EFFECT OF ACETIC ACID ON CO₂ CORROSION OF CARBON STEEL IN VAPOR-WATER TWO-PHASE HORIZONTAL FLOW

Abstract

The effect of acetic acid on the corrosion behavior of X 65 and C 1018 carbon steel in vapor-water two-phase stratified flow (Vsg: 2 m/s; Vsl: 0.1 m/s) at 2 bars total pressure, 1.54 bars CO₂ partial pressure, pH 5.5, and 80°C was studied in a low pressure-high temperature multiphase flow horizontal loop using electrochemical and mass loss techniques. The liquid phase is composed of 1% NaCl aqueous solution containing different concentrations of acetic acid (500 to 5000 ppm total acetic acid), and the gas phase is composed of CO₂-acetic acid-water vapor mixture. The corrosion rates, on both the top and bottom of the line, increase with increase in acetic acid concentration, which was attributed to the contribution of hydrogen ions by the free acetic acid to the cathodic reaction. Partial coverage of the metal surface by FeCO₃ on both the top and bottom of the line is reported to be responsible for the observed localized corrosion. Surface analysis investigated with SEM and XRD is reported.

A vapor-liquid equilibrium model was developed for the system studied.

Keywords:

• Acetic acid
• CO₂ corrosion
• Two-phase horizontal flow

Acknowledgments

P. C. Okafor acknowledges the United States Department of State and the Institute of International Education (IIE) for the Fulbright Visiting Researchers' Grant and the Institute for Corrosion and Multiphase Flow Technology, Athens, Ohio for providing the laboratory facilities.