Abstract:
A method of manufacturing a shrouded pipe comprising an inner pipe section for providing a primary fluid path and an outer pipe section for enclosing the inner pipe section to provide a secondary fluid path. The method includes opening the outer pipe section by separating first and second longitudinal edges which split the outer pipe section along a longitudinal line, assembling the outer pipe section with the inner pipe section by passing the inner pipe section between the separated first and second longitudinal edges, and closing the outer pipe section by bringing the first and second longitudinal edges together and joining the first and second longitudinal edges together. An advantage of this method is that close manufacturing tolerances can be achieved without a complex or difficult assembly process.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to European patent application EP 16 170 735.1 filed May 20, 2016, the entire disclosure of which is incorporated by reference herein. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a method of manufacturing a shrouded pipe, in particular a shrouded pipe for distributing fuel or other fluids within an aircraft. 
       BACKGROUND 
       [0003]    It is sometimes necessary for aircraft fuel lines to be shrouded in order to ensure that a leak within the main fuel pipe is contained by the shrouding. Such shrouding is typically mandatory in areas of the aircraft specified by the relevant certifying authority as ignition control zones, for example pressurized areas of the aircraft occupied by crew, passengers or cargo through which fuel lines must pass. In addition, pipes within aircraft may be shrouded in order to provide two fluid flow paths: one within the inner pipe and another in the volume between the inner and outer pipes. 
         [0004]    A known shrouded fuel line assembly is disclosed in US2004/0026922A1, which describes a support member engaged with ends of inner and outer conduits to prevent or reduce movement of the inner conduit within the outer conduit and to allow for the transfer of loads from the inner and/or outer conduits to one or more external components. 
       SUMMARY 
       [0005]    A first aspect of the disclosure herein provides a method of manufacturing a shrouded pipe comprising an inner pipe section for providing a primary fluid path and an outer pipe section for enclosing the inner pipe section to provide a secondary fluid path, the method comprising: opening the outer pipe section by separating first and second longitudinal edges which split the outer pipe section along a longitudinal line; assembling the outer pipe section with the inner pipe section by passing the inner pipe section between the separated first and second longitudinal edges; and closing the outer pipe section by bringing the first and second longitudinal edges together and joining the first and second longitudinal edges together. 
         [0006]    An advantage of the disclosure herein is that close manufacturing tolerances can be achieved without a complex or difficult assembly process. In the known arrangement disclosed in US2004/0026922 it is necessary to assemble the inner conduit with the outer conduit before joining these parts to the support member and end fittings. That is, it is necessary to weld the inner conduit to the support member and end fitting while the outer conduit is in situ, a process which is very difficult due to the lack of visibility of the joint. In contrast, the method of the present disclosure avoids this problem by enabling the outer pipe section to be assembled with the inner pipe section after the inner pipe section has been joined to another member, such as an end fitting or a connection fitting. 
         [0007]    The shrouded pipe may be for transporting any fluid, including any liquid or any gas. The secondary fluid path may provide a conduit for fluid which has leaked from the primary fluid path. Alternatively, the primary fluid path and secondary fluid path may provide separate dedicated fluid flow paths. In some embodiments the primary fluid path may be for transporting a first fluid and the secondary fluid path may be for transporting a second liquid. In other embodiments the primary fluid path and secondary fluid path may provide fluid flows in opposite directions. 
         [0008]    In preferred embodiments joining the first and second longitudinal edges together comprises forming a longitudinal weld seam between the first and second longitudinal edges. Welding provides a sealed joint with good mechanical properties. 
         [0009]    Opening the outer pipe section preferably includes elastically deforming the outer pipe section to provide a generally C-shaped cross-section. The outer pipe section (and, optionally, inner pipe section) may be formed from a metal such as titanium or aluminum. Appropriate metals are typically capable of being deformed in the required manner without experiencing plastic deformation. They are also capable of being welded, resistant to corrosion caused by aviation fuel, and/or able to withstand the necessary mechanical loads with an acceptable fatigue life. 
         [0010]    In some embodiments the shrouded pipe further includes an annular collar part for maintaining a given spacing between the inner and outer pipe sections, the method including: joining a first circumferential edge at a first end of the outer pipe section with a first outer circumferential portion of the collar part, optionally by forming a first circumferential weld seam. 
         [0011]    The first outer circumferential portion of the collar part preferably comprises a circumferential recess in a radially outwardly-facing face of the first outer circumferential portion, whereby closing the outer pipe section includes seating the first circumferential edge of the outer pipe section in the circumferential recess, prior to joining the first circumferential edge with the first outer circumferential portion. By seating the first circumferential edge in the circumferential recess, the outer pipe section can be accurately located with respect to the inner pipe section. The assembly process can therefore be carried out to close dimensional tolerances. 
         [0012]    Preferred embodiments of the method include the step of, before assembling the outer pipe section with the inner pipe section and before joining the first circumferential edge of the outer pipe section with the first outer circumferential portion, joining a first circumferential edge at a first end of the inner pipe section with a first inner circumferential portion of the collar part, optionally by forming a second circumferential weld seam. Thus, forming the join between the inner pipe section with the collar part can be carried out without the outer pipe section being in the way. 
         [0013]    The annular collar part (connection fitting) is preferably for connecting a second outer pipe section to the outer pipe section, the method then including joining a second circumferential edge at an end of the second outer pipe section with a second outer circumferential portion of the collar part adjacent to the first outer circumferential portion. In this way, a long shrouded pipe can be assembled from two or more inner and outer pipe sections connected together by one or more collar parts. 
         [0014]    A second aspect of the disclosure herein provides a kit of parts for manufacturing a shrouded pipe, including: an inner pipe section for providing a primary fluid path; and an outer pipe section for enclosing the inner pipe section to provide a secondary fluid path, the outer pipe section being split along a longitudinal line to provide first and second longitudinal edges, wherein the outer pipe section is elastically deformable to enable assembly with the inner pipe section by separating the first and second longitudinal edges and passing the inner pipe section between the first and second longitudinal edges. 
         [0015]    A third aspect of the disclosure herein provides a shrouded pipe comprising: an inner pipe section for providing a primary fluid path; and an outer pipe section for enclosing the inner pipe section to provide a secondary fluid path, the outer pipe section comprising a longitudinal joint joining first and second longitudinal edges of the outer pipe section together. The longitudinal joint preferably comprises a longitudinal weld seam. 
         [0016]    In some embodiments the shrouded pipe comprises an annular collar part joined to the inner and outer pipe sections to maintain a given spacing therebetween, the collar part having a circumferential recess in a radially outwardly-facing face in which a first circumferential edge of the outer pipe section is seated, and a circumferential joint joining the first circumferential edge to the collar part, the circumferential joint preferably comprising a circumferential weld seam. 
         [0017]    A fourth aspect of the disclosure herein provides an aircraft fuel system comprising a shrouded fuel pipe according to the third aspect, or a shrouded fuel pipe manufactured according to the first aspect. 
         [0018]    Any of the optional, or preferred, features or advantages described or claimed herein can be applied to any of the various aspects of the disclosure herein, either alone or in any combination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Embodiments of the disclosure herein will now be described with reference to the accompanying drawings, in which: 
           [0020]      FIG. 1  shows an isometric view of a shrouded fuel pipe according to an embodiment of the disclosure herein during its manufacture; 
           [0021]      FIG. 2  shows a detail view of  FIG. 1 ; 
           [0022]      FIG. 3  shows a longitudinal cross-section of a shrouded fuel pipe according to an embodiment of the disclosure herein; 
           [0023]      FIG. 4  shows a detail view of  FIG. 3 ; and 
           [0024]      FIG. 5  is a schematic illustration of a shrouded fuel pipe according to an embodiment of the disclosure herein, showing the locations of weld seams. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIGS. 1 through 5  illustrate embodiments of a shrouded fuel pipe  100  according to the disclosure herein, both part way through the manufacturing process ( FIGS. 1 and 2 ) and after manufacture ( FIGS. 3 to 5 ). 
         [0026]    The completed shrouded fuel pipe  100  ( FIGS. 3 to 5 ) comprises one or more outer pipe sections  20  ( 20   a,    20   b,    20   c ) which are each co-axial with an inner pipe section  30  ( 30   a,    30   b,    30   c ) that has a smaller diameter than the outer pipe section  20 . Each pipe section comprising an outer pipe section  20  and inner pipe section  30  is connected to another pipe section by a connection fitting  40  to which the inner  30  and outer  20  pipe sections are joined. Thus, the shrouded fuel pipe  100  comprises a series of pipe sections connected together by connection fittings  40 , with an end fitting  50  (which will not be described in detail herein) at each end. The inner pipe sections  30  together provide a primary fuel flow path  110 , while the annular volume between the inner pipe sections  30  and the outer pipe sections  20  provides a secondary fuel flow path  120  for any fuel which has leaked from a damaged, or otherwise compromised, portion of the primary fuel flow path. Alternatively, the secondary fuel flow path  120  may be a dedicated flow path for fuel or any other fluid. For example, the secondary fuel flow path  120  may be used to provide fuel flow in the opposite direction to that of the primary fuel flow path  110 , or may be used to provide a flow of a fluid other than fuel. 
         [0027]    The inner  30  and outer  20  pipe sections, the connection fittings  40  and the end fittings  50  are each formed from titanium, or any other metal that is suitable for resisting corrosion caused by aviation fuel, can be welded, and is capable of withstanding the necessary mechanical loads and with a suitable fatigue life. The selected metal should also be capable of elastic deformation to the degree necessary to enable assembly of the inner  30  and outer  20  pipe sections, as discussed below. Other suitable metals are aluminum, steel or stainless steel, for example. 
         [0028]    Each connection fitting  40  is a generally annular member which has a generally “I” shaped cross section. That is, the connection fitting  40  comprises a ring-shaped web  41 , from an inner circumferential edge of which first  42  and second  43  inner flanges extend in respective opposite axial directions. First  44  and second  45  outer flanges extend in respective opposite axial directions from an outer circumferential edge of the web  41 . The first  44  and second  45  outer flanges are for joining the outer pipe section  20  to the connection fitting  40 , while the first  42  and second  43  inner flanges are for joining the inner pipe section  30  to the connection fitting  40 . The first  42  and second  43  inner flanges are longer (i.e. extend further in their respective axial directions from the web  41 ) than the first  44  and second  45  outer flanges. 
         [0029]    A plurality of apertures  49  extend through the web  41  of the connection fitting  40 , and are distributed evenly around the web  41 . The apertures  49  enable leaked fuel flowing through the secondary fuel flow path  120  to travel across the connection fittings  40  if necessary, e.g. if the secondary fuel flow path  120  for one of the pipe sections becomes filled with fuel so that overspill to the secondary fuel flow path of neighboring pipe section. 
         [0030]    Each inner flange  42 ,  43  of the connection fitting  40  has a circumferential welding notch  46  that comprises a recess around the circumference of the inner face of the inner flange  42 ,  43  into which a circumferential end edge  31  of the respective inner pipe section  30  is seated. The welding notch  46  thus forms a socket into which the circumferential end edge  31  is fitted. The circumferential end edge  31  is then joined to the inner flange  42 ,  43  via an inner pipe circumferential weld seam  60  which provides a sealed connection between the inner pipe section  30  and the connection fitting  40 . The inner pipe circumferential weld seam  60  is created at the outwardly facing surface of the joint between the inner flange  42 ,  43  and the inner pipe section  30 , rather than at the inwardly-facing surface. This arrangement ensures a much easier welding process, since access and visibility is very good (as discussed further below). 
         [0031]    In the embodiment of  FIGS. 3 and 4  the welding notch  46  is formed by a grow-out portion  47  which extends both radially outwardly and longitudinally outwardly (away from the web  41 ) from the free end of each inner flange  42 ,  43 . The grow-out portion  47  provides filler material for the inner pipe circumferential weld seam  60 . In the embodiment of  FIG. 5  the welding notch  46  is instead formed merely as a notch or recess in the inner flange, and filler material for the weld seam  60  is provided separately. In other embodiments there may be no welding notch  46 , and the circumferential end edge  31  of each inner pipe section  30  may be joined to the respective inner flange  42 ,  43  via a butt joint, lap joint, or other suitable joint. In yet further embodiments the inner pipe section  30  may be joined to the connection fitting  40  via a joining process other than welding, such as by bonding, fastening, compression fitting or any other suitable joining method. 
         [0032]    Each outer flange  44 ,  45  of the connection fitting  40  also has a circumferential welding notch  48  which, in contrast to the notch of the inner flanges, comprises a recess around the circumference of the outer face of the outer flange into which a circumferential end edge  21  of the outer pipe section  20  is seated. The circumferential end edge  21  is then joined to the outer flange  44 ,  45  via an outer pipe circumferential weld seam  62  which provides a sealed connection between the outer pipe section  20  and the connection fitting  40 . The outer pipe circumferential weld seam  62  is created at the outwardly-facing surface of the joint between the outer flange  44 ,  45  and the outer pipe section  20 , rather than at the inwardly-facing surface. This arrangement ensures a much easier welding process, since access and visibility is very good (as discussed further below). 
         [0033]    In the illustrated embodiments the welding notch  48  is formed as a cut-away portion of the outer flange  44 ,  45 , but in other embodiments it may be formed by a grow-out portion in a similar fashion to the inner flanges  42 ,  43 . In other embodiments the welding notch  48  may be omitted, and the circumferential end edge  21  of each outer pipe section  20  may be joined to the respective outer flange  44 ,  45  via a butt joint, lap joint or other suitable joint. 
         [0034]    The connection fitting  40  thus serves both to maintain a given radial spacing between the inner  30  and outer  20  pipe sections, and to connect neighboring pipe sections. 
         [0035]    Each outer pipe section  20  comprises first  22  and second  23  longitudinal edges that extend the full axial length of the outer pipe section  20  and are joined together by a longitudinal weld seam  64  following assembly with the inner pipe section  30 , as described below. 
         [0036]    The weld seams  60 ,  62 ,  64  are formed by any suitable welding process, such as laser beam welding or TIG (tungsten-inert-gas) welding. 
         [0037]    To manufacture each pipe section of the shrouded fuel pipe  100 , the inner pipe section  30   a  is first assembled with the connection fitting  40   a  by seating the circumferential end edge  31  within the welding notch  46  of the inner flange  42 . The inner pipe section  30   a  may also be connected at its other end to an end fitting  50 . The inner pipe section  30   a  and connection fitting  40   a  are then joined together via a circumferential weld seam  60  at the interface between the circumferential end edge  31  and the welding notch  46 . The inner pipe circumferential weld seam  60  thus seals the primary fuel flow path  110  at the interface between the inner pipe section  30   a  and the connection fitting  40   a.  The fact that the inner flange  42  is longer than the outer flange  44  ensures that the person performing the welding step has easy access to, and full visibility of, the joint as the weld seam  60  is created. 
         [0038]    To assemble the outer pipe section  20   a  with the inner pipe section  30   a  and the connection fitting  40   a,  the first  22  and second  23  longitudinal edges of the outer pipe section  20   a  are separated away from one another to create a longitudinal gap therebetween, as shown in  FIGS. 1 and 2 . During this process the outer pipe section  20   a  elastically deforms so that it temporarily adopts a generally C-shaped cross section. The outer pipe section  20   a  is elastically deformed such that there is no, or substantially no, plastic deformation of the metal (or other material) of the part. The inner pipe section  30   a  (which is pre-assembled with the connection fitting  40   a,  and optionally with the end fitting  50 ) is then inserted through the longitudinal gap into the outer pipe section  20   a.  The outer pipe section  20  may be provided with the first  22  and second  23  longitudinal edges pre-formed, or alternatively the first  22  and second  23  longitudinal edges may be formed at the point of manufacture. 
         [0039]    Once the inner pipe section  30   a  has been inserted within the outer pipe section  20   a,  the first  22  and second  23  longitudinal edges are drawn together to close the longitudinal gap and the circumferential end edge  21  is seated in the welding notch  48  of the outer flange  44  of the connection fitting  40   a.  The outer pipe section  20   a  is then joined to the connection fitting  40   a  by forming the outer pipe circumferential weld seam  62  at the interface between the circumferential end edge  21  and the welding notch  48 . If the inner pipe section  30   a  is assembled with an end fitting  50 , the outer pipe section  20   a  is also joined to the end fitting  50 . Finally, the longitudinal weld seam  64  is formed between the first  22  and second  23  longitudinal edges. In this way, the outer pipe circumferential weld seam  62  and longitudinal weld seam  64  together seal the secondary fuel flow path  120 . 
         [0040]    To form longer sections of shrouded fuel pipe, the second inner pipe section  30   b  is joined to the first connection portion  40   a  via an identical process to that described above in respect of the first inner pipe section  30   a.  Similarly, the second outer pipe section  20   b  is assembled with the second inner pipe section  30   b  and with the first connection fitting  40   a  via an identical process to that described above in relation to the first outer pipe section  20   a.  This process is continued for the third (and subsequent) inner  30   c  and outer  20   c  pipe sections and second (and subsequent) connection fitting  40   b,  until the desired length of shrouded fuel pipe has been achieved. 
         [0041]    A particular advantage of the above-described design and method of manufacture is that close tolerances can be achieved, without a complex assembly process. In the known arrangement disclosed in US2004/0026922 it is necessary to weld the inner conduit to the support member and end fitting while the outer conduit is in situ. This process is extremely difficult due to the lack of visibility of the joint, which is almost entirely shrouded by the outer conduit. In contrast, the shrouded fuel pipe of the present disclosure, and the associated method of manufacture, avoids this problem by enabling the inner pipe section to be joined to the connection fitting(s) (and/or end fitting) before assembly with the outer pipe section. The improved visibility ensures improved accuracy and quality of the weld seam. 
         [0042]    In a variation to the above method of manufacture, the outer pipe section  20   a  may be split longitudinally so that it is in two halves, the first  22  and second  23  longitudinal edges of the outer pipe section  20   a  being separated away from one another to create the longitudinal gap by separation of the two halves. The two halves of the outer pipe section  20   a  may then be joined together by two longitudinal weld seams, or two other suitable longitudinal joints. 
         [0043]    Although the illustrated embodiments show a straight section of shrouded pipe  100 , the disclosure herein may also be applied to bent, curved or otherwise non-straight sections of shrouded pipe. 
         [0044]    While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.