In situ synchrotron X-ray diffraction study of surface scale formation during CO2 corrosion of carbon steel at temperatures up to 90 °C

In situ synchrotron X-ray diffraction was used to follow the formation of corrosion product scales on carbon steel in CO2 saturated brine at temperatures from 40 to 90 °C. The corrosion process was accelerated by applying a small anodic current, and in selected tests a scale inhibitor, amino trimethylene phosphonic acid (ATMPA), was added. Siderite was identified as the major phase in the scale formed in all conditions. With increasing temperature, the scale formation rate increased, while the scale thickness and crystallite size decreased. Above 60 °C, the scale became increasingly protective. The scale thickness and crystallite size decreased with increasing ATMPA concentration.