Abstract:
An internal floating roof for use in large volatile or hazardous liquid storage tanks constructed of a plurality of open-top panel systems including C-shaped sidewalls having flanges extending inward along the top and bottom of the sidewall and another flange extending downward from the bottom. The panel systems are secured together using top and bottom bracket means to construct a rigid, non-flexing roof structure to contain the hazardous gases and vapors beneath the floating roof.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an internal floating roof located atop a fluid body in a fluid storage tank. Bulk fluids such as petroleum and other liquid fuel and chemical products are often stored in large cylindrical tanks. These tanks are commonly designed with internal floating roofs or covers to minimize product losses through leakage or evaporation to the atmosphere. The present invention describes a floating roof that is comprised of integral panels having a lower profile than existing floating roofs. 
         [0002]    A large number of industrial processes require the use of substantial quantities of volatile liquids such as gasoline, alcohol, etc. The industries utilizing these processes store a wide range of liquids in large storage vessels. The storage vessels are typically constructed of steel, stainless steel, aluminum and reinforced concrete, among other construction materials, depending upon the size and location of the storage vessel, the material stored inside the tank, and the industrial process generating or using the contained liquid. Many of these storage vessels have a fixed roof either integral with the vessel or retrofitted over the vessel for the dual purposes of keeping contaminants, e.g., water, dust and other particulate contaminants, out of the stored liquid and for reducing evaporative losses of the stored liquid for both economic and regulatory reasons. Storage vessels with a roof are commonly referred to as “covered” storage tanks. 
         [0003]    If the liquid stored in the large-scale vessels is readily subject to evaporation at ambient pressure and temperature based upon their physical and chemical properties, additional control devices are commonly used to minimize losses from evaporation. Escaping vapors of many hydrocarbon based liquids can present health, safety or fire hazards. Vapors from flammable liquids can form an explosive mixture with air when an appropriate blend of stored liquid vapor and oxygen exists. Other liquids, particularly those containing sulfur, can present an objectionable odor when permitted to evaporate freely. 
         [0004]    Over the years a variety of additional evaporative control devices have been utilized to control the escaping vapors from the liquids contained in the large-scale storage tanks. One common and effective variety of such control devices are liquid and vapor impervious buoyant structures that float on the liquid surface and are commonly referred to as “floating roofs.” If the storage vessel is covered with a separate structural roof, the floating roof is denominated as an “internal” floating roof. If the storage vessel does not have a roof or cover, the floating roof is denominated as an “external” floating roof. An external floating roof serves the dual purposes of keeping weather and airborne contaminants away from the stored liquid and in reducing evaporative losses. 
         [0005]    Although many different types of floating roofs have been manufactured, most fit into two categories: vapor space and full contact floating roofs. Vapor space floating roofs typically contain a plurality of closed and sealed buoyant members for supporting an impervious membrane above the liquid surface. The buoyant members create a vapor space between the liquid surface and the underside of the impervious membrane. If any mechanical joints, seams or holes exist or are created through continued use in the membrane, liquid vapors from the vapor space below the membrane can leak through the membrane to the ambient atmosphere above the membrane creating a potentially hazardous atmosphere as well as an evaporative condition for the stored liquid. Full contact floating roofs are configured with the membrane in substantial contact with the surface of the stored liquid eliminating any vapor space below the membrane. Such full-contact membranes are typically the lower portion of closed and sealed buoyant members. While this is an improvement in creating a floating barrier for retaining the liquid in a non-evaporative state, thus controlling evaporation, there still exists the problem of mechanical joints, seams and holes that provide points of leakage. Additionally, creating and testing the closed and sealed buoyant compartments requires specialty materials, highly skilled designers and fabricators while testing and maintaining these compartments involves additional skills and work. 
         [0006]    Existing designs for full contact floating roofs fall into two broad categories, i.e., monolithic and segmented. The present invention falls into the category of a segmented floating roof. Segmented floating roofs are typically fabricated off site and assembled within the storage tank. Each of the plural segments is typically comprised of a composite panel with edge closures that facilitate assembly one to the other. The composite panel is a structural component comprising an upper and a lower strong relatively thin metallic skin separated by and bonded to a lightweight edge material that creates a box-like form for the panel. Within the composite panel may be a core comprised of, for example, polyurethane foam or honeycomb aluminum to fill the void between the top and bottom skins and to assist in the buoyancy of the floating roof. The edge materials are connected together along their top and/or bottom edges with, for example, bolts and nuts or, for another example with a retaining hook along the bottom of a first panel for holding a distending flange of a second panel within the hook of the first panel as described in U.S. Pat. No. 5,704,509. 
         [0007]    This description of a composite panel floating roof is provided to afford the reader with a reasonable understanding of the types of construction used in presently available floating roofs. However, there remain structural flaws that need to be addressed to further reduce evaporation, collection of volatile gases below and in the enclosed panel spaces, and reduce the vertical height to achieve less overall weight increasing the buoyancy and permitting greater storage capacity in the tank. 
         [0008]    One of the noticed problems with the present design for floating roof panels was the penetration through the hook and distending flange attachment between panels. This type of attachment arrangement permits the slow leakage (evaporation) of the contained liquid upward through any joint that is not rigidly held in absolute parallel to its adjoining edge member. Further, the hook may allow for some slippage away from the rigid joint through continued use. It is, therefore, an object of the present invention to eliminate the potential for slippage of adjoin panel edges away from one another by substituting a securing member for holding the edge joint in rigid contact along its entire length. 
         [0009]    Another of the problems with the present designs for floating roof panels was the presence of fasteners that allow the passage of vapors to the space above the floating roof. The present invention eliminates the need for such fasteners or connections. 
         [0010]    Another of the problems was the leakage of the liquid and/or vapors into the interior space of the composite panel creating a potentially hazardous condition and defeating the buoyancy characteristics for that panel. The present invention eliminates the top skin which, in turn, eliminates a potential collection space for harmful vapors in the core space of the panel. The present invention also eliminates the core material as the space between the edge members is now open to the ambient atmosphere. Thus, it is an object of the present invention to eliminate a collection space for harmful vapors by eliminating the upper skin and the core space. This, in turn, eliminates the need for buoyant core materials and allows for direct inspection of the bottom skin for leakage. 
         [0011]    One other problem has been the additional buoyant members placed beneath the floating roof to maintain its buoyancy where required (typically at the outer edge of the floating roof where additional equipment is installed on top of the floating roof) and the subsequent loss of contact with the liquid surface. The buoyant members continually were in need of replacement as the liquids contained in the tanks seeped into them and destroyed their buoyancy. The present invention is a full contact floating roof that does not require additional buoyant members for floating support. It is another object of the present invention to eliminate the need to test and inspect the additional buoyant members for content and/or replacement. It is another object off the present invention to reduce the vertical profile of the internal floating roof and gain the efficiencies of lesser height increasing the potential volumetric capacity of the tank or container. 
         [0012]    One additional problem is vapor leakage through the elongated mechanical seams between the edge members of the panels. Evaporative leakage is a problem as vapors can build up in the ambient atmosphere within the tank above the floating roof. If the seams are not absolutely tight, vapor can leak between the adjoining surfaces of the edge members even if they look as if there is no visible space therebetween. The present invention eliminates this source of leakage by placing a sealing means along the entire elongated surface of adjoining panel edge members. In this way leakage due to poor sealing between edges or due to panel warpage is eliminated. 
         [0013]    Other objects will appear hereinafter. 
       SUMMARY OF THE INVENTION 
       [0014]    An internal floating roof system comprising a series of panel systems including at least three or more C-shaped sidewalls having an upper inwardly extending flange, a vertical section, a lower inwardly extending flange, and a downwardly extending flange and a flat bottom panel extending across the space defined by the C-shaped sidewalls leaving the internal space open to the atmosphere. The panel systems are attached together by a plurality of bracket means for securing together adjacent panel systems at their respective top and bottom corners so that the adjacent panels are held in an abutting array. The bracket includes an upper bracket secured to the upper inwardly facing flange of the C-shaped sidewall of each adjacent panel and a lower bracket secured to the downwardly extending flange of the C-shaped sidewall of each adjacent panel. When totally secured in this fashion, the plurality of panel systems is retained in sealing engagement against each adjacent panel system along their common sidewalls. 
         [0015]    The internal floating roof composed of the panel systems may also include further sealing means along the top side of the abutting C-shaped sidewalls to reduce any potential for gas or vapor emissions through the sidewall joint. The sealing means can be a running weld along the joint or a resilient sealing caulk or similar compound that is resistant to the stored liquid. The C-shaped sidewalls may be made from metals, such as aluminum, steel or stainless steel, or from extruded fiber glass, carbon or graphite composites or similar synthetic materials having suitable physical properties. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    For the purpose of illustrating the invention, there is shown in the drawings forms which are presently preferred; it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
           [0017]      FIG. 1  is a top plan view of the internal floating roof of the present invention showing the panels arrayed in a checkerboard pattern. 
           [0018]      FIG. 2  is a perspective top view of the junction point of four adjacent panel systems of the present invention with the bottom panel of the nearest panel system not shown to show the combined top and bottom the attachment mechanism for retaining a rigid leak resistant floating roof. 
           [0019]      FIG. 3  is a perspective bottom view of the junction point of four adjacent panel systems of the present invention with the bottom panel of the nearest panel system not shown to show the combined top and bottom attachment mechanism for retaining a rigid leak resistant floating roof. 
           [0020]      FIG. 4  is a partially broken away view of a roof edge panel of the floating roof of  FIG. 1 . 
           [0021]      FIG. 5  is a plan view of the floating roof panels arrayed in a herringbone pattern. 
           [0022]      FIG. 6  is a plan view of the floating roof panels arrayed in a running brick pattern. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    The following detailed description is of the best presently contemplated mode of carrying out the invention. The description is not intended in a limiting sense, and is made solely for the purpose of illustrating the general principles of the invention. The various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings. 
         [0024]    Referring now to the drawings in detail, where like numerals refer to like parts or elements, there is shown in  FIG. 1  the internal floating roof  10  of the present invention. The internal floating roof  10  is joined together from a plurality of individual reinforced panels such as the reinforced panel  12  indicated in  FIG. 1 . The reinforced panel system  12  is shown as a rectangular panel system, but other geometric shapes can be utilized, e.g. triangular, square, diamond or other parallelogram, hexagonal, etc. The reinforced panel system  12  is comprised of four C-shaped beams  14 ,  16 ,  18  and  20  arrayed around the perimeter of the panel system  12  with open portion of the C facing inward towards one another. In the rectangular form of the panel system  12 , the C-shaped beams on opposite sides of the panel system are of the same length. Thus, C-shaped beams  14  and  18  are of the same length as are beams  16  and  20 . Each of the C-shaped beams is chamfered in relation to the next adjacent beam in order that their opposing ends can be joined together forming the rectangle without overlapping parts. Extending across the bottom of the panel system  12  and lying atop the lower inward facing portion of the C-shaped beams is a bottom plate  22  that extends across the entire space formed between the C-shaped beams overlapping a portion of the lower portion of the C-shaped beams. The bottom plate  22  is attached to each of the four C-shaped beams  14 ,  16 ,  18  and  20  along its perimeter forming a leak-proof panel system that is open on its top facing side. 
         [0025]    For ease of understanding of the structural formation of each of the panel systems  12  and the method of retaining the rigidity required for structural integrity several adjacent panel systems  12   a - 12   d  have been marked in  FIG. 1  to show the panels being described and their interconnection to each other. Reference should now be made the  FIGS. 2 and 3  and the following description. In  FIG. 2  there is shown the junction point of four adjacent panel systems  12 . Starting with panel system  12   a , the C-shaped beam  14   a  has an upper inwardly extending flange, a vertical wall, and a lower inwardly extending flange forming the C-shape and a bottom flange extending downward below the C-Shape. C-shaped beam  16   a  is similarly configured as are the other two C-shaped beams of panel system  12  although not shown. The bottom plate  22   a  is attached to the lower inward extending flange of C-shaped beams  14   a ,  16   a , as well as to the other two C-shaped beams although not shown, by a method of attachment that creates a leak-proof seal between the bottom plate  22   a  and each of the C-shaped beams  14   a ,  16   a  and the other two beams although not shown. Likewise, the C-shaped beams  14   b ,  20   b  of panel system  12   b , as well as the other two beams although not shown, are structurally configured in the same way as described for panel system  12   a . The bottom plate  22   b  is attached to the lower inward extending flange of C-shaped beams  14   b ,  20   b , as well as to the other two C-shaped beams although not shown, by a method of attachment that creates a leak-proof seal between the bottom plate  22   b  and each of the C-shaped beams  14   b ,  20   b  and the other two beams although not shown. 
         [0026]    C-shaped beams  18   c ,  20   c  of panel system  12   c , as well as the other two beams although not shown are structurally configured in the same way as described for panel system  12   a . The bottom plate  22   c  is attached to the lower inward extending flange of C-shaped beams  18   c ,  20   c , as well as to the other two C-shaped beams although not shown, by a method of attachment that creates a leak-proof seal between the bottom plate  22   c  and each of the C-shaped beams  18   c ,  20   c  and the other two beams although not shown. As above, the C-shaped beams  16   d ,  18   d  of panel system  12   d , as well as the other two beams although not shown, are structurally configured in the same way as described for panel system  12   a . In this instance, however, the bottom plate is not shown so as to provide a view of the mounting plates or brackets that connect each of the panel systems  12   a - 12   d  together. The bottom plate would be attached to the lower inward extending flange of C-shaped beams  16   c ,  18   d , as well as to the other two C-shaped beams although not shown, by a method of attachment that creates a leak-proof seal between the bottom plate and each of the C-shaped beams  16   c ,  18   d  and the other two beams although not shown. 
         [0027]    Creating the rigid orthogonal connection at the four-way joint among the adjacent panel systems  12   a - 12   d  is mounting plate  24 . Mounting plate  24  extends outward from the apex of the joint overlapping not only the joint but extending over the upper flanges of the C-shaped beams of each of the panel systems. Holes in the mounting plate are placed so that the holes are grouped in sets of at least two that are aligned over the center of each of the upper inward facing flanges of the C-shaped beams extending outward from the vertical walls of the beams. In viewing just the mounting plate  24 , the holes appear to be arranged in groups of four positioned at point that are 90° apart from one another. The groups of four holes are actually two sets of two holes that will be used to bolt adjacent panel systems to each other. 
         [0028]    Starting in the lower right of  FIG. 2 , panel system  12   a  presents C-shaped beam  14   a  to be placed against C-shaped beam  18   d  of panel system  12   d . In this way the individual C-shaped beams  14   a ,  18   d , when placed against one another, form an I-beam creating added strength for the combined panels. The mounting plate  24 , with the two sets of bolts extending through the upper inward extending flanges of C-shaped beams  14   a  and  18   d  hold the two C-shaped beams  14   a ,  18   d  in such close touching proximity that there is no space between them. This same method of joining the other C-shaped beams to each other is performed for each of the C-shaped beams  16   a  and  20   b ,  14   b  and  18   c , and  20   c  and  16   d  such that each of these C-shaped beams forms an I-beam at the junction of the two adjacent panel systems. However, for greater strength and rigidity, an additional bracketing system is utilized along the bottom of the panel systems  12   a ,  12   d.    
         [0029]    Referring now to  FIG. 3 , a first elongated bracket member  26  is positioned overlapping the bottom flanges of C-shaped beams  16   d ,  20   c  and on the other side of the four-way joint overlapping the bottom flanges of C-shaped beams  16   a ,  20   b . The bracket member  26  is secured to the named C-shaped beams by using bolts extending through holes in the bracket member  26  that are coaxially aligned with holes in the bottom flanges of the C-shaped beams. The holes are positioned such that they are centered vertically on the downwardly extending bottom flanges. The holes are spaced back from the four-way joint to allow for the chamfer on each C-shaped beam and are shown grouped in sets of three. The bracket member  26  thus retains C-shaped beams  16   d  and  20   c , as well as  16   a  and  20   b , in such close touching proximity that there is no space between them. Completing the bottom portion of the four-way joint is overlying elongated bracket member  28  that is positioned on top of bracket member  26  and overlaps the bottom flanges of C-shaped beams  14   b ,  18   c  and on the other side of the four-way joint overlaps  14   a ,  18   d . The overlying bracket member  28  is secured to the named C-shaped beams by using bolts extending through holes in the overlying bracket member  28  that are coaxially aligned with holes in the bottom flanges of the C-shaped beams. The holes are positioned such that they are centered vertically on the downwardly extending bottom flanges. The holes are spaced back from the four-way joint to allow for the chamfer on each C-shaped beam and are shown grouped in sets of three. The overlying bracket member  28  thus retains C-shaped beams  14   b  and  18   c , as well as  14   a  and  18   d , in such close touching proximity that there is no space between them. When finished, the mounting plate  24  and the elongated bracket  26  and overlying elongated bracket  28  retain the four panel systems  12   a - 12   d  in a non-flexing, rigid orthogonal alignment with sufficient strength at the joint to support at least one man walking atop the panels for safety and leak inspection. 
         [0030]    The structure of each panel system  12  is repeated for each of the panel systems shown in  FIG. 1  for the internal floating roof system. The four-way joint described in connection with  FIGS. 2 and 3  is repeated at each four-way joint throughout the internal floating roof to join the adjacent panel systems together as a rigid non-flexing structure. However, along the perimeter of the internal floating roof  10 , there are a number of partial panel systems that have been truncated to conform to the outer perimeter curvature requirement of the internal floating roof and the need to conform to the curvature of the inner walls of the tank or other container system with which the floating roof is utilized. A partial panel system  32  is marked in  FIG. 1  and will be described in more detail below. 
         [0031]    Referring to  FIG. 4 , the partial panel system  32  is structural configured the same as the panel systems  12 , excepting that the outer C-shaped beam  34  is curved to match the curvature of the tank or container system in which the internal floating roof  10  will be used. The curved C-shaped beam  34  has an upper inwardly extending flange, a vertical wall section and an inwardly extending lower flange just as the other C-shaped beams. Curved C-shaped beam  34  also has a downwardly extending bottom flange for use in bolting the panel systems  12 ,  32  together as described above. 
         [0032]    As with each of the other C-shaped beams, curved C-shaped beam  34  is chamfered at its distal ends in relation to the next adjacent beam in order that their opposing ends can be joined together without overlapping parts. Extending across the bottom of the panel system  32  and lying atop the lower inward facing portion of the C-shaped beams is a bottom plate  22  that extends across the entire space formed between the C-shaped beams overlapping a portion of the lower portion of the C-shaped beams. The bottom plate  22  is attached to each of the C-shaped beams along its perimeter forming a leak-proof panel system that is open on its top facing side the same as the other panel systems  12 . 
         [0033]    Although the bolting scheme using the mounting plate  24  and the elongated brackets  26 ,  28  for interlocking the panel systems  12 ,  32  creates an extremely tight fitting wall abutment between adjacent panels  12 ,  32 , there may still be some vapor leakage between the C-shaped outer wall segments of the panel systems  12 ,  32 . In order to further reduce the potential for leakage, if the C-shaped beams of a suitable rigid material (metallic, etc.) are utilized, a running weld along the top side of the joint between two adjacent C-shaped beams is laid down. In the preferred embodiment, the weld is not required to assist the structural integrity of the panel system, but only as a barrier to gaseous or vapor leak through between the C-shaped beams. Another method of reducing the potential for leakage is to insert a resilient seal along the top of the joint between two adjacent C-shaped beams when bolting them together. Either the weld or the resilient seal is selected so as to be chemically resistant to the stored liquid in order to retain its function of preventing unwanted escape of harmful gas or vapors. 
         [0034]    The C-shaped beams can be made from metal such as aluminum, steel, stainless steel or alloys of the same where the metals or alloys are resistant to corrosion from the chemical, hydrocarbon liquid or other liquid in the tank or container system. Other substances can be used such as extruded fiber glass, carbon or graphite composites and similar synthetic structural components having appropriate physical characteristics. These composite materials, while much lighter in weight, must also be resistant to the corrosive effects of the liquids with which they will be used. 
         [0035]    Although the internal floating roof  10  is shown in  FIG. 1  in a checker board pattern, other layouts and arrangement are possible. The internal floating roof  10  may also be structured in the herringbone pattern of  FIG. 5  or the running brick pattern of  FIG. 6 . If these patterns are utilized, then the mounting plate  24  and the brackets  26 ,  28  are modified to accept the three-way joint among the adjacent panel systems  12 . 
         [0036]    The internal floating roof  10  of the present invention is constructed from a plurality of interlocked panel systems that contain no enclosed spaces. Without enclosed spaces, the internal floating roof  10  can exhibit a lower vertical profile that results in spatial gains both above and below the floating roof. Without enclosed spaces, safety inspections for leaks take less time and there is no need for a secondary seal along the top of the enclosed space. The method of interlocking the panel systems  12  creates a much tighter seam, augmented by either a weld or resilient sealant system, resulting in lower emissions, i.e., leakage of harmful vapors. The internal floating roof  10  with the interlocked panel systems  12  is designed, when structurally interlocked, to provide a 12.5 psf live load so that walking across the floating roof on the joined C-shaped beams will not cause excessive flexure of the roof or panel systems. 
         [0037]    The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, the described embodiments are to be considered in all respects as being illustrative and not restrictive, with the scope of the invention being indicated by the appended claims, rather than the foregoing detailed description, as indicating the scope of the invention as well as all modifications which may fall within a range of equivalency which are also intended to be embraced therein.