Research On In-service Detection Technology Of Plate And Pipe Defects Based On Remote-field Eddy Current

Ferromagnetic materials have superior material properties,is one of the most widely used metal materials,and is widely used in all walks of life,used in the manufacture of storage tank floor,train box,car shell,transport pipeline and ship deck and other components.In the case of long-term service will produce more serious cracks,corrosion,holes and weld cracking,etc.,these defects will bring a certain degree of safety risks.Remote-field eddy current detection technology is not affected by the skin effect,and has the same sensitivity to the internal and external walls of the pipe,simple operation,low cost,has certain advantages.The classical remote-field eddy current inspection technique is to detect when the probe inside the pipeline,and because there is fluid flow in the in-service pipeline,the inspection needs to be stopped and cannot be performed in-service.In this thesis,by designing the probe electromagnetic shielding structure to shield the propagation of direct magnetic field energy,so that the indirect magnetic field energy twice penetrates the flat plate or pipe wall back to the same side of the excitation coil and the remote-field eddy current phenomenon occurs,realizing the remote-field eddy current detection technology to detect defects on the flat plate as well as outside the pipe.In order to design the electromagnetic shield structure of the probe,this paper firstly uses two-dimensional finite element simulation to compare and analyze the materials and composition of the electromagnetic shield structure of the detection probe,and finds that the shielding effect of the mixed multi-layer electromagnetic shield structure is better than that of the single-layer electromagnetic shield structure.Finally,it is determined that the optimal electromagnetic shield structure of the remote-field eddy current detection probe without lifting off the plate is pure iron + copper + pure iron three-layer shield structure.Based on the design of remote-field eddy current detection probe without lifting plate,a probe with lifting plate remote-field eddy current detection probe is designed.Its electromagnetic shielding structure is pure iron structure with the shape of "F" added on the basis of the three-layer electromagnetic shielding structure of pure iron + copper + pure iron.By comparing and analyzing the detection signals of different lift distances,it is concluded that the remote-field eddy current detection probe is not sensitive to lift.Because the outer wall of the pipeline has a certain curvature,this paper uses three-dimensional finite element simulation to study the design of the pipeline probe,and applies the design of the plate nonlift remote-field eddy current detection probe structure to the pipeline after a small change,the change is to extend the electromagnetic shield structure to the outer wall of the pipeline.After verification,the design of the probe can realize the remote-field eddy current phenomenon.In this paper,the designed remote-field eddy current inspection probe is used to detect and analyze crack defects as well as porosity defects.The variables studied for crack defects are crack depth and crack width,and the variables studied for porosity defects are porosity diameter.The detection signal is extracted and analyzed,and at the location where the defect is set,the curve of the detection signal change is close to a horizontal straight line when there is no defect,and the curve is raised upward to form a peak when a defect is present.When the defect size changes,the height of the peak also changes.The detection signal feature quantities have amplitude and phase.In the study of the effect of defect width change on the detection signal,the amplitude integral and the phase integral are used as new feature quantities,which contain not only the size of the crack defect but also the width of the crack defect.It is found that there is a specific linear fit or quadratic fit relationship between the detection signal characteristic quantity and the defect size,so that the defect size can be quantitatively analyzed by the specific value of the detection signal characteristic quantity.The peak detection signal amplitude can be used to identify the upper and lower surface defects or internal and external pipe wall defects.Both the amplitude and phase integration of the detection signal can distinguish whether the defect is located in the outer or inner pipe wall.In summary,this paper designed three different remote-field eddy current detection probe structure,and use the probe to detect for different types of defects from different angles,and analyze the law of its detection signal changes,for the practical application of engineering plate and pipe defects in the remote-field eddy current in-service detection to provide some theoretical guidance and research ideas.