Behaviour of materials in geothermal environments

Results are presented of operational experience with equipment and materials used in drilling geothermal wells and in exploiting geothermal fluids in turbines. Detailed descriptions are given of breakdowns occurring during plant operation. Materials such as carbon steel and low alloy steels (e.g. UNI 38 NC D4 and AISI 4137 H) have proved inadequate for use in high temperature wells and in contact with geothermal fluids. Damage to the drill string occurred within a few days. Glass resin and AISI 316 stainless steel are being used more and more often for the equipment in the power plants where there is circulation of water up to 100°C in temperature. Traditional-type materials are still being used for turbines and rotor-blades, but the corrosive fluids are flushed in steam beforehand. Research is now under way on alternative steel alloys for use in this sector.