Surface analysis of metal alloys exposed to geothermal fluids with high non-condensable gas content

Nine types of carbon steels and corrosion resistant alloys (CRA) were exposed to high enthalpy geothermal fluid with high non-condensable gas content (NCG). Surface evaluation showed that Carbon steel sustained relatively high corrosion rates (>0.15 mm/y). Scales completely covered the surface of most of the other coupons and consisted of 33-35 μm thick micro-crystalline iron sulfides outer layer and iron oxides, sulfides and silica inner layer. CRA's were immune to uniform corrosion. However, the duplex stainless steel 2205, Alloy 825 and Alloy 59 suffered crevice corrosion. Thin (∼4 μm) scales were observed in most of the CRA's with high concentration of chromium and nickel.