Deep geothermal energy can contribute a significant portion of electricity to the future energy mix. However hydrochemistry-related issues such as corrosion and scaling often results in down-time periods and their control remains challenging. Using appropriate materials can enhance power plant availability and thus decrease operating costs. This study focuses on the geothermal site Soultz-sous-Forêts France. The produced brine is characterized by high contents of Na Ca and Cl (TDS ? 100 g/L) and the presence of CO2 setting up a corrosive environment.Exposure tests and electrochemical measurements on metal coupons have been conducted in in-situ and laboratory environments mainly focusing on 80 °C reinjection conditions. All laboratory experiments were carried out with original geothermal water from Soultz. Mild steels stainless steels special iron-base alloys nickel-base alloys and titanium were chosen as test materials for mainly two reasons: they are commonly used in brine processing or they are promising options for geothermal service. Several aspects of metal-brine interaction have been evaluated the corrosion resistance being one of them. On the basis of these results different materials could be ranked with regard to their performance. Mild steels mainly exhibit uniform corrosion (corrosion rate < 0.2 mm/y) accompanied by the formation of (potentially) protective scales. Standard Cr and CrNiMo stainless steels are strongly challenged and may undergo pitting corrosion which is a more severe form of corrosion. Higher alloyed material could be identified as promising options for a reliable long-term service. This approach will be complemented by further laboratory and in-situ investigations under geothermal production conditions (T ? 160 °C).Besides corrosion resistance material selection for surface equipment of geothermal power plants needs also to focus on topics like abrasion resistance and scale adherency. At the Soultz-site scale occurence is mainly related to the cold part of the power plant. Strontium rich barite (Ba1-xSrxSO4) is formed due to the temperature decrease of 160?C to 70?C in the heat exchangers of the binary system. Intensive mechanical cleaning procedures were required in the past in order to remove the inorganic deposits which decreased significantly the efficiency of the heat transfer. Besides the dominating barite layer also minor amounts of galena (PbS) and trace amounts of mixed sulfides ((FeSbAs)Sx) are present in the Soultz scales. Their formation conditions either electrochemical processes and/or microbiological activity are still under investigation.It was observed that the intensity of scale adherency on materials of the power plant surface installations showed a variation as a function of the utilized material. Strong scale adherency was recorded especially for mild steels of the surface pipe network. Only weak scale adherency was recorded for more noble metal alloys and for polymer surfaces like coatings. This observation is in agreement with exposure tests of metal coupons under in-situ conditions at the re-injection side. Scaling layers on mild steel surfaces were characterized by REM/EDX analyses and formation conditions were evaluated. The base layer of the scale is a corrosion product as a result of material degradation. It mainly consists of a siderite (FeCO3) layer of variable thickness and compactness. It often provides the substrate for other scales. The formation is directly correlated with ongoing electrochemical corrosion processes and the release of ferrous iron from the corroding material. The layer carries characteristics which are controlled by various factors e.g. temperature flow conditions the microstructure of the material and exposure time.A main challenge is to merge the different scaling processes and to better understand the formation mechanisms involved.