Barlow’s Formula is a calculation used to show the relationship between internal pressure, allowable stress (also known as hoop stress), nominal thickness, and diameter. It is helpful in determining the maximum pressure capacity a pipe can safely withstand.
The formula is expressed as P=2St/D, where:
- P
- pressure, psig
- t
- nominal wall thickness, in inches(i.e. .375)
- D
- outside Diameter in inches
- S
- allowable stress in psi, which depends on the pressure being determined utilizing Yield or Tensile depending on what is trying to be determined
Specifically, Barlow’s Formula can be used to determine:
- Internal Pressure at Minimum Yield:
S = SMYS - minimum yield for grade of pipe - Ultimate Bursting Pressure:
S = SMTS - minimum tensile strength for grade of pipe - Maximum Allowable Operating Pressure:
S = SMYS - reduced by a design factor - Mill Hydrostatic Test Pressure:
S = SMYS - reduced by a design factor depending on OD and grade
While this calculator is useful when planning your piping project, we recommend you contact us if you need additional information or have unusual or special applications.
Internal Burst Pressure Chart
| SCHEDULE 5S | SCHEDULE 10S | SCHEDULE 40S | SCHEDULE 80S | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Nominal I.P.S. (in.) | Nominal O.D. (in.) | Wall (in.) | Pressure (p.s.i.) | Wall (in.) | Pressure (p.s.i.) | Wall (in.) | Pressure (p.s.i.) | Wall (in.) | Pressure (p.s.i.) |
| 1/8 | 0.405 | 0.049 | 18150 | 0.068 | 25175 | 0.095 | 35175 | ||
| 1/4 | 0.54 | 0.065 | 18050 | 0.088 | 24450 | 0.119 | 33050 | ||
| 3/8 | 0.675 | 0.065 | 14450 | 0.091 | 20225 | 0.126 | 28000 | ||
| 1/2 | 0.84 | 0.065 | 11600 | 0.083 | 14825 | 0.109 | 19475 | 0.147 | 26250 |
| 3/4 | 1.05 | 0.065 | 9275 | 0.083 | 11850 | 0.113 | 16150 | 154 | 2200 |
| 1 | 1.315 | 0.065 | 7425 | 0.109 | 12450 | 0.133 | 15175 | 0.179 | 20425 |
| 1 1/4 | 1.66 | 0.065 | 5875 | 0.109 | 9850 | 0.14 | 12650 | 0.191 | 17250 |
| 1 1/2 | 1.9 | 0.065 | 5125 | 0.109 | 8600 | 0.145 | 11450 | 0.2 | 15800 |
| 2 | 2.375 | 0.065 | 4100 | 0.109 | 6875 | 0.154 | 9750 | 0.218 | 13775 |
| 2 1/2 | 2.875 | 0.083 | 4325 | 0.12 | 6250 | 0.203 | 10600 | 0.276 | 14400 |
| 3 | 3.5 | 0.083 | 3550 | 0.12 | 5150 | 0.216 | 9250 | ||
| 3 1/2 | 4 | 0.083 | 3100 | 0.12 | 4500 | 0.226 | 8475 | ||
| 4 | 4.5 | 0.083 | 2750 | 0.12 | 4000 | 0.237 | 7900 | ||
| 5 | 5.563 | 0.109 | 2950 | 0.134 | 3625 | 0.258 | 6950 | ||
| 6 | 6.625 | 0.109 | 2475 | 0.134 | 3050 | 0.28 | 6350 | ||
| 8 | 8.625 | 0.109 | 1900 | 0.148 | 2575 | 322 | 5600 | ||
| 10 | 1.75 | 0.134 | 1875 | 0.165 | 2300 | 0.365 | 5100 | ||
| 12 | 12.75 | 0.156 | 1825 | 0.18 | 2125 | 0.375 | 4400 | ||
| 14 | 14 | 0.156 | 1675 | 0.188 | 2025 | ||||
| 16 | 16 | 0.165 | 1550 | 0.188 | 1775 | ||||
| 18 | 18 | 0.165 | 1375 | 0.188 | 1575 | ||||
| 20 | 20 | 0.188 | 1400 | 0.218 | 1625 | ||||
| 24 | 24 | 0.218 | 1375 | 0.25 | 1550 | ||||
| 30 | 30 | 0.25 | 1250 | 0.312 | 1550 | ||||
*Bursting pressure calculated using Barlow's formula: P = 2ST/D
S=75,000 psi fiber stress
T=nominal wall
D=nominal O.D.=outside diameter
I.P.S.=inside pipe size
Download Printable Version of the Chart
Frequently Asked Questions About Barlow's Formula
What Does Barlow's Formula Determine?
Barlow's Formula is an equation that determines the relationship of internal pressure, allowable stress, nominal thickness, and diameter for pipe products.
What Type of Product is the Barlow's Formula Calculator Used For?
Barlow's Formula Calculator can be used to determine the maximum pressure capacity of line pipe. Worldwide pipe offers line pipe to a wide range of industries.
What is Hoop Stress?
Hoop Stress, also known as allowable stress, is the stress in a pipe wall. It is the circumferential force per unit areas (Psi) in the pipe wall caused by internal pressure.
What is the Hoop Stress Formula for Pipe?
The standardequationforhoop stressis H= PDm/2t. In this equation, His allowable or hoop stress, the P is the pressure, t is the thickness of the pipe, and D is the diameter of the pipe.
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