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One of the main challenges associated with the operation and maintenance of binary geothermal power plants is the degradation of construction materials. In this sense, it is crucial to apply appropriate preventive maintenance in critical components (such as the wellheads, heat exchangers, or pipes), while reducing shutdown times. Based on electrochemical measurements performed in an autoclave corrosion testing setup, we studied the corrosion mechanism of API L80 steel grade as a function of operational and/or maintenance procedures. We used a test fluid representative for a site in Switzerland, but the main observations made may be applicable in a wider context. We found that changes in the fluid temperature (from 200 to 100 °C) or temporary oxygen ingress significantly influenced the corrosion behavior of this carbon steel and increased its corrosion rate (from approx. 20 µm/year to > 120 µm/year). After a few days, the corrosion rate was found to decrease and stabilize around values of 50–70 µm/year, as a result of a porous corrosion product layer formed on the metal surface (approx. 250 µm thick). Electrochemical impedance spectroscopy indicated an increase in capacitance of the double layer over time, most likely due to an increase in the effective surface area of the steel sample, as a consequence of surface roughening due to corrosion. The results from this study may be implemented in the design and operation of future power plants in Switzerland and elsewhere to ensure reliable and cost-effective energy production from geothermal resources. [ABSTRACT FROM AUTHOR]

In Switzerland, deep geothermal energy can give a promising contribution to the future energy scenario. However, the expertise in operational issues of deep geothermal power plants is limited, and technical challenges, such as corrosion, are a determining factor for their reliable and long-term operation. In this work, two representative fluids of optimal geothermal conditions in Switzerland were studied. The corrosiveness of the solutions was assessed using two experimental setups that allow investigating the range of temperatures and pressures that apply to the reservoir and power plant conditions. The corrosion behaviour of API L80 steel was analyzed by means of electrochemical measurements (at 100 and 200 ∘ C ) and of gravimetric tests (at 100 ∘ C ). After the tests, the morphologies and composition of the corrosion products were obtained by scanning electron microscopy (SEM) coupled with energy dispersive X-Ray (EDX) and X-Ray diffraction (XRD). Results show that corrosion rates are significantly high at 100 ∘ C in environments with a chloride concentration of around 600 mg/L and pH around 7. The corrosion products deposited on the metal surface mainly consist of magnetite and/or hematite that might potentially form a protective layer. This study gives a first insight of the potential corrosiveness of geothermal fluids in Switzerland. [ABSTRACT FROM AUTHOR]