Page 484 - Pipelines and Risers

Pipe-in-Pipe and Bundle Systems 45 1

The reeling method can be very efficient, particularly for relative short length pipelines with
the number of reloads can be minimized. The method is suitable for outer pipe diameter up to
16" with no concrete coating. Plastic strains developing reeling and the unreeling, and hence
particular attention needs to be given to stresdstrain conditions at bulkheads. Up till now, its
application has been restrained by the relatively low tension capacity currently available.
There are several large reel lay vessels under construction. The vessels will have very high
tensions capacity, large drum and near vertical departure angle, make reel lay a strong
alternative to J-lay for small to medium diameter, short to medium length pipelines.

Towing methods include several arrangements, mid-depth off-bottom and on -bottom tows. It
can be very cost effective for flowline of short lengths. However, it may be restrained by
factors such as the maximum pull of the tow vessels, the Ocean current conditions, availability
for a suitable onshore fabrication and launching site, and the seabed topography and soil
condition along the tow route. Towing is particularly suitable for the installation of pipeline
bundles where a large outer pipe can be used to house several flowlines and umbilicals.

Installation Analysis
In this section, various aspects of installation analysis for a J-lay operation starting with are
considered. First of all, layability checks are performed for the worst cases as part of the wall
thickness and steel grade selection exercise. Once the wall thickness and steel grade are
finalized, detailed pipeline analyses are carried out covering both normal lay and contingency
operations.

Static normal lay analysis establishes the optimum lay parameters, Le., barge tension and J-lay
tower inclination angle, for various sections along the entire pipeline route. Dynamic analyses
on selected static conditions are then performed to confirm that the resultant stresdstrain is
acceptable and the vessel tensioner capacity is adequate. The cumulative fatigue damage a
weld is estimated accounting for the various stress ranges it experiences as the pipe is lowered
towards the seabed or is suspended below the water surface during undesirable weather
conditions.

24.3 Bundle System

24.3.1 General
A pipeline bundle system consists of an outer carrier pipe, inner sleeve pipe, several internal
flowlines, insulation system and appurtenances such as spacer, valves, chains, supports, etc.
The carrier pipe is a continuous tubular structure that contains flowlines, sleeve pipe and is
used to provide additional buoyancy to the bundle components during installation, structural
strength mechanical protection during operation and corrosion free environment for the
flowlines. Sleeve pipe is used to provide dry pressurized compartment for internal flowlines.
The internal flowlines are continuous linepipes without frequent branches used for
transportation of fluids within the filed. Spacers are non-stress distribution elements provided
to locate and support flowlines within the bundle configuration. Usually, the pipeline bundle