Combined Effect of Carbon Dioxide, Hydrogen Sulfide, and Acetic Acid on Bottom-of-the-Line Corrosion

摘要

This research work presents a study of the combined influence of the partial pressure of hydrogen sulfide (H^sub 2^S) and the concentration of free acetic acid (CH^sub 3^COOH) on the general and localized carbon dioxide (CO2) corrosion at the bottom of the line. Experiments were carried out for up to 21 days in three 4-in (101.6-mm) internal diameter flow loops at 70° C with 2 bars of CO2. The flow regime was stratified for all of the experiments. It was found that trace amounts of H^sub 2^S (from 0.004 bar to 0.13 bar) greatly retards the CO2 corrosion with general corrosion rates usually 10 to 100 times lower than their pure CO2 equivalent. However, the most protective conditions were observed at the lowest partial pressure of H^sub 2^S, while corrosion increased when more H^sub 2^S was added. The presence of a mackinawite film on the coupon surface seems to be the origin of this protectiveness. When 1,000 ppm of free acetic acid was added to the system, the general corrosion rate doubled compared with a baseline CO2 environment and by between one and two orders of magnitude compared to baseline H^sub 2^S/CO2 mixtures. [PUBLICATION ABSTRACT]