Study Of The Corrosion Inhibition Mechanism And Synergistic Effect Of Inhibitor On Carbon Steel In CO₂ System

CO₂ corrosion can cause serious damage to oil and gas pipeline equipment, filling corrosion inhibitor is one of the economically efficient means of anti-corrosion. Adding a single corrosion inhibitor often can not meet corrosion requirements of the equipment, people often use the synergistic effect theory of corrosion inhibitor and get compound inhibitors which have higher inhibition efficiency. In this paper, the corrosion inhibition mechanism and synergistic effect of imidazoline ?IM? and octadecylpropylenediamine?18N3N? were studied in CO2 saturated simulated solution. The corrosion inhibition mechanism and synergistic effect of IM and 18N3N were studied by electrochemical method, computer molecular simulation, X-ray photoelectron spectroscopy, scanning electron microscopy, surface tension test and potential and current scanning techniques on wire beam electrode. The main results of research work are as follows:1. The corrosion inhibition and synergistic effect of IM and 18N3N in CO2 saturated simulated solution were studied by electrochemical method,XPS and SEM. The results showed that the highest inhibition efficiency was 95.3% after adding 150 mg·L-1IM and 50 mg·L-118N3N. IM and 18N3N adsorbed on the surface of carbon steel, and compound corrosion inhibitor can significantly reduce the corrosion of carbon steel.2. The model of IM and 18N3N complex corrosion inhibitor was established by molecular dynamics simulation. The fractional free volume?FFV? of the model was calculated and the result indicated that The value of FFV is the smallest at the middle of a concentration ratio of IM and 18N3N,revealing that corrosion inhibitor film is the most dense at that ratio. The electrochemical results and the contact angle test showed that the compound corrosion inhibitor had the best corrosion inhibition effect at the intermediate concentration ratio. The FFV value calculated by the molecular simulation can provide some theoretical guidance for the study of the synergistic effect of the corrosion inhibitor.3. Effect of compound corrosion inhibitor on local corrosion was studied by using wire electrode current and current scanning technology. The results indicated that addition of IM and 18N3N will cause the characterization of localization of corrosion increase on the electrode surface, the addition of surfactants ?SAA? and thiourea ?TU? in the complex system reduced the characterization of localization of corrosion and inhibition efficiency of compound inhibitor was improved at the same time by electrochemical test and SEM method.4. A compound corrosion inhibitor IM-4 was prepared and tested for water solubility and emulsification. The results showed that the water solubility was good and IM-4 had almost no emulsification tendency. The corrosion inhibition rate of IM-4 was evaluated by dynamic weight loss method and polarization curve. The highest inhibition efficiency was 95.6%when the concentration was 150 mg·L-1, which is in line with the use of gas field corrosion inhibitor requirement.