Formation of iron-carbonate scale-layer and corrosion mechanism of API X70 pipeline steel in carbon dioxide-saturated 3% sodium chloride

摘要

This work presents the electrochemical results obtained during the study of the corrosion of X70 pipeline steel samples immersed in a 3 % wt NaCI solution saturated with CO2 at 20 °C under static and controlled turbulent flow conditions. In order to control the hydrodynamic conditions of the system, a rotating cylinder electrode (RCE) was used. Electrochemical techniques, Linear Polarization Resistance (LPR) and polarization curves, were used to determine the effect of turbulent flow upon the corrosion kinetics of the steel. We also elucidate the effect of temperature on the corrosion rate of the API X70 steel under the experimental conditions studied. Often, the corrosion of carbon steel in aqueous environments containing CO2 involves the formation of solid iron carbonate, FeCO3, as a corrosion product. The protective property of the formed FeCO3 scale layer to corrosion in brine solutions containing CO2 was established as the possible cause of the corrosion rate decrease above 60 °C._