drilling · casing design
Casing Burst Pressure (Barlow)
Pburst = 0.875 × (2 Yp t)/D
click formula to derive ↑
Inputs
ksi
in
in
Description
Computes the API-rated internal burst pressure of a casing string using Barlow's thin-wall equation with the standard 0.875 design factor for wall-thickness manufacturing tolerance. This is the baseline burst design check applied to every casing string before running.
Variables
| Symbol | Unit | Description |
|---|---|---|
| Pburst | psi | Burst Pressure Rating |
| Yp | ksi | Minimum yield strength of the casing steel grade. 551.6 MPa (80 ksi) corresponds to N-80 grade; common grades range from K-55 (379 MPa/55 ksi) to P-110 (758 MPa/110 ksi). |
| t | in | Nominal casing wall thickness from the API tubular tally. |
| D | in | Specified outside diameter of the casing (e.g., 244.48 mm = 9-5/8 in). |
Assumptions
- Thin-wall assumption holds (D/t typically > ~20) — thick-wall tubulars deviate from Barlow and may be conservatively rated by this equation
- Steel yield strength used is the specified minimum (API grade minimum), not an actual mill test value
- No axial load or bending stress is present — combined loading reduces the effective burst rating (see casing_buoyed_weight for axial load context)
Limitations
- Does not account for biaxial stress effects from simultaneous axial tension/compression — see Yp reduction formula in API 5C3 for combined loading
- Connection burst rating is frequently lower than pipe-body burst rating and must be checked separately against the connection manufacturer rating
- Does not model burst behavior in the presence of corrosion, wear, or perforations
Use Cases
- → Casing string design verification: Confirm each casing string section meets the required burst design factor against the worst-case internal pressure (kick, stimulation, or displacement) it will see in service.
- → Stimulation treatment pressure limits: Set maximum allowable surface treating pressure during fracturing or acid jobs so that the casing burst rating is not exceeded.
- → Casing grade/weight selection: Compare burst ratings across candidate grade and weight combinations when optimizing a casing string design for cost.
Related Calculations
Region Notes
Permian Basin
Intermediate casing in the Wolfcamp/Bone Spring is commonly P-110, 9-5/8 in, 47-53.5 lb/ft to handle high-rate slickwater fracturing treating pressures often exceeding 10,000 psi surface.
Haynesville
Extreme treating pressures and HPHT conditions typically require P-110 or higher-grade casing with burst ratings well above 10,000-12,000 psi for production casing.
Global
The 0.875 design factor is an API-mandated minimum; many operators apply an additional company-specific safety factor (commonly 1.1-1.25) on top of the rated burst pressure.
References
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