The effect of acetic acid and acetate on corrosion behavior of carbon steel (N80) in CO2 saturated I%NaC1 at different temperature and pressure was investigated by using weight-loss, electrochemical methods (polarization curve, impedance) and surface analysis techniques (SEM, XRD). The attention was focused on the effect of acetic acid and acetate on the anodic and cathodic reactions respectively. The results indicate that @the determining step of cathodic reaction of CO2 corrosion is a inhomogeneous chemical reaction (CO2 hydrated reaction) at the electrode surface. Because acetic acid adsorbed on electrode surface can be reduced directly by electrochemical reaction, acetic acid and acetate promote the cathodic reduction reaction, and as a result, the corrosion rate was accelerated and independent of pH value of solutions. @The intermediates produced in the anodic processes play an important role in the anodic dissolution. Acetic acid and acetate affect evidently on the formation and adsorption of the intermediates, and run to form more soluble corrosion products. @The effect of acetic acid and acetate on CO2 corrosion depends on the CO2 fractional pressure, temperature and corroded surface state etc.
]INTRODUCTION
In CO2 corrosion environments, from field experiences, the corrosion rate of carbon steel increased when Ac- is present in the produced liquids, though Ac can increases pH of the liquid. This observation is contrary to most models for CO2 corrosion prediction. Laboratory researches 13 showed that both HAc and Ac- can increase the rate of CO2 corrosion of carbon steel. However, there are only few reports about the effect of acetic acid and acetate on CO2 corrosion of carbon steel, and very little information has been reported in the literature concerning the electrochemical behavior and the mechanism of enhanced corrosion of acetic acid and acetate. In this work, the effect of HAc and Ac on corrosion behavior of carbon steel in CO2-saturated 1%NaC1 solution at different temperature and pressure was investigated by weight-loss, potentiodynamic polarization, impedance measurement, and surface analysis techniques. The attention was focused on effect of HAc and Ac- on the cathodic reduction and anodic dissolution processes of CO2 corrosion of carbon steel.
