WO2002075103A1

WO2002075103A1 - Cover and method of making same

Info

Publication number: WO2002075103A1
Application number: PCT/NO2002/000031
Authority: WO
Inventors: Geir Huseby
Original assignee: Abb Offshore Systems As; WEUM, Håkon
Priority date: 2001-02-13
Filing date: 2002-01-22
Publication date: 2002-09-26
Also published as: GB2389602A; NO20010738D0; GB0314182D0; NO311902B1; NO20010738A; GB2389602B

Abstract

Cover (1) adapted to be opened/closed in order to cover and open, respectively, an inspection opening (6) in a protective structure (2} adapted for protecting an installation under the sea surface against mechanical impacts. The cover is along one edge provided with an outwardly protruding lug (12) and/or at least one inwardly directed recess (13), and the side edges of the inspection opening (6) are made with a complementary shape. Thus, the cover edge and the edge of the cover opening fit together in a complementing manner. The invention also relates to a method of manufacturing such a cover so that it fits the cover opening.

Description

COVER AND METHOD OF MAKING SAME

The present invention relates to a cover which is adapted to be opened/closed in order to open and cover, respectively, an inspection opening in a protective structure adapted for protecting an installation under the sea surface against mechanical impacts. The invention also relates to a method of manufacturing such covers.

The protective structures considered herein are usually located on the seabed or at least under water in order to protect subsea installations, in particular such as valves and tubes, for example in connection with oil wells on the seabed, against trawl loads and/or falling objects. Such protective structures are often provided with inspection covers so as to provide access to components during the installation and/or operating phase. The covers should as a rule be dimensioned for large loads.

Lately, some protective structures made of laminate have been provided, for example of synthetic material such as fibre-reinforced plastics (FRP) . Such FRP elements are often moulded in a mould. For this reason, details such as flanges etc. which has to be added after manufacturing the main body become unreasonably expensive, inter alia, because much supplementary work is required. Bolted or glued connections of fibre-reinforced plastics (FRP) are generally weaker than the original strength of the laminate from which the protective structure is manufactured, among other things because FRP for strength reasons are sensitive to stress concentrations which occur in such connections.

Reference is made to US patent No. 3,910,056 as an example of prior art in this field (applicant: Oceaneering International Inc., inventor E il. E. Dopyera) .

Further examples of prior art can be found in Norwegian Patent No. 175.7B9 and Norwegian Patent No. 177.647, which both describe protective structures for subsea installations .

The object of the present invention is to provide a cover in a protective structure, preferably made of a plastic material or of a fibre-reinforced plastic, which can be manufactured easily, which requires little supplementary finishing work after manufacture, and which in a small degree weakens the structure with a view to the strength properties, and which can receive and transfer large loads without deforming the cover, the structure or the transition between these components.

In order to describe the principle behind the present invention, at first some theoretical consideration should be made.

A cover which covers an opening, and which is to be moved away from the opening so as to provide access thereto, can theoretically be opened by being moved in six independent manners, which can be expressed by saying that the cover has six degrees of freedom for movement in relation to the structure with which it cooperates. This means that if the cover is restrained for movement in all six degrees of freedom, the cover cannot be opened by pushing, tilting or pivoting along or about an axis of random orientation.

The present idea can according to this be expressed as follows :

Some chosen of the above movement manners can be locked, each movement manner by means of a suitable geometrical lock.

Each geometrical lock may be formed as a non-linearity in the intersectional line separating the cover from the opening, and any such non-linearity creates at least one flange which blocks any movement. Or the slide line may itself be non-linear.

A geometrical lock may also be in the shape of slide grooves, hinges, lugs or other forms of locking against certain movement patterns.

The structure and the cover are moulded simultaneously and separated thereafter, for example by sawing which separates the cover from the structure, possibly by formation of separable, double wall portions under the moulding process.

The cover itself is formed so that when being in a closed condition, geometrical locking is obtained for at least one of its, at the starting point non-locked, degrees of freedom. the geometrical locks and their location should be chosen so that forces impacting the cover are transferred to and are received by the structure itself without deformation of this in an unfortunate manner. the geometrical lock may be formed by means of lugs or flaps with inclined flanges or straight, or possibly wavey, flanges for determining the cooperation of the cover with the structure in a closed condition.

The geometrical locks may be used for distributing loads from the cover into the structure or for guiding the direction of the load in a convenient manner from cover to structure and therefrom to the base or the support location.

Testing for determining convenient locations for local geometrical locks may be made using the "finite element" method without having to make a complete data model of the geometry of the locking element. Testing and optimization may be made in a simple and quick manner.

A cover according to the present invention is made so that it, for a suitable number of degrees of freedom, geometrically locks to the structure to be closed, only by means of the shape of the cover and the shape of the surroundings of the cover, without using fittings, latch pins, bolts, screws or other mounted locking mechanisms. Only the locking of the cover in a completely closed position should possibly be undertaken with a final conventional barrier. As use of the cover will take place under water and for this reason should be operated by divers, ROV (remotely operated vehicle) or similar, it is an advantage that the cover can be attached to the structure in a simple manner, very likely before the structure is arranged on location; and that it can be opened/closed by means of a ROV.

Geometrical locking is achieved by cutting the cover according to a particular pattern, and the pattern of the cutting determines the number of degrees of freedom to be locked. Moreover, flaps can be cut locally, which locks movement along the cut of the cover. For being able to be locked in more than three degrees of freedom, the cover should extend to three dimensions, which often is the case for covers made of FRP.

Geometrical locking is of particular interest for use on protective structures of fibre-reinforced plastic because a protective structure often has a suitable geometrical three-dimensional shape, and because the cover can be moulded in the same operation as the structure to be closed by the cover, because FRP can very easily be cut in complex patterns, and also because the most effective load transfer mechanism of the material by pressure between two edge zones can be utilised. This provides a cover structure which are able to receive large loads, which can be made with few manufacturing operations and with very little finishing work.

For practical reasons, it could be to the purpose to hinge such a cover in such a manner that it can be opened and closed without being displaced. Geometrical locking along the edge area of the cover against a precisely adapted edge area along the edge of the opening then becomes essential for avoiding that large loads have to be received by the hinge points, but instead can be transferred directly into the wall boards of the structure.

All the above advantages and merits are achieved by shaping the cover according to the apparatus claims provided below and manufacturing it according to the method claims mentioned below.

In order to provide a clearer understanding of the invention, reference is made to the description mentioned below of some preferred embodiments and to the accompanying drawings, wherein: Fig. 1 is a simple sketch showing the six degrees of freedom of a cover, fig. 2 shows a tunnel-shaped protective structure for arrangement on the seabed over pipelines or similar; and this structure is provided with a substantially rectangular opening and a lid adapted thereto, fig. 3 shows a structure with a hinged cover, locked in five degrees of freedom, fig. 4-10 shows some details about geometrical locks of different kinds, and fig. 11-18 shows assemblies in pairs of different covers, shown in open and closed condition together with corresponding structure.

Even here it should be mentioned that the same reference numerals are used in all figures for the same or corresponding component, as long as this has been found to be appropriate, that the figures are not necessarily shown on the same scale, and that the scale does not have to be the same in different directions in the one and the same figure. Likewise, the examples are only intended to be examples of embodiments which is not limiting. Thus, the shape, size, relative proportions and choice of material and thickness can be changed in several ways without extending beyond the scope of the invention. Finally the invention may be made with modifications and changes in many different ways as long as this does not contradict the claims presented below. It follows that the invention can also be made with additional purely practical details which do not alter the principle of the invention.

In order to facilitate the explanation of the principle with geometrical locking, reference is first made to fig. 1.

In fig. 1 it has been attempted by means of six examples to show the interpretation of β degrees of freedom. At first, in fig. 1A it is indicated that the cover may be translated in the x-direction. Correspondingly, in fig. IB it is shown that the same cover may be moved in the y- direction; and finally, in fig. 1C, it is indicated how the cover is intended to be moved in the z-direction. In all the examples the cover has been shown with solid-drawn lines in the start position, and in a moved position it is shown with dot-and-dash lines.

Correspondingly, in fig. ID it is shown that the cover may be tilted about the x-axis, in fig. IE tilting about the y-axis, and finally, in fig. IF, tilting about the z-axis is shown. Each of these six manners of movement thereby represents one degree of freedom, so that the cover has a total of six degrees of freedom for movement. A random movement may then include components of one or more of these ways of movement.

Referring now to fig. 2, a "tunnel-shaped" protective cover 2 is shown herein. This structure has a roof plate 3, side walls 4, base plates 5 and an inspection opening 6. Within this structure 2, e.g., pipes or cables may lie on the seabed (not shown) , and the structure has been arranged over these elements in order to protect them against mechanical damages.

On the top side of the structure 2 a rectangular opening 6 are formed, and by the very fact that the lid or cover 1, is made of the material which has been removed from the opening (e.g., by means of a compass saw or other cutting tools) , the shapes of the cover 1 and the opening 6 will be made complementary, and such a manufacturing manner ensures that cover 1 and opening 6 always fit to each other and complement each other.

The geometrical locking is achieved without having linear dividing lines between cover 1 and opening 6, but allowing one or more of the dividing lines change direction, as shown in fig. 2. Thus, flanges are formed which impede lateral sliding of cover 1 lengthwise or crosswise of the opening 6, while the flanges 9 and 10 impede sliding of the cover 1 along the structure 2. If such recesses/projections are utilised on all four side edges, the cover 1 will be locked and the loads will be appropriately distributed, both when the cover is impacted in the longitudinal direction as well as the crosswise direction. In order to remove the cover 1 from the structure 2, it should be lifted directly upwards, or possibly pivoted about one of the axes x-x or y- y-

Fig. 3 shows another embodiment of both a protective structure 2 and a cover 1. Here, the cover 1 is locked in 5 degrees of freedom, as it can only be pivoted up about the x-x axis. This is implemented by means of a hinge 11. The hinge 11 may be manufactured in many different manners, but here it is shown as a cylindrical element which is mounted in a cylindrical opening. The cylinders can be very short, i.e. only correspond to the material thickness of the structure 2 and the cover 1; or at least one of the cylinders can be longer crosswise of the paper plane and possibly extend through the whole structure, from the visible front side to the covered back side.

In figs. 4-7 such geometrical locking lugs are shown in more detail. Figure 4 shows in this case a lugs 12 and a corresponding, complementary recess 13 with a straight 14 and an inclined 15 flange. The straight flange 14 will block all movements laterally, while the inclined flange 15 will tend to force cover 1 and opening 2 apart from each other by impact as indicated by the arrows 0 and 0' . Fig. 4A is a schematic sectional view of the cover 1 and a protective structure 2 of a cover edge with a lug 12 and an edge along the inspection opening 6 with an inwardly directed recess 13, and further illustrates fig. 4. In a similar manner the inclined flanges 16 and 17 in fig. 5 force cover and opening into tighter engagement by external impact as indicated by the arrows S and S' . The flanges can also be somewhat curved, and may have rounded corners. It is possible, in particular by arranging the flanges in correct positions and partly by allowing them to be either straight or inclined in the desired direction, to guide the loads to which the cover is exposed when being mounted and closed, so that the loads in a suitable manner are transferred from the cover to the structure without twisting and impacting it in an unfortunate manner.

It will be apparent for persons skilled in the art that each lug 12 along the cover edge can in one embodiment of the invention be substituted by an inwardly directed recess. Likewise, in another embodiment of the invention it is possible to combine lug 12 and inwardly directed recess along the cover edge. The side edges of the inspection opening 6 of the protective cover will in each case be made with corresponding complementary shapes.

Such lugs 12 and recesses 13 which are shown in figs. 4 and 5, can also be repeated along the complete extent of the cover/opening edges. This is indicated by means of simple variants in fig. 6 and 7. The pattern of such lugs and recesses may be repeated regularly or irregularly along the complete length or a part of the edge portions.

In order to avoid for deformations which may occur to bring the cover more or less out of engagement with the structure, a geometrical locking crosswise of the wall planes may be provided, e.g., by crosswise profiling by means of "groove and tongue" or "mortise and tenon". This is indicated in fig. 8 and fig. 9.

The actual separation of cover and structure is made along a dividing line with an extent which exhibits one or more direction changes so that flanges or lugs/recesses are formed on the cover/opening edge; and these flanges or lugs and recesses are automatically made complementary to each other when the cover is cut , which ensures that the cover; in the case of impact from e.g. trawl equipment, will transfer the loads to the structure itself. In this connection it is important to make the structure/cover and the transitional areas between the structure and the cover as appropriately as possible.

Figs. 11-18 show in pairs a protective structure arranged under water for protecting an installation surrounded by the structure against damage due to trawling across the structure, falling of heavy objects or similar impacts. The structure is provided with hinged covers.

The top figures show the structures with open covers, and the bottom figures show the structures with closed covers. In other respects, the figures should speak for themselves. The covers and the opening edges may of course additionally be provided with transverse locking by means of groove and tongue or similar non-linear forms across the material thickness.

According to the present invention, the hole may be cut after the structure has been manufactured, wherein the cut material is directly utilised as a cover element. In advance, the zone wherein the separation process between the cover and the opening takes place is generally reinforced, e.g, by increasing the material thickness in this zone.

As an example of different cover constructions, reference is made to two similar structures, namely the ones which are shown in fig. 13 and fig. 17. A difference here is that the lid which is formed across the opening in the structure in fig. 13 is hinged along a long side, while the lid which is shown in fig. 17 and fig. 18 is hinged along its short side. More important it is that in fig. 17 and fig. 18 the hinge is integrated, which hinge can be specially constructed for receiving large loads, as a part of the actual lid or cover 1, and wherein a geometrical lock 30 is located so that the hinge points can receive a favourable load. The hinge points are located on the side edge of the structure as an integrated part of the same and are made as broad as possible in order to reduce the load thereon. It should be mentioned that the side walls of the cover and the structure are made so that they butt against each other, and a geometrical lock 31 is also located here, see fig. 17 and fig. 18.

Concerning how these covers can be manufactured, a method is preferred wherein the cover is cut from the structure after the moulding process has been finished. The cut may, in the simplest embodiment of the invention, be made by means of a simple compass saw. In a more sophisticated process, a film or membrane may be applied to a predetermined location in the mould. This film or membrane does not adhere to the material to be used. Thus, a moulded unit may be obtained wherein the material has several layers in the same place in the mould, layers which do not adhere to each other during cure and which therefore, after cure, easily can be separated into structure and cover, possibly after some sawing or similar separation. Thus, the cover and the structure may be moulded in a single moulding process.

The reinforcement to be utilised in the zone wherein separation of cover from structure is to take place, can be a simple increase of the material thickness on the location wherein the structure is to be separated. Thereby no finishing work is required.

The cover according to the present application can be varied and modified in many different manners without extending beyond the scope of the invention. For example, the structure may be a purely local structure covering a valve or similar. However, the structure may also be a very elongate structure covering pipelines which extend across long distances on the seabed. The covers can preferably be manufactured before the structures are deployed, but it is also possible to manufacture the cover after the structure has been submerged to the seabed.

The cover shape which is indicated in figs. 13, 14; 17, 18, are often advantageous at transition areas from pipe trenches and in towards Christmas trees or similar installations. Here, the cover is made as a surrounding cover having a reversed U-shaped cross section, while the shaft constituting the hinge extends crosswise; preferably as two short shafts according to what is shown in fig. 10. However, the shaft may also extend completely from one side of the structure to the opposite side.

The cover does not have to be manufactured by cutting an already produced structure. It can also be manufactured separately in a form of its own, in particular if the design indicates this.

The cover does not have to be made of a single part, but can be divided into several cover sections which can be connected with geometrical locks and/or hinges. Moreover, it may be advantagous to build a cover from modules being constructed to co-operate and for transferring loads to each other via geometrical locks.

Claims

C l i s

1. Cover (1) adapted to be opened/closed for opening and covering, respectively, an inspection opening (6) in a protective structure

(2) adapted for protecting an installation under the sea surface against mechanical impacts, c h a r a c t e r i z e d i n that the cover (1) along at least one edge is provided with at least one protruding lug (12) and/or at least one inwardly directed recess, and that the side edges of the inspection opening (6) is made with a complementary shape; so that the cover edge and the edge of the cover opening fit together in a complementing manner and form a geometrical lock.

. Cover according to claim 1, c h a r a c t e r i s e d i n that it comprises at least one cover section and that the individual sections engage each other, at least when the cover is closed.

3. Cover according to claim 1 or 2, c h a r a c t e r i z e d i n that it is provided with a pattern of lugs and recesses.

4. Cover according to claim l, 2 or 3, c h a r a c t e r i z e d i n that the pattern is repeating.

5. Cover according to one of the claims 1-4, c h a r a c t e r i s e d i n that each of the lugs/recesses has at least one straight flange (13;14).

6. Cover according to one of the claims 1-5, c h a r a c t e r i z e d i n that each of the individual lugs/recesses has at least one inclined flange (15;16,17).

7. Cover according to one of the claims 1-6, c h a r a c t e r i z e d i n that the cover edge and the side edge of the inspection opening are provided with groove and tongue pattern (19,20) along at least a portion of its lengt .

6. Cover according to one of the claims 1-7, c h a r a c t e r i z e d i n that the cover edge and the edge of the inspection opening,, respectively, locally are provided with at least one lug (22) and a thereby cooperating hole (23) which co-operates when the cover (1) is closed.

9. Cover according to one of the claims 1-θ, c h a r a c t e r i z e d i n that the cover moreover is mounted on the protective cover along one of its side edges by means of a hinge (15;25) .

10. Cover according to claim 9, and wherein cross section of the actual cover is U-shaped and complements the protective structure (2) and are hinged to this by means of shafts (24) or similar mounting means formed in the side walls (26) to the cover (1) and the side walls (27) to the structure (2) .

11. Method of manufacturing a cover (1) adapted for opening and closing an inspection opening (6) in a protective structure (2) adapted for protecting an installation under the sea surface against mechanical impacts, and wherein the protective structure (2) and also the cover (1) are moulded of synthetic material such as fibre-reinforced plastic (FRP) , c h a r a c t e r i z e d i n that the protective structure (2) and the cover (1) are moulded simultaneously and are separated only after the material is cured.

12. Method of manufacturing a cover according to claim 11, c h a r a c t e r i z e d i n that at least parts of the cover (1) and the protective structure (2) adjacent thereto are separated from each other already during the moulding process by placing a non-adhesive film or membrane between the protective structure and the cover, which film or membrane may extend partly perpendicular to the material and partly along this.

13. Method for manufacturing a cover (1) according to claim

11 or 12, c h a r a c t e r i z e d i n that the cover (1) and the structure (2) are separated by sawing, water jet cutting or burning.

14. Method of manufacturing a cover according to one of the claims 11-13, c h a r a c t e r i z e d i n that the area wherein the cover (1) and the structure (2) are to be separated/ is reinforced before separation takes place.