Inhibition of corrosion of mild steel in simulated oil well water by an aqueous extract of Andrographis paniculata

Abstract

An aqueous extract of Andrographis paniculata has been used as corrosion inhibitor, in controlling corrosion of mild steel in simulated oil well water (SOWW). Weight loss method reveals that 10 mL of the extract offers 94% inhibition efficiency to mild steel immersed in simulated oil well water (SOWW). The mechanistic aspects of corrosion inhibition have been investigated by electrochemical studies such as polarization study and AC impedance spectra. Polarisation study reveals that the inhibitor system controls the cathodic reaction predominantly as revealed by the shift of the corrosion potential to the cathodic side in presence of the inhibitor system. The corrosion protective nature of the inhibitor is confirmed by the increase in the linear polarization resistance value and decrease in the corrosion current value. The formation of a protective film on the metal surface is confirmed by the AC impedance spectra. This is confirmed by the fact that there is increase in charge transfer resistance value and decrease in double layer capacitance value. The adsorption of the inhibitor molecule obeys Langmuir adsorption isotherm. The protective film has been analyzed FTIR spectra. It confirms that the inhibitor has coordinated with ferrous ion the metal surface through the polar atoms of the inhibitor molecule. The surface morphology of the protective film has been investigated by SEM and AFM. It is observed that in presence of inhibitor the surface of the corroded metal becomes smoother. The Vickers hardness of the metal surface before experimentation and after experimentation has been measured. It is observed that the surface becomes harder in presence of inhibitor than in the absence of inhibitor under the influence of corrosive medium, namely simulated oil well water. The findings have potential application in petroleum industry. The inhibitor extract can be added along with the simulated oil well water in the pipelines made of mild steel.