Ships – Floating or semi-submersible storage vessel
Patent
1990-05-29
1992-01-28
Sotelo, Jesus D.
Ships
Floating or semi-submersible storage vessel
114292, B65D 8878
Patent
active
050835238
DESCRIPTION:
BRIEF SUMMARY
In the offshore oil business floating structures such as semi-submersibles and tension leg platforms (TLP's) are sometimes used to support drilling and/or production equipment. These structures are very weight sensitive in that the less structural steel content used the more equipment payload can be carried. A major structural steel weight component is the outer shell of the columns and pontoons which are usually circular or rectangular in cross section and consist of plate circumferentially or longitudinally stiffened with T stiffeners or bulb flats at close centres. Such a form of construction is both expensive and time consuming to construct to the fine tolerances required due to the load capacity sensitivity of compression shells to imperfections.
Both TLP's and semi-submersibles have hull pontoons and columns which are prismatic elements which may have circular, square, rectangular, hexagonal or other shapes in cross section. In order to resist the hydrostatic pressure around these elements when they are submerged the external shell plating is stiffened by transverse stiffeners and/or longitudinal stiffeners located inside the shell plating to prevent the plate from buckling.
Since this stiffening is very labour intensive to fabricate and adds both cost and weight to the hull it would be of great benefit to eliminate it altogether. Furthermore, it would be of benefit to configure the external plating in such a way that it is not subjected to bending stresses at all and therefore cannot buckle. By so doing, the external plating can also be made lighter than it would be as presently configured in today's floating structures.
It is the purpose of this invention to eliminate the requirement for stiffeners and to lighten the external shell plating on both pontoon and column elements.
In accordance with the present invention there is provided a structural form comprising a hollow member having a shell with alternate concave and convex surfaces relative to the longitudinal axis of the member and an internal framing arrangement to support the shell, characterised in that the concave surfaces are unstiffened and run substantially the whole of the length of the member, the member being capable of resisting an applied pressure loading.
This structural configuration will reduce the weight and cost of such structures when compared with conventional stiffened fixed curvature cylindrical external pressure vessels. Such structures will offer advantages over conventional designs particularly where external pressure is the dominant loading, for example in the offshore marine and subsea environments.
This framing invention lends itself to any external pressure vessel and is not restricted to TLP's and semi-submersibles or even to water pressure for that matter. Nor is the idea restricted to steel or any other metal since this invention would lend itself very well to the introduction of carbon fibre technology for the exterior shell material.
External pressure vessles are required wherever people or equipment are required to be kept dry beneath the sea and this framing invention could be used to great advantage in such structures. Examples would include habitats for people, enclosures for offshore oil production equipment, diving vessels, submarines, buoyancy chambers and tanks, etc. There are instances where the corner longitudinal framing tubes could be of additional use e.g. guides for tension leg platform tethers and pile guides for steel offshore jacket buoyancy legs.
This framing invention would also be of advantage in resisting external pressure from ice. Whenever a structure becomes frozen in ice great pressure is exerted by the ice on the structure as the ice expands and this pressure could be resisted very efficiently by the framing invention. In addition where the corner pipes are used to form the convex portions of the shell they could carry steam or other hot gas or fluid to melt the ice local to the structure and thereby reduce the external pressure.
Such shapes have not been used before for offshore vessel
REFERENCES:
patent: 1575226 (1926-03-01), Pichler
patent: 3823563 (1974-07-01), Lovie
patent: 4155671 (1979-05-01), Vos
patent: 4570678 (1986-02-01), Ziemek et al.
Abbott Phillip A.
Osborne-Moss David M.
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