Double wall storage tank and method of making same

Abstract

A double wall tank for the storage of liquids is manufactured from a rigid single wall inner tank by applying to at least a portion of the exterior surface of the inner tank a release agent for preventing bonding of a curable synthetic resin to the inner tank exterior surface, applying over the inner tank exterior surface and the release agent a substantially rigid outer sheath of a curable synthetic resin that, when cured, is substantially fluid tight, and breaking engagement between the inner tank exterior surface and outer sheath.

What is claimed is: 
     
       1. A method of manufacturing a double wall tank from a .Iadd.rigid .Iaddend.single wall inner tank for storage of liquids, said inner tank including a generally cylindrical sidewall and pair of end walls, said method comprising; applying to at least a portion of the exterior surface of said rigid inner tank a release agent for substantially preventing bonding of a curable synthetic resin to said inner tank exterior surface portion;   applying over said inner tank exterior surface and said release agent a substantially rigid outer sheath of .[.a.]. .Iadd.said .Iaddend.curable synthetic resin that, when cured, is substantially fluid tight; and   breaking engagement between said inner tank exterior surface and said outer sheath, whereby is formed a double wall tank in which said inner tank defines an inner wall and said outer sheath defines an outer wall.   
     
     
       2. The method of claim 1 in which said step of breaking engagement includes the step of applying between said inner tank exterior surface and said outer sheath a fluid under pressure that is sufficient to break, at least temporarily, engagement between said inner tank exterior surface and the outer sheath. 
     
     
       3. The method of claim 2 in which said step of applying a fluid under pressure includes the steps of connecting a fluid conduit to said double wall tank such that a discharge opening of said conduit is disposed within said outer sheath but outside said inner tank exterior surface, and introducing a pressurized fluid to said conduit to apply a positive fluid pressure between said inner tank exterior surface and said outer sheath. 
     
     
       4. The method of claim 1 wherein said sheath comprises at least one layer of fibrous material coated with .[.a.]. .Iadd.said .Iaddend.curable resin which, upon curing, provides a coating which is resistant to the passage of water or hydrocarbon liquid. 
     
     
       5. The method of claim 1 wherein said release agent is applied to substantially the entire exterior surface of said inner tank. 
     
     
       6. The method of claim 1 wherein said outer sheath has a configuration generally of a cylinder with closed ends, and wherein said release agent is applied to said cylindrical sidewall, whereby the release agent will serve to prevent bonding between the outer surface of the cylindrical sidewall of the inner tank and the outer sheath. 
     
     
       7. The method of claim 6 wherein .[.the.]. cylindrical sidewall portions of said outer sheath overlying said inner tank cylindrical sidewall are formed separately from .[.the.]. end portions of said sheath overlying .[.the.]. closed end portions of said inner tank, and wherein said sheath end portions are sealingly joined to said sheath cylindrical .[.wall.]. .Iadd.sidewall .Iaddend.portions, whereby is formed a continuous outer sheath overlying said inner tank. 
     
     
       8. The method of claim 1 further comprising the step of forming an aperture through said sheath and through a portion of a wall of said inner tank, whereby is provided access to the interior of said inner tank. .[.9. A double wall tank for storage of liquids manufactured in accordance with 
     
     
        the method of claim 1..]. 10. A tank for storage of liquids comprising; a substantially rigid inner tank having a generally cylindrical sidewall and a pair of end walls;   a substantially rigid and substantially fluid tight outer sheath enclosing said inner tank and formed of a resin impregnated fibrous material that is substantially fluid tight;   a release agent interposed between at least said inner tank cylindrical sidewall and said outer sheath to prevent bonding between said outer sheath and said .[.release agent coated.]. sidewall of said inner tank; and   means for applying between the exterior surface of said inner tank and said outer sheath a fluid under a pressure that is sufficient to break engagement between said outer sheath and the exterior surface of said inner tank, whereby is formed a double wall tank in which said inner tank exterior surface defines an inner wall and said outer sheath defines an   
     
     
        outer wall. 11. The tank of claim 10 in which said means for applying pressure includes a fluid conduit that extends through said outer sheath and has a discharge opening that communicates with the exterior surface of said inner tank and the interior surface of said outer sheath.