Duct metal thickness

[op9]

I will be installing a large burner on an asphalt plant which requires a duct to be installed between fan outlet and burner. There will be two straight sections of duct in and out of an "Air distribution box" or plennum which will be situated below the burner. So the inlet horizontal duct will be about 1500mm long and 500 x 620 cross section. The outlet vertical duct from the "box" to the burner is about 700mm long and 720 x 720 cross section.Both ducts will be rigidly flanged to the box but connected by flexible expansion joints to both fan and burner.

What I would like to know is what would be the minimum thickness/ gauge of steel sheetmetal recommended to be rigid enough so as no "panting" or "oil canning" and associated noise will occur. The pressure in the duct will be say 4 kPa and the max air flowrate at 20,000 cubic metres/ hr. Minimum about 4,000.

Thanks in advance,
Rod.

Rod Nissen.
Combustion & Engineering Diagnostics

 

[willard3]

If you will convert this to inch/pound, I can help you.

 

[op9]

OK.
Inlet duct 60" long and 20" x 25"
Outlet duct 28" long and 28" x 28".
Air distribution box 45" x 45" x 28" high.
Pressure in duct 0.6 psi
Rate 11,770 cfm max minimum 2354 cfm.

Rod Nissen.
Combustion & Engineering Diagnostics

 

[dvd]

You need to get a copy of "Rectangular Industrial Duct Construction Standards" published by SMACNA.


Table of contents:

http://www.smacna.org/bookstore/pdf_toc/RectIP_04_TOC.pdf

Purchase from:

http://www.smacna.org/bookstore/index.cfm?fuseaction=search_results&cfid=6444462&cftoken=5944904

 

[trashcanman]

Use minimum 20 gage galvanized sheet steel. I don't know about the "panting" or "oil canning", but why worry about noise at an asphalt plant?

 

[op9]

You would be surprised these days how low the noise levels asphalt plants have to comply with. The combustion rumble in the drum has to be minimised and many burners which will comply with sound levels in a tight sealed solid boiler furnace fail dismally in a asphalt mixer or drier drum. We can usually get burners down to 80 - 85dbA at 10 ft. Any additional noise from whatever, we can do without! Working at nights is the most demanding requirement and unfortunately thats when some roadwork has to be done.

I do however think (respectfully)that 20gauge is a mite too small.

Rod Nissen.
Combustion & Engineering Diagnostics

 

[VinceNY]

Go with 18ga. and cross-break all sides. If your only using those 2 peices(28" Long & 60" Long), go with 16ga., It's kinda over kill, but with so few peices I can't imagine there being a bit cost difference.
However, like I said 18ga. cross-broken should be fine.

 

[op9]

Thanks Vince. I appreciate the advice.

Rod Nissen.
Combustion & Engineering Diagnostics

 

[ActiveSolar05]

Just fold your sheet metal so you have 1 or 2 longitudinal Ribs down the length of the duct on each face.....

jrr