Corrosion Testing in Direct Geothermal Steam of Cladded and Stand Alone Materials at 210°C and 450°C

Abstract

Selection of materials for high-temperature geothermal wells follows oil and gas (O&G) standards and recommendations and the same applies for wellhead design, well design and drilling. Geothermal wells differ from O&G wells with higher temperatures and non-condensable gases such as H2S and CO2 and often low pH level. These are all parameters that have corrosive effect on the well material and often with more complicated forms of corrosion than in common O&G wells. It is therefore of high importance for long life of geothermal wells to select casing materials that can both withstand the high temperature and the corrosive nature of the geothermal fluid. The subject of this paper is corrosion testing in a custom-built autoclave system in geothermal steam. The test was carried out at temperatures of 210°C and 450°C in a flow through system to test the corrosive nature of geothermal environment against candidate materials, especially cladded materials made with several cladding methods. The cladded corrosion resistant materials, cladded on low or medium carbon steels were in direct contact with the steam/brine at 210°C and 450°C, at Reykjanes geothermal field that is operated by HS-Orka. The autoclave system for the testing, is built up be three autoclaves, one 5 L and two smaller for sampling, made of C276 material and capable of providing testing conditions up to 4500°C at 300 bars. Additionally, a custom-made autoclave was built for testing in direct conditions at 210°C. For comparison with older results a selection of “stand alone” materials were as well tested.