bobbbb
Materials
- Dec 29, 2011
- 4
Hi all, New to forum.
Not an exhaustive search but enough to frustrate me. Cant seem to find any readily available solid information out there regarding this. So I'm hoping there is a metallurgist on this forum that can shed a little light on the subject. I am constructing a heat exchanger(using air flow to transfer heat, not liquid) where the heat source temperature is somewhat uncontrollable, like in a naturally aspirated wood burning stove, and the system will use natural convection creating a draft as the primary mover of exchanged air and not a fan forced air that would naturally provide additional heat exchanger material cooling.
The last unit I built was just carbon steel. but since the heat exchanger is buried in the coal bed I have long term service life concerns where heat scale or corrosion from caustic ash may eat away enough material to cause air leaks similar to what is seen in an automotive tailpipe. in turn contaminating air with CO, etc. that will be circulated into an inhabited room rendering the unit unsuitable for further use. So I would like to explore stainless as a more corrosion resistant material option for a longer service life.
My concern is any off-gassing of toxic heavy metals like Ni or Cr while in service, as I am cautioned against while welding these materials, and thermal fatigue from potentially daily heat/cool cycles.
So I guess the big question would be are these valid concerns? At what temperature or material state does stainless start off-gassing any toxic/heavy metal fumes or vapors? A little off point, but can a wood fire, naturally or fan aspirated create enough heat to cause this concern? I have read 1600*F is common in the coal bed of a hot wood stove. Would the specific alloy make a difference in this application? I know 321 is typically used in high heat applications where pressure strength needs to be retained like jet engines, but is also cost prohibitive for this. Will thermal expansion cracking or heat scaling be an issue with an alloy that is readily available like 303 or 304? What would be the most ideal material from a suitability/cost effective relationship for an application like this?
Thanks in advance for any solid light anyone can shed on this issue or point me to other resources/forums discussing this issue, and feel free to make it a discussion thread as I'm sure I'm not the only one pondering this question for one reason or another. P.S.: I'm ok with logical speculations as they sometimes lead to useful debate or point one in the right direction even if it is inaccurate upfront. However, if you don't actually know and are making a logical speculation that can't be backed up by an industry reference please state it as such so no one takes it as gospel.
Thanks again and happy new year everyone.
Not an exhaustive search but enough to frustrate me. Cant seem to find any readily available solid information out there regarding this. So I'm hoping there is a metallurgist on this forum that can shed a little light on the subject. I am constructing a heat exchanger(using air flow to transfer heat, not liquid) where the heat source temperature is somewhat uncontrollable, like in a naturally aspirated wood burning stove, and the system will use natural convection creating a draft as the primary mover of exchanged air and not a fan forced air that would naturally provide additional heat exchanger material cooling.
The last unit I built was just carbon steel. but since the heat exchanger is buried in the coal bed I have long term service life concerns where heat scale or corrosion from caustic ash may eat away enough material to cause air leaks similar to what is seen in an automotive tailpipe. in turn contaminating air with CO, etc. that will be circulated into an inhabited room rendering the unit unsuitable for further use. So I would like to explore stainless as a more corrosion resistant material option for a longer service life.
My concern is any off-gassing of toxic heavy metals like Ni or Cr while in service, as I am cautioned against while welding these materials, and thermal fatigue from potentially daily heat/cool cycles.
So I guess the big question would be are these valid concerns? At what temperature or material state does stainless start off-gassing any toxic/heavy metal fumes or vapors? A little off point, but can a wood fire, naturally or fan aspirated create enough heat to cause this concern? I have read 1600*F is common in the coal bed of a hot wood stove. Would the specific alloy make a difference in this application? I know 321 is typically used in high heat applications where pressure strength needs to be retained like jet engines, but is also cost prohibitive for this. Will thermal expansion cracking or heat scaling be an issue with an alloy that is readily available like 303 or 304? What would be the most ideal material from a suitability/cost effective relationship for an application like this?
Thanks in advance for any solid light anyone can shed on this issue or point me to other resources/forums discussing this issue, and feel free to make it a discussion thread as I'm sure I'm not the only one pondering this question for one reason or another. P.S.: I'm ok with logical speculations as they sometimes lead to useful debate or point one in the right direction even if it is inaccurate upfront. However, if you don't actually know and are making a logical speculation that can't be backed up by an industry reference please state it as such so no one takes it as gospel.
Thanks again and happy new year everyone.
