Research On Optimization Of Cathodic Protection Potential Of Long-Distance Pipeline Under AC Transmission Line

Long-distance pipeline is the main carrier of oil and gas transportation.Due to the limitation of geographical conditions,the phenomenon of sharing ’ public corridor ’ between AC transmission lines and long-distance oil and gas pipelines occurs from time to time.The traditional cathodic protection range of pipelines is only applicable to the absence of AC transmission line interference,when the AC transmission line is working,the AC induced voltage is generated around the adjacent pipeline,which interferes with the effect of the existing cathodic protection system of the pipeline and accelerates the corrosion of the pipeline.Therefore,it is very important to carry out research on the optimization of cathodic protection potential of AC transmission lines for long-distance pipelines.In this paper,the geodetic return impedance of AC transmission lines and pipelines in uniform soil and layered complex soil is deduced.The model of AC induction of AC transmission lines to long-distance pipelines is established by using CDEGS software.By changing the diameter,wall thickness and buried depth of pipelines in the model,the height of transmission lines to the ground and the parallel length with pipelines,the influence of the change of characteristic parameters on the induced voltage of pipelines is simulated and analyzed.A simulation experiment platform for steel test pieces subjected to AC interference in neutral simulated solution was built.The constant potential polarization in the electrochemical workstation was used to simulate the cathodic protection system.According to the AC induced voltage calculated by the simulation model of transmission lines and long-distance pipelines,the AC interference and cathodic protection potential applied to the test pieces were changed respectively.The polarization curve and AC impedance spectrum of the metal test pieces were obtained by electrochemical test,and the electrochemical parameters and corrosion rate of the test pieces under different experimental conditions were analyzed.Through the simulation experiment platform,in the cathodic protection system with AC interference,the polarization curve and AC impedance spectrum of the test piece under different AC interference and protection potential are analyzed,and the equivalent circuit of the threeelectrode system in the experiment is established.The Zsimpwin software is used to fit the data of each curve to obtain the charge transfer resistance under different experimental conditions.By comparing the charge transfer resistance,the protection potential is optimized and calculated,and the cathodic protection range that should be set when different AC interference is discussed.Compared with the traditional cathodic protection potential range,the optimized protection range can select the appropriate protection potential according to the size of AC interference,which provides a reference method for the optimization of cathodic protection potential of pipelines under AC transmission lines.