Investigation of the corrosion inhibition of X42 carbon steel in CO₂-saturated brine using phaseolus vulgaris L. Bean extract

Abstract

This study introduces a green corrosion inhibitor derived from white bean (Phaseolus vulgaris L.) extract (PVL), an abundant agricultural source, for X42 carbon steel in a CO₂-saturated 3.5 wt% NaCl solution. The anticorrosion performance of the synthesized PVL-extract was evaluated over a concentration range of 50–1000 ppm using weight loss, electrochemical polarization, and impedance spectroscopy (EIS). According to the results, the optimal concentration was 500 ppm, which reduced the corrosion rate by 95.9 ± 8.8 % (from 34.0 ± 2.0 mpy to 1.4 ± 0.3 mpy) and the corrosion current density by 94 ± 1 % (from 12.1 ± 0.2 µA/cm² to 0.7 ± 0.09 µA/cm²), while increasing charge transfer resistance by 88.8 ± 3.6 % (from 330 ± 5 Ω·cm² to 623 ± 7 Ω·cm²). Considering various adsorption isotherms, it was determined that the adsorption of PVL-extract on the carbon steel substrate obeyed the Langmuir adsorption isotherm. AFM provided quantitative surface analysis, revealing a dramatic reduction in average roughness (Sa) from 78 nm (Ra = 285 nm) on the blank coupon to just 0.86 nm (Ra = 5.6 nm) on the sample protected by 500 ppm PVL-extract. This profound smoothing effect was also visually confirmed by SEM. FTIR spectroscopy confirmed the adsorption of the tested inhibitor on the surface of the tested coupons, and UV-Vis spectroscopy verified the formation of inhibitor-iron complexes.