Cathodic protection is applied especially to protection of coating fault on a buried pipe line in a soil. According to some authors, the mechanism of cathodic protection of carbon steel is a shift of open circuit potential into the immunity region or reducing of anodic reaction rate in the active state. The importance of change of pH and soil electrolyte composition during applying cathodic protection is sometime ignored.The study deals with influence of cathodic protection on pH change and anions migration in soil electrolyte close to protected carbon steel surface. Concentration of chlorides, sulphates and hydrogen carbonates decreased about two orders of magnitude during applying cathodic protection. The migration rate of hydroxides during cathodic polarization is lower than their production by cathodic reduction of oxygen. As a result of cathodic reduction of oxygen, the pH of soil electrolyte close to protected surface gradually increases up to 12.The final pH of soil electrolyte close to protected surface depends on the migration rate of anions, the diffusion rate of oxygen into soil electrolyte and neutralizing capacity of soil.Keywords: Cathodic protection, soil electrolyte, migration
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