Page 299 - Offshore Electrical Engineering Manual

286 CHAPTER 1 Installation Practice

1. Manufacturer’s bend, tee and crossover sections should be used rather than site
fabrication from straight sections. Site fabricated sections tend to be weaker
mechanically and are more likely to damage cables by burring or unfinished
metal. If it is necessary to cut a section of a tray, it should be cut along a line of
plain metal rather than through the perforations.
2. Admiralty pattern and reverse flange trays should not be used in the same area,
as the two types cannot be easily joined together. Reverse flange tray is nor-
mally used for external areas only.
3. At 25 m maximum intervals along the tray, it should be bonded to the platform
structure.
4. With most types of trays, earth bonding continuity will be provided between
sections by the tray itself, although some operators require a braided bonding
connector to be used.

LADDER RACK
There is a variety of rack types used offshore, but all are based on a ladder design
with various standard components which allow any three-dimensional configura-
tions, including multitier, to be built up ‘meccano fashion’. If stainless steel rack
is to be used, great care will need to be exercised in quality control as there is a
tendency for distortion to appear in some production batches. If reinforced glass
fibre (grp) type ladder is used, the stronger ‘pulltruded’ type is recommended. As
there is some fire risk associated with this type of tray, its use should be restricted
to lower areas of the installation where sea spray is likely to cause corrosion
with metal racking. For the same reason, long vertical runs of grp rack are not
recommended.

THE DECOMMISSIONING AND REMOVAL/ABANDONMENT
PHASES
It is vital that the same or better level of planning and monitoring of the work is main-
tained during these phases in the life of the installation. The organisation involved
during decommissioning and removal is complex, as it is necessary to maintain ser-
vices and utilities at every stage. This will include safe accommodation and provision
of meals, etc. for the workforce. At some point, it will be necessary to provide an
accommodation barge, i.e., before the platform accommodation can be decommis-
sioned. In some cases the entire platform topsides is removed by a heavy-lift vessel,
in which case the workforce can be accommodated on this vessel while preparations
are made for the heavy lift.
If part of the structure is to be abandoned, some form of navigational aid package
will need to be installed on the remaining structure, and possibly facilities for main-
tenance access should be provided.