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Restrained Pipe Longitudinal Stress Calculator and Equations per. ASME B31.9

Hydraulic & Pneumatics
Fluids Flow Design and Engineering

Pipe Restrained Longitudinal Stress Components Stress Calculator and Equations per. ASME B31.9

The restraint condition is a factor in the structural behavior of the pipeline. The degree of restraint may be affected by aspects of pipeline construction, support design,soil properties, and terrain. For purposes of design, this AMSE recognizes two axial restraint conditions, “restrained” and “unrestrained.”.

Pipe in which soil or supports prevents axial displacement or flexure at bends is "restrained:. Restrained piping may include the following:

(1) straight sections of buried piping
(2) bends and adjacent piping buried in stiff or consolidate soil
(3) sections of above ground piping on rigid supports

Piping that is freed to displace axially or flex at bends is "unrestrained". Unrestrained piping may include the following:

(1) above ground piping that is configured to accommodate thermal expansion or anchor movements through flexibility.
(2) bends and adjacent piping buried in soft or unconsolidated soil
(3) an un backfilled section of otherwise buried pipe - line that is sufficiently flexible to displace laterally or that contains a bend
(4) pipe subject to an end cap pressure force

Preview Pipe Restrained Longitudinal Stress Components Stress Calculator

Longitudinal Stress due to internal pressure restrained Pipe

Eq. 1
S_p = 0.3 · S_H

Longitudinal Stress due to internal pressure unrestrained Pipe

Eq. 2
S_p = 0.5 · S_H

The longitudinal stress due to thermal expansion in a restrained pie

Eq. 3
S_T = E · α ( T₁ - T₂ )

Where

S_H = hoop stress
E = the elastic modulus, psi (MPa), at the ambient temperature
T₁ = the pipe temperature at the time of installation, tie-in, or burial,°F (°C)
T₂ = the warmest or coldest pipe operating temperature,1 / °F ( 1 / °C )

If a section of pipe can operate either warmer or colder than the installed temperature, both conditions to T₂ may need to be examined.

Source:

ASME B31.9, Gas Transmission and Distribution Systems

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