US3793842A - Self-stabilizing submarine tank - Google Patents

Abstract

A submarine tank formed of pre-stressed concrete comprises central cells and outward peripheral ballast cells. The cells are interconnected and can be filled with liquid hydrocarbons. Appropriate control means can be provided for effectuating the controlled submerging of the tank. Vertical pillars can be provided to remove any vertical force effect of swells. Lower stud members can be provided on the bottom of the tank.

Description

United States Patent .[191

Lacroix [451 Feb. 26, 1974 SELF-STABILIZING SUBMARINE TANK [7 5] Inventor:

[73] Assignee: Sea Tank Co., Paris, France [22] Filed: Mar. 6, 1972 [21] Appl. No.: 231,933

Roger Lacroix, Sceaux, France [30] Foreign Application Priority Data Mar. 5, 1971 France 71.07723 [52] US. Cl. 6l/46.5, 61/50 [51] Int. Cl. 865g 5/00, E02d 27/38 [58] Field of Search..... 6l/46.5, 46, .5, 50; 114/57;

[56] References Cited UNITED STATES PATENTS Roulet et a1. 61/46 Starr et al. 6l/46.5

2,938,353 5/1960 Vorenkamp.... 61146.5 3,396,544 8/1968 Manning 61/46.5 X 3,385,464 5/1968 Courbon 6l/46.5 X

Primary Examiner-Jacob Shapiro Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT A submarine tank formed of pre-stressed concrete comprises central cells and outward peripheral ballast cells. The cells are interconnected and can be filled with liquid hydrocarbons. Appropriate control means can be provided for effectuating the controlled submerging of the tank. Vertical pillars can be provided to remove any vertical force effect of swells. Lower stud members can be provided on the bottom of the tank.

5 Claims, 4 Drawing Figures PATENTEDFEBZB 1914 3,793,842 SHEET- 2 BF 2 FIG .3 ?=f 23 1 SELF -STABILIZING SUBMARINE TANK BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to submarine tanks, more particularly for hydrocarbons, made of prestressed reinforced concrete, comprising several cells located between two plates. The lower plate or apron is substantially planar, and rests on the sea bed, the upper plate has an upswept shape and acts as a cover adapted to receive connections to the cells and the operating unit necessary for using the tank for storing fluids.

2. Description of the Prior Art The submarine tanks produced up to now have had various disadvantages that result from the complexity of their construction. Further, there is a danger of instability when they are submerged and, once laid on the sea bed, and also subject to the effects of the swell and of sea currents.

SUMMARY OF THE INVENTION The object of the present invention is to remedy the various past defects by producing a structure having inherent resistance, comprising, on its periphery, compartments specially intended for ballasting the structure and by the specialization of the various compartments for functions facilitating the submerging operation, the structure having on its lower plate, ribs jutting out to resist horizontal movement after it has been laid in position.

A characteristic of the present tank is that its constituent cells are formed into two types of compartments, the ones forming a reinforced core having an upswept cover, the others, called ballasting compartments, being peripheral and downswept.

BRIEF DESCRIPTION OF THE DRAWINGS in FIG. 2;

FIG. 2 shows a vertical cut-away view of the tank along ll--II in FIG. 1; FIG. 3 shows a tank in an elevation view, provided 7 with an emerging column;

FIG. 4 shows a tank in an isometric projection in the mode of construction by elements assembled at sea, on the surface.

SUMMARY OF THE INVENTION FIGS. 1 and 2 show, at l, the peripheral part of the tank that is used for the ballasting cells. The part 2 is the resisting core shown here as a truncated pyramid with square bases. 3v is a ballasting cell and 4 is a cell of the resisting core. The resisting core is separated sure can be either the pressure of the total height of the sea water, for current depths in the order of a hundred or so metres, or that which separates two consecutive submerging levels for greater depths.

Openings are made in the walls separating the cells to allow them to communicate with one another. To provide a more versatile aspect for the relative use of the tank as well as mastering of problems concerned with its submerging, it should be possible to cut off communications between certain cells, and to do this, the corresponding openings are provided with waterproof doors which, when operated, enable respectively the cutting off and the establishing of the communication between adjacent cells. On the walls of the cells of the core there are openings 7a at the lower part, and 7b at the upper part, whereas on those of the ballasting cells 3, openings 70 are provided. The gates with which certain of the openings are fitted have not been illustrated.

Inasmuch as concerns the ballasting cells 3, they are grouped together into compartments of two types: angle compartment 13 with five cells and intermediate compartments 14 with six cells having substantially the same capacity. The cells of a same compartment communicate with one another, by openings 70 in their walls.

from the ballasting compartments by the wall 5. This wall 5 and the plates, respectively 9 forming the cover, and 10 forming the apron, are supported, moreover, by vertical walls 6 separating the cells and embedded in the plates to resist against great differences in pressure between the outside and inside. This difference in pres- The four compartments of a same type form a group of cells which can be filled simultaneously and independently from those of the other group.

The empty tank floats and, at 15, FIG. 2, its empty water line is illustrated.

To fill the ballasting cells with water, all that is necessary is to open the valves of a manifold, not illustrated, taking water from beneath the line 15 and bringing it to the lower part of one of the cells of a compartment, whereas the air escapes through a circuit connected to the upper part of the cell and ending up at the operating unit, in which the corresponding control valves are arranged.

When the cells of the four compartments of a group are completely filled with water, the water line moves up to 16, whereas after complete filling of the cells of the second group, the water line then moves up to 17, at a distance in the order of a metre from the upper base of the truncated pyramid having square bases forming the cover 9 of the core having inherent resistance. The head-room thus provided for the tank ensures the required stability of the latter during towing.

It need hardly be mentioned that the subdivision of the ballasting cells into a greater number of compartments and into various groupings of the compartments should be considered if the need is felt, while respecting the balancing rule specifying that compartments having the same capacity placed symmetrically in relation to the axis of symmetry of the tank should be filled simultaneously.

Inasmuch as concerns the cells of the core, they are also grouped together into compartments having specific functions during the submerging of the tank. These cells are grouped into compartments of three types: a central compartment 18 acting as an extra'ballasting and taking part, due to its progressive and partial filling, in the submerging operation, four balancing compartments 19 used for removing the faulty balance by selective filling of the latter and, lastly, four storage compartments 20 remaining empty during submerging.

A pumping system, not illustrated, enables water to be brought into the base of the compartment 18, whereas air is evacuated from the upper part. This system can be reversed and enables, in case of need, the unballasting of the compartment.

Balancing by the compartments 19 can be effected with a constant volume of water without modifying the water line, by pumping water from the compartment 19 in which suitable pumps and hydraulic circuits are provided for that purpose; on the other hand, the grouping together'of these cells into compartments momentarily independent from one another cancels the water ballast effects.

The dimensions of the tank, the total number of the cells and the number of cells assigned to the functional compartments organized for the submerging operation are connected with the dimensions of the tank, the product to be stored and the storage conditions of the product.

The plate forming the apron can be thickened at 11 in order to embody the support surface of the tank on the bottom. The spade studs, which can possibly be arranged on the outside of the apron, are shown at 12. These studs are intended to improve, according to the kind of sea bed, the resistance of the tank to horizontal movement, and also to avoid any possible erosion caused by undercurrents. The tank rests on the sea bed by its own weight which is sufficient to counteract the alternating vertical efforts of the swell which would tend to lift it periodically; nevertheless, the hollow pillars 21, FIG. 1, are arranged vertically in the compart ments which they pass through from one end to the other, to balance permanently the pressures exerted on the lower and upper plates, of the tank, and hence to compensate the effects of the vertical components of the swell on the tank.

When the tank is submerged to a shallow depth, it is then arranged so as to resist the total pressure exerted at the end of the submerging, which can then be effected in a continuous way by continuous injection of water in the extra ballasting compartment 18.

For a greater depth, submerging requires, in that case, stoppages at imtermediate levels, spaced out vertically at heights defined previously, and corresponding to the permissible differential pressure. At these levels, all the compartments of the reinforcing core and filled with a compressed gaseous fluid enabling the outside water pressure to become balanced again and submerging to be resumed down to the next level. In that case, the inherent resistance of the tank is then only partial; but in relation to known structures which are less resistant, it enables the number of levels required during submerging to be reduced. The actual submerging operation can be controlled; either by floats arranged in chains round the tank, the floats of each chain being linked together by an anchor chain; or by a pillar rising above the tank and constantly remaining above the surface. This pillar can subsequently connect the tank for the material to be stored therein with possible access to the control valves at the upper part of the tank which can be assigned for that purpose, and the positioning of the superstructures which can be installed at its summit easier.

FIG. 3 shows an elevation view of the tank provided with such an emerging pillar 22; it enables submerging to be controlled, access to the control valves placed above the tank and, possibly, as is known, an upper platform 23 to be arranged above the level 24 of the sea.

After the submerging of the tank, and the laying of the latter on the sea bed according to techniques suited to the kind of sea bed, all communications are again established between the cells of the various compartments, both by opening gates and by manipulating the valves of the various circuits connected to the control unit. The tank is then completely filled with sea water, when the air has been completely removed, whereas the ballasting compartments filled with water at the beginning of the submerging operation are cut off from the sea water, the corresponding valves being closed. Then the connection is made, at the level of the control unit, with the fill pipes for the fluid to be stored, in this case, hydrocarbons. After having re-established the communication of the ballasting compartments with the sea, the hydrocarbons, which remove the sea water, can then be injected into the tank. Injection is thus effected under pressure. Injection is stopped when a volume of hydrocarbons sufficient for filling the tank up to a height less than one metre, for example, from the total height has been injected, thus leaving a water clearance.

The pumping of hydrocarbons can be effected either by allowing the oil to flow subsequent to the pressure exerted by the sea water, or by setting up a pressure by pumping.

As is known, the various openings 7a, 7b and providing communication between the cells, take part in the stabilization of the water to hydrocarbon interface, in combination with the dimensions of the orifices for making the tank communicate with the sea. This stabilization is valid both for movements caused during filling or emptying and for movements caused during filling or emptying and for movements due to the swell and to sea currents. It can then be noted that there is an attenuation and a dephasing of the interface movements in relation to the movements caused by the sea, more particularly by the swell.

The apparent weight of the tank completely filled with hydrocarbons is sufficient, despite the lightening force created by the difference in density between hydrocarbons and sea water, to provide a pressure on the sea bed opposed to lifting and sliding of the tank.

Thus, a total stability of the reservoir, both during towing and submerging is obtained by the value of its metacentric head, which is kept high, and during use, by the combined action, of its weight and of the compensation of the efforts exerted by the swell.

Inasmuch as concerns construction, the tank illustrated in FIGS. 1 and 2 is built entirely on land, in an excavation, then floated to its submerging site.

According to another method of construction, the tank is made of several elements, prefabricated on land, floated to a calm water site where they are assembled so as to form a single tank which is then towed to its submerging site.

FIG. 4 shows a tank according to this method of construction, comprising prefabricated elements 25 and assembled at sea: by way of an example, three elements 25 have been illustrated. The lines 26 show the fluidtight assembling lines. Here, also, the ballasting compartments, placed in the downswept part 27 of the tank and the higher reinforced core in the part 28 can be distinguished. This leads to the forming of a parallelepiped having horizontal generating lines, from modular elements enabling the constructing of tanks having different capacities, using identical and recurring elements, whose number depends on the capacity required. These tanks thus formed and having the advantages of low cost, and the versatile qualities of modular construction, can have an emerging pillar such as 22 in H6. 3 rising above them, and the cells which they contain can be grouped in compartments assigned to specialized functions to take part in the submerging of the tank and then assigned to general functions during use.

The various walls and partitions are pre-stressed in two directions, and considering the effort exerted at the level of the embedded joints, the tank is then under three-dimensional pre-stress. Both the inner and outer surfaces of the tank can be coated with known materials, more particularly, synthetic resin, to prevent their corrosion and to improve their fluid-tight qualities, and can be physiochemically treated in a known way to counteract the effects of sea water and of the fluids to be stored therein.

It should be noted that the invention is in no way limited to the particular form of embodiment which has just been described, but that it comprises all possible variations corresponding to the general definition thereof which has been given.

Thus, while a tank having a square shape is shown in the drawing, other shapes such as a rectangular shape may meet the requirements of the present invention.

Likewise, the example given of the hydrocarbon storage tank is only one possible application. More particularly, submerged tanks comprise any hollow body which can be submerged by specialization of the compartments it comprises, so as to effect, so to speak, automatic submerging; and, in this case, a container which submerges itself by the means described, will be considered as a submerged tank.

What is claimed is:

1. In a pre-stressed concrete submarine storage tank formed by a plurality of scaled cells extending between an upper cover plate and a flat lower plate resting on the sea bed, the improvement wherein: said plates are similarly rectangular, of generally equal size, with said upper plate being of truncated pyramidal shape at its center, said cells are grouped into multiple types of sealed core and peripheral compartments including means for effecting fluid communication between cells of the same compartment, and wherein; said cells extending about the periphery of said tank are shorter in height than the sealed core cells and comprise two types of peripheral compartments with all peripheral compartments of the same type being symmetrical in relation to the axis of symmetry of said tank, and means are provided for filling all peripheral compartments of the same type simultaneously with sea water to act as ballasting compartments or with fluid hydrocarbon to act as storage compartments, said core cells internal of the peripheral compartments are taller and include at least one central compartment having means for progressively and partially filling said central compartment cells to control submerging of said tank, and said core cells further form at their four corners thereof, complementary ballast compartments and means are provided to control filling of said complementary ballast compartments for facilitating submerging of said tank, and a plurality of storage compartments surround said central storage compartment, between said central compartment and said peripheral compartments, and have means for selectively filling said storage compartments with fluid hydrocarbon subsequent to submerging of said tank.

2. A submarine tank as in claim 1 wherein the peripheral ballasting cells are of such a size relative to the central cells that when only those cells are filled withwater the tank will float.

3. A submarine tank as in claim 1 further including lower stud members attached to the lower plate which help prevent relative errosion of the sea bed beneath the tank.

4. A submarine tank as in claim 1 further including hollow vertical pillars passing from the bottom to the top of the tank and open to the sea water, whereby the vertical lifting effects of swells of water are neutralized.

5. The submarine storage tank as claimed in claim 1, further comprising means for filling said core compartment cells with compressed gaseous fluid to balance the water pressure acting on the tank during submergence.

Claims (5)

1. In a pre-stressed concrete submarine storage tank formed by a plurality of sealed cells extending between an upper cover plate and a flat lower plate resting on the sea bed, the improvement wherein: said plates are similarly rectangular, of generally equal size, with said upper plate being of truncated pyramidal shape at its center, said cells are grouped into multiple types of sealed core and peripheral compartments including means for effecting fluid communication between cells of the same compartment, and wherein; said cells extending about the periphery of said tank are shorter in height than the sealed core cells and comprise two types of peripheral compartments with all peripheral compartments of the same type being symmetrical in relation to the axis of symmetry of said tank, and means are provided for filling all peripheral compartments of the same type simultaneously with sea water to act as ballasting compartments or with fluid hydrocarbon to act as storage compartments, said core cells internal of the peripheral compartments are taller and include at least one central compartment having means for progressively and partially filling said central compartment cells to control submerging of said tank, and said core cells further form at their four corners thereof, complementary ballast compartments and means are provided to control filling of said complementary ballast compartments for facilitating submerging of said tank, and a plurality of storage compartments surround said central storage compartment, between said central compartment and said peripheral compartments, and have means for selectively filling said storage compartments with fluid hydrocarbon subsequent to submerging of said tank.

2. A submarine tank as in claim 1 wherein the peripheral ballasting cells are of such a size relative to the central cells that when only those cells are filled with water the tank will float.

3. A submarine tank as in claim 1 further including lower stud members attached to the lower plate which help prevent relative errosion of the sea bed beneath the tank.

4. A submarine tank as in claim 1 further including hollow vertical pillars passing from the bottom to the top of the tank and open to the sea water, whereby the vertical lifting effects of swells of water are neutralized.

5. The submarine storage tank as claimed in claim 1, further comprising means for filling said core compartment cells with compressed gaseous fluid to balance the water pressure acting on the tank during submergence.

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