Pipe Schedule Calculator Formula
Understand the math behind the pipe schedule calculator. Each variable explained with a worked example.
Formulas Used
Minimum Wall Thickness
min_thickness = pressure * outside_dia / (2 * allowable * weld_eff + 2 * pressure) + corrosionBarlow Thickness (no CA)
barlow_thickness = pressure * outside_dia / (2 * allowable * weld_eff)Variables
| Variable | Description | Default |
|---|---|---|
pressure | Design Pressure (P)(MPa) | 10 |
outside_dia | Pipe Outside Diameter (OD)(mm) | 168.3 |
allowable | Allowable Stress (S)(MPa) | 137.9 |
weld_eff | Weld Joint Efficiency (E) | 1 |
corrosion | Corrosion Allowance (CA)(mm) | 1.5 |
How It Works
Pipe Wall Thickness Design
The required pipe wall thickness depends on the internal pressure, pipe diameter, material allowable stress, and safety factors. The Barlow formula provides the starting point.
Barlow Formula
t = P × D / (2 × S × E)
The ASME B31.3 modified version: t = P × D / (2 × (S × E + P)) + CA
where P is pressure, D is outside diameter, S is allowable stress, E is weld joint efficiency, and CA is corrosion allowance.
Worked Example
A 6" Sch pipe (OD=168.3 mm) at 10 MPa, S=137.9 MPa, E=1.0, CA=1.5 mm.
pressure = 10outside_dia = 168.3allowable = 137.9weld_eff = 1corrosion = 1.5
- 01Barlow: t = 10 × 168.3 / (2 × 137.9 × 1.0) = 1683 / 275.8 = 6.10 mm
- 02ASME modified: t = 10 × 168.3 / (2 × (137.9 + 10)) + 1.5
- 03t = 1683 / 295.8 + 1.5 = 5.69 + 1.5 = 7.19 mm
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