hollow cylinders under high external pressure

[neondd]

I try to design a hollow cylinder which can be used under high hydrostatic pressure, about 60Mpa.
But I cannot find any formulars for pressure vessels under external pressure.
Which property is the most important?
Buckle modulus? compressive strengh?

 

[desertfox]

Hi neondd

Have a look in ASME VIII or PD5500 they are codes for pressure vessels.

regards desertfox

 

[unclesyd]

Here is quick and somewhat conservitive calculator for the collapsing pressure if this purely for mechanical use. Please read the text above the calculator.
A lot of the pipe tables from vendors have the collapsing pressure.
If you need to accurately work to a certain pressure comeback with the restraints, including working media.
If you want a more detailed calculation or there are people or safety involved you should post a little more information as to size and use to get a more definitive direction such as those posted by desertfox.

http://www.rathmfg.com/collapsingpressure.htm

If there is any question at all please post it as there are well qualified people to steer you in the right direction.

 

[neondd]

Thank you

 

[neondd]

What is the most important property for the material?
the stiffness, strengh or buckle modulus?

 

[desertfox]

Hi neondd

Depending on the diameter to length ratio buckling of your vessel might be the worst case, however you need to give dimensions of your vessel so that we can help you further and its application as requested by "unclesyd".

regards desertfox

 

[sreid]

"Roark's Formulas for Stress and Strain" gives formulas for externally pressurized thick walled cylinders.

 

[CRG]

It is the ratio of material thickness to cylinder diameter that is the most critical. Any eccentrics will affect the collapse pressure of the cylinder. In the “Piping Handbook” by Crocker & King there is a discussion of this and it references “Theory of Elastic Stability,” by S. Timoshenko. If you can find a copy of the Piping Handbook, there are equations referencing stability and collapse pressure. Looking at the equation, the critical ration of diameter to thickness is a function of Poisson's ratio squared, (t/d) squared, yield strength, and modulus of elasticity. So it looks like yield strength and modulus of elasticity are of equal importance. And Posson's ratio and (t/d) being the most important.

CRG

 

[bvi]

The most critical material property is the elastic modulus, for elastic buckling. For thick walled cylinders, elastic-plastic buckling occurs, in which case it is the tangent modulus (draw a line tangent to the stress strain curve, the slope of the line is the tangent modulus). In the Section VIII rules, the graphs to determine B are used to determine the tangent modulus, when the stress is between the proportional limit and the 0.2% yield strength. This is the region for elastic-plastic buckling.
As stated above, the most critical geometric property is D/t ratio.