Corrosion mitigation by an eco-friendly inhibitor: Beta vulgaris (beetroot) extract on mild steel in simulated oil well water medium

Abstract

The inhibition efficiency (IE) of an aqueous extract of Beta vulgaris (beetroot) in controlling corrosion of mild steel in simulated oil well water (SOWW) in the presence and absence of Zn2+ has been evaluated by weight loss method. The formulation consisting of 10% aqueous extract of Beta vulgaris extract and 50 ppm Zn2+ offers 94% inhibition efficiency to mild steel immersed in simulated oil well water. A synergistic effect exists between Beta vulgaris extract and 50 ppm Zn2+.The polarization study reveals that this formulation acts as a barrier film controlling the cathodic reaction predominantly. The corrosion potential is shifted from –777 mV SCE to –789 mV SCE. The inhibitor system functions as mixed type of inhibitor because the shift in corrosion potential is within 50 mV. The linear polarization value increases from 482 Ohm∙cm2 to 1838 Ohm∙cm2. The corrosion current decreases from 1.034∙10–4 A/cm2 to 1.887∙10–5 A/cm2. These factors confirm that the Beta vulgaris extract controls the corrosion of mild steels in SOWW. The AC impedance spectra confirm that the protective coating is very stable as revealed by the fact that in the presence of Beta vulgaris on mild steel, its charge transfer resistance increases, impedance increases, whereas double layer capacitance decreases. The surface morphology has been analyzed by SEM. FTIR spectra study leads to the conclusion that the Fe2+– betanin complex formed on the anodic sites of the metal surface controlled the anodic reaction, and Zn(OH)2 formed on the cathodic sites of the metal surface controlled the cathodic reaction. Synergism parameters are found to be greater than 1 indicating that a synergistic effect exists between Beta vulgaris and Zn2+. SEM study reveals that in presence of inhibitor system the surface of the metal becomes very smooth. The outcome of the study may be used in petroleum industry. The inhibitor formulation may be added along with mild steel pipelines carrying oil well water.