Assessing underdeposit corrosion inhibitor performance for carbon steel in CO2/Sulfide environment

Abstract

Under deposit corrosion (UDC) that occurs due to the deposition of solid particles, like iron sulfide or organic solids, and CO2 corrosion, cause disasters for pipelines and fluid-handling apparatus. This research investigated the impact of mineral deposits, like iron disulfide, iron sulfide, and sand, on the inhibition performance of the commercial UDC inhibitor in sulfated CO2-saturated brine solution at 60 °C and 1000 rpm flow rates for different immersion times. The deposit characteristics, type, and coverage technique on the steel (full/partial) were explored. The surface morphology, elemental analysis, and particle size of deposits in the absence and presence of the inhibitor were analyzed. The inhibitive effect at different inhibitor concentrations and the corrosion rates of steel in the absence and presence of the deposits were calculated from the fitting process of the electrochemical impedance spectroscopy (EIS) results. The utilized UDC inhibitor has the highest efficiency (about 95 %) at a concentration of 400 ppm. The FeS, FeS2 and SiO2 deposits in the presence of the inhibitor offered a 77.5 %, 94.5 % and 94.6 % inhibition efficiency after 6h of immersion time, resulting in about 77.5 %, 25.6 % and 60.1 % increase in their efficiencies before the addition of the inhibitor. Therefore, the inhibitor can effectively inhibit the UDC triggered by FeS and SiO2 deposits in an aqueous environment containing sulfated CO2. However, it is unavailable in the steel underneath the FeS2 deposit to inhibit corrosion. EDX and XPS analyses confirm the success of the inhibitor movement through deposits and its adsorption on steels.

Keywords

• UDC inhibitor
• Deposits
• Sweet/sour conditions
• Under-deposit corrosion
• Carbon steel