Collapse pressure of a thick walled cylinder

[vtmike]

Hi,

I am trying to find the collpase pressure of a thick walled cylinder (thick walled since thickness, t>ro/10). The yield of the material is 130000 psi. The cylinder has a inner radius of ri=1.8125in, outer radius of ro=2.25in, and a length L=48in.
Can anyone provide me a reference to calculating the collapse pressure? I am also not sure if I can use Lame's equation to find the collpase pressure?
Found one formula in the design handbook but it is not for a cylinder closed at both ends, and they have no information on how they arrived at the equation.

Thanks,
Mike

 

[hacksaw]

Marks handbook has good coverage, so does the ASME pressure vessel code, although the Lame formulas are a good starting point.

The end-closure will have some impact on the collapse pressure,as will the tube filling (liquid,gas, etc.).

 

[vtmike]

Yeah I tried to use Lame's equations but am getting unreasonable answers. I have attached my procedure in which I have tried to use Lame's equations.I know I'm doing something wrong but can't point to it.

 

[prex]

What do you mean by unreasonable values? Too low or too high?

EN13445 gives a formula to calculate the buckling pressure for a cylinder of given length, but of course, with your proportions and as you correctly implied, it is much higher (about 3 times) than the pressure required to fully yield the thickness.
The latter is simply calculated as Yt/r=28 ksi. This value would be the basis for determining the allowable external pressure, not far from half of it.
But if you are trying to determine the actual collapse pressure, then things are more complex.
First observation is that, if your pipe was a solid bar, then virtually no collapse would be observed for any pressure. So your pipe will go well beyond the above value without displaying any failure, with only a small permanent reduction in diameter.
Now how far will it go? I suppose that some answers could be found in the literature, but suspect that if the pipe has no dimensional or material non uniformities, it would resist up to the buckling pressure (around 80 ksi).

prex

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[hacksaw]

You might try Brock's paper. It goes into the pressure ratings of thick walled tubes, although the vessel codes also cover the external pressure rating.

via Google search for

stress analysis of thermowells

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