7462Alloys 800 800H 800HT and 45TM

Alloy 800 (20% Cr, 32% Ni, and 46% Fe as balance) is used primarily for its oxidation resistance and strength at elevated temperatures. One of its major benefits is that the alloy does not form embrittling sigma phase even after long time exposure between 650 and 870° C. This fact coupled with its high creep and stress rupture strength have led to many applications in the petrochemical industry such as in the production of styrene (steam-heated rectors). The alloy exhibits good resistance to carburization and sulfidation and thus has been used in coal gasification in components such as heat exchangers, process piping, carburizing fixtures, and retorts. Two major applications are electric range heating element sheathing and extruded tubing for ethylene and steam methane reformer furnaces.

In aqueous corrosion service, alloy 800 is generally not widely used since its corrosion resistance is somewhere between type 304SS and 316SS. Even though alloy 800H has been used in coal gasification due to its good carburization and sulfidation resistance, it undergoes accelerated attack in some processes. To enhance resistance to these modes of degradation, a higher chromium, silicon-containing alloy was developed, known as alloy 45TM (UNS N06045). This is a chromia/silica forming alloy with excellent resistance to high-temperature attack in coal gasification and thermal waste incinerators, and in refineries and petrochemical industries, where sulfidation has been a major problem. Details on this alloy are available in the open literature [4, 17].

7.4.7 Ni-Cr-Fe-Mo-Cu Alloys










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