Corrosion control in the tubing steel of oil wells during matrix acidizing operations
Dodecyl dimethyl benzyl ammonium bromide (DDBAB) was used as a corrosion inhibitor for carbon steel pipelines in 8% sulfamic acid solution during matrix acidizing operations. The inhibition efficiency (η%) has been studied using chemical (weight loss) and electrochemical (electrochemical impedance spectroscopy (EIS), potentiodynamic polarization) techniques. The surface active properties of this surfactant were calculated from surface tension measurements. Results obtained from both chemical and electrochemical techniques reveal that this compound is a very good corrosion inhibitor even at low concentrations and the maximum inhibition efficiency (93.7%) was obtained with 150 ppm of DDBAB. Polarization curves showed that the corrosion current density was decreased by increasing the inhibitor concentration until the critical micelle concentration (CMC) is reached. The Tafel polarization data indicate that the selected compound acts as a mixed type inhibitor. The slopes of the cathodic and anodic Tafel lines (βc and βa) are approximately constant and independent of the inhibitor concentration. Analysis of the impedance spectra indicates that it is the charge transfer process that mainly controls the corrosion process of carbon steel in 8% sulfamic acid solution both in the absence and presence of the inhibitor. The data obtained using the EIS technique were analyzed to model the corrosion inhibition process through equivalent circuits (ECs). The effect of the molecular structure on the inhibition efficiency was investigated using quantum chemical calculations. The adsorption of this compound on the surface of the carbon steel follows the Langmuir adsorption isotherm. From the adsorption isotherm, the values of the adsorption equilibrium constant (Kads) and the free energy of adsorption were calculated and discussed. The relatively high value of Kads reveals a strong interaction between the inhibitor molecules and the carbon steel surface. The strong adsorption ability of this compound can be attributed to the presence of the adsorption center of nitrogen as well as π donor moieties. Finally, EDX and SEM surface analysis tools were used to examine the nature of the protective film formed on a carbon steel alloy.