| Ferromagnetic materials are widely used in all kinds of industrial equipment,and magnetic flux leakage(MFL)testing is one of the main ways to detect ferromagnetic materials.The accuracy and data volume of MFL testing are positively related to the spatial resolution.But for a specific object,the required spatial resolution is limited.The spatial resolution exceeding the demand only increases the amount of data without increasing the inspection accuracy.The most reasonable spatial resolution should just meet the demand of detection accuracy and achieve the balance between accuracy and data amount.At present,the spatial resolution of MFL detection is getting higher and higher,which is unnecessary in some cases.Therefore,it is necessary to study the influence of spatial resolution of MFL detection,and get a reasonable spatial resolution.Weld crack is a common defect with high spatial resolution requirement in magnetic flux leakage testing.To meet the detection requirements of weld crack can ensure the detection requirements of most defects.The existing research on MFL detection is lack of systematic analysis of weld crack,and the weld crack is usually simplified as ordinary crack treatment,with large error.In this paper,the MFL characteristics of weld cracks are analyzed in detail,and the MFL simulation model of weld cracks is established,which is different from ordinary cracks.Based on the simulation model,the spatial resolution requirement analysis method for MFL detection of weld cracks is proposed.The experimental results show that the spatial resolution detection can collect the MFL information completely,and has good anti-noise ability.The analysis results can provide reference for setting the spatial resolution of MFL detection and avoid unnecessary data processing cost.The main contents of this paper are as follows:1)A more accurate MFL model of weld crack is established.Based on the basic physical principle,the mechanism of MFL generated by weld crack is discussed.The difference between weld crack and common crack is pointed out.The main influence factors of weld crack on MFL detection signal are summarized.The magnetic dipole model and finite element model of weld crack are established respectively.Based on the simulation model,the influence of weld crack parameters such as crack,reinforcement and permeability distribution on MFL detection signal is analyzed in detail,which provides a theoretical basis for the analysis of spatial resolution requirement of weld crack.2)A spatial resolution requirement analysis method for magnetic flux leakage testing is proposed.According to the relationship between MFL detection signal and spatial resolution requirement of weld crack,the spatial resolution requirement is determined by the maximum bandwidth of detection signal.The characteristics of MFL detection signal are analyzed,and the bandwidth selection method suitable for MFL detection signal is selected.The influence of main parameters of weld crack on signal bandwidth is analyzed by model simulation.Combined with the simulation results and the actual engineering background,the MFL detection signal with the maximum bandwidth is obtained,and then the spatial resolution requirement of the weld crack is obtained.3)The simulation models of magnetic flux leakage test and magneto-optical imaging test are designed respectively to analyze the anti-noise ability of the above spatial resolution,and the magneto-optical imaging test is used to verify the effect of magnetic flux leakage test after reducing the resolution. |
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