CO₂ Top-of-the-Line Corrosion in Presence of Acetic Acid: A Parametric Study

This research presents the results of an experimental study, performed in a flow loop, of five parameters identified as having a significant influence on top-of-the-line corrosion (TLC): partial pressure of carbon dioxide (CO₂), condensation rate, gas temperature, organic acid concentration, and gas velocity. A comprehensive analysis of the effect of each of these five parameters on the type of corrosion is performed. Experimental data related to uniform corrosion, pitting, and mesa attack are presented and provide an inclusive view of the phenomena involved in TLC in sweet environments. It is proposed that the relatively small volume of the droplet can become supersaturated with respect to iron carbonate (FeCO₃), as a result of the initially high average corrosion rate. Depending on the conditions, the precipitation of FeCO₃ on the metal surface can decrease significantly the average corrosion rate. However, the protectiveness of this layer is challenged by the rate of droplet renewal (water condensation rate) and the overall corrosivity of the environment (CO₂ content, acetic acid concentration). Very aggressive localized corrosion can be initiated and sustained. The extent of TLC is definitively the result of complex interactions between all of these parameters. Threshold values, often used as engineering guidelines in the industry, should be used with caution, and a solid understanding of the mechanisms involved is a prerequisite for the development of effective TLC inhibition program.