ALLOY800 HT is an austenitic high-strength solid-solution Ni-Fe-Cr Alloy with controlled levels of C, Al, Ti, Si and Mg and increased content of (Al + Ti).
A special solution anneal treatment gives highest creep-rupture strength above
700 ‹C (1290 ‹F) due to the precipitation of TiC.
Below 700 ‹C (1290 ‹F), gamma prime (ÁL) precipitates combined with loss of ductility.
excellent creep strength at temperature above 700 ‹C (1290 ‹F)
•good resistance to reducing, oxidizing and nitriding atmospheres and to atmospheres which alternate between reducing and oxidizing conditions
•metallurgical stability in long-term application at high temperatures
For applications where frequent excursions to temperatures lower than 700 ‹C (1290 ‹F) during service cannot be excluded or parts of the material are permanently exposed to a temperature below 700 ‹C (1290 ‹F), the use of ALLOY800H is recommended.
The high nickel and chromium contents of Alloy800H/HT ensure excellent resistance to oxidation.
The alloys are also very resistant to carburization, nitridation and oxidizing sulphur-bearing atmospheres.
The protective oxide film which is formed is adherent in both static and cyclic conditions of heating and cooling, and resistance to carburization is enhanced when a thin film of oxide is formed on the alloy through pre-oxidation prior to service. Resistance to hydrogen is excellent and Alloy800H/HT are standard materials used in the production of hydrogen in steam/hydrocarbon reforming processes.
Due to high strength during long periods of service and resistance to carburization and nitridation, ALLOY800H/HT have found many applications in steam/hydrocarbon reforming for components such as: pigtails, headers/collectors/manifolds, transfer piping, catalyst tubes (in lowpressure processes) and quench-system piping.
Typical applications are:
•ethylene pyrolysis tubing in convection and radiant sections - resistance to carburization and good mechanical properties
•ethylene dichloride cracking tubes ? resistance to carburization and to dry hydrogen chloride and chlorine
•cracking tubes used in the production of acetic anhydride and ketene - high strength, resistance to both carburization and the formation of sigma phase
•components, e.g. heat exchangers, piping systems etc., in coal conversion plants
•steam generator tubing in helium cooled, high temperature reactor systems ? high strength, resistance to helium and to steam