Synergistic Effect and Statistical Model of Terminalia avicennioides as Anti-corrosion Inhibitor of Steel Pipelines in Acidic Environment

Abstract

Investigation of Terminalia avicennioides (T. avicennioides) extract as corrosion inhibitor for steel pipelines in acidic medium using gravimetric method with and without potassium iodide (0.5 M KI−) and statistical modelling was carried out. Qualitative and quantitative analyses were used to determine the phytochemical constituents of the extract. The inhibitor concentration, temperature and time were varied in the range of 2.5–15.0 g/L at 2.5 g/L interval, 35–80 °C at 15 °C interval and 12–72 h at 12 h interval in a static solution. Scanning electron microscope/energy dispersive spectroscopy (SEM/EDS) technique was used to characterize the coupon surfaces before and after corrosion tests. A statistical design for the corrosion process was carried out to determine which parameters (inhibitor concentration, temperature and exposure time) that were statistically significant using ANOVA. The results revealed the presence of tannins, saponins, glycosides, flavonoids, alkaloids with reasonable amounts. Inhibition efficiency results without and with KI− at the optimum concentration of 10 g/L were 94.86 and 99.12%. Langmuir adsorption isotherm was followed. The activation energy in the presence of inhibitor was greater than 80 KJ/mol in the absence of inhibitor and physisorption in nature. The SEM/EDS revealed cracks, pitting and rough in the sample without inhibitor while the surface at optimum of 10 g/L of inhibitor and (0.5 M KI−) had smooth surface. ANOVA results showed that the inhibitor was the most significant parameter having the highest statistical influence of 78.39% followed by time (11.09%) and temperature (10.43%). Results therefore confirmed the high inhibition efficiency values obtained in the studies.