888.903.3433 # Barlow's Formula Calculator

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.

Enter only 3 numeric values.

ATTRIBUTES VALUE
P = Pressure
psig
t = Nominal Wall Thickness
inches
D = Outside Diameter
inches
S = Allowable Stress
psi.

### Internal Burst Pressure Chart

SCHEDULE 5SSCHEDULE 10SSCHEDULE 40SSCHEDULE 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

#### 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 standard equation for hoop stress is H = PDm /2t. In this equation, H is 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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