NO863428L - DEVICE FOR SUPPORTING, PROTECTING AND TRANSPORTING ONE OR MULTIPLE CABLES CALCULATED ON AA IS INSTALLED ON A SEASON AND PROCEDURE FOR PRODUCING THE SAME. - Google Patents

Description

The present invention relates to an arrangement of one or more lines (pipe bundles) intended to be placed on a seabed, such as a well power line, control line, cable and the like, as well as a device for submerging, protecting and transporting such lines.

The device according to the present invention is particularly, but not exclusively, suitable for supporting and transporting pipe bundles. The present invention further relates to a method for manufacturing such a device as well as assembly of the device and said wire(s).

Underwater pipelines can be produced and installed individually according to several known methods. However, when several cables are to be laid between two points on the seabed, it is advantageous to collect these cables in so-called "flowline bundles", hereafter called pipe bundles. The production and assembly of such pipe bundles is known technology, as the individual wires are placed in a protective pipe (carrier pipe) which has several functions beyond serving as protection. Such other functions may consist of providing the necessary strength and buoyancy for transport and installation of the unit.

The production of such a construction is relatively complicated and requires a production site that can either accommodate the entire pipe bundle, i.e. have an extent of up to 3.5-4 km, or which can take at least 600 - 800 m of the pipe bundle and which at the same time has good opportunities for storing the finished part of the construction in a floating state in a sheltered, non-trafficked sea area, such as, for example, an arm of a fjord or on; the bottom of the fjord.

After installation, the wires in the protective tube are inaccessible for inspection, repair and replacement. It is also not possible to increase the number of wires in a ready-made bundle.

The conventional manufacturing method of pipe bundles is also complicated in that the protective pipe is pulled in short lengths (approx. 12 - 24 m) over previously welded internal pipes and wires. This operation requires that all or a significant part of the pipe bundle (approx. 1/2, 1/3 or exceptionally 1/4, i.e. up to approx. 800 m) lies on the production base on land. The support consists of a long line of rollers or sled carriages on land. This operation represents several elements of risk in the manufacture, as the pipes must be handled carefully in this phase so that vulnerable wires are not damaged.

The purpose of the present invention is to provide a solution for bundled pipes that enables the production of very long units on land areas that do not necessarily have a sufficiently long accessible area for the production of the cable in full length in one operation. A further object of the invention is to provide a system which enables the addition of new wires in the bundle even after the bundle has been installed on the seabed. Furthermore, the purpose is to provide an economical manufacturing method for such bundled pipes, where the pipes can be inspected at any time and possibly replaced/repaired and reinstalled. Protection against impacts from fishing gear is also provided.

According to the present invention, it is therefore proposed to use at least two elongated, parallel and spaced structural elements, e.g. in the form of cellular tubular bodies which are interconnected with each other by means of transverse connections. Said transverse connection can be made up of a frame, individual cross braces or the like, arranged for the pipes at their lower part. The underside of the frame may have a keel-shaped lower edge, while said transverse connection(s) at its upper part may be equipped with clips or clamps which are elastic and which are intended for receiving and clamping said one or more submarine cables. The clips or clamps can advantageously have such a shape and elasticity that they release the wire(s) when the pulling force to extract the wire(s) exceeds a predetermined value. Another way of attaching cables is a regular fixed connection, such as brackets, straps or the like.

The solution according to the present invention is suitable for the transport, protection and installation of one or more pipelines and these can be arranged in bundles, situated in one or more layers in said longitudinal channels.

On the underside of the solution, there can also be a ballast chain or ballast device, for example in the form of a plumb bob or the like, which is attached to one or more arms, hinged at least at one end to the elongated body. The arms can rotate about an axis which is substantially situated across the longitudinal axis of the elongated body, whereby the arm(s) can be swung to a retracted position below the elongated body.

The support device can have the same length as the pipe bundle itself and can be constructed as described in Norwegian patent application no. 86.0673.

In the following, the present invention will be described in detail, with reference to the embodiment examples shown in the figures, where

figure 1 shows a vertical cross-section through an embodiment of the device according to the present invention with the wires installed;

figure 2 shows a vertical cross-section through a second embodiment with the wires arranged in several horizontal levels;

figure 3 shows a vertical cross-section through a third preferred embodiment where wires are also placed on the outside of the protective device;

figure 4 shows a vertical cross-section through the means for retaining the wires, as fig. 4A shows clips or clamps with the wire in place, while fig. 4B and 4C show corresponding clips or clamps where the wire is respectively pulled out and pressed down;

figures 5A and 5B show two preferred ways of increasing the device's floating stability in the surface position and in the submerged position by means of ballasting;

figure 6 shows a vertical cross-section through a further embodiment, equipped with insulation elements for thermal insulation of the wires;

figure 7 schematically shows a plant for producing the solution according to the present invention;

figure 8 shows a principle for supporting the solution according to the present invention during its manufacture, and

figure 9 shows a vertical cross-section through the device according to

horizontal invention in a floating position, with devices for adjusting the freeboard or buoyancy to be prepared for discharge

Figures 1, 2 and 3 show a vertical cross-section through three typical variants of the device according to the present invention. The solution includes a pipe bundle I. The pipe bundle consists of lines 1, 2, 3 such as production pipes, service pipes and cable. These pipes 1, 2, 3 are laid into a structure 10 which consists of support and protection pipes 4 which are mutually attached to each other by means of a connecting structure 5. In most cases, the wires 1, 2, 3 are laid into the structure 10 so that these are sufficient protection against fishing gear. The degree of protection can be increased by means of a covering device 7, placed over the wires 1, 2, 3. (shown in figure 2).

The wires 1, 2, 3 rest on supports 6, preferably arranged on the connecting structure 5. The supports 6 and in some cases also the connecting structures 5 are arranged at certain intervals along the structure 10, for example at intervals of 6 - 12 m. If the wires 1, 2 , 3 have sufficiently large negative buoyancy in all operational phases, including installation and operation out in the field, then it is not necessary to attach these wires 1, 2, 3 to the structure 10.

Otherwise, the wires 1, 2, 3 must be attached to the structure 10, for example by means of clamps or clips 8 (see figure 4). It may also be desirable to fasten the wires 1, 2, 3 based on the requirement to absorb forces, induced in the wires 1, 2, 3 due to strain, for example caused by temperature and pressure changes.

If it is required that the cables 1, 2, 3 can be easily lifted out of the structure 10 and/or that other cables 1, 2, 3 can be inserted, these can be held in place by means of a spring-loaded device 8 which releases the cable when the extraction force exceeds a predetermined holding force.

Such a device 8 can e.g. is designed as shown in Figure 4. In Figure 4A, the wire 9 is held in position by means of a spring member 8. This is designed so that a certain vertical force can bend the spring member 8 to the side so much that the wire 9 can be released as shown in Figure 4B.

The line 9 can also be put in place from above by the spring member 8 being opened when the vertical force from above, for example caused by the line 9's negative buoyancy, acts on the spring member 8 as shown in Figure 4C. The design and material selection of the spring member 8 can be made so that the extraction force is greater than the insertion force.

It may be relevant to improve the buoyancy and transverse stability of the construction 10 in the submerged position before the construction 10 is set down on the seabed if it is exposed to horizontal hydrodynamic forces induced by current and/or waves. This can be achieved either by increasing the strength of the construction 10 or by increasing the distance between the buoyancy and center of gravity of the construction 10, hereafter referred to as ballasting. Since increasing the strength has clear physical and financial limitations, ballasting represents the most relevant method.

The ballasting can be carried out, for example, as shown in Figures 5A and 5B, where Figure 5A shows an arrangement for stabilizing the construction 10 in a horizontal position, while Figure 5B shows an arrangement for stabilizing the construction I when it is in an inclined position. According to the design example shown in figure 5, the construction 10 is provided with a hoop 11, wire 12 and plumb/ballast 13. The hoops 11 are attached to the construction 10 by means of hinges 14. The hinges 14 make it possible to swing the hoops 11 and the plumb 13 in under the structure 10 to a retracted position when the structure 10 is installed on the seabed. The hinges 14 or the hoops 11 can be equipped with stop devices (not shown) which limit the opening angle of the hoops 11 during the transport phase and the installation phase. In this way, the stoppers contribute to the hoops 11 being placed under the structure 10 in a certain direction after the structure 10 has been laid down on the seabed.

If the structure 10 is transported and submerged in an inclined position as shown in figure 5B, the hoops 11 should be asymmetrical.

The length of the hoop 11 and the weight 13 are determined based on the requirements for floating and rotational stability.

In order to further increase the distance between the center of gravity and the buoyancy point, it may be appropriate to use floating bodies. These can be attached to the upper side of the construction 10 by means of hinged hoops (not shown). However, the buoyancy bodies must either be removed after installation or laid down so that fishing gear can pass unhindered over the construction 10 in areas where this is required.

If the installation and connection procedures require that the construction

10 is held floating in a position above the seabed with low contract pressure against the bottom, in order to be able to move the construction 10 along the seabed in a controlled manner, it is natural to use chains hanging vertically down

as weight 13. Utilization of chain in this way is in and of itself known technology for the installation of conventional pipe bundles.

If required, the lines 1, 2, 3 can be insulated to reduce heat loss in the transported medium. This can be done in a conventional way so that the individual wires are required to have their own insulation. Such a solution enables the inspection/replacement of individual cables. If inspection/replacement is not applicable and/or great demands are placed on installation ability; it is advantageous to encapsulate the wires 15, 16, 17 into insulation elements 18, 19 as shown in figure 6.

Temperature changes in production pipes are different than in the support structure and induce forces or relative movements, or a combination of these, between the lines and the support structure. From constructional considerations, it is advantageous to reduce or eliminate relative movements between the wires and the structure at each end. This leads to axial forces in the wires. These can either be as rigid, e.g. caused by the fact that the supports 6 are placed at a small distance from each other, that they withstand thermal forces, or that they break under a certain load according to a predetermined pattern. Alternatively, the wires can be equipped with expansion elements to compensate for changes in dimensions in the longitudinal direction. In the event of buckling, it may be advantageous to insert during the assembly of the construction (10) and/or the wires a small but sufficient curvature to control the direction of buckling. Material thermal elongation is assumed to be approx. 0.001 of the length which gives a buckling from the pipe axis approx. 0.005 - 0.01 of pipe length breaking out. Typical pipe length in this described construction, which can break, is approx. 10 m, which gives a deflection of 50-100 mm in the middle

the storage points.

The effect of pressure and temperature changes is reduced by the fact that the cables and the structure are laid on the seabed with a permanent tensile force (in a pressure and temperature unloaded state). Such a tensile force is often a natural result of installing the entire structure.

Structural elements exposed to corrosion should be protected according to known principles.

In the following, a possible manufacturing method will be described in more detail with reference to figures 7 and 8.

With the solution according to the present invention, it is possible to produce pipe bundles at construction sites with a limited extent (down to approx. 100 - 200 m) if these lie towards a sheltered sea area (e.g. an arm of a fjord). The production can also be carried out in a floating production facility if requirements for environmental conditions are met.

The production can take place continuously in such a way that both the wires 1, 2, 3 and the support and protection structure hereinafter called (PSI) 5, 6 are welded together by lengths of e.g. 12 m and after each completed joint, the finished part of the pipe bundle I is pushed with PSI into the water where the pipe bundle I floats supported by PSI while other parts are successively produced on land.

An example of the manufacturing process and arrangements in principle shown in fig. 7. The process is divided into eight work stations 20 to 27. The steel frame 5 for mounting carrier and protection pipes (BB pipes) and line supports is assembled in station 20. BB pipes are welded together and the welds are tested/inspected at station 21. Pipelines (production, service lines) are welded together and tested/inspected at station 22. If necessary, the joints of these lines are provided with corrosion protection and insulation at station 23. At station 24, the steel frame 28 is arranged on the underside of BB pipe 29 and welded together to form of the PSI construct. If necessary, the joints are protected against corrosion and any sacrificial anodes are mounted at this station. At station 25, finished cables 30 are laid in finished PSI construction and fixed as required. At station 26, cables 31 are laid in the finished construction where the pipelines are also installed. The cables (electrical, hydraulic) are delivered in full length on drum 32. The maximum delivery length of these cables (as of today approx. 3.5 - 4 km) can be limiting the maximum length of an individual section of the overall construction. If a longer construction is necessary, the construction is built in sections that are joined together.

Stations 20, 21 and 22 are arranged in parallel. It is advantageous that station 20 lies below 21, so that the construction 29 forms a straight line and the flexible frame 28 is bent up to the construction for welding. In contrast, station 22 can be placed at the same level as station 21 and the wires 30 are bent slightly by their own weight when these are lifted into place into construction 29 at work station 25. Stations 23, 24, 25 and 26 are arranged in series with parallel stations 20 . and allows horizontal transport of the elements 28, 29, 30 and 33. The floating part of the finished construction 34 is applied with a certain tensile force to increase the stiffness and thus resistance to environmental loads (current, wind and wave forces). The tensile force is achieved by of winch(s) 35, 36 and cables 37 and 38. The tensile force is held between two fixed points, one on land at the production site 33 and one in water, equipped with an anchor system 40. This anchoring point can also be established on land on the opposite side of the production site if this is advantageous. Attachment point 39 can, for example, be arranged as one or more pairs of wheels (with rubber tires and brakes) which clamp BB tubes, or in principle a movable gripper arm which stands in the way of the cross brace on the steel frame 28 and thus prevents movement of the entire structure 34.

Another manufacturing method is based on a greater degree of prefabrication. Sections of finished support structure (length e.g. 24-36 m) are brought to the production site where these are welded together. The rest of the process is basically the same as described above.

An arrangement of support for construction parts 28, 29, wires 30 and finished construction 33 is shown in principle in fig. 8. The rollers 43 on the support structure 44 are arranged so that they form a rectilinear support for the structure in section A. In section B, 43 and 44 are arranged so that they form a transition ramp that takes the structure down into a floating position without inducing unacceptable stresses. Another method of support and movement is based on the use of wheeled undercarriage which is removed as the structure is transferred to a floating position. Such a method does not require the underside of the construction to be "smooth" without protruding parts, e.g. individual crossbars that tie the supporting elements together.

When the entire construction is finished, the last part is kept on land and the necessary testing of wires, BB pipes and cables is carried out. Any errors are corrected. The weight of water used for testing cables is compensated by the structure's buoyancy without the need for special buoys. If required, the BB tubes are filled with nitrogen and pressurized. Safety for all handling in water is increased if the pressure in the BB pipe is measured and in the event of a pressure drop, the loss of gas is automatically replaced.

When the testing has been carried out and the construction is prepared for transfer to water, the end of the construction which is still on land is attached to a cable and winch which ensures the necessary tension in the construction after the entire length has passed the holding point 39 in fig. 7. In a floating state, the structure can be handled in sheltered waters with the help of two tugboats. The construction can now be transferred to either a storage or trimming location.

Regardless of the thawing and immersion method, the structure is now checked

buoyancy and weight ratio and possibly adjusted. This operation can be done in a known way, if the construction is to have a negative buoyancy to be transported under the sea surface according to the so-called* "controlled depth tow" principle. If the construction is to have positive buoyancy (for transport in surface position), this can be adjusted by adding or removing suitable ballast, e.g. chain, until the desired buoyancy is achieved. Fig. 9 shows a device for determining buoyancy by measuring the depth of construction 45. A frame 46 is attached to construction 45. The frame carries two identical, transparent pipes 46, 47 provided with a scale for reading the water level in the pipes. In order to dampen the movement of the water level inside the pipes, these are equipped with hoses 48, 49 which stick down to a depth where the water pressure is not affected by short surface waves. This keeps the water level in the pipes stable.

There can be various reasons why the construction must be made in

sections and then connected.

If there are only production reasons for the construction to be made

in several sections, the connection of these can take place before the actual thawing in sheltered waters.

If the maximum construction length is determined by inward shear mooring, the connection can take place before outward shear mooring begins. The connection is carried out in a sheltered place.

If the maximum construction length is determined by external shear towing, the connection must be carried out at the installation site.

Connecting the carrier pipes is done first and carried out according to known methods, e.g. by means of screw connection of flanges or welding. The end walls of the carrier tubes are waterproof to achieve the desired buoyancy. When the sections are connected, it is not necessary to open the entire internal cross-section of the carrier pipes. The connection between the sections which is necessary for internal air and water transport during the immersion can be established with the help of smaller pipes which can preferably be equipped with non-return valves.

The interconnection of individual wires in the construction can be carried out according to known methods, e.g. when using connectors or welding. To simplify the connection operation, it is possible to lift some wires from the structure, place them temporarily on a surface supported by

the carrier pipes and perform the connection and testing in air. Then add

t

the wires in place again in the construction.

Transport of the construction can be carried out in the same way as transport of conventional pipe bundles, e.g. bottom tow or "control depth tow" (CDT). These methods are known and are not described here.

It is also possible to transport the structure floating in surface position. Its strength, flexibility, buoyancy and size together with wave and current conditions determine whether this is possible. The rigidity of the structure in the vertical direction can be increased and wave forces reduced significantly if transport is carried out in an inclined position as shown in fig. 3B. This position is particularly favorable if the transport takes place parallel to

the wave direction.

A very important feature of the device 1 is that its buoyancy or submerged weight can be adjusted. There are two types of adjustment that are relevant:

1) Adjustments along the wire

2) Adjustments in the following time phases:

- Transport of the device

to the installation location.

- Assembly before installation.

- Installation (immersion, positioning).

- Operation (operational and environmental forces, etc.)

Possibly also:

- Inspection, repairs

- Removal of the structure

For this purpose, the elongated pipes 4 in the support construction I can be equipped with transverse and one or more longitudinal, preferably vertical bulkheads or the like, between which chambers communicating pipe systems can preferably be arranged. The contents of said chambers can be: (a) air at atmospheric pressure (for operation with the structure on

the surface);

(b) air at a pressure equal to the hydrostatic pressure at the installation site

(in the installation and operation phase).

Claims (11)

1. Device for supporting, protecting and transporting one or more submarine cables, such as a well current line, control line, cables and the like, consisting of an elongated body with buoyancy and equipped with one or more longitudinal, upward and/or laterally open channels or similar in which said submarine line(s) are intended to lie, characterized in that said elongate body is formed by two elongate, tubular bodies located at a distance from each other in the longitudinal direction of the elongate body, which are mutually connected to each other by using transverse connection(s). 2. Device as specified in claim 1, characterized in that each transverse connection is made up of a frame or the like with or without a downward-facing keel-shaped lower edge. 3. Device as stated in claim 1 or 2, characterized in that said transverse connection(s) is equipped with clips or clamps at its upper part, which clips or clamps are elastic and are intended for receiving and clamping said one or more underwater wires. 4. Devices as specified in claims 1-3, characterized in that the device is used for the manufacture, transport, installation and support of pipelines. 5. Device as specified in claims 1-4, characterized in that the pipelines are arranged in a bundle, located in one or more layers in an open row between said longitudinal channels. 6. Device as specified in claim 1, characterized in that the elongate body along its outer, lower side(s) is equipped with devices that enable the placement and retention of additional pipelines. 7. Device as stated in claims 1-6, characterized in that on the underside of the elongate body a ballast member is arranged, e.g. in the form of a plumb line, or the like, which is attached to one or more arms, hinged at one or both sides of the structure, so that the arm(s) can rotate about an axis substantially situated across the longitudinal axis of the elongated body, whereby the arm(s) can be swung into a retracted position under the elongated body. 8. Device as specified in claim 4, characterized in that said clip or clamps have such a shape and elasticity that they release the wire(s) when the pulling force exceeds a predetermined value. 9. Procedure for the production of long underwater pipelines, and in particular underwater pipelines consisting of bundles of pipes, characterized by the fact that the underwater pipeline is assembled as a continuous unit at a suitable location on land, as the pipeline system passes through different successive and/or parallel workstations where various operations in the manufacturing process are carried out, after which the finished part of the underwater line is pushed and/or pulled out into the water to preferably be kept in a floating position, preferably placed under an axial pull. 10. Method as stated in claim 9, characterized in that the line system including support device is assembled from prefabricated units that are connected together prior to partial pulling of the finished part into the water. 11. Method as stated in claim 9 or 10, characterized in that a frame is first produced consisting of at least one elongated tube and attachment to said at least one tube arranged - support body, intended to serve as a carrying and support body for pipelines and cables both during manufacture, transport, immersion and operation, in that sections of said at least one pipe with support means are assembled together and inspected, after which the sections are welded together and then brought together with said pipes or cables by bringing the merged sections under said pipes or cables and attached to these, this process being continued continuously until the entire length or the desired section length has been produced.