Hydraulic and earth engineering – Marine structure or fabrication thereof – Structure protection
Patent
1991-05-13
1993-01-05
Bagnell, David J.
Hydraulic and earth engineering
Marine structure or fabrication thereof
Structure protection
166356, F21B 33037
Patent
active
051764717
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an arrangement for protecting components such as valves and control units incorporated in a subsea structure particularly for hydrocarbon production. More specifically, the invention is directed to a protective roof arrangement intended to protect components in the subsea structure against objects dropped from above or moving along the seabed, such as trawls or the like.
The present subsea structure consists of a template which is secured to the seabed and modules retrievable to the surface for maintenance. There are different types of modules, all designed according to a similar pattern so as to interface with installation, maintenance ,and inspection tools. They are "integrated modules", in that, although some parts of the module are retrievable separately from the rest of the module, the module can be installed in one run with all of its components;.mounted thereon. As described hereinafter, these integrated modules include protective roof elements arranged in a specific manner according to the present invention.
2. Discussion of the Related Art
When a subsea station is in production mode, all the units constituting it are or may be installed onto the template main structure. It is important during production periods and also when other operations are performed on or near the subsea station, that, objects, dropped into the water or moved along the seabed, for example in connection with fishing operations, do not interfere with the normal functioning of the subsea station or even cause damage to the station.
For achieving protection similar to what is contemplated here, more conventional designs propose a separate roof, either integrated and hinged into the template structure, or run after installation of the necessary equipment on the template. This results in additional and more delicate operations than what is made possible by the solution according to this invention, as will appear from the following description. One particular drawback with a conventional design, is an increased risk of objects dropped on a module when it is retrieved, since there is no roof protecting it. An example of such known design for protective roofing for subsea installations is found in U.S. Pat. No. 4,273,472, issued Jun. 16, 1981, to A. Piazza. Published GB Patent Application No. 2,195,686 shows an example of a typical subsea station or template structure without any roofing.
SUMMARY OF THE INVENTION
The arrangement according to the present invention provides for full protection against trawls and dropped objects. In short, this is achieved by having roof elements integrated into the modules. This makes it possible to retrieve every module with its protecting roof arrangement intact, which means that there is no added risk of dropped object damage during such operations, and the preparatory work to retrieve a module is simpler than in the case of conventional designs. Moreover, the present roofing arrangement covering the template and the retrievable modules thereon is such that the whole system is over-trawlable and the equipment is well protected against dropped objects.
The novel and specific arrangement according to this invention, involving the above and other advantages, primarily consists in that each of the modules is provided with at least one fixed roof element and at least one completely removable roof element. These fixed and removable roof elements together cover substantially the entire top area of the module, and the roof elements of all modules in the subsea structure together cover a major portion of the top area of the subsea structure to protect against objects falling from above or moving along the sea bed. The roof elements are of a structure adapted to be such as trawls or the like, permanently deformed or crushed when a falling object results in an impact force thereon exceeding a predetermined threshold value, the loads from the roof elements of said modules being transferred to the supporting members of the templa
REFERENCES:
patent: 3247672 (1966-04-01), Johnson
patent: 4273472 (1981-06-01), Piazza et al.
patent: 4625805 (1986-12-01), Ladecky
Frafjord Peter
Grandgeorge Bruno
Bagnell David J.
Den Norske Stats Oljeselskap A.S.
Mobil Oil Corporation
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