The " Mill Test Pressure" refers to the hydrostatic (water) pressure applied to the pipe at the mill to assure the integrity of the pipe body and weld. P a = 2 (30000 psi) 0.72 1 1 (0.5 in) / (8.625 in)īarlow's formula is based on ideal conditions and room temperatures. The " Maximum Allowable Pressure" for the liquid pipe line used in the examples above with F d = 0.72, F e = 1 and F t = 1 - can be calculated as S y = yield strength (psi) F d = design factorį e = longitudinal joint factor F t = temperature derating factor Typical Design Factors - F d
P a = maximum allowable design pressure (psig) Barlow's formula can be used to calculate the maximum allowable pressure by using design factors as Working pressure is a term used to describe the maximum allowable pressure a pipe may be subjected to while in-service. = 5565 psi Working Pressure or Maximum Allowable Pressure The ultimate pressure for the pipe used in the example above with ultimate (tensile) strength 48000 psi can be calculated as S t = ultimate (tensile) strength (psi) Example - Ultimate Burst Pressure 1 toīarlow's formula can be used to calculate the " Ultimate Burst Pressure" at ultimate (tensile) strength as The minimum wall thickness for pressure 2 0 bar (2 MPa) can be calculated by rearranging eq. The yield strength of a 110 mm polyethylene pipe is 22.1 MPa. = 3478 psi Example - Polyethylene PE pipe The internal pressure for a 8 inch liquid pipe line with outside diameter 8.625 in and wall thickness 0.5 in with yield strength 30000 psi can be calculated as Example - Internal Pressure at Minimum Yield Note! - in codes like ASME B31.3 modified versions of the Barlow's formula - like the Boardman formula and the Lame formula - are used to calculate burst and allowable pressures and minimum wall thickness. P y = internal pressure at minimum yield (psig, MPa) Barlow's formula can be used to calculate the " Internal Pressure" at minimum yield
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