Field of the invention

The present invention relates to a top locking system for a riser on a floating vessel.

Summary of the invention

The present invention relates to a top locking system for a riser tube in a supporting tube on a floating unit; the riser tube being inserted in the supporting tube; the riser tube being mounted in a hang-off support tube;

the top locking system being arranged at an upper end of the supporting tube and comprising a plurality of hinged wedges arranged at an external peripheral wall of the upper end of the supporting tube; each hinge wedge being rotatingly moveable from an opened to a closed position around a hinge shaft of a respective support hinge at said peripheral wall, the support hinge comprising a pair of parallel brackets provided with eccentric bushes in which the hinge shaft is mounted.

According to an aspect, the invention provides a top locking system as described above, wherein in the closed position the hinged wedge is positioned between an external periphery of the hang-off support tube and an internal peripheral wall of the supporting tube.

According to an aspect, the invention provides a top locking system as described above, wherein the supporting tube is supported on a lower riser balcony of the floating vessel.

According to an aspect, the invention provides a top locking system as described above, wherein the riser tube is equipped with the hang-off support tube inserted in the supporting tube, and with a gap compensator structure at a lower end of the supporting tube positioned between the external wall of the hang-off support tube and the internal wall of the supporting tube.

According to an aspect, the invention provides a top locking system as described above, wherein an eccentricity of the eccentric bushes is configured to provide an inward or outward displacement of the hinged wedge towards or from a center of the supporting tube, when the hinged wedge is in or is approximating the closed position. According to an aspect, the invention provides a top locking system as described above, wherein the floating unit is a floating production storage and offloading, FPSO, vessel.

According to an aspect, the invention provides a top locking system as described above, wherein the top locking system comprises a number of hinged wedges around the periphery of the riser tube.

According to an aspect, the invention provides a top locking system as described above, wherein the number of hinged wedges is at least three, preferably six.

According to an aspect, the invention provides a top locking system as described above, wherein in the closed position the hinged wedge is positioned below a collar of the riser tube.

According to an aspect, the invention provides a top locking system as described above, wherein the hinged wedges are each rotatingly moveable by an actuator, preferably a hydraulic actuator.

According to an aspect, the invention provides a top locking system as described above, wherein each hinge is individually moveable by the actuator.

According to an aspect, the invention provides a top locking system as described above, wherein the supporting tube has a lengthwise opening over a portion of its circumference.

Also, the invention relates to an offshore floating unit comprising a top locking system as described above.

Advantageous embodiments are further defined by the dependent claims. Brief description of drawings

Figure 1 shows a semi-cross-section of an assembly of a riser hang-off structure equipped with a top locking system according to an embodiment of the invention;

Figure 2 shows a perspective view of the assembly of Figure 1;

Figure 3 shows a top view of the top locking system;

Figure 4 shows a cross-section of the top locking system in a side view;

Figure 5 shows a detail of the top locking system of Figure 4;

Figure 6 shows a top view of a wedge of the top locking system of Figure 5; Figure 7 shows a side view of the wedge of Figure 6;

Figures 8a, 8b and 8c show details of the wedge of Figures 5 - 7.

Detailed description of embodiments

The present invention relates to a support system on a floating unit, that floats on a body of water such as the sea and supports riser tubes that are suspended from the floating unit to wellheads on the seafloor. The floating unit may relate to a floating production storage and offloading FPSO structure.

In an embodiment of the invention, the Top Locking System (TLS; or "ratchet system") consists of a number of hinged wedges (per supporting tube) that together form a circular ratchet system to be installed in the top cone of the supporting tube. The number of hinged wedges is at least three. In an embodiment, the number of hinged wedges is six. The supporting tube is mounted on the hull of the vessel, typically on the lower riser balcony of the vessel's hull.

Other numbers of hinged wedges that define a circular arrangement could be implemented as will be appreciated by the skilled in the art.

The ratchet system is to support a SLWR's (steel lazy wave riser) Hang Off Structure (HOS) or hang-off support tube that is to be inserted in the supporting tube and to convey loads from the riser tube to supporting tube.

In order to attach each hinged wedge to the floating unit's supporting tube, two hinged support brackets are designed, to be bolted or welded onto the available stiffeners at the outer diameter of the upper cone of the supporting tube. These hinged support brackets contain an eccentric hinge shaft and 2 eccentric bushes for proper alignment.

In closed position the hinged wedges clamp the riser tube and take on all vertical force acting on the riser tube, while minor adjustment of the wedges is still allowed.

The adjustment of the wedges in case of for example a gap detection (between riser tube and wedge) is achieved by an eccentricity of the bushes and/or hinge shaft. The eccentricity can be controlled by rotation of bushes and shaft, such that an inward displacement of the wedge, toward the centerline of the supporting tube (or riser tube) is obtained. Figure 1 shows a semi-cross-section of an assembly of a riser hang-off structure equipped with a top locking system according to an embodiment of the invention.

In the hang-off structure shown, a supporting tube 10 is structurally mounted on a hull of the floating unit, e.g., a FPSO structure or vessel. In an embodiment, it is mounted at the lower riser balcony.

Internal of the supporting tube 10 is a hang-off support tube 20, which is coaxial with the supporting tube 10. The hang-off support tube 20 is connected to the riser tube 35 that is mounted internal of the hang-off support tube. In an embodiment, at a lower end (proximate the sea level) between the supporting tube 10 and the hang-off support tube 20 a gap compensator device (e.g. an annulus) 30 is mounted. At an upper end of the supporting tube 10 (proximate the vessel) the top locking system 40 is mounted.

The top locking system is arranged to lock the riser tube 35 at its position by clamping on the hang-off support tube 20 by means of the hinged wedges 45.

Figure 2 shows a downward perspective view of the assembly of Figure 1. The supporting tube 10 is mounted by structural connection 50 to the floating unit's hull (not shown). The top locking system 40 is arranged with for example six hinged wedges distributed around the periphery 55 of the supporting tube in the upper end of the supporting tube 10.

The supporting tube has a supporting collar 60 that rests on the hinged wedges when these are in closed position.

In an embodiment, the supporting tube is a tube with a lengthwise opening over a portion of its circumference.

Figure 3 shows a top view of the top locking system 40 with the hinged wedges 45 in closed position.

Each hinged wedge comprises a wedge block 70 that is connected to a pair of rotating arms 75, a pair of brackets 80 mounted on the periphery 55 of the supporting tube 10, and a hinge shaft 85.

Each bracket 80 comprises an eccentric bush 90 in which the hinge shaft 85 is encompassed. The pair of rotating arms are rotatingly connected with the hinge shaft 85 that provides an axis of rotation for these arms 75.

By rotating the arms 75 around the hinge shaft 85, the wedge block can be moved between an opened (PI) and closed position (P2) in the top locking system as shown in figure 4. Figure 4 shows a cross-section of the top locking system 40 in a side view. In the closed position P2, the wedge blocks 70 of each hinged wedge are clamped against a collar 95 of the hang-off support tube 20 in a manner that prevents a downward (seaward) motion SI of the hang-off support tube 20 and the riser tube 35. Only if the hinged wedges are opened (position PI), the hang-off support tube can be moved in downward and upward axial direction. In position P2, only upward movement of the hang-off support tube is possible.

Figure 5 shows a detail of the top locking system of Figure 4.

In the closed position P2, the wedge blocks 70 of each hinged wedge are clamped against a collar 95 of the hang-off support tube 20.

Figure 6 shows a top view of a wedge of the top locking system of Figure 5.

Figure 7 shows a side view of the wedge of Figure 6.

Figures 8a, 8b and 8c show details of the wedge of Figures 5 - 7.

Figure 8a shows a cross-section of the hinge shaft 85 as mounted with the eccentric bushes 90 and the rotating arms 75.

Figure 8b shows schematically the mounting of the wedge block 70 on the rotating arms 75. The mounting position on the hinge shaft 85 is schematically indicated.

Figure 8c shows schematically the mounting brackets on the periphery of the supporting tube 10 on which the hinge shaft of the hinged wedge is to be mounted. In an embodiment, the brackets extend radially from the periphery 55. Within the openings 81 in the brackets 80, the eccentric bushes 90 on the hinge shaft are to be mounted.

The invention has been described with reference to some embodiments.

Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims.