KEVOS® MAKEOS · Strength
Tube Collapse under External Pressure
At what external pressure will this long tube collapse, and is the margin enough?
Elastic buckling (collapse) pressure and yield-limited pressure of a long thin round tube under external pressure, with the safety factor against an applied pressure.
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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 | Minimum wall thickness. |
| Elastic modulus | GPa | Elastic modulus from the material data sheet (steel is typically about 200 GPa). |
| Poisson’s ratio | Poisson’s ratio (about 0.3 for steel). | |
| Yield strength | MPa | Minimum yield strength from the material certificate or specification. |
| External pressure (net) | MPa | Net external pressure (outside minus inside); full vacuum is about 0.1 MPa. |
| Required safety factor | Factor required by your code (external pressure codes commonly use about 3). |
Method and formulas
- Mean diameter Dm = D − t.
- Elastic collapse (long tube): p_cr = 2E ÷ (1 − ν²) × (t ÷ Dm)³.
- Yield limit: p_y = 2 S_y t ÷ Dm; the lower governs.
- Example: a 100 × 2 mm steel tube collapses at about 3.7362 MPa; the factor at 0.5 MPa is 7.4724.
Limitations
- Long, perfectly round tubes; out-of-roundness and short lengths between stiffeners change the result substantially.
- Pressure vessels under external pressure must be designed to their code charts (e.g. AS 1210, ASME VIII).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check tubes and shells under vacuum
- Check heat exchanger tubes with shell-side pressure
- Screen a jacketed vessel inner shell
Who it is for
- Design engineers
- Structural and mechanical engineers
- Engineering students
What you get
- Elastic collapse pressure
- Yield-limited pressure
- Governing collapse pressure and safety factor
Interpreting the result
- Stiffening rings shorten the effective length and greatly raise the collapse pressure.
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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