Simulation And Experimental Study On Practical Technology Of Remote Field Eddy Current Testing On Pipelines

As a preventive measure,the application of remote field eddy current technology in pipeline safety assessment is of great potential.On the bases of the theory of electromagnetic field,this thesis takes finite element analysis software ANSYS,Ansoft Maxwell and experimental instruments as profiling tools and treats the single and double layer pressure pipelines as the research objects.For the purpose of exploring the characteristics and laws of eddy current signals and their derived quantities,analysing of defects quantitatively,solving the problems of field application to improve the detection rate of pipeline defects,providing the numerical basis for the extraction of defect characteristic signals and the design of probes,the simulation analysis and experimental study on the electromagnetic distribution of pipeline are carried out.Based on the ANSYS software,the control variable method is used to study the effects of various factors on the detection signal in the two-dimensional model without defects,and the characteristics and rules of the change of detection signals are revealed.On the basis of the previous analysis,The signal characteristics of different positions,different number of defects and the whole pipe corrosion thinning are analyzed qualitatively.Based on the simulation of defects with different size,the quantitative relationship among the defect size,the detection signals and the sensitivity of the defect response is discussed.Through data fitting,the detection signal characteristic is approximately exponential relationship with the defect depth,and has a logarithmic relationship with the defect width.The sensitivity of the defect response varies with the change of the defect depth in an exponential form,and is approximately inversely proportional relationship with the defect width.In the simulation analysis of the double layer pipeline,a similar conclusion is obtained,and it is found that the responses of the magnetic field signal to the defects of the inner and outer tubes are different.The feasibility of simultaneous detection of double layer pipeline is explored.In addition,the optimization scheme of the probe is put forward in the single layer and double layer pipeline,and the influence of shield structure on the detection signal is analyzed.Aiming at the problems existing in engineering application,new types of probes and auxiliary devices are developed.Using Ansoft Maxwell to establish a three-dimensional field circuit coupling model and the transient analysis is did.It is proved theoretically that the new far field eddy current probe has the ability to locate the local defects.In this paper,the design scheme of the point-ring eddy current probe is proposed,which combines the advantages of point probe with the advantages of ring probe.In the flaw detection test,the two kinds of probes can accurately locate the local defects.An auxiliary detecting device is developed to improve the stability of detection,in which the axial movement and the circumferential rotation of the probe can be done under the action of two motors.A mechanical probe pulling device used for conveying probe in long pipeline flaw detection is developed.The performance of the two devices is significant in the performance test,and the feasibility of their application in engineering practice is verified.