Civil Engineering Reference
In-Depth Information
Chapter 5
Fabrication and Installation
5.1 INTRODUCTION
The construction of a fixed offshore platform is very specific. Therefore, the
contractor responsible for fabrication and installation should be specialized
and have a competent staff and reasonable facilities for the project. During
this phase, the design of the platform should be checked against transportation,
lifting and installation. There should be strong communication and interface
management in the project between the engineering office and the fabrication
and construction contractors. In some cases, the sea fastening or lifting will
be done by the contractor but it should be checked and approved by the engi-
neering company. Note that the launching and lifting of the platform component
are designed by the engineering company but the input data for the analysis are
delivered to the engineering company based on available barges, cranes and
other equipment.
5.2 CONSTRUCTION PROCEDURE
The engineering firm performing the design of a jacket should take into consid-
eration the lifting, launching or self-floating, which depend primarily on the
available offshore installation equipment and the water depth. In general, the
preference is to lift the jacket into place. The size of jackets has been increasing
as offshore lifting capacity has grown. For jackets in shallow water, the height
of the jacket is of the same order as the plan dimensions, so the erection is
usually carried out vertically in the same direction as the final installation.
Therefore, in this case the jacket may be lifted or skidded onto the barge.
Jackets designed for deeper water depths are usually erected on their side.
Such jackets are loaded by skidding out onto a barge. Historically, most
large jackets have been barge launched. This method of construction usually
involves additional flotation tanks and extensive pipework and valving to
enable the legs to be flooded for ballasting the jacket into the vertical position
on site. This method of construction is currently applicable for jackets up to
25,000 tons. The key fundamental elements are the contract strategy, the
Search WWH ::
Custom Search