Radiant tubes are a method of heating a furnace without contaminating the furnace atmosphere with combustion products.
Radiant tubes are designed to transfer heat as evenly as possible within the tube and into the furnace interior. The efficiency of heat transfer to the tube's inner surface depends on the tube's effective surface area.
A tube with a nominal inner diameter of 100 mm can have a much larger effective inner surface area than its nominal inner diameter due to surface roughness (similar to small bumps and grooves). Furthermore, the inner surface area can be increased by adding internal heat sinks.
Cast or Forged Tubes (Machined Tubes)
Machined radiant tubes offer numerous advantages over cast tubes.
For example, machined radiant tubes are significantly lighter than cast tubes. A 3 mm thick, 150 mm diameter 602 CA® machined tube weighs approximately 75 kg, while a 6 mm cast tube of the same specifications weighs approximately 170 kg.
Thin-walled, lightweight tubes are less prone to sagging and cracking, exhibiting higher resistance to thermal fatigue and better heat transfer performance. Furthermore, they have better ductility, making them less prone to breakage at joints.
In addition, forged pipe fittings, bends, flanges, plugs, and straight pipes can all be repaired or replaced on-site, saving time and costs. Moreover, forged materials do not have the internal or external defects that may exist in cast pipes. While cast pipes may be slightly cheaper in terms of upfront costs, they are heavier, have longer delivery times, higher energy costs, and require downtime for replacements. Therefore, forged pipes are the optimal choice for most applications.