Burst Pressure of Thin Cylinder Calculator

For a thin-walled cylinder under internal pressure, the hoop stress is approximated as:

• Hoop stress: σ_h = P·D / (2·t)
• Axial stress: σ_a = P·D / (4·t)

This calculator estimates burst pressure by setting hoop stress equal to a reduced strength value:

• Allowable stress used: S_allow = (Strength × Efficiency) / SafetyFactor
• Burst pressure: P_burst = 2·t_net·S_allow / D_eff

Thin-wall models are best when t/D ≤ 0.1. If your ratio is higher, consider thick-cylinder methods.

1. Enter diameter and specify whether it is inner or outer.
2. Enter wall thickness and optional corrosion allowance.
3. Select a strength basis and provide the strength value.
4. Set joint efficiency and an appropriate safety factor.
5. Choose your preferred output pressure unit, then calculate.
6. Use CSV or PDF buttons to save results for documentation.

1) Why burst pressure matters

Burst pressure is an upper-limit estimate for internal pressure that drives the hoop stress to a selected strength level. Engineers use it to screen concepts, compare materials, and document margin before detailed code checks. It is commonly referenced in tubing, piping, pressure vessels, and hydraulic components. It is not a replacement for certified design calculations.

2) Thin-wall assumption and geometry

The thin-cylinder model assumes wall thickness is small compared with diameter, commonly expressed as t/D ≤ 0.1. Under this condition, stress is nearly uniform through the wall, and the classic relations σ_h = P·D/(2t) and σ_a = P·D/(4t) are reasonable. Many hand checks use inner or mean diameter; consistency matters more than the specific choice when t/D is small.

3) Material strength, weld efficiency, and safety factor

Strength input should match your intent: ultimate tensile strength for rupture screening, yield strength for conservative plastic onset checks, or a custom allowable stress from a specification. Joint efficiency reduces capacity for weld quality and inspection level; values often range from about 0.70 to 1.00. Safety factor then scales the usable stress downward; early estimates often use 1.5–3.0 depending on uncertainty and consequences.

4) Corrosion allowance and aging

Net thickness controls pressure capacity, so even small losses can matter. A 1 mm allowance on a 5 mm wall is a 20% reduction in thickness, which directly reduces burst pressure by roughly 20% in the thin-wall equation. Consider erosion, pitting, and manufacturing tolerance when selecting the allowance.

5) Typical ranges and quick sanity checks

For steel tubes with strengths around 300–700 MPa, moderate diameters, and a few millimeters of wall thickness, computed burst pressures commonly fall in the tens of MPa (hundreds of bar). As a quick check, doubling thickness approximately doubles burst pressure, while doubling diameter roughly halves it. If your output seems extremely high, re-check units, diameter reference, and whether a thick-wall method is more appropriate.

6) Interpreting hoop and axial stresses

At the computed burst pressure, hoop stress is about twice the axial stress. This is why hoop stress is usually governing for closed-end cylinders. If axial loading, bending, thermal gradients, or external pressure exists, a combined-stress assessment is needed instead of a single-equation estimate.

7) Limitations and next-step methods

Thin-wall formulas ignore through-thickness stress gradients and do not model ductile instability, notch effects, or fracture mechanics. When t/D is above 0.1, consider thick-cylinder theory (Lamé equations). For pressure equipment, apply the governing code, material allowables at temperature, and required test factors. When fatigue is relevant, also evaluate pressure cycling and stress concentrations.

1) What does this calculator output represent?

It estimates the internal pressure that makes the hoop stress reach a reduced strength value after applying joint efficiency and safety factor, using thin-cylinder relations.

2) Should I enter inner or outer diameter?

Use inner diameter when available. If you only have outer diameter, select the outer option; the tool estimates inner diameter by subtracting twice the net thickness.

3) How do corrosion allowance and tolerance affect results?

The tool uses net thickness (thickness minus allowance). Lower net thickness reduces burst pressure nearly proportionally, so even small allowances can create noticeable changes.

4) Why is there a thin-wall ratio warning?

When t/D exceeds about 0.1, stresses vary through the wall and thin-wall equations become less accurate. In that case, thick-cylinder models or code formulas are recommended.

5) What joint efficiency value should I use?

Use a value consistent with your fabrication and inspection assumptions. Fully inspected butt welds may be near 1.0, while lower inspection levels or certain joint types may require smaller values.

6) Does the strength basis change the math?

The equation is the same, but the meaning changes. Ultimate strength gives a rupture-oriented estimate, yield strength is more conservative, and custom allowable stress lets you use a specified limit directly.

7) Can I use these results for final compliance reports?

Treat the result as a screening or documentation aid. Final designs should follow the applicable standard or code, include temperature effects, and consider additional loads and failure modes.