Incoloy® alloys 800H and 800HT® have significantly higher creep and rupture strength than Incoloy® 800. The three alloys have nearly identical chemical composition limits. However, the chemical composition limits vary with carbon, aluminum and titanium. The carbon content of Incoloy® alloy 800 (UNS n08800) is 0.10% max with no limit on the lower end. The carbon content for Incoloy® alloy 800H (UNS N08810) is 0.05% to 0.10% which is the upper end of the 0.10% maximum specified for Incoloy® alloy 800. The chemical limits for Incoloy® 800HT® (UNS08811) are even more restrictive yet still within the limits specified for Incoloy® 800H. The carbon content for Incoloy® alloy 800HT® is further restricted to 0.06%-0.10%. Additionally the Al plus Ti content of Incoloy® alloy 800HT® is restricted to 0.85%-1.20%. Note that the chemical composition for Incoloy® alloy 800HT® will always be within the limits of Incoloy® alloy 800H. Note also that the limits for Incoloy® alloy 800H may or may not be within the limits of Incoloy® alloy 800HT®.
In addition to the controlled carbon content, Incoloy® alloys 800H and 800HT® receive a high temperature annealing treatment that produces an average grain size of ASTM 5 or coarser. The annealing treatment and restricted chemical composition are responsible for these alloys having greater creep and rupture strength.
The mechanical properties of Incoloy® alloys 800H and 800HT®, combined with their resistance to high temperature corrosion, make these alloys exceptionally useful for many applications involving long-term exposure to elevated temperatures and corrosive atmospheres. In the hydrocarbon processing industry, these alloys are used in steam/hydrocarbon reforming for catalyst tubing convection tubing, pigtails, outlet manifolds, and quenching-system piping; in ethylene production for both convection and cracking tubes, and pigtails; in oxy-alcohol production for tubing in hydrogenation heaters; in hydrodealkylation units for heater tubing; and i the production of vinyl chloride monomer for cracking tubes, return bends and inlet and outlet flanges.
Industrial heating is another area of wide usage for both Incoloy® 800H and 800HT®. In various types of heat treating furnaces, these alloys are used for radiant tubes, muffles, retorts, and assorted furnace fixtures.
Alloys 800H and 800HT® are also used in power generation for steam superheating tubing and high temperature heat exchangers in gas cooled nuclear reactors.