US3885699A

US3885699A - Floating roof

Info

Publication number: US3885699A
Application number: US290761A
Authority: US
Inventors: Nestor Leon Pladys
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1971-09-20
Filing date: 1972-09-20
Publication date: 1975-05-27
Anticipated expiration: 1992-05-27
Also published as: DE2245837A1; GB1398581A; FR2153675A1; BE789051A; NL7212718A; JPS4838515A; IT984634B

Abstract

A floating roof suitable for use with large capacity storage tanks comprises a central framework surrounded by one or more concentric floating rims. The rims are connected to the framework by tensioning cables that are adjusted to give a stable structure. The roof also comprises a covering sheet that is supported by the framework and the rims. A further embodiment of the roof has one or more of the rims located within the area of the central framework giving a more flattened roof suitable for some types of smaller capacity storage tanks.

Description

Umted States Patent 11 1 1111 3,85,699

Pladys May 27, 1975 [54] FLOATING ROOF 2,282,772 5/1942 Wiggins 220/26 R 2,282,773 5/1942 Wiggins 220/26 S [75] Inventor: Nest" Pladys, Rosendael1 2,586,856 2/1952 Orr et a1. 220/26 R France 2,606,684 8/1952 Wiggins 220/26 R 2,968,420 1/1961 Harris et al. 220/26 SA [73] Assgnee' {:Egf'ij ggg s gg g 3,116,850 1/1964 Anderson 61 al. 220/26 SA [22] Filed: Sept 1972 Primary Examiner-William 1. Price [21] APPL 290,761 Assistant Examiner-Stephen Marcus Attorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine Foreign Application Priority Data Sept. 20, 1971 France 71.33779 ABSTRACT [52] US. Cl. 220/225; 220/216; 220/219 A floating roof suitable for use with large capacity [51] Int. Cl Bd 87/20 storage tanks comprises a central framework sur- [58] Field of Search 220/26 R, 26 S, 26 SA, rounded by one or more concentric floating rims. The

220/26 D, 216, 219, 220, 225 rims are connected to the framework by tensioning cables that are adjusted to give a stable structure. The [56] References Cited roof also comprises a covering sheet that is supported UNITED STATES PATENTS by the framework and the rims. A further embodiment l 121 057 12/1914 Wilcox et al 22006 R of the roof has one or more of the rims located within 1:267 434 5/1918 MacPherson :::::::::::i:::i:iii 220 26 R the area Of'the Central framework giving a more 1,5202991 12 1924 Wiggins 220/26 R tened roof Suitable for some yp of Smaller Capacity 1,994,478 3/1935 Kueffer 220/26 R Storage tanks. 2,072,798 3/1937 Cranz 2,281,748 5/1942 Carney 220/26 s 24 Clalms, 12 Drawmg Flgures mac SHEET Q% I [III Q lili Ill SHEET FLOATING ROOF The present invention relates to a floating roof suitable for use with a liquid storage tank and being particularly suited for use with storage tanks of large dimensions, such as those intended for the storage of liquid petroleum products.

It is desirable to cover a volatile liquid such as gasoline, crude oil and the like, which is contained within a storage tank, with a roof or deck which normally floats on the surface of the liquid and provides a virtually vapour tight shield to minimise loss of liquid by evaporation.

These storage tanks now constitute an increasing part of the investment in the petroleum industry and the growing size of the tanks give problems in the construction of floating roofs of large diameter. It is well known for a floating roof to comprise a large diameter circular deck joined at the edge to an annular pontoon. These large decks suffer the disadvantage of being heavy and are particularly vulnerable to deformation under the action of external stresses e.g., gusts of wind, weight of snow, and to movement of the liquid stored.

According to the invention there is provided a floating roof suitable for use with large capacity storage tanks which comprises a central framework with one or more substantially concentric floating rims, the rims being connected to said framework by means of tenstoning cables adapted to give a stable structure and a covering sheet adapted to be supported by the framework and rims.

The central framework preferably comprises vertical floats braced at their upper and lower parts by crowns to which are attached to tensioning cables adapted to ensure the concentricity of the floating rims.

Preferably each tensioning cable passes over a pulley adapted to fit on the rim.

The roof proper preferably Consists of an assembly of thin sheets stiffened by parallel ribs and which are fixed on to the above-mentioned floating rims so as to have a slight slope towards the centre or towards the outside, thus ensuring that any rainwater flows towards a Central well or annular well provided for this purpose- For the purpose of providing leakproofness between the said roof and the peripheral wall of the tank, the roof may be provided with a seal comprising an articulated collar to the end of which there is fixed a circular attachment which can be inflated with water or by means of an inert gas or compressed air, this attachment being coupled to another attachment of the same type which plays the part of a restoring spring and ensures the application of the first joint against the peripheral wall of the said tank, the assembly of these two omts supported continuously by th id ti ulated collar operating in accordance with the principle of leyers between the peripheral part of the external floatmg rim provided in the vicinity of the periphery of the said roof and the said peripheral wall. i

The effects of the wind are attenuated by means of brackets possessing suitable respective heights and fitted with horizontal stabilising plates of a suitable area adapted so as to rest on the bottom of the tank when the latter is empty. These brackets act as stabiliscrs or as acks in the stored liquid by damping the movements of the roof due to external stresses because of the incrtin of the oil with which the stabilisers are in contact.

The ill'l()\ki-l'llClTll(lllC(l framework may be made of steel, but it also may be made of any other rigid material, and particularly of a synthetic plastic material.

The central framework comprises standard commercial tubes which may have, for example, a thickness of 12 to ZO/ll) of a millimetre. These tubes may possibly be of the clipped spiral type.

However, in order to avoid costly operations of shaping, these rims are preferably given a polygonal crosssection by making them of an assembly of linear tubular elements, always cut at the same angle at their two ends, for example at an angle of 50, these tubular elements then being assembled by standard sleeves on which the cable attachments are welded.

Preferablythe tensioning cables are encased in a suitable plastics material such as polyvinyl chloride for example. In order to render the floats unsinkable, it is advantageous to fill them with a synthetic foam product, such as for example, polyurethane foam.

All the metal elements may be treated to render them corrosion resistant against the effects of the petroleum products stored and atmospheric agents.

The covering sheet, preferably, comprises panels of shaped material that are juxtaposed and interconnected. The panels are connected together either directly or by means of junction pieces of suitable shape along the edges of said panels. Most preferably the panels have corrugations at right angles to the elements of the rim,

In order to ensure the rigidity of the roof despite its thinness, it is possible to use pre-fabricated sections assembled together by leakproofjoints arranged parallel to the said ribs so as to avoid welding if possible. The foils arranged between the said joints will be referred to below as panels and may possibly co-operate with parts of a triangular shape located between two neighbouring floating rims.

The above-mentioned panels, if they are used, may also be rendered corrosion resistant.

The tension exerted by the said cross-cables shows itself as a compression uniformly distributed in the above-mentioned floating rims and in the vertical floats of the hub and by a flexural moment in the coupling sleeves of the straight elements of the floating rims, this moment being balanced by a reinforcement of the said sleeves, particularly by a horizontal rib.

In the event of tensions which are too large being exerted on certain of the cables which are taut, the risks of collapse are reduced by the fact that the sheets constituting the roof form braces which make it possible to limit the said compressive forces.

In order to avoid excessive loading by snow, the roof may be equipped on its outer surface with an electrical heating device.

Preferably the mean thickness of the elements making up the new roof, including that of the floats, the rims and the cables, does not exceed 4 mm. For purposes of comparison this thickness is of the order of 7 mm. for floating roofs of the single deck type and of the order of i3 to 14 mm. for floating roofs of the double deck" type. The relative thinness of the roof may yield a consequent weight reduction compared t conventional floating roofs.

The tensioning cables for the roof constitute a Faraday cage thus protecting the roof against lightning and helps to reduce the accumulation of static electricity.

Although the roofs according to the present inven tion are of maximum advantage when used with storage tanks of a very large diameter. (for which conventional floating roofs are not always suitable). the new roof according to the invention may also be adapted to tanks of a low capacity of most types, and particularly to those currently used when the bottom of the tank is a horizontal plate.

Thus according to a further aspect of the invention there is provided a floating roofin which one or more of the floating rims lie within the area of the central framework.

In this case the shape of the roof is more flattened so as to avoid a loss of storage when the roof is in the low position. It is in fact important to prevent the tank from breathing for obvious reasons of safety. The level of the petroleum stored, when the brackets rest on the bottom, must therefore be minimum. The roof is flattened whilst ensuring its mechanical strength by removing the hub from the centre and crossing the end tightening cables around the floating rims.

In a further embodiment of the floating roof, this roof comprises in addition an integral leak proof structure, the framework being of the same type as in the first embodiment of the invention but the sealing foil is in this case double and consisting of a first sheet connected to the above-mentioned upper tightening cables and resting on these cables so as to constitute a tent inclined from the centre towards the periphery and a second sheet intended to rest always on the surface of the stored liquid between a peripheral rim and the median part of the central hub.

Thus according to a still further aspect of the invention there is provided a floating roof which comprises only one floating rim, said rim being connected to the central framework by tensioning cables attached to an upper and a lower part of said framework and a covering sheet formed in two parts, one part of which is supported by the upper section of said tensioning cable and the other part being attached to the central framework and floating rim, the two parts of said sheet being adapted to combine with the rim to form a leakproof enclosure. The assembly thus formed constitutes a leakproof structure which can be pressurized (to about 0.01 0.02 bars) to reduce the effect of the weight of the upper sheet on the cable and to allow the lower sheet to rest on the surface of the stored liquid.

Such a pressurised embodiment furthermore prevents any further possibility of the introduction of petroleum vapour or explosive vapour into the pressurised enclosure.

Furthermore, in this embodiment, the slope of the upper sheet ensures the flow of rainwater towards the periphery of the tank.

It is also possible to provide a device for heating the air in the above-mentioned pressurised enclosure so as to prevent. for example, an accumulation of snow in winter on the upper sheet.

In the event of the accidental lack of pressurisation, the consequences are limited since the two sheets are both supported.

Furthermore, in this embodiment, the hub only has one central stabiliser which can possibly slide in a vertical tube planted in the centre of a tank, it being possible for this vertical tube to be stayed so as to ensure that it is kept vertical.

The invention will now be described by example with reference to the drawings accompanying the Specification. The drawings show three types of floating roofs suitable for use with storage tanks according to the invention in which:

FIG. I is a cross-section in elevation of storage tank equipped with a floating roof according to the inven-.

tion.

FIG. 2 is a cross-section in elevation ofa floating roof of a semi-buried storage tank.

FIG. 3 represents an alternative embodiment of the invention in the form of a flattened floating roof in a virtually empty tank having its hub further away from the centre and located around a floating rim.

FIG. 4 is a section along line IV IV of FIG. 5.

FIG. 5 is a plan view of the floating roof of FIG. 2 showing the arrangement of the crossed tensioning cables of the floating rims which are concentric in relation to the central hub and also showing a part of the sheet of the said roof.

FIG. 6 is a complementary diagrammatic view of the same floating roof as FIG. 5 showing the tensioning cables between one rim and the said central hub.

FIG. 7 is an enlarged section along line VII VII of FIG. 5 through the connecting device between the tensioning cables and the assembling sleeves of the tube elements constituting the floating rims.

FIG. 8 is a plan view of part VIII of FIG. 5.

FIG. 9 is a cross-section in elevation of a storage tank similar to that of FIG. I equipped with another embodiment of a floating roof having a double sealing sheet.

FIG. 10 shows a cross section in elevation of a semiburied storage tank also equipped with a floating roof having a double sealing sheet.

FIG. 11 is a plan view of the roof corresponding to FIGS. 9 and 10.

FIG. 12 is an enlarged cross-section in elevation of the roof corresponding to FIGS. 9 and 10.

A typical use of the floating roof is with storage tanks containing liquid petroleum products.

FIGS. 1 and 2 show the central hub l of the framework of the floating roof and the

crowns

2, 3, 4 and 5 on which there are moored the tensioning cables of the different concentric floating rims 6 to 10. These rims are arranged, according to a polygonal contour which facilitate the assembly of the consecutive linear units of these rims.

They are equipped with brackets 6a to 10a of appropriate length, in such a way that the stabilisers 6b and 10b can come to rest on the peripheral part 11 of the bottom part of the tank on which the said floating roof is to be used.

This tank has a circular peripheral wall 12 which is located in the immediate vicinity of the outer rim I0, which is preferably of polygonal shape.

A device 13 for pumping the stored liquid is mounted on the said floating roof by means of articulations which can be seen at I4 of FIGS. 1 and 5, and which permit this device to follow the variations of the level of the free surface of the stored liquid. The device. may be substituted with suitable equivalent existing devices.

In FIG. 2. in the centre of the tank there is a central well 15 at the bottom of which it is possible for the rainwater to collect, this water arriving through a watertight pipe I6 passing through the stored liquid after first of all following the slope of an upper sheet constituting the roof proper 17, which is inclined towards the centre in the direction of the free surface of the stored liquid. The collection of rainwater is not represented in FIG. 1.

For purposes of simplification, the crossed cables which serve to ensure the concentricity of the rims 6 to have been omitted in FIGS. 1 and 2.

These crossed cables, which are shown in FIGS. 5 are arranged as in FIG. 6. When they are above the horizontal median plane they are shown in solid lines and in broken lines when they are below this plane.

The hub and the rim under consideration are only shown by circles corresponding to the points of attachment of the acid cables. A cable bearing the reference no. 18a is anchored to the lower crown of the hub at the point 5a. It passes into the pulley 21a and then, in the upper position 18b, rejoins the upper crown at the point 2a shown in the drawing at 60 in relation to the anchorage 5a, and it is at this point 2a that the cable 18 (18a plus 18b) is anchored and stretched.

The immediate neighbouring cable 19b is situated at in a clockwise direction in front of the cable 18a. It is anchored and stretched at point 2b of the upper crown of the hub, passes into the pulley 21b, becomes 19a, then is anchored to the point 5b of the lower crown of the hub.

Thus the cables oriented in the same manner on FIG. 6 are alternatively above and below the horizontal median plane, and the anchorage pulleys on the floating rims form with the corresponding radial planes angles which are turned alternately to the left and to the right.

This symmetrical arrangement renders the system virtually undeformable by forces in both the vertical and radial planes as well as by rotatory forces whilst imparting to it the desirable elastic properties.

The hub 1 consists of a certain number of vertical floats 1a which can be seen in FIGS. 1 to 5. The free ends of the cables 18 and 19 for centering the floating rims 6 to 8 are moored on to

crowns

3 and 4 of the said central hub, whilst those of cables 18 and 19 for centering the floating rims 9 and 10 are moored on the

outer crowns

2 and 5 of this central hub.

As regards the sheet 17, the slope of which makes it possible to collect the rainwater in the well 15 through the pipe 16, it can be seen in FIGS. 4 and 5 that this sheet consists of the juxtaposition of section sheets of given width known as panels and bearing the references 17a in FIG. 4, each of these panels occupying the space between two parallel sections of FIG. 5, being assembled together along the joints l7b which can be seen in particular in FIG. 4.

The panels also have intermediate ribs of greater or lesser amplitude referred to respectively by the

reference numbers

170 and 17d.

The length of the inclined sides of the trapezoidal elements thus constituted, the junctions between the joints 17b of the outer panels are made by means of shaped pieces (or fillet sections) 17e which also enable assembly by tight fitting on the joints 17b of the neighbouring trapezoidal units.

The sealing sheet is equipped with accessories such as an access ladder, vent holes, and suction valves to permit protection of the tank and allows breathing when the roof is in its low position. For the sake of clarity, these accessories have not been shown in the draw- %n FIG. 5 it is also possible to see the stabilisers which are square in shape, 6b to 10b, and the different concentric floating rims 6 to 10, consisting of linear elements connected together by 24 sleeves of appropriate shape 20, which can be seen particularly in FIG. 8, and on which there are moored the cables 18 or 19 via the pulleys 21 mounted on plates 22 connected by means of two rings 23 which are particularly visible in FIG. 7, to a plate 24 which is integral with the sleeve 20.

The bracket 10a is extended in its upper part, similarly to the other brackets, by means of a tubular unit welded on to the rim 10 which also carries between the said elements We longitudinal brackets 10d which support the sheet 17.

Each tensioning cable 18 or 19 consists of two sections, the upper one 19a, and a lower one 18b, 1%, the free ends of these two sections being fixed respectively to the

symmetrical crowns

2 and 5 or 3 and 4 located symmetrically in relation to the level of the stored liquid in the tank in question.

The detail of assembly between the elements of the rim 6 to 10 and the sleeves 20 can be seen in FIG. 8 and comprises the use of internal sleeves 25 mounted on the elements 20 and on the outside of which there are fixed the linear elements making up the rims 6 to 10.

FIG. 7 shows the detail of articulated collar 28 which includes the leakproof joint 26 mounted on the opposite side of collar 28 between the framework of the floating roof and the skirt of the tank. Joint 26 is inflated by means of a liquid, an inert gas or with compressed air, and another symmetrical joint 27 mounted on the opposite side of collar 28, is similarly inflated to press joint 26 against the cylindrical wall 12 of the tank by lever action thus ensuring a seal.

The lower part of collar 28 of the articulated supports of the joint 27 is polygonal and this lower part is pivotally mounted at 29 on the supports 30 fixed along the sides of the polygonal rims 6 to 10 to provide a pivot.

The upper part 31, which ends in a cylindrical support 31a of the joint 26, is of a left-hand shape which ends in a circle in its upper part and a polygon in its lower part 32.

FIGS. 912 show an alternative embodiment of the roof having a double sealing sheet. The different concentric rims 6 to 10 which are visible in particular in FIG. 5 are replaced by a single peripheral circular rim intended to be applied against the peripheral wall 12 of the tank which is to receive the said floating roof.

In this embodiment, the sheet 17 is replaced by a double sheet consisting of an upper sheet 33 made of plastics material resting on the upper part of the radial cables 34 for tensioning the said rim and of a lower sheet 35 which is more or less horizontal, also made of plastics material and resting on the upper part of the stored liquid, as well as on the central cables 36 also arranged radially.

FIG. 12 shows in greater detail the cables 34, which instead of being moored to the inner part of the floating rim, whose concentricity they have to provide, pass inside the said floating rim 37 following the outer part of this rim and being fixed by their free ends on to a hub lb of a type very different from hub 1, which is capable of sliding on a mast 38 which rests on the centre of a central well 15 (FIG. 10).

The mast 38 may be stayed, for example on the slopes of the retaining well in the case of semi-buried tanks. This stage is not shown in FIG. 10.

The hub lb is fixed to a stabiliser device consisting mainly of a horizontal plate 1c playing the part of shock absorber and preventing the oscillations of the hub 1b during the rapid descent of the level of the free surface of the petroleum liquid contained in the abovementioned tank.

In this embodiment applied to semi-buried tanks, the lower part of the tightening cables 34 comes into contact with the peripheral part 1 1 of the bottom of the tank when the tank is empty.

The two sheets 33 and 35 form a pressurisable enclosure which tends to prevent the upper sheet 33 from weighing on the upper part of the tensioning cables 34 and tending at the same time to apply the sheet 35 against the free surface of the stored liquid.

Moreover, this pressurised enclosure is at a pressure which is sufficient to prevent any re-entry of petroleum vapour or of an explosive mixture between the two sheets 33 and 35.

In the enlarged view of FIG. 12 one can see the sheets 33 and 35 and the two sections of cable 34, the median part of which passes into a groove 40 provided inside the floating rim 37.

In this embodiment, not only the rim 37 comes into contact with the peripheral wall 12 of the tank, but the sheet 33 covers the

rim

37 and 33a, which ensures the flow of rainwater towards the outer part of the floating roof. The rim 37 is integral with rods 37a which end in stabiliser plates 37b which can also be seen in FIG. 11.

I claim:

1. A floating roof suitable for use with a large capacity storage tank comprises (i) a central framework and at least one floating rim, (ii) tensioning cables connected from said central framework to said floating rim, (iii) a covering sheet adapted to be supported by said central framework and said floating rim, and (iv) a seal comprising an articulated collar pivotally attached to the outermost floating rim, said articulated collar being fitted with a first inflatable attachment and a second inflatable attachment which is nearer to the pivot than the first inflatable attachment, said attachments being on opposite sides of said articulated collar and being adapted so that upon inflation of said inflatable attachments, the second inflatable attachment is pressed against the rim and by a level action presses the first inflatable attachment against a surrounding wall.

2. A floating roof according to claim 1 wherein there are a plurality of rims and all the rims are located outside the said framework.

3. A floating roof according to claim 1 in which at least one of said rims is located within the area of said framework.

4. A floating roof according to claim 1 in which each tensioning cable passes over a pulley adapted to fit on the rim.

5. A floating roof according to claim 1 in which the covering sheet slopes down towards the central framework.

6. A floating roof according to claim 1 in which the said sheet is fabricated from a plastics material.

7. A floating roof according to claim 1 in which the floating rim is substantially circular in form.

8. A floating roof according to claim 1 in which the rim is substantially circular in cross section.

9. A floating roof according to claim 1 in which the tensioning cables are arranged so that the rotational forces applied to adjacent elements of the rim are in opposition.

10. A floating roof according to claim 1 in which the covering sheet is adapted to permit collectionand removal of a liquid which may fall on its surface.

11. A floating roof according to claim 1 in which the central framework at least one vertical float.

12. A floating roof according to claim 11 in which said central framework includes a plurality of vertical floats; each upper part of said floats is connected together and each lower part of said floats is connected together by means of upper and lower crowns, respectively.

13. A floating roof according to claim 12, in which each tensioning cable is attached to the upper and lower crowns of the central framework.

14. A floating roof according to claim 1 in which the covering sheet comprises panels of shaped material that are juxtaposed and interconnected.

15. A floating roof according to claim 14 in which the panels of shaped material are connected together, by means of junction pieces of suitable shape, along the edges of said panels.

16. A floating roof according to claim 14 in which the panels of material have corrugations substantially at right angles to the elements of the rim.

17. A floating roof according to claim 1 in which the floating rims are fitted with stabilizers for supporting the roof on the bottom of the tank when the tank is empty.

18. A floating roof according to claim 17 in which the stabilisers comprise substantially vertical legs fitted with horizontal plates.

19. A floating roof according to claim 1 which comprises one floating rim, said rim being connected to the central framework by tensioning cables attached to an upper and a lower part of said framework and a covering sheet formed in two parts, one part of which is sup ported by the upper section of said tensioning cable and the other part being attached to the central framework and floating rim, the two parts of said sheetbeing adapted to combine with the rim to form a leakproof enclosure.

20. A floating roof according to claim 19 in which the leak-proof enclosure is adapted to be pressurised.

21. A floating roof according to claim 19 inwhich the central framework comprises a central sleeve equipped with a stabiliser, the framework being adapted to mate with an external mast.

22. A floating roof according to claim 21 in which the stabiliser comprises a horizontal plate.

23. A floating roof according to claim 1 in which the floating rim comprises a plurality of linear elements connected together substantially in the form of a polygon.

24. A floating roof according to claim 23 in which the linear elements are connected to one another by means of sleeves on the exterior part of which are plates,

adapted so as to connect with the tensioning cables.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,885,699 DATED May 27, 1975 |NVENTOR(S) Nestor Leon Pladys ltis certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 7, Claim line 45, delete "level" and insert -1ever--.

Signed and Scaled this Twelfth Day of April 1977 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oflatents and Trademarks

Claims

10. A floating roof according to claim 1 in which the covering sheet is adapted to permit collection and removal of a liquid which may fall on its surface.

19. A floating roof according to claim 1 which comprises one floating rim, said rim being connected to the central framework by tensioning cables attached to an upper and a lower part of said framework and a covering sheet formed in two parts, one part of which is supported by the upper section of said tensioning cable and the other part being attached to the central framework and floating rim, the two parts of said sheet being adapted to combine with the rim to form a leakproof enclosure.

21. A floating roof according to claim 19 in which the central framework comprises a central sleeve equipped with a stabiliser, the framework being adapted to mate with an external mast.

24. A floating roof according to claim 23 in which the linear elements are connected to one another by means of sLeeves on the exterior part of which are plates adapted so as to connect with the tensioning cables.