# Calculate min thickness of steel pipe

1. Nov 3, 2010

### cherish

Yes, first to say that this's really a basic matter but i've found all around a week & still facing difficulty, hope someone has patient to help me an answer then i can go further myself

As in the attached picture, a few ones have done their calculations & showed the different wall thickness of pipe from 30~60 mm but my boss just made his hand calculation & said that we only need the wall pipe thickness from 5~10 mm.
I confuse what is the correct equation of bending moment to find the necessary thickness that the pipe would not be deformed (use safety factor ~1.5) & where to put the Min. yield strength 235 (mpa) into.
We have the OD = 210 mm, steel grade S235JRG2, total uniform load along 200mm at center from bearing mass 600 kg.
Sorry for long post, looking for a detail formular or just show me which step should i do, thanks many in advanced.

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2. Nov 3, 2010

### PhanthomJay

I am not familiar with the metric units, so I don't have a good feel for the numbers. Nonetheless, you must first calculate the maximum bending moment at the center of the pipe with the ends free to rotate but not translate vertically. You can do this with shear and moment diagrams or with a free body diagram, using simple supports for the end conditions. Once you find maximum moment, then just apply the bending stress formula to determine the section modulus required based on the max (min) stress at the outer fibers, which is given with the appropriate safety factor applied. You can then look up (or derive) the section modulus of the pipe as a function of its thickness, and solve for t. Or ask your boss how he did it and have him show you, why is he/she keeping it a secret? Or is your boss your teacher?

3. Nov 4, 2010

### nvn

cherish: If this pipe is statically loaded, and you are sure your dimensions and applied load values are correct in the diagram, then your OD is far larger than necessary for this application. Hence, the midspan design currently appears to be governed by stability, not global bending strength nor shear strength. Therefore, for the global midspan cross section to be stable (not including localized stresses at the supports and applied load), the pipe wall thickness would need to be 3.5 mm. Therefore, a pipe wall thickness of 5 mm perhaps sounds adequate (although I did not attempt to analyze the stress at the supports).

Therefore, I think the question becomes, how could one verify, by hand calculations, whether or not the tube is adequate to withstand the localized support loads, and the localized applied load? The support load is applied to, e.g., one half of the tube perimeter, and varies as a function of perimeter (?). However, you did not yet give us the material and thickness of the two support plates in your diagram.

4. Jan 14, 2011

### hamdan_neo

hello, i donno if u already solved this problem,
but the way to determine the thickness of the pipe is this :
1- chose an approximate internal diameter of your own
2- check the standard pipe sizes to get the exact internal diameter that is close to the one you chose, you can get also the external diameter.
3- based on the pipe material ans system operating pressure determine the tensile strength (S) and chose a factor of safety (FS)
4-calculate the burst pressure (BP) and working pressure (WP)
where BP=(2tS/ID) t:thickness, S tensile strength, ID internal diameter
WP= BP/FS
5- an acceptable pipe size is the one that meets your requirement and has a working pressure equal or greater than the system operating pressure.

hope this will give you a hand