GB2268955A - Valve assembly to be used in a subsea structure, particularly a mudmat - Google Patents

Abstract

A valve assembly to be used in a subsea structure 8, particularly a mudmat, has a valve closing disc (2) hung, with limited free play, from a support member (2). The support member is provided with pivotable connecting hooks (16) engaging with a flange (7) on the subsea structure, thereby securing the support member and valve closing disc to the subsea structure 8. By means of a central tightening screw (17) the valve closing disc may, when the hooks are in gripping engagement with to the flange, be pressed down so as to bear against a valve seat formed by the free annular surface (6) of the flange. In the open position of the valve assembly, the valve closing means are held in a position above the flange (7) by means of a rod (12) which extends downward from the valve closing means and penetrates a hub sleeve (11) in the aperture, and which may be locked in an open position there. When the through aperture 10 in the subsea structure is to be be closed, the holding engagement between the rod (12) and the hub sleeve (11) is released and the support member (2) and valve closing disc will then sink down toward the flange, whereby the connecting hooks (16) achieve underlying gripping engagement with the flange. <IMAGE>

Description

VALVE ASSEMBLY The invention relates to a valve assembly to be used in a subsea structure, particularly a mudmat, for providing/closing a flow of fluid between an area on the top side and the bottom side of the subsea structure through an aperture between the top side and the bottom side.

The invention has been developed particularly in connection with the problems encountered when submerging a sub sea structure. Subsea structures to be set down on oil or gas fields where seabed conditions are comparatively soft are provided with mudmats so as not to sink down into the soft substrate. Such mudmats can in the main consist of steel deck-like structures surrounded by "skirts," i.e., vertical underlying steel walls which during the positioning of the subsea structure will penetrate the soft surface of the seabed and prevent pressure leaks underneath the mudmat.

Depending upon the conditions of the seabed, mudmats may extend over quite a large area. Similarly, the underlying skirts may be quite high, for example up to 4 meters when serving as anchoring systems as a substitute for piles.

The mudmats may also be used for adjusting the level of the subsea structure. By pumping in water underneath the mudmat it is possible to lift the subsea structure to a desired horizontal position in relation to the ocean floor.

During the first phase of the installation of the subsea structure in the field - when the structure is lowered through the co-called splash zone, an air cushion may be formed underneath the mudmat. If this compressed mass of air is not allowed to escape, a buoyancy will thereby be created with the result that the whole structure may become floating and incapable of submersion. If the air does not escape fast enough, the mass of air that is generated by vertical wave motion may, in addition to the lowering velocity, give a slack with resulting dynamic tugs in the lifting straps. Such dynamic tugs may lead to catastrophic collapse of the lifting equipment and the subsea structure.

In addition, during the final phase of the installation in the field the water underneath the mudmats must be allowed to escape so that the skirts may penetrate the ocean floor.

Both these phases of installation thus necessitate an effective valve operating system. The normal procedure today is to use large flap valves. These valves are thus open during the whole installation phase, and are not closed until the sub sea structure has penetrated the ocean floor to its final position. On large depths of water it is usual to have an unmanned mini-submarine (ROV) go down to close the valve or valves. However, these large valves are very costly, and the cost is out of proportion to the simple one-time function for which they are intended. As indicated, mudmat systems may be used and are increasingly intended to be used for anchoring subsea structures, thus replacing the much more elaborate and costly system of piles, and the currently used valves will thus constitute a significant cost for a project.A great number of such valves may be required for a single project.

It is therefore an object of the invention to provide a valve assembly to be used in a subsea structure, particularly a mudmat, said valve assembly being simple and safe in operation, and also easy to disconnect for reparation or exchange. A special object of the invention is to make possible a valve assembly where the valve function is visible and thus may be observed, for example by a ROV camera.

According to the invention there is proposed a valve system of the type mentioned by way of introduction, characterized in that it comprises valve closing means; tension bridge; means for holding the valve closing means in the tension bridge, allowing some free movement; means for pressing down the valve closing means from the tension bridge within the range of free movement; means for releasable connection of the tension bridge in a position above the through-going aperture; and a holding means for the valve closing means and the tension bridge, designed to hold the valve closing means down in a position over the through-going aperture, in which position the tension bridge is connected to the subsea structure with the releasable connecting means over the through-going aperture, and the valve 'closing means can be pressed down from the tension bridge to a sealing engagement with a valve seat around the aperture, and in a lifted, securely held, free position, respectively.

Such a valve assembly will be located on the top side of the subsea structure (mudmat) and can easily be observed.

The embodiment can be made very sturdy and simple, resulting in low cost. A special advantage is that the valve assembly as such is releasably connected, so that it optionally can be taken up for inspection, reparation or exchange. This is important, particularly in the critical phase where the subsea structure is moving through the splash zone, because the subsea structure may be exposed to such strain that one or several valve assemblies may be disadvantageously affected.

The valve closing means may be especially advantageous in the form of a simple valve closing disc adapted for sealing contact around the through-going aperture.

It may be especially expedient that the holding device comprise a rod extending downward from the valve closing means through hub sleeve in the through-going aperture, with a locking groove/key connection between the rod and the hub sleeve.

According to the invention it may be especially expedient that the means for releasable connection of the tension bridge in a position above the through-going aperture comprise vertically pivotable connecting hooks mounted on the tension bridge, as well as a flange formed around the through-going aperture of the subsea structure, said flange being designed for gripping engagement with the connecting hooks and as valve seat for engagement with the valve closing means. Further features of the invention will appear from the dependent claims.

The invention shall now be described further with reference to the drawings, where: Figs. 1 - 5 show purely schematically the construction and manner of operation of the new valve assembly, Fig. 6 is a perspective view of the valve assembly in open position, corresponding to Fig. 1, Fig. 7 is a perspective view of the valve assembly in a position ready to start closing, corresponding to Fig. 2, and Fig. 8 is a perspective view of the valve assembly in closed position, corre sponding to Fig. 4.

Fig. 9 is a sectioned view of a second embodiment and Fig. 10 is a top view of the second embodiment.

The new valve assembly consists in the main of tension bridge 1 and valve closing disc 2 hung therefrom with a certain freedom of movement. The free movement or play is made possible in that the valve closing disc 2 is hung in the tension member 1 by means of, in this case, two bolts 3, 4, which are screwed into the valve closing disc, but move freely in the bores of the tension bridge 1.

On the bottom side of the valve closing disc 2 there is affixed an O-ring 5 around its circumference. This is intended for sealing contact with a valve seat formed by the upper free annular surface 6 of a flange 7, formed on a protruding cylindrical connecting piece 8 which is attached to said sub sea structure 9 around a through-going aperture 10 in the subsea structure.

In the connecting piece 8 there is mounted a hub sleeve ii.

From the valve closing disc 2 a control rod extends down, penetrating the hub sleeve ii. The control rod 12 and the hub sleeve ii has a locking groove/key connection, there being formed a longitudinal broken key 13, 14 on the rod 12. Correspondingly, the bore in the hub sleeve ii has a groove 14 (see Fig. 6) dimensioned for letting the key pass through. The broken portion of the key has a length corresponding to the length of the hub sleeve, so that in one position the upper key portion 13 will rest against the top side of the hub sleeve, whereas the lower key portion 14 will lie against the bottom side of the hub sleeve, so that the rod 12 in this way will be blocked in both longitudinal directions. By rotating the valve rod 12, the key 13, 14 can be brought to align with the groove 14 of the hub sleeve, so that the rod thereby can be moved in its longitudinal direction in the hub sleeve, as depicted in Figs. 2 and 3; see also Fig. 7.

The tension bridge 1 is in the concrete embodiment example shown in figs. 7-9 formed as a circular disc, having four protruding support brackets for respective connecting hooks 16. These connecting hooks can pivot freely in their brackets and, when the tension bridge and the valve closing disc are lowered, as indicated in Figs. 2 and 3, the hooks will approach the flange 7, slide away and then snap in underneath the flange, as shown in Fig. 3; see also Fig. 8.

Centrally positioned in the tension bridge 1 there is a threaded bore wherein a screw 17 is screwed. This screw is directed toward the underlying valve closing plate 2. By rotating the screw 17, i.e., screw it into the tension bridge, the screw will press against the valve closing disc and push it downward, i.e., away from the tension bridge.

This is depicted in Fig. 4. The connecting hooks 16 will hold the tension bridge back, so that the valve closing disc will press against the flange surface 6 and close the through-going aperture (Fig. 8).

The depicted and described valve assembly is designed for service/operation by means of a ROV, and the bridging plate 1 is therefore provided with a fastening bar 18 for a ROV.

The bolts 3,4 with some free movement and the screw bolt 17 are surrounded by protective collars 19, 20, for protecting the bolts and the screw against blows or jolts from the surroundings, for example from objects which might fall down on the valve assembly. The screw 17 has a cross bar 21, designed to be easily actuated by a suitable tool on a ROV.

The valve assembly operates in the following manner: In the open position the tension bridge, valve closing disc and the pertaining rod are in a lifted, securely held position, as shown in Figs. 1 and 6. The valve assembly is then fully open and water and air can flow freely through the aperture 10. When one wishes to close the valve assembly, the tension bridge is rotated, in this case 900, so that the key 13 is aligned with the groove 15 in the hub sleeve 11. This position is shown in figs. 2 and 7. The tension bridge, valve closing disc and the rod will then sink down as indicated by arrows in Fig. 2, to the position shown in Fig. 3. The hooks 16 will then move toward the flange 7 and swing out and snap back into a gripping engagement underneath the flange. In this position the screw 17 may be actuated.A few turns will be sufficient to press the valve closing disc with the O-ring 5 against the valve seat 6, which is formed by the free annular flange surface. Hooks 16 will serve as the resistance base in the tightening procedure. After such a tightening by means of the screw 17, the valve assembly will be closed, as shown in figs. 4 and 8.

If one wishes to open the valve, one simply unscrews the tightening screw 17 and lifts the valve assembly. This can expediently be accomplished by means of extended wires or lines 21 connected to the connecting hooks 16, as shown in fig. 5. Optionally, the valve means can be lifted off completely and taken up to the surface for inspection, reparation or exchange, if this should be required.

A second valve assembly is disclosed in Fig. 9 and 10. A main difference from the first embodiment as disclosed in Fig. 6-8 is that the tension bridge 1' is hinged at 23 in a bracket 24 fixed on the cylinder 8'. A forked arm 25 extends out from the bridge 1' in the hinge area. This fork has aligned holes 26 for the insertion of a T-piece 27 (fig. 10). In the bracket 24 there is a hole 28 which will be aligned with the holes 26 when the tension bridge 1' and the valve closing disc 2' is swung up to an open position.

In a such open position the T-piece is inserted through the holes 26 and the hole 28, thus securing the bridge and valve disc in an open position. When one wishes to close the valve assembly, the T-piece is withdrawn by means of a ROV and the tension bridge 1' and the valve closing disc 2' will swing down to the position shown in Fig. 9. The hooks 16' will swing out and snap back into a gripping engagement underneath the flange 7'. In this position the screw 17' may be actuated to press down the valve closing disc against the valve seat 6'.

The hinge bolt 23 may be a T-piece corresponding to the Tpiece 27, thus enabling the hinge connection to be easily broken so that eventually the valve assembly may be recovered, i.e. lifted off and taken up to the surface.

Claims (11)

Patent Claims

1.

A valve assembly to be used in a subsea structure, particularly a mudmat, for providing/closing a flow of fluid between an area on the top side and the bottom side of the subsea structure, through an aperture between the top side and the bottom side, c h a r a c t e r i z e d i n that it comprises valve closing means (2); a tension bridge (1); means (3, 4) for holding the valve closing means (2) in the tension bridge (1), allowing some free movement; means (17,21) for for pressing down the valve closing means (2) from the tension bridge (1) within the range of free movement; means (16) for releasable connection of the tension bridge (1) in a position above the through-going aperture; and an adjustable guidance/holding device (12, 13, 14, 15;23,24) for the valve closing means (2) and the tension bridge (1), designed to hold the valve closing means (2) down in a position over the through-going aperture, in which position the tension bridge (1) is connected to the subsea structure (8) over the through-going aperture, with releasable connecting means (16, 7) and the valve closing means (2) can be pressed down from the tension bridge (1) to a sealing engagement with a valve seat (6) around the aperture -- and in a lifted, securely held, free position, respectively.

2.

A valve assembly according to claim 1, c h a r a c t e r i z e d i n that the valve closing means is a valve closing disc (2) designed for sealing contact around the through-going aperture.

3.

A valve assembly according to claim 1 or 2, c h a r a c t e r i z e d i n that the holding means comprises a hinge connection (23,24) between the tension bridge (1') and said subsea structure (8').

4.

A valve assembly according to claims 1 and/or 2, c h a r a c t e r i z e d i n that the adjustable guidance/holding device comprises a rod (12) extending from the valve closing means (2) and passing through -a hub sleeve (11) in the through-going aperture, there being a locking groove/key connection (13, 14, 15) between the rod and the hub sleeve.

5.

A valve assembly according to claims 1, 2,3 or 4, c h a r a c t e r i z e d i n that the means for releasable connection of the tension bridge (1) in a position above the through-going aperture comprises vertically pivotable connecting hooks (16) mounted on the tension bridge (1) and a flange (7) encircling the throughgoing aperture of the subsea structure, said flange being designed for gripping engagement with the connecting hooks and as a valve seat (6) for engagement with the valve closing means (2).

6.

A valve assembly according to one of the preceding claims, c h a r a c t e r i z e d i n that the means for pressing down the valve closing means comprises a tension screw (17) centrally positioned on the tension bridge (1).

7.

A valve assembly according to one of the preceding claims, c h a r a c t e r i z e d i n that the means positioned on the tension bridge (1) for holding the valve closing means (2) while allowing some play comprise threaded bolts (3, 4) which pass freely through the bores in the tension bridge and are screwed into the valve closing means (2).

8: A valve assembly according to one of the preceding claims, c h a r a c t e r i z e d i n that the tension bridge is in the form of a disc (1).

9.

A valve assembly according to one of the preceding claims, c h a r a c t e r i z e d i n that there on the top side of the tension bridge (1) are devised buffer means (19, 20) for the protection of said holding means and tension bridge.

10.

A valve assembly according to one of the preceding claims, c h a r a c t e r i z e d 1 n that the tension bridge is provided with a fastening bar (18) for securing a ROV.

11.

A valve assembly substantially as herein described with reference to the accompanying drawings.