EquipmEnt & cabling updatE 35
768 fibre optic sub-sea riser
cable sets new world record
Einar Magnus Bjelland and Jon-Steinar
water impregnation preventing compound is a Nexans
Andreassen look at the scope of work
proven technology and a basic building block in all our
sub sea cables.
for the 768 fibre riser cable, including The transition between the complete cable pulled in to
the arrangements for the pull-in
the J-tube and the individual cables supporting sub-sea
operation.
cable segments was made without any fibre splices. A
special mechanical component was developed to protect
and secure the transition, where the assembled riser
A
riser cable containing 768 fibres, developed cable is split into four. The cable ends lying on the sea
by Nexans Norway, is claimed to be a bed are prepared with half-joints ready to be connected
world record with regards to number of to the seabed segments.
fibres. Because of the large number of fibres A pre-mounted cable hang-off was used for the pull-
required it was necessary to develop a system optimised in operation. The hang-off including the mechanical
for installation efficiency and which minimised the time termination of the stranded steel wire armoured cables
needed for optical measurements and tests during and could then be prepared in the Nexans facility. Critical
after installation. cable handling and installation time during the offshore
The total scope of work for the 768 fibre riser cable pull-in sequence was avoided. In addition, to the pre-
included arrangements for the pull-in operation, the mounted hang-off, eight meters of flexible steel segments
topside cable hang off arrangement, the assembled riser was put together over the cable cores to protect them
cable, and an arrangement for distribution of fibres into during the pull-in sequence. These segments are flexible
four ‘dead end’ cables for future connection. to manage the J-tube bend and in the same time transfer
To meet these requirements the design incorporates the load down to the hang-off terminated to the riser
four individual steel armoured cable cores helically cable during the pull-in sequence. Having eight metres
stranded together. Each of the four cable cores contains of prepared cable cores inside the pull-in arrangement
192 fibres making a total of 768 fibres (Fig. 1). The makes the installation more efficient and safe. The
armoured cable cores will be connected to the various cables can be routed directly to their junction boxes with
subsea cable segments in the future. The cable cores minimum cable handling.
are robust and act as individual cables on the sea bed. The riser cable system, including pull-in and hang-
Nexans fibre in a laser welded steel tube filled with a off arrangements as well as the transition splitter
arrangement was supplied on one drum.
The above describes a static cable solution for J-tube
pull-in. For dynamic fiber optic riser cables, the basic
cable technology is still applicable however the scenario
in terms of cable loads and exposures for cable service
period requires different and more complicated design
criteria. For dynamic risers, comprehensive site specific
engineering and analysis is necessary. Such analysis
involves meteorological data and data on platform
movements (RAO) for verifying the compatibility between
cable structural properties, cable configuration, subsea
components and topside interface. Fatigue is a key
issue for a dynamic cable, and results from dynamic
analysis are used for establishing fatigue criteria end
determination of parameters for equivalent fatigue
life test, a test which is necessary to include in the
qualification test program. l
Enter 35 or ✔ at
www.engineerlive.com/ihss
Einar Magnus Bjelland and Jon-Steinar Andreassen are with
Fig. 1. Fibre Optic Riser cable with world record breaking 768 fibres. Nexans Norway AS, Etterstad, Oslo, Norway.
www.nexans.no
www.engineerlive.com
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