S235 grade CHS pressure rating help

[Andrew Robson]

Hello, I am trying to find the internal pressure rating of s235 circular hollow section black steel tube.
Is there a brighter spark than myself on here who either knows where to find the specs or how to calculate it from the specs for S235. (Which are for tensile strength, impact pressure, and NDT of the weld). The tube I want to use is 140 x 3 and will be subject to an internal pressure of 100psi.
Many thanks

 

[dan.taylor.1]

Im not sure it would ever be specified, pressure vessels always have a test after welding to be certified. You might be better with either seamless or a rolled and welded tube made from sheet. Then test to suit.

 

[Agroshield]

This will give you an idea of the concepts:

Stress in Thin-Walled Cylinders or Tubes

Hoop and longitudinal stress thin-walled tubes or cylinders.

www.engineeringtoolbox.com

The key terms are 'hoop stress' and 'longitudinal stress'.

Note that the end conditions (flat cap, hemispherical, etc.) of the tube can have a much greater influence on its structural properties/capacity than the straight bit in the middle.

 

[frank horton]

drawn tube or seamless is never as strong a seamed pipe....
with drawn tube the wall thickness can vary quite a bit....

 

[Kram]

I imagine if correctly welded it will be adequate, 100psi is not that much!
3mm is common for compressor tanks or propane cylinders that are refilled, they have enough thickness to allow some corrosion.

Single use, non refillable cylinders of the same pressure are much thinner, about 1mm wall.

Get a hydrostatic tester (its a high pressure manual water pump plus gauge, quite cheap on ebay). Test it to several times your working pressure. If it holds, it should be good.

 

[Andrew Robson]

Thank you all for the info, makes sense to do my own testing as we will be self certifying the end product.
The tube will have flat ends and the user pressure will be specified at 100psi possibly less.
Thanks agroshield, that link was just what I was looking for.
The wealth of knowledge and information on this site is incredible and it I should such a wonderful resource,
Thanks again,
Andrew