Individual and Joint Effect of Oleic Acid Imidazoline and CeCl3 on Carbon Steel Corrosion in CO2-Saturated Brine Solution

In production and transportation systems of the oil industry, brine solutions contain high concentrations of chloride and dissolved CO2, which is a very corrosive medium to which carbon steel is exposed. Therefore, finding new effective and environmentally friendly corrosion inhibitors is of great importance. The effect of CeCl3 (in concentrations from 5 mg dm−3 to 20 mg dm−3) and oleic acid imidazoline (IOA) (in concentrations from 5 mg dm−3 to 20 mg dm−3) separately and their mixtures (in concentrations from 5 mg dm−3 to 15 mg dm−3 of CeCl3 and from 5 mg dm−3 to 20 mg dm−3 of IOA) as corrosion inhibitors of AISI 1018 carbon steel corrosion in simulated brine solution saturated with CO2 at 60 °C were examined by means of weight-loss testing, electrochemical measurements (polarization resistance, linear polarization with Tafel extrapolation, electrochemical impedance spectroscopy) and surface analyses (scanning electron microscopy with energy-dispersive X-ray spectroscopy analyses, Raman spectroscopy and X-ray diffraction). All test methods showed a higher efficiency of compounds′ mixtures (from 62.77% to 97.94%) and a higher degree of corrosion protection compared to the action of individual compounds (efficiency from 3.43% to 94.61% for IOA and from 57.58% to 96.27% for CeCl3). Imidazoline, a common corrosion inhibitor in CO2-saturated systems, most likely forms a surface film with voids via its adsorption on steel surface, while cerium carbonate tends to fill these voids by creating a more compact film. In this way, a denser and thicker surface film is formed.