Non-ferromagnetic Metal Material Defect Detection System Based On AC Electromagnetic Field

Non-ferromagnetic metals are widely used in aerospace,shipbuilding,chemical industry and other fields because of their good corrosion resistance and high strength.Due to its long-term working under high pressure and corrosive environment,cracks will inevitably occur,resulting in equipment failure.Based on the alternating current field measurement(ACFM),this paper establishes the COMSOL simulation model,then designs the electromagnetic detection sensor,develops the electromagnetic detection system,and has achieved good engineering application.The main research contents are as follows:(1)Research on the detection mechanism of alternating current field measurement.A basic ACFM model is established,and the coupling mechanism of magnetic flux leakage effect and eddy current effect in ACFM is discussed.Then,starting from Maxwell’s equations,the magnetic field expressions of the interior of the specimen and the air field are calculated,the boundary conditions of the ferromagnetic and nonferromagnetic specimens are analyzed with the magnetic field composition of the defect part,finally,the magnetic field disturbance expression caused by the defect is calculated.(2)Alternating current field measurement simulation.Based on COMSOL finite element simulation software,a three-dimensional ACFM simulation model is built,the distribution of internal magnetic field and eddy current field of non-ferromagnetic metals magnetized at different frequencies is studied,and the relationship between excitation frequency and detection sensitivity is analyzed.Then,a two-dimensional step-by-step detection simulation model is built,and the scanning results of defective specimens under low-frequency excitation and medium-frequency excitation are studied.(3)Design of electromagnetic detection system.Based on the simulation results and simulation model of ACFM,a simple laboratory detection model is constructed to detect the stainless-steel plate with artificial defects,the detection results verify the simulation results of the two-dimensional step detection simulation model.Then the electromagnetic detection system is designed based on the laboratory detection model,including three parts: sensor car,electromagnetic detection host and computer software,and the design of each part is introduced.(4)Engineering applications of electromagnetic detection system.The designed electromagnetic detection system is applied to two factories of a chemical plant in Maoming.Defects such as cracks and corrosions are found in both factories,which verifies the engineering practicability of the electromagnetic detection system.