Locust Bean Gum: A Natural Polysaccharide as an Eco-Friendly Corrosion Inhibitor for N80 Carbon Steel in CO2-Saturated Saline Solution, Useful for the Oil and Gas Industry

This study evaluated locust bean gum (LBG), a polysaccharide thickening agent, as an anti-corrosion active compound against sweet corrosion for N80 carbon steel used in the oil and gas sector. The assessment involved weight loss and electrochemical measurements at different temperatures (e.g., 25 °C and 80 °C) and immersion durations (up to 168 h) in a CO₂-saturated 2 wt.% KCl solution. The electrochemical results showed that LBG effectively inhibited sweet corrosion at both temperatures, and its efficacy increased with its concentration, reaching maximum inhibition efficiency of 84.11% at 25 °C and 55.81% at 80 °C, using 0.3 g L^-1 of LBG after 24 h of immersion. At 25 °C, and with 0.3 g L^-1 of LBG, the inhibition action of LBG did not change, even after 168 h of immersion (e.g., 83.97%). At 80 °C, LBG showed a good inhibition up to 72 h (e.g., 47.04%), after which LBG had no additional protective effect. This result is attributed to the formation of a FeCO₃ layer that covered the entire metal surface, blocking the adsorption of LBG. Potentiodynamic tests revealed that LBG's inhibitory effect is of a mixed type. The Temkin adsorption isotherm model accurately described the data, indicating that LBG adsorption involves primarily physical interactions, with some chemical contributions. Activation energy and heat of adsorption calculations support the physical nature of LBG's adhesion. FTIR analysis confirmed the interaction between LBG and N80 carbon steel, while SEM-EDS provided visual evidence of LBG's influence on the metal surface.