Effectiveness of an imidazoline-type inhibitor against CO_2 corrosion of mild steel at elevated temperatures (120°C-150°C)

摘要

Production of oil and gas from increasingly aggressive geologic environments requires the development of appropriate corrosion mitigation strategies, including the selection of corrosion inhibitors with adequate performance characteristics. In this study, the inhibition performance of a diethylenetriamine tall oil fatty acid imidazoline-type inhibitor (DETA/TOFA imidazoline) against CO_2 corrosion of an API 5L X65 carbon steel was studied at two temperatures, 120°C and 150°C. The corrosion measurements were performed in a CO_2 saturated 1 wt.% NaCl electrolyte, via electrochemical measurements, in a standard autoclave and in a specially designed two-autoclave system. A two-autoclave design was developed and adopted for transferring heated, deoxygenated aqueous electrolyte to the autoclave containing the working electrode, thereby limiting specimen exposure to oxygen and eliminating long transition times associated with solution heating/cooling. At 120°C, the two autoclave setup successfully enabled the identification of the true corrosion inhibitor behavior by preventing build-up of corrosion product layers. At this temperature, the imidazoline type inhibitor did adsorb on the steel surface with an inhibition efficiency of 61%. At 150°C, the presence of inhibitor did not affect the corrosion profile, whatever the autoclave system used. The surfaces of the specimens retrieved from experiments were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). At 150°C, the rapid formation of Fe_3O_4, rather than the effect of inhibitor, seemed to have controlled the corrosion behavior. However, the presence of the imidazoline-type inhibitor impeded the formation of corrosion product layers.