Incoloy® Alloy 800 (UNS N08800/W. Nr. 1.4876) is a widely used material for construction of equipment requiring corrosion resistance, heat resistance, strength, and stability for service up to 1500°F (816°C). Alloy 800 offers general corrosion resistance to many aqueous media and, by virtue of its content of nickel, resists stress corrosion cracking. At elevated temperatures it offers resistance to oxidation, carburization, and sulfidation along with rupture and creep strength. For applications requiring greater resistance to stress rupture and creep, especially at temperatures above 1500°F (816°C), Incoloy® Alloys 800H and 800HT are used. The chromium in the alloy imparts both aqueous and heat resistance. Iron provides resistance to internal oxidation. The nickel content maintains a ductile, austenitic structure. Thus, alloy 800 is readily formed, welded, and machined.
Incoloy® alloy 800 is used in a variety of applications involving exposure to corrosive environments and high temperatures. It is used for heat-treating equipment such as baskets, trays, and fixtures. In chemical and petrochemical processing, the alloy is used for heat exchangers and other piping systems in nitric acid media especially where resistance to chloride stress-corrosion cracking is required. In nuclear power plants, it is used for steam-generator tubing. The alloy is often used in domestic appliances for sheathing of electric heating elements. In the production of paper pulp, digester-liquor heaters are often made of alloy 800. In petroleum processing, the alloy is used for heat exchangers that air cool the process stream.
Incoloy® Alloy 800 has high mechanical strength over a broad temperature range. In general, alloy 800 is used for its strength characteristics at service temperatures up to about 1500°F (816°C). At those temperatures, equipment design is usually based on tensile properties. For applications that require high creep or rupture strength, Incoloy® Alloys 800H and 800HT are used.
Incoloy® Alloy 800 (UNS N08800) is approved under the Boiler and Pressure Vessel Code of the American Society of Mechanical Engineers (ASME). Rules for construction of power boilers are defined under Section I, and those for pressure vessels under Section VIII, Divisions 1 and 2.
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.