Niobium in centrifugally cast tubes for petrochemical applications

Niobium has been used in centrifugally cast tubes since about 1970 as a eutectic carbide forming element to increase creep strength and creep ductility, as well as carburization resistance. For a long time, the 35Ni-25Cr-Nb or HP Mod.Nb material dominated the market for steam reformer and steam cracker furnace tubes. In the mid eighties, the so called micro alloys were introduced in which other carbide forming elements like titanium, zirconium and Rare Earths (RE) were added to niobium to increase these effects. For increased corrosion resistance, particularly against fuel ash corrosion, the 50Ni-50Cr-Nb was created. It is used in static castings such as tube support plates in the convection section and tube hangers in the radiant section of petrochemical furnaces. (AU)