Fabrication and Installation - Offshore Structures: Design, Construction and Maintenance - page 319

(e)

FIGURE 5.16 (a) Steps in erection of plan frames; (b) Erection of bay; (c) Frame roll-up; (d) Roll-up
of the last frame and fill in between; (e) Jacket ready for roll-out and launching.

The sub-assembly should be managed so that the maximum number of
welds are done in the shop; shops have the highest weld quality because
many node and tubular welds can be double-sided and/or automatic when per-
formed in the fabrication shop.
When defining sub-assemblies, the principal factors to be considered are:

Dimensions (e.g., size and weight), which are the main factors governing the
method of transportation

●

Welding sequence (a difficult welding sequence can induce stresses during
sub-assembly welding/erection and could cause distortion of a member)

●

Construction difficulties (for example, short, large-diameter infillings are
difficult to erect vertically and are best included in sub-assemblies, if
possible).

●

Shop-fabricated sub-assemblies and loose items are incorporated into
assemblies that constitute the major lifts of the erection sequence. Usually,
for a large jacket, the assemblies typically consist of four types:

Jacket levels incorporating conductor guide frames ●

Top frames

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Jacket rows, such as bents or partial bents

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Pile-sleeve clusters

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