Abrasion resistant submarine cable arrangement

Optical waveguides – Optical transmission cable – Loose tube type

Patent

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Details

385101, H01B 1122

Patent

active

058928740

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to submarine cable, and in particular to an abrasion resistant submarine cable arrangement suitable for laying in water exceeding 2 km in depth.


BACKGROUND OF THE INVENTION

Known abrasion resistant cable, such as steel wire armoured cable, has good abrasion resistance and is strong enough to be suspended from a cable laying vessel during laying in water deeper than 5 km.
Such abrasion resistant cable is conventionally used when the section of seabed upon which the cable is being laid includes a zone of abrasion risk.
Once the zone of abrasion risk is passed, abrasion resistant cable is no longer needed; continuing the abrasion resistant cable beyond this zone would be prohibitively expensive. The abrasion resistant cable therefore needs to be connected, by joint or transition, to a cheaper, but lighter and consequently weaker, conventional un-armoured cable.
However, deeper than about 2 km, generally the weight of steel armoured cable is too great to safely permit it to be supported during suspension by the weaker unarmoured cable joined thereto. This means that it is not possible to directly lay from armoured to un-armoured, or recover from un-armoured to armoured cable.
It is still possible to install the armoured cable in water deeper than 2 km, using an appropriate installation sequence where the strong armoured cable always supports the weaker un-armoured cable, and never vice-versa. However, such a sequence requires good weather, additional joints, cable and considerable time. It is accordingly both risky and expensive.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide an armoured cable arrangement which, on the one hand, is light enough that an un-armoured cable can support it in deep water, and on the other hand has abrasion resistance comparable to conventional steel wire armoured cable, and sufficient strength to support heavy armoured cable.
According to the invention there is provided an electric and/or optical cable arrangement including at least one stranded armour layer comprising a plurality of metallic wire elements and a plurality of filler elements, wherein said filler elements are of a material that has a lower weight per unit length in relation to the weight per unit length of the material of the said wire elements.


BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily carried into effect, an embodiment thereof will now be described in relation to the accompanying drawings, in which:
FIG. 1 shows the cross-section of the cable arrangement of the present invention.
FIG. 2 shows the cable shown in FIG. 1 having been subjected to abrasion.
FIGS. 3a-e illustrate the utilization of the cable of the present invention in laying submarine cable.


BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, the cable 1 comprises a conventional vault arrangement 2 surrounding an array of six optical fibres 3. Vault 2 is surrounded by a polyethylene layer 4 which in turn is surrounded by a layer consisting of polypropylene yarn and bitumen 5. The characteristic armour layer 6 comprises an arrangement of 12.times.3.4 mm steel wires 7 and 12.times.3.4 mm fillers 8. Each filler comprises a 0.65 mm steel core wire 9 coated to 3.4 mm with polyvinyl chloride (PVC) 10. The coating of PVC is attached to the core wire 9 by an adhesive (not shown) such as, for example, a solvent based elastomeric nitrile. Steel wires 7 and fillers 8 alternate.
A high density polyethylene coating or a polyurethane coating may substitute the PVC coating 10, in which case suitable adhesives would be required.
Armour layer 6 is covered with an outer sheath 11 of polyisopropylene and bitumen.
Because some of the steel armour wires have been replaced by fillers, the weight and strength of the cable is reduced. Since the original steel armoured cable was much stronger than necessary, a significant reduction of strength is possible without compromising the ability of the cable to support its own weight in deep water.
Removal of st

REFERENCES:
patent: 4552432 (1985-11-01), Anderson et al.
patent: 5212755 (1993-05-01), Holmberg
patent: 5224190 (1993-06-01), Chu et al.
patent: 5408560 (1995-04-01), Seynhaeve et al.
patent: 5463711 (1995-10-01), Chu

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