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# CSA Z662 Flexibility and stress analysis — Stress design for restrained portions of pipeline systems

Note: In the following equations, compressive stresses are negative and tensile stresses are positive in the algebraic equation.

4.7.1 Combined hoop and longitudinal stresses Unless special design measures are implemented to ensure the stability of the pipeline, the hoop stress due to design pressure combined with the net longitudinal stress due to the combined effects of pipe temperature changes and internal fluid pressure shall be limited in accordance with the following formula: Sh – SL ≤ 0.90 S × T

Note: This formula does not apply if SL is positive (i.e., tension). where Sh = hoop stress due to design pressure, MPa, as determined using the formula given in Clause 4.6.5 SL = longitudinal compression stress, MPa, as determined using the following formula: SL = νSh – Ecα(T2 – T1)

where

ν = Poisson’s ratio

Ec = modulus of elasticity of steel, MPa

α = linear coefficient of thermal expansion, °C^–1

T2 = maximum operating temperature, °C

T1 = ambient temperature at time of restraint, °C

S = specified minimum yield strength, MPa

T = temperature factor (see Clause 4.3.9)

4.7.2 Combined stresses for restrained spans 4.7.2.1 For those portions of restrained pipelines that are freely spanning or supported above ground, the combined stress shall be limited in accordance with the following formula:

Sh – SL + SB ≤ S × T

where

Sh = hoop stress due to design pressure, MPa, as determined using the formula given in Clause 4.6.5

SL = longitudinal compression stress, MPa, as determined using the formula given in Clause 4.7.1

SB = absolute value of beam bending compression stresses resulting from live and dead loads, MPa

S = specified minimum yield strength, MPa

T = temperature factor (see Clause 4.3.9)

4.7.2.2 The maximum beam bending compressive stress shall be calculated using a beam column analysis or other acceptable method and the stability of such free spans shall be checked to ensure that the axial compressive load due to pressure plus positive temperature differential is less than 0.8 of the elastic critical buckling load. 4.7.3 Anchors and restraints Expansion of partially restrained buried pipelines can cause unacceptable movement, stress or strain at points where such pipelines terminate, change direction, or change size. Unless such unacceptable movements are restrained by suitable anchors or ground restraint, necessary flexibility shall be provided.

CSA Z662-15 (Oil and gas pipeline systems)

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