Study On Transient Electromagnetic Response Of Metal Pipeline Based On FDTD Algorithm

Buried pipeline,as one of the energy transport tools,is widely used in engineering practice,but the pipeline safety issues are also increasingly prominent,so it is urgent to improve the ability of pipeline corrosion inspection.Compared with other detection methods,the transient electromagnetic method has strong anti-interference ability,and can achieve trenchless detection in service,thus making the pipeline more efficient and efficient detection,but the detection precision of this method needs to be solved urgently.In this paper,the FDTD is used to forward and analyze the response process of the buried metal pipe by TEM.First of all,based on maxwell’s electromagnetic theory,to deduce the FDTD algorithm for transient electromagnetic signal propagation.Reasonably,setting up the relation between the size of the space grid and time step,to ensure the algorithm stability and numerical convergence.Applying CFS-PML in the boundary region,that can effectively control the electromagnetic signal reflection,Secondly,to design the 3D model of 1:1.Combining the approximate homogeneous grid method with the equivalent homogeneous mesh method to achieve optimal contour path grid.The initial conditions of the exciting source are designed as trapezoidal cosine pulse signals,and adopted the method of applying the edge along the horizontal component of electric field,its purpose is to simulate the actual detection loop state trigger.The horizontal depth profile imaging of exciting source and the spatial 3D transient imaging of magnetic field intensity.which can clearly observe the process of magnetic field diffusion in the whole space.Finally,turning two pipes were prefabricated inner wall ring corrosion defects and outer wall truncation corrosion defects,the experimental results are consistent with the results of the algorithm by the transient electromagnetic method detesting,which proves the correctness and reliability of the FDTD forward algorithm.In order to improve the accuracy of transient electromagnetic technology,to design three different models of forward modeling: inside and outside the wall corrosion of different degrees,different characteristics of metal compounds forward corrosion area,different changes in the pipeline caused by the depth of the pipeline.Results show: TEM can effectively detect the loss of metal inside and outside the pipe,the induced electromotive force isinversely proportional with the loss;The method can also detect the change of the resistivity and relative permeability of the wall thickness thinning area due to the corrosion of the pipeline,so as to make the response of the secondary field signal smaller;The forward results also show that the late sampling signal can effectively suppress the signal interference caused by the change of pipeline depth.