Research On Capacitance Imaging Detection Technology For Multi-type Defects Of Insulation Cladding Components

In the oil and gas industry,as a typical application of insulated coating components,insulated coating pipeline is widely used in the process of oil and gas exploration,exploitation,transportation,processing and storage.At present,insulated coating pipeline undertakes most of the transportation of crude oil and natural gas in China.At the same time,the detection,differentiation and quantitative evaluation of multiple types of defects in insulation cladding components can help to take reasonable maintenance programs and eliminate potential safety hazards as soon as possible,which is of great significance to ensure the safety of insulation cladding components in related application fields.This paper is supported by the National Key Research and Development Program "Inspection,Evaluation and Safety Assurance Technology for Offshore Oil and Gas Pipelines and Onshore Terminal Facilities" and the National Natural Science Foundation of China "Research on Direct Imaging Non-destructive Testing Technology of Multi-electrode Capacitance Delamination for Insulated/Coated Oil and Gas Pipelines".Capacitance Imaging(CI)is used to detect surface defects of insulating layer,hidden defects of imsulating layer and surface defects of metal layer.This paper focuses on the key issues of CI detection mechanism,CI system development,multi-type defects discrimination methods,multi-type defects inversion algorithm and de lift-off disturbance algorithm.It makes great progress in CI detection theory,system development,distinguishing method,inversion algorithm and CI detection of multi-type defects.The defect detection,type discrimination,size inversion,safety assessment and maintenance scheme of insulation coated components provide basis for ensuring the safety of the application field of insulation cladding components,which has important academic research value and industrial application value.The main research work is summarized as follows:(1)Research on CI detection mechanism of multi-type defects in insulation cladding componentsAccording to the principle of CI detection,a three-dimensional simulation model of insulation coated components for CI detection is established to reveal the variation of potential lines of different types of defects.The semi analytical model of single electrode rectangular CI probe is deduced by renormalization group method.The mechanism of the influence of multidielectric layer on parallel plate capacitance sensor and CI probe is systematically analyzed.The CI probe(excluding shielding electrode)is deduced by coplanar mapping and local capacitance method.The general MSD for insulating material and metal material is derived.The VOI definition of CI probe is further improved,and the influence of different types of defect disturbance on the VOI region is deeply analyzed.Finally,the CI detection mechanism of different types of defects is constructed.(2)Development of CI detection system for multi-type defects of insulation cladding componentsThe detection performance of CI probe with five different electrode shapes is studied by experimental method,and the influence of six geometric parameters on the detection performance of CI probe is simulated and analyzed.The optimal geometric parameters are obtained,which is used to optimize the CI probe.The multiplexer and lock-in amplifier are designed by using ADG1606 chip and AD630 chip,and the hardware assembly of CI detection system is developed.The platform control program and data processing program are compiled by Lab VIEW,and the software collection of CI detection system is developed.The development of CI detection system is completed,which provides the basis for further research on defect identification method,quantitative inversion algorithm and denoising algorithm.(3)Research on identification method of multi-type defects in insulation cladding componentsBased on MSD and experimental results,the detection mechanism of surface defects of insulating layer,hidden defects of insulating layer and surface defects of metal layer is described.Based on the lift-off of CI probe and the working electrode spacing parameters,the variation rule of VOI region is analyzed,and the internal relationship between lift-off and working electrode spacing is obtained.By fusing the above parameters,the methods based on the change of lift-off and working electrode spacing are proposed to distinguish the three types of defects quickly.By fusing the intensity of detection signal,NVR and gradient map,the theory of Central Gradient Value(CGV)is proposed,and the central gradient threshold method(CGTM)is established to realize the effective differentiation of different types of defects.The establishment of the above distinguishing methods finally breaks through the technical difficulties of distinguishing different types of defects.(4)Research on quantitative algorithm of multi-type defects in insulation cladding componentsBased on the CI detection technology,the unidirectional gradient compensation fusion algorithm and the unidirectional gradient edge compensation fusion algorithm for plane profile quantification of insulation surface defects are proposed.The bidirectional gradient compensation fusion algorithm for plane contour quantization of hidden defects of insulating layer and surface defects of metal layer is proposed.According to size dimension reduction,NVR dimension increased,NVR correspondence between simulation and experiment,and genetic algorithm,the NVR grid algorithm for quantifying the width and depth of defects is proposed,which realizes the quantitative evaluation of insulation cladding components defects.The establishment of the above distinguishing methods finally breaks through the technical problems of quantitative evaluation of multi-type defects.(5)Research on CI detection of multi-type defects in insulation cladding componentsThe CI detection system is used to detect the multi-type defects of plate-shaped insulation coated components and insulation coated pipes.The detection performance of CI detection technology is explored by using differentiation method and quantitative algorithm.According to the lift-off disturbance factors under complex working conditions,this paper studies the variation of lift-off disturbance under different types of defects,and proposes NVR integral double threshold denoising algorithm.Aiming at detection problem for multi-type defects of large thickness insulation cladding components,CI detection technology is used to test multitype defects of large thickness insulation layer.The feasibility of detecting multi-type defects of large thickness insulation cladding components is preliminarily explored.