Receptacles – Closures – Floating closure
Reexamination Certificate
1998-05-15
2001-02-27
Cronin, Stephen K. (Department: 3727)
Receptacles
Closures
Floating closure
C220S222000
Reexamination Certificate
active
06193092
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a floating roof for use in tanks for storing liquids, such as petroleum and its derivatives.
PRIOR ART
Storage tanks are widely used in the petroleum industry and are essential to the functioning of an operational unit. They may be intended, for example, for storing crude oil, intermediate products and final products.
Given the highly volatile nature of these products, use is made, in the storage tanks, of a roof capable of floating over the liquid stored as a way of preventing the undesirable accumulation of gases between the layer of liquid and the roof.
Various types of floating roof are known. One type that is widely used is the pontoon-type floating roof, which, on the periphery, has a toroidal structure which is responsible for guaranteeing the roofs buoyancy. The remaining area of the roof is closed with metal plates which are in contact with the liquid. This type of roof has the disadvantage that it is relatively unstable and may, for example, overturn relatively easily if rainwater is concentrated in one area of its upper part.
Another type of floating roof, known by specialists as a “buoy roof”, is fairly similar to the pontoon-type floating roof. The major difference relates to the use of floats fixed above the metal plates, which substantially improves the roof's buoyancy in the event of the plates or weld beads rupturing. However, unfavourable weather conditions, such as high winds and a significant accumulation of rainwater, may cause the roof to sink. Another problem to be considered is the possibility of an accumulation of gas in the submerged area of the pontoon, which, in addition to creating the right conditions for corrosion, may also promote sinking of the roof when this area is subjected to the load constituted by rainwater, for example.
Another widely used floating roof is the double floating roof, in which one of its faces is in direct contact with the liquid and the other face remains at a certain height above this, supported by a structure. This type of construction has the advantages of being highly buoyant and of the upper part of the roof being practically smooth, which, in the event of high winds, prevents the occurrence of loads which could cause the roof to sink. It does have certain disadvantages such as, for example, the fact that it is extremely heavy and expensive.
A further disadvantage of double floating roofs relates to the reduction in the tank's useful storage volume which may, in certain cases, be significant. This reduction is due to the fact that the floating roof requires a large volume in order to create sufficient upward thrust to enable it to float.
All models of floating roofs known hitherto have one characteristic in common which is that they have a structural component, which makes the roof retain its shape; in the case of pontoon-type roofs or buoy roofs, the structural component is the peripheral pontoon, and, in the case of double roofs, the structural component is the roof itself.
This common characteristic gives rise to a number of disadvantages such as, for example, excessive weight. However, the greatest disadvantage relates to the difficulty these roofs have in withstanding unbalanced loads, such as those caused by access ladders or, alternatively, by a concentration of rainwater arising from deficiencies in the drainage system. Situations may arise in which this unbalanced load causes the floating roof to sink, which would be a disastrous event.
The present invention proposes the use of a roof which has no structural component imparting overall rigidity to the roof, thereby enabling the roof to cope with situations of unbalanced load without a problem.
SUMMARY OF THE INVENTION
The present invention relates to a type of floating roof with non-structural characteristics, as defined in claim
1
.
The number of floats to be used and their dimensions are characteristics which depend on the dimensions of the floating roof and also on the characteristics of the plates which will be used to construct the floats and the floating roof.
To facilitate the installation of a seal to seal the space between the periphery of the floating roof and the side of the storage tank on which it is installed, use is made of a support ring fixed to the periphery of the floating roof.
REFERENCES:
patent: 1698158 (1929-01-01), Glass
patent: 1819401 (1931-08-01), Bailey
patent: 3462040 (1969-08-01), Galloway
patent: 3690502 (1972-09-01), Guber
patent: 3944113 (1976-03-01), Heisterberg
patent: 3972444 (1976-08-01), Adams
patent: 4036394 (1977-07-01), Bodley
patent: 4202460 (1980-05-01), Imbeault
patent: 4213280 (1980-07-01), Sandborn
patent: 5074427 (1991-12-01), Siemerink et al.
patent: 5212090 (1993-05-01), Landine et al.
Avila Mario Luiz Novaaes
Witter Roger Vieira
Avila Mario Luiz Novaaes
Cronin Stephen K.
Nixon & Vanderhye PC
Petroleo Brasileiro S.A. - Petrobras
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