Corrosion Behaviour of Materials in Simulated High-Temperature Geothermal Environments

Abstract

High enthalpy geothermal fluid utilization has a potential for growth for green and sustainable energy production. Geothermal energy production is often limited by the corrosive nature of the geofluids utilized. For successful, safe and economic operation, several technological challenges have to be overcome including the appropriate selection of material(s) for casing, pipelines and other equipment. This dissertation reports the results of a corrosion behaviour study for carbon steel and several corrosion-resistant alloys tested in contact with synthetic geothermal fluids at high temperatures. Corrosion tests were carried out using superheated steam (T = 350 °C and P = 10 barG) containing H2S, CO2 and HCl and the materials tested were carbon steel, stainless steel, nickel-based alloys, titanium alloys, high-entropy alloys. Some of the materials were further tested after silica (SiO2) had been deposited on the surfaces, and under boiling and condensing conditions at lower temperatures. In superheated fluid, carbon steel and Cu added high entropy alloys (HEAs) were prone to corrosion damage but negligible damages were observed in other corrosion-resistant alloys. The carbon steel was prone to more severe corrosion damage in the boiling and condensing conditions in comparison with the superheated test fluid, hence, the corrosion behaviour of carbon steel can be associated with the physical condition and temperature of the corrosive fluid. The extent of corrosion damage of Cu added high-entropy alloys (HEAs) in the superheated fluid is associated with increased Cu content and Cu-rich intermetallics. The corrosion rates of various materials were assessed by the mass loss method (MLM) and were less than 0.1 mm/year in all cases. Microstructural analysis was done via scanning electron microscope (SEM), X-ray energy dispersive spectroscopy (XEDS) and solid and powder X-ray diffraction (XRD) analysis. From the results, it can be concluded that the corrosion-resistant alloys are immune to corrosion damage in high-enthalpy superheated geothermal fluid containing H2S, CO2 and HCl and should be selected in preference to carbon steels and Cu added HEAs in such environments.