Corrosion Protection of 316L Stainless Steel in 15% HCl: Structure Performance Insights into Benzimidazole and Triazole Inhibitors

Stainless steels, especially 316L SS, are extensively used in the oil and gas sector for their mechanical strength and corrosion resistance properties, yet they suffer severe corrosion in high HCl concentrations during acidizing treatments. This study evaluates the inhibition efficiency of two heterocyclic compounds, 2-aminobenzimidazole (AMBZ) and 3-amino-5-methylthio-1H-1,2,4-triazole (AMTZ), on 316L SS in 15% HCl at 25 °C. Electrochemical techniques such as linear polarization resistance (LPR), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) were utilized. Complementary surface and structural analyses were carried out using scanning electron microscopy (SEM–EDS) coupled with X-ray diffraction (XRD), 3D surface profilometry, atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). Density functional theory (DFT) and Monte Carlo (MC) simulations were also employed to determine adsorption sites and energies. Results showed that AMBZ provided superior inhibition, reaching up to 85% efficiency versus 33% for AMTZ (PDP, 3 wt%). SEM–EDX, profilometry, AFM, and FTIR confirmed adsorption of both inhibitors, while theoretical calculations indicated a stronger interaction of AMBZ due to its planar ring and higher negative adsorption energy. These findings demonstrate that benzimidazole-based compounds can act as more effective corrosion inhibitors than triazole derivatives for 316L SS in oil well acidizing environments.