Laboratory and In-Situ Corrosion Studies in Geothermal Environments

Abstract

A major factor in the economic exploitation of geothermal resources will be the cost-effective selection of materials that have sufficient resistance to corrosion to maintain component integrity during plant operation. Various metals have been tested in laboratory and in-situ weight-loss exposure tests (Soultz-sous-Forêts) and instrumented exposure (electrochemical polarization) in geothermal brine from Soultz-sous-Forêts, France. Mild steels (N80, P110, P235GH and P265GH) are subject to corrosion. However, the formation of secondary corrosion products (mainly FeCO3) contributes to materials corrosion resistance and reduces the corrosion rate over time. Potentiodynamic polarization has been used to study the passivation tendency of stainless steels and alloys, showing good agreement with exposure tests. 430F showed pitting after 4 weeks of in in-situ and autoclave exposure, while higher-strength materials (316L, 318L, 904L, alloy 31 and Ti grade 2) showed no obvious sign of surface degradation and/or scaling.