The three-year research program (2010-2012) of the Soultz-sous-Foręts geothermal power plant (France) is associated with a scientific and technical monitoring during geothermal exploitation. Several hydraulic circulation tests have been performed in this time and those tests were used for intensive in-situ material studies concerning corrosion, coating and scaling which resulted in an improved design for a corrosion skid at the high temperature side of the geothermal power plant. At Soultz, saline brine is produced from a granitic EGS reservoir at 160˚C and 20 bars (wellhead GPK-2). This fluid consists mainly of a Na–Ca–Cl brine with a TDS of 97 g/l at a pH of 4.8. Measurement of the redox potential show reducing conditions. Identification and testing of materials which are able to resist in these operational conditions became an essential part of the Soultz research program. Selection of applicable materials for this aggressive environment focuses on their stress resistance against chemical attack, on mechanical stress resistance and durability and on their cost effectiveness. Corrosion studies of metals and tests of the thermal stability of polymer coatings were also conducted over the 3 years, from the first circulation tests to the current operation state but mainly on the cold part of the surface installations at 70˚C and 18 bars. A relatively low corrosion rate of 0.2 mm/year was observed. The ongoing challenge is to conduct material tests at in-situ conditions at the hot side of the geothermal loop. Therefore, an innovative high temperature skid (HTS) has been designed, built and assembled in the hottest zone of the surface installations of the Soultz geothermal site. This tool operates at 160˚C and 20 bars. Flow, temperature and pressure are monitored continuously during skid operation and an internal window provides the direct observation of the inside flow conditions at the upper part of the skid. Testing of metal coupons is still an important part of the corrosion experiments but the main improvement was established by integrating two different geometric setups into the skid equipment: straight pipes and T-shaped pipes. The last one reflects both, dynamic flow and stagnant flow in one sample. Different metals will be tested to investigate the corrosion rate in stagnant and dynamic flow conditions and the type of corrosion, either uniform or pitting. Moreover, corrosion products and scaling layers on the metal surface will be characterized. Besides the corrosion study of metals, the test of different polymer coatings concerning their thermal stability, their abrasion resistance against mechanical attack by quartz and feldspar particles, produced from the granite reservoir, and the formation of scalings on the polymer surface are under investigation. Corrosion and coating in-situ experiments at the high temperature side of the geothermal loop in Soultz provide unique opportunities to test and select materials based on their durability and cost effectiveness for geothermal applications with Upper Rhine Valley type fluids.

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