Types of Steel
Stainless vs. Carbon or Aluminized Steel*
Q. What is the best material for the heat exchanger? Stainless Steel, Carbon Steel or Aluminum Coated (Aluminized) Steel?
A. The answer is that any of these materials are sufficient provided that the builders AND the growers are aware of the limitations of each.
Stainless steel resists corrosion and flame erosion (burnout) but is expensive, difficult to weld and, more importantly, has a relatively low heat transfer ability. Stainless steel has about 1/4 the heat transfer ability of carbon or aluminized steel. Stainless steel also has a high coefficient of thermal expansion which means that it is more likely to warp and get out of shape when it is heated.
Carbon steel will rust and may be subject to flame erosion over a long period but it is less expensive and is a lot easier to cut and weld. Carbon steel sheets and tubes may be three times thicker than stainless steel, yet still less expensive and have better heat transfer characteristics than stainless. Some of the higher stack temperatures we have measured have been with all stainless steel heat exchangers.
Aluminized steel is just carbon steel with a thin coating of aluminum to resist rust. This is the same material automobile mufflers and tail pipes are made of and has a long record of good service in high temperature applications.
*Adapted from comments made by Dr. Mike Boyette, NCSU.