Application of Electrochemical Impedance Spectroscopy as An Alternative Method to Evaluate the Efficiency of Cathodic Protection in Simulated Soil Solution

Buried pipeline steels are exposed to external corrosion due to the aggressive effect of the soil environment. Despite the double protection system consisting of a coating and cathodic protection, the risk of failure is present and can lead to a reduction in the structural integrity of the pipes. Considering the complexity and variability of different soils, a poor estimate of protection conditions can result in either overprotection or underprotection. The current investigation was conducted using a variety of cathodic potentials on X52 carbon steel. The samples were covered by a layer of natural clay and soaked with a simulated soil solution. Chronoamperometry measurements and electrochemical impedance spectroscopy (EIS) technique were used. The analysis of the impedance diagrams revealed significant variations in form and characteristics when the steel was exposed to different cathodic potential degrees. It was also noticed that the charge transfer resistance decreased gradually at lower applied cathodic potentials. On the other hand, it was observed that the passive layer protectiveness could be evaluated by the EIS method. In this study, it was clearly shown that the EIS technique can be used as a method to monitor and control the performance of cathodic protection.