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Barlow's formula

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Barlow's formula

Unread postAuthor: DYI » Fri Apr 25, 2008 6:35 pm

Just a quick question, but I believe I'm doing something wrong here.

Using Barlow's formula, I ended up with a burst pressure of ~4300psig for a 4" Schedule XXS pipe made of plumbing grade steel. As far as I know, that's closer to the rated pressure of 4" Schedule XXS than to the burst pressure.

Can someone else who knows what they're doing try this and see what answer they come up with?
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Unread postAuthor: clide » Fri Apr 25, 2008 7:22 pm

I don't really see much that could go wrong with that equation. What value did you use for material strength? In order to get ~4300 psi bursting pressure for 4" XXS I need to use a material strength of around 10000 psi, which is pretty darn low for steel.
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Last edited by clide on Fri Apr 25, 2008 7:26 pm, edited 1 time in total.
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Unread postAuthor: pat123 » Fri Apr 25, 2008 7:24 pm


X = laminate wall thickness required (in)
P = operating pressure (psi)
D = inside diameter of pipe (in)
γ = design stress (psi)

Is this the one you used?
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Unread postAuthor: Larda » Fri Apr 25, 2008 7:58 pm

If i'm not wrong a 100mm OD (4") pipe with 5mm (0,2") thick walls made of S355JR with tensile strength of 600N/mm2 (87000psi) will have a burst pressure of 600bar (8700psi)
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Unread postAuthor: SpudFarm » Sat Apr 26, 2008 8:29 am

Larda got it to the line..

BTW is that the pipe you was going to use for my hybrid?
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Unread postAuthor: cdheller » Sat Apr 26, 2008 1:49 pm

I'm not coming up with any of the above answers .

using online calculator at

http://www.engineersedge.com/calculator ... t_calc.htm

Engineers Edge Design & Engineering Resources
OD (in) 4.50 (in)
Wall (in) .674 (in)
Material Strength 35000 (psi)
Safety Factor (working) 2 See Above

Calculated Working Pressure 7500
Calculated Bursting/Yield Pressure 15000

that was far enough of everyone else's numbers I looked up pipe charts to see what the #*&@.

using published charts at
http://www.engineeringtoolbox.com/steel ... -d_43.html
answer is about the same

Double Extra Strong Wrought Steel Pipes - XXS
Pipe Dimension
(inches) Double Extra Strong - XXS
Bursting Pressure
(psi) Working Pressure
1/2 28000 3500
3/4 23460 2930
1 21780 2720
1 1/4 18400 2300
1 1/2 16840 2110
2 14680 1840
2 1/2 15355 1920
3 13710 1710
3 1/2 15900 1990
4 14965 1870
5 13475 1690

I may be ignorant of what thickness you have .
the closest sch to X.X.strong pipe is sch.160, but not same.
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