Surface analyses of low carbon steel and stainless steel in geothermal synthetic Na-Ca-Cl brine saturated with CO2

• Published in: Results in surfaces and interfaces 2022-05, Vol.7, p.100040, Article 100040
• Main Authors: Poulain, Marie, Dupin, Jean-Charles, Tillous, Kessein Eric, Ledeuil, Jean-Bernard, Serin, Jean-Paul, Cézac, Pierre, Martinez, Hervé
• Format: Article
• Language: English
• Subjects: Brine; Chemical Sciences; Geothermal corrosion pilot; Material chemistry; Material corrosion; Surface characterization
• ISSN: 2666-8459; 2666-8459
• DOI: 10.1016/j.rsurfi.2022.100040

In a geothermal power plant, certain precautions should be taken to ensure a good efficiency. Indeed, it is important to avoid degassing of the geothermal fluid and to prevent corrosion issues. To address these problems, the gas–liquid equilibrium has to be controlled and the characteristics (composition, temperature…) of the fluid known as well as the nature of the material used. For this reason, in this paper, a laboratory-scale device was developed in order to simulate natural like conditions and achieve corrosion tests. The corrosion behaviour of two materials, a carbon steel (DC01) and a stainless steel (304 L), has been investigated. The testing materials have been exposed to a synthetic brine which composition is similar to the Upper Rhine Graben water formation. The brine was saturated with 2 MPa of CO2 and heated up to 50 °C and 100 °C. Surfaces of tested metals were analysed by spectroscopic (XPS) and microscopic (SEM) methods in order to characterize corrosion products and to get more information onto the corrosion mechanisms process. The use of the laboratory prototype coupled with surface analysis methods allowed to better understand CO2 corrosion in geothermal environment. The role of the brine chemistry and the impact of temperature and CO2 dissolved concentration have been studied in this work. Indeed, different natures of corrosion products regarding the material composition and microstructure have been highlighted. A mixture of CaCO3 and FeCO3 scale is identified on the carbon steel whereas the stainless steel exhibits a mixture of Cr(OH)3 and FeCO 3 on its surface. •Material resistance to corrosion was evaluated in simulated geothermal environment.•A new experimental corrosion device was used to conduct investigations.•XPS and SEM were carried out to characterize the material surface.•The carbon steel surface was covered up with a mixture of CaCO3 and FeCO3.•A mix of Cr(OH)3 and FeCO3 was detected on the stainless steel surface.