Deep Water Offshore Apparatus And Assembly Method

Abstract

A truss type spar that eliminates the need for the more complex and critical attachment of the buoyant hull to the truss section at a fabrication site / yard that is remote from the fabrication yard where the buoyant hull and truss sections were originally built. The buoyant hull and initial truss sections are constructed at the fabrication yard of choice, joined together, and transported to a dock or fabrication yard (a second location) that is as close as possible to the final offshore installation site. Transport of such completed structures, either separately or together, is normally done on a heavy lift vessel to reduce transport time and prevent damage to the buoyant hull and truss sections. Once at the fabrication yard / dock, the joined buoyant hull and initial truss section are floated off the heavy lift vessel and the draft adjusted to a position suitable for joining additional truss sections. One or more additional truss sections can be attached to the initial section, and the completed buoyant hull and truss is then towed to the final offshore installation site.

Description

FIELD AND BACKGROUND OF INVENTION[0001]The invention is generally related to floating offshore structures and more particularly to a spar type structure with a jacket / truss section.[0002]As now known in the offshore oil and gas industry, the spar type structure with a jacket / truss extending from the buoyant hull, such as that described in U.S. Pat. No. 5,558,467, provides a number of advantages over other floating structures such as a traditional spar type structure or a TLP (Tension Leg Platform) that makes it desirable, especially for use in deep water. Versions of the spar can be designed for environment specific locations around the world.[0003]Environmental conditions such as waves, winds, and currents are directly related to the length of the structure required for acceptable motions such as heave, pitch, and yaw. More extreme environmental conditions require longer buoyant hull and truss sections in order to provide acceptable motions. One of the main advantages of the spar i...

AI Technical Summary

Benefits of technology

[0008]The present invention addresses the shortcomings in the known art. What is provided is a truss type spar that allows the extension of the truss to complete the total required length and eliminates the need for the more critical and complex attachment of the buoyant hull to the truss section to be made with these two structural components in a floating condition. Additional truss sections supporting heave plates can be added to the initial truss section at a fabrication site / yard that is remote from the site / yard where the buoyant hull and truss sections were originally built. The extension is completed by adding sections to the initial truss after transport. The buoyant hull and initial truss sections are constructed at the fabrication yard of choice, joined together, and transported to a dockside location or fabrication yard that is as close as possible to the final offshore installation site. Transport of such completed structures is normally done on a heavy lift vessel to reduce transport time and prevent damage to the buoyant hull and truss sections. Once at the fabrication yard / dock, the buoyant hull and initial truss section already connected to the buoyant hull are floated off the heavy lift vessel and the draft adjusted to a position suitable for joining additional truss sections. One or more additional truss sections can be attached to the initial truss section, after which the completed buoyant hull and truss is towed to the final offshore installation site.

Problems solved by technology

This method of tensioning can cause an increase in the spar heave motions.

Because of the specialty facilities required in the fabrication yards to construct the spar, there are a limited number available worldwide.

The world wide number of transport vessels available for this operation is very limited because of the required size of the transport vessel.

Also, these vessels have limitations on the weight and length of the spar that can be transported.

It is more difficult to make the connection in this manner than to make the connection on land.

The connection between the truss and buoyant hull is extremely critical because if the truss separates from the buoyant hull it becomes unstable and can capsize.

High stress areas in the connection that can result in its failure can be caused by misalignments and other dimensional tolerances that are difficult to comply with when the connection is made with the buoyant hull and truss section floating near a dockside.

Performing this construction in this way can present special challenges in the form of extra time, costs, and potential alignment issues.

The difficulties of joining the truss section to the buoyant hull are increased with the longer buoyant hulls and truss sections.

Another critical limitation is that there are only a few fabrication / ship yards around the world with the capability to receive and join these two longer sections.

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