Ships – Floating platform
Patent
1985-06-11
1987-04-14
Basinger, Sherman D.
Ships
Floating platform
114265, 441133, 166350, E21B 712
Patent
active
046569626
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a manner of giving buoyancy support to structures that extend down to great ocean depths.
For the recovery of resources from beneath deep water, forces have to be transmitted from a working platform at the surface to a point on the sea-bed. These forces sometimes may be tensile, sometimes rotary, sometimes compressive. The platform may be in position only temporarily or it may remain there more or less permanently.
When the water is very deep, the length of the strut can be such that most of the strength of the material of the strut goes in supporting its own weight. In such a case, it has been proposed to offset the weight of the strut by providing buoyant support, so that the material of the strut can all be used for carrying useful forces from the platform to the sea-bed.
PRIOR ART
Such a system is that shown in HALE, et al, Canadian Pat. No. 1,136.545, issued Nov. 30 1982. Briefly, this system involves the placing of a large number of hollow canisters along the height or length of the strut. Each canister is effectively open at the bottom, and closed at the top.
The canister is provided with a tube that has a port near the bottom of the canister. When the canister is almost full of air (so that the water in it is almost completely expelled) the port becomes uncovered and further air fed into the canister enters the tube. This extra air is received into the tube and directed by it pipe to a point from which it bubbles up into the next canister above. Air fed into the bottom-most of a vertical series of canisters therefore fills each canister in turn, in cascade from the bottom up.
A huge advantage of this system is that the air pressure in each canister is the same as that of the water that surrounds it; each canister, whatever its depth, can therefore be a mere container and not a pressure vessel. So long as air is initially pressurized sufficiently to force it against the water pressure into the bottom-most canister, air will cascade up through all the canisters in the manner described, and its pressure will be automatically equalized with that of the water at every one of them.
This system may be described as a "cascading-canister" system, and has become known as the CASCAN (TM) system.
BACKGROUND OF THE INVENTION
Struts for ocean platforms are made in prefabricated sections, to be assembled together during final deployment. The assembly process must be done quickly, since the predictable weather window, in which deployment must be completed, is, in those deep oceans of the world where resouces are thought to exist, hardly ever more than two or three days. There is no time for a vigorous inspection procedure, during assembly. There is a need therefore to inspect the strut periodically during its service life.
For this reason, it is preferred that the strut be hollow, so that an inspection device may be lowered internally down the strut.
To describe it in more detail, the inspection procedure comprises sending an ultrasonic send-and-receive transducer down the strut. The transducer moves down in a predetermined spiral, and transmits a trace that can be recorded, and compared with previous traces, to give an early warning of possible weakening of the strut. Ultrasonic measurements of the kind required can only be carried out reliably and economically if the surface of the metal being tested is under water, since ultrasonic signals in air are swamped with noise.
This requirement for internal inspection would seem to rule out the possibility of using the actual walls of the strut to form the canisters for holding the buoyancy air, since the air would block the signals.
However, it is recognized in the invention, that the main critical area of the strut from the point of view of potential weakening, is the area of the joints between the sections of the strut. It is recognized that an inspection procedure that just examined the joints would be quite adequate, since the possibility of a gradually worsening, detectable fault developing in the main lengt
REFERENCES:
patent: 2606003 (1952-08-01), McNeill
patent: 3017934 (1962-01-01), Rhodes
patent: 3359741 (1967-12-01), Nelson
patent: 3858401 (1975-01-01), Watkins
patent: 3992889 (1976-11-01), Watkins
Bartz C. T.
Basinger Sherman D.
Fathom Oceanology Limited
Hewson Donald E.
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