| Electromagnetic non-destructive testing technology has several advantages,including non-contact,high sensitivity,and flexible sensor structure design.These attributes making it well-suitable for intelligent diagnostics in different fields,such as aerospace,energy transportation,and power equipment fault detection.However,several testing challenges still exist.Firstly,a single electromagnetic detection method cannot comprehensively detect multiple types of defects,particularly surface and subsurface defects.The ability to simultaneously detect defect needs to be improved,resulting in low detection efficiency and complex sensing structures.Different detection advantages cannot be complementary;Secondly,the detection system faces issues such as power consumption and speed variations,making it challenging to perform long-term,efficient,and accurate defect detection and evaluation;Lastly,for small-diameter pipelines with limited space and diverse internal defects,complex sensing structures are difficult to achieve simultaneous detection of both surface and subsurface defects.Therefore,there is significant importance in improving the efficiency of multi-type defect detection in complex environments based on active-passive electromagnetic coupling sensing detection technology.In response to the above challenges,this dissertation proposes a series of new electromagnetic coupling defect detection methods based on the active-passive electromagnetic coupling sensing detection mechanism.Firstly,multiple types of defect detection mechanisms were deeply explored and derived from the micro to macro levels.The magnetization process and electromagnetic field penetration theory of the tested piece were analyzed,and mathematical models of magnetic flux leakage(MFL)and alternating electromagnetic fields in the defect area were established.Secondly,research was conducted on the motive eddy current effect of electromagnetic coupling detection at different speeds,exploring the internal magnetic field disturbance of permanent magnets and the distribution of eddy currents in the tested specimens.Based on those models,a new passive electromagnetic coupling detection technology was proposed to achieve detection of multiple types of defects in pipelines using low-power probes.Then,considering the influence of velocity on defect assessment within passive detection systems,an active electromagnetic coupling sensing detection system was designed for operation in variable-speed and low-power detection environments.This system incorporates a dual-physical effect generation mechanism,enabling the concurrent detection of multiple-types defect in complex testing scenarios.Finally,through actual pipe pulling tests,dynamic and static magnetic field composite excitation is applied to the pipe wall to achieve the identification and quantitative analysis of multiple types of defects in pipe under a multi-magnetic excitation architecture,opening up new ways to improve the accuracy and comprehensiveness of electromagnetic non-destructive testing technology.The main research content and innovative points of this dissertation are as follows:1.Due to the single function of dynamic and static electromagnetic non-destructive testing,and the fact that most probe excitation ends belong to independent combination structures,the composite probe sensor has complex structures and high-power consumption.This dissertation delves into the problem of electromagnetic coupling detection from the perspective of perceptual physics.By deeply integrating theoretical research on dynamic and static magnetic fields,it analyzes and deduces the magnetization stage,magnetic circuit distribution,and magnetic field disturbance mechanism in the defect area of the specimen,providing theoretical support for electromagnetic probes to detect multiple types of defects in pipelines.2.Due to issues such as high-power consumption and speed limitations of the probe,it cannot meet the requirements for detecting multiple types of defects.A passive electromagnetic coupling detection system is proposed based on a passive excitation electromagnetic sensor,which utilizes the motive eddy current field generated by the motion of the permanent magnet relative to the specimen as the excitation source,and combines the motive eddy current intensity inside the specimen with the magnetic field reconstruction changes in the internal space of the permanent magnet.Based on the magnetic circuit distribution of the excitation structure,an equivalent circuit model was established among the permanent magnet,the specimen,and the coil.Finite element numerical simulation was used to study the variation law between the voltage signal received by the coil and surface and subsurface defects at different speeds.Effectively detect multiple types of defects in low or high-speed motion.Finally,establish an experimental platform to verify the detection performance of the passive electromagnetic coupling probe.The experimental results show that the probe can achieve high sensitivity detection of various types of defects at low speeds,with a minimum detectable defect width of 1mm;Under high-speed conditions,it can effectively detect subsurface defects with a buried depth of 4mm,and has good dynamic detection ability.It effectively overcomes the limitations of speed and power consumption on sensor detection ability,and achieves effective detection of various types of defects under low-power and variable speed conditions.3.In response to the problem of detecting multiple types of defects in pipelines in complex environments,traditional electromagnetic technology has disadvantages such as single defect detection and low detection efficiency.A novel electromagnetic coupling sensing probe structure is proposed,which couples the sensing structure physically and generates two physical effects simultaneously under a single excitation,achieving physical field coupling of MFL and alternating current fields.Establish a magnetic circuit model of a coupled sensing structure,and analyze the distribution and variation of magnetic permeability from the surface and deep layers of the specimen from the perspective of magnetization,to deeply explore the trend of changes in magnetic field penetration depth on subsurface defect detection;At the same time,establish a detection model for coupled sensing probes and analyze the impact of electromagnetic disturbances in abnormal areas.Finally,establish an experimental platform to detect different types of defects in the specimens.The experimental results show that the proposed active electromagnetic structure coupling diagnosis system effectively detects and locates surface and subsurface defects on the pipe wall,effectively detects defects with a depth of 1mm at a speed of 12m/s,and detects surface defects with a depth of 2mm at a lift-off of 16 mm.Suitable for detecting different types of defects in complex environments,effective detection and evaluation of defects in high lift and high-speed environments.4.Due to the limitations of complex structure and high-power consumption of internal detectors,it is difficult to effectively detect different types of defects in pipelines.This dissertation proposes a pipeline defect detection system based on a new magnetic ring structure(MRS),using the electromagnetic coupling structure proposed in Chapter 4as the probe prototype.By reasonably configuring the static and dynamic magnetic fields,a dynamic magnetic composite circuit model was established under multiple-magnetic excitations.The distribution law of the electromagnetic field under different excitation structure configurations was analyzed through finite element simulation.After experimental verification,the internal detector effectively detects subsurface defects G2-4 with a buried depth of 3.1mm and G1-3 with a surface depth of 0.81 mm.The proposed multi-source excitation structure has significant detection advantages in identifying abnormal information such as defects and welds,further enhancing the localization and evaluation of pipeline surface and subsurface defects by the internal detector.Effectively overcoming the problem of being unable to detect multiple types of defects due to pipe diameter size limitations,it has good application prospects.The above research work compensates for the shortcomings of electromagnetic sensing technology in detecting multiple types of defects in complex environments,and improves its ability to detect surface and subsurface defects.At the same time,the design of passive electromagnetic coupling sensing structure lays a research foundation for achieving low-power and variable speed detection,and provides a basis for the comprehensive detection of different defects in complex environments using electromagnetic coupling sensing technology. |
