Page 60 - Pipelines and Risers

Wall-thickness and Material Grade Selection 33

due to installation and cyclic operating loads may aggravate local buckling and is to be
considered. Here it is recommended that out-of-roundness, due to through life loads, be
simulated using finite element analysis.

The collapse equation, Equation (2.17), is often expressed as below:
(P, -Per 1.6: -P:)=Pc . Per . Pp .to ‘7 (2.20)
DO
The collapse equation can be solved by the following approach:
1
p, =y--b, whereP,=PIinEquation (2.17)
3
where:
b = -pel

u=:[-:b’ +c)

When calculating out of roundness, caution is required on its definition.

If D/t is less than 50, for pipes under combined bending strain and external pressure, strain
criteria may be as the following, ABS (2000):

(2.21)

where:
E =Bending strain in the pipe
t
E, =-
2D

E, =Maximum installation bending strain or maximum in-place bending strain
f =Bending safety factor for installation bending or in-place bending
P, =Collapse pressure