Receptacles – Closures – Floating closure
Reexamination Certificate
1998-02-25
2001-09-18
Shoap, Allan N. (Department: 3727)
Receptacles
Closures
Floating closure
C220S216000
Reexamination Certificate
active
06290083
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an assembly for supporting the floating roofs of tanks for storing liquid products, particularly 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 or final products.
Given the highly volatile nature of these products, these storage tanks have a roof capable of floating over the stored liquid, as a way of preventing the undesirable accumulation of gases between the layer of liquid and the roof.
The floating roof should in no way touch the bottom of the tank, as this would risk causing damage to the installations. It is therefore necessary to limit its travel to prevent it reaching a level which is below a specific minimum height, referred to by specialists as the “minimum operating height”.
On occasions, it is necessary for the floating roof to be stationed at a specific higher level to enable workmen to enter the tank in order to carry out maintenance operations, this height being referred to by specialists as the “maintenance height”.
A minimum operating height is established which prevents the roof coming into contact with the layer of sludge which is generally deposited on the floor of the storage tank. In some situations, this minimum operating height represents 20% of the total height of the storage tank. If the level of liquid stored drops below this height, support legs of the roof touch the floor of the tank and prevent the roof from descending further.
These support legs slide inside guides which are rigidly fastened to the floating roof and make it possible to adjust the operating and maintenance heights of the floating roof. The support legs have at least two transverse orifices which are intended to receive locking pins. The guides also have orifices for the locking pins. In order to adjust the height of the support leg, it is necessary to align the orifice of the guide with one of the orifices of the support leg and to slip in a locking pin through the aligned orifices.
Depending on the size and the weight of each support leg, the height-adjustment operation requires the participation of at least two people, one for handling the leg and the other for inserting the pin into the correct orifice. It is not uncommon for this operation to require three people.
In the storage tanks which are currently used, the difference between the maintenance and operating heights is relatively small since, as stated above, the layer of sludge which has accumulated in the bottom of the tank is generally very thick and requires a high operating height.
Our International Patent Application No. PCT/BR 97/00022 proposes the use of a tank floor whose centre is located at a level below the level of the edges, with a view to concentrating the undesirable liquids which are to be drained off (normally water) in the central region of the bottom of the tank. A ramp conveys the undesirable liquids to the edges of the tank. Automatic or manual drainage systems, as suggested in International Patent Application No. PCT/BR 97/00050, make it possible to draw off all the undesirable liquids. Consequently, the layer of sludge is now an extremely rare phenomenon.
With the adoption of these new technologies, the floating roof of the tank may therefore descend to a position which is much closer to the floor of the tank, because the layer of sludge has been eliminated.
However, another problem arises. As the difference between the maintenance and minimum operating heights of the floating roof is now a relatively high value, somewhere of the order of two metres, if use is made of traditional support legs then when the roof reaches the operating height practically the entire length of the leg is located above the roof, in a manner similar to a post.
Such an occurrence is undesirable and may even damage the support legs, which may for example buckle, so in a situation of this type their fastening to the guides is fairly unreliable. One possible solution would be to strengthen both the legs and the guides, which would give rise to an undesirable increase in the weight of the assembly and, consequently, of the floating roof.
U.S. Pat. No. 5,353,941 proposes a support assembly which employs an easy-to-handle adjustable-height system. This type of leg solves the problem regarding adjustment of the maintenance height. The main drawback of this system lies in the fact that the support legs are in permanent contact with the product being stored throughout the period during which the tank is in operation. This significantly reduces the service life of the support legs, owing to the effects of the corrosion to which they are exposed.
OBJECT OF THE INVENTION
The present invention proposes the use of an assembly for supporting floating roofs which requires the use of support legs only when the roof is in maintenance mode.
SUMMARY OF THE INVENTION
The present invention is characterised in that it comprises:
a) a guide which is substantially vertical and hollow in the longitudinal direction and is rigidly fastened to a floating roof which it is desired to support, wherein the lower end of the guide acts as a support for the floating roof when the roof reaches the lowest position;
b) a support leg which comprises a substantially vertical column having in an upper part a stop which acts as a travel limiter and prevents the support leg from moving downwardly and falling inside the tank beyond a first position when the leg is installed inside the guide;
c) a pair of mutually aligned orifices in the guide above the position of the support leg stop when the support leg is in the first position; and
d) a locking pin able to be inserted through the aligned orifices to prevent upward movement of the support leg from the first position; wherein, when it is necessary to place the assembly in the maintenance mode, the shaft of the locking pin is passed through the orifices.
In order to place the floating roof in maintenance mode, the locking pin has to be inserted in the orifices of the guide, with its longitudinal axis perpendicular to the longitudinal axis of the support leg. The locking pin now acts as an element for locking the support leg.
The position of the locking pins allows remote visual indication of the operating status of the floating roof.
REFERENCES:
patent: 1493091 (1924-05-01), Wiggins
patent: 2735574 (1956-02-01), Williams
patent: 3319329 (1967-05-01), Knutsen et al.
patent: 3583594 (1971-06-01), Belanger et al.
patent: 3587911 (1971-06-01), Creith
patent: 3815775 (1974-06-01), Strunc et al.
patent: 5230436 (1993-07-01), Vaughn
patent: 5353941 (1994-10-01), Benvegnu et al.
patent: 5449084 (1995-09-01), Wade
patent: 5628421 (1997-05-01), Jolly
Pradel Luis Adolfo Velloso
Witter Aldyr
Witter Roger Vieira
Eloshway Niki M.
Nixon & Vanderhye PC
Petroleo Brasileiro S.A.
Shoap Allan N.
Witter Roger Vieira
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