The synergistic inhibition effect between imidazoline and the oxide film on L360 steel in CO2/H2S systems

Purpose – The aim of the present paper was to investigate the inhibition performance of the OF and/or IM on L360 steel in CO2/H2S environments. The pipeline steel surface usually has been pre-treated before using in the oil/gas field, such as by passivation, blackening, and phosphiding. The effectiveness of inhibition can vary because there are many differences between the metal matrix and the treated film. Design/methodology/approach – Imidazoline (IM) was synthesized by using oleic acid and diethylenetriamine, and its composition was verified using Fourier transform infrared spectroscopy. The oxide film (OF) covering a sample of L360 steel was characterized using X-ray diffraction, and its surface morphology was observed using scanning electron microscope. Electrochemical impedance spectroscopy measurements were conducted to study the inhibition performance of IM- and/or OF-covered L360 steel in the CO2/H2S environments. Findings – The results show that IM and OF can prevent corrosion on L360 steel in CO2/H2S environments, and the synergistic inhibition effect of IM and OF was very evident. A possible model is proposed to explain the synergistic inhibition effect in the CO2/H2S environments of IM and OF on L360 steel. Originality/value – Few reports have concerned the effect of the OF on the inhibitor’s performance, especially in CO2/H2S systems. The aim of the present study was to investigate the inhibition performance of the OF and/or IM on L360 steel in CO2/H2S environments. A model is proposed to explain the synergistic inhibition effect mechanism between IM and OF.