Inhibitor performance on carbon steel in high saline geothermal brine related to the Upper Rhine Graben (URG)

摘要

Corrosion and/or scaling control can help to prolongate the lifetime of geothermal power plant facilities from downhole to surface like casing, tubings, pumps or heat exchangers. Corrosion problems are connected with operating problems and equipment maintenance, process shutdown and economic losses. Deep geothermal fluids of the URG are highly aggressive due to their high salinities up to 200 g/L (Na-Ca-Cl brines) and a high CO_2 content. The aim of this work is to evaluate the corrosion processes of carbon steel and the performance of an amine based corrosion inhibitor in the geothermal environment. Experimental conditions were adapted to the conditions existing at the re-injection side of geothermal power plants located in the URG (CO_2-saturated artificial NaCl- and Na-Ca-Cl brine with total dissolved solids of 100 g/L, pH 5, T = 80°C). Laboratory tests were performed by weight loss tests and the use of electrochemical measurements as potentiodynamic polarization and impedance spectroscopy, depending on inhibitor concentration, brine chemistry, surface condition of the mild steel (fresh and pre-corroded) and time. Results showed best inhibitor performance at a concentration of 200 ppm in NaCl- and Na-Ca-Cl brine (static conditions), with higher efficiency in NaCl brine. The presence of Ca~(2+)-ions resulted in the interplay between the formation of carbonate deposits and adsorption of inhibitor molecules on the metal surface resulting in lower inhibitor efficiency at scaling conditions. Inhibitor performance decreased on pre-corroded metal surface compared to fresh samples at same experimental conditions.