Anti-corrosion characteristics of FeCO3 and FexCayMgzCO3 scales on carbon steel in high-PT CO2 environments

Corrosion products formed on carbon steel can be considered as naturally occurring anti-corrosion scales. However, relationships between porosity and anti-corrosion characteristics of such scales remain poorly understood. In this study, characterisation data derived from Focus ion beam (FIB) and X-ray micro-computed tomography (μCT) techniques, combined with image processing algorithms, were applied to reveal the porosity, pore connectivity and pore size distribution within FeCO3 and FexCayMgzCO3 (where x + y + z = 1) scales on a X65 carbon steel substrate. The formation kinetics, chemistry and anti-corrosion capabilities of both scales were also systematically evaluated by Scanning electron microscopy (SEM) coupled with Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), profilometry and electrochemical measurements. The results demonstrate that FeCO3 scales can reduce the availability of active surface areas more efficiently with their lower porosity on the steel surface, providing superior anti-corrosion performance than FexCayMgzCO3 scales. This study elucidates the effects of ubiquitous cations on the formation and relative protectiveness of corrosion product scales, as well as their effectiveness to protect against corrosion.