ABSTRACT
Nickel superalloys are of increasing interest in new and emerging energy production applications for their high temperature mechanical properties, stability, durability and corrosion resistance. The precipitation hardenable Ni-Co-Cr superalloy N07740 has been developed for high pressure – high temperature environments and is an ASME code approved material and originally designed for fossil fuel power generation. New applications for the material include concentrated solar power receiver tubes due to its very high creep and fatigue strength in the temperature range 580 to 825C. The solar receiver tubes contain a heat transfer medium of molten salts used to transfer and store the solar energy. Solar receiver technology is also being combined with new ultrasupercritical power cycles which have potential advantages of high efficiency and reduced demand for water in desert environments. The paper includes molten salt corrosion testing of alloys N06625, N06230 and N07740 in Nitrate salt at 600C for exposure periods up to 4000 hours. Corrosion weight loss data is presented including optical and SEM surface and analysis of cross sections. The paper also reviews corrosion data in other molten salt media and in the ultrasupercritical carbon dioxide used in high efficiency – low emission power generation systems. The development of lower cost product forms and fabrication techniques for the precipitation hardened superalloy N07740 to enable the salt containing receiver tubes and high pressure-high temperature components are also discussed.
