Thermal and surface studies on the corrosion inhibition of petroleum pipeline by aqueous extract of Allium cepa skin under acidic condition

In this study, the temperature effect on the inhibitory action of the cheap, eco-friendly and sustainable hot water extract of onion skin (HWEOS) on the corrosion of C-steel petroleum pipeline in 1 M hydrochloric acid solution was investigated using weight loss technique. Generally, the inhibition was found to increase with inhibitor concentration but decreased with the increase in temperature. The presence of protective inhibitor film on metal surface was confirmed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses. The thermodynamic activation parameters were evaluated, suggesting a physical adsorption, the corrosion process was suggested to be a unimolecular reaction, the enthalpies reflected the endothermic nature of the steel dissolution process. Large and negative values of entropies showed that the activated complex in the rate determining step represented an association rather than a dissociation step. HWEOS adsorbed on the metal surface according to the Langmuir isotherm at all the studied temperatures. The compounds responsible for the inhibitory action of HWEOS were proved to be flavonoids including quercetin and a suggested mechanism of corrosion inhibition was elucidated.