Abstract:
A method and apparatus for forming an elongate tubular from a composite material. The composite material includes fibers and epoxy resin that are disposed around an elongated mandrel. The fibers are wound around the outer circumference of the mandrel and the epoxy resin may be applied to the fibers, before, during, or after, being wound onto the mandrel. A trough is provided that supports the mandrel between ends of the mandrel. An example trough includes a flexible membrane supported on its lateral ends to resemble a catenary.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to a method and apparatus for forming a composite member. More specifically, the present invention relates to a method and apparatus for forming an elongated tubular member from composite constituents. 
     DESCRIPTION OF RELATED ART 
     Tubular composite members may be formed by winding a composite filament of fibers and a polymer matrix around a cylindrical mandrel. Typically, the polymer matrix includes a resin, such as an epoxy resin. After winding the composite filament of fibers and matrix around the mandrel, the composite is cured and then removed from the mandrel. An example of a prior art filament winding system is shown in a schematic view in  FIG. 1 . In this example, the filament winding system  10  includes a frame  12  on which a mandrel  14  is horizontally disposed. One end of the mandrel  14  is mounted into a tailstock  16  with its opposing end in a headstock  18 . The tailstock  16  rotates freely with respect to the frame and the headstock  18  is driven by a motor  20  shown attached to the headstock  18  by a drive shaft  22 . Thus the mandrel  14  may be rotated by energizing the motor  20  to rotate the headstock  18  with the coupled shaft  22  that in turn rotates the mandrel  14 . 
     In the example of  FIG. 1 , a composite tubular  24  is being formed on the mandrel  14 . A rail system  26  is provided with the frame  12  on which a creel assembly  28  slides and is supported. The creel assembly  28  is shown equipped with a series of spools or bobbins  30  having filaments  32  that are fed to the mandrel  14  through a feed eye  33 . As is known, the filaments  32  can include fibers such as natural cotton fibers as well as man-made which include carbon, graphite, and aramid fibers. The filaments  32  may be made up of thousands of individual fibers combined in parallel; which is often referred to as a tow. The creel assembly  28  travels lengthwise on the rail  26  and adjacent the mandrel  14  for feeding the filaments  32  onto the mandrel  14  to create plies or layers of filaments  32  onto the mandrel  14  that is combined with the polymer matrix and used to form the composite tubular  24 . Coordinating the rotation speed of the mandrel  14  with the transverse speed of the creel assembly  28  will produce a defined helical angle at which the filaments  32  are wound onto the mandrel  14 . The polymer matrix may be supplied through an epoxy resin system  34  shown having a reservoir and/or pump attached to a line  36  that feeds a resin bath  38 . The filaments  32  pass through the bath  38  prior to being wound onto the mandrel  14  thereby being impregnated with the polymer matrix and forming the composite. 
     Presently known systems for forming composite tubulars experience a drawback when used to form substantially elongate composite tubulars.  FIG. 1A  graphically illustrates vertical forces acting on the mandrel  14  of  FIG. 1 . The force F A  represents the force from gravitational acceleration and forces F 16  and F 18  represent support forces provided respectively at the tailstock  16  and headstock  18 . Since elongate tubulars tend to sag in their mid portion when supported on their ends; and the filament winding system  10  of  FIG. 1  supports a mandrel  14  on its ends, an elongate mandrel used for forming a composite tubular also sags in the mid portion. A sagging mandrel causes inconsistencies in the side wall of any elongate composite tubular formed thereon. Examples of inconsistencies include wrinkles and uneven spacing of filament within a ply or layer; both of which compromise composite tubular quality and structural performance. 
     SUMMARY OF INVENTION 
     Disclosed herein is an example of a filament winding system having a frame, a flexible membrane trough that is supported along lateral sides of the flexible membrane, a rotatable mandrel having opposing ends mounted in the frame and at least a lengthwise portion of the mandrel between the opposing ends supported in the trough, a filament source, and filaments extending from the filament source onto the outer surface of the mandrel, so that when the mandrel is rotated and the filament source reciprocated the filaments wind around the mandrel to form a composite tubular. 
     Also disclosed herein is a method of forming a composite tubular. In an example, the method includes supporting a length of a mandrel with a substantially continuous flexible membrane, so that the mandrel is substantially straight, winding composite filaments of fibers impregnated with a polymer matrix around the mandrel, and separating the composite of fibers and polymer matrix from the mandrel to provide a substantially straight composite tubular. 
     Yet further disclosed is an example of a filament winding system that in an embodiment, is made up of a frame, a flexible membrane trough that is supported along lateral sides of the flexible membrane, an elongated rotatable mandrel having opposing ends mounted in the frame and at least a lengthwise portion of the mandrel between the opposing ends supported in the trough, and that when unsupported between the opposing ends, the lengthwise portion of the mandrel sags below the opposing ends, a filament source, and filaments extending from the filament source onto the outer surface of the mandrel, so that when the mandrel is rotated and the filament source reciprocated the filaments wind around the mandrel to form a composite tubular. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a prior art filament winding system. 
         FIG. 1A  is a force diagram of a portion of the filament winding system of  FIG. 1 . 
         FIG. 2  is a schematic partial sectional view of an example of a filament winding system in accordance with the present disclosure. 
         FIG. 3  is a side sectional view of a portion of the filament winding system of  FIG. 2 . 
         FIG. 3A  is a force diagram of a portion of the filament winding system of  FIG. 2 . 
         FIG. 4  is a side partial sectional view of a portion of the filament winding system of  FIG. 2 . 
         FIG. 5  is a side view of an example of a composite tubular, in use, and formed from the filament winding system of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The apparatus and method of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. This subject of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
     It is to be understood that the subject of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the subject disclosure and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the subject disclosure is therefore to be limited only by the scope of the appended claims. 
       FIG. 2  illustrates an example of a filament winding system  40  in accordance with the present disclosure. In the example of  FIG. 2 , the filament winding system  40  is shown in a side schematic and partial sectional view. The filament winding system  40  includes a frame  42  on which a cylindrical mandrel  44  is horizontally mounted. One end of the mandrel  44  couples with a tailstock  46  shown within the frame and coaxial along an axis A X . The end of the mandrel  44  opposite the tailstock  46  is shown coupling coaxially with a headstock  48 . A motor  50  is schematically illustrated that is connected to the headstock  48  via a drive shaft  52 . In the example of  FIG. 2 , a composite tubular  54  is in the process of being formed on the outer surface of the mandrel  44 . A rail assembly  56  on the frame  42 , provides support for a creel assembly  58  above the mandrel  44  and defines a path along the length of the mandrel  44  for repeated end to end travel of the creel assembly  58 . Spools  60  provided with the creel assembly  58  dispense filaments  62  in a designated pattern onto the mandrel  44 . A trough assembly  64  is shown supporting the mandrel  44  of  FIG. 2  along a portion of the length of the mandrel  44  and disposed between the ends of the mandrel  44 . The presence and supporting force of the trough assembly  64  prevents sag in the mandrel  44  so the mandrel  44  can maintain a substantially straight axis A X . Accordingly, the composite tubular  54  formed on the mandrel  44  also circumscribes a substantially straight axis A X . 
     Included within the trough  64  is a level of liquid polymer matrix  66 . The polymer matrix  66  combines with the filaments  62  to form a composite. Examples of a polymer matrix  66  include an epoxy resin or other impregnating resin. In addition to impregnating the filaments  62 , the polymer matrix  66 , can also make up a film layer between the mandrel  44  and the trough  64 . Without the film layer, the mandrel  44  would otherwise be in contact with a surface of the trough  64 . Similarly, on the portion of the mandrel  44  having the composite tubular  54 , the polymer matrix  66  can also provide a film layer between the outer surface of the composite tubular  54  and trough  64 . The ends of the trough  64 , shown oriented transverse to the axis A x , include openings fitted with seals  68  that circumscribe the mandrel  44  and prevent the polymer matrix  66  from leaking from within the trough  64 . 
     The polymer matrix  66  may be supplied from a resin delivery system  70  shown having a reservoir and pump  72  attached to a supply line  74 . The supply line  74  can supply polymer matrix directly to the trough  64 , onto the filaments  62 , or both. In the embodiment of  FIG. 2 , the polymer matrix is shown being discharged from a nozzle  76  and into the trough  64 . However, other embodiments exist wherein the filaments  62  pass through a polymer matrix bath prior to being wound onto the mandrel  44 . 
     An axial sectional view of a portion of the filament winding system  40  of  FIG. 2  is provided in  FIG. 3 . In this example, the mandrel  44  is shown circumscribed by impregnated windings  62  that form a portion of a composite tubular  54 . The mandrel  44  and composite tubular  54  are shown partially submerged in a bath of polymer matrix  66  while additional filaments  62  is being provided onto the mandrel  44 . Rotation, as indicated by the arrow, of the mandrel  44  and composite tubular  54  draws the filaments  62  from the creel assembly  58  and onto the mandrel  44 . The trough assembly  64  is made up of an outer housing  78  and flexible membrane  80  held to the housing  78  by coupling mounts  81 . In an embodiment, the housing  78  is substantially rigid. As shown in  FIG. 3 , the outer housing  78  has a horizontally disposed lower member  82  and sidewalls  83  upwardly extending from lateral sides of the lower member  82 . The flexible membrane  80  is supported from an end of the sidewalls  83  opposite the lower member  82 . The coupling mounts  81  are shown schematically attaching lateral ends of the flexible membrane  80  onto outer lateral surfaces of the sidewalls  83 . The membrane  80  and housing  78  can have substantially the same length. 
     The housing  78  and membrane  80  define an enclosed space  84  therebetween. In one alternative example, the space  84  may be pressurized thereby providing additional support for the membrane  80 . Examples of pressurization can include introducing a fluid into the space  84 , such as air, nitrogen, water, or the like. Also evident from the example of  FIG. 3 , is a film  85  between the mandrel  44  and composite tubular  54  and the surface of the membrane  80 . Presence of the film  85  provides a liquid interface on the lower-facing surface of the mandrel  44  or composite tubular  54 , thereby reducing rotational friction during the forming process. An additional advantage of the film  85  is that inconsistency in either the mandrel  44  or membrane  80  may result in localized high stress contact between the mandrel  44  and membrane  80 . Presence of the film  85 , however, can compensate for these material inconsistencies so that a substantially constant upward force is exerted onto the mandrel  44  from the membrane  80 . As the outer diameter of the mandrel  44  and composite tubular  54  increases due to added fiber  62 , the flexible membrane  80  can deflect downward so that the centerline axis A X  remains substantially straight; while continuing to support the mandrel  44  and composite tubular  54 . In an alternative example, centerline axis A X  can be maintained substantially straight by varying the pressure in the space  84  as the thickness of the composite tubular  54  increases. 
       FIG. 3A  graphically illustrates a force diagram of vertical forces acting along the length of the mandrel  44  of  FIGS. 2 and 3 . The force due to gravity F A  is shown directed downward along the length of the mandrel  44 . Countering the gravitation force F A  are forces where the mandrel  44  is held by the tailstock and headstock F 46 , F 48  and the force F 80  from the membrane  80 . In the example of  FIG. 3A , the force F 80  from the membrane  80  is distributed along the length of the mandrel  44  so that the tailstock and headstock forces F 46 , F 48  may be reduced over the tailstock and headstock forces F 16 , F 18  depicted in  FIG. 1A . 
     Referring now to  FIG. 4 , a side partial sectional view is shown of an end of the mandrel  44  projecting through the end of the trough  64 . In this example, the outer circumference of the mandrel  44  is shown pressed within a sealing bearing  68  inserted within an end wall of the housing  78 . The level of polymer matrix  66  partially submerges the mandrel and a layer of film  85  is shown beneath the mandrel  44  and the membrane  80 . The membrane  80  is sealingly attached along the end wall of the housing  78  thereby preventing leakage of the polymer matrix  85  into the space  84 . 
       FIG. 5  schematically provides an example of use of a composite tubular  54  where a portion of a drilling system is illustrated having a vertical riser  86  mounted into a subsea well assembly  88 . Attached to and parallel with the riser  86  are composite tubulars  54  formed from the above-described process. Subsea wellhead assembly  88  is mounted on the subsea floor  90 . An advantage of employing a composite tubular  54  in this application is lines, such as choke and kill lines used in conjunction with these drilling systems, although having an inner diameter much less than the riser  86 , have a large thickness to accommodate the high pressures experienced within. As such, the weight of the choke and kill lines may exceed that of the associated riser  86 . Implementation of a composite tubular  54  for use as a choke and kill line, however, can produce choke and kill lines having a weight less than that of an associated riser  86 . Reduced weight lines can increase ease of handling presently designed systems as well as safety. Additionally, the lighter composite tubulars can allow for drilling operations at previously unattainable depths. 
     The present system and method described herein, therefore, is well adapted to carry out and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, springs and/or pneumatically actuated pistons can be used with or in place of the pressurized fluid in the space  84 . These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.