INGENIEUR
Integrated Float-over
Essentially, there are two ways of installing an
IC topsides using the float-over method; the
conventional method by navigating the float-over
barge in between the jacket legs, or alternatively
by the sides of the jacket legs. The latter method
involves two barges carrying the integrated
topsides at both ends. Instead of sailing through
the opening between the jacket legs, the barges
have to steer around the jacket on each side and,
at the same time, de-ballast to place the topside
onto the jacket. The use of this method is very
rare, although it can be used for both small and
heavy-sized structures (estimated to be around
20,000 MT), depending on the matched pair of
barges used. Another technique is using a special
type of float-over barge which has a ‘fork-like’
stern that wraps around the jacket prior to mating.
There are two ways of mating the topsides to
the jacket legs. The conventional method is by
barge ballasting whereby the IC topside legs are
mated onto the jacket simply by ballasting and
de-ballasting of the float-over barge. The most
recent method is by using the dynamic/hydraulic
jacking system. As a structure with a relatively
high VCG, the height of the IC deck needs to be as
low as possible during transportation especially
in adverse sea conditions. As a result, the jacking
system is required to lift the topsides to a sufficient
height above the jacket legs to enable successful
mating. However, the use of this jacking system
can be costly and would defeat the cost advantage
of the IC method.
Hook-Up and Commissioning (HUC)
The MC concept requires more HUC interfaces
compared to the IC deck, hence it requires a
longer time for offshore hook-up work. Transferring
work offshore increases both cost and duration of
a project as work carried out offshore is:
●●
Much less efficient compared with work
done onshore;
●●
Requires additional expense for marine
spread; and
●●
Utilises manpower at a higher unit rate
compared with onshore.
In comparison, a single integrated topside
design limits the work required for an offshore
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hook-up and commissioning. The complete
integration of facilities in the fabrication yard
allows production and utility systems to be
commissioned much more efficiently than is
possible with the offshore hook-up of a MC
topside. This leads to a significant reduction in
offshore HUC duration and cost, a lower risk of
schedule delay and a smoother start-up.
Project Planning
Figure 4 depicts the project planning for both IC
and MC execution stage.
Figure 4: Front-End Loading of both
IC and MC methods
The IC method requires heavy front-end
loading (FEL) activities to be carried out.
Detailed planning must be undertaken very
early in the project stage as the transportation
and installation barge needs to be identified
and locked in upfront. In contrast, the barge
selection and load out arrangement decision for
a MC can be delayed until the fabrication stage.
For an IC, the design of the LSF and LMU must
be completed as early as the conceptual stage,
to determine the barge capacity requirement.
This enables the barge selection process and
load out arrangements to take place during the
Front-End Engineering Design (FEED) stage.
A thorough analysis of the load out details
would then be undertaken during the Detailed
Design stage which includes yard bulkhead
strengthening, dredging, barge installation
requirements, structure design, weather window