Research On Dual Excitation Pulsed Eddy Current Testing Method For Thickness Measurement Of Steel Plate With Insulation Layer

The steel pipe with insulation layer with large diameter and large wall thickness is widely used in petrochemical,electric power,water conservancy and other fields,which is an important part of the industrial pipeline system.The steel pipe with insulation layer will appear corrosion,insulation layer loss and other defects in use,which seriously affect the safety of industrial production,so it is very important to detect and detect it.In the research of pulsed eddy current testing,because the pipe diameter is much larger than the size of the probe,the insulation layer loss detection of steel pipe with insulation layer can be simplified as insulation layer thickness measurement,and the steel pipe corrosion detection can be simplified as steel plate thickness measurement.In this paper,according to the demand of measuring the thickness of insulation layer and large thickness steel plate in the inspection of steel pipe with insulation layer,the deficiency of the current research is found out from the relevant literature,and on the basis of the basic theory of electromagnetic field,a dual excitation pulsed eddy current testing method is designed,and the corresponding testing system is built to complete the testing experiment.the main contents of the research are as follows:(1)The influence of steel plate with insulation layer on the distribution of induced eddy current in pulsed eddy current testing is analyzed.Aiming at the thickness measurement of insulating layer and large thickness steel plate,a dual excitation pulsed eddy current testing method is proposed to obtain more testing information.A dual excitation testing model is established based on COMSOL Multiphysics simulation software.The simulation results show that the dual excitation pulsed eddy current testing method can use the magnetic field which is difficult to be used in conventional pulsed eddy current,and is expected to improve the detection ability of insulation layer thickness and steel plate thickness.(2)The magnetic flux density distribution of the conventional method and the dual excitation method is compared,and the theoretical detection signal of the dual excitation pulsed eddy current is obtained,which verifies the detection ability of the double excitation pulsed eddy current method for steel plate with insulation layer.Then,according to the time-domain evolution characteristics of the induced magnetic field,the peak time characteristic is selected to represent the thickness of the insulation layer,and the logarithmic domain slope characteristic is selected to represent the thickness of the steel plate.Finally,the stability and effectiveness of the two characteristics are verified by simulation.(3)The dual excitation pulsed eddy current testing probe is optimized,and the influence of double excitation spacing on eddy current skin depth is compared and analyzed,so as to find out the best size for testing steel plate with insulation layer.The simulation results show that the runway shape double excitation probe is more conducive to the aggregation of induced eddy current and has the highest detection sensitivity.(4)the detection signal is denoised by low-pass filtering and average filtering,and a dual-excitation pulsed eddy current testing system is built.The detection signal analysis software is designed based on Lab VIEW and experiments are carried out.The dual excitation pulsed eddy current testing system designed in this paper can detect the insulation layer of 1mm?8mm thickness and the carbon steel plate with maximum thickness 10 mm at the same time.