Abstract:
A double-wall pipe for a transportation means which includes an outer pipe and an inner pipe extending therein. The outer pipe has two pipe segments which are formed like half-shells and are joined together to form the outer pipe along the longitudinal edges thereof. In this way, it is possible to make both the outer pipe and the inner pipe of metal, such that the wall thickness of the inner pipe can be relatively small.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of International Application No. PCT/DE2012/000086, filed Feb. 2, 2012, which application claims priority to German Application No. 10 2011 010 385.6, filed Feb. 5, 2011, which are each incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The technical field relates to double-wall pipes. In particular, the technical field relates to a double-wall pipe, in one example, for a transport means, a transport means with a double-wall pipe and a method of producing a double-wall pipe. 
     BACKGROUND 
     In transport means, and in particular in aircraft, double-wall pipes are joined together to form pipelines for fuel systems. These pipes have an inner pipe and an outer pipe which surrounds the inner pipe while forming an intermediate space. The pipelines can then be used for example for supplying fuel to an additional turbine-driven auxiliary power unit in the rear of the aircraft or for connecting the trim tank, which is generally accommodated in the horizontal stabiliser, to the main tank of the aircraft. 
     The pipelines for aircraft should be designed with double walls in accordance with relevant safety and aviation regulations for the prevention of accidents. 
     Furthermore the use of the double-wall pipes for the purpose of heat transfer is possible. In this case a fluid flows through the inner pipe. Likewise a fluid flows through the space between the inner and the outer pipe, wherein a temperature difference exists between these two fluids. The flow direction is dependent upon the field of use and also the state of matter of the two fluids. The heat transfer is also influenced inter alia by the conductivity of the materials the two pipes. Possible fields of use are both in the construction of stationary and mobile equipment and in transport means. 
     Double-wall curved pipes have for example an outer pipe into which a hose is inserted coaxially. The distance between the hose and the outer pipe is ensured by spacers which support the hose coaxially with respect to the outer pipe. For geometric reasons, however, it may be that a rigid bent inner pipe cannot be integrated (or inserted) into a similarly shaped outer pipe, as is the case in particular with substantial or multiple curvatures. 
     DE 10 2005 028 766 B4 and US 2009/0025815 A1 describe curved pipelines with a metal inner pipe. During production a support core made from polystyrene is laid around the inner pipe and is then wrapped around with fibre-reinforced epoxy resin material. After the curing of the outer pipe produced in this way from fibre-reinforced epoxy resin material the support core of polystyrene is removed by washing out with a solvent. 
     Other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     SUMMARY 
     According to various teachings of the present disclosure, provided is an alternative double-wall pipe and a corresponding method of production. 
     According to one of various exemplary aspects of the present disclosure, a double-wall pipe is provided, wherein the pipe has an outer pipe and an inner pipe extending in the outer pipe. The inner pipe is designed to convey a fluid (for example a gas, a gas mixture or a liquid) and is spaced apart from the outer pipe. In one example, the double-wall pipe may be designed as a fuel line. 
     The outer pipe has two pipe segments in the form of half-shells or two or more channel-like pipe segments which are joined together along their longitudinal edges in order to form the outer pipe. 
     In this way it is possible to provide robust double-wall pipes which have a comparatively low external diameter and thus a comparatively low overall weight. Likewise it is possible to provide double-wall pipes with substantial or multiple curvatures. 
     In a corresponding manner a T-connection can also be produced for such pipes. 
     According to an embodiment of the present disclosure, the inner pipe is metallic. In this way the wall thickness of the inner pipe can have correspondingly small dimension, so that a relatively small external diameter can be produced. 
     According to another exemplary embodiment of the present disclosure the outer pipe is metal. 
     For example the outer pipe can comprise aluminum, a specific aluminum alloy, iron, nickel base, zinc, magnesium or titanium. Likewise the inner pipe can comprise aluminum, a specific aluminum alloy, iron, nickel, zinc, magnesium or titanium. Any metal which can be welded can be used for the outer pipe. In addition, pipes which are made of alloys which cannot be fusion-welded can be used as the inner pipe. Depending upon the application the inner pipe can also comprise plastics material or a reinforced plastics material. 
     In one example, it may be advantageous if both the outer and the inner pipe comprise a material which can be welded, so that the pipe segments of the outer pipe can be welded to one another at manufacture and so that flange connections can be welded on at both ends of the double-wall pipes. The flange connections on the ends can also be swaged. 
     According to one exemplary embodiment of the present disclosure the two pipe segments in the form of half-shells of the outer pipe are produced by splitting an initial pipe. 
     Thus the initial pipe can be fabricated independently of the inner pipe and is then split along its length into two or more parts. The inner pipe can be provided with spacers and the different parts (segments) of the initial pipe can then be laid around the inner pipe and connected (joined) to one another. 
     According to one embodiment of the present disclosure, the double-wall pipe is a bent pipe. For example the two pipe segments in the form of half-shells of the outer pipe are produced by splitting the initial pipe along the neutral bending line of the bent initial pipe. Naturally the initial pipe can also be parted on any other straight or curved line. 
     The neutral bending line is the common centre line of the inner and outer pipe after the different pipe components are assembled. The neutral bending line is distinguished in that relative to the outer pipe it constitutes the plane in which the outer pipe is not stretched or compressed or is at least only slightly stretched or compressed during bending. Moreover the least “distortion” is to be expected on parting and the joining together is possible in a relative simple manner in terms of clamping. This plane defines the parting lines (also called separation points) along which the outer pipe is divided after the bending operation. Likewise this plane defines the position of the joining lines produced when the outer pipe segments are joined together, which may for example be weld seams. 
     According to one of various exemplary embodiments of the present disclosure the double-wall pipe is one pipe of a fuel line. Such a fuel line may comprise a plurality of these double-wall pipes which are positioned adjacent to one another. Alternatively it may be a hydraulic line. It is generally a line with special safety relevance. 
     According to one aspect of the present disclosure a transport means is provided with a double-wall pipe described above and below. 
     The transport means is for example an aircraft, a water craft, a rail vehicle or a road vehicle. 
     In one example, it may be a passenger aircraft. 
     According to one of various aspects of the present disclosure a method for producing a double-wall pipe and a method for producing a T-connection for connecting double-wall pipes are provided. First of all an inner pipe is constructed. Furthermore an initial pipe separate from the inner pipe is constructed, which has a larger diameter than the inner pipe. 
     Then the initial pipe is split into two or more pipe segments. If the initial pipe is split into precisely two pipe segments it may for example involve pipe segments which are in the form of complementary, that is to say largely similar, half-shells. In this case the splitting of the initial pipe takes place for example along the neutral bending line of the initial pipe, in particular if the double-wall pipe is a bent pipe. It can also be parted along another straight or curved line. 
     Then the inner pipe is positioned in the first pipe segment in the form of a half-shell, whereupon the two pipe segments in the form of half-shells are joined together in order to form the outer pipe. 
     According to another embodiment of the present disclosure the pipe thus produced is a double-wall pipe described above and below, in particular a fuel line. Alternatively it may be a hydraulic line. 
     According to one embodiment of the present disclosure the method includes joining one or two flanges to one or both ends of the outer pipe, so that different double-wall pipes produced in this way can be connected to one another in order to form a complete pipeline. 
     According to one exemplary embodiment of the present disclosure a surface protection is then applied to an inner face and to an outer face of the outer pipe. 
     In one example, the inner pipe and the outer pipe can be made of metal or a metal alloy, in which case the pipe segments into which the initial pipe has been split can be joined together by welding. 
     A person skilled in the art can gather other characteristics and advantages of the disclosure from the following description of exemplary embodiments that refers to the attached drawings, wherein the described exemplary embodiments should not be interpreted in a restrictive sense. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
         FIG. 1A  shows a double-wall bent pipe according to one of various embodiments of the present disclosure. 
         FIG. 1B  shows a sectional representation along the section line A-A in  FIG. 1A . 
         FIGS. 2A-2C  show a method for production of a double-wall pipe according to one of various embodiments of the present disclosure. 
         FIG. 3  shows an aircraft with double-wall pipes according to various embodiments of the present disclosure. 
         FIG. 4  shows a flow diagram of a method according to one exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
       FIG. 1A  shows a double-wall pipe  100  according to one exemplary embodiment of the present disclosure. The double-wall pipe  100  has an inner pipe  101  and an outer pipe  102  at least partially surrounding the inner pipe. At one end  111  of the outer pipe  102  a flange  109  is attached, said flange being for example welded onto the outer pipe  102  or connected to the outer pipe  102  in some other way. For example it is possible for the flange to be screwed on and/or adhered. A flange may also be attached at the opposite end. 
     The flange is welded on for example along the weld line  114  at the end. 
     On the central axis of the two pipes  101 ,  102  is located the neutral bending line  112 , which is generally used as the parting plane and defines the position of the parting points  113  of the initial pipe. 
     Furthermore a plurality of spacers  116  can be provided which ensure that the inner pipe  101  is positioned coaxially with the outer pipe  102 . 
     For this purpose these spacers  116  can be placed for example annularly around the inner pipe and can have a plurality of “legs”  117 ,  118 ,  119  which for example enclose an angle of about 120 degrees relative to one another and ensure the support between the inner pipe  101  and the inner wall of the outer pipe  102 . This can be seen in  FIG. 1B , which shows a sectional representation along the section line A-A in  FIG. 1A . 
       FIG. 1B  also shows the two weld seams along the two parting lines  113  by which the upper half-shell  104  of the outer pipe is connected to the lower half-shell  103  of the outer pipe. 
     It should be noted that in  FIGS. 1A and 1B  the ratio of length to diameter of a typical pipe is shown shortened. Pipe diameters of up to about 145 mm or above may be provided. In one example, the outer pipes may have diameters of about 50 mm. A possible pipe length is about 1 m. However, longer or shorter pipe can also be provided. 
     Furthermore the spacers and the flange on the outer pipe are only illustrated by way of example. Other flanges and other types of spacers can also be used. It may also be that the attachment of a flange is not necessary, since for example no joining to a further pipe is required or the joining takes place in another way. 
     Moreover, a corresponding flange may of course also be provided at the other end of the pipe. 
     The welded connection between the two pipe segments of the outer pipe is made for example by laser welding. 
       FIGS. 2A-2C  show a method for production of a double-wall pipe according to one of various embodiments of the present disclosure. First of all the inner pipe  101  and an initial pipe  110  which will later constitute the outer pipe are formed separately from one another so that they have a neutral bending line  112  extending in a similar manner ( FIG. 2A ). The initial pipe  110  is generally split along the neutral bending line, so that two pipe segments  103 ,  104  in the form of half-shells are produced. Then the inner pipe  101  provided with spacers is introduced into the lower half-shell  103  of the outer pipe ( FIG. 2B ). Next the outer pipe is joined together again along the previously parted bending line. For this purpose the two pipe segments in the form of half-shells  103 ,  104  are joined together along their longitudinal edges  105 ,  106 ,  107 ,  108  for example by welding ( FIG. 2C ). In this case weld seams are produced at the former parting points  113 . 
     In the next step the flanges of the outer pipe are joined and the surface protection is applied to the inner and outer faces of the outer pipe. For this, the flange regions and electrical contact surfaces can be covered. 
     Thus a significant reduction in the weight of components can be achieved. A criterion for the internal diameter of the outer pipe is the minimum distance to be maintained from the inner pipe (or, as in the prior art, from the inner hose), so that when a metal inner pipe is used, because of its greater strength the outer pipe diameter can be reduced. This may lead to a reduced amount of space being required for the pipe system and to reduced production costs, since the semi-finished products can have smaller dimensions and less material is necessary in order to produce the outer pipe. 
       FIG. 3  shows an aircraft  300  which has the double-wall pipes described above. These pipes are used for example as fuel lines between a fuel tank and a propulsion unit or for connecting a trim tank to a main tank. 
       FIG. 4  shows a flow diagram of a method according to various exemplary embodiments of the present disclosure. In  401  the formation of an inner pipe takes place. In  402  an initial pipe is formed separately from said inner pipe, and has a correspondingly larger diameter than the inner pipe. In  403  this initial pipe is parted along two parting lines into two pipe segments in the form of a half-shell and in  404  the inner pipe is provided with spacers. In  405  the inner pipe is laid into one of the two pipe segments. In  406  the second pipe segment is brought into position and the two pipe segments are connected to one another in  407 , for example by welding along the two parting lines. 
     In  408  flanges can be attached to the pipe ends and in  409  the application of a surface protection to the inner and outer faces of the outer pipe takes place. 
     By the use of metal double-wall pipes (so-called pipe-in-pipe assemblies) the total weight of components can be significantly reduced by comparison with double-wall pipes with coaxially attached inner pipes, since the heavy hose which is used in the conventional solution is replaced by a lightweight inner pipe. The introduced hose is relatively expensive, whereas the introduced pipe can be produced very simply and cost-effectively. Moreover in this way double-wall pipes with substantial or multiple curvatures are possible. For the various teachings of the present disclosure it is irrelevant as to which metallic materials are used for the inner or outer pipe. If welding methods are employed for the joining process, the use of metals or metal alloys which can be welded is possible. For example the pipes can be fabricated from titanium or aluminum. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims and their legal equivalents.