Fabrication and Installation - Offshore Structures: Design, Construction and Maintenance - page 306

The use of wedges or other techniques to assist rolling should be subject to
the visual acceptability of the product and to acceptable mechanical test results
on test specimens taken from regions of maximum strain.
According to ISO recommendation, any materials that require straightening
before use, to achieve the specified tolerances, may be cold straightened if the
strain does not exceed 5%. Similarly, tubular cans for members or joints may be
re-rolled after welding to meet the dimensional tolerances if the strain during
re-rolling does not exceed 5%.

Rat-holes, Penetrations and Cut-outs
Rat-holes, penetrations and other cut-outs should be avoided wherever possible. If
the rat-holes are approved by the engineering office for critical needs, they should
be marked on shop drawings and are subject to the following requirements:

Permanent rat-holes should have a radius of 50 mm (2 inches) or twice the
plate thickness, whichever is larger, and should be ground smooth. Fillet
welds should be returned through the rat-holes.

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Temporary rat-holes should have a radius not less than twice the plate thick-
ness and should be reinstated to an approved welding procedure. Note that
filling with weld metal is not permitted.

●

The radius of any approved cut-outs other than rat-holes should not be less
than 100 mm (4 inches). It is preferred that the area be checked using UT
before cutting to ensure that no cut is made within 300 mm (12 inches)
of internal stiffeners. The original plate should be clearly marked and should
be welded back into the cut-out.

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Movement, Erection and Roll-up of Sub-assemblies
To ensure good-quality construction, sub-assembly and weld-up should be done at
the ground level or under cover. When sub-assemblies are moved and installed into
position in larger sub-assemblies or within the structure, care should be exercised
to ensure that no members or joints within the sub-assemblies are overstressed or
distorted.
Suitable supports may include: webbing slings; wire slings, when the com-
ponents are protected from damage; and temporary lifting attachments welded
to the sub-assemblies.
Sub-assemblies may be rolled into the correct orientation in the structure or
to allow lifting at the correct orientation into the structure. Roll-up saddles
should be designed and positioned to ensure that the structure is not over-
stressed during roll-up and should be well greased or otherwise lubricated.

Fabrication Tolerances
As per the contract, the contractor should provide qualified persons approved
by the owner

s representative and also should deliver good equipment and
the necessary instruments to perform checks and to monitor and to control

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