Laboratory investigation of cathodic protection of ASTM A36 carbon steel in seawater under alternative potentials

Abstract

Cathodic protection is a technique used to prevent corrosion of structures in seawater. In the present work, cathodic protection of ASTM A36 carbon steel was investigated under two polarization conditions in synthetic and natural seawater, at 25°C and 4°C. Open circuit potential (OCP) of the material in seawater was approximately −700 mV_Ag/AgCl enabling investigation of an alternative protection potential of −750 mV_Ag/AgCl compared to the standard value of −800 mV_Ag/AgCl. Laboratory polarization experiments were complemented by thermodynamic equilibrium simulations. Results demonstrated that steel integrity is preserved at the alternative potential, with uniform corrosion rate decreasing at lower temperatures. This study advances the understanding of cathodic protection in subsea systems by integrating kinetic and thermodynamic criteria, while highlighting the role of temperature directly linked to installation depth. This analysis contributed to improving knowledge on cathodic protection mechanisms in subsea systems by integrating kinetic considerations into existing thermodynamic criteria, ensuring minimal risk to structural integrity. These findings pave the way for reducing the need for submarine interventions to restore cathodic protection systems and facilitate maintenance of electrode potentials slightly above the limits set by standards.