Study of Corrosion Resistance Properties of Heat Exchanger Metals in Two Different Geothermal Environments
Résumé
Geothermal fluids harnessed for electricity production are generally corrosive because of their interaction with the underground. To ensure the longevity and sustainability of geothermal Organic Rankine Cycle (ORC) powerplants, the choice of heat exchanger material is essential. The performance of heat exchangers is affected by corrosion and scaling due to the geothermal fluids, causing regular cleaning, part replacement, and in the worst cases, extensive repair work. The properties of geothermal fluids vary between geothermal settings and even within geothermal sites. Differences in exposure conditions require different material selection considerations, where factors such as cost, and material efficiency are important to consider. This work studies in-situ geothermal exposure testing of four metals at two geothermal locations, in different geological settings. Four corrosion-resistant materials were exposed for one month at Reykjanes powerplant in Iceland and four months at Chaunoy oil field in France as material candidates for heat exchangers. The tested alloys were analysed for corrosion with macro- and microscopic techniques using optical and electron microscopes, which give an indication of the different frequencies of repairs and replacement. Inconel 625 showed no effects at Reykjanes and cracks at Chaunoy. The others (316L, 254SMO, and titanium grade 2) showed either corrosion or erosion traces at both sites.