Preliminary Corrosion Testing of Nickel Alloys in Simulated High Temperature Geothermal Environment

摘要

To explore the potential of obtaining more energy output per geothermal well, deep drilling (～5000 m depth) of geothermal wells was started in Iceland few years ago, within the Iceland Deep Drilling Project (IDDP). The first IDDP well produced superheated steam at high temperatures and pressures during its lifetime. The geothermal steam contained acidic gas components including H_2S, HCl and CO_2, which upon condensation became extremely corrosive with pH level of 2.5-3. To gain more understanding of the corrosion behavior of several alloys at saturation and superheated conditions in deep geothermal wells, preliminary testing of highly corrosion resistant nickel alloys, UNS N06625 and N10276, was done in simulated geothermal environment. The UNS N10276 and UNS N06625 were tested 350°C in flow through reactor with a pressure of 10 bar for a 1 and 3 week exposures. The UNS N06625 was additionally tested at 180°C with same pressure and exposure time conditions. The simulated environment was composed of a generated steam containing H_2S, HCl and CO_2 gases at the given temperature and pressure with a pH level of 3 upon condensation. The UNS N06625 performed very well at 180°C where corrosion rate was measured insignificant at 1 week exposure but very low at 3 weeks exposure. At 350°C the corrosion rate of UNS N06625 was lower than UNS N10275, but corrosion rate for both alloys were though higher than generally accepted. Microstructural and chemical analysis revealed localized corrosion damage and corrosion products cracks in UNS N06625 but no localized damage in UNS N10276. High molybdenum content in UNS N10275 is possible the reason for better localized corrosion resistance The future work is to develop the tests and the testing facility further i.e. test more alloys at higher temperature and pressure levels and investigate the effect of SiO_2 scaling on under deposit and localized corrosion of the alloys.