WO2010085156A1

WO2010085156A1 - Device of fairlead, and use thereof

Info

Publication number: WO2010085156A1
Application number: PCT/NO2010/000028
Authority: WO
Inventors: Morten LIABØ; Morten Hopland
Original assignee: I.P. Huse As
Priority date: 2009-01-23
Filing date: 2010-01-25
Publication date: 2010-07-29
Also published as: NO330879B1; NO20090354L

Abstract

The document describes a fairlead with an anchor line stopper (15) and a guiding element (36) for locking and guiding of an anchor line (50) between an offshore structure (12) and an anchor. The fairlead with the anchor line stopper (15) comprises a pivot housing (22) which is rotatably mounted on a vertical axle (20) connected to the offshore structure, and the pivot housing comprises a pivotally stopper housing (32) surrounding the anchor line stopper (15). The guiding element (36) is connected to a support adjacent the offshore structure via a stiff connection (40) which range between a guiding element axle and the offshore structure.

Description

DEVICE OF FAIRLEAD.AND USE THEREOF

The present invention relates to a device of a fairlead with a stopper and guiding body to lead and lock an anchor line between an offshore structure and an anchor, where the fairlead with the line stopper encompasses a pivot housing which is rotary fitted on a vertical shaft connected to the offshore structure and the pivot housing comprises a rotary stopper housing with the anchor line stopper, as can be seen in the introduction of the subsequent claim 1. The invention also relates to an application.

A roller fairlead is also a common term for a fairlead and is an installation that is used to guide and lead chains or wires during anchoring operations, or for the handling of cargo.

In more detail, the invention is related to anchoring of offshore structures in the form of large installations at sea, such as platforms, drilling ships and production ships for activities within production of oil and gas. When such large installations shall be anchored, the anchoring constructions must have large dimensions and be very robust.

Normally, the winch systems for such anchor chains are fitted high up on the platform, while the anchoring point of the chain itself is placed in a suitable position further down the construction, for example, a distance down on the platform leg, above or below the waterline. The anchor chain runs from the winch through guiding bodies at the edge of the deck, vertically down to a rotary fastening construction with a chain stopper down on the platform leg, and then diagonally further on down to an anchor fastening on the sea bed.

It is the fastening construction with its chain stopper that takes up all the tensile strain when the chain is fitted and the platform is in the correct position. The guiding castors for the chain on the deck and the winch itself are, in a way, relieved and do not take up any load. The chain is suspended in a chain lock at the extreme end of the construction which in turn is anchored to the platform leg.

Many anchoring systems that are based on this principle are known, such as Norwegian patent 176.395 (Lange), Norwegian patent NO 324660 (corresponds to Norwegian patent application 1999 4429 (Bardex)) and Finnish patent no. 87000.

Norwegian patent no. 176.395 shows a solution where the guiding castor for an anchor cable is fitted on an extended pipe, the one end of which is rotary fitted in a swivel to the platform leg, while the other end comprises the cable or chain lock. The cable runs through the castor and further up to the chain lock. The aim of the universal rotary joint via the swivel is that the angle of the cable through the fairlead follows the angle of the cable further down towards the anchoring on the sea bed.

The Finnish patent 87000 describes a solution where the element that corresponds to the pipe in NO 173.395, is rotated around a horizontal axis only. The cable runs vertically through the vertical rotary axis. According to this suggestion, there is no bend in the vertical direction so that the cable has a bend at the outlet from the cable lock according to the angle further out from the lock.

The Norwegian patent NO 324660 shows a fairlead (rolling fairlead locking mechanism) with a stopper (lock 42) and guiding body (wheel 27) to lock and lead an anchor line (anchor chain) between an offshore structure and an anchor. The fairlead with the stopper encompasses a pivot housing (rolling fairlead housing and locking housing) which is rotary mounted on a vertical shaft connected to the offshore construction, and the pivot housing comprises a rotary stopper housing (the locking housing 14) with the stopper. Consequently, this means that the connection between the platform leg and the chain lock comprises an additional link, i.e. that the construction comprises that the mechanism is rotary about a vertical axis, while the additional link provides an opportunity for rotation about a horizontal axis.

With the present invention, one aims to provide a new solution for such a fairlead. It is an aim to provide a fairlead stopper where the chain stopper and guiding disc are separated.

Furthermore, it is an aim of the invention to provide a fairlead construction which distributes the vertical and horizontal forces in a better way when the construction is used.

The guiding disc, if desired, can be made so that it is able to be taken apart so that it can be used on several anchor lines. With a separated guiding disc the construction will be more flexible with respect to fitting, maintenance and use.

The background is that the projects where this product is relevant have large variations in what angles the anchor lines have during installation and operation. There is also great variation in what forces shall be taken up by the construction during installation and operation. Therefore, the aim of the invention is to find the most flexible solutions to solve the above mentioned tasks at the same time as the product shall be easy to configure and be production friendly.

The device according to the invention is characterised in that the guiding body is connected with a support adjoining the offshore construction via a rigid connection that runs between the rotary support for the guiding body and the offshore construction.

The rigid connection is preferably a strut, the one end of which is mounted in the shaft around which the guiding body rotates, while the other end is mounted in the offshore construction.

According to a preferred embodiment, the strut is mounted in connection with the upper section of a fairlead fastening bracket.

According to yet another preferred embodiment the strut forms a U-shape with one leg mounted to the shaft on either side of the castor.

According to yet another preferred embodiment the strut itself defines or is mounted in a rotary guiding disc housing fitted above the upper bracket. According to yet another preferred embodiment the shaft on either side of the castor, is set up to loosely rest in respective seats formed in upwardly extending columns connected to the pivot housing to take up possible larger vertical forces.

According to the invention the device is used for anchoring of offshore structures in the form of large installations at sea, such as platforms, drilling vessels and production vessels for activities within oil production and gas production.

The invention shall now be explained in more detail with reference to the enclosed figures, in which:

Figure 1 show a fairlead fitted to one of the legs of an offshore platform.

Figure 2 shows a cross-section of the fairlead construction according to figure 1.,

Figure 3 shows an expanded diagram of the parts that the fairlead is composed of.

Figure 4 shows the preferred fitting of the guiding wheel (the castor) for the anchor line.

Reference is initially made to figure 1. One of the legs of an offshore platform is shown by 12. A fairlead 10 with an anchor line (chain) stopper 14 is connected to the leg 12. The anchor chain is shown by 50 in figures 2 and 4.

The fairlead 10 comprises a bracket construction which is fastened by welding, or the like, to the hull part /platform leg 12. The bracket is comprised of lower and upper bracket parts 16 and 18, respectively. A vertical, permanently fitted rotating peg 20 (figure 2) is inserted between these. A pivot housing 22 comprises a casing part which is fitted so that it can rotate about the rotating peg 20 (see figure 2). The pivot housing 22 is defined by two mutually parallel and horizontally outwardly extending plate-formed arm parts 22a (only one is displayed in the figure). The two arm parts 22a, 22b comprise their own transverse, horizontally running bolt 28 for rotary mounting of the one end of a further housing part 32, the extreme outer end of which comprises the above mentioned anchor line or chain stopper (the lock) 15.

The anchor line stopper 15 at the end of the stopper housing part 32 comprises a chain lock of a known construction with a hydraulically driven, or driven by another power source, mouth construction that can grip over two of the chain links and hold the chain steady or lock the anchor line. When the chain is locked in this way, all forces are taken up by the fairlead parts stopper housing

32, pivot housing 22 and brackets 16,18, while the chain path further up to the platform deck and the castor (the guiding wheel) 36 and other equipment parts such as the winch on the platform deck, are completely relieved of tensile forces from the anchor.

While the pivot housing 22 is horizontally rotary about a vertical axis (at the rotating peg 20, see figure 2) the additional housing part 32 can rotate about a horizontal axis given by 28. The horizontal forces which the construction is exposed to, are divided between the upper bracket 18 and the lower bracket 16, respectively, while the vertical forces are taken up by the lower bracket 16.

Such fairlead constructions always comprise a guiding body often in the form of a chain-carrying castor 36 that ensures the transition of the vertical run for the chain 50 and further out through the chain lock at an oblique angle, for example, at an angle α of about 45 degrees as shown in figure 2. In the previously known solutions, these castors are either connected to the inner part of the stopper housing part, or fitted to the pivot housing 22. As seen in the figure, the guiding body comprises two mutually parallel castor elements 36a and 36B, respectively, to lead the chain 50.

The solution according to the invention relates to a new construction to mount the guiding wheel or castor wheel to be able to distribute the load forces in a better way when the construction is used.

The castor 36 is fitted on a horizontally arranged shaft 60 through the strut 40 so that it can rotate. With reference to the expanded figure 3, each end of the shaft 60 is fitted (bolted down by the bolt 35) to the respective upwardly extending columns 34a and 34b, respectively, one on either part of the pivot housing 22. The strut 40 is preferably fitted at the top of the vertical shaft 20, above the upper bracket, and forms a housing 46 that can swing horizontally about the bolt/shaft 20 in the same way as the pivot housing 22.

In more detail, the strut 40 is preferably shaped with two long, extended legs 40a, 40b and forms a U-shaped loop form. These loop parts 40a, 40b are led together in the housing part and form a bracket part 44 (at the curve of the U- shape) which is rotary fastened in or forms the rotary housing 46 above the upper bracket 18.

According to one embodiment, the bracket part 44 comprises an opening/hole 45 adjusted to the upper part of the permanently fitted rotating peg 20 between the bracket parts 16,18. On fitting, the bracket part 44 with the hole 45 is threaded down over the top part of the peg 20 and is set so that it can be rotated horizontally about the peg 20 together with the rest of the pivot housing 22.

To be able to take up any larger vertically directed forces on the castor 36, the shaft 60 rests in a rounded seat in an upwardly extended column 34 fitted at the top of the extreme outer part of the pivot housing 22. More specifically, there is one such carrier column 34 on either side of the castor 36. But the castor 36 is, in itself, permanently fitted to the strut 40 and has no permanent connection directly to the pivot housing 22.

In more detail, during the fitting of an anchor chain, the horizontal forces on the castor are normally greater than the vertical forces. With the present inventive mounting construction for the castor the horizontal forces are, in the main, taken up by the two loops 40a, 40b and thus the upper bracket 18. The vertical forces above a given value will be taken up by the pivot housing 22 via the shaft 60 and the two columns 34 to which the shaft is fitted.

The strut 40 can be constructed as a trussed construction. Preferably, it is formed as a plate with a main plate form that is fitted in a way so that it can take up forces such that it has a great resistance against horizontal tension and vertical bending, relative to its fastening in the bracket 18. With this solution the horizontal forces are transferred directly to the upper bracket 18 or to the fastening in the platform leg 12, while the vertical forces are transferred via the pivot housing and up into the upper bracket 18.

Furthermore, one achieves that the fastening for the shaft 60 to the castor takes up the forces from the chain 50 and transfers these directly to the bracket 18 when the chain is installed on the sea bed.

The chain stopper housing 32 can rotate vertically upwards and downwards about the horizontal mounting 28 in the pivot housing 22 to ensure that the chain stopper can be moved together with the chain during the installation. This ensures a satisfactory positioning of the chain through the stopper 15 and in on the disc/castor 36 from all installation angles in relation to the horizontal plane.

Figure 3 shows the whole of the fairlead in an expanded diagram including all the components.

Figure 4 shows an enlarged side diagram focussing on the invention itself, how the castor 36 is mounted in the strut via the shaft 60, and also shows the central component parts in connection to the mounting. The figure also shows the column 34 which extends upwards from the outer part of the pivot housing 22, and to which the shaft is fitted to and can rest down on when greater vertical forces arise during the installation of the anchor chain.

The fastening bolts for the chain stopper housing can contain load cells that can show the operator how the forces are distributed in the construction. The castor or guiding disc housing can simply be formed so that it can be dismantled when the chain is installed.

Claims

P A T E N T C L A I M S

1. Device of a fairlead with a stopper (15) and a guiding body (36) to guide and lock an anchor line (50) between an offshore structure (12) and an anchor, where the fairlead with the line stopper encompasses a pivot housing (22) which is rotary fitted on a vertical shaft (20) connected to the offshore structure, and the pivot housing comprises a rotary stopper housing (32) with the anchor line stopper (15), characterised in that the guiding body (36) is connected to a mounting (18,20) adjoining the offshore construction (12) via a rigid connection (40) that runs between the rotary mounting of the guiding body (36) and the offshore construction.

2. Device according to claim 1 , characterised in that the rigid connection (40) is a strut (40a, 40b) the one end of which is mounted in the shaft (60) about which the guiding body (36) rotates, while the other end is mounted in the offshore construction.

3. Device according to one of the claims 1-2, characterised in that the strut is mounted in connection to an upper section (18) of a fairlead fastening bracket (16,18).

4. Device according to one of the claims 1 -3, characterised in that the strut (40) forms a U-shape with one leg mounted to the shaft (60) on either side of the castor (36).

5. Device according to one of the claims 1 -4, characterised in that the strut (40) itself defines or is anchored in a rotary guiding disc housing (44) fitted above the upper bracket (18).

6. Device according to one of the claims 1-5, characterised in that the shaft, on each side of the castor, is set up to rest in respective seats formed in upwardly extending columns connected to the pivot housing to take up possible greater vertical forces.

7. Application of the device according to claims 1-6, for anchoring of offshore constructions in the form of large installations at sea, such as platforms, drilling vessels and production vessels for activities within the production of oil and gas.