Abstract:
Systems and methods for establishing electrical continuity about pipes and other conduits are detailed. The systems may include conductive seals formed, for example, of polymeric and conductive materials. Polymeric materials may include rubber, silicon, and fluorosilicon and conductive materials may include metal charges, carbon, carbon nanotubes, carbon fibers, and intrinsically conducting polymers, although neither type of material is so limited.

Description:
REFERENCE TO PROVISIONAL APPLICATION 
       [0001]    This application claims benefit of U.S. Provisional Application No. 61/379,951, filed Sep. 3, 2010, entitled “Method to Ensure Electrical Current Continuity and Electro Static Dissipation in Connection Between Conductive Fuel Piping Elements,” the contents of which are incorporated herein in their entirety by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to establishing electrical paths capable of dissipating electrostatic charges and more particularly, although not necessarily exclusively, to conductive seals for pipes intended to carry flammable fluids particularly in an aerospace environment. 
       BACKGROUND OF THE INVENTION 
       [0003]    Pipes, conduits, and the like (referred to herein as “pipes” or “piping”) may be used to convey fluids from one location to another. Fluid flow within the pipes may induce build-up of electrostatic charges especially near pipe walls because of friction mechanisms (and the dielectric constant of the flowing fluid). Arcing of the charges conceivably may occur via the fluid itself or through human contact with the piping. If the fluid is flammable, for example, such arcing could be dangerous, in that it might ignite the fluid. High-potential charges arcing through humans likewise could be problematic, as could arcing through objects sensitive to electrical current flow. 
         [0004]    Accordingly, various means have been devised to convey electrical charges from pipes to electrical grounds. However, many of these means are not suitable for use at junctions or similar regions of piping. In particular, any such area needing to be sealed from an external environment presents charge-conveying difficulties, as conventional seals are often electrical insulators (or at best dielectrics) and thus lack sufficient conductivity to convey electrical charges satisfactorily. 
         [0005]    As partial solution of this issue, external metallic conductors or circumferential metallic springs may be employed. Contact efficiency in these systems may vary, however, when (for example) pipe connections deflect and press more on some locations than on others. Corrosion of the metallic material also is problematic, and contact between the metallic material and the piping may not exist over the entire circumferences of the piping. Repairing these systems, furthermore, may require replacing many, if not all, of the components. 
         [0006]    In other contexts, seals such as those of U.S. Pat. No. 4,556,591 to Bannick, Jr. may be used to provide electrical conductivity sufficient to “equalize[] static charges.” These planar seals may include both resin and carbon spheres and be used to adhere graphite-reinforced epoxy plates within fuel tanks of aircraft. However, there remains a need for development of conductive seals for fluid-conveying piping so as to dissipate associated electrical charges while complying with aeronautical rules, guidelines, specifications, and requirements.. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides such means to dissipate electrical charges at junctions between fuel lines using conductive seals. Especially suitable for use in aeronautics, the present seals may be formed of polymeric materials, as are standard aeronautical seals. Suitable polymeric materials include, but are not limited to, rubber, silicon, fluorosilicon, and thermoplastics. Additionally forming the seals may be conductive materials such as metallic charges (from silver or other metals, for example), carbon, carbon fibers or nanotubes, or intrinsically conducting polymers. Preferably the conductive materials are added to the polymeric materials when the seals are formulated, although they conceivably could be applied or added later. 
         [0008]    Although the present invention is well-suited for aeronautical applications, it may be employed in any situation in which dissipation of electrostatic charge is needed or where resistivity of a fuel line is less than 10 9  ohms per meter under 500 volt tension. The fuel line itself may be made of essentially any material, including (but not limited to) rubber, thermoplastic materials, heat-hardening plastics or composites, or metals. However, because resistivity of the conductive seals of the present invention generally will be higher than resistivity of metallic fuel lines, some compensation in resistance may be necessary. 
         [0009]    A presently-preferred coupling for a pair of conductive pipes includes two seals of the present invention, each adjacent the to-be-coupled end of its respective pipe. For cylindrical pipes, each annular seal circumscribes the pipe in contact with its exterior surface (or with an associated ferrule). Surrounding and contacting both seals may be a proof ring made of conductive material, with the proof ring being encapsulated in a (conductive) coupling ring. The proof ring supplies electrical continuity about exterior surfaces of the pair of pipes at their junction. 
         [0010]    It thus is an optional, non-exclusive object of the present invention to provide methods of establishing electrical continuity about objects such as pipes. 
         [0011]    It is also an optional, non-exclusive object of the present invention to provide conductive seals useful as part of systems for establishing electrical continuity about objects such as pipes. 
         [0012]    It is another optional, non-exclusive object of the present invention to provide conductive seals for fuel- and other fluid-conveying pipes, especially such pipes employed in aeronautics fields. 
         [0013]    It is a further optional, non-exclusive object of the present invention to provide conductive couplings including conductive seals. 
         [0014]    Other objects, features, and advantages of the present invention will be apparent to those skilled in the relevant art with reference to the remaining text and the drawing of this application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0015]    The FIGURE is a cross-sectional, partially-schematicized view of a coupling including conductive seals of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Illustrated in the FIGURE are exemplary seals  10 A and  10 B of the present invention. Also depicted are pipes  14 A and  14 B, which are shown as separate and distinct elements each defining a respective channel  18 A or  18 B through which fluid may flow. To ensure continuity of fluid flow through pipes  14 A and  14 B, they beneficially may be connected at a junction or joint. Element  22  illustrates an example of an assembly useful for connecting pipes  14 A and  14 B. 
         [0017]    Element  22  may include seals  10 A and  10 B as well as either or both of proof ring  26  and coupling ring  30 . If present, each of proof ring  26  and coupling ring  30  is preferably made of electrically-conductive material, although coupling ring  30  in particular need not necessarily conduct electricity. Such material may comprise one or more metals, composites, or thermoplastics, although any suitable material may be used. Hence, all of pipes  14 A and  14 B, proof ring  26 , and coupling ring  30  beneficially are configured to conduct electricity. 
         [0018]    This feature likewise is true for seals  10 A and  10 B. Electrically-conductive seals  10 A and  10 B may, if desired, be made of polymeric materials such as (but not limited to) rubber, silicon, or fluorosilicon together with conductive charges which may include (but again are not limited to) metals, carbon, carbon fibers, carbon nanotubes, or intrinsically conducting polymers. Preferably the conductive charges are both mixed with the polymeric materials during formation of the seals  10 A-B and compatible with aeronautical standards, although in some instances such mixing or compatibility might not be necessary. As illustrated, seals  10 A-B are annular in shape, matching the annular cross-sectional shape of respective pipes  14 A-B. Seals  10 A-B may have other shapes, however, if appropriate or desired. 
         [0019]    Seals  10 A and  10 B, proof ring  26 , and coupling ring  30  cooperate to allow element  22  to connect pipes  10 A and  10 B with both mechanical and electrical continuity. As shown in the FIGURE, seal  10 A may be positioned at or near to-be-connected end  34 A of pipe  14 A. If ferrule  38 A is present at end  34 A, seal  10 A may be placed in a cavity thereof. Otherwise, seal  10 A may directly contact and circumscribe exterior surface  42 A of pipe  14 A. Similarly, seal  10 B may be positioned at or near to-be-connected end  34 B or pipe  14 B, either within ferrule  38 B or directly in contact with exterior surface  42 B. 
         [0020]    Depicted in the FIGURE is that proof ring  26  may then be positioned externally of ferrules  38 A-B but preferably in direct contact with seals  10 A-B. As depicted, proof ring  26  is cylindrical and sufficiently long to accommodate the widths of both ferrules  38 A-B and any gap G desired between ends  34 A-B when they are connected. Ferrules  38 A-B, seals  10 A-B, and proof ring  26  may be encapsulated in coupling ring  30  to complete element  22 . As shown, coupling ring  30  may include cylindrical (or other) wall  46 , first end plate  54 , and second end plate  58 , with wall  46  surrounding exterior surface  50  of proof ring  26 . Annular plate  54 , by contrast, surrounds exterior surface  42 A of pipe  14 A, whereas plate  58  similarly surrounds exterior surface  42 B of pipe  14 B. At least for purposes of electrical continuity, wall  46  preferably contacts exterior surface  50 , and plates  54  and  58  preferably contact respective surfaces  42 A and  42 B. 
         [0021]    Testing was performed for an exemplary assembly consistent with the FIGURE. For the testing, pipes  14 A-B comprised two 500 mm long tubes made of conductive, fiberglass-reinforced epoxy resin. Each of ferrules  38 A-B was made of conductive, fiberglass-reinforced polyetheretherketone (PEEK), and proof ring  26  and coupling ring  30  were made of aluminum. Each of seals  10 A-B was made of fluorosilicon charged with carbon and had volumic resistivity less than six ohm-centimeters. Tests conducted on the assembly yielded resistance of only 3×10 6  ohms. 
         [0022]    The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention. As a non-limiting example of such adaptations, either or both of pipes  14  A and  14 B may instead by equipment (e.g. pumps, valves, etc.) or hardware (e.g. pass-walls, T- or Y-connectors, manifolds, etc.). Additionally, the contents of the Bannick, Jr. patent are incorporated herein in their entirety by this reference.