Vented fitting for pressure vessel boss

An apparatus is configured to be positioned between a boss and a shell of a pressure vessel. The boss includes a bore therethrough, and the bore has a longitudinal axis. The apparatus includes an annular body and a gas permeable feature. The annular body includes an inner surface configured to abut the boss and an outer surface configured to abut the shell. The annular body has opposite first and second ends relative to the longitudinal axis. The gas permeable feature is provided on the inner surface and extends at least from the first end to the second end. The disclosure also describes a pressure vessel including a shell, and boss, and an apparatus positioned between the boss and the shell. A method for forming a pressure vessel includes mounting a boss on a mandrel, positioning an annular fitting about a neck of the boss, forming a liner, and forming an outer shell.

BACKGROUND

Pressure vessels are commonly used for containing a variety of fluids under pressure, such as hydrogen, oxygen, natural gas, nitrogen, propane, methane and other fuels, for example. Generally, pressure vessels can be of any size or configuration. The vessels can be heavy or light, single-use (e.g., disposable), reusable, subjected to high pressures (greater than 50 psi, for example), low pressures (less than 50 psi, for example), or used for storing fluids at elevated or cryogenic temperatures, for example.

Suitable pressure vessel shell materials include metals, such as steel; or composites, which may include laminated layers of wound fiberglass filaments or other synthetic filaments bonded together by a thermal-setting or thermoplastic resin. The fiber may be fiberglass, aramid, carbon, graphite, or any other generally known fibrous reinforcing material. The resin material used may be epoxy, polyester, vinyl ester, thermoplastic, or any other suitable resinous material capable of providing fiber-to-fiber bonding, fiber layer-to-layer bonding, and the fragmentation resistance required for the particular application in which the vessel is to be used. The composite construction of the vessels provides numerous advantages, including lightness in weight and resistance to corrosion, fatigue and catastrophic failure. These attributes are due at least in part to the high specific strengths of the reinforcing fibers or filaments.

A polymeric or other non-metallic resilient liner or bladder is often disposed within a composite shell to seal the vessel and prevent internal fluids from contacting the composite material. The liner can be manufactured by compression molding, blow molding, injection molding, or any other generally known technique. Alternatively, the liner can be made of other materials, including steel, aluminum, nickel, titanium, platinum, gold, silver, stainless steel, and any alloys thereof. Such materials can be generally characterized as having a high modulus of elasticity. In one embodiment, the liner20is formed of blow molded high density polyethylene (HDPE).

FIG. 1illustrates an elongated pressure vessel10, such as that disclosed in U.S. Pat. No. 5,476,189, entitled “Pressure vessel with damage mitigating system,” which is hereby incorporated by reference. Vessel10has a main body section12and substantially hemispherical or dome-shaped end sections14. A boss16, typically constructed of aluminum, is provided at one or both ends of the vessel10to provide a port for communicating with the interior of the vessel10. As shown inFIG. 2, vessel10is formed with an inner polymer liner20covered by an outer composite shell18. The composite shell18resolves structural loads on the vessel10.

FIG. 2illustrates a partial cross-sectional view, taken along line2-2ofFIG. 1, of a typical end section14including boss16, such as that disclosed in U.S. Pat. No. 5,429,845, entitled “Boss for a filament wound pressure vessel,” which is hereby incorporated by reference. The boss16typically has a neck22, a port26allowing fluid communication with the interior of vessel10, and an annular flange24extending radially from port26. Boss16is fit to outer shell18and liner20such that port26extends between the interior and exterior of pressure vessel10. Typically, shell18abuts neck22. Generally, flange24is contained between portions of liner20and/or is sandwiched between the liner20and the shell18. In certain embodiments, flange24may include at least one annular groove32shaped to accept corresponding annular tab(s)34on liner20. This construction secures the boss16to the vessel10and provides a seal at the interfaces between the boss16, shell18, and liner20.

A method of forming a pressure vessel10includes mounting a boss on a mandrel and allowing a fluid polymer material for liner20to flow around flange24and into groove32of boss16. The liner material then solidifies, thereby forming a portions of liner20adjacent to flange24and tab34received within groove32. Liner20is thereby mechanically interlocked with boss16. Accordingly, even under extreme pressure conditions, separation of liner20from boss16is prevented.

In an exemplary embodiment, outer shell18is formed from wound fibers and surrounds the liner20and at least a portion of flange24of boss16. In an exemplary method, a dispensing head for the fibers moves in such a way as to wrap the fiber on the liner20in a desired pattern. If the vessel10is cylindrical, rather than spherical, fiber winding is normally applied in both a substantially longitudinal (helical) and circumferential (hoop) wrap pattern. This winding process is defined by a number of factors, such as resin content, fiber configuration, winding tension, and the pattern of the wrap in relation to the axis of the liner20. Details relevant to the formation of an exemplary pressure vessel are disclosed in U.S. Pat. No. 4,838,971, entitled “Filament Winding Process and Apparatus,” which is incorporated herein by reference.

Although the liner20provides a gas barrier under typical operating conditions, the design of a pressure vessel10of this type produces a phenomenon wherein gas diffuses into the liner20under pressurization of vessel10. When depressurization of the vessel10occurs, this gas diffuses out of the liner20, and in some cases into the space between the liner20and the shell18. A pocket of gas may be formed, causing the liner20to bulge slightly inward and possibly become stretched. Moreover, gas at the interface between the liner20and the shell18can promote undesirable separation between the liner20and shell18. Additionally, upon re-pressurization, the gas trapped between liner20and shell18may be expelled abruptly through microcracks in shell18that form at high pressures. The relatively sudden expulsion of gas can set off leak detectors, when, in actuality, pressure vessel10exhibits no steady leak.

SUMMARY

In one aspect, an apparatus is configured to be positioned between a boss and a shell of a pressure vessel. The boss includes a bore therethrough, and the bore has a longitudinal axis. The apparatus includes an annular body and a gas permeable feature. The annular body includes an inner surface configured to abut the boss and an outer surface configured to abut the shell. The annular body has opposite first and second ends relative to the longitudinal axis. The gas permeable feature is provided on the inner surface and extends at least from the first end to the second end.

In another aspect, a pressure vessel includes a shell, and boss, and an apparatus positioned between the boss and the shell. The boss includes a bore therethrough, and the bore has a longitudinal axis. The apparatus includes an annular body and a gas permeable feature. The annular body includes an inner surface configured to abut the boss and an outer surface configured to abut the shell. The annular body has opposite first and second ends relative to the longitudinal axis. The gas permeable feature is provided on the inner surface and extends from the first end to the second end.

In another aspect, a method for forming a pressure vessel includes mounting a boss on a mandrel. The boss has a neck, the neck having a bore with a longitudinal axis. The boss has a flange that extends radially outwardly from the bore. The method includes positioning an annular fitting about the neck of the boss. The fitting includes opposite first and second ends relative to the longitudinal axis. The method includes forming the liner of the pressure vessel on at least a portion of the flange. The outer shell is formed to surround the liner, the flange, and the fitting. The method is performed so that a gas permeable feature extends at least from the first end to the second end.

This disclosure, in its various combinations, either in apparatus or method form, may also be characterized by the following listing of items:1. An apparatus configured to be positioned between a boss and a shell of a pressure vessel, the boss including a bore therethrough, and the bore having a longitudinal axis, the apparatus including:an annular body including an inner surface configured to abut the boss and an outer surface configured to abut the shell, wherein the annular body has opposite first and second ends relative to the longitudinal axis; anda gas permeable feature provided on the inner surface and extending at least from the first end to the second end.2. The apparatus of item 1, wherein the gas permeable feature includes a plurality of channels.3. The apparatus of item 2, wherein at least one of the plurality of channels is substantially aligned with the longitudinal axis.4. The apparatus of any of items 2-3, wherein at least some of the plurality of channels are substantially evenly circumferentially spaced about the inner surface.5. The apparatus of any of items 2-4, wherein at least one of the plurality of channels has a substantially rectangular cross-sectional profile.6. The apparatus of any of items 1-5, wherein the annular body includes a neck and a flange that extends radially from the neck.7. A pressure vessel including:a shell;a boss including a bore therethrough, the bore having a longitudinal axis;an apparatus positioned between the boss and the shell, the apparatus including:an annular body including an inner surface configured to abut the boss and an outer surface configured to abut the shell, wherein the annular body has opposite first and second ends relative to the longitudinal axis; anda gas permeable feature provided on the inner surface and extending at least from the first end to the second end.8. The pressure vessel of item 7 wherein the pressure vessel includes a liner disposed within the shell to form an interface between the liner and the shell, and wherein the gas permeable feature is in fluid communication with the interface at the first end and with an exterior of the vessel at the second end.9. The pressure vessel of any of items 7-8 wherein the gas permeable feature includes a plurality of channels.10. The pressure vessel of item 9, wherein at least one of the plurality of channels is substantially aligned with the longitudinal axis.11. The pressure vessel of any of items 9-10, wherein at least some of the plurality of channels are substantially evenly circumferentially spaced about the inner surface.12. The pressure vessel of any of items 7-11, wherein the annular body includes a neck and a flange that extends radially from the neck.13. A method for forming a pressure vessel including:mounting a boss on a mandrel, the boss having a neck, the neck having a bore with a longitudinal axis, and the boss having a flange extending radially outwardly from the bore;positioning an annular fitting about the neck of the boss, the fitting including opposite first and second ends relative to the longitudinal axis;forming a liner of the pressure vessel on at least a portion of the flange; andforming an outer shell surrounding the liner, the flange, and the fitting;wherein a gas permeable features extends at least from the first end to the second end.14. The method of item 13, wherein positioning the annular fitting about the neck of the boss occurs before forming the liner.15. The method of any of items 13-14, wherein positioning the annular fitting about the neck of the boss occurs after forming the liner.16. The method of any of items 13-15, wherein forming the liner includes disposing a non-metallic material around the mandrel and at least the portion of the flange.17. The method of any of items 13-16, further including positioning the gas permeable feature on the liner before positioning the annular fitting about the neck of the boss.

This summary is provided to introduce concepts in simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the disclosed or claimed subject matter and is not intended to describe each disclosed embodiment or every implementation of the disclosed or claimed subject matter. Specifically, features disclosed herein with respect to one embodiment may be equally applicable to another. Further, this summary is not intended to be used as an aid in determining the scope of the claimed subject matter. Many other novel advantages, features, and relationships will become apparent as this description proceeds. The figures and the description that follow more particularly exemplify illustrative embodiments.

While the above-identified figures set forth one or more embodiments of the disclosed subject matter, other embodiments are also contemplated, as noted in the disclosure. In all cases, this disclosure presents the disclosed subject matter by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope of the principles of this disclosure.

The figures may not be drawn to scale. In particular, some features may be enlarged relative to other features for clarity. Moreover, where terms such as above, below, over, under, top, bottom, side, right, left, etc., are used, it is to be understood that they are used only for ease of understanding the description. It is contemplated that structures may be oriented otherwise.

DETAILED DESCRIPTION

The present disclosure describes a fluid venting structure for use in a pressure vessel that prevents separation of the liner from the shell under pressure. The disclosed apparatus allows venting of gas trapped between the liner and the shell. This disclosure relates, in one aspect, to a fitting28, provided in the form of a sleeve in an exemplary embodiment, that is placed over portions of a boss16of a pressure vessel10. Fitting28has features to allow gas that accumulates between liner20and shell18to vent to the atmosphere outside of pressure vessel10. For example, as shown inFIGS. 3 and 6, channels30on fitting28provide paths through which gas may vent from an interface56between shell18and liner20to the environment exterior to pressure vessel10. Thus, potential damage to liner20and unwanted venting through shell18can be reduced or prevented.

FIG. 3shows exemplary embodiments of a boss16and an annular fitting28. Boss16includes neck22having a port or bore26that allows fluid communication between an interior I of pressure vessel10′ and an environment E exterior to pressure vessel10′ (seeFIG. 5). Port26has longitudinal axis36. Boss16typically has an annular flange24extending radially outwardly from port26and configured to attach to a liner20. In an exemplary embodiment, flange24has an annular groove32to accept a complementary annular tab34in liner20, as shown inFIG. 5. Mechanical inter-locks (i.e., elements that are structurally inhibited from separation) are shown, but it is contemplated that other methods of mechanically, frictionally, or chemically (e.g., by the use of adhesives) securing liner20to boss16may be used. It is noted that, in an exemplary embodiment, a portion35of liner20extends over the external surface of flange24to aid in connecting liner20and boss16.

In an exemplary embodiment, fitting28has a generally annular body. In this description, the term “annular” is not strictly ring-shaped, but more broadly describes a body that has a through-passage40between opposite ends42and44. The body may have a generally radially symmetrical shape about longitudinal axis36. The body may follow the contours of underlying boss16and/or liner20. In the illustrated embodiments, a gas permeable feature on (i.e., on, in, or adjacent to) inner surface38is provided in the form of one or more channels (such as interior vent channels30) on or through fitting28to fluidly connect the interface56between shell20and liner18to the environment exterior to vessel10′, via vent path54, shown in exemplary embodiments inFIGS. 6 and 8. Fitting28thereby prevents fluid that has permeated through liner20and into the interface56from becoming trapped. Fitting28may be formed of a metallic or non-metallic material. For metallic materials, such as, for example, aluminum or steel, formation of fitting28by machining is especially suitable. For a non-metallic material, such as, for example, a polymer or composite material, formation of fitting28by injection molding is especially suitable. However, other known methods of part formation can also be used.

In an exemplary embodiment, fitting28is configured as a sleeve that has a neck29and a flange31that extends radially outward from neck29. While only half of fitting28is shown, it is to be understood that the other half may be a mirror image of the illustrated half. Curved inner surface38of fitting28defines opening40and includes vent channels30that extend from end42of flange31to end44of neck29. In an exemplary embodiment, a gas permeable feature includes channels30, which are evenly spaced about the circumference of opening40, have a substantially rectangular cross-sectional profile, and follow substantially straight paths (e.g., substantially aligned with longitudinal axis36) on the curved inner surface38between end42and end44. However, other gas permeable features including different channel configurations, vent structures, or mechanisms are contemplated. For example, inner surface38may include more or fewer channels and/or channels of various depths, widths, or shapes (e.g., curved channels and/or channels with generally hemispherical, elliptical or rounded cross-sectional shapes). Moreover, inner surface38may be at least partly formed of—or coated with—a gas-permeable material, and/or may include raised portions or bumps between which gas may flow from end42to end44. In yet another embodiments, a gas permeable feature may include a layer of gas-permeable material provided on inner surface38and/or between inner surface38and an outer surface of boss16.

In still another embodiment, a gas permeable feature may include longitudinal vents provided on an outer surface of liner20and/or boss16, such as the longitudinal vents described in U.S. Patent Application Publication No. US 2012/0048865, entitled “Pressure Vessel Longitudinal Vents,” which is hereby incorporated by reference in its entirety. Where the gas permeable feature is a longitudinal vent, a strip of a vent defining element is applied to an exterior surface of the liner20. Suitable vent defining elements include, for example, a wire; fiber glass strands; open weave fiber glass tape; polyethylene; nylon release cloth; or a folded or unfolded strip of other textile or film. Fitting28in an exemplary embodiment is provided over and covers the vent defining element, so that the gas permeable feature is on (i.e., adjacent) inner surface38of fitting28. Where the vent defining element may be a textile that has “wicking” properties (such as, for example, a glass cloth material), the gas permeable features are thereby protected by fitting28from resin infusion during subsequent formation of the composite shell18by resin and filament winding. Thus, fitting28prevents clogging of the porous characteristics of the gas permeable feature. A gas permeable feature may include either, or a combination of, channels and gas permeable materials in, on, or adjacent to inner surface38of fitting28. Moreover, a gas permeable feature may extend beyond either end42or44of fitting28.

In certain embodiments, the fitting28may not be completely annular, but instead may fit over one or more portions of the circumference of neck22instead of encircling the entirety of neck22. In some embodiments, fitting28may be longer than illustrated, so that end42extends beyond flange24of boss16. In such cases, fitting28may be fit around boss16and a portion of liner20after the formation of liner20on boss16. Fitting28may even extend beyond domed end section14of pressure vessel10to main body section12. Moreover, end42may taper in thickness. The venting mechanism may depend on the desired application, so long as fitting28allows for a gas-flow path from at least a portion of the interface56between liner20and shell18to the environment E external to pressure vessel10′.

As shown inFIG. 4, an assembly48includes fitting28and boss16. Neck22of boss16is inserted into opening40of fitting28such that neck29of fitting28fits over at least a portion of neck22of boss16. Flange31of fitting28fits over at least a portion of flange24of boss16and optionally over a portion of liner20. Inner surface38is contoured to substantially complement an outer contour of boss16, including at least portions of neck22and flange24, and optionally a portion of liner20. An interference fit, complementary snap lock features, adhesive in tape or other form, or other means can be provided on fitting28and boss16and/or liner20to prevent unintentional separation.

FIGS. 5 and 6show an exemplary embodiment of assembly48on end section14of pressure vessel10′. In an exemplary embodiment, to form pressure vessel10′, boss16is inserted into fitting28and mounted on a mandrel that is configured to define the shape of pressure vessel10′. Fluid polymer (or other non-metallic) liner material is allowed to flow over the mandrel and about a portion of flange24so that liner material20fills groove32and abuts end42of fitting28. In an exemplary embodiment of fitting28′, as shown inFIG. 7, channels30′ extend onto end42and liner material is allowed to flow over flange31in such a way that liner material does not enter or plug channels30′. The polymer material solidifies to form liner20.

In another method of pressure vessel formation, liner20is formed on a mandrel-mounted boss16without fitting28. Gas permeable features such as longitudinal vent defining elements are placed on liner20. Then fitting28is attached around boss16, at least a portion of the gas permeable features, and optionally a portion of liner20. The gas permeable features are thereby sandwiched between an outer surface of boss16and an inner surface38of fitting28.

As shown inFIG. 6, in an exemplary embodiment, inner surface38of fitting28abuts boss16in a manner that allows for gas venting through channels30, which are in fluid communication with the interface56between liner20and shell18. In an exemplary embodiment, neck29of fitting28is tapered from end44radially inward (as at58) to provide a recess for shell18that prevents axial movement (such as along longitudinal axis36) of shell18relative to assembly48. In the illustrated embodiment, end44of fitting28and the adjacent gas permeable features (e.g., ends of channels30), are exposed to the atmospheric environment exterior to pressure vessel10′ (e.g., at E ofFIGS. 5, 6 and 8).

In the exemplary embodiment shown inFIG. 6, a pocket of gas50is trapped at an interface56between shell18and liner20, causing a deformation52of liner20. As shown by path54, following a path of least resistance, gas50travels from deformation52along the interface56between liner20and shell18to end42of fitting28. The gas enters channels30at end42and travels through channels30to end44, where the gas50vents from channels30to the environment E external to pressure vessel10′. Deformation52is shown to be a bulge or bubble in liner20near end section14′, but is shown as such merely for discussion purposes. Different amounts of gas50may exist anywhere in the interface56between liner20and shell18. Moreover, the size of deformation52is greatly exaggerated for illustration purposes; it should be understood that in reality, the provision of fitting28on boss16allows for venting that prevents the formation of such deformations52.

FIG. 8is a partial radial cross-sectional view of an end section of a pressure vessel10″ including a third exemplary embodiment of a vented fitting28″. In this embodiment, the radial extent of flange31″ of fitting28″ is substantially equal to the radial extent of flange24of boss16. Moreover, end42″ of fitting28″ is tapered, thereby providing a smoother vent path54″ between deformation52and end44of fitting28″ that is exposed to the atmosphere outside of pressure vessel10″.

Although the subject of this disclosure has been described with reference to several embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the disclosure. In addition, any feature disclosed with respect to one embodiment may be incorporated in another embodiment, and vice-versa.