Study on corrosion influencing factors and corrosion inhibition mechanism of L360N pipeline in a Middle East oilfield

To address the corrosion prevention and control challenge of L360N pipeline steel in the high-salinity and high-Cl − oilfield environment of the Middle East, and to clarify the inhibition behavior and mechanism of the field-applied corrosion inhibitor CR-1, this study systematically investigated the corrosion inhibition performance and microscopic mechanism of CR-1 on L360N steel under the coupled effect of temperature and concentration. Different from previous studies that mainly evaluated single-component or newly synthesized inhibitors in conventional corrosive media, this work for the first time systematically integrates macroscopic corrosion tests, microscopic surface characterizations, and multi-scale DFT/MD simulations to clarify the temperature–concentration coupled inhibition mechanism of a field-applied composite inhibitor under the authentic high-salinity and high-Cl − formation water of a Middle East oilfield, and quantitatively correlates the temperature-dependent adsorption energy and Cl − diffusion with the attenuation of inhibition efficiency. Weight loss experiments, electrochemical measurements, surface microscopic characterizations (SEM, EDS, 3D morphology, contact angle, FT-IR, XPS), combined with density functional theory (DFT) and molecular dynamics (MD) simulations were adopted. The results showed that at 293 K with a CR-1 concentration of 800 mg/L, the inhibition efficiencies measured by the weight loss method, electrochemical impedance spectroscopy (EIS), and Tafel polarization reached 95.41%, 93.47%, and 94.25%, respectively. The inhibition efficiency decreased gradually with increasing temperature. CR-1 obeyed the Langmuir adsorption isotherm on the surface of L360N steel, and acted as a mixed-type corrosion inhibitor. It formed Fe N and Fe S coordination bonds between its polar heteroatoms and the Fe matrix, constructing a dense hydrophobic adsorption film. Quantum chemical calculations indicated that among the components of CR-1, CR-D exhibited the optimal reaction activity. MD simulations confirmed that high temperature would reduce the adsorption energy of the corrosion inhibitor and accelerate the diffusion of Cl − , leading to the degradation of the protective film. CR-1 achieved efficient corrosion inhibition through the synergistic effect of chemical coordination, electrostatic adsorption, and hydrophobic barrier, which can effectively meet the corrosion protection requirements of L360N pipeline steel in Middle East oilfields.