The Toolkit
The working, laid bare to check.
Barlow's formula, the code factors, and your pipe — with every step of the working shown, because engineers check.
How this is calculated.
Barlow relates pressure to pipe geometry and grade. Design pressure is where hoop stress reaches the code design factor of SMYS; test pressure applies the test factor above it. Every figure is substituted so you can check it against your project specification and code edition.
Pdesign = 2·S·t·F / D (S = SMYS, t = wall, F = design factor, D = OD) Ptest = Pdesign · testFactor hoop %SMYS = Ptest·D / (2·t·S)
Standards · ASME B31.4 · ASME B31.8
Questions
Which design factor do I use?
It depends on location class (B31.8) or service (B31.4). Common values: 0.72 for cross-country liquid lines; lower near populated areas. Your line's design basis governs.
B31.4 or B31.8?
B31.4 covers liquid petroleum pipelines; B31.8 covers gas transmission and distribution.
What is SMYS?
Specified Minimum Yield Strength — the grade's guaranteed yield stress, the S in Barlow's P = 2St/D.
Need this done in the field?
Talk to our engineersIndicative per ASME B31.4/B31.8 methodology. Verify against your project specification and current code edition.
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