Patent Publication Number: US-2005115622-A1

Title: Collapsible flexible pipe and method of manufacturing same

Description:
CROSS-REFERENCE  
      This application relates to, and claims priority of, co-pending provisional application No. 60/426,174, filed Nov. 13, 2002. 
    
    
     BACKGROUND  
      Flexible pipes currently used in offshore oil and gas fields for the transport of fluids underwater between the subsea wellhead and the surface facilities are designed to retain a circular cross-section when subject to external hydrostatic pressure. This is usually achieved by the inclusion of metallic layers that extend around and support a polymer fluid barrier. The metallic layers are usually relatively large and heavy so that they do not deflect significantly under the collapse force. However, for deep water applications, the strength and the weight of the metallic layers required to resist collapse becomes a limiting factor in flexible pipe design. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIGS. 1 and 2  are cross-sectional views of a flexible pipe according to an embodiment of the invention, showing the pipe in a non-collapsed and a collapsed condition, respectively.  
       FIGS. 3 and 4  are views, similar to  FIGS. 1 and 2 , depicting a flexible pipe according to another embodiment.  
       FIGS. 5 and 6  are views, similar to  FIGS. 1 and 2 , depicting a flexible pipe according to another embodiment.  
       FIGS. 7 and 8  are views, similar to  FIGS. 1 and 2 , depicting a flexible pipe according to another embodiment.  
       FIGS. 9 and 10  are views, similar to  FIGS. 1 and 2 , depicting a flexible pipe according to another embodiment.  
       FIGS. 11 and 12  are views similar to  FIGS. 1 and 2  depicting a flexible pipe according to another embodiment. 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIGS. 1 and 2  of the drawings, the reference numeral  10  refers, in general, to a pipe according to an embodiment of the invention which is adapted to receive a fluid at one end for the purposes of transporting the fluid. The pipe  10  is formed by an inner tubular layer  12 , of a plastic, or polymeric material, for containing fluid and for serving as a liner/barrier. A series (in the example shown, five) of reinforcing layers  14  extend around the layer  12 . The layers  14  can be in the form of helically wound or braided aramid, carbon and/or steel fibers and can be wrapped around the layer  12  to resist the internal pressure forces in the pipe  10 .  
      An outer tubular layer  16 , also of a plastic, or polymeric material, extends around the outermost reinforcing layer  14  to serve as a shield to protect the layers  14  from the external environment. The inner layer  12  and the outer layer  16  can be formed by a plastic, or polymeric material. The layers  12 , 14  and  16  form a tubular assembly, shown in general by the reference numeral  20 .  
      An insert  24 , having an arcuate cross-section, is disposed in the tubular assembly  20  in a coaxial relationship, with the insert normally conforming to the corresponding inner surface of the inner layer  12  in an abutting relationship, for the entire length of the inner layer. The insert  24  can be made from thermal plastic or thermal-set material, such as a nylon or rubber-like material, so that it has appropriate flexibility to conform to the shape of the assembly  20 , which is tubular when the pipe is internally pressurized ( FIG. 1 ) and flat when the pipe is externally pressurized ( FIG. 2 ).  
      A series (in the example shown, five) of axially-extending, angularly-spaced, parallel, steel, or fiber, solid cylindrical reinforcing members  26  are embedded in the insert  24  and extend for the length of the insert.  
      The insert  24  extends angularly for approximately one-half the internal diameter of the tubular assembly  20 , or for approximately 180 degrees. In this context, the outer surface of the insert  24  is substantially equal to the inner circumferential surface of the layer  12 . Therefore, when the tubular assembly  20  is flattened as shown in  FIG. 2  under conditions to be described, the insert  24  fully supports the tubular assembly in the flat condition while limiting the strain in the structural layers  12 ,  14  and  16  at the longitudinal fold. The pipe  10  thus possesses sufficient strength and integrity to withstand the internal pressure of the fluid being transported, yet has the flexibility to collapse under external pressure with limited strain on the tubular assembly  20 .  
      A pipe according to the embodiment of  FIGS. 3 and 4  is referred to, in general, by the reference numeral  30  and includes a tubular assembly  32  which is identical to the tubular assembly  20  of the embodiment of  FIGS. 1 and 2 , but for the fact that the inner tubular layer  12  is eliminated and the insert  24  of the latter embodiment have been replaced with an insert  34 . The insert  34  extends within the tubular assembly  32  in a coaxial relationship, with the innermost layer of the series of layers  14  extending around the insert  34  in an abutting relationship for the entire length of the tubular assembly.  
      The insert  34  is fabricated from a material, such as thermal plastic or thermal-set material which can be in the form of nylon or rubber-like material. Thus, the insert  34  has appropriate flexibility to conform to the shape of the assembly  32 , which is tubular when the pipe  30  is internally pressurized ( FIG. 3 ) and flat when the pipe is externally pressurized ( FIG. 4 ).  
      As shown in  FIG. 3 , the inner diameter of the insert  34  varies around the inner circumference of the insert from two diametrically opposed areas of minimum diameter to two diametrically opposed areas of maximum diameter. These changes in diameters of the layer/insert  34  are gradual from the minimum to the maximum diameters, and the medium thickness of the layer/insert  34  is substantially equal to the thickness of the tubular assembly  32 .  
      Therefore, when the pipe  30  collapses to the position shown in  FIG. 4 , the upper half of the insert  34 , as viewed in  FIG. 3 , nests in the lower half of the insert, as shown in  FIG. 4  to enable the nested inserts to attain a substantially flat configuration. This limits the strain in the layers  14  and  16  of the tubular assembly  32  at the longitudinal fold of the pipe  30 .  
       FIGS. 5 and 6  depict another embodiment of a pipe shown, in general, by the reference numeral  40  which includes a tubular assembly  42  which is identical to the tubular assembly  20  of the embodiment of  FIGS. 1 and 2 . An insert  44  extends within the tubular assembly  42  in a coaxial relationship, with the innermost layer of the series of layers  14  ( FIG. 1 ) extending around the insert  44  in an abutting relationship for the entire length of the tube.  
      The insert  44  is fabricated from a material, such as thermal plastic or thermal-set material, which can be in the form of nylon or rubber-like material. Thus, the insert  44  has appropriate flexibility to conform to the shape of the assembly  42 , which is tubular when the pipe  40  is internally pressurized ( FIG. 5 ) and flat when the pipe is externally pressurized ( FIG. 6 ).  
      The insert  44  consists of two arcuate sections  44   a  and  44   b , each of which extends for approximately 180 degrees. The corresponding ends of the sections  44   a  and  44   b  engage each other in an abutting, diametrically opposed, relationship in a manner to form articulations to permit pivotal movement between the engaging ends when the pipe  40  collapses in the same manner as discussed in the previous embodiment. Thus, when collapsed, the corresponding inner surfaces of the sections  44   a  and  44   b  engage so that the insert  44  and the pipe  40  attain a substantially flat configuration as shown in  FIG. 6 . The insert  44  thus limits the strain in the structural layers of the tubular assembly  42  at the longitudinal fold of the pipe  40 . It is understood that the insert  44  may also serve as an insulating layer.  
      A pipe according to the embodiment of  FIGS. 7 and 8  is referred to, in general, by the reference numeral  50  and includes a tubular assembly  52  which is identical to the tubular assembly  20  of the embodiment of  FIGS. 1 and 2 .  
      An insert  54  is disposed in the tubular assembly  52  and extends angularly for approximately one-half the internal diameter of the tubular assembly  52 , or for approximately 180 degrees. The insert  54  is formed by a flexible metallic ply, or layer, normally having a circular cross section, but with approximately one half portion (the upper half portion as viewed in  FIG. 7 ) being folded over the other half portion, to form a substantially arcuate configuration having enlarged side portions  54   a  and  54   b.    
      The external surface of the above-mentioned other half portion of the insert  54  conforms to the corresponding inner surface of the tubular assembly  52  in an abutting relationship for the entire length of the pipe  50 . Thus, when the pipe  50  collapses from its normal position shown in  FIG. 7  to a collapsed position shown in  FIG. 8 , the enlarged side portions  54   a  and  54   b  control the radius of the longitudinal fold in the wall of the pipe. This limits the strain on the structural layers of the tubular assembly  52  at the longitudinal fold.  
       FIGS. 9 and 10  depict another embodiment which is shown, in general, by the reference numeral  60  and includes a tubular assembly  62  which is identical to the tubular assembly  20  of the embodiment of  FIGS. 1 and 2 . A tubular insert  64  extends within the tubular assembly  62  and is disposed in a coaxial relation to the assembly. The insert  64  is fabricated from a material, such as thermal plastic or thermal-set material, which can be in the form of nylon or rubber-like material. Thus, the insert  64  has appropriate flexibility to conform to the shape of the assembly  62 , which is tubular when the pipe  60  is internally pressurized ( FIG. 9 ) and flat when the pipe is externally pressurized ( FIG. 10 ).  
      The circumference of the outer diameter of the insert  64  is constant and normally conforms to the corresponding inner surface of the tubular assembly  62  in an abutting relationship for the entire length of the tube.  
      The circumference of the inner diameter of the insert  64  is constant but for two diametrically opposed areas, each having a reduced cross-section, or groove. This enables the insert  64  to attain a substantially flat configuration when the pipe  60  collapses to the position shown in  FIG. 10 . In this collapsed condition, the insert  64  controls the radius of the longitudinal fold in the wall of the pipe  62  which limits the strain on the structural layers of the tubular assembly  62  at the longitudinal fold. It is understood that the insert  64  may also serve as an insulating layer.  
      A pipe according to the embodiment of  FIGS. 11 and 12  is referred to, in general, by the reference numeral  70  and includes a tubular assembly  72  which is identical to the tubular assembly  20  of the embodiment of  FIGS. 1 and 2 . An arcuate insert  74  extends angularly within the tubular assembly  72  for approximately one-half the internal diameter of the tube  12 , or for approximately 180 degrees. The insert  74  is fabricated from a material, such as thermal plastic or thermal-set material, which can be in the form of nylon or rubber-like material. Thus, the insert  74  has appropriate flexibility to conform to the shape of the assembly  72 , which is tubular when the pipe  70  is internally pressurized ( FIG. 11 ) and flat when the pipe is externally pressurized ( FIG. 12 ).  
      A series (in the example shown, five) of spaced, parallel articulated cylindrical members  76  are embedded in the insert  74  and are joined together by extruded links  78  extending between the adjacent cylindrical members and connected thereto in any conventional manner. The member  76  can be in the form of tubes, solid cables, or the like. When collapsed, the pipe  70  attains a substantially flat configuration as shown in  FIG. 12 , and the insert  74  controls the radius of the longitudinal fold in the wall of the tubular assembly  72  and limits the strain on the structural layers of the tubular assembly at the longitudinal fold. Also, the above cylindrical members could serve as an umbilical that carries power and/or fluids for wellhead control, chemical injection or heating.  
      The pipes of the above embodiments possess sufficient strength and integrity to withstand the internal pressure of the fluid being transported, yet have the flexibility to collapse under external pressure. In each embodiment, the insert limits the strain in the wall structure of the pipe to a level which will not impair the structural integrity of the pipe when it is subjected to external pressure and is in a collapsed condition.  
     Variations and Alternatives  
      1. Although each embodiment discussed above was referred to as a stand-alone pipe, each embodiment can also form a portion of a larger pipe having additional components, such as protective layers, anti-wear layers, and the like.  
      2. The above additional layers can also be placed between the reinforcing layers discussed above.  
      3. The particular material forming the layers and the inserts of the above embodiments can be varied within the scope of the invention as long as the above results are achieved.  
      4. The inserts could be integral with the inner layer of each tubular assembly.  
      5. The inserts may incorporate longitudinal members of steel or fiber to provide the required axial strength and to act as a ballast when required to stabilize the pipe on the sea bed.  
      6. The cross-sections of the arcuate inserts can extend for angular distances other than 180 degrees.  
      7. The insert  64  of the embodiment of  FIGS. 9 and 10  can be replaced by a plain, non-grooved tubular insert, depending on the elastic properties of the insert material.  
      8. The specific composition of each of the layers forming the pipes  10 ,  30 ,  40  and  50  can be varied within the scope of the invention.  
      9. One or more of the layers forming the pipes  10 ,  30 ,  40  and  50  can be eliminated.  
      10. One or more of the layers forming the pipes  10 ,  30 ,  40  and  50  can be replaced by another layer of a different design.  
      11. Two or more of the layers  12 ,  14 , and/or  16  can be provided.  
      12. Additional layers of a different design can be added to layers  12 ,  14  and/or  16 .  
      13. The relative thicknesses of the layers forming the pipes  10 ,  30 , 40  and  50  are shown in the drawing only for the purpose of example, it being understood that these relative thicknesses can be varied within the scope of the invention.  
      14. The spatial references, such as “under”, “over”, “between”, “outer”, “inner” and “surrounding” are for the purpose of illustration only and do not limit the specific orientation or location of the layers described above.  
      15. The relative radial positions of the layers  12 ,  14 ,  16 ,  18 , and  20  can be changed.  
      16. The size of the inner diameter of the inserts in the embodiment of  FIGS. 3 and 4  can vary from only one minimum diameter to only one maximum diameter around the inner circumference of the insert.  
      Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many other modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.