Bend / Elbow Wall Thickness

Minimum wall thickness of a pipe bend per ASME B31.3 para 304.2.1 (intrados governs)

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Engineering Tips

Minimum pressure-design thickness for a pipe bend. The same Barlow core as straight pipe with a bend correction factor I — the intrados (inside of the bend) needs the most metal and governs.

Bend thickness:

• t = P·D / [2·(S·E·W/I + P·Y)]

• I_intrados = (4(R1/D)−1)/(4(R1/D)−2)

• I_extrados = (4(R1/D)+1)/(4(R1/D)+2)

• I_crown = 1.0 (= straight pipe)

Recommended values

R1/D: 1.5 = long-radius elbow, 1.0 = short-radius elbow, 3.0/5.0 = pipe bends.
Allowable stress S: Take S at the design temperature from the code stress tables — never estimate.
E, W, Y: Match the pipe-thickness inputs: seamless E = 1.0, W = 1.0 below creep, Y = 0.4 for ferritic ≤ 482°C.

Limitations

Pressure only: Containment thickness only — flexibility, SIFs and sustained/occasional stresses are separate checks.
Forming thinning: Cold/hot forming thins the intrados. Add a bending allowance so the finished wall meets tm.

About the standards

ASME B31.3 para 304.2.1: pressure design of pipe bends (bend correction factor I).
ASME B31.3 para 304.1.2: straight-pipe pressure design (the crown case).

Bend / Elbow Wall Thickness

Input Parameters

Design Conditions

Geometry

Code Factors & Allowances