Evaluation of Gambir extract as green corrosion inhibitor for API 5L X65 steel in 3.5 % NaCl solution containing 100 ppm NaHCO3

The corrosion inhibition characteristics of Gambir extract (GE) as a green inhibitor for API 5L X65 pipeline steel in a 3.5 % NaCl solution containing 100 ppm NaHCO₃ at temperature of 25 °C (298 K) have been investigated. The purpose of the present work was to evaluate the potency of GE for protection of the steel from sweet corrosion which often occurs in oil and gas industries. The results of potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS) demonstrated that GE was a mixed-type inhibitor having a maximal inhibition efficiency of 89.7 % based on PP which was equivalent to 90.5 % based on EIS at a concentration of 700 ppm. The adsorption mechanism of GE on the API 5L X65 pipeline steel surface obeyed the Langmuir adsorption isotherm equation. Furthermore, the results of AFM/SEM examination demonstrated that the steel samples in the solution with GE were smoother than those immersed in the blank solution. Based on the quantum chemical calculations, the inhibition effect of GE was mainly attributable to its phytoconstituents, namely catechin and tannin.