ELECTROCHEMICAL INVESTIGATION OF CARBON DIOXIDE CORROSION OF MILD STEEL IN THE PRESENCE OF ACETIC ACID
The corrosion behavior of mild steel in the presence of acetic acid and carbon dioxide has been investigated using electrochemical techniques and weight loss (WL) measurements. Acetic acid (HAc) was found to retard the anodic reaction (iron dissolution) and act as an additional source of hydrogen ions, which increased the measured limiting currents. The corrosion rate of carbon steel in the presence of HAc was found to be under charge transfer control and the mechanism for both the cathodic and anodic reactions remained the same. The possibility of direct reduction of HAc was not supported from the experimental results and electrochemical modeling. A series of experiments was also performed to study the effect of calcium ions and simulated brines on the corrosion rate of mild steel in the presence of acetic acid. The corrosion rates of mild steel were found to be similar in simulated brines and sodium chloride solutions. Increasing amounts of calcium ions was found to decrease the corrosion rate of mild steel. However, when acetic acid is present, the corrosion rate still remains at a high value. A wide range of HAc concentrations (0-5000 ppm), temperatures (22-80°C), pHs (4-6) and rotational velocities (500-4000 rpm) was used to develop an electrochemical model to predict the experimental data. The cathodic limiting currents were not found to result from a chemical reaction limitation but rather a mass transfer one. The model and the experimental potentiodynamic sweeps are in very good agreement at low temperatures. Thus, the predicted corrosion rates are in very good agreement with LPR and WL measurements at low temperatures. A modification to the de Waard (1995) model was made to account for the presence of HAc. The de Waard model, with the modification, agrees well with the experimental data at temperatures of 40°C and above. At low temperatures, the de Waard model is not in agreement with the experimental data and is too conservative in the prediction of the corrosion rate.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:corrosion electrochemistry acetic acid electochemical modeling
Date of Publication:01/01/2003