Metal corrosion in geothermal brine environments of the Upper Rhine graben – Laboratory and on-site studies

Corrosion of construction materials in geothermal brine environments may play a major role in the long-term operation and stability of geothermal power plants. Herein the results obtained from laboratory and on-site experiments are compared in order to evaluate candidate materials as to their stability in hot brine environments. Weight-loss experiments in the Soultz-sous-Forêts (Upper Rhine graben, France) enhanced geothermal system, and electrochemical measurements in the laboratory were conducted using 8 metals (unalloyed steels, stainless steels, and Ni-based alloy). Weight loss and electrochemical measurements of the corrosion rate for unalloyed steels were found to be in good agreement. ethods reveal unalloyed steels suffer surface recession with uniform corrosion rates <0.2 mm/y, accompanied by surface deposits, providing minor protection. Stainless steel 1.4104 shows insufficient stability during 4-week exposure, whereas 1.4539 and 1.4404 do not exhibit any visible corrosion. However, electrochemical measurements on stainless steels result in pitting corrosion with pitting potentials defined for each steel quality. The very low corrosion rates obtained by electrochemical measurements for the Ni-based alloy 2.4856 were confirmed by on-site exposure tests.