Fabrication and Installation - Offshore Structures: Design, Construction and Maintenance - page 322

thoroughly developed three-dimensional layouts, firm and level foundations for
the cranes and very competent operators.
Structural analysis should be performed to check the structure

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stresses during the erection process for a given assembly; this is usually done
using a computer model with all relevant structural characteristics. The assem-
bly is analyzed for the load cases that correspond approximately to the support
conditions of the assembly, with assumed locations of the cranes, bogies, sad-
dles and others when the panel is being transported and when it is in horizontal
and vertical positions. Structural analysis for lift and transport identifies the
worst cases from the structural stress perspective. These cases are then analyzed
to determine the maximum stresses and displacements. The calculations should
show that global and local stresses are within allowable limits according to API/
AISC codes.
The sequence for erection of all major components is:

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● Technical appraisal of lift methods. Calculations for crane configuration,
rigging accessories.
● Preparation of cranes for lift, preparation for rigging and transport assembly
to lift location. Roll-up into position with scaffolding and staging in posi-
tion, if possible.
● Preparation of fixing system and wind bracing, which is usually done by
means of guy wires and turnbuckles. Weld-out at least sufficient to allow
crane release.
● Crane release. Removal of rigging and temporary attachments.
Jacket structural completion is followed by a short phase during which all
the jacket systems, both permanent and those required during installation, are
completed and rendered functional.
Figure 5.17 presents the fabrication of one face of the jacket frame on the
ground; the erection of the other side is shown in Figure 5.18 .
The erection of additional steel framing to strengthen the jacket structure
during launching is presented in Figure 5.19 .
After construction of the first frame, erection of temporary and permanent
horizontal bracing is started, as shown in Figure 5.20 , at the same time that con-
struction of the diagonal bracing is started, as shown in Figure 5.21 .
Figure 5.22 illustrates the erection of the last horizontal level for the jacket,
whereas Figure 5.23 presents fabrication of the conductor guide with the hori-
zontal frame.
The last face on the jacket is fabricated on the ground, as shown in Figure 5.24 ,
where one can see the exterior conductor guide, and then this face is lifted, as
shown in Figure 5.25 , to finalize construction of the jacket.
The fabrication of the topside is shown in Figure 5.26 .
The accessories, such as the flare tip, riser guard and boat landing, are fab-
ricated on site and are attached to the jacket after its installation.