ASME 31.3 Piping Materials - Allowable Pressure Calculator
Calculate ASME 31.3 allowable pressure
The ASME code B31.3 recommends allowable tensile stress levels in pipe materials.
- maximum stress to be applied on a structural material
The equations used in B31.3 are
t = P D / (2 (S E + P Y) (1)
where
t = thickness of pipe (in)
P = internal pressure in pipe (psi)
D = outside diameter of pipe (in)
S = allowable tensile stress (psi)
E = quality factor for the piping according ASME 31.3
Y = wall thickness coefficient according ASME 31.3 (y = 0.5 for thin pipes and y < 0.5 for thick pipes)
or
t = P (d + 2 c) / (2 (S E - P (1 - Y)) (2)
where
d = inside diameter of pipe (in)
c = sum of the mechanical allowances (thread or groove depth) plus corrosion and erosion allowances (in) - typical 0.02 in where tolerances are not specified
Eq. (1) can be rearranged to express allowable internal piping pressure as
p = 2 t S E / [D - 2 t Y] (1b)
Eq. (1b) can be modified to compensate for thinner pipes due to the thickness tolerances used by the industry.
where
α = thickness tolerance (%)
For ASTM A53, A106 and other codes the accepted thickness tolerances are 12.5%.
Example - Allowable Pressure in a Steel Pipe
The allowable pressure in a 4 inch schedule 40 carbon steel pipe with outside diameter 4.5 in, wall thickness 0.237 in, thickness tolerance 12.5% and allowable stress 16000 psi - can with quality factor E for steel 0.8 and wall thickness coefficient 0.4 be calculated as
p = 2 (0.237 in) (1 - 12.5 / 100) (16000 psi) (0.8) / ((4.5 in) - 2 (0.237) 0.4)
= 1232 psi
ASME 31.3 Allowable Pressure Calculator (from eq. 1b)
Quality Factors E
Some quality factors according ASME 31.3:
- furnace butt weld joint, continuous weld joint, straight seam: 0.6
- electrical resistance weld joint, straight or spiral seam: 0.85
- double butt weld joint, straight or spiral seam, 100% radiographed: 1.0
Thickness Coefficients Y
The values of coefficient Y depends on type of material, temperature and thickness limits.
Thickness coefficients when t > D / 6:
Y = (d + 2 c) / (D + d + 2 c) (3)
Thickness coefficients when t < D / 6:
| Material | Temperature (oF) | |||||
|---|---|---|---|---|---|---|
| < 900 | 950 | 1000 | 1050 | 1100 | > 1150 | |
| Ferritic steels | 0.4 | 0.5 | 0.7 | 0.7 | 0.7 | 0.7 |
| Autenitic steel | 0.4 | 0.4 | 0.4 | 0.4 | 0.5 | 0.7 |
| Other ductile materials | 0.4 | 0.4 | 0.4 | 0.4 | 0.4 | |
| Cast iron | 0.0 | |||||
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