GB2537828A

GB2537828A - Gas-tight metal-composite interface

Info

Publication number: GB2537828A
Application number: GB1506946.1A
Authority: GB
Inventors: E Spencer Brian; Spencer Zachary
Original assignee: Blue Wave Co SA
Current assignee: Blue Wave Co SA
Priority date: 2015-04-23
Filing date: 2015-04-23
Publication date: 2016-11-02
Also published as: EP3286486A1; WO2016170192A1; GB201506946D0

Abstract

A method of forming a gas-tight metal-composite interface at a boss for compressed gas systems has metal and composite portions of a compressed gas system with respective flanges 701,710. The flanges are pressed against one another using a collar 14 or other clamping device. The collar may comprise at least two part-annular, generally C-shaped in cross section segments having proximal and distal damping arms. The flanges and clamping arms may be chamfered so that pressing the arms against the flanges results into compression of ends of the metal and composite portions which form the gas-tight metal-composite interface. The collar may be secured by welding, or by using threaded connections. Such gas-tight metal-composite interfaces are particularly suitable to marine CNG applications.

Description

GAS-TIGHT METAL-COMPOSITE INTERFACE

Brian E. Spencer, Ph.D. Zachary B. Spencer

FIELD

This invention relates to a gas-tight metal-composite interface for compressed gas systems comprising metal and composite portions that must be joined in a gas-tight manner. A compressed gas system having one or more of these interfaces is particularly suitable for containment and transport of compressed gasses, particularly compressed natural gas (CNG), particularly in the cargo holds of marine transport vessels.

BACKGROUND

Among fossil fuels, natural gas is the cleanest burning and therefore a clear choice for energy production. There is, therefore, a movement afoot to supplement or supplant, as much as possible, other fossil fuels such as coal and petroleum with natural gas as the world becomes more conscious of the environmental repercussions of burning fossil fuels. Unfortunately, much of the world's natural gas deposits exist in remote, difficult to access regions of the planet. Terrain and geopolitical factors render it extremely difficult to reliably and economically extract natural gas from these regions and to use pipelines and overland transport to deliver the extracted natural gas to its ultimate destination. Interestingly, a large portion of the earth's remote natural gas reserves is located in relatively close proximity to the oceans and other bodies of water having ready access to the oceans. Thus, marine transport of natural gas from these remote locations is attractive. The problem with marine transport of natural gas lies largely in the economics. Ocean-going vessels can carry just so much laden weight and the cost of shipping by sea reflects this fact, the cost being calculated on the total weight being shipped, that is, the weight of the product plus the weight of the containment system in which the product is being shipped. If the net weight of the product is low compared to the tare weight of the containment system, the cost of shipping per unit mass of product becomes prohibitive. This is particularly true of the transport of compressed gasses, which conventionally are transported in all-metal cylinders capped with metal domes (type I pressure vessels), the resulting pressure vessels being extremely heavy compared to the weight of the contained gas. A problem is how to reduce the weight of type I pressure vessels while maintaining their currently approved features, so as to avoid or substantially reduce the usually lengthy approval process associated with introduction of entirely new types of lighter pressure vessels. A solution to this problem lies in the use of composite end domes and/or composite end bosses. Such composite end domes and bosses are respectively described in PCT patent applications number PCT/EP2011/071813 and PCT/2011/071810, the contents of which is herein fully incorporated by way of reference, and can provide substantial savings in terms of pressure vessel weight.

A problem, however, arises with the use of composite components, in that it may be presently undesired or forbidden to have threaded connections in any part of a pressure vessel contained in the cargo hold of a transport ship for transporting compressed gasses. Under current practices, welding metallic pressure vessel to metallic piping parts solves the problem. Composites, however, cannot be welded to metal.

Composites may show an undesired degree of permeability to gases, and particularly to compressed gases. With the introduction of light composite parts in pressure vessels, it may therefore be necessary to provide a barrier to impermeably contain the compressed gas. This barrier is usually provided in the form of a pressure vessel liner. Depending on the design of the lined pressure vessel, there may be a mechanical discontinuity between the liner and the pressure vessel's structural material which may become exposed to pressure. This discontinuity may represent a point of weakness for lined pressure vessels, both in terms of mechanical strength and impermeability. It is therefore desirable to prevent any such mechanical discontinuities from becoming exposed to high levels of pressure, by isolating them from the compressed gas, while maintaining design simplicity.

It is an object of the present invention to solve, or at least mitigate, at least one of the aforementioned problems in light of the drawbacks associated with the prior art.

The invention provides a method of forming a gas-tight metal-composite interface 5 for use in compressed gas systems including those intended for marine transportation of compressed gases such as CNG. Compressed gas systems comprising one or more gas-tight metal-composite interfaces formed in accordance with one or more of the methods disclosed herein are also an aspect of the invention. In addition, marine transport vessels comprising one or more gas-tight metal-composite interfaces formed 10 in accordance with one or more of the methods disclosed herein are also an aspect of the invention.

In some applications, threaded connections may not be undesired or forbidden. Gas-tight metal-composite interfaces formed in accordance with one or more of the methods disclosed herein may however still be desired due to the dramatic effect of substituting metallic parts with lighter composite parts on the weight of the containment system. In these cases, gas-tight metal-composite interfaces formed in accordance with one or more of the methods disclosed herein, but with added one or more threaded fittings, may be used to either provide the primary measure of gas tightness as described hereinbelow, or to provide a secondary measure of assurance that the interface is gas-tight.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a method of forming a gas-tight metal-composite interface for compressed gas systems. We provide a hollow metal portion of a compressed gas system, the metal portion having a metal flange at or near an end of the metal portion, the metal flange comprising a metal flange chamfered surface. We also provide a hollow composite portion of the compressed gas system, the composite portion having a composite flange at or near an end of the composite portion, the composite flange comprising a composite flange chamfered surface. We also provide a collar for pressing the metal and composite flanges towards each other. The collar comprises at least two part-annular, generally C-shaped in cross section segments. Each segment comprises proximal and distal clamping arms. The clamping arms define the generally C-shaped profile of the cross section of the collar. The proximal arms comprise each a proximal arm chamfered surface. The proximal arm chamfered surfaces are each chamfered as a mirror image with respect to the metal flange chamfered surface. The distal arms comprise each a distal arm chamfered surface. The distal arm chamfered surfaces are each chamfered as a mirror image with respect to the composite flange chamfered surface. A distance between the proximal and distal arm chamfered surfaces is less than a corresponding distance measured between the metal and composite flange chamfered surfaces when the ends of the metal and composite portions are contiguous. The end of the metal portion is then placed contiguous to the end of the composite portion. The C-shaped segments are then pressed onto the metal and composite flanges. The collar is formed by mechanically securing at least a pair of the C-shaped segments together, to form the gas-tight metal-composite interface between the two contiguous ends, i.e. the end of the metal portion and the end of the composite portion.

The hollow metal portion and/or the hollow composite portion may have a generally cylindrical configuration, a cylindrical configuration, or a configuration according to a hollow solid of revolution with respect to an axis passing through the hollow metal and composite portions.

The collar may have an interrupted annular configuration (i.e. gaps between consecutive segments may be present) or a full, i.e. continuous or uninterrupted, annular configuration (i.e. without such gaps).

The C-shaped segments may be pressed onto the metal and composite flanges until adjacent segment end surfaces meet, or are disposed in closer proximity to each other.

Forming the collar by mechanically securing together at least a pair of the C-shaped segments may comprise welding together at least two end surfaces of respective adjacent or contiguous C-shaped segments.

Alternatively and/or additionally, forming the collar by mechanically securing together at least a pair of the C-shaped segments may comprise securing at least one threaded fitting. The threaded fitting may comprise two aligned through holes, each formed on a respective C-shaped segment, and a bolt cooperating with these through holes.

The gas-tight metal-composite interface may be formed by, at or between opposing surfaces provided at or near the metal and composite portion ends.

The gas-fight metal-composite interface may be formed by, or comprise, a 15 mechanical seal disposed between the ends of the metal and composite portions. The mechanical seal may be an 0-ring. The 0-ring may be made of a metallic or elastomeric material.

The compressed gas system may comprise a pressure vessel having a composite boss, the composite boss comprising said composite portion. The pressure vessel may be lined, i.e. it may comprise a pressure vessel liner. The composite boss may be internally lined with the liner. The liner may be folded to extend between the ends of the metal and composite portions. The metal portion may comprise, or be provided as part of, a pipe, through which compressed gas can be loaded into and unloaded from the pressure vessel.

The metal portion may comprise a gas transfer appendix, or projection, for insertion into an inlet of the pressure vessel. Said pressure vessel inlet may be formed through the composite boss. The gas transfer appendix/projection may comprise an outer surface configured to form the gas-tight metal-composite interface in cooperation with an inner surface of the composite boss, or with the liner, if a liner lines the composite boss.

In preferred embodiments, the gas-tight metal-composite interface isolates a mechanical discontinuity present between the material of which the composite boss is made and the material of which the liner is made from the compressed gas stored in the pressure vessel. In other words, the gas-tight metal-composite interface is responsible for protecting the discontinuity from exposure to pressure.

The outer surface of the fluid transfer appendix or projection and the inner surface of the pressure vessel's inlet, which inner surface may be lined, may have cooperating frusto-conical profiles. In use, the profile of the appendix or projection may be press-fitted to (i.e. forced or compressed against) the profile of the inner surface of the composite boss. The frusto-conical profiles may be fully or partially mating.

The mechanical seal may be disposed around the outer surface of the fluid transfer appendix or projection. The mechanical seal may be disposed at or near an edge of the fluid transfer appendix or projection. Said edge may be inserted into the pressure vessel's inlet to couple the fluid transfer appendix or projection to the pressure vessel.

The mechanical seal may be configured to increase its sealing action in response to an increase of pressure in the pressure vessel According to another aspect of the invention, there is provided a method of forming a gas-tight metal-composite interface for compressed gas systems. We provide a hollow metal portion of a compressed gas system, the metal portion having a metal flange at or near an end of the metal portion, the metal flange comprising a metal flange clamping surface. We also provide a hollow composite portion of the compressed gas system, the composite portion having a composite flange at or near an end of the composite portion, the composite flange comprising a composite flange clamping surface. We also provide a clamp assembly for pressing the metal and composite flanges towards each other. The clamp assembly may comprise at least two clamping units. At least one of the clamping units may comprise a first clamping unit surface for clamping the metal flange. At least one of the clamping units may comprise a second clamping unit surface for clamping the composite flange. A distance between the first and the second clamping unit surfaces may be less than a corresponding distance between the metal flange and the composite flange clamping surfaces when the ends of the metal and composite portions are contiguous. The end of the metal portion is then placed contiguous to the end of the composite portion. A load may then be applied on the clamping units until ends of the clamping units meet or are displaced closer to each other. We form the clamping assembly by welding the clamping units together at the meeting, or closely spaced apart, ends to form the gas-tight metal-composite interface between the end of the metal portion and the end of the composite portion.

According to another aspect of the invention, we provide a method of separating a mechanical discontinuity present in lined pressure vessels from compressed gas stored in the pressure vessels. The method comprises providing a hollow metal portion, the metal portion comprising a pipe through which the compressed gas can be loaded into and unloaded from the pressure vessel, wherein the metal portion has a metal flange at or near an end of the metal portion, the metal flange comprising a metal flange clamping surface. The pressure vessel has a composite boss defining a composite portion lined with a liner. The mechanical discontinuity may be defined between a first material of which the composite portion is made and a second material of which the liner is made. The composite portion has a composite flange at an end of the composite portion, the composite flange comprising a composite flange clamping surface. We then provide a clamp assembly for pressing the metal and composite flanges against each other. The clamp assembly comprises at least two clamping units, at least one of the clamping units comprising a first clamping unit surface for clamping the metal flange, and at least one of the clamping units comprising a second clamping unit surface for clamping the composite flange. A distance between the first and the second clamping unit surfaces when the clamp assembly is assembled to clamp the metal and composite flanges is less than a corresponding distance (i.e. measured using the same criterion, e.g. along the same direction) between the metal flange and the composite flange clamping surfaces when the ends of the metal and composite portions are contiguous. The end of the metal portion is then placed contiguous to the end of the composite portion. The clamping units are then loaded (i.e. compressed against one another) to compress the metal and composite portions against one another. By securing the clamping units, the clamp assembly is formed and, consequently, the gastight metal-composite interface between the metal portion and the liner.

DETAILED DESCRIPTION

The figures are offered solely for the purpose of aiding in the understanding of the invention. They are not intended nor are they to be construed as limiting the scope of the invention in any manner whatsoever.

It is further noted that in some of the figures some surfaces are shown spaced apart while the description below states that such surfaces are contiguous, that is, in contact with one another. It is understood that such surfaces are shown spaced apart in the figures simply for the purpose of making it easier to see and understand the relationship between such surfaces.

Figure 1 is a schematic representation of an external flange that may be used with either or both of the portions of a gas-tight metal-composite interface as described herein; Figure 2 is a schematic representation of an internal flange that may be used with either or both of the portions of a gas-tight metal-composite interface as described herein; Figures 3A and 3B are, respectively, schematic plan and cross-sectional representations of an annular collar as described herein; Figure 4 illustrates the concept of chamfered surfaces that are formed as mirror images of one another; Figures 5A and 5B are, respectively, schematic cross-sectional and plan representations of a compressed gas containment system comprising gas-tight metal-composite interfaces according to two different embodiments of the invention; Figure 6 is a schematic representation of a method of forming a gas-tight metal-composite interface according to another embodiment of the invention that includes a sleeve with a mechanical seal; Figure 7 is a schematic representation of two gas-tight metal-composite interfaces according to embodiments of the invention; Figures 8A and 8B are schematic representations each showing one or more gas-tight metal-composite interfaces according to embodiments of the invention; Figure 9 is a cross-sectional representation, slightly in perspective, of a gas-tight metal-composite interface according to another embodiment of the invention; Figure 10 is a perspective representation of a CNG system incorporating the gas-tight metal-composite interface of Figure 9; Figure 11 is a cross-sectional representation of a gas-tight metal-composite interface according to another embodiment of the invention; and Figure 12 is a further cross-sectional representation of the gas-tight metal-composite interface of Figure 11.

It is understood that, with regard to this description and the appended claims, that any reference to any aspect of this invention made in the singular includes the plural and vice versa unless it is expressly stated or unambiguously clear from the context that such is not intended.

As used herein, any term of approximation such as, without limitation, near, about, approximately, substantially, essentially, and the like, mean that the word or phrase modified by the term of approximation need not be exactly that which is written but may vary from that written description to some extent. The extent to which the description may vary will depend on how great a change can be instituted and have one of ordinary skill in the art recognize the modified version as still having the properties, characteristics and capabilities of the word or phrase unmodified by the term of approximation. In general, but with the preceding discussion in mind, a numerical value herein that is modified by a word of approximation may vary from the stated value by around ±10%, unless expressly stated otherwise.

As used herein the term "providing" refers simply to the provision of the indicated materials to the inventive methods per se and is not intended nor should it be construed as in any manner referring to any sort of participation in the method by any third party not directly involved in the performance of the method.

As used herein, a "compressed gas system" can refer to a pressure vessel alone, such as, without limitation, a cylindrical pressure vessel made of metal with a polymeric dome. It also, however, can refer to a pressure vessel coupled to an external pipe for introducing and extracting a compressed gas from the pressure vessel, wherein the gas-tight metal-composite interface comprises at least the connection of a composite boss or nozzle to the external, metal pipe. In addition, a compressed gas system can refer to a marine transport vessel laden with pressure vessels comprising one or more gas-tight metal-composite interfaces according to embodiments of this invention. And, of course, a compressed gas system can refer to any combination of the foregoing.

As used herein a "pressure vessel" refers to a tank comprising an internal volume that can be completely isolated from the external environment. The pressure vessel is presently preferably for use as a vessel for the containment and transport of compressed gasses, in particular marine transport of such compressed gassed, in particular CNG. The gas-tight metal-composite interfaces described herein may be incorporated into pressure vessels of any size and shape including but not limited to cylindrical, geodesic, toroidal, spherical and oblate spheroidal. A presently preferred pressure vessel comprises that having a cylindrical center section and one or two domed end sections.

As used herein a "mechanical seal" refers to a device that helps to join systems together to form the gas-tight metal-composite interface so as to help prevent, or greatly reduce, leakage from the formed joint. For the purposes of this invention, a mechanical seal can comprise, without limitation, an 0-ring seal, a lip seal, a cup seal, a V-seal, a bore seal and a face seal.

As used herein, a "boss," sometimes referred to as a "nozzle," refers to a component as such would be understood by those skilled in the art. In brief, a boss or nozzle is a component used to connect a pressure vessel with external piping through which the pressure vessel is filled with or emptied of a fluid, in particular a compressed gas, preferably CNG. Bosses in current use are made of metals such as stainless steel, nickel alloys, aluminum and the like. Unfortunately, these bosses, in particular with regard to large pressure vessels, are extremely heavy and have been estimated to comprise as much as 70% of the weight of a type III (composite structural shell and metal liner) or type IV (composite structural shell and polymeric liner) pressure vessel. Preferred, then, are bosses made of polymeric composites, referred to, not surprisingly, as "composite bosses." A "one-piece composite boss" refers to a boss that is fabricated as a single construct as set forth in patent application PCT/2011/071810, which is incorporated herein by reference as if fully set forth, including the drawings.

The terms "proximal" and "distal" simply refer to opposite ends of a construct with respect to an axial direction, and are used herein as a manner of orienting an object with relation to another object such as the orientation of a flange or surfaces thereof with regards to the ends of the metal and composite portions of the gas-tight metal-polymer interfaces described herein, or the orientation of clamping arms of a C-shaped clamping collar as described herein. In general, which end is designated as proximal and which as distal is purely arbitrary, unless the context unambiguously expresses otherwise.

As used herein, "contiguous" refers to two surfaces that are adjacent and that are in direct contact or would be in direct contact were it not for an intervening layer of another material. For example, without limitation, a metal surface would be considered contiguous to a composite surface, these surfaces forming a gas-tight metal-composite interface as described herein, if there is nothing interspersed between the surfaces but also if a portion of a liner is placed between the two surfaces, the liner in fact being the entity that is in direct contact with the metal surface and the polymer surface.

As used herein, the use of "preferred," "presently preferred," preferably," or "more preferred," and the like refers to preferences as they exist at the time of filing of this patent application As used herein, a "metal-composite interface" refers to a metal surface that is contiguous with a polymeric surface of a composite portion. The surfaces cooperate (with or without the presence of a mechanical seal) to create a contact line or a contact area, as the case may be, which are impenetrable or virtually impenetrable to the compressed gas (note that a minor degree of permeability to the compressed gas may be acceptable depending on the application). Thus, as used herein, "gas-tight" refers to a property of the interface wherein the interface is impermeable or virtually impermeable to the gas, in particular when under pressure, held within a confined space delimited by the interface, that is, in simple terms the interface does not leak gas (or it does so at very minimal, acceptable rates). For the purposes of this invention, the interfaces described herein do not leak gas when used in a pressure vessel containing a gas under low, medium or high pressure. The terms low, medium and high refer to CNG storage and transportation and are readily understood by the skilled person. For example, 30bar would be categorized as low pressure, 110bar as medium pressure and 250bar as high pressure.

As used herein, a "portion" of a construct such as metal "portion" of a gas-tight metal-composite interface refers to any part of a whole construct. For example, a bicycle wheel spoke is a portion of a wheel as well as a portion of the bicycle and the wheel itself is also a portion of the bicycle. Similarly, a metal portion of a gas-tight metal-composite interface may be considered a portion of the interface per se or a portion of a compressed gas system as described elsewhere herein. Thus the term "portion" is intended to be generic and requires further investigation to determine exactly what "portion" it refers to. Such, however, will be apparent to the skilled artisan both from the context of the written description as aided by the figures.

As used herein a "flange" refers to an external or internal ridge or rim used for the coupling of one object to another. For the purposes of this invention, flanges are used for the coupling of a metal portion to a composite portion of a gas-tight metal-composite interface. An external flange is shown in Fig. 1 and 4, and an internal flange is shown in Fig. 2. With respect to the present invention, the flange of the metal portion and/or the polymeric portion may be independently external or internal.

As used herein, "chamfer" or "chamfered surface" has the meaning ordinarily associated with the term. That is, specifically with regard to this invention, a "chamfered surface" refers to a surface that is beveled with respect to a horizontal line perpendicular to the centerline axis of a cylindrical portion of a construct herein. This is depicted graphically in Fig. 1 and Fig. 2 in which surface 7 is chamfered at an angle 8 with respect to horizontal line 6. For the purpose of the present invention, a chamfered surface is angled such that a complementary annular collar, or alternative clamping device, i.e. an annular collar or clamping device designed to cooperate with the chamfered surface, can be used so as to press against one another a flanged metal portion and a flanged composite portion to form a gas-tight metal-composite interface as described herein.

As used herein, an "annular collar" refers to a construct comprising two concentric rings, one forming inside diameter 11 of the collar and defining cylindrical lumen 102 as shown in Fig. 3A and the other, diameter 12 shown in Fig. 3A, describing outer surface 103 of the collar. The annular collar according to aspects of the present disclosure comprises two half-circular segments 13 and 14. This annular collar is referred to as "C-shaped," for reasons that are evident from Fig. 3B. Proximal and distal arms 15 and 16 of the C-shape are clearly shown in Fig. 3B.

A "weldable-metal" simply refers to any metal that can be welded such as, without limitation, iron, steel, aluminum and alloys thereof.

As used herein, a "mirror-image" surface has the general meaning associated with the term, that is, a reflected duplication of at least a portion of one object wherein the two versions are essentially identical but are reversed. For the purposes of the present disclosure, in some embodiments of the invention mirror-image chamfered surfaces of a collar (or other clamping device) and of respective flanges are used to form a gas-tight metal-composite interface. In particular, it will readily be understood by the skilled artisan that a first conical coupling may be formed between a first chamfered surface of the collar (or other clamping device) and a chamfered surface of a metal flange, and a second, opposite conical coupling may be formed between a second chamfered surface of the collar (or other clamping device) and a chamfered surface of a composite flange, as shown in the figures. These two, opposed conical couplings are adapted so as to allow the half circular segments of the collar to be pressed horizontally, radially around the flanges so that as a result the flanges are simultaneously pressed against one another, as shown in the figures. An example of conical coupling is schematically shown in Fig. 4, wherein chamfered surface 17 of construct 18 is the mirror-image of chamfered surface 19 of construct 20.

As used herein, "pressing" (or "loading" or "compressing") when referring, for example, to the fitting of the C-shaped segments onto the flanges of the metal and composite portions may refer to applying sufficient pressure to force-fit the chamfered surfaces of the C-shaped segments onto the chamfered surfaces of the metal and polymer portions when the chamfered surfaces of the C-shaped segments are closer together than the chamfered surfaces of the flanges prior to application of the collar.

The pressure can be applied, without limitation, using a vice, hammering the C-shaped segments into place, or placing a strap around the C-shaped segments after alignment with the contiguous flanges of the metal and polymer portions and then tightening the strap. Other manners of application will be known to the skilled person.

When it is stated herein that a diameter is "slightly smaller" than another diameter, it is understood to mean that a construct having the smaller diameter will fit with some clearance into a lumen described by the larger diameter.

A flange is "set back" from the proximal end of a boss when a length of the boss extends beyond an unchamfered surface of the flange. In Fig. 6, as an example, flange 410 is set back from proximal end 430 of boss 400. An unchamfered surface of a flange refers to the surface of the flange opposite a chamfered surface. That is, surface 460 of metal pipe 440 is unchamfered and opposite chamfered surface 470 of metal pipe 440 in Fig. 6. Likewise, unchamfered surface 420 of composite boss 400 is opposite chamfered surface 425.

As used herein, a "liner" refers to a polymeric material that is disposed contiguous to the inner surface of a pressure vessel and that separates the material of which the structural shell of the pressure vessel is constructed from a gas contained in the pressure vessel. For the purposes of this invention, a liner can be fabricated of any suitable polymer, in view of the gas to be contained, such as, without limitation, Teflon, high molecular weight polyethylene or polydicyclopentadiene.

As used herein, a "composite" refers to two or more distinct but structurally 30 complementary substances such as metals, ceramics, glasses and polymers which combine to produce structural or functional properties not present in the individual components. In this specific patent application, with the wording "polymeric composite" or, simply, "composite" we refer specifically to a composite material in which a polymer forms a matrix in which a fibrous or filamentous material is dispersed as a "filler." As such, the composites referred to in the present application comprise polymeric surfaces defined by the polymer matrix in which the filler is embedded. As used herein, a "filamentous composite" refers to a composite comprised of long threads of a filler material that is impregnated with or embedded in a matrix material. As used herein, a "fibrous composite" refers to a composite comprised of short lengths of the thread described above; that is, a fibrous material can be considered a filamentous material that is cut into shorter lengths.

The polymeric matrix of the polymeric composite can be selected from the group consisting of epoxy resins, polyester resins, vinyl ester resins, polyimide resins, dicyclopentadiene resins and combinations thereof. Presently preferred are dicyclopentadiene polymers. As used herein, a "dicyclopentadiene polymer" refers to a polymer that comprises predominantly, that is 85% or more, dicyclopentadiene monomer. The remainder of the monomer content then would comprise other reactive ethylene monomers.

In general, any type of fibrous material may be used to create polymeric composites. Such materials include, without limitation, natural (silk, hemp, flax, etc.), metal, ceramic, basalt and synthetic polymer fibers and filaments. Presently preferred materials include glass fibers, commonly known as fiberglass, carbon fibers, aramid fibers, which go mostly notably under the trade name Kevlar® and ultra-high molecular weight polyethylene, such as Spectra® (Honeywell Corporation) and Dyneeva® (Royal DSM N.V.).

A method according to an embodiment of the present invention is first described below in conjunction with Fig. 5A and 53. Fig. 5A shows in cross section two gas-tight metal-composite interfaces according to embodiments of this invention combined into one system. One interface is created between a composite boss that is coupled to a pressure vessel and an external metallic pipe through which a compressed gas is introduced and withdrawn from the pressure vessel. The other interface is created between a composite dome and a metallic cylindrical center section of the pressure vessel. This is not intended or any manner construed as limiting this invention in any way: the gas-tight metal-composite interfaces shown in Fig. 5A may be used independently one from the other, and may also be used in other types of pressure vessels as those may be known to those skilled in the art.

While the gas-tight interface of this invention may find applications in any field where gases are contained in a vessel under pressure, it is a particular embodiment of this invention that the pressure vessel be one intended for use in the marine transport of compressed gasses, in particular CNG. This is so because current regulations as set forth by the American Bureau of Shipping for the marine transport of compressed gasses prohibits, or at least limits, the use of threaded fittings at any location on or close to a pressure vessel that is contained in the cargo hold of a ship. Thus, if any two surfaces cannot be otherwise interfaced, such as by welding if the surfaces are both constructed of an appropriate metal, the surfaces cannot be bolted together with or without a gasket between the surfaces to establish a gas-tight interface. Interfaces according to at least some embodiments of this invention are intended to solve this problem. Embodiments of the present invention eliminate the use of any threaded fasteners.

A pressure vessel for the containment and transportation of compressed gas is shown in Fig. 5A. The vessel is comprised of a cylindrical center section 21 and one or two domed end sections of which one, 22 in Fig. 5A, is shown. Boss 23 in Fig. 5A is coupled to the pressure vessel through an opening in one of the domed end sections. As mentioned previously, it is desirable to make a pressure vessel for marine transport of compressed gasses as light as possible so as to maximize the economics of the system. In patent applications PCT/2011/071810 and PCT/2011/071813, one piece composite bosses and composite domes for use with metal cylindrical center sections are respectively described. The coupling of the composite bosses to external piping, which is almost universally metal, is, however, depicted as being accomplished using nut and bolt fasteners in these patent applications. While this coupling mechanism is widely accepted in many scenarios, such as, without limitation, overland transport of compressed gassed, it is not currently acceptable for marine transport of compressed gasses when the boss connection is in the cargo hold of a ship. The coupling mechanism of at least certain embodiments of this invention eliminates this problem. Gas-tight interfaces according to embodiments of this invention can also be used to couple a composite dome to a metal cylindrical section of a pressure vessel and vice versa. Two non-limiting examples of gas-tight metal-composite interfaces are shown in Fig. 5A where a composite boss 23 is shown coupled to an external metal pipe 24 using a gas-tight metal-composite interface 25. Also shown is the use of such an interface to couple composite dome 22 to metal cylindrical center section 21. It is, of course, not necessary that both gas-tight metal-composite interfaces be used. Such an interface may only apply to the boss-external piping connection or, in another embodiment, a metal boss, which can be welded to external piping, can be used with a composite dome that is coupled to a metal cylindrical center section of a pressure vessel.

Both gas-tight metal-composite interfaces shown in Fig. 5A are created in the same manner. We will now describe a method of forming a gas-tight metal-composite interface in accordance with an embodiment of the present invention with reference only to the composite dome 22 and the metal cylindrical section 21. Thus, to form the gastight metal-composite interface, surface 210 of cylindrical section 21 and surface 220 of composite dome 22 are brought together, that is, made contiguous. Then the C-shaped half-circular segments 13, 14 of an annular collar 100 are fitted over contiguous flanges 300, 310. The half-circular segments 13, 14 of the annular collar 100 are then pressed onto said flanges 300, 310. By pressed is meant that a pressure must be applied to the half-circular portions 13, 14 because, as noted previously, the distance between the chamfered surfaces of the half-circular portions 13, 14 is less than the distance between the chamfered surfaces of the contiguous flanges 300, 310. This distance can be measured, for example, in the axial direction. However, the skilled person will appreciate that other direction can be taken for reference. As mentioned previously, the pressure may be applied, without limitation, using a vice or vice-like device or using a band that is tightened around the entire annular collar. Pressure is applied until end surfaces 35, 36 of the half circular segments 13, 14 are contiguous, as shown in Fig. 5B. While maintaining the pressure, in this embodiment, the end surfaces 35, 36 are welded together to complete the gas-tight metal composite interface between the flanges 300, 310.

Fig. 6 illustrates an embodiment of this invention in which the method further comprises using a boss 400 having set-back flange 410 wherein outside diameter 405 of boss 400 along section 450 of boss 400 is slightly less than inside diameter 445 of pipe 440. Mechanical seal 480 is placed onto segment 450 and then segment 450 is inserted into pipe 440. Section 450 of boss 400 is inserted into the end of pipe 440 until unchamfered surface 420 of flange 410 is contiguous with unchamfered surface 460 of pipe flange 470. Once the unchamfered surfaces 420, 460 are contiguous, the C-shaped semi-circular segments 13, 14 are fitted onto contiguous pipe and boss flanges 410, 470. The C-shaped segments are then pressed together until the respective end surfaces 35, 36 of the semi-circular segments 13, 14 are contiguous. Then, while maintaining the pressure used to press the segments together, the end surfaces 35, 36 are welded together to complete the gas-tight metal-composite interface and boss-pipe junction 490.

Fig. 7 shows a similar pressurized gas containment system to that shown in Fig. 5A and 5B except that in this embodiment a mechanical seal 250 is disposed between surface 210 of metallic cylindrical center section 21 and surface 220 of composite dome 22 prior to bringing the surfaces contiguous. The mechanical seal 250 is provided to improve the gas tightness of the metal-composite interface. C-shaped segments 13 and 14 are then fitted over flanges 300 and 310 as described with regard to Fig. 5A and 5B, and the C-shaped segments 13, 14 are pressed together until ends 35, 36 meet, that is, are contiguous, as shown in Fig. 5B, at which time, the C-shaped segments are welded together to form the annular collar 100 and, as a consequence, the gas-tight metal-composite interface.

Fig. 8A and 8B show yet another embodiment of the invention. In Fig. 8A, a liner 500 is provided so as to fully cover the internal surfaces of the composite dome 522 and boss 523, but not those of metal center section 521. An end 510 of the liner 500 extends beyond the end of the composite boss 523 and is folded over a flange surface 520 of the composite boss 523. Then, surface 535 of flange 530 is brought contiguous to flange surface 520 with the end 510 of the liner 500 interspersed between these surfaces. As before, the C-shaped segments 13, 14 are pressed onto the contiguous flanges 530, 540 until the end surfaces of the segments 35, 36 meet. The C-shaped segments are then, in the present embodiment, welded together along the interface of surfaces 35, 36 to complete the formation of the gas-tight metal-composite interface. The opposite end of the liner (not labelled in Fig. 8A) is folded between the flange of the composite dome and the corresponding flange of the metal center section 521. The pressure vessel shown in Fig. 8B is instead a type IV pressure vessel having an outer composite shell and an inner polymeric liner 500 extending over the whole internal surface of the outer shell, i.e. no metal center section is present. The only interface is however formed following the same procedure.

Referring now to Fig. 9, 10, 11 and 12, a gas-tight metal-composite interface according to another embodiment of the invention is illustrated. This interface is formed between either a flanged metallic pipe 704 or a flanged metallic interface component 1004, and a composite nozzle 701, 1001 of a pressure vessel 702, 1002. The pressure vessel 702, 1002 and the flanged metallic pipe 704 or flanged metallic interface component 1004 form compressed gas systems 700, 1000, 2000 for storage and transportation of CNG. An annular clamp 110, 1110 is provided to clamp the flanged metallic pipe 704 or the flanged metallic interface component 1004 to the composite nozzle 701 1001 thereby forming the interface, as previously discussed. In the present embodiment, however, the interface is formed between an outer surface 707, 1007 of a conical projection 705, 1005 of the flanged metallic pipe 704 or the flanged metallic interface component 1004, and an inner surface 709, 1009 of the composite nozzle 701, 1001. This conical projection 705, 1005 is inserted into the composite nozzle through an opening thereof, and then secured thereto by means of the annular clamp 110, 1110. In the illustrated systems 700, 1000, 2000, CNG can flow in and out of the pressure vessel via a passageway 710, 1010, 2010 that extends through the flanged metallic pipe 704 or the flanged metallic interface component 1004. Note that the system 2000 shown in Fig. 12 shows a further length of pipe 1017 which has been welded to the flanged metallic interface component 1004.

The gas-tight metal-composite interface prevents, in use, the CNG (which, as previously described, can be stored at pressures of up to hundreds of bars in the pressure vessel) from reaching through to a mechanical discontinuity 711, 1011 which, in this embodiment of the invention, would otherwise be accessible to the compressed gas. As shown in Figures 9, 11 and 12, this mechanical discontinuity is defined at the inlet of the composite nozzle, between a liner 720, 1020 (which lines the composite nozzle as well as the inner surfaces of the pressure vessel), and the composite material of the nozzle itself. Such a configuration promotes safety of the fluid connection between the flanged metallic pipe 704 or the flanged metallic interface component 1004 and the composite nozzle while maintaining simplicity in the design of the compressed gas system comprising a liner, a composite nozzle and a pressure vessel, thus keeping manufacturing costs down. The CNG is prevented from flowing through the gas-tight metal composite interface 711, 1011, since the interface is gas-tight. The interface, therefore, isolates the mechanical discontinuity 711, 1011, which discontinuity is a potential point of weakness for the structural integrity of the pressure vessel if exposed to the pressure of the gas. The inventors have appreciated that it is possible to advantageously exploit the necessity of having to fluidly connect a metallic pipe to a lined composite nozzle to achieve a simple, straightforward yet safe design of pipe, nozzle and pressure vessel assembly. By contrast, in certain designs of the prior art, the liner is embedded into the nozzle or other structure of the pressure vessel so that no mechanical discontinuity can ever be exposed to the pressure of the gas stored in the pressure vessel.

Returning to the flanged metallic pipe 704 or the flanged metallic interface component 1004, as described above, either of these components presents, in the described embodiment, a conical projection 705, 1005 for insertion into the composite nozzle. The conical projection has a tapered, frusto-conical profile having a conical outer surface 707, 1007. The flanged metallic pipe 704 or the flanged metallic interface component 1004, also present a flanged portion 720, 1020 in the form of an annular flange surrounding a corresponding tubular portion 730, 1030. The annular flange 720, 1020 and the tapered profile of the conical projection form a shoulder which determines a maximum insertion length of the conical projections 705, 1005 of the flanged metallic pipe 704 or the flanged metallic interface component 1004 into the composite nozzle 701, 1001 through the inlet thereof. Such an insertion length is determined when the shoulder becomes contiguous with the end surface of the composite boss. In the described embodiment, the insertion length of the conical projections 705, 1005 of the flanged metallic pipe 704 or the flanged metallic interface component 1004 is greater than the diameter of the passageway 710, 1010. This provides for ease of insertion and facilitates the creation of a stable gas-tight interface.

As mentioned earlier in this disclosure, the gas-tight metal-composite interface may, if desired and if intended for use where threaded fitting are not forbidden as is presently the case with marine transport of compressed gases in the holds of ships, include threaded fittings in addition to or in place of a welded connection between the two C-shaped half-circular segments described above. A collar 110 adapted to be fastened to form the metal-composite interface by means of threaded fittings is illustrated in connection with the compressed gas containment system 700 depicted in Fig. 9 and 10. In Fig. 9, one of the C-shaped half-circular segments 113 is shown end on. As can be seen, the C-shaped half segment now has flanges 600, 610, which include through-holes 605, 615. The through-holes may have smooth inner surfaces or threaded inner surfaces. The other, corresponding C-shaped half segment (not shown) is similarly configured such that when the two half segments are brought together to form the metal-composite interface, the four through-holes 605, 615 align. Bolts 616 can then be passed through the aligned through-holes and tightened down with corresponding nuts (not shown) to secure the collar 110 thus forming the gas-tight metal-composite interface. The resulting exemplary compressed gas system 700 configuration including the pressure vessel 702 joined to the external flanged metallic interface component 704, 1004 by means of the collar 110 is also illustrated in perspective view in Fig. 10.

As previously mentioned, a presently preferred use of a pressure vessel having one or more gas-tight metal-polymer interfaces according to embodiments of this invention is for the containment and marine transport of natural gas, often referred to as "compressed natural gas" or simply "CNG." CNG may be contained and transported in pressure vessels forming compressed gas systems according to embodiments of this invention both as a purified gas and as "raw gas." Raw gas refers to natural gas as it comes, unprocessed, directly from the well. It contains, of course, the natural gas (methane) itself but also may contain liquids such as condensate, natural gasoline and liquefied petroleum gas. Water may also be present as may other gases, either in the gaseous state or dissolved in the water, such as nitrogen, carbon dioxide, hydrogen sulfide and helium. Some of these may be reactive in their own right or may be reactive when dissolved in water, such as carbon dioxide and hydrogen sulfide which produces an acid when dissolved in water. In general, the metal of the center section of a pressure vessel of this invention is well-suited for containment and transport of raw gas. The composite dome, on the other hand may be, due to its inherent structure, somewhat permeable and possibly reactive toward some components of raw gas in which case the use of an impervious and inert liner over those portions of the dome that will come in contact with the raw gas can be used.

The present invention has therefore been described above purely by way of example. Modifications in detail may be made to the invention within the scope of the 30 claims appended hereto

Claims

CLAIMS: 1. A method of forming a gas-tight metal-composite interface for compressed gas containment systems, comprising: providing a hollow metal portion of a compressed gas containment system, the metal portion having a metal flange at or near an end of the metal portion, the metal flange comprising a metal flange chamfered surface; providing a hollow composite portion of the compressed gas system, the composite portion having a composite flange at or near an end of the composite portion, 10 the composite flange comprising a composite flange chamfered surface; providing a collar for pressing the metal and composite flanges towards each other, wherein: the collar comprises at least two pad-annular, generally C-shaped in cross section segments, each segment comprising proximal and distal clamping arms; the proximal arms comprise each a proximal arm chamfered surface, chamfered as a mirror image with respect to the metal flange chamfered surface, and the distal arms comprise each a distal arm chamfered surface, chamfered as a mirror image with respect to the composite flange chamfered surface, wherein: a distance between the proximal and distal arm chamfered surfaces is less than a corresponding distance between the metal and composite flange chamfered surfaces when the ends of the metal and composite portions are contiguous; placing the end of the metal portion contiguous to the end of the composite portion; pressing the C-shaped segments onto the metal and composite flanges; and, forming the collar by mechanically securing together at least a pair of the C-shaped segments to form the gas-tight metal-composite interface between the end of the metal portion and the end of the composite portion.
2. The method of claim 1, wherein the collar has a continuous annular configuration.
3. The method of claim 2, wherein the C-shaped segments are pressed onto the metal and composite flanges until at least two end surfaces of respective, adjacent C-shaped segments meet, or are located in closer proximity to each other.
4. The method of claim 3, wherein forming the collar by mechanically securing together at least a pair of the C-shaped segments comprises welding the at least two end surfaces of the adjacent or contiguous C-shaped segments.
5. The method of any one of claims 1 to 3, wherein forming the collar by mechanically securing together at least a pair of the C-shaped segments comprises securing at least one threaded fitting, wherein the threaded fitting optionally comprises two aligned through holes formed on respective adjacent C-shaped segments, and a bolt cooperating with the through holes.
6. The method of any one of claims 1 to 5, wherein the ends of the metal and composite portions define respective opposing planar surfaces, and the gas-tight metal-composite interface is formed between said opposing surfaces.
7. The method of claim 6, wherein the gas-tight metal composite interface comprises a mechanical seal disposed between the opposed planar surfaces, the mechanical seal optionally being an 0-ring.
8. The method of any one of claims 1 to 7, wherein the compressed gas containment system comprises a pressure vessel having a composite boss, the composite boss comprising the composite portion and being optionally lined with a liner for containing compressed gas, said liner being optionally folded to extend between the ends of the metal and composite portions between said opposing planar surfaces, and wherein the metal portion comprises a pipe through which the compressed gas can be loaded into and unloaded from the pressure vessel.
9. The method of claim 8, wherein the metal portion comprises a projection for insertion into an inlet of the pressure vessel, the projection comprising an outer surface configured to form the gas-tight metal-composite interface in cooperation with an inner surface of the composite boss, or of the liner.
10. The method of claim 8 or 9, wherein the gas-tight metal-composite interface isolates a mechanical discontinuity present between a first material of which the composite boss is made and a second material of which the liner is made from the pressure of the compressed gas.
11. The method of claim 9 or 10, wherein the outer surface of the projection and the inner surface of the composite boss, or the liner, have complementary frusto-conical profiles which cooperate to form the gas-tight metal-composite interface, optionally wherein the projection is compressed against the composite boss when the gas-tight metal-composite interface is formed.
12. The method of any one of claims 8 to 11 when dependent on claim 7, wherein the mechanical seal is disposed around the outer surface of the projection, and is optionally disposed at or near an edge of the projection.
13 The method of claim 12, wherein the mechanical seal is configured to increase its sealing action in response to a pressure increase in the pressure vessel.
14. The method of claim 8, wherein the composite portion comprises an extension for insertion into an opening of the pipe, said extension comprising an outer surface configured to form the gas-tight metal-composite interface in cooperation with an inner surface of the pipe.
15. The method of any one of claims 1 to 7, wherein the compressed gas system comprises a pressure vessel having a composite dome and a central body, the composite dome comprising the composite portion, and the central body comprising the metal portion.
16. The method of any one of the preceding claims, wherein the composite portion comprises a polymer matrix selected from the group consisting of epoxy resins, polyester resins, vinyl ester resins, polyimide resins, dicyclopentadiene resins and combinations thereof.
17. The method of any one of the preceding claims, wherein the composite portion comprises a fibrous filler selected from the group consisting of metal fibers, ceramic fibers, natural fibers, glass fibers, carbon fibers, aramid fibers, ultra-high molecular weight polyethylene fibers and combinations thereof.
18. A compressed gas system, comprising one or more gas-tight metal-composite interfaces formed according to any one of claims 1-17.
19. The compressed gas system of claim 18, wherein the compressed gas system is adapted for storage and transportation of CNG.
20. A water-going vessel for transportation of compressed gas comprising a compressed gas containment system according to claim 18 or 19.
21. A method of forming a gas-tight metal-composite interface for compressed gas systems, comprising: providing a hollow metal portion of a compressed gas system, the metal portion having a metal flange at an end of the metal portion, the metal flange comprising a metal flange clamping surface; providing a hollow composite portion of the compressed gas system, the composite portion having a composite flange at an end of the composite portion, the 30 composite flange comprising a composite flange clamping surface; providing a clamp assembly for pressing the metal and composite flanges against each other, wherein: the clamp assembly comprises at least two clamping units, at least one of the clamping units comprising a first clamping unit surface for clamping the metal flange, and at least one of the clamping units comprising a second clamping unit surface for clamping the composite flange, wherein a distance between the first and the second clamping unit surfaces when the clamp assembly is assembled to clamp the metal and composite flanges is less than a corresponding distance between the metal flange and the composite flange clamping surfaces when the ends of the metal and composite portions are contiguous; placing the end of the metal portion contiguous to the end of the composite portion; loading the clamping units until ends of the clamping unit meet or are closer to each other; and, forming the clamp assembly by welding the clamping units together at the ends to form the gas-tight metal-composite interface between the end of the metal portion and the end of the composite portion.
22. A method of forming a gas-tight metal-composite interface for compressed gas systems, the method comprising: providing a hollow metal portion comprising a pipe through which compressed gas can be loaded and unloaded, the metal portion having a metal flange at or near an end of the metal portion, the metal flange comprising a metal flange clamping surface; providing a pressure vessel having a composite boss lined with a liner, a mechanical discontinuity being defined between a first material of which the composite boss is made and a second material of which the liner is made, the composite boss having a composite flange at or near an end of the composite boss, the composite flange comprising a composite flange clamping surface; providing a clamp assembly for clamping the metal portion to the composite boss, wherein: the clamp assembly comprises at least two clamping units comprising a first clamping unit surface for cooperating with the metal flange, and a second clamping unit surface for cooperating with the composite flange, wherein a distance between the first and the second clamping unit surfaces when the clamp assembly is clamped is less than a corresponding distance between the metal flange and the composite flange clamping surfaces when the ends of the metal portion and the composite boss are contiguous; placing the end of the metal portion contiguous to the end of the composite boss; and, securing the clamping units to form the clamp assembly to form the gas-fight metal-composite interface between the metal portion and the liner, wherein the gas-tight metal-composite interface isolates the mechanical discontinuity from compressed gas stored in the system.
23. The method of claim 22, wherein the metal portion comprises a projection for insertion into an inlet of the pressure vessel, said projection comprising an outer surface configured to form the gas-tight metal-composite interface in cooperation with the liner.
24. The method of claim 23, wherein the outer surface of the projection and the inner surface of the liner have complementary frusto-conical profiles which cooperate to form the gas-tight metal-composite interface.