Inhibitive performance of Sida acuta and monoethylene glycol on the under deposit corrosion of UNS S30403 stainless steel

The synergistic effects of monoethylene glycol (MEG) and leaf extract of Sida acuta on UNS S30403 stainless steel under sand deposit in aerated 3.5-wt.% NaCl solution were studied through open circuit potential measurements, potentiodynamic polarization curves, and atomic force microscopy. Phytochemical analysis of the Sida acuta shows the presence of phenol, alkaloid, steroid, flavonoid, and saponin. It was found that the leaf extract inhibited the general and localized corrosion of the stainless steel, especially at a concentration of 400 ppm. With the leaf extract alone, the corrosion resistance increases with increase in inhibitor dosage up until 400 ppm; then, a drop in corrosion resistance was experienced at 600 ppm. However, with the addition of 20 wt.% monoethylene glycol to the environment, the green inhibitor was only effective at 600-ppm dosage. These results show that the presence of MEG can only be tolerated with the inhibitor at higher inhibitor concentrations for this alloy in the environment under study. Adsorption of Sida acuta inhibitor on the steel surface does not follow any adsorption isotherm.