Page 525 - Pipelines and Risers

492 Chapter 26

use of the B31G codes for the wall-thickness design of new flowlines. The conclusions
allowed the corrosion allowance to be minimized, this resulted in a saving of 30 million NOK
in steel costs for a flowline of 100 km.

26.2.4 Limit-state Design
In order to permit a greater utilization of the pipe capacity to save large intervention costs,
limit-state design approach was required.

The limit state design addressed the following areas (Bai and Damsleth (1998):

0 local bucklingkollapse
fracture
0 fatigue
0 burst
0 ratcheting

The limit state design approach has been applied to all aspects of the flowline design such as:

0 installation
0 in-place behavior
0 Vortex-shedding
on-bottom stability
trawl board and dropped objects protection
0 Tpieces

Details on limit-state design of Asgard flowlines are discussed by Bai and Damsleth(l997).

26.3 Asgard Transport Project

26.3.1 General
The Asgard Transport (AT) diameter 42-inch export pipeline transports rich gas from the
Asgard field (located 150km from the coast in mid Norway) to Kht0 (located 30km North of
Stavanger, Norway). The line traverses a total distance of 700km in water depths varying
from 60m to 37Om. The design life of AT is 50 years. The seabed varied from very soft clays
to hard clays, the most notable point being the extremely rough terrain over 200km of the
route. The line has 5 pre-installed tees to permit gas from fields along the route to transport
gas in AT. The line is to be installed in 1998/9 and operated in year 2000.