LINER COLLAPSE MITIGATIONS FOR TYPE IV CONFORMABLE PRESSURE VESSELS

Abstract

A type IV pressure vessel has improved permeate gas management. The pressure vessel comprises an inner polymeric liner, a breather layer disposed on the liner, and an outer composite shell structure disposed on the breather layer. The breather layer is gas permeable, impermeable to liquids, and provides a flow passageway for gas permeating through the liner wall collected by the breather layer. The outer composite shell is formed by one or more layers of fiber of a first fiber type and resin. Gas permeating from an interior space of the liner is received by the breather layer and directed to a predetermined exit location on the pressure vessel.

Claims

1. A pressure vessel for containing liquids and/or gases under pressure, said pressure vessel comprising: a polymeric liner comprising a hollow body defined by an elongated cylindrical wall having an outer surface extending between a first terminal end and a second terminal end of said liner; a breather layer surrounding said outer surface of said cylindrical wall and extending between said first terminal end and said second terminal end of said liner, said breather layer being gas permeable and impermeable to liquids, said breather layer providing a flow passageway for gas permeating through said cylindrical wall collected by said breather layer; and an outer composite shell comprising resin and fibers of a first fiber type, said outer composite shell surrounding an outer periphery of said breather layer and extending between said first terminal end and said second terminal end of said liner; wherein said gas permeating through said cylindrical wall collected by said breather layer is directed to a predetermined exit location on said pressure vessel.

2. The pressure vessel as set forth in claim 1, wherein: said first fiber type comprising one or more of carbon fiber, glass fiber, basalt fiber, boron fiber, aramid fiber, high-density polyethylene fiber (HDPE), polyethylene naphthalate (PEN), Zylon™ poly(p-phenylene-2,6-benzobisoxazole fiber (PBO), aramid fiber, Kevlar® poly-paraphenylene terephthalamide fiber, polyethylene terephthalate fiber (PET), Nylon fiber (PA), polyester fiber (PL), polypropylene fiber (PP), and/or polyethylene fiber (PE); said polymeric liner comprising one or more of Nylon (PA), ethylene-vinyl acetate (EVA), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), ethylene vinyl alcohol (EVOH), polytetrafluoroethylene (PTFE), polyurethane (PU), and/or polyvinyl chloride (PVC); and said resin comprises one or more of an epoxy resin, a thermoplastic resin, a vinylester resin, a polyester resin, and/or urethane.

3. The pressure vessel as set forth in claim 2, wherein: said breather layer comprises one or more of linear low-density polyethylene (LLDPE), polysiloxane, polyurethane (PU), polytetrafluoroethylene (PTFE), Nylon, synthetic rubber, silicone, ethylene propylene diene terpolymer (EPDM), polyethylene (DPE), polypropylene (PP), polyvinyl chloride (PVC), acrylonitrile butadiene rubber (Nitrile), and/or polyethylene terephthalate (PET).

4. The pressure vessel as set forth in claim 3, wherein said breather layer is one or more of a tape, a film, a sheet, a wrap, and/or molded rubber.

5. The pressure vessel as set forth in claim 2, wherein: said breather layer includes one or more stacked braided fiber layers of a second fiber type; said second fiber type comprising one or more of carbon fiber, glass fiber, basalt fiber, boron fiber, aramid fiber, high-density polyethylene fiber (HDPE), polyethylene naphthalate (PEN), Zylon™ poly(p-phenylene-2,6-benzobisoxazole fiber (PBO), aramid fiber, Kevlar® poly-paraphenylene terephthalamide fiber, polyethylene terephthalate fiber (PET), Nylon fiber (PA), polyester fiber (PL), polypropylene fiber (PP), and/or polyethylene fiber (PE); and said second fiber type being different than said first fiber type in one or more of material composition and/or fiber outer diameter.

6. The pressure vessel as set forth in claim 5, wherein said fibers of said second fiber type have a larger outer diameter than an outer diameter of said fibers of said first fiber type.

7. The pressure vessel as set forth in claim 4, wherein: said breather layer includes one or more of glass fiber woven fabric and/or glass fiber non-woven fabric wrapped around said outer periphery of said cylindrical wall.

8. The pressure vessel as set forth in claim 2, wherein: said pressure vessel includes at least one non-structural metal film layer surrounding said outer periphery of said cylindrical wall and extending longitudinally along at least a portion of said cylindrical wall; said at least one non-structural metal film layer being in direct contact with one or more of said cylindrical wall, said breather layer, and/or said outer composite shell; and said at least one non-structural metal film layer comprising one or more of a metalized film and/or a metal foil.

9. The pressure vessel as set forth in claim 2, wherein: said outer composite shell includes at least one venting hole extending through said outer composite shell; and said at least one venting hole fluidically connecting said breather layer to an external atmosphere such that gas permeating into said breather layer flows through said breather layer into said at least one venting hole, flows through said at least one venting hole, and disperses into said external atmosphere.

10. The pressure vessel as set forth in claim 2, wherein: said liner including an inlet opening near said first terminal end of said liner; said pressure vessel including a stem and a ferrule; said stem having a cylindrical boss extending in a longitudinal direction and configured to be inserted into said inlet opening of said liner, said stem including a mounting ridge projecting from said cylindrical boss and extending circumferentially around an outer periphery of said stem; said stem being inserted into said inlet opening of said liner such that said inlet opening of said liner circumferentially surrounds said cylindrical boss adjacent said mounting ridge; and said ferrule fixedly coupling said mounting ridge to said outer composite shell.

11. The pressure vessel as set forth in claim 10, wherein: said mounting ridge including a liner mounting surface orientated towards said liner and an opposing mounting surface oriented away from said liner when said stem is assembled with said liner, said mounting ridge including a vent slot extending between said liner mounting surface and said opposing mounting surface; and said vent slot fluidically coupling said breather layer to an external atmosphere such that gas permeating into said breather layer flows through said breather layer into said vent slot, flows through said vent slot, and disperses into said external atmosphere.

12. The pressure vessel as set forth in claim 11, wherein: crimping said ferrule to said mounting ridge of said stem forms an axial hole through said vent slot; and said gas flowing through said vent slot passes through said axial hole.

13. The pressure vessel as set forth in claim 10, wherein: at least one venting hole extends through said ferrule and said outer composite shell; and said at least one venting hole fluidically connecting said breather layer to an external atmosphere such that gas permeating into said breather layer flows through said breather layer into said at least one venting hole, flows through said at least one venting hole, and disperses into said external atmosphere.

14. A pressure vessel for containing liquids and/or gases under pressure, said pressure vessel comprising: a polymeric liner comprising a hollow body defined by an elongated cylindrical wall having an outer surface extending between a first terminal end and a second terminal end of said liner; a breather layer surrounding said outer surface of said cylindrical wall and extending between said first terminal end and said second terminal end of said liner, said breather layer formed by braiding fibers of a first fiber type around said cylindrical wall, said breather layer providing a flow passageway for gas permeating through said cylindrical wall collected by said breather layer, and said breather layer being free of resin; and an outer composite shell comprising resin and fibers of a second fiber type, said outer composite shell surrounding an outer periphery of said breather layer and extending between said first terminal end and said second terminal end of said liner; wherein said first fiber type is different from said second fiber type in one or more of material composition and/or fiber outer diameter; wherein said gas permeating through said cylindrical wall collected by said breather layer is directed to a predetermined exit location on said pressure vessel.

15. The pressure vessel as set forth in claim 14, wherein: each of said first fiber type and said second fiber type comprising one or more of carbon fiber, glass fiber, basalt fiber, boron fiber, aramid fiber, high-density polyethylene fiber (HDPE), polyethylene naphthalate (PEN), Zylon™ poly(p-phenylene-2,6-benzobisoxazole fiber (PBO), aramid fiber, Kevlar® poly-paraphenylene terephthalamide fiber, polyethylene terephthalate fiber (PET), Nylon fiber (PA), polyester fiber (PL), polypropylene fiber (PP), and/or polyethylene fiber (PE); said polymeric liner comprising one or more of Nylon (PA), ethylene-vinyl acetate (EVA), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), ethylene vinyl alcohol (EVOH), polytetrafluoroethylene (PTFE), polyurethane (PU), and/or polyvinyl chloride (PVC); and said resin comprises one or more of an epoxy resin, a thermoplastic resin, a vinylester resin, a polyester resin, and/or urethane.

16. The pressure vessel as set forth in claim 15, wherein said first fiber type having fibers with a first outer diameter, said second fiber type having fibers with a second outer diameter, and said first outer diameter being larger than said second outer diameter.

17. The pressure vessel as set forth in claim 15, wherein: said pressure vessel includes a resin barrier layer surrounding an outer periphery of said outer surface of said cylindrical wall and/or an outer surface of said breather layer, said resin barrier layer being gas permeable and liquid impermeable; and said resin barrier layer comprises one or more of linear low-density polyethylene (LLDPE), polysiloxane, polyurethane (PU), polytetrafluoroethylene (PTFE), Nylon, synthetic rubber, silicone, ethylene propylene diene terpolymer (EPDM), polyethylene (DPE), polypropylene (PP), polyvinyl chloride (PVC), acrylonitrile butadiene rubber (Nitrile), ethylene vinyl alcohol (EVOH), and/or polyethylene terephthalate (PET).

18. The pressure vessel as set forth in claim 17, wherein said resin barrier layer is one or more of a tape, a film, a sheet, a wrap, and/or molded rubber.

19. The pressure vessel as set forth in claim 15, wherein: said pressure vessel includes at least one non-structural metal film layer surrounding said outer periphery of said cylindrical wall and extending longitudinally along at least a portion of said cylindrical wall; said at least one non-structural metal film layer being in direct contact with one or more of said outer surface of said cylindrical wall, said breather layer, and/or an inner surface of said outer composite shell; and said at least one non-structural metal film layer comprising one or more of a metalized film and/or a metal foil.

20. The pressure vessel as set forth in claim 15, wherein: said outer composite shell includes at least one venting hole extending through said outer composite shell; and said at least one venting hole fluidically connecting said breather layer to an external atmosphere such that gas permeating into said breather layer flows through said breather layer into said at least one venting hole, flows through said at least one venting hole, and disperses into said external atmosphere.

21. The pressure vessel as set forth in claim 15, wherein: said liner including an inlet opening near said first terminal end of said liner; said pressure vessel including a stem and a ferrule; said stem having a cylindrical boss extending in a longitudinal direction and configured to be inserted into said inlet opening of said liner, said stem including a mounting ridge projecting from said cylindrical boss and extending circumferentially around said stem; said stem being inserted into said inlet opening of said liner such that said inlet opening of said liner circumferentially surrounds said cylindrical boss adjacent said mounting ridge; and said ferrule fixedly coupling said mounting ridge to said outer composite shell.

22. The pressure vessel as set forth in claim 21, wherein: said mounting ridge including a liner mounting surface orientated towards said liner and an opposing mounting surface oriented away from said liner when said stem is assembled with said liner; said mounting ridge including a vent slot extending between said liner mounting surface and said opposing mounting surface; and said vent slot fluidically coupling said breather layer to an external atmosphere such that gas permeating into said breather layer flows through said breather layer into said vent slot, flows through said vent slot, and disperses into said external atmosphere.

23. The pressure vessel as set forth in claim 21 wherein: at least one venting hole extends through said ferrule and said outer composite shell; and said at least one venting hole fluidically connecting said breather layer to an external atmosphere such that gas permeating into said breather layer flows through said breather layer into said at least one venting hole, flows through said at least one venting hole, and disperses into said external atmosphere.

24. The pressure vessel as set forth in claim 21 wherein: at least one venting hole extends through said outer composite shell; and said at least one venting hole fluidically connecting said breather layer to an external atmosphere such that gas permeating into said breather layer flows through said breather layer into said at least one venting hole, flows through said at least one venting hole, and disperses into said external atmosphere.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0015] FIG. 1 is a perspective view of a portion of a pressure vessel having a stem with vent slots, according to one embodiment of the present invention;

[0016] FIG. 2 is a cross-sectional view of an embodiment of the pressure vessel of FIG. 1, illustrating a breather layer between an inner liner and an outer composite shell;

[0017] FIG. 3A illustrates a known method of wrapping a strand of resin impregnated fibers around a liner in a helical pattern;

[0018] FIG. 3B illustrates a method of wrapping a strand of dry fibers around a liner in a helical pattern according to one embodiment of the present invention;

[0019] FIG. 4 illustrates a method of braiding a plurality of strands of fibers around a liner having a larger outer diameter portion, a tapered diameter portion, and a smaller outer diameter portion;

[0020] FIG. 5 is a perspective view of the stem of FIG. 1, illustrating vent slots extending through a mounting ridge of the stem;

[0021] FIG. 6 is a cutaway view of a portion of the pressure vessel of FIG. 2, illustrating gas flow through the liner, into the breather layer, through the breather layer, and exhausted through a predetermined exit location to atmosphere;

[0022] FIGS. 7A and 7B illustrate porosity within a layer of fibers for larger diameter fibers and smaller diameter fibers, respectively;

[0023] FIG. 8 is an enlarged cross-sectional view of another embodiment of the pressure vessel of FIG. 1, illustrating an inner liner, a breather layer of a first fiber type, and an outer composite shell formed of resin and a second type of fiber,

[0024] FIG. 9 is a cross-sectional view of another embodiment of the pressure vessel of FIG. 1, illustrating a resin barrier layer between the breather layer and the outer composite shell;

[0025] FIG. 10 illustrates a method of wrapping a barrier film around a liner covered in a layer of braided strands of dry fiber,

[0026] FIG. 11 is an enlarged cutaway view of a portion of the pressure vessel of FIG. 9, illustrating gas flow through the liner, into the breather layer and the resin barrier layer, and through the breather layer and the resin barrier layer, and exhausted through a predetermined exit location to atmosphere;

[0027] FIG. 12A is an enlarged cross-sectional view of another embodiment of the pressure vessel of FIG. 9, illustrating one or more non-structural metal layers between the inner liner, the breather layer comprising dry fiber, the resin barrier layer, and the outer composite shell;

[0028] FIG. 12B is an enlarged cross-sectional view of another embodiment of the pressure vessel of FIG. 9, illustrating one or more non-structural metal layers between the inner liner, the breather layer comprising glass fiber fabric, a resin barrier layer, and the outer composite shell;

[0029] FIG. 13 is an enlarged cross-sectional view of another embodiment of the pressure vessel of FIG. 1, illustrating a breather layer comprising a polymeric film applied to the liner and an outer composite structure applied to the breather layer;

[0030] FIG. 14 illustrates a method of wrapping a polymeric film around an outer surface of a liner to form a breather layer;

[0031] FIG. 15 is an enlarged cross-sectional view of the pressure vessel of FIG. 2, illustrating gas flow along the breather layer, through the vent slot in the stem, and exhausted to an external atmosphere;

[0032] FIG. 16 is an enlarged cross-sectional view of the pressure vessel of FIG. 9, illustrating gas flow along the breather layer and along the resin barrier layer, through the vent slot in the stem, and exhausted to an external atmosphere;

[0033] FIG. 17 is a cross-sectional view of a portion of a pressure vessel having breather layer between a polymeric liner and an outer composite shell, a stem inserted into an opening in the liner, and a ferrule fixedly coupling the stem to the outer composite shell, according to another embodiment of the present invention;

[0034] FIG. 18 is an enlarged cross-sectional view of the pressure vessel of FIG. 17, illustrating gas flow along the breather layer, through a crimp joint between the stem and the ferrule, and exhausted to an external atmosphere;

[0035] FIG. 19 is a cross-sectional view of another embodiment of the pressure vessel of FIG. 17, illustrating a resin barrier layer between the breather layer and the outer composite shell;

[0036] FIG. 20 is an enlarged cross-sectional view of the pressure vessel of FIG. 19, illustrating gas flow along the breather layer and the resin barrier layer, through a crimp joint between the stem and the ferrule, and exhausted to an external atmosphere;

[0037] FIG. 21 is a cross-sectional view of another embodiment of the pressure vessel of FIG. 17, illustrating venting holes through the outer composite shell fluidically coupling the breather layer to an external atmosphere;

[0038] FIG. 22 is an enlarged cross-sectional view of a portion of the pressure vessel of FIG. 21, illustrating gas flow along the breather layer and the resin barrier layer, through a venting hole in the outer composite shell, and exhausted to an external atmosphere; and

[0039] FIG. 23 is an enlarged cross-sectional view of a portion of the pressure vessel of FIG. 21, illustrating gas flow along the breather layer and the resin barrier layer, through a venting hole extending through the outer composite shell and the ferrule, and exhausted to an external atmosphere.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a type IV pressure vessel 10 for containing liquids and/or gases 12 under pressure and having improved management of permeation gas 14 is shown in FIGS. 1 and 2, according to one embodiment of the present invention. The pressure vessel 10 includes a polymeric liner 16 comprising an interior hollow body or space 18 defined by an elongated cylindrical wall 26. An outer surface 28 of the cylindrical wall 26 is covered by at least a breather layer 30 and an outer composite shell structure 34, as shown in FIG. 2. The liner 16 includes at least one inlet opening 36 at a first terminal end 38 of the liner 16 through which a stem 44 is inserted for adding and removing gas 12 from the interior hollow body 18 of the liner 16. In addition, a ferrule 48 fixedly couples the outer composite shell 34 to the stem 44.

[0041] The pressure vessel 10 is suitable for storage of compressed liquids and/or gases 12, such as nitrogen, hydrogen, natural gas, helium, dimethyl ether, liquefied petroleum gas, xenon, and the like. A pressure vessel 10 for storage of hydrogen for automotive applications typically is designed for about 5,000 PSI to about 10,000 PSI of nominal working pressure. In comparison, pressure vessels 10 for storage of compressed natural gas are typically designed for about 3,000 PSI of internal pressure during normal use.

[0042] Referring to FIG. 2, the breather layer 30 provides an escape path 52 for gas 14 that permeates through the cylindrical wall 26 of the liner 16. The breather layer 30 comprises a porous material 30 installed between the liner 16 and the outer composite shell 34 that can be used to drain gas 14 from a gap 54 between the liner 16 and the outer composite shell 34, along the length of the pressure vessel 10 to an external atmosphere 60 through an opening 64 near the stem 44 located at one end 68 of the pressure vessel 10. This results in the lower gap 54 pressure at steady state and significantly reduces the amount of gas 14 absorbed in the outer composite shell 34 and the liner 16.

[0043] Referring to FIG. 2, conformable pressure vessels 10 tend to have longer overall length of the liner 16 per unit of liner outer diameter 16A than typical non-conformable pressure vessels 10. The overall length of the liner 16 is measured along the outer surface 28 of the cylindrical wall 26 from the first terminal end 38 of the liner 16 to an opposing terminal end 38′ of the liner 16. The overall length of a liner 16 for a typical pressure vessel 10 is about the same as a linear distance between one end 68 and an opposing end 68′ of the pressure vessel 10. However, conformable pressure vessels 10 can have a liner 16 that has an overall liner length that is many times greater than a linear distance between one end 68 and an opposing end 68′ of the conformable pressure vessel 10. During the manufacturing of a conformable pressure vessel 10, the liner 16 is covered with at least the outer composite shell 34 and folded and/or spirally wrapped to fill a predefined space prior to curing resin 72 in the outer composite shell 34. Thus, the overall exterior dimensions of the conformable pressure vessel 10 are generally determined by the predefined space with the overall length of the liner 16 being greater than the length, the width, and/or the height of the predefined space defining the pressure vessel 10 exterior dimensions. The overall length of the liner 16 for a conformable pressure vessel 10 is a challenge for gas flow 52 to vent the permeate gas 14 to atmosphere 60 since the liner 16 is significantly longer than the overall exterior dimensions of the conformable pressure vessel 10.

[0044] Various embodiments of breather layers 30 with improved permeate gas 14 management, as well as improvements in venting the breather layers 30 to an external atmosphere 60, are shown in FIGS. 1, 2, and 5-23. Each of the disclosed embodiments includes at least a polymeric liner 16, a breather layer 30, an outer composite shell 34 of fiber and resin, a stem 44, and a ferrule 48, as illustrated in FIG. 2.

[0045] The polymeric liner 16, shown in FIG. 2, is generally formed from one or more polymeric materials such as Nylon (PA), ethylene-vinyl acetate (EVA), linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), ethylene vinyl alcohol (EVOH), polytetrafluoroethylene (PTFE), polyurethane (PU), and/or polyvinyl chloride (PVC). The polymeric liner 16 may be formed of a single layer of polymeric material or may comprise a multi-layered structure of two or more polymeric layers and further may include one or more non-structural metal film layers and/or non-structural metal foil, as desired for specific applications.

[0046] The outer composite shell 34 of the pressure vessel 10, shown in FIG. 2, is generally formed by disposing resin impregnated fibers 70 onto the liner 16, as illustrated in FIGS. 3A and 4. A plurality of fiber filaments 70 is grouped to form a strand 70′ of fiber 70. Fiber strands 70′ can be applied to the liner 16 by continuous wrapping one or more strands 70′ of fibers 70 around the liner 16 in overlapping helical patterns to form one or more layers of wrapped fiber 70A, as illustrated in FIG. 3A. The fiber strands 70′ can be coated with liquid resin 72 prior to being wrapped on the liner 16, as shown in FIG. 3A. Alternatively, the fiber strands 70′ can be coated with liquid resin 72 after being wrapped on the liner 16 and/or the fiber 70 can be pre-impregnated with resin 72. Alternatively a plurality of fiber strands 70′ can be braided around the liner 16 to form a braided layer 70B of fiber 70, as illustrated in FIG. 4. Further, the fiber strands 70′ can be impregnated with liquid resin 72 prior to and/or after braiding the fibers strands 70′ around the liner 16.

[0047] The outer composite shell 34 shown in FIG. 2 includes one or more layers 70A, 70B, of fiber 70 coated in resin 72. Suitable fibers 70 for the outer composite shell 34 include one or more of carbon fiber, glass fiber, basalt fiber, boron fiber, aramid fiber, high-density polyethylene fiber (HDPE), Zylon™ poly(p-phenylene-2,6-benzobisoxazole fiber (PBO), aramid fiber, Kevlar® poly-paraphenylene terephthalamide fiber, polyethylene terephthalate fiber (PET), Nylon fiber (PA), polyethylene naphthalate (PEN), polyester fiber (PL), polypropylene fiber (PP), and polyethylene fiber (PE), and the like. A plurality of fiber filaments 70 are grouped to form a strand 70′ of fibers 70 prior to being disposed onto the liner 16. The fiber filaments 70 are defined by at least a material composition and a fiber outer diameter. Suitable resins 72 include one or more of epoxy resin, vinylester resin, thermoplastic resin, polyester resin, urethane, and the like. The selection of materials and dimensions for the liner 16, as well as the type and amount of resin 72 and fiber 70 forming the outer composite shell 34, are selected based in part on the desired operating conditions of the pressure vessel 10.

[0048] FIG. 5 illustrates one embodiment of the stem 44 prior to assembly with the liner 16. The stem 44 comprises a cylindrical boss 80 having a passageway 82 extending longitudinally through the cylindrical boss 80 through which gas 12 is inserted and removed from the interior space 18 of the liner 16. The cylindrical boss 80 is configured to be inserted into the inlet opening 36 in the liner 16, as shown in FIG. 2.

[0049] Referring to FIG. 5, the stem 44 includes a mounting ridge 92 that projects radially away from the cylindrical boss 80 and extends circumferentially around an outer peripheral surface 80′ of the stem 44. The mounting ridge 92 includes a generally vertical liner mounting surface 92A spaced apart from an opposing generally vertical mounting surface 92B with an outer periphery surface 92C extending between a distal end 94A of the liner mounting surface 92A and a distal end 94B of the opposing mounting surface 92B, as illustrated in FIG. 2.

[0050] A channel 100 extends circumferentially around the outer periphery surface 92C of the mounting ridge 92, as shown in FIGS. 2 and 5. The channel 100 is configured to matingly engage with a lip 106 extending circumferentially around an inner surface 120B of the ferrule 48, as shown in FIG. 2.

[0051] The exterior surface 80′ of the cylindrical boss 80 optionally includes retention features 110 such as angled teeth or ribs 110 projecting radially away from the exterior surface 80′, as shown in FIG. 5.

[0052] A plurality of spaced apart vent slots 112, as shown in the embodiment of FIG. 5, extend through the mounting ridge 92 between the liner mounting surface 92A and the opposing mounting surface 92B. The vent slots 112 comprise spaced apart opposing side walls 112A, 112B. Any number and configuration of vent slots 112, including axial holes, may be included in the stem 44 as desired for specific applications.

[0053] Referring to FIG. 2, the ferrule 48 fixedly couples the outer composite shell 34 to the stem 44. The ferrule 48 comprises a generally cylindrical hollow tube 120 having an outer surface 120A and an opposing inner surface 120B extending in a longitudinal direction. One embodiment of the ferrule 48, shown in FIG. 2, includes tooth-like projections 126 extending radially away from the inner surface 120B of the ferrule 48 configured to frictionally engage with the outer composite shell 34 of the pressure vessel 10. Also shown in FIG. 2, the ferrule 48 includes a lip 106 projecting radially inward from the inner surface 120B of the ferrule 48 and configured to matingly engage with the channel 100 in the mounting ridge 92 of the stem 44. Alternatively, the lip 106 of the ferrule 48 and/or the tooth-like projections 126 are formed during a crimping process to mechanically fasten the ferrule 48 to the outer composite shell 34 and to the stem 44.

[0054] The breather layer 30 surrounds the outer periphery 28 of the cylindrical wall 26 and extends between the first terminal end 38 and the second terminal end 38′ of the liner 16, as shown in FIG. 2. FIG. 6 shows a cut-away view of the pressure vessel 10 of FIG. 2 illustrating gas 14 permeating through the liner 16 and into the breather layer 30. The breather layer 30 is gas permeable and provides a pathway 52 for gas 14 permeating through the liner 16. Gas 14 collected by the breather layer 30 is directed towards a predetermined exit location 64 on the pressure vessel 10. In the embodiment shown in FIG. 6, the breather layer 30 is also liquid impervious, as represented by arrow A. Thus, liquid resin 72 applied to the fibers 70 of the outer composite shell 34 will not be absorbed by the breather layer 30. Preventing absorption of resin 72 within the breather layer 30, and particularly preventing resin 72 intrusion between the breather layer 30 and the liner 16, maintains gas permeability of the breather layer 30.

[0055] One embodiment of the breather layer 30, shown in FIG. 6, comprises dry fiber 70C that has increased porosity over the fiber 70 forming the outer composite shell 34. Dry fiber 70C is fiber 70C that is not impregnated with resin 72. The breather layer 30 can be formed by wrapping one or more layers 70D of dry fiber strands 70C′ around the cylindrical wall 26 in overlapping helical patterns. An exemplary method of wrapping fiber strands 70C′ around a liner 16 is shown in FIG. 3B. Preferably, a plurality of dry fiber strands 70C′ are braided around the cylindrical wall 26 for elongated liners 16 to form a braided dry fiber layer 70E. An exemplary process of braiding fiber strands 70′, 70C′ around a liner 16 is illustrated in FIG. 4. Braiding a plurality of dry fiber strands 70C′ around the liner 16 allows the breather layer 30 to closely adhere to the outer surface 28 of the cylindrical wall 26 even when the liner 16 includes larger outer diameter sections 136A, smaller outer diameter sections 136B, and tapered sections 136C between the larger and smaller outer diameter sections 136A, 136B, as illustrated in FIG. 4. The breather layer 30 can include one or more layers 70E of dry fiber 70C.

[0056] The porosity of the breather layer 30 is related to the outer diameter 138, 138′ of the dry fibers 70C, as illustrated in FIGS. 7A and 7B. FIGS. 7A and 7B show cross-sectional views of a grouping of fibers 140, 140′ having larger outer diameters 138 and fibers 144, 144′ having smaller outer diameters 138′ respectively, of fiber type 70C. Empty space 148 between adjacent larger diameter fibers 140, 140′ is larger in FIG. 7A than empty space 148′ between adjacent smaller diameter fibers 144, 144′ in FIG. 7B. The porosity of the breather layer 30 is directly related to the amount of empty space 148, 148′ between adjacent fibers 140, 140′, 144, 144′ since the empty space 148, 148′ forms air channels 52 through the breather layer 30. Thus, the porosity of the breather layer 30 can be increased by selecting fibers 70C having larger outer diameters 138 than the outer diameter of fibers 70 incorporated into the outer composite shell 34.

[0057] For example, using glass fiber to form the breather layer 30 will improve the porosity of the breather layer 30 over carbon fiber if the outer diameter 138 of the glass fiber is larger than the outer diameter of the carbon fiber. Glass fiber is typically available in a range of about 3 μm to about 20 μm. In comparison, carbon fiber is typically available in a range of about 5 μm to about 10 μm. Thus, glass fiber having a diameter of about 18 μm would result in greater empty space 148, 148′ in the breather layer 30 than if carbon fiber having a diameter of about 7 μm was used to form the breather layer 30, as a non-limiting example.

[0058] In addition, selecting a fiber 70C having a non-circular cross-section can increase the empty space 148, 148′ in the breather layer 30 over a breather layer 30 comprising fibers 70C with a circular cross-section. While circular and non-circular fibers 70C are suitable for use in the breather layer 30, non-circular fibers 70C are preferred as higher porosities can be achieved than with circular fibers 70C. Optionally, fibers 70C originally aligned in a strand 70C′ can be mixed with an air nozzle immediately before a braiding process to increase the porosity within the fiber strand 70C′.

[0059] The breather layer 30 can include a plurality of layers of braided and/or wrapped dry fiber strands 70C′ as desired for a specific application. Suitable fibers 70C for the breather layer 30 include one or more of carbon fiber, glass fiber, basalt fiber, boron fiber, aramid fiber, high-density polyethylene fiber (HDPE), Zylon™ poly(p-phenylene-2,6-benzobisoxazole fiber (PBO), aramid fiber, Kevlar® poly-paraphenylene terephthalamide fiber, polyethylene terephthalate fiber (PET), polyethylene naphthalate (PEN), Nylon fiber (PA), polyester fiber (PL), polypropylene fiber (PP), polyethylene fiber (PE), and the like. These fibers 70C are available in a range of fiber diameters, fiber shapes, transverse compressive strength, various material compositions, cost, and weight. Selection of a fiber type 70C for the breather layer 30 is based in part, on the gas management requirements for the pressure vessel 10, material cost, material properties, thickness of the fiber layer, and the like. Preferably the selected fiber 70C of the breather layer 30 is different than the selected fiber 70 for the outer composite shell 34 in one or more of material composition, cross-sectional shape, and/or the outer diameter 138 of the fiber 70C. Selecting a fiber 70C for the breather layer 30 having a larger diameter than fiber 70 selected for the outer composite shell 34 will improve the porosity of the breather layer 30 over using the same fiber 70 for both the breather layer 30 and the outer composite shell 34.

[0060] FIG. 8 shows a cross-sectional view of the pressure vessel 10 having a breather layer 30 formed of dry fiber 70C between the liner 16 and the outer composite shell 34. At least a portion of the radial thickness 160 of the breather layer 30 is free of resin 72 along the outer surface 28 of the liner 16 in order to assure gas 14 flows through the breather layer 30.

[0061] Referring to FIG. 8, intrusion of liquid resin 72 into the breather layer 30 must be controlled when the breather layer 30 comprises one or more layers of dry fiber 70C applied to the liner 16. One method to restrict intrusion of liquid resin 72 into the breather layer 30 is to include one or more sacrificial layers 160′ of the breather layer 30 prior to applying the outer composite 34, formed by the fiber 70 and resin 72, to the liner 16. The sacrificial layer(s) 160′ absorbs the excess liquid resin 72 from the outer composite shell 34 and prevents the intrusion of liquid resin 72 in interior fiber layers 160 adjacent to the liner 16. It is preferable to include additional layers of the breather fiber 70C to form the sacrificial layer 160′ if the fiber 70C of the breather layer 30 is of a lower cost and/or lower weight than the fiber 70 of the composite 34.

[0062] Alternatively, the breather layer 30 can be covered by a resin barrier layer 170 to prevent liquid resin 72 intrusion into the breather layer 30, as illustrated in an embodiment of the pressure vessel 10 shown in FIG. 9.

[0063] Preferably, the resin barrier layer 170 comprises a resin barrier material 170′ that is liquid impermeable. Suitable resin barrier materials 170′ include one or more of linear low-density polyethylene (LLDPE), polysiloxane, polyurethane (PU), polytetrafluoroethylene (PTFE), Nylon, synthetic rubber, silicone, ethylene propylene diene terpolymer (EPDM), polyethylene (DPE), polypropylene (PP), polyvinyl chloride (PVC), acrylonitrile butadiene rubber (Nitrile), ethylene vinyl alcohol (EVOH), polyethylene terephthalate (PET), and the like. The resin barrier material 170′ can be a tape, a film, a sheet, a wrap, and/or molded rubber, as non-limiting examples. One preferred embodiment of a resin barrier material 170′ is a polymeric film 170′ wrapped around an outer periphery 30′ of the breather layer 30, as shown in FIG. 10. Wrapping a protective film 170′, such as polyethylene stretch wrap, around the outer periphery 30′ of the breather layer 30 will prevent liquid resin 72 from clogging the breather layer 30 during the curing process of the resin 72.

[0064] FIG. 11 shows a cut-away view of the pressure vessel 10 of FIG. 9 illustrating gas 14 permeation through the cylindrical wall 26, into the breather layer 30, and into the resin barrier layer 170. The breather layer 30 is gas permeable and provides a flow path 52 for gas 14 permeating through the cylindrical wall 26. Gas 14 collected by the breather layer 30 is directed towards a predetermined exit location 64 on the pressure vessel 10. In the embodiment shown in FIGS. 9 and 11, the resin barrier layer 170 is liquid impervious, as represented by arrow A, as well as being gas permeable. Thus, liquid resin 72 applied to the fibers 70 forming the outer composite shell 34 will not be absorbed by the breather layer 30 since the resin barrier layer 170 is liquid impervious. Preventing absorption of liquid resin 72 within the breather layer 30, and particularly preventing liquid resin 72 intrusion between the breather layer 30 and the cylindrical wall 26, maintains the gas permeability and porosity of the breather layer 30.

[0065] Alternatively, a non-structural metal layer 180, such as metal foil and/or metalized film, can be used in addition to the resin barrier layer 170 and the breather layer 30. As shown in FIG. 12A, a metal layer 180 can be inserted between the liner 16 and the breather layer 30, between the breather layer 30 and the resin barrier layer 170, and/or between the resin barrier layer 170 and the outer composite shell 34. Further, the non-structural metal layer 180 can be included when the pressure vessel 10 lacks a resin barrier layer 170. Metals have low permeability when compared to polymers. One or several layers of metalized film, such as aluminized Mylar (PET), can be placed around the constant outer diameter (OD) sections of the liner 16 before braiding fiber strands 70C of the breather layer 30 around the liner 16. This significantly slows down the absorption of gas 14, such as hydrogen, by the outer composite shell 34 in the covered areas. This reduces the overall amount of gas 14 absorbed in the outer composite shell 34, therefore mitigating liner 16 collapse. Optionally, metallized Mylar (PET) strips of approximately equal width to the fiber strands 70C and/or carbon fiber rows 70′ can be braided around the liner 16 providing the advantage of higher liner 16 coverage and process continuity compared to sheets applied discontinuously only on certain liner 16 sections.

[0066] Another embodiment of the breather layer 30 is shown in FIG. 12B wherein the breather layer 30 is formed of one more layers of wrapped glass fiber cloth 190 in place of the dry fiber 70C layer. The glass fiber cloth 190 can be woven or non-woven. A resin barrier layer 170 of protective film 170′, such as polyethylene stretch wrap, is wrapped around an outer periphery 30′ of the breather layer 30 to prevent liquid resin 72 from clogging the breather layer 30 during the curing process of the resin 72. Further, one or more non-structural metal layers 180, such as metal foil and/or metalized film, can be inserted between the liner 16 and the breather layer 30, between the breather layer 30 and the resin barrier layer 170, and/or between the resin barrier layer 170 and the outer composite shell 34, as shown in FIG. 12B.

[0067] FIG. 13 shows a cross-sectional view of another embodiment of the pressure vessel 10 of FIG. 1 wherein the breather layer 30 comprises a polymeric film 200. Preferably, the polymeric film 200 is gas permeable as well as liquid impermeable. Thus, the breather layer 30 can collect gas 14 permeating through the liner 16 and direct the gas 14 towards the predetermined exit location 64 on the pressure vessel 10. One preferred embodiment is a polymeric film 200 wrapped around the outer periphery 28 of the liner 16, such as shown in FIG. 14. The polymeric film 200 can be wrapped around constant outer diameter sections 136A, 136B and the tapered sections 136C of the liner 16 for conformable pressure vessels 10.

[0068] Suitable polymeric films 200 for the breather layer 30 include one or more of linear low-density polyethylene (LLDPE), polysiloxane, polyurethane (PU), polytetrafluoroethylene (PTFE), Nylon, synthetic rubber, silicone, ethylene propylene diene terpolymer (EPDM), polyethylene (DPE), polypropylene (PP), polyvinyl chloride (PVC), acrylonitrile butadiene rubber (Nitrile), polyethylene terephthalate (PET), and the like. The polymeric film 200 can be a tape, a film, a sheet, a wrap, and/or molded rubber, as non-limiting examples.

[0069] Permeate gas 14 collected by the breather layer 30 is vented to the atmosphere 60 through predetermined exit locations 64, such as illustrated in FIG. 15. FIG. 15 shows an enlarged cross-sectional view of portion 17 of the pressure vessel 10 of FIG. 2. The stem 44 includes one or more vent slots 112 extending between the liner mounting surface 92A and the opposing mounting surface 92B of the mounting ridge 92, as shown in FIGS. 3 and 15. When the ferrule 48 is crimped to the outer composite shell 34 and to the mounting ridge 92 of the stem 44, an axial hole 220 is formed in each vent slot 112. Permeate gas 14 collected by the breather layer 30 flows from the breather layer 30, through the axial hole 220 between the ferrule 48 and the mounting ridge 92, and is exhausted to the atmosphere 60. Permeate gas 14 flows from the breather layer 30 into the axial hole 220 when the breather layer 30 comprises dry fiber 70C and when the breather layer 30 comprises a polymer film 200. The amount of gas 14 passing through the axial holes 220 is dependent at least on the gas permeability and porosity of the breather layer 30 as well as the overall liner 16 length.

[0070] FIG. 16 illustrates the flow of permeate gas 14 through the axial hole 220 when the liner 16 is covered by a breather layer 30 and a resin barrier layer 170. Since both the breather layer 30 and the resin barrier layer 170 are gas permeable, gas 14 flows from both the breather layer 30 and the resin barrier layer 170 into the axial hole 220 through the mounting ridge 92 and exhausted to the atmosphere 60.

[0071] A second embodiment of venting the breather layer 30 to atmosphere 60 is shown in FIGS. 17 and 18, wherein the permeate gas 14 passes through a crimp joint 240 between the ferrule 48 and the stem 44. FIG. 17 illustrates a pressure vessel 10 having a breather layer 30 between the liner 16 and the outer composite 34. The pressure vessel 10 of FIG. 17 includes a stem 44 inserted into an opening 36 in the liner 16 and a ferrule 48 fixedly coupling the outer composite shell 34 to the stem 44. However, the stem 44 of FIG. 17 lacks vent slots 112 in the mounting ridge 92 shown in FIG. 2. The crimp joint 240 of the ferrule 48 is configured to convey gas 14 under the ferrule 48 and out to the atmosphere 60. Permeate gas 14 flows from the breather layer 30, through the crimp joint 240 between the ferrule 48 and the stem 44, and out to the atmosphere 60, as illustrated in FIG. 18.

[0072] FIG. 19 illustrates an embodiment of a pressure vessel 10 having a breather layer 30 and a resin barrier layer 170 between the liner 16 and the outer composite shell 34, as well as having the stem 44 and ferrule 48 shown in FIG. 17. Permeate gas 14 flowing along the breather layer 30 and the resin barrier layer 170 passes through the crimp joint 240 between the ferrule 48 and the stem 44, and out to the atmosphere 60, as illustrated in FIG. 20.

[0073] Another way of mitigating the gas pressure increase in the gap 54 between the liner 16 and the outer composite shell 34, and therefore preventing a subsequent collapse of the liner 16, is to provide venting holes 250, 260 through the outer composite shell 34, as shown in FIG. 21. The one or more venting holes 250, 260 fluidically connect the breather layer 30 through the outer composite shell 34 to the atmosphere 60.

[0074] The pressure vessel 10 can include one or more venting holes 250, 260 in the outer composite shell 34 near a terminal end 68 of the pressure vessel 10. Optionally, the pressure vessel 10 can include an array of venting holes 250 distributed along the entirety of the pressure vessel 10 and/or along selected longitudinal sections of the pressure vessel 10. An array of venting holes 250 in the outer composite shell 34 can be created by inserting needles into the outer composite shell 34 after braiding, but before curing of the resin 72. The needles are removed from the outer composite shell 34 after the resin 72 is cured. The diameter, number, and position of the venting holes 250, 260 are selected based on the amount of venting required to mitigate the gas pressure in the gap 54 between the liner 16 and the outer composite shell 34.

[0075] FIG. 22 illustrates the flow of gas 14 from an interior space 18 of the liner 16, through the liner wall 26, into the breather layer 30, through the venting holes 250 in the outer composite shell 34, and exhausted to the atmosphere 60. Permeate gas 14 also flows along the optional resin barrier layer 170 to the venting holes 250 if the resin barrier layer 170 is gas permeable. An array of venting holes 250 in the outer composite shell 34 may provide sufficient mitigation of gas pressure in the gap 54 between the liner 16 and the outer composite shell 34 such that a breather layer 30 is not required. In this case, the array of venting holes 250 drains gas 14 from the gap 54 between the liner 16 and the outer composite shell 34. The diameter, spacing, and number of the venting holes 250, 260 through the outer composite shell 34 is selected based in part on the amount of gas 14 that is to be vented to the atmosphere 60.

[0076] Gas 14 is similarly exhausted to atmosphere 60 when the venting holes 260 pass through both the outer composite shell 34 and the ferrule 48, as shown in FIGS. 21 and 23. Referring to FIGS. 21 and 23, one or more venting holes 260 may extend through the ferrule 48 and through the outer composite shell 34 to the breather layer 30. To prevent interference with the sealing and mechanical grip features 126 of the crimped ferrule 48, the one or more drilled venting holes 260 would be located beyond these features 126 near the terminal end 68 of the pressure vessel 10. This way, the abilities of the ferrule 48 to contain gas 14 and secure the outer composite shell 34 to the stem 44 are not affected by the one or more venting holes 260 through the ferrule 48. Additionally, the ferrule 48 is designed such that the presence of the venting hole(s) 260 does not degrade its structural integrity to an unacceptable extent. The breather layer 30 must continue to operate as expected under the pressure of the crimped ferrule 48, i.e., air channels 52, 148 in the breather layer 30 to convey gas 14 must remain open. If the ability of the breather layer 30 to maintain porosity under crimp pressure is of concern, additional porous material (such as sintered metal inserts, more fibers, glass beads) may be installed between the liner 16 and the outer composite shell 34 to ensure gas 14 flow.

[0077] One benefit of a pressure vessel 10 having improved porosity of a breather layer 30 over the porosity of a helically wrapped dry fiber layer of the same fiber as used for the outer composite shell 34 is improved permeate gas 14 management. A second benefit is a breather layer 30 that can be disposed onto a liner 16 having larger outer diameter sections 136A spaced apart by smaller diameter sections 136B as in certain conformable pressure vessels 10. A third benefit is preservation of the porosity of the breather layer 30 by preventing intrusion of liquid resin 72 into the breather layer 30 and preventing intrusion of liquid resin 72 between the breather layer 30 and the liner 16. A fourth benefit is a breather layer 30 that is both gas permeable and liquid impermeable such that the breather layer 30 prevents resin 72 intrusion between the breather layer 30 and the liner 16 while also allowing gas 14 permeation along the breather layer 30 to a predetermined exit location 64 on the pressure vessel 10.

The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.