Bacterial Detection in Corrosive Media and Assessment of Corrosion Inhibition Efficiency of Novel Paints

Abstract

Anti-corrosive pigments such as zinc chromate, frequently used in paint formulations to combat steel corrosion, are potentially toxic. In this study, the corrosion inhibition properties of eleven water-based paints formulated with novel corrosion inhibitors were compared with a reference conventional paint (2). The paints were applied on galvanized steel (GS) and mild steel (MS). Painted and unpainted [control (C)] steel samples were immersed in corrosive media (1M HCl, 3.5% NaCl, and tap water). Bacterial population and pH of the corrosive media, as well as corrosion rates of immersed samples, were determined over six months. Escherichia coli, Klebsiella sp., Providentia stuartii, Staphylococcus aureus, S. epidermidis, Pseudomonas aeruginosa, P. oleovorans, and Bacillus anthracis were detected in the corrosive media. Bacterial populations ranged from 3.0×10⁴ to 1.00×10⁶, 3.5×10⁴ to 1.80×10⁶, and 3.0×10⁴ to 2.50×10⁶ CFU/mL for acid, 3.5% NaCl, and water with painted MS, respectively. For painted GS, bacteria ranged from 3.0×10⁴ to 9.0×10⁴, 3.2×10⁴ to 7.0×10⁴, and 3.0×10⁴ to 1.20×10⁶ CFU/mL for acid, salt, and water, respectively. The pH decreased for all samples: 2.4 to 0, 6.5 to 1.0, and 7 to 1.6 for acid, salt, and water, respectively. Paints 1, 2, 5, 7, 11, and 12 showed the lowest MS corrosion rate (0.0002 mm/y) in salt, while paint 9 had the lowest GS corrosion rate (0.0002 mm/y) in salt. All samples corroded completely in acid after six months. Paint 9 (MS) achieved the highest inhibition efficiency of 66.66%. The novel paints performed comparably to conventional paints.