Nickel/Chromium
The high-chromium casting alloys (50% nickel, 50% chromium and 40% nickel, 60% chromium) are designated for use at temperatures up to 900*C in furnaces and boilers fired by fuels containing vanadium, sulfur and sodium compounds (e.g., residual petroleum products). Alloys with lower chromium contents cannot be used with residual fuel oils at temperature above 650*C because the nickel reacts with the vanadium, sulfur and sodium ■impurities to form compounds that are molten above 650*C [27].
Nickel/Chromium/Iron
Alloy 800 (32% nickel, 20% chromium and 46% iron) is used for furnace equipment such as muffles, trays and radiant tubes and in oil and petrochemical plants as furnace coils for the reforming and pyrolysis of
hydrocarbons. Higher-strength versions of alloy 800 were developed to meet this situation (802 has a higher carbon content; alloy 807 has a higher hot strength by adding cobalt and tungsten). For 807, the stress to produce rupture in 100,000 hr at 900°C is 13.8 N/mm2 compared with 8.5 N/mm2 for alloy 800.