Criteria to Choose Superheater Tube Material (ASTM Spec)

Phil,

Yes, superheater tube material is selected primarily on the basis of maximum gas temperature. I am assuming that you are interested in a coal fired boiler (but you didn't state this)

However, not all gas streams are the same. Some gas streams are highly corrosive and oxidizing. You would not expect the superheater tube material to be the same for a waste heat boiler and a pulverized coal burning boiler.

My opinion only.....

Hi Phil,

Outer pipe of a superheater tube is typically steel, be it carbon, stainless or alloy. I expect Sandvik's product comparison should be a good start. It list products, product materials and their specs.

Hopefully someone else can answer your tube temperature question, since it seems manufacturer's tend to reference the steam temperature.

When any heat exchangers tubes are selected it is selected on the basis of service fluids temperature and corrosion. According to temperature and corrosive nature it may be Carbon Steel , Stainless Steel or Alloy Steel i.e. ASTM A179, A213, A209 etc.So please check the fluids(Gas, Steam or water)temperature and corrosive nature and decide accordingly. Also you have to select whether requirement is for seamless or electric resistance welding tubes and that also depends upon pressure also.

ASME Section II part D and ASME Section I PG9 will be of your help. Depending on your requirement, tubes are selected such that they are able to withstand gas temperature for limited time due to dry run at start-up or in emergency. Such dry run cycles are generally specified during design stages

Material selection criteria is not so simple. First you decide how much heat/ energy is to be utilized. What is temperature of available hot gas? What is temperature of the fluid at the entry of the super heater? What shall be temperature after super heat?

Based on above facts, and gas side and fluid side mean thermal conductivity, Lowest common mean temperature differential (LMTD) is calculated for the system,

Taking consideration of fouling factors and tube sizes, over all heat transfer coefficient is obtained.