Phytochemicals and gravimetric analysis of Hibiscus Sabdariffa Zobo Leaf Extracts (ZLE) as green corrosion inhibitor for natural gas pipeline (api5lx70) in acid-base solutions

Abstract

Corrosion of API 5L X70 carbon steel in mixed acidic oil and gas environments remains a critical challenge, prompting the need for eco-friendly, cost-effective inhibitors such as plant-based extracts. In this research, the corrosion inhibition of carbon steel (API 5LX70) using the weight-loss method and Hibiscus sabdariffa Zobo Leaf Extracts (ZLE) in a mixed acid medium was studied to confirm its anti-corrosion properties. The prepared steel sample was characterised by XRF analysis, which indicated a high iron content (Fe2O3: 89.68 wt%). Acid-base mixtures (H₂SO₄, HNO₃, HCl, NaCl, Na₂CO₃) were optimised by using RSM/Simplex Lattice Tool in order to simulate the amphoteric conditions within a typical oil and gas well. Optimum inhibitor concentration of ZLE leaf extracts in acid-based solution was established as 1.1 g/L, 1.42 g/L and 1.72 g/L, respectively. The physicochemical analysis indicated that ZLE leaf extract was acidic (pH:3.46) with a moisture content of 0.001% while the phytochemical properties were rich in secondary metabolites, especially flavonoids, being the most
abundant (22.46) for ZLE leaf extract, confirming its suitability as a corrosion inhibitor. The weight loss and corrosion rate of the carbon steel sample decrease as the ZLE extract concentration rises, but they increase with the temperature and immersion time. At the highest concentration (1.72g/L) of ZLE leaf extracts, the highest inhibitor efficiency was 91.89% with attendant corrosion rate of 22.63 mm/yr at 80°C for 6 hr, while the lowest corrosion rate was 1.09 mm/y at 40°C for 4hr. The study concluded that the ZLE leaf extracts at a concentration of ≥1.72 g/L could serve as a green corrosion inhibitor for carbon steel pipelines in the Nigerian oil and gas industries.