Straight Pipe Under Internal Pressure Formula and Calculator per. ASME B31.5

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Straight Pipe Under Internal Pressure Formula and Calculator per. ASME B31.5

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Hydraulic and Pneumatic Design and Engineering

The required wall thickness of straight sections of pipe can be determined for metallic pipe with diameter–thickness ratios D_o / t > 4, the internal pressure design wall thickness, t, shall be calculated using eq. (1) or (2).

Preview: Straight Pipe Under Internal Pressure Calculator

Eq. 1
t = P D_o / [ 2 ( S + Py - P) ]

Eq. 2
t = P d / [ 2 ( S + Py - P) ]

where:

Eq. 3
P = 2 St / ( D_o - 2 y t )

NOTE: The following simpler alternative equations, which give somewhat greater wall thickness, may be employed:

Eq. 4
t = P D_o / ( 2 S )

Eq. 5
t = P d / [ 2 ( S - P) ]

where:

Eq. 6
P = 2 St / D_o

D_o = outside diameter of pipe, in. (mm).
d = inside diameter of pipe, in. (mm), excluding metal required for corrosion or erosion allowance, manufacturer’s minus tolerance, and any allowance required for the depth of internal threads or grooves.
d = inside diameter of pipe, in. (mm), excluding metal required for corrosion or erosion allowance, manufacturer’s minus tolerance, and any allowance required for the depth of internal threads or grooves.
P = internal design pressure, psi (kPa), or external design pressure, psi (kPa).
S = applicable allowable hoop stress, psi (kPa).
t = pressure design wall thickness, in. (mm), as calculated from eqs. (1) and (2) for internal pressure.
y = coefficient for materials indicated: for ductile nonferrous materials, use y = 0.4 (see Note); for ferritic steels, use y = 0.4 (see Note); for austenitic steels, use y = 0.4 (see Note). For cast iron, use y = 0.0.

Note: If D_o/t is in the range of 4–6, use y =d/(d + D_o) for ductile materials.

Reference:

ASME Code for Pressure Piping, B31.5, Refrigeration Piping and Heat Transfer Components