Permeation of different cations through cathodically protected coated API X-120 steel at elevated temperature

Abstract

The electrochemical behaviour of coated API X-120 steel in 0.5M of NaCl and KCl with and without cathodic protection (CP) at elevated temperature was investigated. CP was applied at -0.78 and -1.1V vs Saturated Calomel electrode (SCE) on day 5 of immersion. Temperature of solutions was set at 50 °C. Electrochemical Impedance Spectroscopy (EIS) was used to characterize the coating. Energy Dispersive X-Ray Analysis (EDAX) was used to map the metal surfaces. Visual inspection was used to support EIS data. The extent of corrosion was evaluated using Image tool analysis. A correlation was found between the size of the cations and the performance of the coating. Mapping of metal surfaces showed dense areas of Na+ and K+ at -1.1V. K+ was found to be faster than Na+ due to its smaller hydrated size.