Research On Detection Technology Of Ferromagnetic Materials Based On Pulsed Eddy Current

Pressure vessels made of metal materials are widely used in petroleum and natural gas transportation,chemical industry,nuclear power and other fields.It is of great significance to detect and ensure the safety and health of metal materials structure for production quality.However,metal materials are prone to fatigue cracks or defects in the long-term use process.For example,double-layer pipelines in oil and gas wells are buried in damp and complex environment all the year round,accompanied by high-pressure working conditions and severe electrochemical corrosion.During the use process,because of internal or external corrosion,wear and tear gradually thinning,these defects are mostly sub-surface defects,while the long-term existence of defects conducts.Failure of metal materials can easily lead to safety accidents,which have a serious impact on life,property and living environment.Nondestructive testing does not cause macro damage to structural materials,nor does it affect the integrity of response structures.Under the condition of complete components,the key parts of the structure can be monitored repeatedly on-line by physical methods such as sound,light,electricity and magnetism,and the safety of the service structure can be effectively confirmed by periodic testing.Pulsed eddy current testing is an important method in electromagnetic nondestructive testing technology.It has the characteristics of deep detection depth and fast detection speed.In this paper,pulsed eddy current testing technology is studied based on the detection of deep sub-surface defects in ferromagnetic materials.The main research contents are as follows:(1)Based on the principle and theory of pulsed eddy current testing technology,a structure of pulsed eddy current sensor with weak coupling transmission principle is proposed to solve the problem of deep defects detection of ferromagnetic materials,and the parameter optimization model is established by using finite element analysis software COMSOL.The influence of geometric parameters of pulsed eddy current sensing structure on detection sensitivity is studied,and a set of optimum geometric parameters of pulsed eddy current sensing structure is obtained.(2)The verification platform of pulsed eddy current testing system is built.Including generation of excitation signal,design of driving power amplifier circuit of coil,manufacture of pulsed eddy current detection probe,design of signal conditioning circuit and acquisition of detection signal.(3)Establish the model of deep sub-surface defect detection in metal materials in COMSOL,and obtain the simulation results.In addition,on the verification platform of pulsed eddy current testing system,the deep sub-surface defect detection in ferromagnetic and non-ferromagnetic materials was experimentally verified,and the experimental verification results were obtained.By comparing the results of the two methods,the mapping relationship between sub-surface defects at different depths and response signal characteristics was analyzed and established.For the detection of deep subsurface defects,the pulsed eddy current sensing structure and experimental platform designed in this paper can correctly detect all deep sub-surface defects in ferromagnetic and non-ferromagnetic materials.