Research On Development And Application Of Magnetic Shielding Bidirectional Excitation Eddy Current Probe

The steel stainless materials have the characteristics of good corrosion resistance in oxidizing environment,no magnetic properties,excel ent mechanical properties,high toughness,good plasticity,impact resistance and reliable performance.They are widely applied to pressure vessels,nuclear power,aerospace,petrochemical,food,medical and other fields.However,due to the daily work in high temperature,high pressure and alternating load environment,the steel stainless equipments are easy to produce cracks,corrosion and other damage,and these defects will not only cause cracking and leakage accident,but also seriously threat to the safety of the lives and property of people.Therefore,in view of surface and sub-surface defects detection of stainless steel,based on the theory of magnetic shielding and the bidirectional excitation,magnetic shielding bidirectional excitation eddy current probe in pulse-echo mode is developed,and it is applied to defect detection of stainless steel components in this dissertation.The research work mainly includes:(1)Study on the effect of eddy current probe on detection performance.Based on COMSOL finite element simulation platform,the simulation model of bidirectional excitation eddy current probe with different core structure is established.The coil magnetic field of different types of core structure probes in the model is studied,the magnetic field is induced and the spatial distribution of the induced vortex is measured.The sensitivity of the probe in the test piece is measured at the induced eddy current density and the magnetic induction at the receiving position,and the sensitivity of the different core structure probes to different types of defect detection is determined and the optimum probe structure is determined.(2)Orthogonal optimization of bidirectional excitation eddy current probe.Based on the principle of statistical orthogonal test,the factors affecting the probe defect detection ability and sensitivity(shielding core size,coil size and lift distance)are studied based on the probe structure with better detection performance.Based on the orthogonal test table,the COMSOL dimensional axisymmetric simulation model was established according to the orthogonal test table.The optimal combination of shielding core,coil and lift distance was determined according to the optimization index,and the orthogonal test was carried out.And the optimal parameters of the magnetic shielded eddy current probe are obtained.(3)Experimental study for defect detection of magnetic shielded bidirectional eddy current probe.Based on the optimal size of the orthogonal experiments,the magnetic shielded bidirectional eddy current probe was used to detection the different types of defects(notches,holes and buried defects)in the surface and sub-surface position of the stainless steel plates.Magnetical y shielded bidirectional excitation eddy current probe has high sensitivity on the stainless steel components in the surface and sub-surface defects,which can effectively detect 7mm deep defects far from the stainless steel specimen surface.