Mitigation of top‐ and bottom‐of‐the‐line CO 2 corrosion in the presence of acetic acid (I): pH control using methyl diethanolamine

Temperature differences between the top and the base of pipelines can, in specific circumstances, drive severe corrosion due to condensed fluids at the top-of-the-line. Here, we measure corrosion at the top-of-the-line in the condensate phase and, simultaneously, in the immersed phase at the bottom-of-the-line using an electrochemical approach. With CO ₂-saturated chloride brine, corrosion at the top-of-the-line increased with fluid temperature (due to increased condensation rates), whereas at the bottom-of-the-line, the corrosion rate decreased (due to ferrous carbonate precipitation). The addition of acetic acid increased the corrosion rate at both top and bottom of the line, with any ferrous carbonate films being removed by dissolution. The addition of methyl diethanolamine (MDEA) reduced corrosion rates significantly because of the increased pH in both the condensate at the top-of-the-line and under immersion at the bottom-of-the-line, reducing the solubility of FeCO ₃. Overall, the addition of acetic acid was confirmed to damage and remove protective FeCO ₃ films. However, continuous films were not re-established after MDEA additions, rather porous and generally unprotective films were formed.