Return Bends and Headers Material
Return bends are typically made of the same material as tubes. They should be wrought, not cast, due to the poorer mechanical properties and greater likelihood of defects in castings. Avoid longitudinal welds in return bends.
In fired heaters using several different tube materials, you will have dissimilar metal welds at the transitions. Make sure you choose the proper welding electrode and welding procedures. Consult the welding manual for assistance here. Try to avoid dissimilar metal welds within the firebox when the two materials being joined have greatly different coefficients of expansion.
Headers and header plugs are seldom recommended for newer furnaces, but when used, they are also typically made of the same material as the tubes. However, some compromise must occasionally be made when you lack variety of available materials. If the header must be of a different material than the tube, consider corrosion resistance, coefficients of expansion, and weldability in making the choice. Headers and header plugs may be cast or wrought. The poorer properties of castings can be accepted in lower pressure services like crude units and delayed cokers, because the headers are relatively massive in cross-section.