Iranian Journal of Oil and Gas Science and Technology

Abstract This study investigated the corrosion inhibition robustness of an eco-friendly garlic corrosion inhibitor (GCI) for X70 carbon steel in simulated sour oilfield water saturated with hydrogen sulfide (H₂S) environment. The functional groups o GCI were identified using a Fourier-transform infrared spectroscopy (FTIR) technique, confirming the presence of alcohols, phenols, amines, carbonyls, and sulfur-containing compounds, which contribute to adsorption and protective layer formation on the steel surface. The inhibition performance was assessed using the WLM technique, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). At the optimal GCI concentration of 200 mg L⁻¹, the inhibition efficiencies determined by weight-loss, polarization, and EIS measurements were 73.9%, 93.9%, and 96.3%, respectively. The differences among these values are attributed to the distinct principles of the techniques: WLM analysis represents cumulative material loss during immersion, whereas polarization and EIS characterize the electrochemical response of the steel–solution interface. Increasing the inhibitor concentration to 500 mg L⁻¹ produced only marginal improvements in the electrochemical efficiencies, reaching 94.0% by polarization and 96.4% by EIS. More importantly, the potentiodynamic polarization and EIS analyses revealed a mixed-type inhibition mechanism and the formation of a protective film with high polarization resistance. Surface analyses by the SEM and EDX techniques demonstrated the development of a relatively homogeneous organic layer enriched with nitrogen and sulfur, effectively preventing localized corrosion. On the whole, the acquired outcomes demonstrated that GCI is a promising green corrosion inhibitor for corrosion retardation of metals in sour environments, offering an eco-friendly alternative to conventional chemical inhibitors.

Abstract The effect of using Conocarpus extract as a green inhibitor on the corrosion behavior of mild steel in a 1 M HCL environment is investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). The impedance tests show that the polarization resistance increases from 29 for the blank solution to 299 for the solution containing 2500 ppm of Conocarpus extract. The polarization test results show that at room temperature, the corrosion current density for the blank solution decreases from 3.5 × 10^–4 to 2.6× 10^–5 for the solution containing 2500 ppm of Conocarpus extract, and the potential is shifted to negative values. The polarization test is performed at three temperatures of 25, 55, and 85 °C. The results show that the efficiency of 1925 ppm decreases from 93% at room temperature to 86% at 85 °C. The high-temperature efficiency does not decline significantly, indicating the effectiveness of Conocarpus extract at high temperatures. The FTIR tests also prove that the corrosion inhibitory effect of Conocarpus extract is due to the presence of heteroatoms such as N, S, and O. The adsorption isotherm results show that the adsorption of the extract as a single layer on the surface is consistent with the Langmuir isotherm.