US2754026A - Sealing mechanism for floating tank roofs - Google Patents

Description

July 10, 1956 J. H. WIGGINS 2,754,026

SEALING MECHANISM FOR FLOATING TANK ROOFS Filed Jan. 29, 1953 FIGZ.

INVENTOR, JOHN H. WIGGINS,

BY MMM A TTORNEY United States Patent SEALING MECHANISM FOR FLOATING TANK ROOFS John H. Wiggins, Chicago, Ill. Application January 29, 1953, Serial No. 334,006

1 Claim. (Cl. 220-26) This invention relates to floating tank roof sealing mechanisms of the particular type or kind that comprise an annular, limber shoe mounted on the floating roof in such a manner that said shoe is maintained in sliding engagement with the side wall of the tank, and a sealing element constructed of flexible, gas tight material, attached at its inner and outer edges to the roof and to said side wall shoe respectively, so as to form the top wall or top portion of a gas tight vapor space at the periphery of the roof in which gases and vapors will collect in the event the material stored in the tank consists of oil or a volatile liquid such as gasoline.

One object of my invention is to provide a floating tank roof sealing mechanism which as an entirety is new and a decided improvement on sealing mechanisms of conventional construction, in that it is composed of several separate units that coact with each other to produce or attain the following results, namely (a) greatly prolong the life of the flexible sealing element and eliminate the possibility of said element being ruptured by an explosion occuring in the vapor space, (b) greatly reduce thermal breathing of the vapor space due to the action of the suns rays and daily changes in temperature, thereby cutting down evaporation loss of the product stored in the tank, (c) and protect the side wall shoe supporting means from the action of destructive gases and vapors and also prevent snow and ice from collecting thereon.

And another object of my invention is to provide a seal for floating tank roofs whose vapor space comprises a flexible sealing element of such construction and arrangement that said vapor space is incapable of collecting and holding a relatively great quantity of gases or vapors, and in the event a fire occurs in said space or the pressure in said space becomes excessive or abnormal from any other cause, the internal volume of the vapor space will automatically increase to such an extent or degree as to relieve the pressure and prevent serious damage to the sealing element and other parts of the vapor space.

In conventional floating tank roof sealing mechanisms of the general type previously referred to, the side wall shoe consists of a relatively deep, circumferentially flexible or limber annular member, arranged in sliding engagement with the tank side wall and in spaced, concentric relation with an annular rim on the roof, the shoe having its lower edge portion submerged in the liquid on which the roof floats and the rim being of substantial depth or height and constituting the peripheral portion of the roof. The flexible sealing element which invariably is made of fabric treated to make it gas tight and fire resistant, bridges the gap between said shoe and rim and is attached to the upper end portions of said parts so as to coact with same to form a gas tight vapor space of inverted trough shape in cross section, whose top wall is formed by said sealing element. Due to the relatively great height or depth of the shoe and rim and the distance the sealing element is located above the surface of the liquid which constitutes the-bottom of the vapor space, the said vapor space is so large that the relatively great quantity of gases and vapors that collect and remain in same form a dangerous fire hazard, for if said gases become ignited the resulting fire or explosion creates a pressure which is liable to rupture the fabric sealing element and create a fire that may be difiicult to extinguish before considerable damage has been done to the sealing mechanism. Also the relatively great internal volume of the vapor space causes a considerable thermal breathing due to daily temperature change and heat from the sun, with the result that there is a high evaporation loss of the product stored in the tank. Still another objection to a sealing mechanism whose fabric sealing element is attached to the upper end portions of the side wall shoe and roof rim, is that said sealing element is at all times subjected to full impact of the suns rays and to rain and snow which tend to cause deterioration of the fabric of which the sealing element is constructed. In tank roof seals of conventional construction, the mechanism that supports and carries the side wall shoe is arranged either inside of the vapor space between the sealing element and the surface of the liquid on which the roof floats, or is mounted on the top side of the roof. If arranged inside of the vapor space, said mechanism is subjected to the action of corrosive vapors and gases confined in the vapor space and if said mechanism is mounted on the top side of the roof ice and snow are liable to collect on said mechanism and interfere with the operation of same.

I have devised a peripheral sealing mechanism for floating tank roofs which comprises an expansible and contractable sealing element that is of such area and which is combined with the side wall shoe and rim on the roof in such a manner, that under normal conditions said sealing element is disposed in such a position or condition that it forms a wall portion of a gas tight vapor space of relatively small internal volume, and in the event a fire occurs in said space, or the pressure of said space becomes excessive or abnormal, said sealing element will flex and move bodily into such a position or condition as to increase the internal volume of the vapor space sufficiently to reduce the pressure to a degree that is not great enough to rupture the sealing element or injure the same. Said sealing element is preferably constructed of gas tight fabric, it is of annular form and its width, from its inner edge to its outer edge, is considerably greater than the width of the fabric sealing element used in conventional floating tank roof seals, so that it will have sufiicient fullness or excess material between its inner and outer edges to enable it to assume two different positions or conditions, namely a contracted or folded condition wherein it coacts with the side wall shoe and rim on the roof to produce a vapor space of relatively small internal volume, and an expanded or distended condition wherein it coacts with said shoe and rim to produce a vapor space of relatively great internal volume. When the vapor space is under a normal pressure said sealing element assumes the form of a dependent or downwardly hanging loop suspended from the side wall shoe and the rim on the roof and disposed either in contact with or in close proximity to the surface of the liquid at the bottom of the vapor space, and when an abnormal pressure is created in the vapor space said sealing element expands or distends and moves bodily in an upward direction and assumes the shape of an upwardly disposed loop or umbrella like member of substantially convexed form, that extends upwardly from its points of attachment to the shoe and rim. In the preferred form of my invention herein shown, the inner and outer edges of the sealing element are rigidly attached to the side Wall shoe and to the rim on the roof at points above but in close proximity to the surface of the liquid on which the roof floats.

I have also devised a novel mechanism for supporting the side wall shoe of a peripheral seal for floating tank roofs, that has the desirable characteristic of being small and compact enough to enable it to be arranged between the shoe and the rim on the ,roof. Said shoe supporting mechanism forms the subject matter of my .copending applicationSerial No. 501,877, filed April 1 8, 1955. It is distinguished from prior side wall shoe supporting mechanisms in that it is composed of a plurality of pairs :of rock arms pivotally mounted on .the outer side of the roof rim, the two rock arms ofeach .pair being of different length and having their upper ends joined to the shoe in such a way that the shoe moves radially, inwardiy and outwardly with relation to the rim on the roof, with very little change in elevation of the shoe. When the two above described units are used in ,combination with a thh'd unit consisting of .a weather shield mounted at the upper end of the side wait shoe in a position where it overhangs the annular space between the shoe and the rim on thereof, said three units coact with each other to produce a floating tank roof sealing mechanism, which as an entirety is new, and which overcomes or minimizes all of the previously mentioned defects of conventional floating tank roof sealing mechanisrns.

Figure l. of the drawings is a fragmentary vertical sec tional view of a floating tank roof sealing mechanism constructed in accordance with my invention,,and equipped with a flexible sealing element disposed so that a portion of said sealing element is normally in contact with the liquid on which the roof floats.

Figure 2 is an elevational view of the mechanism that supports or carries the side wall shoe, with certain parts of the structure omitted so as to more clearly show said mechanism, and

:Figure 3 is a sectional view similar to Figure l, illustrating the side wall shoe in its extreme outward position and showing, in broken lines, how the flexible sealing element can expand or distend so as to increase the volume of the vapor space.

In the drawings thereference character 1 designates the side wall of a tank that is used for storing oil and volatile liquids, 18 designates the deck of a roof that floats on the liquid in the tank, C designates an annular rim that projects upwardly from the peripheraledge of said deck, and 19 designates the top portion of an annular pontoon, one of whose side w '11s is formed by the rim :C. The mechanism that is used to seal the annular space between the roof and the tank side wall, comprises a .limber or circumferentially flexible side wall shoe A of considerable depth or height arranged in sliding engagement with said tank side wall with the lower edge portion of ,said shoe submerged in the liquid on which the roof floats, and a flexible, gas tight sealing element D, preferably constructed of treated fabric, bridging the space between the rim C and the side wall shoe A and rigidly attached in a gas tight manner to said ports. The shoe A mounted on the roof in such a manner that said shoe .is capable of moving radially, inwardly and outwardly, relativeiy to the roof so as to insure proper engagement of iheshoe with the tank side wall even when said side wall goes out of round or when the roof .assumesan eccentric position with relation to said side wall, and the sealing element D is of such width between its inner and outer edges that it provides for such radial movement of the shoe A. In Figure l of thedrawings theshoeis shown in broken lines in its extreme outward position and in Figure 3 the shoe is shown in solid lines in its extreme outward position.

Instead of attac ing the sealing element D to the stop edges or upper ends of the rim C and shoe Aland making said sealing element of such transverse widthasto provide only for the maximum radial movement of the shqe, as has heretofore been the universal custom in nk roof seals of this particular type, previously mentioned, I have made the following changes in the arrangement and constructionofithe sealing-element D:

(a) I arrange said sealing element at the lower end of the annular space between the side wall shoe and the rim on the roof and attach the sealing element to said parts at points in relatively close proximity to the surface of the oil or other liquid on which the roof floats, and

(b) I increase the transverse width of the sealing element D (the distance between its outer and inner edges) to such an extent that said seal will have sufficient fullness or excess material to enable it to lie in sufflciently close proximity to the surface of the buoyant liquid to produce a vapor space of relatively small internal volume when said vapor space is under nearly zero pressure and to flex or move upwardly and assume the form of a convexed shaped member or umbrella like member, when an abnormally high pressure is created in the vapor space E bounded by the sealing element D, the shoe A, the rim C and the surface B of the liquid on which the roof floats. Depending upon the nature and characteristics of the particular material from which the sealing element D is constructed, said sealing element can be arranged so that the major portion of same is in direct contact with the liquid in the vapor space when said space is under a normal pressure, or said sealing element can be arranged so that no portion of same ever contacts with or dips into the liquid in the vapor space. If the sealing element D is constructed of treated fabric which after long usage in direct contact with the liquid will remain in a gas tight condition free from pinholes through which liquid might leak and collect on the top side of the sealing element where it would be lost by evaporation, the sealing elementis attached to the roof rim C and shoe A very close to the surface of the liquid in the vapor space, and said element is proportioned or made of such size that when the side wall shoe is in its extreme inward position as shown in full lines in Figure l and the vapor space E is under a normal pressure, the sealing element will be in a collapsed condition in the form of a dependent or downwardly hanging loop whose intermediate portion rests on the liquid, thus producing a vapor space of relatively small volume. When the shoe moves outwardly themajor portion of the sealing element D will still remain in contact with the liquid but it will be noted from the broken lines in Figure 1 that there is still considerable slack or fullness in the sealing element. As shown in the drawings the sealing element is attached to the shoe and rim at points a few inches above the surface of the liquid in the vapor space, by means of seal bars 3 and 4 respectively.

In the event an excessive pressure or abnormally high pressure is created in the vapor space as the result of a fire or from any other cause, the seal D flexes or moves upwardly and assumes the form of an ,upwardlydisposed loop or a convexed member or umbrella like member as indicated by the broken lines D in Figure 3 of thedrawings, thereby causing the vapor space to change from a space of relatively small internal volume into a space of relatively great internal volume as indicated by the small circles in Figure 3. The normal position of the side wall shoe is the position it necessarily takes .on the average all the way around the tank. Thus theexpansible volume of the vapor spaceshownby broken lines D is the average amount of expansion available in the event an abnormally high pressure is created in the vapor space by an explosion or other cause, the expanded volume of said vapor space being denoted by the small circles previously mentioned, and said expanded volume being from two to three times the normal volume of the vapor space. This is sufficient to take care of an explosion without any gases being vented through a vent pipe leading from-the vapor space. If desired, however, :thernechanism maybe provided with a pressure-vacuum valve 5 .mountedpn a Pi 4 adi to the ap pa Due to :the fact that the vapor space E is normally very small, the thermal expansion daily from the :sun

will alsobe small ginvolume. In addition the available expansibility of vapor space E is many times greater than any possible thermal expansion that could occur. This is not true in the case of a tank roof seal equipped with a sealing element constructed and arranged in the conventional manner. Hence by my invention I also save thermal expansion loss that exists in floating tank roof seals of the kind now in general use, which loss is quite large and usually of the order of one third of the total loss.

In order to protect the sealing element D from the sun and also prevent rain, snow and ice from collecting on said sealing element and thus interfering with the proper operation of same, I prefer to mount a sun shade and weather protector 9 on the upper end portion of the side wall shoe A in such a position that said protector inclines downwardly and inwardly and overhangs the roof sutliciently to protect the sealing element D from the sun and eliminate the possibility of rain, snow, or the like beating into the space between the side wall shoe A and mm C and collecting on the said sealing element. The weather protector 9 herein shown is attached to the side wall shoe A by means of a flexible hinge 14 that provides for the circumferential flexibility of said shoe, and the inner edge portion of the protector 9 is maintained in spaced relation with the top edge of the rim of the roof by supports 9 or any other suitable means on the roof.

In a floating tank roof seal of the construction above described, there is no possibility of the fabric sealing element being subjected to pressure in excess of the pressure it is designed to successfully withstand, due to the fact that the vapor space is of such construction that under normal conditions it is so small that it holds only a relatively small quantity of gases or vapors and in the event an abnormally high pressure is created in said space as the result of an explosion or other cause, the fabric sealing element which constitutes the top wall of said vapor space moves bodily into a position to expand the volume of said space many times its normal volume and of a size sufficient to take care of the increased pressure Without rupturing the sealing fabric. Also since the fabric sealing element is attached to the side wall shoe and to the rim of the roof at points in close proximity to the oil on which the roof floats, the relatively small areas of said shoe and rim that are exposed to the pressure in the vapor space are strong enough to successfully withstand any pressure that could be created in the vapor space.

Any suitable means can be used to support the side wall shoe A and mount it on the roof. In Figures 1 and 2 I have shown a shoe supporting mechanism that is novel in that it is of such design and construction that it is compact and small enough to be housed within the annular space between the side wall shoe and roof rim, at a point between the sealing element D and the Weather protector 9. Due to the fact that said shoe supporting mechanism is located above the sealing element D, outside of the vapor space E, it is not subjected to the action of corrosive vapors and gases, and as the weather protector 9 extends over the space in which said mechanism is located, snow and ice cannot collect on said mechanism and interfere with the operation of same. Briefly described, the said shoe supporting mechanism is composed of a plurality of pairs of rocks arms 6 and 7 pivotally mounted on the exterior of the rim C and having their upper ends pivotally attached to radially disposed, hinged links 11 that project inwardly from the upper end portion of the side wall shoe, said rock arms and links being so designed and proportioned that they maintain the side wall shoe at a substantially constant level when said shoe moves radially, inwardly and outwardly. The arm 6 of each pair is considerably longer than the arm 7 and the lower end of the arm 6 is rockably mounted in brackets 8 carried by top and bottom cross bars 10 attached to the exterior of the roof rim C, said top cross bar being provided with lugs in which the lower end of the short arm 7 is rockably mounted. The link 11 previously mentioned is connected by a pintle pin or hinge pin 13 to lugs 12 on the side wall shoe and the inner end of said link is pivotally connected to an inwardly bent portion at the upper end of the arm 7 which is disposed at substantially right angles to the upright body of said arm so as to produce an elbow shaped lever. The upper end of the long rock arm 6 is pivotally connected to the link 11 intermediate the points of attachment of said link to the shoe and to the upper end of the short arm 7. The rock arms 6 and 7 are herein illustrated as being substantially yoke shaped in general form or outline so that each arm will comprise two side portions whose free ends are joined together by a cross piece as shown in Figure 2. Obviously the particular construction of the arms 6 and 7 is immaterial so far as my invention is concerned. Under certain conditions the upper end portion of the rock arm 7 and the inner end portion of the link 11 will overhang the rim C on the roof as shown in full lines in Figure 1, thereby decreasing the portion of the annular space -between the shoe and the roof rim required for the shoe supporting mechanism. In a mechanism of the construction above described the arm 7 coacts with the arm 6 through the link 11, in such a manner that the outward thrust of the link on the shoe is a very small percentage of the total weight of the shoe. This percentage will vary from about 5% in the closed position or extreme inward position of the shoe, to about 11% in the full open position or extreme outward position of the shoe as shown in broken lines in Figure 1. This is very desirable in that it prevents a great outward force on the shoe which would cause excessive friction between the shoe and the tank side wall. My improved construction makes it possible to design a mechanism in which the radial distance of the space required for the rock arms that support the shoe is only five inches for a shoe that moves radially a distance of approximately eleven inches. In Figure 1 of the drawings the reference character F designates the point at which the long rock arm 6 is mounted on the rim, F designates the point at which the short arm 7 is mounted, F designates the point of connection of the arm 7 to the link 11, F designates the point of connection of the arm 6 to said link and F designates the point of attachment of the link 11 to the shoe. In a structure in which the distance from the broken line position of the shoe shown in Figure 1 to the solid line position is eleven inches, the distance between F -F is 5"; F F is 2%"; slanting or inclined distance F lis 10"; slanting distance F*F is 23" and horizontal distance F F is 3". The above described combination of distances produces a shoe supporting mechanism having the desirable characteristics pointed out, without increasing the height of the shoe or the height of the rim on the roof.

Having thus described my invention, what I desire to secure by Letters Patent is the following:

In a storage tank for inflammable volatile liquids having an upstanding substantially cylindrical side wall and a roof floating freely upon the liquid within the tank and adapted to rise and to fall with variations that may occur from time to time in the liquid level in the tank, an explosion retaining sealing structure providing a seal between the roof and the inner surface of the side wall of the tank, comprising an upstanding rim defining the perimeter of the roof, said rim being disposed radially inwardly of the inner surface of the side wall of the tank and in spaced relation with respect thereto, the lower edge portion of said rim being submerged in the liquid with the upper portion of said rim extending upwardly Well above the surface of the liquid, a substantially cylindrical metal shoe carried by the roof with its outer periphery in intimate sliding engagement with the inner surface of the side wall of the tank throughout the circumference of said wall, the lower edge portion of said shoe being submerged in the liquid with the upper portion of said shoe extending upwardly at least as high as said rim above 7 the surface of the liquid, said shoe throughout its circumference being spaced radially outwardly with respect to said rim to provide va substantially toroidal chamber therebetween having side walls defined respectively by said rim and said shoe and having its bottom defined by the surface of the liquid, an annular weather shield supported at its inner edge portion upon said roof and extending radially outwardly therefrom to provide a venting cover for the top of said toroidal chamber, the outer edge portion of said shield terminating at and being supported by said shoe so as to avoid collection beneath said cover of any vapors that may escape from said tank between said shoe and the inner surface of the side wall of the tank, and an annular flexible diaphragm of gas impervious material extending across the interior of said toroidal chamber with its inner and outer edges respectively secured in gas-tight relation to said rim and to said shoe above the surface of said liquid, thereby avoiding any tendency for said liquid to seep upwardly between said diaphragm and said rim and between said diapraghm and said shoe, said diaphragm'beingloosely draped downwardly from the respective lines of its attachment to said rim and to said shoe to a level closely adjacent to said liquid, said diaphragm thereby dividing said toroidal chamber into a lower explosion compartment of relatively small volume forcontaining the explosive vapors of said liquid and a complementary upper expansion compartment of relatively great volume ventingly covered by said weather shield and containing only air, said diaphragm being adapted, upon the occurrence of an explosion in said lower compartment, to balloon reversely upwardly into said expansion compartment so as to increase the volume of said lower explosion compartment sufiiciently to accommodate the explosion products and at the same time to prevent rupture of said diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS 1,463,268 Hutf July 31, 1923 1,481,099 Jagschitz Jan. 15, 1924 1,662,225 \Viggins Mar. 13, 1928 1,673,984 Kuhl June 19, 1928 1,831,020 Maker Nov. 10, 1931 2,148,811 Griflin Feb. 28, 1939 2,329,965 Wiggins Sept. 21, 1943 2,329,966 Wiggins Sept. 21, 1943 2,464,804 Goldsby et al Mar. 22, 1949 2,536,019 Allen Jan. 2, 1951 2,540,802 Wiggins Feb. 6, 1951 2,611,504 Busse et a1. Sept. 23, 1952

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