Fabrication and Installation - Offshore Structures: Design, Construction and Maintenance - page 376

The topside and jacket structures should be structurally checked against the
effect of impact loads during the float over for installation and the loads should
be calculated as a parameter in the motion analysis by the naval architect. The
analysis should consider the selected barge, the stiffness of the structures and
leg mating units and the full range of installation scenarios from initial docking
through to final load transfer. Vertical loads should be based on the dry weight
of the structure obtained from the weight-control report.

5.13 INSTALLATION AND PILE HANDLING
After launch of the jacket and lifting of the jacket by the crane barge, as shown
in Figure 5.48 , the next step is to start driving the piles into the legs.
There are various ways of providing lifting points for positioning pile sections.
Padeyes are welded in the fabrication yard; their design should take into considera-
tion the changes in load direction during lifting. Padeyes are then carefully cut
before lowering the next pile section.
Figure 5.49 presents configurations for internal and external stabbing guides.
Figure 5.50 presents the sequence of the pile installation process.
Different solutions for connecting pile segments back-to-back are welding
(shielded metal arc welding (SMAW) or flux-cored) or segments held tempora-
rily by internal or external stabbing guides (see Figure 5.49 ). Welding time
depends upon the pile wall thickness [because it takes 3 hr for a 1-inch thickness
(25.4 mm) and 16 hr for a 3-inch thickness (76.2 mm) (typical)], the number and
qualification of the welders, the environmental conditions, and the mechanical
connectors, breech block (twisting method) and lug type (hydraulic method).
In summary, pile installation includes:

Lifting from the barge deck ●

Positioning over pile by booming out or any other method depending on the
weather condition

●

Add-on

Welds

Add-on

Welds

Friction fit
at joint

Pile

Pile

Internal stabbing guide External stabbing guide

FIGURE 5.49 Configurations for the different types of stabbing guide.