Seaweed (Sargassum polycystum) extract as eco-friendly corrosion inhibitor for mild steel in CO2-saturated 3.5% NaCl solution.

In the petroleum industry, sweet corrosion is the most severe corrosion concern for steel-based crude oil transportation pipelines. It is a type of severe localized corrosion caused by the aqueous phase of petroleum, consisting of CO2 gas dissolved in the saline drilling fluid. Inhibitors are compounds that prevent corrosion on the surface of metals used in the oil and gas industry. The inhibitor is adsorbed on the surface of the metal, generating a thin protective coating. Due to increasing awareness of the environment, various research about green corrosion inhibitors using plant extract was developed. Plant extracts are abundant, inexpensive, less or nontoxic, biodegradable, and biocompatible, so the study of corrosion prevention, particularly on mild steel, utilizing plant-based corrosion inhibitors is of great interest. Seaweed (Sargassum polycystum) extract was used to reduce the corrosion of mild steel in a CO2 environment. The seaweed was dried (100 g) and extracted using ethanol (900 ml). Then the extract was evaporated and used as a corrosion inhibitor. Tafel polarization test was conducted using the Gamry instrument. The polarization test was carried out at 30, 40, and 50°C; the inhibitor variations were performed at 100, 200, 300, and 400 ppm in CO2-saturated 3.5% NaCl solution. The addition of 400 ppm seaweed extract reduces the corrosion rate of mild steel with the highest efficiency of 87% at 40°C. The difference in potential corrosion (Ecorr) after adding seaweed extract below 85 mV indicated that the extract is a mixed-type inhibitor. [ABSTRACT FROM AUTHOR]