The Influence of Rust Layers on Calcareous Deposits’ Performance and Protection Current Density in the Cathodic Protection Process

Calcareous deposits are a consequential outcome of cathodic protection in marine environments, exerting significant influence on the cathodic protection process and current density prerequisites. This study investigates the process of calcium deposition and its impact on the cathodic protection current density of carbon steel under the influence of a rust layer in different corrosion periods. This was investigated using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results demonstrate that the formation processes of calcareous deposits vary after exposure to the corrosive environment for 0, 7, and 30 days. While a longer corrosion period leads to thicker rust layers on the metal surface and a higher initial cathodic protection current, the presence of these rust layers facilitates the deposition of calcium and magnesium ions, resulting in a rapid decrease in cathodic protection current density after a certain period. Meanwhile, long-term cathodic protection facilitates the thickening and densification of the oxide layer, thereby enhancing its protective efficacy, effectively reducing the corrosion rate of the metal surface and stabilizing the cathodic protection current density at a lower level. This study provides theoretical data and experimental evidence to support the maintenance of corroded marine engineering equipment.