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

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

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

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

or

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

where:

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

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

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

or

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

where:

Eq. 6
P = 2 St / Do

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

Related:

Reference:

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