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Discussion Forums - The Hendrix Group
HomeHomeDiscussionsDiscussionsMaterial Select...Material Select...carbon vs. stainless in condensing boilerscarbon vs. stainless in condensing boilers
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9/3/2004 9:00 AM
 
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hi: high efficiency condensing boilers seem to make sense but are a little confusing to me on what is the best material for where the condensing takes place...stainless or carbon? flue gas contains sulfur and chlorides and would think cracking to be a major problem for stainless although stainless is known for less corrosion problems than carbon generally. Manufacturers each say theirs is best. What do you think? What is the best out of the two? Stainless or a thicker carbon steel?
 
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9/14/2004 9:00 AM
 
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kyle, I am not familiar with, nor have I ever heard of the term "condensing boiler". It is difficult to understand what you are asking...... Is your question: "What is the best boiler tube material selection for a boiler with sulfur and/or chlorides in the flue gas" ? If so, I can answer it this way.......for virtually all boilers burning natural gas, fuel oil or any grade of coal, the boiler waterwall tubes are made from a grade of carbon steel. If there is a superheater section in the boiler and if the outlet steam temperature is above 700F, the superheater tubes will be of an alloy steel construction. (usually, but not always 2.25Cr-1 Moly material)Some boiler vendors have used stainless tubes in the superheater sections....but it is an expensive construction. If the boiler burns garbage or municipal waste refuse, a variety of boiler materials have been tried for the waterwall tubing and superheater tubes. Some boilers have been constructed with an Inconell layering to protect the waterwalls from the chlorides generated during burning..... An excellent text on boiler tube materials and selection is the book "Steam" from Babcock and Wilcox (about $100 US) What is your fuel and what temperature are you generating steam ?????!! MJC
 
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9/20/2004 9:00 AM
 
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Thanks MJC: The fuel is Natural Gas and it is a water boiler with returning water temperatures less than 100F and heating to approximately 140F. I keep hearing that the chlorides in the water even though it is a closed loop system will attack the stainless if stainless is used. Also, the flue gas will be condensing since less than the dew point and am not sure that 300 series stainless is much better than carbon for this type of application. The carbon tubes being proposed is twice as thick as the 316L stainless tubes and comes with a longer warranty. I'm just not sure what is the correct decision based on corrosion potential and which one would last longer? The boiler is a ASME Section IV design with 30 psig operating pressure.
 
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