Page 55 - Pipelines and Risers

28 Chupter 2

where:
au = material strength factor
ym = material resistance factor
ySc = safety class factor
vinc = incidental to design pressure ratio

2.3.3 Hoop Stress Criterion of ABS (2000)
As the requirement for pressure containment, the allowable hoop stress Fh to be used in design
calculations is to be determined by the following equation:
Fh =)).SMYS*k, (2.5)
where:
q = design factor (see Table 2.2, originally from B31.4 and B31.8)
SMYS = Specified Minimum Yield Strength of the material
kT = temperature derating factor (when temperatures is above 5OOC).

Table 2.2 Design Factors q for Pipelines, Platform Piping, and Risers (originally from ASME B31.4 and
B31.8).

Hoop stress Longitudinal Equivalent
stress stress
Oil & Gas pipelines, 0.72 0.90
Liquid hydrocarbon
uiuing and risers I Oe80
Gas risers on non- 0.60 0.80 0.90
production platform
Gas piping, Gas risers 0.50 0.80 0.90
on production platform

The hoop stress fh in a pipe can be determined by the equation:
f,, = (5 - p, - W(2t)
where:
fh = hoop stress
Pi = internal or external design pressure
P, = external design pressure
D = nominal outside diameter of pipe
t = minimum pipe wall thickness

For relatively thick-walled pipes, where the ratio D/t is equal to or less than 10, a more
accurate hoop stress calculation methods, resulting in a lower stress, may be used.