Inhibition of corrosion of mild steel pipeline carrying simulated oil well water by Allium sativum (Garlic) extract

Abstract

The inhibiting effect of Allium sativum in controlling corrosion of mild steel in simulated oil well water (SOWW) in the absence and presence of Zn2+ has been investigated by different techniques like weight loss method, potentiodynamic polarization and electrochemical impedance spectroscopy for different concentrations of the plant extract. The formulation consisting of 10 mL of (10% aqueous extract) Allium sativum (garlic extract) and 50 ppm of Zn2+ provides 87% of inhibition efficiency. The results indicate that the corrosion inhibition efficiency increased on increasing plant extract concentration. The inhibitor system was found to be a cathodic inhibitor with the optimum inhibition concentration of 10 mL of Allium sativum and 50 ppm of Zn2+ in potentiodynamic polarization study. The corrosion potential is shifted from –777 mV vs. SCE to –880 mV vs. SCE. The linear polarization resistance (LPR) value increases from 482 Ohm·cm2 to 1831 Ohm·cm2. The corrosion current decreases from 1.034×10–4 A/cm2 to 0.1515×10–4 A/cm2. These factors confirm that the Allium sativum controls the corrosion of mild steel in SOWW. The AC impedance spectra confirm that the protective coating is very stable as revealed by the fact that in the presence of inhibitor on mild steel, the charge transfer resistance increases, impedance increases, whereas double layer capacitance decreases to a great extent. Surface analysis has been carried out to find out the surface morphology of the mild steel in the presence and absence of the inhibitor. The obtained results show that the Allium sativum extract acts as a good inhibitor for the corrosion of mild steel in SOWW.