Electrochemical Evaluation of 5-aminosalicylic Acid as an Inhibitor for Under Deposit Corrosion of X60 Pipeline Steel in Marine Environments

Inhibition effects of 5-aminosalicylic acid (5-ASA) on the under deposit corrosion of X60 steel in 3.5 % NaCl solution saturated with CO2 have been investigated by the techniques of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The sand-covered electrode was prepared by covering the X60 steel electrode with a layer of silica sand. The increase of 5-ASA concentration up to 600 ppm led to increasing the inhibition efficiency of X60 steel against under deposit corrosion in the brine solution. The Langmuir isotherm can describe the adsorption behavior of 5-ASA on the surface of the steel. Measurements of potentiodynamic polarization indicated that 5-ASA is an anodic inhibitor. The effects of temperature on the under deposit corrosion behavior of carbon steel were studied both in the absence and presence of 600 ppm 5-ASA. The enthalpy of the 5-ASA adsorption was obtained from the temperature dependence of the corrosion inhibition process. A reasonable agreement was observed between the IE values resulted from the Tafel and the EIS techniques. The electronic properties of 5-ASA were calculated in both the gas phase and the aqueous phase by a density functional theory (DFT) approach to establish the relationship between the inhibitive effect and molecular structure of 5-ASA