AU2016100370A4 - Chain connector - Google Patents

Abstract

Chain connector for mooring a floating structure to the seabed, comprising a main tubular 5 body (2) having an upper end (4), a lower end (6) and an elongated tubular housing (8) arranged there between, wherein the upper end (4) is provided with a releasable chain stopper mechanism (10) for anchoring a mooring line (3) to the chain connector (1). The upper end (4) of the main tubular body (2) is further provided with a curved slot (7) for accommodating a pull-in cable (5) and providing sliding contact with the pull-in cable (5) 10 during installation of the mooring line (3). [Figure 1] Fig I 10 ' -- - - -- - -- -- - - -- - - - -- - - - ii8 6i 6ai 3i

Description

1 Chain connector Field of the invention The present invention relates to a chain connector for mooring a floating structure 5 to the seabed. Prior art International publication WO 2010/112603 discloses a connector for use with a mooring leg extending up from the seabed to connect a floating structure thereto. 10 Connection and release of the mooring leg is accomplished by pulling in and out a connector elongated body extending in a mooring leg direction, wherein the connector comprises a latch mechanism for affixing the mooring leg to the floating structure and preventing movement in the direction of the seabed. A flexible part is provided with a double articulation axes located at the bottom of the connector elongated body above an 15 attachment member, wherein the connector elongated body is received in a housing that is fixed to a part of the floating structure. The latch mechanism comprises guiding means and followers or orientation pins between the body of the connector and the housing. Summary of the invention 20 The present invention seeks to provide an improved chain connector for mooring a floating structure to the seabed, wherein the chain connector restricts bending angles as well as friction forces imposed on an installation cable or pull-in cable extending through the chain connector when connecting a mooring line thereto. According to the present invention, a chain connector of the type defined in the 25 preamble is provided, comprising a main tubular body having an upper end, a lower end and an elongated tubular housing arranged there between, wherein the upper end is provided with a releasable chain stopper mechanism for anchoring a mooring line to the chain connector. The upper end of the main tubular body is provided with a curved slot or recess for accommodating a pull-in cable and providing sliding contact with the pull-in 30 cable during installation of the mooring line. According to the invention, the curved slot may be envisaged as an curved recess or groove applied to the upper end of the chain connector through which the pull-in cable slides as the mooring line is pulled toward the chain connector for anchoring a floating structure to the seabed. The curved slot provides stable and protective support to the pull 35 in cable and prevents excessively small bending radii thereof by imposing a 2 predetermined bending radius to the upper end. So by smoothly guiding the pull-in cable through the curved slot, friction forces as well as excessive bending stress can be reduced, thereby minimizing cable wear and risk of cable failure. 5 Short description of drawings The present invention will be discussed in more detail hereinafter based on a number of exemplary embodiments with reference to the drawings, in which Figure 1 shows a cross section of an embodiment of the chain connector according to the present invention; and 10 Figure 2 shows a three dimensional view of an upper part of the chain connector according to the present invention. Detailed description of exemplary embodiments Chain connectors allow for secure and reliable anchoring of a floating structure, 15 e.g. FPSO or FLNG vessel, to the sea bed. For example, chain connectors may be adapted for use with a turret mooring system allowing free "weathervaning" of the floating structure at a predetermined anchoring position at sea. To that end the turret mooring system comprises a swivel assembly or mooring buoy provided with a plurality of chain connectors each of which is connected to a mooring line that extends at least in part 20 through the chain connector. To connect a mooring line to a chain connector an installation cable or pull-in cable is often used for pulling an end of the mooring line toward the chain connector. In most installation scenarios such a pull-in cable extends through the chain connector and comes into sliding contact therewith as the cable is reeled in. As the pull-in cable moves through the chain connector, relatively high friction forces as well 25 as excessively small bending angles may be imposed on the pull-in cable, causing excessive wear, degeneration or even failure of the cable. To facilitate safe and reliable anchoring of a floating structure to a mooring line, there is a need for a chain connector that reduces friction forces on a pull-in cable as well as bending stresses in the pull-in cable during installation of the mooring line. 30 Figure 1 shows a cross section of an embodiment of the chain connector and Figure 2 shows a three dimensional view of an upper part of the chain connector according to the present invention. As depicted in Figures 1 and 2, the chain connector 1 comprises a main tubular body 2 having an upper end 4, a lower end 6 and an elongated tubular housing 8 35 arranged there between. The upper end 4 is provided with a releasable chain stopper 3 mechanism 10 for anchoring a mooring line 3 to the chain connector 1. In an embodiment the releasable chain stopper mechanism 10 may be pivotally arranged on the upper part 4. According to the present invention, the upper end 4 of the main tubular body 2 is 5 provided with a curved slot or recess 7 for accommodating a pull-in cable 5 and providing sliding contact with the pull-in cable 5 during installation of the mooring line 3. The curved slot 7 provides an integrated cable guide to the chain connector 1 so that the use of separate sheaves, deflectors, sliders and the like is circumvented. Furthermore, the curved slot 7 of the present invention not only provides a smooth, stabilising sliding 10 surface for the pull-in cable 5 but also imposes a limit or restriction on the bending radius for various bending angles of the pull-in cable 5 during installation of the mooring line 3, see e.g. angles X1, X2. As a result mechanical wear due to friction forces and bending stresses in the pull-in cable 5 is significantly reduced, which is advantageous when e.g. a steel pull-in cable 5 is used. 15 Note that the curved slot 7 can be adapted to comprise any bending radius and any length deemed necessary for its function to accommodate any required cable size, so that the chain connector 1 can be used for both small and large floating structures. In the embodiment of Figure 2, the curved slot 7 may extend in longitudinal direction from an upper rim portion 4a of the upper end 4 into the main tubular body 2. 20 The upper rim portion 4a provides a further smooth sliding surface as well as a further desired bending radius associated with the upper rim portion 4a to reduce friction forces and to avoid sharp bends in the pull-in cable 5 as it enters the chain connector 1. For example, in a practical embodiment the upper rim portion 4a is a rounded upper rim portion 4a having a radius between 40 mm to 100 mm, e.g. 60 mm, and the curved slot 7 25 has a radius between 500 mm to 1200 mm, e.g. 900 mm. These ranges for the radius of the upper rim portion 4a and the radius of the curved slot 7 allow for improved sliding engagement between the pull-in cable 5 and the chain connector 1 as well as an acceptable and safe bending radius for the pull-in cable 5 during installation of the mooring line 3. 30 To further facilitate smooth sliding contact between the pull-in cable 5 and the chain connector 1, an embodiment is provided wherein the lower end 6 of the main tubular body 2 comprises a rounded or curved lower rim portion 6a for providing sliding contact with the pull-in cable 5 during installation of the mooring line 3. As with the curved slot 7, the rounded or curved lower rim portion 6a of the lower end 6 not only improves sliding 35 engagement between the pull-in cable 5 and the chain connector 1 but also limits or 4 restricts the bending radius of the pull-in cable 5 to an acceptable value when it extends beyond the lower rim portion 6a. Also, a further add-on or external cable guide such as a separate sheave, deflector, slider and the like may not be needed as the lower rim portion 6a already provides a smooth sliding surface as well as a safe and improved bending 5 radius for the pull-in cable 5. The chain connector 1 of the present invention can be deployed in numerous ways for reliably anchoring a floating structure. For example, a floating offshore vessel may be provided with a turret mooring system or a spread mooring system comprising one or more chain connectors 1 according to the present invention for connection to one or more 10 mooring lines 3. In particular, a floating offshore vessel, such as an FPSO or FLNG vessel, may be provided with a turret mooring system comprising a mooring buoy and a plurality of mooring lines 3. A chain connector 1 according to the present invention may then be provided for each mooring line 3 mounted in a chain table at a bottom of the mooring buoy. When the floating offshore vessel is connected to the plurality of mooring 15 lines 3, each of the chain connectors 1 and the respective curved slot 7 thereof not only provides a smooth and stable sliding contact between a pull-in cable 5 and chain connector 1 but also limits the bending radius of the pull-in cable 5 for various bending angles X1, X2 of the pull-in cable 5 during installation of the mooring line 3. Consequently, each pull-in cable 5 is subjected to reduced friction forces and bending stresses during 20 installation. In practice the chain connector 1 as disclosed above can be effectively connected to a mooring line 3 by means of the following method, comprising the step of extending a pull-in cable 5 through the chain connector 1. In this step the pull-in cable extends fully through the chain connecter 1. The method then comprises the step of connecting the 25 pull-in cable 5 to the mooring line 3. Once the pull-in cable 5 is secured to the mooring line 3, the method comprises pulling the mooring line 3 through the chain connector 1 by retracting the pull-in cable 5. In this step the pull-in cable 5 is reeled in by the floating structure so that the mooring line 3 is pulled toward the chain connector 1 and ultimately extends at least in part there through. As the pull-in cable 5 is retracted, the method 30 further comprises limiting a cable bending angle as well as friction forces imposed on the pull-in cable 5 by the curved slot 7 provided in the upper part 4 of the chain connector 1. The above method allows a pull-in cable 5 to be safely used for connecting a mooring line 3 to a chain connector 1, wherein the curved slot 7 of the chain connector 1 accommodates the pull-in cable 1 and provides smooth and stable sliding contact there 35 between. The curved slot 7 further restricts the bending angle of the pull-in cable to an 5 acceptable value during installation to decrease mechanical wear and to reduce the risk of failure. The present invention has been described above with reference to a number of exemplary embodiments as shown in and described with reference to the drawings. 5 Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an 10 inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 15

Claims (5)

1. A chain connector (1) for mooring a floating structure to the seabed, comprising a 5 main tubular body (2) having an upper end (4), a lower end (6) and an elongated tubular housing (8) arranged there between, wherein the upper end (4) is provided with a releasable chain stopper mechanism (10) for anchoring a mooring line (3) to the chain connector (1); and wherein the upper end (4) of the main tubular body (2) is further provided with a curved slot (7) for 10 accommodating a pull-in cable (5) and providing sliding contact with the pull-in cable (5) during installation of the mooring line (3).

2. The chain connector according to claim 1, wherein the curved slot (7) extends in longitudinal direction from an upper rim portion (4a) of the upper end (4) into the main 15 tubular body (2).

3. The chain connector according to claim 2, wherein the upper rim portion (4a) is a rounded upper rim portion (4a) having a radius between 40 mm to 100 mm, e.g. 60 mm, and wherein the curved slot (7) has a radius between 500 mm to 1200 mm, e.g. 900 mm. 20

4. The chain connector according to claim 1, 2, or 3, wherein the lower end (6) of the main tubular body (2) comprises a rounded lower rim portion (6a) for providing sliding contact with the pull-in cable (5) during installation of the mooring line (3). 25

5. A floating offshore vessel provided with a turret mooring system or a spread mooring system comprising one or more chain connectors (1) according to any one of the preceding claims.