A study by electrochemical impedance spectroscopy and surface analysis of corrosion product layers formed during CO2 corrosion of low alloy steel

Abstract

In the following research, electrochemical and surface analysis techniques are used to define the main contributing factor to the protectiveness offered by a scale formed at high temperature and pH under CO2 saturated conditions. At 80 °C and pH 6.6, trace amounts of a magnetite (Fe3O4) phase was identified at certain locations beneath a more dominant iron carbonate (FeCO3) film. Furthermore, over time, the evolution of the corrosion product layer towards a very low porosity results in a “diffusion barrier” that is indicated by a positive shift in the open circuit potential and is considered key to corrosion protection.