In this study, the effect of Thyme leaves hydroalcoholic extract (as a green corrosion inhibitor) on corrosion behavior of API 5L carbon steel in 0.5 M H2SO4 solution was investigated by Tafel polarization and electrochemical impedance spectroscopy (EIS). Tafel polarization plots showed that Thyme is a mixed inhibitor. Also, Tafel polarization and EIS results indicated that the inhibition efficiency increases with increasing Thyme leaves hydroalcoholic extract concentration to attain 89% at 12 g/L. Impedance parameters change with increasing concentration of extract shows that the adsorption of this extract on the steel surface will form a protective layer on the steel surface. Moreover, Temkin isotherm revealed that Thyme physically is absorbed on API 5L carbon steel surface in 0.5 M H2SO4 solution. The adsorption isotherm was obtained -17.86 kJ mol-1.
