The influence of carbon steel surface roughness on mass transfer and corrosion kinetics in CO_2-containing environments

摘要

CO_2 corrosion is a major problem in internal pipeline corrosion since the presence of CO_2 leads to the formation of carbonic acid which accelerates the corrosion of carbon steel. There are a range of mechanistic, semi-empirical and empirical models to predict carbon steel corrosion rates in CO_2-containing environments, each taking into account various influential parameters such as flow rate, operating temperature, pH and partial pressure amongst other. However, one property which has received less attention is the internal surface roughness of pipework. The internal condition of the pipework inevitably plays an important role in the process of corrosion and has not only the ability to increase the surface area of steel exposed to the electrolyte but also, influences the mass transferof electrochemically active species to and from the steel surface. This research implements rotating cylinder electrode (RCE) experiments to understand the role of surface roughness on the mass transfer characteristics. Four cylindrical samples with different roughness were tested at rotations speeds of 1000, 1500 and 4000 rpm in solutions of pH 4 at 25C. The observed changes in mass transfer enabled a new correlation to be proposed to determine the mass transfer coefficient for different degrees of surface roughness. The correlation was then implemented into a well-known mechanistic CO_2 corrosion model in literature to assist in accounting for surface roughness effects in flowing environments. The modified model was validated against experimental results using the RCE and excellent agreement was obtained across all conditions tested.