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Mundhenk N.,Institute of Applied Geosciences KIT | Huttenloch P.,Institute for Energy Research of Germany | Bassler R.,BAM Federal Institute of Materials Research and Testing | Kohl T.,Institute of Applied Geosciences KIT | And 2 more authors.
Corrosion Science | Year: 2014

Corrosion of metallic engineering materials accounts for problems during geothermal operation in the Upper Rhine Graben (URG). Herein, we study the electrochemical behaviour of various metal alloys in an 80. °C simulated geothermal environment by using potentiodynamic polarisation and open-circuit potential measurements. Two different natural geothermal waters from URG geothermal sites were used for the experiments. The measurements reveal spontaneous passivation to be a key process for all alloys. This ennoblement protects more noble alloys from significant corrosion (e.g. titanium gr. 2, alloy 625) and brings less noble alloys to failure, mostly due to pitting corrosion (e.g. 316L). © 2014 Elsevier Ltd.

Mundhenk N.,Institute of Applied Geosciences KIT | Huttenloch P.,Institute for Energy Research of Germany | Kohl T.,Institute of Applied Geosciences KIT | Steger H.,Institute of Applied Geosciences KIT | Zorn R.,Institute for Energy Research of Germany
Geothermics | Year: 2013

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.Both methods 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. © 2012 Elsevier Ltd.

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