For which type of fittings is cast iron prohibited when dealing with superheated steam?

Cast iron is not recommended for use with superheated steam due to its brittleness and tendency to fail under the high temperatures and pressures associated with superheated steam systems. The properties of cast iron make it prone to crack and break when subjected to these conditions, which could lead to catastrophic failures in piping systems.

When dealing with superheated steam, the material used for fittings must possess adequate strength and ductility to withstand the thermal stress. Options such as standard fittings, galvanized fittings, or schedule 40 fittings may include materials that can appropriately handle these conditions, such as carbon steel or stainless steel, but cast iron does not meet the necessary mechanical properties for this application. Therefore, any type of fittings made from cast iron should be avoided when dealing with superheated steam.