Role of Acetic Acid in CO2 Top-of-the-Line Corrosion of Carbon Steel

It has been well established based on lab and field data that the presence of acetic acid (HAc) in oilfield brines enhances the occurrence and the rate of localized Top-of-Line Corrosion (TLC). The additional contribution of HAc to the corrosion rate of pipeline steel in CO₂-containing environments has been extensively investigated over a wide range of conditions during the last few years. However, the fundamental role of this organic compound in CO₂ corrosion is still a controversial topic so far, particularly in terms of its electroactive participation in the overall cathodic mechanism. In an attempt to assess this issue, the effect of HAc on the kinetic behaviour of API 5L X65 carbon steel was addressed in this study by means of both electrochemical measurements and electron microscopy examinations. Whether HAc acts as a specific cathodic reactant or just as a proton source or both was the central idea of the present work. The results are further discussed in terms of repercussions on TLC corrosion.

Keywords: CO₂ corrosion; Top-of-line corrosion; Acetic acid; Pipeline steel.