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# Spiral Duct Weight

## Spiral Duct Weight

(OP)
Does anyone know the formula for finding the weight of a spiral lockseam duct? I have been looking online for a day, but I can only find weight charts, but not the actual formula. I'm trying to find the Lb/Ft for my company because I think that our weights are wrong. The attachment is a drawing of the lateral section of spiral lockseam pipe.

### RE: Spiral Duct Weight

No attachment

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### RE: Spiral Duct Weight

(OP)

I'm sorry if I didn't get a chance to respond. It's been hectic around here.

I know the steel is 5.395" wide coils.

I also know that the nominal weights are:
24 Ga. - .0276"
22 Ga, - .0336"

I would like the formula to be able to be changed for several diameters.

### RE: Spiral Duct Weight

First off figure out for each nominal length how much more steel is used in those seams.

This will give you a multiplier for the unit length you choose (ft or metre)

Then its Pi x D x thickness x density of steel x multiplier.
Note your "weights" are in fact thickness of pipe. Pretty thin!

Spiral might add a bit more but not much. Depends on the angle of the seam relative to axis of pipe. maybe add another 5%.

How far out are you from the catalogue - they SHOULD know better than you.

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Also: If you get a response it's polite to respond to it.

### RE: Spiral Duct Weight

(OP)
The "weights" was a typo from me. My bad. We have been using: W=(10.68*(D-(T/0.875))*(T/0.875))/0.956

T=Nominal Thickness
D= Diameter in Inches

For some reason nobody knows what the .956 is.

### RE: Spiral Duct Weight

Can't work that out.

Should be

3.142 x D x T x 0.28 x 1.15 x 1.05

The coil to length ratio is 1.15, the extra length for the spiral I reckon is 1.05.

All in inches, give you lb per linear foot.

How does that work?

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