GB2071431A

GB2071431A - Underwater Cable Jointing

Info

Publication number: GB2071431A
Application number: GB8008238A
Authority: GB
Original assignee: STERLING CABLE CO Ltd; Star Offshore Services Ltd
Current assignee: STERLING CABLE CO Ltd; Star Offshore Services Ltd
Priority date: 1980-03-11
Filing date: 1980-03-11
Publication date: 1981-09-16
Also published as: GB2071431B; NO810817L

Abstract

A method of making a cable joint under water which does not require the use of a dry habitat comprises passing each cable 1, 2 through an aperture in a respective resilient sealing element, or, as shown, in a common resilient sealing element, rigidly securing together the conductors of the cables fitting a casing 3 to between the sealing element(s) to form a housing enclosing the joined conductors, the housing having two connectors 4, 5 for the supply or discharge of fluid to the housing, the connectors being at or close to opposite ends of the casing. Water initially within the housing is expelled by gas under pressure, the interior of the housing then being cleaned while preventing ingress of ambient water. A hardenable, electrically insulating composition is then pumped into the housing, the composition sitting in situ to form a solid filling surrounding the joined conductors and occupying the entire interior of the housing. <IMAGE>

Description

SPECIFICATION Underwater Cable Joint This invention relates to a method of making a cable joint under water without the use of a dry habitat, and to cable joints so made.

There are many applications where it is necessary to make a cable joint under water. In many locations, it is possible for the joint to be made in a dry habitat such as a diving bell which is lowered to the cable location and in which the cable jointing work is carried out. In other, more restricted locations, the use of a dry habitat may be difficult or impossible. Hitherto, it has been extremely difficuit to make a satisfactory cable joint without using a dry habitat. The method of the present invention enables a cable joint to be made in the wet, and accordingly under conditions which require less space and the use of less costly equipment than for conventional cable jointing techniques.

According to one aspect of the present invention, there is provided a method of making a cable joint under water without the use of a dry habitat, which method comprises (1 ) passing each cable through an aperture in a respective resilient sealing element, or in a common resilient sealing element, so that the sealing element(s) fit(s) tightly about the cables; (2) stripping each of the cables so as to expose the conductors which are to be joined together; (3) rigidly securing together the or each conductor of the first cable to the, or to each corresponding, conductor of the second cable; (4) fitting a casing between the sealing elements, or to the common sealing element, so as to form a housing enclosing the joined conductors, the said casing being provided with two connectors for supply or discharge of a fluid to the housing the connectors being at or close to the ends of the casing; (5) expelling water from the housing by causing a gas under pressure to flow into the housing via one of the connectors, and discharging water from the housing through the other connector; (6) cleaning the interior of the housing; and (7) pumping into the housing under pressure a hardenable electrically insulating composition which set in situ to form a solid filling surrounding the joined conductors and occupying the entire volume of the housing.

According to another aspect of the invention, there is provided an underwater cable joint which comprises a housing including two connectors disposed so as to permit fluid flow through the housing; at least one resilient sealing element including one or more apertures for the passage of cable(s) into the housing, the or each sealing element being positioned in an end of the housing; and means for holding together in electrical contact exposed portions of the electrically conductive element(s) of two or more cables, wherein (a) the aperture(s) in the or each resilient sealing element are stepped so as to provide at least two coaxial regions of different diameter whereby a cable with successive layers stripped away can be engaged in the aperture with at least its central element(s) extending into the housing and (b) the or each resilient sealing element is formed of a resilient elastomeric material and is provided with compression means whereby it can be compressed into tight-fitting engagements with the walls of the housing and with the or each cable located in the aperture(s) thereof in order to effect a water-tight seal.

In contrast to conventional methods of making cable joints under water, the method defined above proceeds in the wet so that eventually a joint is made and a casing is fitted so as to surround the joint which casing, initially, is filled with the ambient water. This water is removed from the interior of the casing by a pressurised gas. Subsequently, the interior of the casing is cleaned and then filled with an electrically insulating composition which hardens within the casing to provide a solid, electrically insulating filling.

Normally, the method of the invention will be used to join together two cables each having the same number of conductors. The method of the invention is not limited in this way, however; thus three cables may be joined together if desired, and/or several conductors from one cable can be joined to a single conductor from another cable.

The joining together of the conductors is preferably effected using compression lugs attached to the exposed ends of the conductors and clamped together, e.g. by a nut, bolt and washer arrangement.

The casing which forms the housing is preferably formed of a metal, e.g. steel, or a suitable plastics material. A base plate or cap is preferably used in conjunction with the housing and should be formed of the same material as the rest of housing if the assembly is to form part of a cathodic protection system.

The or each sealing element is preferably in the form of an apertured bung which may, for example, be formed of a hard rubbery material.

The or each aperture in the sealing element preferably comprises an outer portion of relatively large diameter and an inner portion of relatively small diameter, the inner portion being that which will eventually be adjacent to the interior of the housing. A sealing element of this type is more effective than one with a simple aperture of constant diameter, since it enables the entire cable including its outer insulation to be embedded within a part of the sealing element.

The inner portion of the aperture is occupied by the central conductor or conductors of the cable together with its or their individual insulation layers only.

Where a common sealing element is used to receive the two or more cables which are to be joined together, the common sealing element preferably includes a screwthreaded portion which co-operates with a similarly threaded region provided on the exterior surface at one end of the casing, so that the casing can be screwed onto the common sealing element thereby completing the housing. With an arrangement of this sort, the casing is preferably a cylindrical tube and the joint is preferably arranged so that the tubular casing is disposed with its cylindrical axis substantially vertical. Positioning the cable joint in this way facilitates the expulsion of water from the housing and the cleaning of the interior of the housing.One of the two connectors can be provided in the upper end face of the casing, and the other of the two connectors can be provided in the cylindrical wall of the casing adjacent to the opposite end of the casing.

The connectors are preferably of a type incorporating a nonreturn facility, e.g. hydraulic snap connectors.

The gas used to expel water from the housing after the cable conductors have been joined together must be an inert or unreactive gas, for example dry nitrogen or a mixture of argon and carbon dioxide. The latter mixture can be used in commercially available forms, for example 20% argon and 80% carbon dioxide, by volume.

The interior of the housing is preferably cleaned by subjecting it to at least one cycle comprising (a) pumping a solvent through the housing, and (b) after a predetermined time expelling residual solvent from the housing by causing gas under pressure to flow through the housing. In a preferred embodiment of the invention, four such cycles are employed; the solvent in the first is distilled water, that in the second is industrial ethanol, that in the third is dichloroethylene, while that in the fourth is acetone. A priming agent can be incorporated into the acetone to prepare the surfaces within the housing to receive the hardenable electrically insulating composition which is subsequently pumped under pressure into the housing.The pressurised gas which is passed through the housing to eliminate each of the solvents in turn can be the same as the gas used to expel water from the housing initially. The same pressurized gas can also be used to pump the solvents into the housing. In all of these steps, the gas is preferably at a pressure of about 1 50 psig. The gas can conveniently be supplied from a pressurised bottle and where this is done the bottle can be fully vented after the final solvent cleaning stage to ensure that the interior of the housing is completely dry and clean prior to being filled with the electrically insulating composition.

The total volume of gas used in the cable joining method will generally be given approximately by the formula: V=27(x+33)/33, where V is the volume in cu.ft at NTP, and x is the operating depth in feet. For an operating depth of 1 50 feet, the volume is advantageously about 1 50 cubic feet at NTP.

When the preferred cleaning cycle as described above is used with a casing mounted vertically on a single common sealing element, the flow of gas and of each solvent used can be such that the fluid enters the casing via the upper connector and leaves the casing via the lower connector.

The hardenable electrically insulating composition is preferably a mixture of a synthetic resin and a hardener therefor. The two components can be pre-mixed and injected under a pressure of about 1 50 psig into the housing.

The direction of flow of the insulating composition is preferably the reverse of that used for the gas and the or each solvent in the cleaning stage-in other words with the casing mounted substantially vertically on a common sealing element, the resin will be injected via the lower connector and vented from the upper connector.

When operatig in this way, the insulating composition fills the casing evenly. After a sufficient quantity of resin has been vented from the casing via the top connector, it is preferred to seal the top connector while continuing to apply the pressurised composition to the casing via the lower connector. Because of the internal pressure thereby created, this ensures that the interior of the housing is completely filled and it also drives the resin composition back into the cables which are located within the common sealing element. If both of the connectors on the casing are hydraulic snap connectors, it is merely necessary to disconnect the vent pipe from the top snap connector in order to achieve this sealing. It is preferred to maintain the application of pressurised insulating composition for a period of five to ten minutes before it is disconnected from the lower connector.

Conveniently, the hardenable electrically insulating composition can be supplied to the casing from a cylinder using a pressurised gas bottle to drive the composition from the cylinder through piping and into the casing. In one embodiment, a single cylinder containing a mixture of synthetic resin and a hardener is employed. Obviously, the contents of the cylinder must be injected into the casing sufficiently quickly to prevent the mixture from setting within its cylinder. In situations where this embodiment is not practical, there may be employed two cylinders, each containing a separate component which is stable in storage.The contents of the two cylinders are supplied, for example by use of an air-ram cylinder, to a mixer connection, in which the two flows are combined into a single stream, and thence to a mixer unit, for example an active paddle mixer, in order to ensure a homogeneous mixture between the two components. The mixture thus obtained is then supplied to the casing.

Conveniently, the means for cleaning the interior of the housing and for injecting the hardenable electrically insulating composition into the housing can be mounted on a skid which is lowered to the site of the housing and is operated by the diver who is making the cable joint.

For a better understanding of the invention, and to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 illustrates one embodiment of a cable joint in accordance with this invention; and Figure 2 illustrates part of a second embodiment of a cable joint in accordance with the invention.

Referring to Figure 1 of the drawings, the cable joint shown is between two similar cables 1 and 2. These are located in a housing or pot 3. The pot 3 is provided with a first hydraulic snap connector 4 located at the centre of the top end of the pot as shown in the drawing and a second hydraulic snap connector 5 located near the base of the pot on one side thereof. The cables 1 and 2 pass through an outer steel plate 6, a resilient elastomeric sealing element 7 and an inner steel plate 8. The apertures in the resilient elastomeric seal 7 through which the cables pass are stepped, so that the entire cables including all their insulation layers extend partly into the seal 7. The region of the cables indicated at 9 comprises the central conductor of the cable together with its individual insulation layers only.The outer cable sheath has been stripped away from this portion of each cable. The central conductors 10 of the two cables are exposed over a small area above the point where their individual insulation layers (as at 9) have been removed.

The ends of the central conductors 10 are clamped in compression lugs 11 as shown. The dashed lines bounding the area 12 in the cable on the left as shown in Figure 1 indicate the area within compression lug 11 occupied by the compressed portion of central conductor 10. The two lugs are tightly bolted to one another by a nut and bolt arrangement 1 3 and 14 which passes through palms 15 located at the upper end of each of lugs 13 and a metal spacer plate 1 6 disposed between the palms 1 5.

The metal plates 6 and 8 can be dispensed with in an alternative embodiment in which an elastomeric sealing element 1 7 is formed as part of a lower cap 18. The sealing element 17 is located beneath a metal compression plate 23 to which there are attached four bolts 24. These bolts are positioned symmetrically on opposite sides of the two apertures in sealing element 1 7, and extend through the sealing element 1 7 and the cap 18. Cap 18 includes an annular lip 19 the inner surface 20 of which is formed as a screw threaded portion (see Figure 2) which is adapted to engage a correspondingly threaded area on the outer surface of pot 3.The seal between the pot 3 and cap 1 8 is effected by compressing the sealing element 17 by the action of a nut and a washer arrangement 25 which draws the compression plate 23 downwardly onto the element 17 to compress it.

The making of a joint such as that shown in the drawings without the use of a dry habitat will now be described. A diver will first of all prepare the cables 1 and 2 for their subsequent connection.

Firstly, a predetermined length of the cables' outer sheaths are removed. Next, the cables are located within the sealing element 7 taking care to ensure that there is a tight fit. At this stage, no part of the central conductors 10 of the two cables is exposed.

The subsequent steps will be described with reference to Figure 2. After the two cables have been inserted into sealing element 17, a portion of the central conductor 10 of each cable is exposed to give an arrangement as shown in the cable on the right hand side of Figure 2. Thus the exposed area 10 is located between two insulated areas 9 and 22. The cable is then severed along line 21 so that the exposed area 10 is still located between two insulated sections of cable.

Thereafter, insulation 22 is removed and a compression lug 11 is fitted to give an arrangement substantially the same as that shown in Figure 1. When both cables have been similarly treated, the flanges 1 5 of lugs 11 are tightly bolted to one another in the manner shown in Figure 1. It is preferred to effect the compression of the lugs 11 in order to retain the conductors 10 after nut and bolt arrangement 1 3 and 14 has been tightened.

Next, the pot 3 is connected to cap 1 8 so as to enclose the cable joint. With the arrangement of Figure 1, plates 6 and 8 would be fitted on either side of the resilient elastomeric sealing element 7, after which the pot 3 would be fitted about the assembly thereby obtained. Bolts provided between plates 6 and 8 would then be tightened so as to compress the sealing element 7, thereby ensuring that the housing is fluid-tight.

As a result of the steps just described, a cable joint is produced which is enclosed by a housing 3 which will be filled with water, generally with sea water. It is therefore necessary to expel the water from the housing and to clean the interior of the housing prior to injecting thereinto a hardenable, electrically insulating composition which sets in situ to form a'solid filling surrounding the joined conductors. In a preferred embodiment of the method of the invention, this will be achieved by the diver connecting a pressurised gas cylinder to hydraulic snap connector 4 on top of housing 3 while leaving connector 5 open. The gas can be dry nitrogen or a mixture of argon and carbon dioxide, for example in the ratio 20:80 by volume.

Conveniently, the gas is at a pressure of 1 50 psig.

The gas is flowed through the housing 3 for a predetermined time which will be slightly longer than the time taken for a steady flow of gas bubbles to emerge from connector 5. Connector 5 is then closed, and the source of gas removed from connector 4. At this stage, there will be a small residual amount of water in contact with the surfaces on the interior of housing 3. In order to clean the interior a supply of distilled water is connected to connector 4, and a clear walled discharge pipe is connected to connector 5. Gas under pressure is used to drive the distilled water through the housing 3. Again after a predetermined time, connector 5 is closed and the supply of distilled water is removed from connector 4. At this stage, the interior of housing 3 will be filled with distilled water. This is expelled by using a gas sparge applied via connector 4.

Next, industrial ethanol is supplied under pressure to connector 4, leaving the housing 3 via connector 5. The industrial ethanol is passed through the housing for a predetermined time interval. This is followed by a further gas sparge, after which a degreasing solvent, for example dichloroethylene, is passed through the housing for a predetermined time through connector 4, leaving the housing via connector 5. This is again followed by a gas sparge, after which acetone in which there is dissolved a priming agent (for example a rubber solution adhesive) is passed through the housing for a predetermined time, again entering through connector 4, and leaving via connector 5.The sequence of steps is just described ensures firstly that all ambient water, e.g. sea water, is removed from the interior of the housing, and each successive solvent used contributes to the cleaning of the interior of the housing and effectively removes any traces of solvent from the preceding stage. The last solvent employed, i.e. acetone, is evaporated from the housing by a further, prolonged gas sparge, thereby depositing the priming agent over the surfaces of the interior of the housing 3. In order to ensure that all acetone is removed, it is preferred to vent fully the gas cylinder which has been used in previous steps.

Conveniently, the four solvents employed (i.e.

distilled water, industrial ethanol, dichloroethylene and acetone) can be contained in cylinders mounted side by side and connected to a source of gas under pressure so that the contents of each cylinder in turn can be passed through the interior of housing 3.

After the housing has been cleaned and primed, a hardenable, electrically insulating composition is pumped into the housing through connector 5 (i.e. in the reverse direction to that employed for each of the four solvent stages), and excess of the composition is allowed to flow freely out of connector 4. A pressurised gas cylinder may be used to drive the composition into and through the housing. After a predetermined time interval, connector 4 is closed, while maintaining the application of composition under pressure through connector 5.

This state is maintained for from five to ten minutes, with the result that the high internal pressure due to the composition in housing 3 forces some of the composition between the conductors 10 and their insulating layers, thereby giving additional corrosion protection to the cables. The source of hardenable composition is then removed from connector 5, and the completed cable joint is left for a period sufficient to ensure that the hardenable insulating composition has set. The time required will depend upon the nature of the composition employed, but generally a period of about twelve hours will be sufficient.

If the cable joint is to be made in relatively shallow waters, it will be possible for a cylinder containing the prepared hardenable composition to be carried down to the site and connected to the apparatus for supplying the composition to housing 3. If the joint is to be made in deeper water, the two components of the hardenable composition may be taken down to the site separately, and apparatus will be used to feed the two components to a mixer connection and then preferably to an active paddle mixer prior to the mixture being supplied via connector 5 to housing 3.

After the insulating composition within the housing 3 has set, the housing can be fixed in its permanent location. If the cable joint is associated with an oil rig, for example as part of a cathodic protection system, it is preferred to attach the base of the housing 3 (for example cap 1 8 as shown in Figure 2) to a support which itself is attached to part of the rig (for example, to the "Jtube"). The steel cap 18 can be welded to the support. For cathodic protection purposes, it is necessary to ensure that the metal parts which are in contact with one another are at the same electrical potential.

Claims

1. A method of making a cable joint under water without the use of a dry habitat, which method comprises performing the following steps in the ambient underwater environment: (1) passing each cable through an aperture in a respective resilient sealing element, or in a common resilient sealing element, so that the sealing element(s) fit(s) tightly about the cables; (2) stripping each of the cables so as to expose the conductors which are to be joined together; (3) rigidly securing together the or each conductor of the first cable to the, or to each corresponding, conductor of the second cable;; (4) fitting a casing in a fluid-tight manner between the sealing elements, or to the common sealing element, so as to form a housing enclosing the joined conductors, the said casing having two connectors for supply or discharge of a fluid to or from the interior of the housing, the connectors being at or close to opposite ends of the casing; (5) expelling water from the housing by causing a gas under pressure to flow into the housing via one of the connectors, and discharging water from the housing through the other connector; (6) cleaning the interior of the housing while preventing ingress of ambient water; and (7) pumping into the cleaned interior of the housing under pressure a hardenable, electrically insulating composition which set in situ to form a solid filling surrounding the joined conductors and occupying the entire interior volume of the housing.

2. A method according to claim 1, wherein the respective conductors are rigidly secured together by attaching compression lugs to the exposed ends of the conductors and clamping the said compression lugs together.

3. A method according to claim 1 or 2, wherein each cable is passed through an aperture in a common resilient sealing element so that the whole of each of of the cables (including the outer insulation) extends into, but does not extend fully through, the resilient sealing element.

4. A method according to claim 3, wherein the cables are prepared by stripping their outer insulation and then inserting the cables into preformed apertures in the resilient sealing element, which apertures comprise an outer portion of relatively large diameter adapted to receive the cable together with its outer insulation, and an inner portion of relatively small diameter adapted to receive the cable without its outer insulation.

5. A method according to claim 3 or 4, wherein the resilient sealing element is fitted to the casing by being screwed thereto.

6. A method according to any preceding claim, wherein the casing is in the form of a cylindrical tube and wherein the casing and the or each resilient sealing element are positioned with the cylindrical axis of the casing in a substantially vertical orientation while expelling water from the housing.

7. A method according to any preceding claim, wherein the gas used to expel water from the housing is dry nitrogen or a mixture of argon and carbon dioxide.

8. A method according to any preceding claim, wherein the cleaning of the interior of the housing comprises (a) pumping a solvent through the housing, and (b) after a predetermined time expelling residual solvent from the housing by causing gas under pressure to flow through the housing.

9. A method according to claim 8, wherein steps (a) and (b) are repeated four times, and wherein in the first stage the solvent is distilled water; in the second stage the solvent is ethanol; in the third stage the solvent is dichloroethylene; and in the fourth stage the solvent is acetone.

10. A method according to claim 9, wherein a priming agent is incorporated into the acetone used in the fourth stage of cleaning the interior of the housing.

11. A method according to claims 8, 9 or 10, wherein the gas used to expel residual solvent from the housing is the same as that used to expel water from the housing prior to the cleaning step.

12. A method according to claim 8, 9 or 10, wherein the gas is at a pressure of about 1 50 psig.

13. A method according to any preceding claim, wherein in the water-expulsion and cleaning steps, the fluids used are introduced into the housing via the upper of the two connectors and leave the housing via the lower of the two connectors.

1 4. A method according to any preceding claim, wherein the hardenable, electrically insulating composition is pumped into the housing via the lower of the two connectors and is allowed to vent freely from the housing via the upper of the two connectors before the supply of the said composition is cut off.

1 5. A method according to claim 14, wherein, after the said composition has vented from the upper of the two connectors, the said upper connector is sealed while maintaining the supply of the said composition under pumping pressure to the lower of the two connectors.

1 6. A method of making a cable joint under water, substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.

1 7. An underwater cable joint which comprises a housing including a casing having two connectors disposed so as to permit fluid flow through the housing; at least one resilient sealing element including one or more apertures for the passage of cable(s) into the housing, the or each sealing element being positioned in an end of the casing; and means for holding together in electrical contact within the housing exposed portions of the electrically conductive element(s) of two or more cables, wherein (a) the aperture(s) in the or each resilient sealing element is or are stepped so as to provide at least two coaxial regions of different diameter whereby a cable with successive layers stripped away can be engaged in the aperture with at least its central element(s) extending into the housing and with the whole of the cable extending part way into the resilient sealing element; and (b) the or each resilient sealing element is formed of a resilient elastomeric material and is provided with compression means whereby it can be compressed into tight-fitting engagement with the walls of the housing and with the or each cable located in the aperture(s) thereof in order to effect a water-tight seal.

1 8. A joint as claimed in claim 1 7, wherein the casing is in the form of a cylindrical tube.

19. A joint as claimed in claim 18 or 19, wherein the casing is formed of steel or a plastics material.

20. A joint as claimed in claim 17, 18 or 19, wherein the two connectors are hydraulic snap connectors.

21. A joint as claimed in claim 17, 18, 19or 20, wherein the or each resilient sealing element constitutes part of an end cap for the housing, and wherein the or each resilient sealing element is positionedned between a metal sealing plate and the end of the said cap, the resilient sealing element being compressed by the action of connectors extending between the end of the said cap and the metal compression plate.

22. An underwater cable joint substantiaiiy as hereinbefore described with reference to, and as illustrated in, Figure 1 of the accompanying drawings.

23. An underwater cable joint substantially as hereinbefore described with reference to, and as illustrated in, Figures 2A and 2B of the accompanying drawings.