In-situ photometric reflectance measurements of carbon steel surfaces upon cathodic protection

Abstract

Cathodic protection (CP) is an electrochemical technique used to reduce corrosion rate of carbon steel to negligible values. CP has been used since almost 100 years to protect underground structures, e.g., soil buried pipelines. Despite the worldwide use of the technique, the working mechanism of CP is still under debate. On the one side, researchers suggest that the modification of the electrolyte in the vicinity of the steel surface (i.e., increase in pH and oxygen consumption) might promote the formation of a passive film that contributes to the protection mechanism by reducing the corrosion rate of steel to negligible values. On the other side, other researchers suggest that the protection mechanism achieved by the CP system can be explained based on corrosion kinetic considerations, with the iron dissolution reaction being reduced to negligible values. On both sides, experts based their reasoning on theoretical approaches or indirect measurements. Up to now, investigation regarding the modifications of the steel surface upon the application of cathodic protection is still missing. To fill this gap of knowledge, the aim of the work is to analyze the changes of the carbon steel surface with in-situ photometric reflectance measurements upon the application of CP. Carbon steel samples were immersed in a soil simulated solution and CP was applied for 30 minutes at different potentiostatic conditions. During the experiments, the increase in the absorbance in the UV region of the light upon the application of CP suggested the formation and growth of an oxide film at the carbon steel surface in presence of a cathodic current. The results obtained in this study are of main importance concerning the advancing in understanding cathodic protection mechanisms.