KEVOS® MAKEOS · Strength
Tube or Shell under External Pressure (Collapse Thickness and Factor)
How thick must this long tube or vacuum shell be to resist collapse under the outside pressure, and what safety factor does the chosen wall give after corrosion?
Design of a long round tube or cylindrical shell under external pressure or vacuum: elastic collapse pressure and the yield-limited pressure for the wall left after corrosion allowance, the governing mode and safety factor (as the tube collapse tool), the least wall that gives your required factor (found by search) plus allowance, the diameter-to-thickness ratio and the mass per metre.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Outside diameter | mm | Outside diameter of the tube or shell. |
| Wall thickness | mm | Nominal wall thickness. |
| Corrosion allowance | mm | Corrosion allowance removed before the check. |
| Elastic modulus | GPa | Elastic modulus at temperature. |
| Poisson’s ratio | Poisson’s ratio. | |
| Yield strength | MPa | Yield strength at temperature. |
| External pressure (net) | MPa | Net external pressure (0.1 MPa for full vacuum with atmosphere outside). |
| Safety factor required | Safety factor on collapse you require (often 3 or more for buckling; follow your code). | |
| Density | kg/m³ | Density for the mass per metre. |
Method and formulas
- Long tube elastic collapse p_cr = 2E ÷ (1 − ν²) × (t ÷ D_m)³; yield limit p_y = 2 S_y t ÷ D_m, with D_m = D − t and t after corrosion (as the tube collapse tool).
- Safety factor = smaller collapse pressure ÷ applied pressure.
- Least wall found by bisection on t for the required factor, plus corrosion allowance.
- Example: 2 mm (1.5 mm corroded) collapses elastically at 1.5523 MPa, a factor of 3.1047; 1.9832 mm is needed.
Limitations
- Long tube without stiffening rings; short shells between stiffeners are stronger.
- Out-of-roundness lowers the collapse pressure sharply: keep it within the code limit.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a vacuum pipe or vessel shell
- Check a heat-exchanger tube for shell-side pressure
- Check a submerged pipe
Who it is for
- Mechanical engineers
- Design engineers
- Inspection engineers
What you get
- Elastic and yield collapse pressures, governing mode and factor
- Least wall for the required factor
- D/t and mass per metre
Interpreting the result
- Collapse pressure rises with the cube of the wall ratio: a little more wall or a stiffening ring helps greatly.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 293–294. Topic reference; no source tables or recommended settings are reproduced.
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Open the Tube or Shell under External Pressure (Collapse Thickness and Factor) calculator
