Exhaust Ducting Thickness
Exhaust Ducting Thickness
(OP)
My question is regarding the thickness of Material needed for exhaust ducting from a generator to a heat exchanger. A microturbine generator with (5) engines will be supplying its exhaust to a heat exchanger.
The design criteria is:
Exhaust Temperature: 535-600 F
Exhaust Flow: 11,720 SCFM or 22,0003 ACFM
Exhaust Specific Heat: 0.265 Btu/lb-degF
The ducting will be 30" diameter to keep the back pressure below the maximum threshold of 8 in W.C. but I am unsure on the thickness of material needed for this. I have seen on a previous job 304 stainless steel 16 Ga was used but my question is how did they come to that conclusion. Would 18 GA be sufficient as long as it is supported properly?
The design criteria is:
Exhaust Temperature: 535-600 F
Exhaust Flow: 11,720 SCFM or 22,0003 ACFM
Exhaust Specific Heat: 0.265 Btu/lb-degF
The ducting will be 30" diameter to keep the back pressure below the maximum threshold of 8 in W.C. but I am unsure on the thickness of material needed for this. I have seen on a previous job 304 stainless steel 16 Ga was used but my question is how did they come to that conclusion. Would 18 GA be sufficient as long as it is supported properly?





RE: Exhaust Ducting Thickness
RE: Exhaust Ducting Thickness
RE: Exhaust Ducting Thickness
RE: Exhaust Ducting Thickness
All I have found regarding thickness is something like this:
Fume Exhaust Ductwork and Plenums:
41. Stainless Steel Construction:
a. Round ducts and fittings: Longitudinal seam 316L 16 gauge stainless steel for all sizes with welded seams and fitting joints.
Which was from a building specifications for a project. Nothing yet that says why they would make decision to choose the stainless to be a thicker gauge then the galvanized steel.
RE: Exhaust Ducting Thickness
RE: Exhaust Ducting Thickness
10 GA 304 Stainless Weight per Sqft: 5.67 Lbs
16 GA 304 Stainless Weight per Sqft: 2.50 Lbs
18 GA 304 Stainless Weight per Sqft: 2.01 Lbs
Going from 18 to 16 GA would increase your cost of material by 25% while going to 10 Ga would increase it by 282%.
RE: Exhaust Ducting Thickness
Use of stiffener rings can also extend the support spacing for a given gauge.
There isn't a single solution. Say for instance the ductwork is running along a wall where inexpensive supports can be used at shorter spacing. In that case it may make sense to use a lighter material and more supports (at least from total cost perspective). If the duct is running high in the air between structures, fewer supports are cheaper than the added material cost of thicker ductwork.
There are also forces on the ductwork that need to be resisted; thermal, wind, snow (maybe), insulation, etc. SMACNA's design guide is definitely a big help, but involving the fabricator is the best way to get material and installation costs.
RE: Exhaust Ducting Thickness
RE: Exhaust Ducting Thickness
RE: Exhaust Ducting Thickness
– Ducting used for conveying solid particulates, such as refuse, dust, fumes, and smoke; liquid particulate matter, such as spray residue, mists, and fogs; vapors, such as vapors from flammable or corrosive liquids; noxious and toxic gases; and air at temperatures exceeding250ºF (121ºC).
You are looking at industrial ducting. The SMACNA code does give a minimum wall thickness of 22Ga for spiral and 20 GA for long seam for galvanized unreinforced pressure duct at 10" w.g., 27" -36" diameter. Then in the next paragraph in the commentary section It says " Designers should consult SMACNA's Round Industrial Duct Construction Manual" for : Systems other than clean air. Extended hangar spacing, Engineering design of bolted flanged joints. Etc..
B.E.
You are judged not by what you know, but by what you can do.
RE: Exhaust Ducting Thickness
https://law.resource.org/pub/us/cfr/ibr/005/smacna...
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RE: Exhaust Ducting Thickness
The section I was quoting from was page 3.3 and the other section I quoted was 3.2 Commentary .
B.E.
You are judged not by what you know, but by what you can do.
RE: Exhaust Ducting Thickness
https://law.resource.org/pub/us/cfr/ibr/005/smacna...
RE: Exhaust Ducting Thickness
RE: Exhaust Ducting Thickness
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RE: Exhaust Ducting Thickness