Instrumental and static assessment of antiscaling efficiency of Vigna subterranea pod extracts on stainless steel in a brine solution

This study evaluates the antiscaling performance of Vigna subterranea pod extract against calcium carbonate (CaCO 3 ) scale deposition on stainless steel surfaces. Stainless steel, widely used in oil pipelines and other industrial systems, is highly susceptible to scale formation, which compromises operational efficiency and material integrity. The locally sourced pod extract was prepared and characterized using Fourier Transform Infrared (FT-IR) spectroscopy and Gas Chromatography–Mass Spectrometry (GC–MS). The chemical composition of the stainless steel coupons was determined using Optical Emission Spectroscopy (OES), confirming iron as the principal component (Fe < 77.6%). Surface morphology and elemental analysis were examined using Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM–EDS). Phytochemical screening revealed the presence of flavonoids, phenolics, tannins, alkaloids, saponins, steroids, and terpenoids. GC–MS analysis identified and quantified major bioactive constituents, including eugenol (14.9 mg/kg), 4,4-methylguaiacol (13.3 mg/kg), vinylphenol (11.6 mg/kg), 4,4-vinylguaiacol (10.6 mg/kg), vanillin (5.9 mg/kg), levoglucosan (5.3 mg/kg), 2-hydroxymethylfuran (5.3 mg/kg), methylphenol (4.5 mg/kg), dimethylphenol (3.7 mg/kg), phenol (3.9 mg/kg), and 2-furaldehyde (3.3 mg/kg). FT-IR spectra confirmed the presence of hydroxyl groups associated with phenolic and tannic acids and flavonoids (3420 cm −1 ), as well as aliphatic C–H and conjugated C=C stretching vibrations at 2923 and 2346 cm −1 , respectively. Gravimetric analysis demonstrated concentration- and exposure-time-dependent inhibition efficiency. At 0.5 mg/mL, efficiencies increased from 10.52% (day 6) to 64.37% (day 21). At 1.0 mg/mL, inhibition reached 58.83% by day 12; 2.0 mg/mL achieved 63.38% (day 12); 3.0 mg/mL yielded 66.90% (day 12); while the highest concentration (4.0 mg/mL) attained 80.28% inhibition by day 12. Electrochemical impedance spectroscopy (EIS) revealed a maximum inhibition efficiency of 96.60%, indicating significant enhancement of charge transfer resistance in the presence of the extract. SEM–EDS observations corroborated these findings, showing marked reduction in CaCO 3 crystal deposition on treated surfaces. Overall, Vigna subterranea pod extract demonstrates strong potential as a sustainable, eco-friendly antiscalant for mitigating calcium carbonate scaling in industrial systems.