Research On Some Key Issues Of Microwave Surface Defect Detection Technology

With the rapid development of science and technology,metal materials,as the main structure supporting the development of industrial production,are widely used in aerospace,military,oil and gas pipelines,building materials and other fields.During the use of materials,with the increase of service life,environmental changes,soil erosion and other factors,it is easy to cause changes in the structure of metal materials,resulting in damage to the materials,resulting in major accidents,so regular testing is essential for its safe operation.Traditional magnetic flux leakage nondestructive testing technology and ultrasonic testing technology have been matured,but due to the high demand of some testing environments,traditional nondestructive testing technology still has problems such as difficult conditions or limited detection objects and scope.For example,the effective detection of rail surface defects under high-speed conditions,the magnetic leakage detection,ultrasonic testing and other technologies are still difficult to overcome the problem of high-speed online detection of rails;For example,the detection of internal surface defects of urban gas small-diameter pipelines,because urban gas pipelines have the characteristics of small pipe diameter,small turning radius,low pressure and slow flow rate,conventional detection technology is difficult to achieve equipment integration in pipelines with pipe diameter less thanΦ100mm,and there is no effective online detection method at present.In view of the above problems,combined with the characteristics of high microwave frequency,strong penetration ability,long propagation distance,and adaptability to high-speed detection,this paper carried out a lot of research on microwave detection technology in the detection of rail surface defects and inner surface defects of urban gas small-diameter pipelines.Aiming at the actual detection requirements of rail surface and inner surface defects of small-diameter pipelines,this paper proposes a detection method based on microwave reflection method.Starting from the mechanism of microwave propagation in space,the wave equation of microwave in space is established,and the equations of microwave incidence wave,electric field and magnetic field of reflected wave and transmitted wave at microwave vertical incidence and oblique incidence are analyzed,and the mathematical relationship model of reflection coefficient and transmission coefficient in the process of microwave oblique incidence propagation is analyzed,and the laws of microwave electric field,magnetic field and current distribution at the defect are studied.Therefore,the microwave detection model of the inner surface defects of the rail surface and the city gas small-diameter pipeline is established.From the perspective of practical engineering application,the influencing factors of microwave detection signal in the defect detection problem of rail surface and inner surface of urban gas small-diameter pipeline were analyzed,and a microwave detection experimental platform was built to verify its feasibility and effectiveness.Aiming at the problem of rail surface defect detection,this paper innovatively proposes a microwave detection method for rail surface defects based on microwave reflection method,and establishes the microwave field distribution equation of rail surface defects propagation based on Maxwell’s equation.According to the boundary conditions of the rail surface,the microwave detection model of the rail surface defect is established,and the relationship model between the microwave reflection coefficient,the microwave propagation mode and the defect size is obtained.The microwave detection model of rail surface defects when the propagation modes are TE₁₀,TE₀₁,TE₀₂ and TM₁₁are established,and when the microwave frequency of TE₀₁mode is 5.5-6GHz,it has effective detection ability for rail surface defects.Aiming at the analysis of rail surface defect engineering applications,based on Maxwell equation,the relationship model between the dimension of rail surface defect detected by TE₀₁mode and the characteristic quantity detected by microwave was established.A rail surface defect experimental detection platform was built to detect rail surface defects,and it was obtained that:with the increase of defect depth,the absolute value of microwave reflected wave return loss increased;As the width of the defect increases,the microwave detection frequency at the defect decreases;When the defect is perpendicular to the propagation direction of the pipe wall current,microwave has a good ability to detect rail surface defects.By setting a composite inspection probe on the rail surface,the full-angle detection of rail surface defects can be realized.Microwave can effectively detect the defect width of 0.1mm,defect depth of 1mm,defect length of 1mm.Aiming at the problem of detecting defects on the inner surface of urban gas small-diameter pipelines,a microwave detection technology for internal surface defects of urban gas small-diameter pipelines based on microwave reflection method is proposed.The microwave detection mechanism of the inner surface defects of the city gas small-diameter pipeline was analyzed,and the microwave field distribution equation of the propagation of the inner surface defects of the urban gas small-diameter pipeline when the TE mode and TM mode propagated were established.According to the microwave distortion equation at the defects of TE mode and TM mode,the microwave detection model of the inner surface defect of the small-diameter pipeline can be established,and the relationship between microwave reflection coefficient,return loss,defect size and microwave propagation mode can be obtained.Microwave detection models for internal surface defects of urban gas small-diameter pipelines with propagation modes TE₁₁,TE₀₁ and TM₁₁ were established.TE₀₁ mold has the smallest propagation loss in the pipeline,can be transmitted stably,and has good detection ability for defects on the inner surface of the pipeline.Aiming at the problems in the practical engineering application of urban gas small-diameter pipelines,a method for detecting defects on the inner surface of TE₀₁ modular microwave small-diameter pipelines is proposed.The damage of the inner wall of the small-diameter pipeline was detected by the terminal short circuit method,the microwave propagation mode transition at the defect was analyzed,and the field distribution equation,the current equation of the pipe wall and the microwave detection model of the TE₀₁ mode microwave in the pipeline based on Maxwell’s equation were established.Build an experimental platform for in-pipeline detection with an inner diameter of 52mm to detect defects on the inner surface of small-diameter pipelines,and with the increase of defect width,the number of microwave field propagation propagated by the inner surface of the pipeline decreases,the microwave wavelength increases,and the microwave detection frequency at the defect decreases;With the increase of defect depth,the absolute value of return loss of microwave detection signal increases.Microwave can effectively detect the annular defects of the inner surface of the small diameter pipe with a depth of 1mm and a width of 1mm.The microwave coupling wave model at the pipe elbow is established,the coupling coefficient at different angles of the pipeline elbow is analyzed,and the influence of the pipe elbow on the TE01 mode microwave detection signal of the pipeline is analyzed.When the elbow angle in the pipe is 90°,the microwave coupling wave at the elbow is TM₁₁ mode,and the elbow detection signal is formed in the 5.6GHz range.TE₀₁ mold has good detection ability for the detection of inner surface defects of city gas small-diameter pipelines.Aiming at the detection of rail surface defects and the inner surface defects of urban gas small-diameter pipelines,a microwave detection scheme is provided,which can initially realize the detection of rail surface defects and inner surface defects of urban gas small-diameter pipelines.