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Minimum Wall Thickness
7.19 mm
Minimum Wall Thickness vs Design Pressure (P)
Formula
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.
Esempio Risolto
A 6" Sch pipe (OD=168.3 mm) at 10 MPa, S=137.9 MPa, E=1.0, CA=1.5 mm.
- 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
Domande Frequenti
What is weld joint efficiency?
It accounts for the quality of weld examination. Full radiographic exam: E = 1.0, spot radiography: E = 0.85, no radiography: E = 0.60. Higher examination quality allows higher efficiency and thinner pipe.
How do I select the actual pipe schedule?
After calculating minimum thickness, select the next heavier standard schedule (Sch 40, 80, 160, etc.) that exceeds the minimum. ASME B36.10 lists standard pipe schedules with their wall thicknesses.
What is corrosion allowance?
CA is extra thickness added to account for material loss over the design life. Typical values: 1.5-3 mm for carbon steel in mildly corrosive service, 0 for stainless steel in clean service.
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