Reformer furnaces are used widely in the petrochemical industry to produce hydrogen from hydrocarbons. The hydrogen production takes place in radiant tubes containing a catalyst, as a result of endothermic reactions between hydrocarbons (mostly methane) and water vapor. The design of reformer furnaces has improved greatly over the past 30 years. New alloys and manufacturing processes have been developed to meet the severe requirements imposed on the tubes in the radiation zone and in the hot reaction gas outlet. There has been improvement in catalysts to provide lower reaction temperatures. However, at the same time, there has been a trend towards increased temperature and pressure to achieve further increases in production and efficiency. The number of columns varies between 15 and 200, depending on the number and size of the walls. Most modern furnaces are of the top-fired type with burners disposed in rows on both sides of the columns, while older furnaces may be of the side-fired type with burners distributed in two or more layers. The columns receive the charge through the inlet pigtails of Cr–Mo low alloy steel above the roof of the radiation chamber. The pigtails have a shape that provides flexibility to accommodate the axial displacement of the horizontal inlet manifold and of the vertical columns produced by thermal expansion.