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What is the ASME B31.3 pipe wall thickness formula?

Per ASME B31.3 Paragraph 304.1.2, the minimum required wall thickness is t_m = (P × D) / (2 × (S × E + P × 0.4)) + corrosion allowance, where P is internal design pressure, D is outside diameter, S is allowable stress, and E is joint efficiency.

What is the typical joint efficiency (E) for ASME B31.3?

E = 1.0 for seamless or 100% radiographed pipe, E = 0.85 for spot radiographed, and E = 0.80 for non-radiographed welds. Refer to ASME B31.3 Table A-1B for specific values.

How much corrosion allowance should I add?

Corrosion allowance varies by service. Common values: 1.5 mm (0.06 in) for carbon steel in benign service, 3.0 mm (0.12 in) for corrosive service, and 0 for stainless steel in clean service. The owner specifies the value based on service life expectations.

ASME B31.3 Pipe Wall Thickness Calculator

Design Pressure, P (psig)

Outside Diameter, D (in)

Allowable Stress, S (ksi)

Joint Efficiency, E

Corrosion Allowance (in)

Code Compliance Note

Calculated per ASME B31.3 Paragraph 304.1.2, Eq (3a). The formula accounts for the 0.4P term which accounts for the non-linear relationship between pressure and wall thickness in thin-walled cylinders. For thick-walled pipe (D/t < 6), use the Lame equation per Paragraph 304.1.2(b).

Joint Efficiency Values

E = 1.0 for seamless pipe or 100% radiographed butt welds · E = 0.85 for spot radiographed · E = 0.80 for non-radiographed. Always verify against ASME B31.3 Table A-1B for the specific material grade.