Page 96 - Pipelines and Risers

Limit-state based Strength Design 69

Limit Pressure for Internal Overpressure Condition:
The limit pressure will be equal to the bursting pressure given by:
2t
p, = O.S(SMTS + SMYS)- (4.1 1)
D
where:
SMYS = Specified Minimum Yield Strength in hoop direction
SMTS = Specified Minimum Tensile Strength in hoop direction

Load and Usage Factors:
Load factor yc and usage factor VR are listed in Table 4.3.

Table 4.3 Load and usage factors.

1 naM I Moment 1 0.80 I 0.73 1 0.65 I
Guidance notes:
- Load Condition Factors may be combined e.g. Load Condition Factor for pressure test of pipelines resting
on uneven seabed, 1.07xO.93 = 1 .OO
- Safety class is low for temporary phases. For the operating phase, safety class is normal and high for area
classified as zone 1 and zone 2 respectively.

For displacement-controlled situations the following strain capacity check is given to ensure
structural strength against local buckling:
/ ,0.8

(4.12)
I
YE YR

where:
E~,~= characteristic functional longitudinal strain
characteristic environmental longitudinal strain
E~,~= characteristic buckling strain capacity
ysnc,-= strain concentration factor accounting for increased strain in the field
joints due to coating stiffness discontinuities