Flowline thickness calculation?

Asked by lilianlope 5 years, 11 months ago | 4 Answers

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


4 Answers

1
beccadonetti 5 years, 11 months ago

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


1
beccadonetti 5 years, 11 months ago

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
beccadonetti 5 years, 11 months ago

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


0
beccadonetti 5 years, 11 months ago

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:

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