Page 333 - Pipelines and Risers

306 Chapter I7

- Presence of unfavorable shipping or fishing activity;
- Suitability of landfall sites, where applicable.
17.2.2 Fabrication, Installation and Operational Cost Considerations

A significant proportion of the total cost to install a pipeline which is directly affected by the
chosen route is incurred during fabrication and installation. The associated activities are:

1. Length of fabricated pipeline pipe (coated);
2. Pre sweeping of route;
3. Pre lay installed freespan correction supports;
4. Post lay installed freespan correction supports;
5. Trenching, burying or rockdumping.

Some or all of these activities will be present within the selected pipeline route. As a general
rule the design should be performed to:

- Minimize length of pipeline required;
- Avoid requirement for presweeping;
- Avoid pre-lay installed freespan correction supports;
- Minimize post-lay freespan correction supports;
- Minimize trenching, burying and rock dumping.

17.2.3 Route Optimization
Optimization of pipeline routing is usually not performed as the route probably has no
obstruction, is in an accessible water depth and the seabed topography is flat: Hence a straight
line between the two termination points would suffice. However, on seabeds with onerous
terrain significant savings on fabrication and installation costs can be made if route
optimization is performed.

To perform a route optimization, reasonably accurate costs for the following activities are
required

- Supply of additional pipeline pipehnit length;
- Presweeping a corridorhnit length, including cost of reduced lay rate due to a smaller lay
comdor;
- Prelay freespan correction supports (each), again including cost of reduced layrate due to
smaller lay comdor;
- Post lay freespan correction supports (each);
- Trenching, burying and rockdumpinglunit length (for each).