Corrosion inhibition of API X120 steel in a highly aggressive medium using stearamidopropyl dimethylamine

- SAPDA has an outstanding inhibition efficiency in acidic medium for API X120 C-steel.
- Different techniques were used to characterize the rate and form of corrosion.
- Thermodynamic and quantum chemical parameters were calculated.
- Mode of adsorption was found to be mixed i.e. chemi/physisorption that follows Langmuir isotherms.
- O and/or N atoms with the highest e− densities were adsorbed on surface.

The inhibition efficiency of the stearamidopropyl dimethylamine (SAPDA) surfactant for the corrosion of API X120 steel in a 0.5 M HCl solution at different temperatures was investigated using different electrochemical and microscopy techniques. The kinetics and thermodynamic parameters were discussed. The overall results showed that SAPDA significantly decreased the corrosion rate of API X120 steel with an inhibition efficiency of approximately 99% at an inhibitor concentration of 136 μmol L− 1. It was revealed that the adsorption of the SAPDA surfactant on the API X120 steel surface followed Langmuir's adsorption isotherm. Polarization studies indicated that SAPDA is chemi/physisorbed on the steel surface. Quantum chemical calculations, using the density functional theory, were applied to better understand the relationship between the inhibitor efficiency and its molecular structure.

Measured EIS Nyquist plots (dotted) and their fittings (solid lines) for API X120 steel in 0.5 M HCl in presence of 8, 16, 33 and 50 ppm of the highly efficient stearamidopropyl dimethyl-amine (SAPDA) corrosion inhibitor at 20 °C. Inset shows the same plots for API X120 in in 0.5 M HCl in absence of the inhibitor at 20, 30, 40 and 50 °C.96