🛢️ Barlow's Formula Calculator
Calculate the internal, allowable, and ultimate burst pressure of a pipe using Barlow's formula.
🛢️ Barlow's Formula Calculator
Calculate the internal, allowable, and ultimate burst pressure of a pipe using Barlow's formula.
✅ Calculation Result
Pressure Limits Overview
Calculator Description
Barlow's formula calculator is derived from the circumferential (hoop) stress equilibrium of a pipe or pressure vessel. It gives the pressure at minimum yield, the ultimate burst pressure, and the maximum allowable pressure with design factors applied — a foundation of pipeline design, construction and remaining-life assessment.
What this calculator finds
Enter outside diameter D_o, wall thickness t, yield/ultimate strengths (S_y, S_t) and the design/joint/temperature factors (F_d, F_e, F_t) to get yield pressure P_y, burst pressure P_t and allowable pressure P_a.
Why it matters
- Setting pipeline design (MOP) pressure and burst safety margin
- Assessing remaining allowable pressure of in-service pipe (wall loss, temperature)
- Reviewing how factors (welded joint, high temperature) affect allowable pressure
Formula
Barlow's Formula
Derived from hoop-stress equilibrium σ = P·D/(2t), using the outside diameter D_o in the denominator (other variants use the mean diameter).
- P_y — Pressure at yield [MPa (Metric) or psi (Imperial)]
- P_t — Burst (ultimate) pressure [MPa or psi]
- P_a — Maximum allowable pressure [MPa or psi]
- S_y, S_t — Yield / Ultimate tensile strength [MPa (Metric) or psi (Imperial)]
- t — Wall thickness [mm (Metric) or in (Imperial)]
- D_o — Pipe outside diameter [mm (Metric) or in (Imperial)]
- F_d, F_e, F_t — Design / Joint / Temperature factors (often 0.72 · 1.0 · 1.0)
How the formula works
- Doubling thickness doubles the pressure it can hold; larger D_o lowers pressure (inverse proportionality).
- P_a multiplies yield strength by the design factor F_d (e.g. 0.72), so it is well below P_y — that is the safety margin.
- Joint factor F_e (welded-joint reduction) or temperature factor F_t (high-temp strength drop) below 1 lowers allowable pressure.
Worked example
For D_o = 219.1 mm, t = 8.18 mm, S_y = 240 MPa, S_t = 415 MPa, F_d = 0.72, F_e = F_t = 1.0: P_y = 2×240×8.18/219.1 ≈ 17.9 MPa, P_t = 2×415×8.18/219.1 ≈ 31.0 MPa, P_a = 17.9×0.72 ≈ 12.9 MPa.
Useful Tips
Practical tips
- Pipeline design usually checks burst margin (typical FS ≥ 1.25–2.0) and strain limits, not just yield.
- At high temperature S_y, S_t drop, so apply F_t or use temperature-dependent strength tables.
- For corroded pipe, enter the measured minimum t to assess remaining P_a.
Limitations & cautions
- Barlow's formula is a thin-cylinder ideal-stress relation; thick walls, plasticity and flaws (cracks) are not captured.
- Real burst pressure varies with weld quality, residual stress and ovality, so apply conservative factors.
- Keep units consistent (Metric MPa·mm vs Imperial psi·in).