Numerical Simulation Of Non-uniform Grid Time-domain Electromagnetic Method For Detecting Buried Pipeline Corrosion

Buried pipeline has wide application fields as the main transport carrier of current energy necessities,it is a great convenience for people's daily life.However,the pipeline safety issues are also increasingly prominent,how to effectively improve detection ability the corrosion of buried pipelines is the most important problem.Compared with other detection methods,the time domain electromagnetic method is sensitive to metal loss of tube body.This method detects trenchless pipes rapidly and has reliability and efficiency in corrosion detection of buried pipelines.In this paper,the finite difference time domain algorithm is used to forward response characteristic signal of buried pipeline corrosion,so as to provide reliable evidence for detecting buried pipelines in time domain electromagnetic method.First of all,the present study derives finite difference algorithm of non-uniform grid technology in the three-dimensional truncation space based on the existing difference equation.The coefficient of difference equation were modified and then applied to the numerical simulation.Secondly,space sampling step and time step were rationally set to ensure stability and numerical dispersion of numerical simulation algorithm.Propagation direction deformation of the truncated space field source was reduced.What's more,absorbing boundary condition and upper-extention condition of the earth-air boundary were introduced.These different absorption conditions were compared to find the best one.Finally,according to the detection principle,non-uniform grid algorithm model was adopted.This model was filled with related attribute medium,wherein diffusion equation of time domain electromagnetic method was introduced and was discreted to calculation domain.The excitation source was applied to horizontal electric field edge of the Yee grid as an initial condition to simulate primary field diffused over time generated by transmitting probe.Through imaging and transient display diffusion law of magnetic field and electric field on three-dimensional space slice,and set up multi-group buried pipeline corrosion detection influence factor,observation and analysis the change trend of response characteristics signal.According to the numerical simulation results,this study designed related experimental model pipe prefabricated different types of corrosion characteristics.The time domain electromagnetic method was used to detect annular grooves and the method calculating residual wall thickness was put forward to deal with data and identify abnormal signals,which verified the correctness of experimental scheme and the accuracy of results.Compared the experimental results with the forward results of numerical algorithm,accuracy of time domain finite difference algorithm of non-uniform grid technology can be verified,which provided basis for the time domain electromagnetic method detecting buried pipelines corrosion.Results show that time domain electromagnetic method can effectively identify the pipeline metal loss in the late signal interval,namely induction electromotive force and metal loss is proportional to the amount of the medium loss;with pipe diameter and conductivity increases,induced electromotive force amplitude is gradually increase and its change trend is obvious;with the depth increases,induced potential amplitude decreases gradually,and its change trend is obvious.These proved the effectiveness and reliability of distinguish tube corrosion by using induced electromotive force in the late signal interval.