ABSTRACT
A key factor successfully leading to long-term operation of the equipment in the aggressive environment at geothermal power plants is the proper selection of materials with high erosion-corrosion-resistant properties. One group of materials called to improve the erosion, corrosion, and wear resistance of pumps, turbines, and heat exchangers operated in the geothermal industry, is the titanium (Ti) alloys. In this paper, we report the comparative analysis of corrosion resistance for a newly developed hot isostatically pressed Ti6Al4V reinforced with a 10vol%-titanium diboride titanium matrix composite and a wrought Ti64 alloy (UNS designation R56400). Both the Ti64+10vol%TiB2 and wrought Ti64 alloys were tested under simulated geothermal "steam/liquid" conditions at T=185 °C and P=10.2 barG for seven days. The liquid phase’s controlled pH was 4, whereby concentrations of non-condensable gases of H2S and CO2 were 170 ppm and 1012 ppm, respectively. Using SEM/EDS and XRD analyzing techniques, the tested Ti64+10vol%TiB2 and Ti64 samples were examined for localized corrosion and corrosion products penetration into the materials. The findings showed that the Ti64 alloy has a greater corrosion resistance than the Ti64+10vol%TiB2 due to the titanium boride (TiB) phase being more susceptible to corrosion in the simulated geothermal environment.
