Pipe connector

A pipe connector is disclosed, comprising two connector elements, arranged for interconnection of two pipes, wherein one or both of the connector elements is formed from electrically resistive material so as to provide electrical resistance between the connected pipes.

RELATED APPLICATIONS

The present application is based on, and claims priority from, British Application Number 1014699.1, filed Sep. 6, 2010, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF INVENTION

The present invention relates to a pipe connector.

BACKGROUND OF THE INVENTION

A significant consideration in the design of an aircraft is the effect on lightning strike. When most of the airframe structure is metallic, lightning current is carried by the primary structure. Since the metallic structure generally has large cross sectional areas, lightning currents are thus not considered to have a significant effect on fuel, hydraulic, electrical and utility duct sub-systems. Fibre-reinforced composites are increasingly commonly used for many aspects of airframe design and manufacture, including structural elements. With composite structures the resistance of the primary structure is significantly higher than an equivalent metallic structure resulting in the traditional metallic tubing or duct systems being the most conductive element in the airframe. In many applications, such as fuel, venting or inerting systems, where flammable fluids or vapours can be present in a pipe run. Thus any electrical arcing resulting from a lightening strike within or around the pipe run will be potentially hazardous and thus must be minimised.

For a typical fuel system made of pipe connectors and pipes, there are two fundamental design approaches to avoid this problem. The first is to use short non-metallic isolator or resistor sections in a largely metallic tubing system to electrically separate the lengths of metallic tubing. An insulating section of pipe may be formed from a polymer such as nylon.

The second approach is to replace part of the metallic tubing system with longer non-metallic sections. In that case, the static charge accumulated on the non-metallic components need to be discharge. The non-metallic section is made of highly resistive material which allows static discharge while limiting lightning current to flow though it. A highly resistive section of pipe may be formed from a composite material loaded with conductive fillers. While it is technically possible to form the entire tubing system from highly resistive material, due to the application of conventional manufacturing and stress approaches, this is not a practical solution and would in any case carry a high cost.

A problem with both if these approaches are that the insulators or isolators are expensive and relatively heavy.

SUMMARY OF THE INVENTION

An embodiment of the invention provides a pipe connector comprising:a first connector element comprising a hollow body member providing a connection for a first electrically conductive pipe means at one end and first coupling means at the other end;a second connector element comprising a hollow body member providing a connection for a second electrically conductive pipe means at one end and second coupling means at the other end arranged for coupling with the first coupling means, wherein at least one of the first or second connector elements is formed from electrically resistive material; andbonding means arranged to enable a predetermined level of electrostatic discharge between the first and second electrically conductive pipe means.

The first connector element only may be formed from the electrically resistive material. The bonding means may be connected between the first and second pipe means. The second connector element only may be formed from the electrically resistive material. The bonding means may be connected between the first pipe means and the second connector element. Both the first and second connector elements may be formed from the electrically resistive material. The bonding means may be connected between the first and second connector elements.

The or each connector element when formed from the electrically resistive material may be fixed to the respective pipe means using electrically conductive fixing means. The first and second connector elements may provide an electrical resistance of at least 500 KW between the first and second electrically conductive pipe means. The connector elements may provide and electrical resistance of at least 1 MW between the first and second electrically conductive pipe means. The electrically resistive material may be an electrically insulating material for providing electrical isolation between the first and second electrically conductive pipe means. The pipe connector may be arranged for use in a fuel system. The pipe connector may be arranged for use in aircraft.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

With reference toFIG. 1, an aircraft101comprises a pair of wings102faired into a fuselage103. Each wing102carries an engine104and an internally located fuel tank105. The fuel tanks105are connected to the engines104by a set of metallic fuel lines or pipes106. The supply of fuel from the fuel tanks105to the engines104is controlled by a fuel management system107. The metallic fuel pipes106are constructed from a series of lengths of pipes jointed using pipe connectors108. As will be understood by those skilled in the art, an aircraft may comprise a large number of pipe connectors108. For clarity, only five pipe connectors are shown inFIG. 1.

With reference toFIG. 2, each pipe connectors108comprises a metallic female pipe connector element201comprising an annular body member202having a central axis X that provides an internal space for fuel flow. The body member202comprises pipe connection means203, in the form of a first cylindrical socket, formed at one end. In the present embodiment, a metallic pipe connector body204having a corresponding central axis X and providing an internal space for fuel flow is connected to the pipe connection means203. The pipe connector body204comprises a flange that enables the pipe connector body204to be fitted to the interior structure of one of the wings102. The body member202further comprises a second cylindrical socket205formed at the end opposite to the first socket203. The second socket205has an internally linearly tapered opening206that is tapered inwardly towards the central axis X. The internal surface of the socket205provides a cylindrical seat207.

The pipe connector108further comprises a male pipe connector element208in the form of an annular body member having a central axis X and providing an internal space for fuel flow. The male pipe connector element208further comprises pipe connection means209, in the form of a cylindrical socket, formed at one end, for connecting to a pipe106. The body member208further comprises a cylindrical spigot210formed at the end opposite to the socket209. The spigot210further comprises two radial flanges211on its outer surface which together form a cylindrical seal seat212at the distal end of the spigot210. An o-ring seal213is retained within the seal seat212. The seal213is arranged to provide a fluid-tight seal between cylindrical seat207of the second socket205of the female pipe connector element201and the spigot210thus enabling the pipe connector108to provide a fuel-tight joint for pipes106.

In the present embodiment, the male pipe connector element208is formed from a non-conductive or isolative material, that is, a material that provides electrical insulation. In the present embodiment, the non-conductive material is polyether ether ketone (PEEK) structurally reinforced with 30% glass fibre. As will be understood by those skilled in the art, other materials such as polyphenylene sulfide (PPS) or nylon reinforced by short glass fibre may also be used depending on the given application. The electrically insulating feature of the male pipe connector element208enables the pipe connector108to be used in place of a traditional pipe insulator.

FIG. 3shows two insulating pipe connectors108each connecting a pipe connector body204, fitted to the interior structure of one of the wings102, to a common pipe element106. A bonding lead301is provided fitted between tabs302,303formed on respective pipe connector body204and pipe element106. The bonding lead301is arranged to provide a route for the discharge of static electricity that may build up on the common pipe element106. For example, the flow of fluid through the common pipe element106may cause the build up of a static charge in that pipe element.

In another embodiment, with reference toFIG. 4, the male and female pipe connector elements201,208are both formed from a resistive material arranged to provide the pipe connector108with a predetermined degree of electrical resistance. In the present embodiment, the resistive material used is thermoplastic PEEK with added conductive filler, in the form of black carbon. As will be understood by those skilled in the art, other conductive fillers such as graphite, short carbon fibres, composite carbon nano tubes or metallic powder such as silver or nickel may be used. The type and proportion of the conductive filler determines the resistivity of the material. As will be understood by those skilled in the art, other thermoplastic materials such as nylon or PPS may be used. Because such PEEK materials with added conductive filler are slightly conductive, they are capable of electrostatic discharge (ESD), that is, of dissipating or conducting static electrical charges.

With further reference toFIG. 4, bonding leads401,402are provided fitted between respective sets of tabs403,404formed on respective female and male connector elements201,208. In addition, conductive fixing agent in the form of a conductive adhesive405is used for bonding each connector element201,208to the respective pipe connector body204and pipe element106. In the present embodiment, the adhesive405comprises an epoxy resin with conductive filler in the form of nickel. The bonding leads401,402, in combination with the adhesive405, are arranged to provide a route for the discharge of static electricity that may build up in the pipe assembly. In the present embodiment, the electrical resistance across each pipe connector108is arranged to be within the range of 500 kilo-ohms (KW) and 1 mega-ohm (MW).

In a further embodiment, with reference toFIG. 5a, only the female connector element201is formed from a resistive material such as PEEK with added conductive filler. The male connector element208is formed from metal such as aluminium. In the present embodiment, the bonding lead401is connected between the common pipe element106fixed to the male connector element208and the female connector element201. Furthermore, in the present embodiment, no conductive fixing means is required between the common pipe element106and the male connector element208.

In another embodiment, with reference toFIG. 5b, only the male connector element208is formed from a resistive material such as PEEK with added conductive filler. The female connector element201is formed from metal such as aluminium. In the present embodiment, the bonding lead401is connected between the male connector element208and the female connector element201. Furthermore, in the present embodiment, no conductive fixing means is required between the pipe element106and the female connector element201.

In a further embodiment, with reference toFIG. 2, both the male connector element and the female connector element are formed from an insulating, non-conductive or isolative material. In another embodiment only the female connecter element is formed from an insulating, non-conductive or isolative material.

As will be understood by those skilled in the art, the female connector element201may be formed as a single part if the annular body member202and the pipe connector body204are formed from compatible materials. For example, if the annular body member202and the pipe connector body204are formed from the same material they can be machined, cast or moulded as a single piece.

As will be understood by those skilled in the art, the pipe connector108may be arranged to connect two pipe elements, with the additional pipe element being fixed directly into the annular body member202in place of the pipe connector body204. In other words, the pipe connector may be used to interconnect either a pipe connector body204with a pipe element106, two pipe connector bodies204or two pipe elements106. Therefore, the term pipe means is used herein to refer generally to a pipe connector body204or to a pipe element106.

As will be understood by those skilled in the art, the selection of suitable materials for forming each element of the pipe connector and connected pipe is dependent on the given application as is the level of electrical insulation, conduction, isolation, resistance of the or each relevant pipe connection elements.

As will be understood by those skilled in the art, the pipe connectors described herein may be applied to any suitable pipe installation or system for carrying any suitable substance.

As will be understood by those skilled in the art, where the accumulation, discharge or dissipation of static electrical charge is concerned, consideration needs to be given to the minimum applicable clearance, air gap or tracking distance between conductive elements such as the bonding leads, connection tabs or other related fixings and other conductive fixings so as to avoid possible sparking. The maximum length of non-metallic isolative parts so as to avoid accumulation of static charge also needs to be considered.