Research On Crack Detection Method And Technology Of Oil And Gas Pipeline Based On Rotating Electromagnetic Field

As a new technology of Nondestructive Testing,rotating electromagnetic field testing can theoretically detect defects in any direction on the metal surface,which has great potential for development.But at present in various fields,especially in the field of pipeline detection,the relevant theoretical research and the development of instruments and equipment is still in its infancy.This paper focuses on the key technologies of rotating electromagnetic field detection,mainly focusing on the theory of rotating electromagnetic field detection,simulation and experiment of detection probe,noise reduction of detection signal,suppression of uneven permeability and defect reconstruction technology.The main contents of this thesis are as follows:1.Starting from the mathematical model of rotating electromagnetic detection technology,this thesis is expounded the principle of rotating the inductive magnetic field of the electromagnetic field of cycles and the distribution characteristics of different defects in the direction of the magnetic field,and designed a new type of arc excitation probe structure,arc excitation coil of the magnetic induction intensity were deduced,and the mathematical model of rectangular crack defects.2.COMSOL Multiphysics simulation is used to establish the static simulation model and dynamic parameter sweep model of rotating electromagnetic field detection probe.The crack length of relative error is used to probe optimization,horizontal magnetic field component sensitivity and sensitivity of three parameters,such as vertical magnetic field component,analyses the lift-off distance,excitation frequency,coil diameter,coil number,sensor arrangement,coil number of turns,the coil current on the effects of the defect detection and work parameters for the optimization of the above analysis.3.According to the characteristics of rotating electromagnetic field detection technology,a rotating electromagnetic field detection probe and a testing platform for defect detection are developed.In order to improve the precision of defect detection,the signal was de-noised by using empirical mode decomposition and wavelet de-noising method.4.Based on Fast ICA blind source separation technique,an inhomogeneous magnetic permeability suppression method is proposed.The influence of global permeability and local heterogeneity on the detection results is analyzed.The blind source separation of the imbalanced signal and the imbalanced signal is realized under the underdetermined condition.5.Particle swarm optimization based least square vector machine is used to reconstruct the defect contour.According to the relationship between the change of the induced magnetic field on the metal specimen surface and the defect length and depth,the penalty coefficient and kernel function parameters in the vector machine were optimized by particle swarm optimization method,and the semi-elliptic and rectangular defect contours were reconstructed by the optimized least square vector machine method.