Patent Application
20140270976
The invention is generally related to the installation of topsides of offshore structures and more particularly to the leg mating units between the topsides and the supporting legs.
Traditionally, the standard methodology for installing a topside structure onto its supporting structure, whether the supporting structure is bottom founded or a floating structure, involves lowering the topside structure onto the lower supporting structure.
The topside structure may be supported on a barge or pontoons used to position the topside structure over the lower supporting structure and legs. Once in position, the barge or pontoons are ballasted down to transfer the weight of the topside to its supporting structure.
The topside may also be lifted from the barge by a crane and lowered into position on the legs of the supporting structure by the crane.
In either method of installation, the weight transfer of the topside to the supporting structure must be controlled to prevent damage to both the topside and the supporting structure. Also, the heave motion of waves acting on the barge, pontoons, or vessel on which the crane is mounted must be taken into account to prevent damage to the topside and its lower support structure by repeated contact due to wave action. In order to eliminate or greatly reduce the chances for damage to the topside and legs of the lower support structure, it is preferable to quickly transfer a predetermined portion of the load of the topside onto the legs of the lower support structure. This serves to retain contact between the two structures and prevent damage that would occur due to wave action causing repeated contact. Because topsides structures can weigh as much as 80,000 tons, the full load cannot be immediately transferred. Otherwise, significant damage would occur to the supporting structure. After the initial transfer to insure that contact is maintained, the transfer of the remaining weight is done in a controlled manner.
This has typically been addressed in the offshore construction industry by the use of sacrificial leg mating units (LMUs).
The sacrificial LMUs have been mounted on the inside of the legs of the lower support structure and been a crushable material such as elastomeric material that is designed to absorb the initial load and then progressively crush as the remainder of the topside load is transferred. As a result of the size and weight of the structures involved, and the forces that must be dealt with, a single LMU can cost as much as one million dollars or more, and larger offshore structures can require as many as twelve LMUs during installation. Because the load absorbing characteristic of the LMUs is destroyed, and the LMUs have been an integral member of the legs, they are not reusable.
It is seen from the above that a more cost and material efficient means of achieving the same result is desirable in the offshore construction and installation industry.
The present invention addresses the shortcomings in the prior art by providing a less costly LMU structure and installation method. One or more LMUs (leg mating units) are attached to each of one or more legs of a lower support structure, such as a jacket, for the topside. The LMUs absorb the load of a topside as it is installed onto a lower support structure. A stop ring is rigidly attached around the outer diameter of the lower end of corresponding legs of the topside. An LMU assembly ring is attached around the upper end of the LMUs and is sized to receive the stop ring during installation of the topside onto the lower support structure. The LMUs include a plunger and material for absorbing the load of the topside on the lower structure. The LMUs are attached to the outside of the leg structure to allow removal and reuse of the LMUs.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. For a better understanding of the present invention, and the operating advantages attained by its use, reference is made to the accompanying drawings and descriptive matter, forming a part of this disclosure, in which a preferred embodiment of the invention is illustrated.
In the accompanying drawings, forming a part of this specification, and in which reference numerals shown in the drawings designate like or corresponding parts throughout the same:
As seen in
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A plurality of layers of elastomeric material 14 is preferably used for selectively adjusting the load absorption and compression characteristics to match the weight of the topside being installed. The elastomeric material 14 may be of any type suitable for absorbing large loads. Such elastomeric materials are well known in the offshore installation industry.
Ram 16 has an exterior diameter that closely matches the interior diameter of the housing and is movably received in the housing 12. The ram 16 is in the initial installation configuration/position as seen in
The load absorbing ring 18 is either received on or rigidly attached to the ram 16 of each of the leg mating units 12 mounted on the piling 22 or jacket leg. As seen in
The stop ring 20 (best seen in
In operation, the barge or pontoons (hereinafter referred to as “installation vessel”) supporting the topside is floated into a position such that the topside is above the lower supporting structure onto which the topside will be lowered. The legs 34 of the topside and the tubular members 22 of the lower supporting structure having leg mating units 10 are aligned as seen in
As seen in
Once contact of the stop ring 20 with the load absorbing ring 18 is made, the speed of the downward ballasting is preferably increased a predetermined amount to insure that the topside and lower support structure maintain contact to prevent damaging impacts that could result from rising and falling wave action.
After the one hundred percent load transfer illustrated in
This releases the pressure on the elastomeric material 14 and allows the ram 16 and elastomeric material to move downward. The lip 38 of the topside leg 34 then rests on the piling 22. As seen by the space indicated by the arrows in
The invention provides a number of advantages.
The invention saves the costs of expensive, sacrificial, single use LMU's and reduces the cost of float over operations.
The invention can reduce engineering and fabrication costs for fabrication of new LMU's.
The invention can increase the flexibility of changing the configuration of LMU's, which allows an increase in offshore workability and reduced impact loadings during topside installation.
While specific embodiments and/or details of the invention have been shown and described above to illustrate the application of the principles of the invention, it is understood that this invention may be embodied as more fully described in the claims, or as otherwise known by those skilled in the art (including any and all equivalents), without departing from such principles.
