Patent Publication Number: US-2005131749-A1

Title: Storage tank roof protection system

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application claims priority of U.S. Provisional Patent application Ser. No. 60/528,492 filed Dec. 11, 2003, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      The invention involves methodology and apparatus for providing protection of interior roof surfaces in structural enclosures such as tanks, more particularly for sealing inner roof surfaces and discontinuities in the roof of the tank from the gases or condensates that emanate from the fluids and gases contained in the vessel.  
     BACKGROUND OF THE INVENTION  
      This invention relates to storage tanks that contain a variety of fluids that emit gases or condensates and that have overhead roof structures to cover and protect the containment vessel and its contents. The interior surfaces on the roofs of such vessels are subject to corrosion and deterioration through contact with the gases or condensates that emanate from the fluids and gases that are contained in the vessel.  
      The prior art methodology for protecting the inner surface of the roofs from gases or condensates is to apply a coat of paint, chemicals or other materials to the inner surface of the roof and/or to any structures that support the inner surface of the roof. The paint, chemicals or other materials are resistant to corrosion and deterioration from the gases or condensates. The preparation of roof surfaces for coating is difficult, time consuming and costly, particularly as the supporting structures for such roofs can be complex and inaccessible. As a result the application of coatings to interior roof surfaces and their supporting structures are prone to failure from peeling, cracking, or other deterioration.  
      A second approach is to remove and replace the corroded roof structure with a new roof structure. Again, this approach is very costly, and results in the tank remaining out of operation for considerable periods of time.  
      A third approach is to inject a gas blanket inside the tank that prevents or minimizes the escape of gases or condensates from the fluids in the tank. This approach requires special construction of the tank, and has limited application to certain fluids and gases.  
      A fourth approach is to attach a continuous layer of geosynthetic membrane to the roof, and/or supporting structures of roof, using sealing systems for floors and walls as described in Provisional Patent Application 60/462,301 around the perimeter of the membrane and discontinuities. Structural support to the membrane is provided by attaching the membrane directly to the interior surface of the roof, or to the structures supporting the roof. This method proves to be a costly and difficult process. Inherent in this approach is the creation of many discontinuities in the membrane increasing the risks of permeability and functional failure.  
      There is a need for a system which protects and seals interior roof surfaces in structural enclosures such as tanks, more particularly for sealing inner roof surfaces around inner roof perimeters and discontinuities in the roof of the tank from the gases or condensate that emanate from the fluids and gases are contained in the vessel, and which is not susceptible to the costs and failures associated with prior art.  
     SUMMARY OF THE INVENTION  
      Embodiments of the invention provide systems for suspension of prior art geosynthetic membranes and related technologies used to seal said membranes to tank surfaces so as to protect the interior surfaces of the tank roof from the gases or condensate that emanate from the fluids and gases contained in the vessel.  
      The objects of the invention are achieved through a liner system that creates an impermeable barrier of geosynthetic material that is suspended or upheld below the inner surface of the roof and around discontinuities in the structural envelope of the roof, if such exist. The liner system is sealed to the upper perimeter of the tank so as to form an impenetrable layer to liquids, or gases or condensates that may emanate from the vessel to the interior surfaces and structures of the roof of the tank.  
      Embodiments of the roof seal comprise a geosynthetic membrane, fabricated and suspended in such a way as to provide a continuous, impermeable layer that completely and continuously separates the lower internal environment of the storage vessel containing fluids and gases from the upper internal environment of the storage vessel and the roof, the layer that separates the lower region of the structural envelope from the upper region of the structural envelope requiring a membrane that contains no discontinuities, and which extends at least to the extremities of the structural envelope; and a series of attachments to sealably attach the extremities of the membrane for forming a reliable continuous membrane liner.  
      More particularly, the outer extremities of the membrane are sealably attached to the inner surface of the structural envelope, while the inner surface can be attached, preferably to a center column of the tank, at some point below the roof of the structural envelope.  
      One potential method of perimeter attachment, among many, is an adaptation of mechanical attachments or seals described in Provisional Patent Application 60/462,301 to Applicants. In addition, tanks may contain other internal penetrations or connections between the roof of the tank and the lower regions of the tank, such as support columns, gage boards, or pipes. The continuous geosynthetic membrane must be sealed to such penetrations so as to maintain an impenetrable barrier between the lower internal environment of the storage vessel containing fluids and gases, and the upper internal environment of the storage vessel and the roof. This may be achieved by any number of sealing methods.  
      A preferred embodiment of the invention further comprises a supporting structure that suspends the membrane above the lower internal environment of the structural envelope. Such supporting elements may consist of elements within the geosynthetic material itself that provide strength and integrity to the barrier, external supports such as tensioned filaments, cables, or rigid supports, capable of supporting or lifting the weight of the geosynthetic material. While some geosynthetic materials contain filaments or structures designed to provide the material itself with sufficient lateral strength to withstand the lateral forces of being suspended, the use of external structures, such as tension cables, or rigid supports, minimize stress on the material itself, and provide better control of the positioning and installation of the material within the tank environment.  
      Structures to support the material can be attached to the interior of the structural envelope, above or below the continuous synthetic membrane, and the membrane can rest on the supporting elements, or be supported by the supporting elements with various methods of attachment from above.  
      Another embodiment of the invention envisages a system of ventilating the upper region of the structural envelope above geosynthetic membrane from outside the tank, ensuring that minute permeations of gases or elements that pass through the geosynthetic membrane do not accumulate above the geosynthetic membrane, resulting in corrosion and deterioration of the interior surface of the roof. Such ventilation systems may be simply apertures in the upper regions, allowing the flow of air, or any variety of active ventilation systems as those used in rigid roof structures for homes or other commercial buildings requiring ventilation.  
      An alternate embodiment of the invention includes the use of a boot of liner material to seal discontinuities within the tank roof that penetrate the liner membrane. The boot is welded or similarly attached to the liner membrane at the penetration to the membrane, and is mechanically sealed or attached to the roof or discontinuity. This provides a continuously sealed liner membrane about the discontinuity preventing the discontinuity and upper tank region from corrosion or damage from tank liquids, gases, or condensates.  
      A system for installing a roof liner includes attaching and sealing a membrane adjacent an attachment or discontinuity on the roof, attaching support elements within the interior of the envelope, raising the support elements and membrane to the tanks periphery, securing the support elements to the tank&#39;s periphery and sealing the membrane to the tank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view of a roof liner suspended according to an embodiment of the invention;  
       FIG. 2  shows a roof liner with suspended cables underneath for supporting the roof liner;  
       FIG. 3  is a view from underneath a roof liner suspended over tension cable supports, illustrating details of cable attachment;  
       FIG. 4   a  illustrates details of the sealing of the geosynthetic membrane to the perimeter of a tank by means of a mechanical compression system;  
       FIG. 4   b  illustrates details of the attachment of a cable directly to the mechanical compression system according to  FIG. 4   a;    
       FIG. 5  illustrates one embodiment of attachment of the geosynthetic liner to a discontinuity;  
       FIG. 6  illustrates a variation of the attachment of the geosynthetic liner to a discontinuity according to  FIG. 5 ;  
       FIG. 7  illustrates an embodiment utilizing vents in the upper region of the tank to ventilate the region above the roof liner;  
       FIG. 8  is a upward perspective view of a plurality of supporting elements attached about a central support member at a roof in a tank, prior to suspending a membrane therein; and  
       FIG. 9  is an upward perspective view according to  FIG. 8  following suspension of the membrane therein and attachment of the supporting elements to the inner surface of the tank.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Having reference to  FIGS. 1-7 , embodiments of unique systems are shown for suspension of prior art geosynthetic membranes  10  and related technologies used to seal said membranes  10  to inner tank surfaces  11  so as to protect an interior surface  12  of a tank roof  13  from the gases or condensate that emanate from fluids and gases contained in a storage vessel or tank  14 .  
      A liner system creates an impermeable barrier using the geosynthetic material or membranes  10  by upholding or suspending the membrane  10  below the inner surface  12  of the roof  13  and around discontinuities in the structural envelope of the roof  13 , if such exist. The liner system is sealed adjacent an upper perimeter  15  of the tank  14  so as to form an impenetrable layer to liquids, or gases or condensates that may emanate from the tank to the interior surfaces  12  and structures of the roof  13  of the tank  14 .  
      Embodiments of the sealing system comprise the geosynthetic membrane  10 , which is fabricated and suspended in such a way as to provide a continuous, impermeable layer that completely and continuously separates the lower internal environment L of the tank  14 , containing fluids and gases, from the upper internal environment U of the tank  14  and the roof  13 . Further, the membrane  10  extends at least to the extremities E of the structural envelope or tank  14 . A plurality of attachments  20  sealably attach inner and outer extremities  21 , 22  of the membrane  10  to the extremities E of the tank  14  for forming a reliable continuous membrane liner.  
      More particularly, the outer extremities of the membrane  22  are sealably attached to the inner surface  11  of the structural envelope or tank  14 , while the inner extremities  21  are preferably attached to a center column  30  of the tank  14 , both at a point below the roof  13  of the tank  14 .  
      As shown in  FIGS. 1, 2  and  4   a,b - 7 , one method of attaching the extremities  21 , 22  of the membrane  10  to the inner surfaces  11  of the tank  14 , among many, is an adaptation of mechanical attachments or seals  40  as described in co-pending U.S. patent application Ser. No. 10/740,409 and claiming priority of Provisional Patent Application 60/462,301 to Applicants, the entirety of which is incorporated herein by reference.  
      As shown in  FIGS. 5 and 6 , in addition, tanks  14  may contain other internal penetrations or connections  50  between the roof  13  of the tank  14  and the lower regions L of the tank  14 , such as support columns, gage boards, or pipes and the like. The continuous geosynthetic membrane  10  is sealed to such penetrations or discontinuities  50  so as to maintain the impenetrable barrier provided by the membrane  10 . This may be achieved by any number of sealing methods.  
      As shown in  FIG. 4   a,  and in a preferred embodiment, the mechanical attachment or sealing system as incorporated above is used to further compress and seal the extremities  21 ,  22  of the membrane  10  therein at either the inner surfaces of the tank  14  or at a discontinuity  50  formed therein.  
      In a preferred embodiment of the invention, as shown in  FIGS. 2-7 , the system further comprises supporting elements  60  to support the suspended membrane  10  above the lower internal environment L of the tank  14 . Such supporting elements  60  may consist of elements formed within the geosynthetic material of the membrane  10  itself that provide strength and integrity to the barrier, or external supports such as tensioned filaments, cables, or rigid supports, capable of supporting or lifting the weight of the geosynthetic membrane  10 . While some geosynthetic materials contain filaments or structures designed to provide the material itself with sufficient lateral strength to withstand the lateral forces imposed when suspended, the use of external supporting elements  60 , such as tension cables, or rigid supports, minimize stress on the material itself, and provide better control of the positioning and installation of the membrane  10  within the tank  14 .  
      As shown in  FIGS. 2, 3 ,  4   b  and  7 , supporting elements  60  can be attached to the interior  11  of the tank  14 , above or below the continuous membrane  10 , using attachments means such as D-rings  61 , eye bolts  62  and anchors  63  and the like, and the membrane  10  may either rest on the supporting elements  60 , or be supported by the supporting elements  60  with various methods of attachment (not shown) from above. Optionally, cables  60  can be encased in protective sleeves  64 , such as PVC pipes to protect the membrane  10  supported thereby and in contact therewith.  
      In another embodiment, shown in  FIGS. 5-7 , ventilation of the upper region U of the tank  14 , above the geosynthetic membrane  10  and having access from outside the tank, ensures that minute permeations of gases or elements that pass through the geosynthetic membrane  10  do not accumulate above the geosynthetic membrane  10 , resulting in corrosion and deterioration of the interior surface  12  of the roof  13 . Such ventilation systems  70  may be simply apertures in the upper regions of the roof  13 , allowing the flow of air, or any variety of active ventilation systems  70 , such as those used in rigid roof structures for homes or other commercial buildings requiring ventilation.  
      An alternate embodiment, as shown in  FIG. 6 , further comprises a boot  80  typically made of liner material, to seal discontinuities  50  within the tank roof  13  that penetrate the membrane  10 . The boot is welded or similarly attached to the membrane  10  at the penetration to the membrane  10 , and is mechanically sealed or attached to the roof  13  or discontinuity  50 . The boot  80  provides a continuously sealed membrane  10  about the discontinuity  50 , preventing the discontinuity  50  and upper tank region U from corrosion or damage from tank liquids, gases, or condensates.  
      In use, as shown in  FIG. 8  and  9 , the system for installing a roof liner of membrane  10  comprises attaching and sealing the membrane  10  adjacent the roof  13  at an attachment  40  on the inner surface of the tank  14  or around a discontinuity  50  on the roof  13 , attaching supporting elements  60  within the interior of the tank  14  and typically at one extremity E or about a center support  30 , raising the support elements  60  and the membrane  10  to the tanks opposing extremity E or to the periphery at the inner surface  11 , securing the supporting elements  60  to the tank&#39;s extremity and sealing the membrane  10  to the tank&#39;s inner surface  11 .