GB2380709A

GB2380709A - Offshore load transfer system

Info

Publication number: GB2380709A
Application number: GB0223333A
Authority: GB
Inventors: Hans Linden; Per Johansson
Original assignee: Master Marine AS; SKF AB
Current assignee: Master Marine AS; SKF AB
Priority date: 2001-10-10
Filing date: 2002-10-08
Publication date: 2003-04-16
Anticipated expiration: 2022-10-08
Also published as: GB0223333D0; GB2380709B

Abstract

An offshore load transfer system comprises a floater (20, Fig 1) equipped with a supporting structure which carries the loads to be transferred. The supporting structure comprises an elongated transfer beam 3 projecting from the floater, with a load carrying point 10 connected to the elongated transfer beam. The transfer beam comprises an arm structure 2 which supports a trolley 9 that is displaceable in the longitudinal direction of the arm structure and carries the load carrying point. The arm structure is rotatably supported at one of its ends relative to the floater, such that it can be swung in a substantially horizontal plane about a substantially vertical shaft 6.

Description

AN OFFSHORE LOAD HANDLING SYSTEM The present invention refers to a system for load handling for offshore load transfer operations, wherein a floater is taken to a transfer site at sea and loads are transferred between the floater and the transfer site. The floater is equipped with a supporting structure carrying the load to be transferred. The floater has adjustable buoyancy for offshore transport, installation and removal of structural elements.

Such a system is primarily intended for transport, installation and removal of heavy construction elements to or from offshore oil and gas platforms, and uses a floater, having load transfer elements protruding from the floater.

The floater may have any form adapted to or suited for these tasks, and it may for example be of the type disclosed by US 6,244, 786, which illustrates and describes a column stabilized floater, or a catamaranlike floater, for example as disclosed by US 3,078, 680. Other suitable floaters are shown for example in EP 000 462 Al, FR 247 992, NO 160424 and NO 135056.

This floater will be deployed for transportation and installation or removal of heavy construction elements, to or fixed structures or floating structures, hereinafter referred to as"marine structure", offshore at open sea, where the floater could be exposed for waves.

The heavy construction element is carried from underneath by beam elements, also referred to as loadtransfer beams, which are protruding from the floater.

The weight of the heavy construction elements is transferred from the floater to the marine structure by ballasting the floater, i. e. filling ballast into ballast tanks of the floater or discharge ballast from the tanks.

The removal of heavy construction elements from the marine structures, which are in most cases platform topsides or similar structures is a reverse operation to installation. The weight of the heavy construction element is now transferred from a marine structure to the floater by de-ballasting the floater, i. e. removal of ballast from ballast tanks.

The above described installation and removal technique are not new but has mainly been used for inshore operations, in sheltered waters.

The technique for load-transfer of heavy construction elements to/from marine structures by ballasting/deballasting operations will however introduce huge dynamic horizontal loads from the floater acting on the marine structure when performing this operation offshore, in open sea, where the floater is exposed for waves.

This is a serious problem, which could cause damage to the marine structure, especially to old and corroded oil and gas platforms, where topsides have to be removed from platform substructures, of the"jackets" type, where the horizontal dynamic load from the floater can introduce large bending moments at the bottom of the substructure, which is fixed to the seabed and large shear forces in the substructure as well as large horizontal forces at the contact point between the platform topside and the load carrying point on the load-transfer beams.

For solving this problem it now is proposed to make the floater allow for horizontal motions relative to the marine structure, and especially wave frequency motions during the load-transfer operation.

A purpose of the present invention is to propose an offshore load handling, which will reduce the horizontal dynamic loads from the floater acting on the marine structure, and which will permit horizontal motions of the floater relative to the marine structure during the load-transfer operation in order to limit horizontal dynamic forces from the floater acting on the marine structure, and this has been achieved in an offshore load handling system in accordance with the preamble of the accompanying claim 1, in that the system has been given the features defined in the characterizing part of the claim 1.

Hereinafter the invention will be further described, by way of example only, with reference to an embodiment of the system schematically shown in the accompanying drawings, in which: Fig. 1 shows schematically one type of a floater used in the load handling system according to the invention; Fig. 2 shows schematically and in perspective an outer part of a load transfer beam forming part of the offshore load handling system according to the invention; and Fig. 3 is a schematic cross section of the load transfer beam shown in Fig. 2.

In Fig. 1 is schematically shown a perspective view of a floater 20, which in this embodiment has two hulls

21, thereby being of the catamaran type, and which floater 20 supports a number of load transfer beams 1, each one supported on a connecting structure 3, attached to the floater 20, and preferably as illustrated projecting toward the opposite hull.

In Fig. 2 is shown that the load transfer beam 1, comprises a hinged arm 2 connected to the structure 3 from the floater. In the embodiment shown, the structure 3 is preferably a box girder, which is firmly connected to the not shown floater or forms an integrated part thereof, and having at its free end a forked bracket. The two lugs 4,5 of the forked bracket are arranged one above the other substantially in parallel, and supports a journalled shaft 6, which is arranged to extend substantially vertically between the two lugs. The hinged arm 2 is rotatably in the horizontal plane round the journalled shaft 6. As can be seen from Fig. 2, which is showing the load transfer beam 2 according to Fig. 1 in perspective, the bending moment of the hinged arm 2, at the connection to the structure 3 from the floater, is taken up by two or more radial bearings 7a 7b and the vertical load is taken by one or more axial bearings 8.

The radial bearings 7a, 7b could preferably be spherical roller bearings as illustrated and the axial bearing (s) 8 could preferably be a spherical roller thrust bearing.

A trolley 9 that is able to move along the hinged arm 2 in a direction from the journalled shaft 6 and towards the free outer end of the arm 2, supports a load carrying point 10. The trolley 9 is supported in linear bearings 11 (or other bearings with the same feature) on the hinged arm 2.

In the embodiment shown the trolley 9 is designed to straddle the arm 2, and the arm is provided with a number of elongated ribs 12 spaced apart in vertical direction and extending along the vertical sides of the arm 2. These ribs 12 are arranged to cooperate with (not visible) corresponding ribs or ledgers inside the vertical sidewalls of the trolley 9, whereby the ribs 12 in the arm and the ledgers inside the trolley act as supporting structures for the linear bearings 11.

The combination of rotation of the arm 2 and linear motions of the trolley 9 allows the load carrying point 10 to operate within an area limited by the rotation angel of the hinged arm and the horizontal stroke of the trolley 9.

The load carrying point 10 could preferably be a steel plate, supported by a spherical roller thrust bearing 13 or other bearing allowing for rotation round the zaxle and tilt round the x-and y-axles.

The spherical roller thrust bearing 13 (or other bearing with the same feature) could preferably be supported by a hydraulic jack 14, in order to adjust height of the load carrying points 10 and to control loads on each lifting point 10 when more than one lifting point 10 are working in multiple.

The invention is not limited to the non-limiting embodiment illustrated and described, but modifications and variants are possible within the scope of the accompanying drawings.

Claims

CLAIMS 1. A load handling system for offshore load transfer operations, using a floater equipped with a supporting structure for transfer of heavy construction elements between the floater and a transfer site, whereby the supporting structure is carrying the heavy construction elements to be transferred, the supporting structure comprising an elongated transfer beam projecting from the floater or a structure attached thereto, and a load carrying point connected to the elongated transfer beam, wherein the elongated transfer beam comprises an arm structure, supporting a trolley, which is displaceable arranged in the longitudinal direction of the arm structure and carrying the load carrying point, which arm structure at one of its end being rotatably supported relative to the floater or a structure attached thereto, in a manner allowing it to be swung in a substantially horizontal plane about a substantially vertical shaft.
2. A load handling system as claimed in claim 1, wherein the arm structure near one of its ends is arranged about a substantially vertical shaft rotary supported to an outer end portion of the floater or a structure attached thereto.
3. A load handling system as claimed in claim 2, wherein the shaft is supported in at least two bearings accommodating radial loads, and at least one bearing accommodating axial loads.
4. A load handling system as claimed in claim 3, wherein the bearings accommodating radial loads are spherical roller bearings, and the bearing accommodating axial loads is a spherical roller thrust bearing, both types of bearings permitting certain

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angular misalignment.
5. A load handling system as claimed in any one of the preceding claims, wherein the trolley is supported in linear bearings provided between the trolley and the sidewalls of the arm structure.
6. A load handling system as claimed in any one of the preceding claims, wherein the load supporting point supported by the trolley is designed as a structure being rotary supported in a bearing accommodating both axial and radial loads.
7. A load handling system as claimed in any one of the preceding claims, wherein the load supporting point is supported on a hydraulic jacket allowing vertical adjustment of the supporting point.
8. A load handling system as claimed in any one of the preceding claims, wherein means are positioned under the load supporting point allowing this to make tilting motions in horizontal planes.
9. A load handling system as claimed in any one of the preceding claims, wherein the arm structure is a girder box, having means for guiding the trolley.
10. A load handling system substantially as hereinbefore described with reference to or as shown in the accompanying drawings.

10. A load handling system substantially as hereinbefore described with reference to or as shown in the accompanying drawings.

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Amendments to the claims have been filed as follows 1. A load handling system for offshore load transfer operations, using a floater equipped with a supporting structure for transfer of heavy construction elements between the floater and a transfer site, whereby the supporting structure carries the heavy construction elements to be transferred, the supporting structure comprising an elongated transfer beam projecting from the floater or a structure attached thereto, and a load carrying point connected to the elongated transfer beam, wherein the elongated transfer beam comprises an arm structure, supporting a trolley, which is displaceable in the longitudinal direction of the arm structure and carries the load carrying point, which arm structure at one of its ends is rotatably supported relative to the floater or a structure attached thereto about a substantially vertical shaft fitted to the floater or said structure, in a manner allowing it to be swung in a substantially horizontal plane about said substantially vertical shaft.

2. A load handling system as claimed in claim 1, wherein the vertical shaft is rotary supported by an outer portion of the floater or a structure attached thereto.

3. A load handling system as claimed in claim 2, wherein the shaft is supported in at least two bearings accommodating radial loads, and at least one bearing accommodating axial loads.

4. A load handling system as claimed in claim 3, wherein the bearings accommodating radial loads are spherical roller bearings, and the bearing accommodating axial loads is a spherical roller thrust bearing, both bearings being of types having an

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ability to take up angular misalignment.

5. A load handling system as claimed in any one of the preceding claims, wherein the trolley is supported in linear bearings provided between the trolley and the sidewalls of the arm structure.

6. A load handling system as claimed in any one of the preceding claims, wherein the load supporting point supported by the trolley comprises a structure being rotary supported in a bearing accommodating both axial and radial loads.

7. A load handling system as claimed in any one of the preceding claims, wherein the load supporting point is supported on a hydraulic jacket allowing vertical adjustment of the supporting point.

8. A load handling system as claimed in any one of the preceding claims, wherein a bearing is positioned under the load supporting point to allow the point to make tilting motions in a horizontal plane.

9. A load handling system as claimed in any one of the preceding claims, wherein the arm structure is a girder box, having means for guiding the trolley.