A detailed DOE study on temperature, concentration and their interactions on corrosion protection of carbon steel

An imidazoline based inhibitor was synthesized using oleic acid and diethylenetriamine (DETA). The characteristic properties of the synthesized inhibitor were investigated by FTIR and HNMR tests. Tafel polarization technique and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical and corrosion inhibition properties of the inhibitor in CO2 saturated 3% NaCl solution. Potassium iodide was added to the corrosion media to enhance the inhibition efficiency of the inhibitor. The measured corrosion rates were optimized by Design Expert 10.0.7 software using central composite design and response surface method. Temperature and inhibitor concentration were selected as the most effective parameters. Analyses of variance (ANOVA) were performed on the results of the designed experiments. It was found that temperature and inhibitor concentration effects on corrosion rate and inhibition efficiency are complicated and their interactions. Addition of KI to the inhibitor system had a synergistic effect on the corrosion inhibition. It almost eliminated the dependency of the corrosion rate to temperature and inhibitor concentration which is a great achievement in inhibitor applications in oil and gas industries. DOE data revealed that the best inhibition of corrosion occurred at 25oC with 37.7ppm of synthesized Imidazoline inhibitor and 2000ppm KI. It is estimated by the software that at this point the corrosion rate is 6µm/year and polarization resistance is 30788Ω. The synthesized inhibitor conforms perfectly to the Langmuir adsorption isotherm.