove type and the material is 20# carbon steel,the detection accuracy of surface defect is: length 10mm× width 0.4mm,depth 20% of plate thickness;The buried depth can reach 10mm× 0.4mm in length,and the buried depth is 40% of the plate thickness.When the material is 304 stainless steel,the corrosion defect characterization effect is stronger than the groove.When the defect is corrosion,the minimum detection depth of the surface can reach 1.5mm,and the corresponding buried depth can reach 8mm.When the component type is pipeline and the defect type is flat bottom hole,the optimal detection accuracy of the scanning surface is 5mm in diameter and 20% in depth of the tube,and it can be found that the detection ability of20# carbon steel for buried defects is stronger than that of 304 stainless steel.