Synergistic inhibition effect of imidazoline and thiourea on pitting corrosion of Q235 carbon steel

Pitting corrosion is a significant issue which significantly shorten the service life of carbon steel. In this study, imidazoline and thiourea are combined to assess the synergistic in the localized corrosion of Q235 carbon steel by a combined system. In detail, five different proportions of corrosion inhibitors are used in the simulated corrosion solution (5 wt. % NaCl + 0.5 wt. % CH3COOH + 1.0 wt. % Na2S) in the closed area to investigate the corrosion inhibition performance of Q235 steel at 80 °C. The corrosion behavior of the steel in the simulated solution was investigated using potentiodynamic polarization test and electrochemical impedance spectroscopy test. Due to the combination of imidazoline (IM) and thiourea (TU) corrosion inhibitors, the corrosion inhibitors in the simulated solution of the occlusion zone reduce the migration of corrosive anions to the occlusion zone and slowed the acidification of the solution resulting in lower concentrations of Cl- and S2- to varying degrees and reaching a higher pH of the solution. As a result, the compounded corrosion inhibitors exhibit improved corrosion inhibition rate (80 mg/L IM+20 mg/L TU (86.91 %), 50 mg/L IM+ 50 mg/L TU (95.67 %), 20 mg/L IM+ 80 mg/L TU (86.16 %)) to Q235 steel, which is superior to that using imidazoline (63.42 %) or thiourea (92.77 %) alone. This enhanced performances fully prove the synergistic effect of imidazoline with thiourea.