TPT July 2007

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Technology Update
47 July /August 2007
further to the United Kingdom in a sub-sea
pipe called Lange-Led. This gas will cover
approximately 20 per cent of the UK’s gas
consumption.
During the past decade, Nexans has
developed a new generation of umbilicals
for controlling sub-sea systems that
carry energy, telecommunications, fluids,
methane, fibre-optics, and chemicals via
super duplex tubes. In the Norwegian ‘Snow
White’ project for Statoil, a single 146km
umbilical of this design transfers all wellhead
control functions to shore, eliminating costly
platform facilities. In another current project,
umbilicals are being installed in the Gulf of
Mexico beyond 2,000m water depths.
Nexans Norway started manufacturing
umbilical cables in 1991. From the
beginning, orbital welding was
recognised as the only
way to manufacture these
lengthy tube assemblies,
and to obtain perfect
welds in a repetitive and
precise manner.
In a welding plant which
is approximately 150m
in length, nearly 120m of
plant floor are devoted to
the production process for
the three orbital welding
lines. Bundles of super
duplex tubes with IDs
from ½" to 2½", in lengths
of 12m to 40m, are
brought into the factory,
unwrapped, and lifted
to a sorting station on a
dispensing platform at one
end of the factory. Tubes are dispensed
automatically to each of the welding stations
which is manned by one operator.
The three orbital welding stations each
employ Polysoude PC systems. The
welding station equipment is on tracks, and
can be moved to accommodate welding
tube lengths from 14m to 40m. Polysoude
orbital welding equipment has been used
for umbilical production by Nexans since
1994. In 2005, 1.6 million metres of tubing
were welded, using 75,000 welds.
Nexans uses open weld heads having AVC
and oscillation features with wire feed (cold
wire TIG). The cycle time from the beginning
of setup to the beginning of the next setup
at a weld station is dependent upon the tube
diameter. A diameter of ¾" may take one
minute to weld (diameters referenced are
always ID, since various ODs are used.)
As the welded tube advances out of a weld
station, each weld is X-rayed. If a defect is
revealed, the weld is cut out and re-welded.
The welded lengths are then collected on
a large reel, with an outside diameter of
approximately 4m. Each reel can hold more
than 20,000m of ½" tubing.
The tubes on the reel are then filled with
water and pressure tested, usually with
1.5x normal working pressure, in a special
pressure testing room.
In the umbilical lay-up machine there may be
as many as a dozen large reels containing
stainless steel tubing with various IDs and
ODs. The actual lay-up point is placed
approximately 12m above the large rotating
turntable. Each reel feeds its contents
upwards to the lay-up standing point where
the super duplex tubes are spiralled around
a larger centre tube, forming the interior
of an umbilical cable. The cable can then
go to the armouring operation first, or be
wrapped in a plastic material to hold it
together, prior to the PE sheet extruding
operation.
When contents of one of the tube-
feeding reels comes to an end,
the lay-up process halts while
the empty reel is replaced.
A welder will then use the
Polysoude orbital welding
equipment to weld the new
reel’s tube to the end of
the previous reel’s tube.
This welding is
performed on a platform
approximately 10m above
the plant floor. A special
extension cable has been constructed by
Polysoude to permit the welding machine to
remain on the floor below. When the welding
is complete, the lay-up process continues.
The umbilical is produced to an outside
turntable measuring more than 35m across,
with a capacity more than 7,000t. The
completed umbilicals are loaded onto ships
at the plant’s quay-side.
Article supplied with input from Mr Truls Nordahl,
welding coordinator, Nexans Norway AS
Polysoude SAS – France
Fax: +33 2 4068 1188
Email:
Website:
Nexans – France
Fax: +33 15669 8484
Website:
› Full function welding head, Type MU