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# Flowline thickness calculation?

What formulas do people in Flow Assurance use to calculate pipeline wall thickness?

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answered Oct 22, 2014 by (1,280 points) | selected Apr 25, 2015 by odadmin

Pipeline wall thickness is calculated as per API RP-1111, ASME B31.8 (multiphase pipeline) and ASME B31.4 (Water injection pipeline) using the following expression:

tnom = {[(Pi - Po)D] / [2(F1 - Lf - T - sy)]} + tcorr

Where:

Pi = Internal Pressure

Po= External hydrostatic pressure

Lf = Longitudinal joint weld factor (1.00)

T = 1.0, temperature derating factor (Equals 1.0 for T<250°F)

sy= Specified Minimum Yield Stress

tcorr = Internal corrosion allowance

D = Pipe outside diameter

F1 = Design Factor

tnom = Nominal pipe thickness

+1 vote
answered Oct 22, 2014 by (1,280 points)

To calculate the external pressure of the pipe, the collapse pressure must exceed the net external pressure everywhere along the pipeline in accordance with API 1111 as follows:

Where:

f0 = Collapse factor (A 0.70 Collapse factor is required for seamless or ERW pipe)

Pc= Collapse pressure of the pipe

Pe = elastic collapse pressure of the pipe

Py = yield pressure at collapse

E = modulus of elasticity

v = Poisson’s ratio (0.3 for steel)

+1 vote
answered Oct 22, 2014 by (1,280 points)

To calculate Buckling due to combined Bending Strain and External Pressure, use API 1111, 1999 as follows:

answered Oct 22, 2014 by (1,280 points)

Regarding buckle resulting from excessive bending or another cause that may propagate (“travel” along the pipeline). Offshore hydrocarbon pipelines can fail by a propagating buckle caused by the hydrostatic pressure of the surrounding seawater on a pipeline with a diameter-to-wall-thickness ratio that is too high. The minimum wall thickness, which will prevent the formation of propagating buckles, is as follows: