Design And Analysis Of Eddy Current Probe For Small Diameter Tubes Based On Magnetic Conductor Framework

Pipeline has a large number of applications in nuclear power,traditional power and petrochemical industries.With the development of industry,a large number of pipelines have been in service for more than 20 years and a large number of defects in the pipeline have seriously affected the safety of the pipeline.Defects on Pipes with Small Pipe Diameters probes currently used for eddy current testing typically use an externally eddy current probe for defect detection,but since the eddy currents excited by the probes currently used on the market are parallel to the circumferential cracks.Therefore,there is a phenomenon that the circumferential crack is insensitive during the detection process.Therefore,this paper develops and designs a pipe eddy current probe with a small diameter of non-ferromagnetic tube.The principle is to wind the coil through the axial direction to generate a circumferential electromagnetic field,which will induce an axial flow eddy current field on the pipe.In this way,the eddy current can pass through the circumferential defect vertically,causing a large disturbance to the eddy current field.The simulation model was applied and the detection platform was built.The probe was researched and designed through simulation and experiment.The paper mainly studies from the following aspects.1.Studied the effect of the size of the magnetic ring on the sensitivity of the probe by means of simulation.The thickness and width of the magnetic ring were changed to study the influence of these two parameters on the detection capability of the probe.It has been found through research that the peak value of the differential signal increases as the thickness of the magnetic ring increases.Under the experimental conditions in this paper,when the thickness of the magnetic ring is larger than 4 mm,the peak value gradually decreases with the increase of the thickness of the magnetic ring.Similarly,the differential peak signal increases as the width of the magnetic ring increases,and when it reaches 7 mm,the peak reaches its maximum value.Therefore,in this paper,the thickness of the magnetic ring is selected to be 4 mm and the width is 7 mm.2.For the optimization of the number of turns of the excitation coil,it is found that as the number of turns of the excitation coil increases,the peak differential signal gradually increases,but in the experiment,excessive turns are found to increase the inductance of the probe,resulting in a signal generator.The load becomes large,resulting in severe signal distortion,so the final choice is 80 as the excitation coil turnsof the probe.In the optimization of the wire diameter of the excitation coil,it is found that when the coil wire diameter is small,the probe generates heat seriously,and the differential peak signal is small,and the peak value of the differential signal of the excitation coil wire diameter is 0.3 mm,and when the wire diameter is larger than 0.3mm,The peak value of the differential signal begins to gradually decrease.3.The placement position of the receiving device is optimized.After the distance between the two magnetic rings exceeds 2 mm,the peak value of the differential signal is rapidly reduced.Therefore,the spacing between the two magnetic rings should be controlled within 2 mm,so the placement of the receiving device The space is only2 mm.The sensitive direction of the TMR chip is the most uniform when the detection signal is perpendicular to the tube wall,and the magnetic field strength is large,so the sensitive direction of the TMR chip should be placed perpendicular to the tube wall.When the distance between the TMR chip and the tube wall is greater than 2 mm,the magnetic field decays faster,and should be less than 2 mm when placing the TMR chip.4.According to the distribution of the eddy current field generated by the probe and the interference of the defect on the magnetic field,a suitable signal characteristic value is designed to quantify the length and depth of the defect.The length of the defect is quantified by the magnetic field component of the magnetic field component Bz perpendicular to the wall of the tube,and the effect of the depth and width of the defect on the length quantification is analyzed.The BP neural network is used to quantify the depth by using the differential peak in the time domain of the defect and the peak value of the fundamental frequency in the frequency domain as the eigenvalues of the defect depth.