General Corrosion of Stainless Steels and Nickel Base Alloys Exposed Isothermally in Superheated Steam

Abstract

Abstract Results are reported for a comprehensive corrosion study sponsored by the Atomic Energy Commission on commercially available materials that might be suitable for nuclear superheat fuel cladding application. Several nickel alloys (Inconel 600, Inconel 625, Incoloy 800, Incoloy 825 and Hastelloy X) and two stainless steels (Types 304 and 406) were exposed isothermally to 1050 and 1150 F (656–621 C) superheated steam in a dynamic corrosion facility. Hydrogen and oxygen content of the steam was controlled to simulate that found in boiling-water reactor steam. Generally an initially high corrosion rate decreased to a lower constant rate. Initial corrosion rate period appeared to vary in time for different materials although most seemed to reach a linear rate in the first 1000 hours. Hastelloy X, Incoloy 825, Inconel 625 and Incoloy 800 had low initial and long-time linear corrosion rates and formed good protective and tenacious oxides up to 1150 F. Type 406 stainless steel (SS) had a high initial but low long-time linear corrosion rate and formed a protective and tenacious oxide up to 1150 F. Inconel 600 had adequate corrosion resistance to 1050 F but formed a nonprotective oxide film, a significant portion of which was lost to the system at 1150 F. Type 304 SS had significant corrosion rates at 1050 and 1150 F but formed a relatively tenacious oxide at both temperatures that eventually reached a limiting thickness with subsequent spalling.