Page 95 - Pipelines and Risers

68 Chapter 4

yc = Condition load factor
?)R = Strength usage factor

0 Correction Factor:
P
a = 0.25-1 for external overpressure (4.4)
FI
P
a = 0.25L for internal overpressure (4.5)
4
If possible, the correction factor should be verified by finite element analyses.

Plastic (Limit) Moment:
The limit moment may be given as:

(4.6)

0 Limit Longitudinal Force for Compression and Tension:
The limit longitudinal force may be estimated as:
6 = 0.5. (SMYS + SMTS). A (4.7)

0 Limit Pressure for External Overpressure Condition:
The limit external pressure ‘p{ is to be calculated based on:
(4.8)

where:
(4.9)

pP= 9 SMYS - (4.10)
2t 1)
D
fo = Initial out-of-roundness *), @--Dmin)/D
E = Young’s Module
2) = Poisson’s ratio

Guidance note:
1. qfab is 0.925 for pipes fabricated by the UO process, 0.85 for pipes fabricated by the UOE process and 1 for
seamless or annealed pipes.
2. Out-of-roundnss caused during the construction phase is to be included, but not flattening due to external
water pressure or bending in as-laid position.