Page 334 - Pipelines and Risers
P. 334
Route Optimization, Tie-in and Protection 307
Based on the derived costs, a total cost for each route can be derived.
It is worth noting that the optimization cannot be completed until all the pipeline design
parameters are finalized (for instance the number of freespan correction supports will not be
known until the allowable freespan has been determined).
17.3 Pipeline Tie-ins
It might be natural to assume that each pipeline has two tie-ins, one at each end. This is
however, not always the case. Where the installation method is only suitable for limited
lengths of pipeline, midline tie-ins may be required.
The methods of pipeline tie-in are discussed under the following headings (see Figure 17.1).
- Spoolpiece;
- Lateral pull;
- J-tube;
- Connect and lay away;
- Stalkon.
Based on the review of the above tie-in methods it may appear that there is a good choice of
tie-in methods, but closer review shows that this is not the case. Only certain combinations of
installation and tie-in methods are practical and other factors limit the selection. These are
discussed in the following subsections.
17.3.1 SpooIpieces
General Principle
This method is probably the most popular method of tie-in for flowlinedpipelines. Divers
measure and then assist the installation of a piece of pipe to fit in between the two ends of
flowline to be tied together.
Installation CapabilitiesKonstraints
This method is popular because of the flexibility of the method. Misalignment of the two
pipes can be accommodated by installing bends into the spool, and inaccuracies in placing the
pipelines down can be accommodated when the spool is made up (after diver measurements).
The connection method can either be by flanges or welding. The welding method requires a
hyperbaric habitat. From a design viewpoint, should there be large flowline expansion, then
this can also be accommodated by incorporating a dogleg in the spool. This will permit
expansion of the pipe without transmitting high loads into the adjacent pipe.
