Note: Descriptions are shown in the official language in which they were submitted.
lZ10619
AN IMPROVED ~:hECTRIC A~D/OR OPTICAL CABLE
This invention reLates to electric and/or
optical cables and more particular`ly to waterproof
electric and/or optical cables for use under water,
buried directly in the ground or in any other location
in which entry of water or moisture into the interior of
the cable might occur if the cable were not rendered
waterproof.
It is common practice to render waterproof an
electric cable that is to be installed under water by
10 enclosing the cable within an extruded sheath of metal
or metal alloy that i5 suitably protected against
corrosion. However, where it is required to suspend an
electric cable under water under its own weight
substantially vertically or in a catenary curve, e.g.
when feeding an oil or gas production facility on the
seabed at a depth of several hundreds of metres, the
cable must be of such a construction that, not only must
it be able to withstand an external water pressure which
might be in the region of one hundred bar, but, whilst
20 in service, it must also be capable of withstanding many
millions of flexing cycles caused by the he~vy water
currents to which the cable will be subjected when
suspended at such water depths. Under such conditions
an electric cable with an extruded metal sheath is
unable to withstand the many millions of flexing cycles
to which it will be subjected and, consequently, a metal
sheathed electric cable is not suitable for feeding an
oil or gas production facility located on the seabed at
a depth of several hundreds of metres.
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It is an object of the present invention to
provide an improved electric and/or optical cable which
is suitable for use when suspended under water at depths
of at least 1000 metre~ and which, during its service
life at such depths, is capable of withstanding at least
several million flexing cycles, and which is suitable
for direct burial in the ground.
According to the invention, the improved
electric and/or optical cable comprises at least one
10 electric and/or optical cable core, and, surrounding the
core or assembly of cores, a water-impermea~le barrier
comprising a cushioning layer of elastomeric material; a
substantially circumferentially continuous wall of metal
or metal alloy constituted by at least one
longitudinally applied, transversely folded metal tape
which carries a coating of plastics material on its
outwardly facing surface, at least one elongate flexible
binder helically wound around the metal wall under such
a tension that a helically extending corrugation or
20 helically extending corrugation~ is or are formed in the
metal wall throughout the length of the cable and that
elastomeric material of the cushioning layer fills the
trough of the or each helical corrugation in the inner
surface of the metal wall; and, surrounding the metal
wall, an extruded sheath of plastics material which is
bonded to the plastics coating on the outer surface of
the metal tape or tapes constituting the metal wall.
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1210619
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At least the outer surface of the or each
flexible binder preferably is of plastics material and
preferably, also, the plastic~ material of the overlying
sheath bonds not only to the pla tic~ coating on the
outer surface of the or each metal tape but also to the
plastics surface of the or each flexible binder. The or
each flexible binder may be a plastics coated wire or
strand, a bare wire or strand, or a plastics coated non-
metallic filament, e.g. a filament of terylene or an
10 aromatic polyamide, such as that sold under the Trade
Mark "Kevlar".
Preferably, the or each metal tape constituting
the metal wall also carries a coating of plastics
material on its inwardly facing surface and, preferably
also, this plastics coating is bonded to the elastomeric
material constituting the cushioning layer.
The or each metal tape forming the metal wall
is preferably of copper or a copper-based alloy or of
aluminium or an aluminium-based alloy.
; 20 Where the cable of the present invention is an
electric cable, it may be an electric power cable and,
in this case, the core may be a single stranded electric
conductor. Alternatively, the cable may be a
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06~9
telecommunications cable and, in this case, the core may
be a multiplicity of plastics insulated conductors.
Where the cable of the present invention is an optical
cable, the core may ~e an extruded elongate body of
plastics material having a bore in which a separate
optical fibre and/or an optical bundle is loosely housed
or the core may be at least two plastics tubes assembled
together, in at least one of which tubes at least one
separate optical fibre and/or at least one optical-
10 bundle is loosely housed. The cable of the presentinvention may be a combination of any two or more of an
electric power cable, a pilot or telecommunication
cable and an optical cable.
A single core electric power cable in accordance
with the present invention may also constitute ~ne core of
a multi-core el~ctric power cable.
The water-impermeable barrier of the improved
electric and/or optical cable of the present invention
provides the important advantage that it will withstand
20 heat and pressure cycling under service conditions more
satisfactorily than other forms of water-impermeable
barrier hitherto proposed and used and that, therefore,
it has improved resistance against fatigue.
The invention will be further illustrated by a
description, by way of example, of a preferred 11 KV
multi-core electric power cable for suspension under
water under its own weight in a catenary curve with
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reference to the accompanying diagrammatic drawing whi-h
shows a transverse cross-sectional view of the cable.
Referring to the drawing, the cable comprises
a central flexible tensile member 1, six cores 2 laid
helically around the central tensile member and,
surrounding the cores, a binding iayer 3 of helically
wound tape of tin-bronze, the direction of lay of the
tape being opposite to that of the helically laid cores,
and a serving layer 4 of helically lapped tape of
polypropylene, the direction of lay of the serving layer
being opposite to that of the binding layer.
The central tensile member 1 comprises a
multiplicity of filaments 6 of Kevlar, which filaments
all lie substantially parallel to the axis of the cable
and, surrounding the multiplicity of filaments, a sheath
7 of polyethylene~
The six cores 2 are arranged two cores per
phase and each core comprises a flexible stranded
conductor 11; a conductor screen 12 comprising a layer
of semi-conducting tape and an extruded layer of semi-
conducting cross-linked polyethylene; a dielectric wall
13 comprising an extruded layer of cross-linked
polyethylene; a dielectric screen 14 comprising an
extruded layer of semi-conducting cross-linked
polyethylene; a water-impermeable barrier comprising a
cushioning layer 15 of non-vulcanised butyl rubber a
circumferentially continuous copper wall constituted by a
` 1210619
longitudinally applied transversely folded copper tape
17 having on its inner surface a coating 16 of polyester
which is bonded to the cushioning layer 15 and having on
its outer surface a coating 18 of polyethylene and a
plastics coated terylene filament 19 helically wound
around the tran~versely folded polythene-coated copper
tape 17 under such ten~ion as to form in the copper wall
a helical corrugation, the helical trough on the inner
surface of the transversely folded polythene-coated
10 copper tape being filled with non-vulcanised butyl
rubber; and, overlying and bonded to the polyethylene
coating 18 and to the plastics coated terylene filament
19, an extruded overall sheath 20 of nigh density
polyethylene.
The cable illustrated in the drawing, when
suspended under water in a catenary curve to a depth o~
lOOOm, is capable of withstanding an external water
pressure o 100 bar and at lea~t several million flexing
cycles. In addition, the central tensile member takes
20 substantially all the tensile load to which the
suspended cable will be subjected so that there is
negligible risk that the suspended cable will twist or
become tangled.
The cable illustrated in the drawing is also
suitable for burial directly in the ground.
