Pressure Vessel with controlled vessel weight/gas weight ratio

The present invention relates to pressure vessels, and particularly ones that enable them to be used for new applications given the developments being made thereto.

The present application claims priority from PCT/EP201 1/071793,

PCT/EP201 1/071797, PCT/EP201 1/071805, PCT/EP201 1/071794,

PCT/EP201 1/071789, PCT/EP201 1/071799, PCT/EP201 1/071788,

PCT/EP201 1/071786, PCT/EP201 1/071810, PCT/EP201 1/071809, PCT/EP201 1/071808, PCT/EP201 1/071800, PCT/EP201 1/07181 1 ,

PCT/EP201 1/071812, PCT/EP201 1/071815, PCT/EP201 1/071813,

PCT/EP201 1/071814, PCT/EP201 1/071807, PCT/EP201 1/071801 and PCT/EP201 1/071818, all of which are incorporated herein in full by way of reference. The features of the pressure vessels disclosed in those prior filings are relevant to the present invention in that they can provide the structure of suitable storage means for storing the fluid at the required pressure.

Pressure vessels for the carriage or transport of compressed fluids presently constitute four regulatory agency approved classes or types, all of which are cylindrical with one or two domed ends:

Type I. Consists of an all metal, usually aluminum or steel, construct. This type of vessel is inexpensive but is very heavy in relation to the other classes of vessels. The entire vessel is of sufficient strength to withstand the intended pressure exerted on the vessel by a contained compressed fluid and therefore does not require any manner of strength-enhancing over-wrap, including the dry filamentous over-wrap of this invention. Type I pressure vessels currently comprise a large portion of the containers used to ship compressed fluids by sea, their use in marine transport incurs very tight economic constraints.

Type II. Consists of a thinner metal cylindrical center section with standard thickness metal end domes such that only the cylindrical portion need be reinforced, currently with a composite over-wrap. The composite wrap generally constitutes glass or carbon filament impregnated with a polymer matrix. The composite is usually "hoop wrapped" around the middle of the vessel. The domes at one or both ends of the vessel are of sufficient strength to withstand the pressures developed in the vessel under normal use and are not composite wrapped. In type II pressure vessels, the metal liner carries about 50% of the stress and the composite carries about 50% of the stress resulting from the internal pressure of the contained compressed fluid. Type II vessels are lighter than type I vessels but are more expensive.

Type III. Consists of a thin metal liner that comprises the entire structure, that is, the cylindrical center section and the end dome(s). Thus, the liner is currently reinforced with a filamentous composite wrap around entire vessel. The stress in Type III vessels is shifted virtually entirely to the filamentous material of the composite wrap; the liner need only withstand a small portion of the stress. Type III vessels are much lighter than type I or II vessels but are substantially more expensive. Type IV. Consists of a polymeric, essentially gas-tight liner that comprises both the cylindrical center section and the dome(s), all of which is currently fully wrapped with a filamentous composite. The composite wrap provides the entire strength of the vessel. Type IV vessels are by far the lightest of the four approved classes of pressure vessels but are also the most expensive.

As noted above, Type II, III and IV pressure vessel currently require a composite overwrap over a vessel liner to give them the necessary strength to withstand the intended pressure exerted by a compressed fluid contained in the vessel. The present invention concerns the pressure vessels and new applications to which these and further types of pressure vessel as discussed below can be applied.

According to the present invention there is provided a type 3, 4 or 5 pressure vessel, the pressure vessel being for storage or transportation of a fluid-based fuel and having one or more composite nozzle integrated in the vessel structure.

Preferably the pressure vessel has an internal wall or surface formed of a material that is substantially inert relative to, i.e. it will tend not to corrode when in contact with, the fuel to be stored or transported. To be deemed substantially inert relative to the fuel to be stored or transported, the material may have corrosion resistance properties relative to the fuel to be stored or transported of at least an AISI 316 stainless steel. For example, this degree of corroson resistance may be determined relative to one or more of the anticipated contaminates therein, one such contaminate being the expected level of typically aggressive compounds such as H ₂ S, e.g. in the presence of H ₂ 0. Another mode of determining whether the material is deemed to be substantially inert relative to the fuel to be stored or transported it to determine whether the material, or internal wall, is essentially H ₂ S resistant, i.e. substantially H ₂ S resistant, or preferably H ₂ S resistant. One approach for determining this is to determine whether it is in accordance with IS015156.

According to the present invention there is also provided a type 3, 4 or 5 pressure vessel, the pressure vessel being for storage or transportation of a fluid-based fuel and having a lower weight per gas capacity ratio than both approved type 1 pressure vessels of an equivalent size and approved type 2 pressure vessels of an equivalent size. Such weights and gas capacities are typically assigned to specific pressure vessels, or to specific designs of pressure vessels, by the relevant regulatory bodies as "certificated" characteristics thereof. This is since pressure vessels usually have to be certificated before being put into service. As before, preferably the pressure vessel has an internal wall or surface formed of a material that is substantially inert relative to, i.e. it will tend not to corrode when in contact with, the fuel to be stored or transported. For example, the pressure vessel may have having corrosion resistance properties of at least an AISI 316 stainless steel or it may be substantially H ₂ S resistant, or preferably H ₂ S resistant, in accordance with IS015156.

According to the present invention there is also provided a type 3, 4 or 5 pressure vessel, the pressure vessel being for storage or transportation of a fluid-based fuel and having a weight/gas capacity ratio in the range of 13 to 65t/Mscf. t/Mscf means metric tons per million standard cubic feet, where million standard cubic feet is a standard term for quantifying the amount of useable CNG within a pressure vessel. The weight refers to the empty weight (mass) of the vessel in metric tonnes.

A standard cubic foot (abbreviated as scf) is a measure of quantity of gas, equal to a cubic foot of volume at 60 degrees Fahrenheit (15.6 degrees Celsius) and either 14.696 psi (1 atm or 101 .325 kPa) or 14.73 psi (30 inHg or 101 .6 kPa) of pressure. A standard cubic foot is thus not a unit of volume but of quantity, and the conversion to normal cubic metres is not the same as converting cubic feet to cubic metres (multiplying by 0.0283...), since the standard temperature and pressure used are different. Assuming an ideal gas, a standard cubic foot using the convention of 14.73 psi represents 1 .19804 moles (0.0026412 pound moles), equivalent to 0.026853 normal cubic meters.

Common oilfield units of gas volumes include ccf (hundred cubic feet), Mcf (thousand cubic feet), MMcf (million cubic feet), Bcf (billion cubic feet), Tcf (trillion cubic feet), Qcf (quadrillion cubic feet), etc. The M refers to the Roman numeral for thousand. Two M's would be one thousand thousand, or one million. The s for "standard" is sometimes included, but often omitted and implied. We have used it above in the statements of invention.

As before, preferably the pressure vessel has an internal wall or surface formed of a material that is substantially inert relative to, i.e. it will tend not to corrode when in contact with, the fuel to be stored or transported. For example, the pressure vessel may have having corrosion resistance properties of at least an AISI 316 stainless steel or it may be substantially H ₂ S resistant, or preferably H ₂ S resistant, in accordance with IS015156.

Preferably the ratio measurements are calculated from the rated values of the pressure vessels, i.e. according to the pressure vessel's certification. These typically will be assigned to the pressure vessel based upon the intended design parameters and appropriate safety factors used, e.g. in accordance with relevant Standards. In particular a pressure vessel will typically be assigned a maximum certificated storage capacity for standardised storage conditions. The structural weight of a pressure vessel can be determined by weighing an empty pressure vessel - one that is removed from any pipework. However, given the size of the pressure vessels, the weight (mass) might more often be a calculated or determined value - e.g. upon considering wall thicknesses, size and shapes, and material compositions thereof, and often it will be indicated on the certification. This can be so as to allow appropriate structures to support it, e.g. on board a ship, to be designed to be in compliance with appropriately applicable factors of safety as set by available regulations and, and vehicle specifications, and by relevant regulatory bodies.

Preferably the structural weight over transported gas weight ratio is in the range of 0.7 to 3.4 [t/t], e.g. when loaded to a CNG pressure of 250 bar and a temperature of 20°C, or possibly when loaded to a pressure of 300 bar at that temperature, or when loaded to its certified (or certificated) maximum pressure or gas capacity (e.g. in scfs).

Since a gas quantity in scfs has a constant weight (mass) irrespective of its pressure and temperature, the ratio presented by fully loaded pressure vessel (i.e. one loaded to its certificated capacity) is not dependent on temperatures and pressure.

In case of a glass-based composite Type 3 or 4 pressure vessel the weight/certified maximum gas capacity ratio is preferably in the range of 35 to 65 [t/Mscf]. This can be according to the safety factor used by the certification. Further, preferably the structural weight over certificated maximum transported gas weight ratio is in the range of 1 .8 to 3.4 [t/t].

In case of a carbon-based composite Type 3 or 4 pressure vessel the weight/certified maximum gas capacity ratio is preferably in the range of 13 to 22 [t/Mscf]. This can be according to the safety factor used by the certification. Further, preferably the structural weight over certificated maximum transported gas weight ratio is in the range of 0.7 to 1 .2 [t/t]. Preferably the invention relates to a car comprising such a pressure vessel, with the pressure vessel being connected to the engine of the vehicle so as to supply fuel thereto.

To date, road-going vehicles have been fitted with type 1 and type 2 pressure vessels for serving as the vehicle's fuel tank. The present invention is novel over those prior art arrangements.

Further, in view of the mass of the inventive pressure vessels being low for the internal storage capacity thereof compared to equivalent type 1 or type 2 pressure vessels, the pressure vessels of the present invention, including the preferred type 3 or type 4 pressure vessels, and other similarly lighter weight pressure vessels, can be used in a larger size than that achievable when instead using type 1 or type 2 pressure vessels without their overall mass being greater than that found in the prior art arrangements, even when fully loaded with CNG - the CNG accounts for a relatively low proportion of the total mass of the filled vessel, i.e. typically less than 60%, and more often less than 50%, as supported by the above-mentioned range of possible mass ratios of between 0.7 to 3.4, with a value of 1 representing the 50% figure. Therefore a greater volume of fuel storage can be provided within a given transport vehicle (which vehicle may have one or more pressure vessels, but which vehicle will certainly have a maximum total transportation weight, e.g. set by its buoyancy on a ship, or its maximum axle weight for a truck or train) without increasing the overall weight of the vehicle when fully loaded, whereby more efficient transportation (i.e. transfer from one location to another) of the fuel becomes achievable (or longer ranges become possible since the vehicles themselves become lighter, thus using less fuel). These novel solutions are therefore inventive.

This increase in storage capacity is particularly present when the contained fuel is CNG since CNG has a density of perhaps between a quarter and a fifth of petrol or diesel, even when compressed to pressures in the order of 300 bar.

Other fuel typed transportable within these pressure vessels, however, include pressurised/liquid hydrogen, LNG, GTL (gas to liquid) and LPG.

In addition to cars, the pressure vessels can be used as fuel tanks for trains, lorries, busses, airplanes, especially light aircraft, boats and ships.

The pressure vessels can also be used for non-fuel applications, including breathing tanks as used by scuba divers, hospitals, emergency services and firemen, whereupon the contained gas may be pressurised air or oxygen, or other breathable gas mixes, or even for non breathing applications, including storing compressed gases such as helium, compressed nitrogen, compressed C02 and other gases that are in current pressurised storage, e.g. in chemical plants. The low-weight of these type 3 and 4 pressure vessels, and the other lightweight vessels disclosed herein, make the storage and manageability of these compressed gas storage devices far more user-friendly than the current, heavy, all-steel type 1 tanks that are widely in use today, which in turn can also mean greater capacities are also provideable while still allowing the pressure vessel to be manageable by a user in terms of manoeuvrability (a very heavy pressure vessel is more awkward to handle or manoeuver than a more lightweight one of the same size, or even, for many applications, a more lightweight one of a larger size).

As suggested above, in addition to type 3 and 4 pressure vessels, newer forms of pressure vessel can be applied to these various applications. These newer forms of pressure vessels include those that can be referred to as type 5, type 6, and type 7 pressure vessels. It is also possibly to apply other modified versions of these various different pressure vessel types.

A type 5 pressure vessel comprises no separate liner, with the liner instead being either integral to the composite wall or it is a removable mandrel used for the forming of the wound composite wall, that mandrel then being removed after the winding process.

A type 6 pressure vessel has a steel cylindrical section and composite end-domes.

A type 7 pressure vessel has a steel liner, a composite overwrap of the cylindrical section and composite end domes.

Other variants can include type 4 pressure vessels with a metallic internal coating, which coating can improve the imperviousness of the pressure vessel to gases.

It also is known, however, that the polymeric matrix of the composite wrap adds little or no strength to the overwrap. Thus, this invention also can be used with a further novel winding arrangement that uses a dry filamentous material that is disposed over a pressure vessel liner in a dry state and that is remains in essentially a dry state (i.e. not bonded throughout with an impregnation of resin) for the life-time of the pressure vessel. This dry wrapping with filamentous materials also avoids possibility of air entrapments in the impregnating resin, which would lead to a non-homogeneous load transfer inside the composite structure.

"Essentially in a dry state" is not intended to be limited to scenarios where the pressure vessel is not exposed to water, e.g. marine or river applications (e.g. scuba diving). After all, in those scenarios the filamentous material may become wetted or dampened by environmental moisture or the water in which the diver submerges. Therefore, the term "dry state" is instead used to refer to the condition of the filamentous material when it is disposed over the vessel's liner - it is at that time "dry", i.e. not impregnated with resin, and it remains in that dry (not impregnated with resin) state even while the vessel is put to use. Essentially dry in this context therefore does not exclude situations where the filaments/fibres are wetted by, or submerged in, water. It is dry only in the sense that it is not resin impregnated.

An external polymeric layer or coating can be applied over the dry filamentous material for environmental exposure protection or resistance on the outer surface of the dry filaments.

These additional "dry wrap" pressure vessel types - the dry wrap can be applied to any of the type 2 to 5 and type 7 pressure vessel forms - can also be used in these novel ways.

One structure for a preferred pressure vessel is a vessel having a generally cylindrical shape over a majority of its length and at least one stainless steel layer as a first layer for being in contact with the compressed fluid within the vessel, the first layer being made of low-carbon stainless steel, and the vessel further having a further external composite layer made of at least one fiber-reinforced polymer layer that will not be in contact with the fluid contained within the vessel.

The vessel will have at least an opening for gas loading and offloading. Typically it is at one end. Generally an opening is also provided at the opposite end. Such openings at each and can be referred to as axial openings. In case of Type 3 to 5 pressure vessels, the more similar are the two axial openings, the more efficient is the wrapping pattern of filaments. For example, the axial openings may both be round and they may both have the same diameter.

A plurality of the pressure vessels can be arranged in a module or compartment, and the pressure vessels can be interconnected for loading and offloading operations. Preferably the vessels all have the same height, length or diameter. Some may have different heights, lengths or diameters to allow the vessels to be custom-fitted into the space provided for them within the relevant vehicle or module or compartment. Another preferred structure for the pressure vessel is a generally cylindrical shape over a majority of its length and at least one opening for gas loading and offloading and for liquid evacuation, the pressure vessel comprising a non-metallic internal coating, a metallic liner; and at least one external fiber layer. The non-metallic internal coating is preferably substantially inert.

The non-metallic internal coating may advantageously have a corrosion resistance of at least that of stainless steel. The non-metallic internal coating may be selected from the group comprising: HDPE, epoxy resins, PVC, etc.

The metallic liner may be acidic gas corrosion resistant. The metallic liner may be made of low-carbon steel.

The fiber layer may be made of fiber wound about the metallic liner. The fiber layer may comprise carbon fibers.

This or any of the other pressure vessels may further comprise an insulating layer interposed between the liner and the composite layer (e.g. a carbon fiber layer).

The insulating layer may be a gas permeable layer.

The fiber layer may comprise glass fibers.

The pressure vessel may further comprise a gas permeable layer interposed between the metallic liner and the fiber layer. The gas permeable layer may comprise glass fibers.

The pressure vessel may further comprise a gas detector connected to the gas permeable layer for detecting a gas leakage.

The pressure vessel may be of essentially cylindrical shape, inside and outside, along the majority of its length.

Another configuration for the pressure vessel may be again a generally cylindrical shape over a majority of its length and at least one opening for gas loading and offloading. However, in this configuration the pressure vessel comprises a metallic liner, a first fiber layer external and adjacent to the metallic liner, and a second fiber layer external and adjacent to the first fiber layer. The first and second fiber layers are made of different materials.

The metallic liner may be gas impermeable and/or corrosion resistant.

The metallic liner may be selected from the group comprising steel, stainless steel, nickel-based alloys, bi-phase steel, aluminum, aluminum alloys, titanium, and titanium alloys.

Either or both of the fiber layers may be made of fibers wound about the metallic liner. The first fiber layer may comprise carbon fibers.

The second fiber layer may comprise glass fibers.

Yet another configuration can be where the pressure vessel comprises:

at least one opening for gas loading and offloading and for liquid evacuation; a non-metallic liner; and

at least one external fiber layer provided on the outside of the non-metallic liner.

The non-metallic liner may be substantially chemically inert. The non-metallic liner may have a corrosion resistance of at least that of stainless steel, e.g. an AISI 316 stainless steel, e.g. in relation to hydrocarbons or CNG, or impurities in such fluids, such as H ₂ S and C0 ₂ . For example, the liner may be essentially, preferably or substantially H ₂ S resistant, for example in accordance with IS015156.

The non-metallic liner may be selected from the group comprising: high-density polyethylene, high-purity poly-dicyclopentadiene, resins based on poly- dicyclopentadiene, epoxy resins, polyvinyl chloride, or other polymers known to be impermeable to hydro-carbon gases, especially compressed natural gas polymers - the liner is desirably capable of hydraulic containment of raw gases, such as hydrocarbons and natural gas mixtures. The liner is also preferably inert to attack from such gases.

The fiber layer may be made of fiber wound about the non-metallic liner.

The fibers in the fiber layer may be selected from the group of carbon fibers, graphite fibers, E-glass fibers, or S-glass fibers.

The carbon fibers may be coated with a thermoset resin.

The thermoset resin may be selected from the group comprising epoxy-based or high- purity poly-dicyclopentadiene-based resins.

The vessel may further comprise a metallic internal coating provided on the inside of the non-metallic liner.

The metallic internal coating may be essentially, preferably or substantially H ₂ S resistant, for example in accordance with IS015156. The metallic internal coating should preferably not present sulfide stress-cracking at the 80% of its yield strength with a H ₂ S partial pressure of 100 kPa (15 psi), being the H ₂ S partial pressure calculated (in megapascals - pounds per square inch) as follows:

^X H ₇ S

PH 9 = P ^X where

p is the system total absolute pressure, expressed in megapascals (pounds per square inch;

x _{H S} is the mole fraction of H ₂ S in the gas, expressed as a percentage.

The vessel may further comprise a gas permeable layer interposed between the non- metallic liner and the fiber layer. The gas permeable layer may comprise glass fibers.

The vessel may further comprise a gas detector connected to the gas permeable layer for detecting a gas leakage. The gas permeable layer may advantageously comprise an integrated gas detection device able to warn in case of leakage from the liner. The connection to such a device may be integrated into the wall of the vessel, e.g. in that layer. The device may be operated via a wireless transmission to a receiving unit cited elsewhere, e.g. in the dashboard, or on a wristwatch.

Another form of pressure vessel that can be utilised in these ways has a body defining an internal volume in which the compressed gas/fluid can be stored and an inlet for loading the compressed gas/fluid into the vessel, the body of the vessel comprising a structural shell made entirely and solely of a fibre-reinforced filament-wound composite material comprising fibres and a matrix that is substantially impermeable to the intended contents of the pressure vessel, i.e. the compressed gas or fluid.

It is preferred that in use, the compressed gas/fluid will be in direct contact with an inner side of the structural shell.

Preferably the structural shell comprises a cylinder section and two terminations, one at either end of the cylinder section, all being made of the fibre-reinforced filament-wound composite material. Preferably the terminations are dome-like terminations. Preferably the dome-like terminations have a geodesic shape in respect of helical wrapping of fibres around the vessel. Preferably the fibres of the composite material comprise at least one of carbon fibres, glass fibres or Kevlar®.

Preferably the resin of the composite material comprises at least one of a polyester resin, a vinylester resin, an epoxy resin, a phenolic resin, a high-purity dicyclopentadiene resin, a bismaleimide resin and a polyimide resin.

The method of manufacturing this composite pressure vessel involves the steps of providing a disposable mandrel and winding filament fibres around the disposable mandrel to form the shape of a pressure vessel, the shape including an inlet/outlet. The inlet/outlet is typically an aperture in an end thereof. There may be two apertures, one in each end. The ends are typically opposing ends.

The method typically involves the step of removing the disposable mandrel through the inlet/outlet after the composite is cured.

Preferably the method comprises the step of aggregating the filament fibres to form a tape before winding them around the disposable mandrel.

Preferably the method comprises the step of impregnating the filament fibres with a resin before winding the fibres around the disposable mandrel.

Preferably the impregnation of the fibres takes place after the fibres have been formed into a tape and by immersing the tape into a batch of resin, such as in a bath of resin.

Preferably the method comprises the step of curing the composite while it is around the disposable mandrel, at least to a sufficient extent for it to be self-supporting.

Preferably the method comprises the further the step of curing the composite and removing the disposable mandrel once the composite has been cured at least to a sufficient extent for it to be self-supporting. Preferably the mandrel comprises ice, and the removal of the mandrel may then comprise melting the ice. Preferably the mandrel comprises compacted sand, and the removal of the mandrel then may comprise shaking the sand out of the vessel.

The mandrel may comprise a scaffold, and the removal of the mandrel may then comprise collapsing the scaffold.

The mandrel may comprise a structure formed from a disolvable chemical compound (such as one that is desolvable in water) and the removal of the mandrel may then comprise the dissolution of the structure to a liquid state. The present invention also envisions the combination of the various optional or preferred features listed above into the other types of pressure vessel, and also the use of those so modified pressure vessels in the applications listed.

CNG loading and offloading procedures and facilities depend on several factors linked to the locations of gas sources and the composition of the gas concerned.

With respect to facilities for connecting to ships (buoys, platform, jetty, etc ..) it is desirable to increase flexibility and minimize infrastructure costs. Typically, the selection of which facility to use is made taking the following criteria into consideration: · safety;

reliability and regularity;

bathymetric characteristics water depth and movement characteristics; and ship operation: proximity and manoeuvring. A typical platform comprises an infrastructure for collecting the gas which is connected with the seabed.

A jetty is another typical solution for connecting to ships (loading or offloading) which finds application when the gas source is onshore. From a treatment plant, where gas is treated and compressed to suitable loading pressure as CNG, a gas pipeline extends to the jetty and is used for loading and offloading operations. A mechanical arm extends from the jetty to a ship.

Jetties are a relatively well-established solution. However, building a new jetty is expensive and time-intensive. Jetties also require a significant amount of space and have a relatively high environmental impact, specifically in protected areas and for marine traffic.

Solutions utilizing buoys can be categorized as follows:

· CALM buoy;

STL system;

SLS system; and

SAL system. The Catenary Anchor Leg Mooring (CALM) buoy is particularly suitable for shallow water. The system is based on having the ship moor to a buoy floating on the surface of the water. The main components of the system are: a buoy with an integrated turret, a swivel, piping, utilities, one or more hoses, hawsers for connecting to the ship, a mooring system including chains and anchors connecting to the seabed. The system also comprises a flexible riser connected to the seabed. This type of buoy requires the support of an auxiliary/service vessel for connecting the hawser and piping to the ship.

The Submerged Turret Loading System (STL) comprises a connection and disconnection device for rough sea conditions. The system is based on a floating buoy moored to the seabed (the buoy will float in an equilibrium position below the sea surface ready for the connection). When connecting to a ship, the buoy is pulled up and secured to a mating cone inside the ship. The connection allows free rotation of the ship hull around the buoy turret. The system also comprises a flexible riser connected to the seabed, but requires dedicated spaces inside the ship to allow the connection.

The Submerged Loading System (SLS) consists of a seabed mounted swivel system connected to a loading/offloading riser and acoustic transponders. The connection of the floating hose can be performed easily without a support vessel. By means of a pick up rope the flexible riser can be lifted and then connected to a corresponding connector on the ship. The Single Anchor Loading (SAL) comprises a mooring and a fluid swivel with a single mooring line, a flexible riser for fluid transfer and a single anchor for anchoring to the seabed. A tanker is connected to the system by pulling the mooring line and the riser together from the seabed and up towards the vessel. Then the mooring line is secured and the riser is connected to the vessel.

These and other features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

Fig. 1 to Fig 4 show a car featuring a plurality of pressure vessels in accordance with the present invention;

Fig. 5 is a schematic view showing a pressure vessel according to the invention;

Fig. 6 is a partial sectioned view showing schematically a layered composition of a pressure vessel according to the present invention;

Fig. 7 is a schematic view showing a pressure vessel according to another embodiment of the invention;

Fig. 8 is a schematic view showing a pressure vessel according to another embodiment of the invention; Fig. 9 is an enlarged view of a detail in the pressure vessel of Figure 8;

Figure 10 is a schematic view showing a pressure vessel according to another embodiment of the invention; Figs 1 1 and 12 are detailed views of ends of a pressure vessel in accordance with the present invention;

Fig 13 is a pressure vessel featuring the ends of Figs 1 1 and 12; Figs 14 and 15 show a winding technique; Figure 16 shows a section through a final embodiment of pressure vessel;

Figs. 17 and 18 show a train featuring a plurality of pressure vessels in accordance with the present invention; and

Figs. 19 and 20 show a truck (tractor) featuring a plurality of pressure vessels in accordance with the present invention.

Figures 1 to 4 show a car featuring a plurality of pressure vessels, which pressure vessels may take the form of any of the embodiments discussed herein, for example approved type III or type IV pressure vessels, or any of the lighter designs discussed herein (non-all-steel). Figs 17 to 20 show similar arrangements, but for a train (the engine car or locomotive) or a truck or lorry (as shown the tractor part of an articulated lorry, rather than the trailer, put possibly also for an integrated lorry - one without a removeable trailer).

[0055] Suitable pressure vessels can be made of various materials, and using a variety of production technologies.

We list below eight different categories of pressure vessel:

Type 1 : All-steel pressure vessels, with the metal being used as the structure for the containment;

Type 2: Composite Hoop-Wrapped steel tanks with structural steel heads (domes) and hybrid a hybrid material body (steel + fibre-reinforced polymer, the fibre- reinforcement being in hoop sections), the hybrid material being in a load sharing condition;

Type 3: Metallic liner with non-metallic structural overwrap. The metal liner is only there for fluidic containment purposes. The non-metallic external structural overwrap is made out of, in the preferred arrangements, a fibre-reinforced polymer; other non-metallic overwraps are also possible.

Type 4: Non-metallic liner with non-metallic structural overwrap. The non-metallic liner (such as a thermoplastic or a thermosetting polymer liner) is only there for fluidic containment purposes. The non-metallic external structural overwrap can again be made out of, in the preferred arrangements, a fibre-reinforced polymer. Type 5: A fully non-metallic structure (no separate liner), with the non-metallic structure having been built on a substrate that is removed after the manufacturing process.

Type 6: Steel body section fitted with composite heads or domes. The pressure vessels have a structural steel body section and fibre-reinforced polymer heads or domes fitted thereto with a sealed joint;

Type 7: Composite Hoop-Wrapped steel bodies, with composite heads or domes. The pressure vessels have hybrid steel + fibre-reinforced polymer hoop wrapped body section, with the materials in a load sharing condition and fibre-reinforced polymer heads or domes fitted thereto with a sealed joint.

Type 8: Near-Sphere shaped pressure vessels formed from a non-metallic liner with a non-metallic structural overwrap (like the type 4 above, but with the specific near spherical shape). These pressure vessels have a non-metallic liner (such as a thermoplastic or a thermosetting polymer) which serves only for fluidic containment purposes. The non-metallic external structural overwrap is typically made out of, in the preferred arrangements, a fibre-reinforced polymer.

Prior applications describing preferred aspects of some of these types of pressure vessel include PCT/EP201 1/071793, PCT/EP201 1/071797, PCT/EP201 1/071805, PCT/EP201 1/071794, PCT/EP201 1/071789, PCT/EP201 1/071799,

PCT/EP201 1/071788, PCT/EP201 1/071786, PCT/EP201 1/071810,

PCT/EP201 1/071809, PCT/EP201 1/071808, PCT/EP201 1/071800,

PCT/EP201 1/07181 1 , PCT/EP201 1/071812, PCT/EP201 1/071815, PCT/EP201 1/071813, PCT/EP201 1/071814, PCT/EP201 1/071807,

PCT/EP201 1/071801 and PCT/EP201 1/071818, all of which were mentioned above, and all of which are incorporated herein in full by way of reference. The features of the pressure vessels disclosed in these prior filings, and their structure and/or methods of manufacture, are relevant to the present invention in that they can provide the appropriate structure for the storage means (pressure vessel) for storing the compressed fluid (e.g. fuel). As such, they can each either separately or collectively assist in differentiating the present invention over prior art arrangements.

[0056] Fibre-reinforced polymer, also known as fibre-reinforced plastic, is a composite material, consisting in a polymer matrix reinforced with fibres, which are usually fibreglass, aramid or carbon; the polymer is generally an epoxy, vinylester, polyester or another thermosetting polymer or mixture thereof. It is desireably a component of suitable pressure vessels for the applications or embodiments described herein, and is to be found in each of types 2 to 8 pressure vessels.

The pressure vessels of the present invention, according to the first embodiment of Figures 1 to 4, or the embodiments of Figures 17 to 20, are arranged to be fuel tanks for fuel for an engine of the vehicle, i.e. in the car, the locomotive or the truck. For that purpose, fuel lines (not shown) extend from the pressure vessels 10 to the engine, which can be designed or adapted to run on the particular fuel being transported in the pressure vessels 10.

In preferred embodiments the fuel may be CNG or LPG. Preferably it will be a compressed gas that can be stored at room temperature. This makes the arrangement of the tanks more simple to implement since no cooling hardware will be required for cooling the tanks. CNG and LPG are therefore ideal, although CNG is the preferred fuel. As can be seen from these figures, a plurality of pressure vessels 10 may be mounted in the roof of the vehicle. As illustrated there are seven small diameter pressure vessels - perhaps with an internal diameter of between 5 and 10 cm, and a length in excess of 1 metre. These can line the underside of the metalwork of the roof of the vehicle, and may be separated from the cabin of the vehicle by a lower liner 12.

Fewer or more pressure vessels are likewise possible, although space limitations will curb the number.

An impact absorbing foam may surround the vessels to offer protection for the vessels.

A thermally insulating material may be used to reduce heat exchange if required.

The thermally insulating material and the impact absorbing material can be the same material. As shown these pressure vessels extend longitudinally with respect to the vehicle. However, they might instead run perpendicular thereto, depending particularly on the given shape of the roofline since some shapes will accommodate a greater number/volume of pressure vessels in one orientation rather than the other.

The pressure vessels may even have different shapes to that shown, such as disc shapes, or cuboid shapes, albeit usually with curved surfaces (e.g. rounded corners) so as to better accommodate internal wall stresses due to the pressure of the contents thereof. The shapes can be chosen, nevertheless, to provide a suitable or desired storage volume within a given space shape.

As shown in these figures, in addition to the roofline pressure vessels there are also pressure vessels mounted at the level of the chassis, e.g. under the driver and passenger seats, or between front and rear wheels. These pressure vessels are likewise shown to be extending longitudinally with respect to the vehicle. However, again they may be transverse to the vehicle, or of a different shape, if that better suits the design of the chassis, or the space provided in these areas.

Referring specifically to Figure 2, it is seen that there numerous such pressure vessels in these arrangements - nine are shown. However, there could be fewer or more pressure vessels than that shown, or a wider range of sizes and shapes, with the number and size again being limited by the design, e.g. width or length, of the vehicle.

Finally, a rear mounted pressure vessel is also shown in Figures 1 and 4, mounted in the region of the rear bumper, or it could be within the boot of the car. This is shown to be arranged transverse to the vehicle's longitudinal axis, but it could also be arranged differently or it could be provided with a different shape.

The chosen locations for the pressure vessels are relatively arbitrary in that they might be placed in any available space within the vehicle, e.g. behind the dashboard, in the boot, within the chassis, under the seats, in the roof line, in the door/windscreen pillars, in the engine bay, and other arrangements to that shown will be understood by a skilled person, depending upon the spaces available within a particular vehicle. Further a vehicle can be designed to increase the sized of those spaces better to accommodate pressure vessels of a standardised size or shape - usually spherical, near spherical, cylindrical, toroidal or oval, or cuboid with rounded corners. Spaces can even be designed into the vehicles at the design stage thereof.

The benefit here is that the pressure vessels used are lightweight pressure vessels, but nevertheless ones aboe to contain the desired fuel - usually CNG, which might be stored at pressures of up to 300 bar. Being lighter than all steel pressure vessels (type 1 ), and typically lighter than composite tube wrapped type 2 pressure vessels, makes them more readily locatable anywhere on the vehicle where there is the space for doing so. That is because their low weight - even when loaded in the case of CNG, which has a density of perhaps 25% of water/petrol/diesel, - means they will not cause any significant imbalance to the vehicle if located above the centre of gravity of the vehicle.

Further, because of their lightweight nature, and because of the lightweight nature of CNG when stored in these pressure vessels, the suspension of the vehicle does not need to be adapted to account for a specifically located point of mass, as occurs in the case of petrol tanks, which when loaded may weigh in the order of 120kg. Equivalently sized, fully loaded, CNG pressure vessels would weigh instead closer to 30kg. This may mean that there would need to be a larger storage volume capacity. However, they could be distributed around the vehicle since they would not cause the disruption to the balance of the vehicle.

Prior art vehicles have previously been fitted with type I and type 2 pressure vessels - see for example public transport buses converted to run on LPG, and other vehicles such as cars that have likewise been converted. However, those vehicles have typically had either low total volumetric capacities or have been low pressure vessels unsuitable for containing CNG, or have been all steel tanks unsuitable for non commercial vehicles such as cars - buses and trucks, for example, can adequately accommodate the weight of an all steel or type 2 pressure vessel, but a car cannot - since performance is important in cars. In cars, therefore, the additional weight of either a type 1 or a type 2 pressure vessel is not going to be acceptable, other than for a supplemental tank designed to supply a dual fuel vehicle. Therefore there has been little commercial interest in such mono-fuel arrangements for cars. The present invention's use of the lightweight pressure vessels, such as types 3 to 5 and 7, and the other disclosed variants below, however, addresses that concern since the pressure vessels now proposed are of a significantly reduced weight, even when filled with their fuel, whereby they will not compromise the vehicle's performance.

Likewise these arrangements can be incorporated into other modes of transport, such as motorbikes, boats, ships, racing vehicles, airplanes, especially non-commercial airplanes, and even hot air balloons or blimps/airships.

These arrangements may additionally be desireable for use in trains - e.g. see Figures 17 and 18, lorries - e.g. see Figures 19 and 20, in buses, in coaches and in other vehicles requiring fuel since the increased performance benefits would make those modes of transport more efficient which is inevitable an advantage.

It should also be noted that these pressure vessels can also be applied to non vehicular uses, including those where instead of a fuel, some other gas is desired to be contained, e.g. air supplies, general gas distribution applications, medical services, industrial services, recreational services such as scuba diving and emergency service requirements such as fire extinguishers and breathing apparatus. Indeed anywhere where a steel pressure vessel is currently in use, a benefit would be found in swapping to one of the lighterweight solutions provided herein.

Referring now to the remaining drawings, examples of suitable pressure vessels will be described. These are in addition to standard type III and type IV pressure vessels, since all these pressure vessels will have a lower weight than type I pressure vessels. The pressure vessel of Figures 5 and 6 is made of an internal metallic liner as at least a first layer (100) capable of hydraulic or fluidic containment of raw gases such as CNG (20) (Compressed Natural Gas), with an external composite layer (200).

Said metallic liner, as the first layer (100), is not needed to be provided in a form to provide a structural aim during CNG (20) transportation. However, it is preferred that it should be at least corrosion-proof. The preferred material is a stainless steel, or some other metallic alloy. This construction also allows the tank to be able to carry other gases, such as natural gas (methane) with C0 ₂ allowances of up to 14% molar, H ₂ S allowances of up to 1 .5% molar, or H ₂ and C0 ₂ gases. The preferred use, however, is CNG transportation. CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , C ₅ H ₁₂ , C ₆ H ₁₄ , C ₇ H ₁₆ , C ₈ H ₁₈ , C ₉ + hydrocarbons, C0 ₂ and H2S, plus potentially toluene, diesel and octane in a liquid state.

The stainless steel is preferably an austenitic stainless steel such as AISI 304, 314, 316 or 316L (with low carbon percentages). Where some other metallic alloy is used, it is preferably a Nickel-based alloy or an Aluminum-based alloy, such as one that has corrosion resistance.

The metallic liner forming the first layer (100) preferably only needs to be strong enough to withstand stresses arising from manufacturing processes of the vessel, so as not to collapse on itself, such as those imposed thereon during fiber winding. This is because the structural support during pressurized transportation of CNG (20) will be provided instead by the external composite layer (200).

The external composite layer (200), which uses at least one fiber layer, will be a fiber- reinforced polymer. The composite layer can be based on glass, or on carbon/graphite, or on aramid fibers, or on combinations thereof, for example. The external composite layer is used as a reinforcement, fully wrapping the pressure vessels (10), including vessel ends (1 1 , 12), and providing the structural strength for the vessel during service. In case of glass fibers, is it preferred but not limited to the use of an E-glass or S-glass fiber. Preferably, however, the glass fiber has a suggested tensile strength of 1 ,500 MPa or higher and/or a suggested Young Modulus of 70 GPa or higher. In case of carbon fibers, is it preferred but not limited to the use of a carbon yarn, preferably with a tensile strength of 3,200 MPa or higher and/or a Young Modulus of 230 GPa or higher. Preferably there are 12,000, 24,000 or 48,000 filaments per yarn.

The composite matrix is preferred to be a polymeric resin thermoset or thermoplastic. If a thermoset, it may be an epoxy-based resin. The manufacturing of the external composite layer (200) over the said metallic liner (the first layer (100)) preferably involves a winding technology. This can potentially gives a high efficiency in terms of production hours. Moreover it can potentially provide good precision in the fibers' orientation. Further it can provide good quality reproducibility.

The reinforcing fibers preferably are wound with a back-tension over a mandrel. The mandrel is typically the liner. The liner thus constitutes the male mould for this technology. The winding is typically after the fibers have been pre-impregnated in the resin. Impregnated fibers are thus preferably deposed in layers over said metallic liner until the desired thickness is reached for the given diameter. For example, for a diameter of 6m, the desired thickness might be about 350 mm for carbon-based composites or about 650 mm for glass- based composites.

Since this invention preferably relates to a substantially fully-wrapped pressure vessel (10), a multi-axis crosshead for fibers is preferably used in the manufacturing process.

The process preferably includes a covering of the majority of the ends (1 1 , 12) of the pressure vessel (10) with the structural external composite layer (200).

In the case of the use of thermoset resins there can be a use of an impregnating basket before the fiber deposition - for impregnating the fibers before actually winding the fibers around the metal liner (100).

In the case of the use of thermoplastic resins, there can be a heating of the resin before the fiber deposition in order to melt the resin just before reaching the mandrel, or the fibers are impregnated with thermoplastic resin before they are deposited as a composite material on the metal liner. The resin is again heated before depositing the fibers in order to melt the resin just before the fiber and resin composite reaches the metal liner (100).

The pressure vessel (10) is provided with an opening (120) (here provided with a cap or connector) for gas loading and offloading. It is provided for connecting to pipework - e.g. fuel lines/breathing regulators, and the like. The vessel also has an opening 31 at the top end (1 1 ). This, however, is optional - it may be preferred to have a fully domed second end. A plurality of the pressure vessels (10) can be arranged in modules or in compartments and they can be interconnected, for example for loading and offloading operations, such as via pipework. Figures 1 to 4 show arrangements where multiple such pressure vessels are arranged in arrays. The supports for holding the pressure vessels can be designed to accommodate vessel expansion, such as by having some resilience, or by mounting the vessels at their ends, whereby the cylindrical sections can expand radially without restriction.

Referring next to Figure 7, another vessel 10 in accordance with the present invention is shown. It is made of an internal metallic liner 2 capable of hydraulic or fluidic containment. The inside of metallic liner 2 is internally coated with a non-metallic layer 1 , such as a polymeric layer, which is capable of containing, for example, CNG. The metal liner 2 is not needed to be provided in a form to provide a structural aim during the CNG transportation, loading and offloading.

The metal liner 2 is internally coated with the non-metallic corrosion-proof layer 1 and that liner is capable of carrying the compressed gas. Preferred material may be a carbon-steel coated metallic liner 2 with a thin polymer non-metallic layer 1 such as an epoxy resin, HDPE (High-Density Polyethylene) or PVC (Polyvinyl Chloride). Preferably it has a tensile strength of 50 MPa or higher. Preferably it has a Young Modulus of 3 GPa or higher. Preferably it is able to be substantially chemically inert. Preferably it is corrosion-proof for a wide range of chemical compositions, including chlorides.

This construction also allows the vessel 10 to be able to carry other gases, such as natural gas (methane) with C0 ₂ allowances of up to 14% molar, H ₂ S allowances of up to 1 .5% molar, or H ₂ or C0 ₂ gases. The preferred use, however, is CNG.

CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , C ₅ H ₁₂ , C ₆ H ₁₄ , C ₇ H ₁₆ , C ₈ H ₁₈ , C ₉ + hydrocarbons, C0 ₂ and H ₂ S, plus potentially toluene, diesel and octane in a liquid state.

The metal liner 2 preferably only needs to be strong enough to withstand the mechanical stresses arising from manufacturing processes of the vessel, such as those imposed thereon when an external fiber layer 3 is being applied. This is because the structural support during pressurized transportation of gas will be provided instead by the external fiber layer 3. Where the metal liner 2 is of carbon-steel, it could be selected from an API (American Petroleum Institute) 5L X42 or X60 or ASTM (American Society for Testing and Materials) A516 with a preferred tensile strength of 350 MPa or higher.

The external fiber layer 3 may preferably be selected from a fiber-reinforced polymer based on carbon/graphite fibers, advantageously fully wrapping the vessels 10 (including the vessel ends) and providing the structural contribution during service.

When carbon fibers are used in the external fiber layer 3, it is preferred, but not limited thereto, to use a carbon yarn with a preferred tensile strength of 3,200 MPa or higher and/or a preferred Young Modulus of 230 GPa or higher. The yarn may advantageously have 12,000, 24,000, or 48,000 filaments per yarn.

The composite matrix is preferred to be a polymeric resin thermoset or thermoplastic. More precisely, if a thermoset resin is used, it is preferred that it should be an epoxy- based resin, or alternatively a vinyl ester or polyester-based resin. This also allows achieving a cost reduction.

Since the external fiber layer 3 comprising the carbon/epoxy composite is electrically conductive like the steel used for the metallic liner 2, it is advantageous to provide an additional insulating composite layer with isolating properties in order to avoid possible galvanic coupling.

This insulating layer may advantageously be made of glass fibers embedded in epoxy resin, hence matching the resin of the external layer. Concerning glass fibers, it is preferred but not limited to the use of E glass or S glass fiber. Preferably, however, the glass fibers have a suggested tensile strength of 1 ,000 MPa or higher and/or a Young Modulus of 70 GPa or higher.

Alternatively, as shown in Figure 8, it may be useful to apply a polymeric coating as an insulating layer 4. In this embodiment it is between the liner 2 and the fiber layer 3. The insulating layer 4 may advantageously be selected from materials such as an epoxy resin, HDPE (High-Density Polyethylene) or PVC (Polyvinyl Chloride). Preferably the coating has a tensile strength of 50 MPa or higher and/or a Young Modulus of 3 GPa or higher.

The insulating layer 4, which typically has only to carry compressive stresses, may have porous characteristics, i.e. it may be permeable to gases in the case of leakage from the steel liner. The insulating layer 4 may advantageously then further comprise an integrated gas detection device able to warn in case of leakage from the inner liner 2. Figure 9 schematically shows a connection to such a device, which may be integrated into the wall of the vessel. Such a device might be operated via a wireless transmission to a receiving unit located nearby.

The manufacturing of the external composite layer 3 over the said metallic liner 2 (the first layer) preferably involves a winding technology. This can potentially gives a high efficiency in terms of production hours. Moreover it can potentially provide good precision in the fibers' orientation. Further it can provide good quality reproducibility.

The reinforcing fibers preferably are wound with a back-tension over a mandrel. The mandrel is typically the liner. The liner thus constitutes the male mould for this technology. The winding is typically after the fibers have been pre-impregnated in the resin. Impregnated fibers are thus preferably deposited in layers over said metallic liner until the desired thickness is reached for the given diameter. Since this invention preferably relates to a substantially fully wrapped pressure vessel 10, a multi-axis crosshead for fibers is preferably used in the manufacturing process.

The process preferably includes a covering of the majority of the ends 1 1 , 12 of the pressure vessel 10 with the structural external composite layer 3. In the case of the use of thermoset resins there can be a use of an impregnating basket before the fiber deposition - for impregnating the fibers before actually winding the fibers around the metal liner 2. In the case of the use of thermoplastic resins, there can be a heating of the resin before the fiber deposition in order to melt the resin just before reaching the mandrel, or the fibers are impregnated with thermoplastic resin before they are deposited as a composite material on the metal liner. The resin is again heated before depositing the fibers in order to melt the resin just before the fiber and resin composite reaches the metal liner 2.

The pressure vessel 10 may be provided with an opening 7 (here provided with a cap or connector) intended for gas loading and offloading and liquid evacuation. The opening may be placed at either end 1 1 , 12 of the vessel 10.

The vessel 10 also is shown to have a second opening 6 at the other end 1 1 . This is optional - the end dome may be fully rounded instead.

Referring next to Figure 10, a further embodiment of pressure vessel is shown for use with the present invention's intended purposes. The vessel is made of an internal metal liner 1 capable of hydraulic or fluidic containment of raw gases. The metal liner 1 is not needed to be provided in a form to provide a structural aim, during CNG transportation, loading and offloading phases. The metallic liner 1 should be corrosion-proof and capable of containing CNG. Preferably the material used is a stainless steel, aluminum or other corrosion-proof metallic alloy.

In case of stainless steel, it is preferred but not limited to the use of an austenitic stainless steel such as AISI 304, 314, 316 or 316L (with low carbon percentages).

In case of other metallic alloys, it is recommended but not limited to the use of a Nickel- based alloy or an aluminum-based alloy capable of corrosion resistance. This construction also allows the vessel to be able to carry other gases, such as natural gas (methane) with C0 ₂ allowances of up to 14% molar, and/or H ₂ S allowances of up to 1 .5% molar, and also such as H ₂ and/or C0 ₂ gases. The preferred use, however, is CNG.

CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , C ₅ H ₁₂ , C ₆ H ₁₄ , C ₇ H ₁₆ , C ₈ H ₁₈ , C ₉ + hydrocarbons, C0 ₂ and H ₂ S, plus potentially toluene, diesel and octane in a liquid state.

The liner 1 preferably only needs to be strong enough to withstand the stresses arising from manufacturing processes of the vessel, such as those imposed thereon during fiber winding. The structural support during pressurized transportation of gas will instead be provided by the external composite layer(s) 2, 3.

The first fiber layer 2 about the liner 1 , according to the illustrated embodiment, is a fiber-reinforced polymer based on carbon/graphite. It substantially is fully wrapping the vessel (including most of the vessel ends) and it is arranged to be providing the structural contribution during service. Is it preferred but not limited to the use of a carbon yarn, preferably with a tensile strength of 3,200 MPa or higher and/or a preferred Young Modulus of 230 GPa or higher. Advantageously it can have 12,000, 24,000 or 48,000 filaments per yarn. The second fiber layer 3, according to the illustrated embodiment, has an isolating and protective function. In use it will be in direct contact with the external environment. For these mentioned reasons, the second external fiber layer 3 can preferably be a polymer or a fiber-reinforced polymer based on glass fibers, due to its inert behavior in aggressive and marine environments, and due to its isolating properties in terms of low thermal conductivity. Is it preferred but not limited to the use of an E-glass or S-glass fiber. Preferably the fibers have a suggested tensile strength of 1 ,000 MPa or higher and/or a suggested Young Modulus of 70 GPa or higher.

The composite matrix, regardless of the composite layer considered, is preferred to be a polymeric resin thermoset or thermoplastic. More precisely, if a thermoset, it could be and epoxy-based resin, or alternatively a vinylester or polyester-based resin. This allows a cost reduction compared to other possible arrangements, including the traditional steel arrangement. The manufacturing of the external composite layer 2, 3 over the said metallic liner 1 preferably involves a winding technology. This can potentially gives a high efficiency in terms of production hours. Moreover it can potentially provide good precision in the fibers' orientation. Further it can provide good quality reproducibility. The reinforcing fibers preferably are wound with a back-tension over a mandrel. The mandrel is typically the liner. The liner thus constitutes the male mould for this technology. The winding is typically after the fibers have been pre-impregnated in the resin. Impregnated fibers are thus preferably deposited in layers over said metallic liner until the desired thickness is reached for the given diameter. For example, for a diameter of 10 cm, the desired thickness might be about 6 mm for carbon-based composites or about 1 1 mm for glass- based composites.

Since this invention preferably relates to a substantially fully-wrapped pressure vessel 10, a multi-axis crosshead for fibers is preferably used in the manufacturing process.

The process preferably includes a covering of at least most of the ends 1 1 , 12 of the pressure vessel 10 with the structural external composite layer 2, 3.

In the case of the use of thermoset resins there can be a use of an impregnating basket before the fiber deposition - for impregnating the fibers before actually winding the fibers around the metal liner 1.

In the case of the use of thermoplastic resins, there can be a heating of the resin before the fiber deposition in order to melt the resin just before reaching the mandrel, or the fibers are impregnated with thermoplastic resin before they are deposited as a composite material on the metal liner. The resin is again heated before depositing the fibers in order to melt the resin just before the fiber and resin composite reaches the metal liner. The pressure vessel 10 has an opening 7 (here provided with a cap or connector) addressed to gas loading and offloading. It is for connecting to pipework.

The vessel 10 also has an opening 6 at the other end 1 1 . It is optional, and the end may instead be fully domed.

As examples of the present invention, the following are presented:

1 . A corrosion-proof metallic liner made out of AISI 316 stainless steel with a tensile strength of at least 500 MPa and a carbon content below or equal to 0.08%, overwrapped by a structural composite carbon fiber-based with a tensile strength of 3,200 MPa or higher and a preferred Young Modulus of 230 GPa or higher, with advantageously 12,000, 24,000 or 48,000 filaments per yarn and a second external layer made out of non-reinforced epoxy resin with a tensile strength of at least 80 MPa and a thermal conductivity of about 0.2 W»m ^"1 »K ^"1 for insulating reasons.

2. A corrosion-proof metallic liner made out of AISI 316 stainless steel with a tensile strength of at least 500 MPa and a carbon content below or equal to 0.08%, overwrapped by a structural composite carbon fiber-based with a tensile strength of 3,200 MPa or higher and a preferred Young Modulus of 230 GPa or higher, with advantageously 12,000, 24,000 or 48,000 filaments per yarn and a second external glass fiber-based composite layer with an E-glass or S-glass fiber with an suggested tensile strength of 1 ,000 MPa or higher and a suggested Young Modulus of 70 GPa or higher impregnated with an epoxy resin with a thermal conductivity of about 0.2 W»m ^{" 1} ·Κ ^"1 for insulating reasons.

3. A corrosion-proof metallic liner, overwrapped by a structural composite carbon fiber-based with a tensile strength of 3,200 MPa or higher and a preferred Young Modulus of 230 GPa or higher, with advantageously 12,000, 24,000 or 48,000 filaments per yarn and a second external glass fiber-based composite layer with an E- glass or S-glass fiber with an suggested tensile strength of 1 ,000 MPa or higher and a suggested Young Modulus of 70 GPa or higher impregnated with an epoxy resin with a thermal conductivity of about 0.2 W»m ^"1 »K ^"1 for insulating reasons plus a third external layer made out of non-reinforced epoxy resin with a tensile strength of at least 80 MPa and a thermal conductivity of about 0.2 W»m ^"1 »K ^"1 for insulating reasons. This configuration also allows the vessel to have a higher thermal stability, giving the transported gas a lower temperature gradient.

Referring next to Figures 1 1 t 13, a further embodiment of the present invention is shown. They relate to a pressure vessel, in particular for compressed natural gas containment or transport. As shown in Fig 13, the pressure vessel 10 comprises at least one opening 71 , 72 for gas loading and offloading and for liquid evacuation, a non-metallic liner 2, and at least one external fiber layer 3 provided on the outside of the non-metallic liner 2. With this arrangement, it is possible for the liner 2 to be wrapped or encased by an external composite layer 3.

The internal non-metallic liner 2 is capable of hydraulic containment of raw gases since a suitable thermoplastic or thermoset material is chosen for the liner such that it is non- permeable to the gas because of its micro-structural properties. Natural gas molecules cannot go through the liner because of both spacial arrangement and/or chemical affinity in these materials. Suitable materials for the liner include polymers such as high-density polyethylene (HDPE) and high-purity poly-dicyclopentadiene (DCPD). However, other materials capable of hydraulic containment of raw gases are known, and as such they might instead be used.

The internal liner 2 preferably has no structural purpose during CNG transportation, loading and offloading Phases.

The non-metallic liner 2 should be corrosion-proof and will in most situations be capable of carrying non-treated or unprocessed gases, i.e. raw CNG. When the non- metallic liner 2 is made from thermoplastic polymers it may be preferred to use a polyethylene or similar plastic which is capable of hydrocarbon corrosion resistance.

The manufacturing of such liners is preferably achieved through rotomolding. For example, a heated hollow mold is filled with a charge or shot weight of material. It is then slowly rotated (usually around two axes perpendicular with respect to each other) thus causing the softened material to disperse and to stick to the walls of the mold. In order to maintain an even thickness throughout the liner, the mold continues to rotate at all times during the heating phase, and to avoid sagging or deformation also during the cooling phase. When the non-metallic liner 2 is made from thermoset resins it may be preferred to use a polyester, an epoxy, a resin based on poly-dicyclopentadiene or similar plastic capable of hydrocarbon corrosion resistance. The manufacturing of such liners may again be done through rotomolding. For example, a hollow mold is filled with an unhardened thermoset material, and it is then slowly rotated causing the unhardened material to disperse and stick to the walls of the mold.

It is to be appreciated that rotating in only one axis could be enough, especially for this latter embodiment due to the lower viscosity of thermoset compounds.

In order to maintain an even thickness throughout the liner, the mold will typically continue to rotate at all times during the hardening phase (through catalysts). This can also help to avoid sagging or deformation.

This construction also allows the tank to be able to carry a variety of gases, such as raw gas straight from a bore well, including raw natural gas, e.g. when compressed - raw CNG or RCNG, or H ₂ , or C0 ₂ or processed natural gas (methane), or raw or part processed natural gas, e.g. with C0 ₂ allowances of up to 14% molar, H ₂ S allowances of up to 1 ,000 ppm, or H ₂ and C0 ₂ gas impurities, or other impurities or corrosive species. The preferred use, however, is CNG applications, be that raw CNG, part processed CNG or clean CNG - processed to a standard deliverable to the end user, e.g. commercial, industrial or residential. CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , C ₅ H ₁₂ , C ₆ H ₁₄ , C ₇ H ₁₆ , C ₈ H ₁₈ , C ₉ + hydrocarbons, C0 ₂ and H ₂ S, plus potentially toluene, diesel and octane in a liquid state, and other impurities/species.

The non-metallic liner 2 can be provided such that it has only to carry the stresses due to manufacturing during the winding of fibers 3, while the structural support during pressurized transportation of gas will be carried out or provided by the external composite layer 3. The internal surface of the non-metallic liner 2 may advantageously be coated by an internal coating 1 in order to enhance the permeability and corrosion resistance. See the optional dotted line in Figure 12, only shown on a part of the inner surface. It would in practice be located across the entire surface, but is only shown for illustrative purposes.

The internal coating 1 of the non-metallic liner 2 may be either a special thin layer of a resin with specific low permeability properties or a thin metallic layer. The deposition of the thin protective layer 1 in the case of metals may preferably involve a catalyst able to provide chemical bonding between the organic (polymeric) substrate and the selected low permeability metal or a solution comprising a salt of the preferred metal, a complexing agent and a reducing agent.

The external composite layer 3 will typically be a fiber-reinforced polymer (composite based on glass fibers, or carbon/graphite fibers, or aramid fibers), and it is provided as a reinforcement. It is formed so as to be substantially fully wrapping the vessel 10 (including the majority of the vessel's ends) and so as to be providing the structural contribution during service. When glass fibers are used, it may be preferred, but not limited thereto, to use an E- glass or S-glass fiber, preferably with a suggested ultimate strength of 1 ,500 MPa or higher and/or a suggested Young Modulus of 70 GPa or higher. When using carbon fibers, is may be preferred, but not limited thereto, to use a carbon yarn, preferably with a strength of 3,200 MPa or higher and/or a Young Modulus of 230 GPa or higher. Preferably there are 12,000, 24,000 or 48,000 filaments per yarn.

The composite matrix may preferably be a polymeric resin thermoset or thermoplastic and more precisely, if thermoset, it may be an epoxy-based resin. The pressure vessel 10 may further comprise a gas permeable layer interposed between the non-metallic liner 2 and the fiber layer 3. Advantageously, the gas permeable layer comprises glass fibers. The pressure vessel 10 may further comprise a gas detector connected to the gas permeable layer for detecting a gas leakage. The outermost portion of the external composite layer 3 may further be impregnated using a resin with a high fire resistance, such as in accordance with NGV2-2007 or other internationally recognized standards and testing procedures in order to protect the vessel 10 from fire occurrence. This resin could be a thermoset such as a phenolic polymer. This, like most of the features disclosed herein, can be beneficially applied also to the other embodiments.

With reference to Fig 1 1 , the opening 71 and/or 72 at at least one of the tank ends 1 1 and/or 12 may take the form of a nozzle that is also made out of composite materials, preferably in which the reinforcing fiber is carbon or graphite and the resin matrix is epoxy-based.

The composite nozzle may be integrated in the composite pressure vessel structure so that the winding forces of the fibers on the pressure vessel head induce a compression state in the nozzle, being the nozzle between the wound composite and the liner,

The composite nozzle may have threaded holes in the outer surface being able to directly connect valves, pipes and other components in the process or fuel lines, without having pieces being out of the pressure vessel shape hence reducing the required room for accommodating the pressure vessel itself.

The manufacturing of the composite nozzle may involve the so-called closed-mold technique. The manufacturing of the external composite layer 3 over the said non-metallic liner 2 preferably involves a winding technology. This can potentially give a high efficiency in terms of production hours. Moreover it can potentially provide good precision in the fibers' orientation. Further it can provide good quality reproducibility. The reinforcing fibers preferably are wound with a back-tension over a mandrel. The mandrel is constituted by the non-metallic liner 2. The non-metallic liner 2 thus constitutes the male mould for this technology. The winding is advantageously performed after the fibers have been pre-impregnated in the resin. Impregnated fibers are thus preferably deposited in layers over said non-metallic liner 2 until the desired thickness is reached for the given diameter. Since this invention relates to a substantially fully-wrapped pressure vessel 10, it may be preferable to use a multi-axis crosshead for fibers in the manufacturing process. The process preferably also includes a covering of the majority of the ends (1 1 , 12) of the pressure vessel 10 with the structural external composite layer 3.

When using thermoset resins an impregnating basket may be used for impregnating the fibers before actually winding the fibers around the non-metallic liner 2.

When using thermoplastic resins, there can be a heating of the resin before the fiber deposition in order to melt the resin just before reaching the mandrel, or the fibers may be impregnated with thermoplastic resin before they are deposited as a composite material on the metal liner. The resin is again heated before depositing the fibers in order to melt the resin just before the fiber and resin composite reaches the non- metallic liner 2.

The pressure vessel 10 may preferably be provided with at least one opening 71 and/or 72 intended for gas loading and offloading. The opening 71 and/or 72 may be placed at either end 1 1 , 12 of vessel 10. It will generally be for connecting to pipework such as fuel lines or breathing regulators.

The pressure vessel 10 also has an opening 71 at the top end 1 1 , although this is optional. The second end may instead be fully domed.

Examples:

1 . A thermoplastic liner 2 such as high-density polyethylene - HDPE with a density between 0.9 and 1 .1 g/cm ³ , a tensile strength of at least 30 MPa over-wrapped with a composite structure 3 based on carbon or graphite fiber reinforcement preferably using a carbon yarn with a strength of 3,200 MPa or higher and a Young Modulus of 230 GPa or higher, with 12,000, 24,000 or 48,000 filaments per yarn and a thermoset resin (epoxy-based or high-purity poly-dicyclopentadiene-based resins). The thermoplastic liner 2 is produced by multi-axis rotomolding as explained in the description of the invention. 2. A thermoset liner 2 such as high-purity poly-cyclopentadiene - pDCPD with a density between 0.9 and 1.1 g/cm ³ , a tensile strength of at least 65 MPa over-wrapped with a composite structure 3 based on carbon or graphite fiber reinforcement using a carbon yarn with a strength of 3,200 MPa or higher and a Young Modulus of 230 GPa or higher, with 12,000, 24,000 or 48,000 filaments per yarn and a thermoset resin (epoxy-based or high-purity poly-dicyclopentadiene-based resins). The thermoset liner 2 is produced by a single-axis rotomolding machine as explained in the description of the invention.

3. A thermoset liner 2 such as high-purity poly-cyclopentadiene - pDCPD with a density between 0.9 and 1.1 g/cm ³ , a tensile strength of at least 65 MPa over-wrapped with a composite structure 3 based on carbon or graphite fiber reinforcement using a carbon yarn with a strength of 3,200 MPa or higher and a Young Modulus of 230 GPa or higher, with 12,000, 24,000 or 48,000 filaments per yarn and a thermoset resin (epoxy-based or high-purity poly-dicyclopentadiene-based resins) and a metallic internal coating 1 of the liner capable of H ₂ S resistance in accordance with the International Standard (ISO) 15156. The thermoset liner is produced by a single-axis rotomolding machine to be produced as explained in the description of the invention.

4. A thermoplastic liner 2 such as high-density polyethylene (HDPE) with a density between 0.9 and 1 .1 g/cm ³ and a tensile strength of at least 30 MPa is over-wrapped with a composite structure 3 based on an E-glass or S-glass fiber with an suggested ultimate strength of 1 ,500 MPa or higher and a suggested Young Modulus of 70 GPa or higher and thermoset resin (epoxy-based or high-purity high-purity poly- dicyclopentadiene-based resins). The thermoplastic liner 2 is produced by multi-axis rotomolding as explained in the description of the invention.

5. A thermoset liner 2 such as high-purity poly-cyclopentadiene - pDCPD with a density between 0.9 and 1.1 g/cm ³ , a tensile strength of at least 65 MPa over-wrapped with a composite structure 3 based on an E-glass or S-glass fiber with an suggested ultimate strength of 1 ,500 MPa or higher and a suggested Young Modulus of 70 GPa or higher and thermoset resin (epoxy-based or high-purity poly-dicyclopentadiene- based resins). The thermoset liner 2 is produced by a single-axis rotomolding machine as explained in the description of the invention. 6. A thermoset liner 2 such as high-purity poly-cyclopentadiene - pDCPD with a density between 0.9 and 1.1 g/cm ³ , a tensile strength of at least 65 MPa over-wrapped with a composite structure 3 based on an E-glass or S-glass fiber with an suggested ultimate strength of 1 ,500 MPa or higher and a suggested Young Modulus of 70 GPa or higher and thermoset resin (epoxy-based or high-purity poly-dicyclopentadiene- based resins) and a metallic internal coating 1 of the liner 2 capable of H ₂ S resistance in accordance with the International Standard (ISO) 15156. The thermoset liner 2 is produced by a single-axis rotomolding machine as explained in the description of the invention.

Another form of pressure vessel for the present invention is a "type 3" vessel. It has an external structural layer made of a composite, fibre reinforced, material and an inner metallic liner, which can be thin. The external composite material provides the structural strength of the vessel, while the inner liner provides an impermeable layer for containment of the gas. The liner is generally made of a metal which is highly chemically resistant. The purpose of the liner, however, is not just to provide a layer suitable for contact with the gas but also that of providing a substrate over which the composite material can be formed. A way of forming said composite material is by winding its fibres around the liner. The liner, therefore, is designed so as to be able to withstand fibre winding stresses.

One method of forming such a resistant liner is that of line welding one or more sheets of metal together along edges. A plurality of similarly curved sheets of metal would usually be welded together to form the liner, although a single sheet may be rolled and then joined along a common seam. Alternatively the tube might be extruded. Further welding between the hoop section and the end domes is then performed. Those end domes can be formed through a spin forming process or by a pressing process if of a small radius (e.g. less than 1 m), which processes are well known in the industry.

The welds are then usually ground down to give a smooth finish.

It should be highlighted that these methods produce the need for a significant number of welds, each of which presents numerous potential points of failure since weld lines are usually weaker than the sheet metal itself, in terms of their strength/durability properties, due to the structural changes to the material that can occur during or after the thermal shock of the welding process. In light of this, manufacturing a suitable liner requires know-how, materials, time and suitable equipment, such as welding equipment and specialist sheet-clamping equipment, and this is all adding to the costs involved.

In a further embodiment of the present invention, disclose herein with reference to Figures 14 to 16, it is possible to dispense with the liner inside the finished vessel. In order to manufacture a liner-free vessel suitable for containment of CNG, the method illustrated in Figure 14 is provided.

In that method, a plurality of reels 31 , 32, 33, 34 is provided, each housing a reel of a selected fibre, for example a carbon fibre, or an aramid fibre, or Kevlar®. In one embodiment, the reels accommodate individual filaments of the selected fibre. In other embodiments, yarns of fibres can be reeled, or the fibres can be bundled into tows, ropes or cords, or braids. Alternatively, the fibres may be woven into ribbons or narrow sheets of material (a fabric of fibre), including flat-fibres or webbing. The single fibres, yarns, tows, ropes or narrow ribbons of fibre(s) are then fed to a tape machine 35. The tape machine arranges those multiple "fibres", which are effectively one-dimensional, into a single tape 37. The tape will still be relatively narrow, but it will now be in a wider, or two-dimensional, form, i.e. it will be wider that the individual "fibres" that come off the reels 31 , 32, 33, 34.

The tape can be treated as being effectively a substantially parallel arrangement of "fibres", the fibres extending largely side by side, i.e. transversally or perpendicularly to the direction of travel, along the length of the tape. The tape 27 is then immersed into a resin, such as a batch of resin in a bath 38. Suitable resins can be, for example, polyester resins, vinylester resins, epoxy resins, dicyclopentadiene resins, phenolic resins, bismaleimide resins and polyimide resins. Such resins can generally be classified as either a thermoplastic resin or a thermosetting resin, according to their behaviour when heated and cooled. Thermoplastic resins can be re-heated and softened after they have been cured, while thermosetting resins, once cured, cannot be re-heated to soften them without causing permanent damage, i.e. they will not melt at normal manufacturing temperatures. On the other hand, thermosetting resins allow higher stiffness and higher general mechanical properties to be provided, along with their generally lower viscosity before curing of the resin (these advantages typically allow a better or faster winding/manufacturing process and a better impregnation of the composite fibers). It is observed, therefore, that thermosetting resins and thermoplastic resins can both be suitable for this method, provided that the resin of choice is formulated to be chemically CNG resistant and substantially, or virtually completely, impermeable to the component parts of CNG at the desired operating pressures of the vessels. Those component parts will comprise one or more of the following compounds: C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , C ₅ H ₁₂ , C ₆ H ₁₄ , C ₇ H ₁₆ , C ₈ H ₁₈ , C ₉ + hydrocarbons, C0 ₂ and H ₂ S, plus potentially toluene, diesel and octane in a liquid state. The resin impregnated tape 39 is then fed to a mechanical head 40 which is responsible for winding the impregnated tape (now shown in the drawings by reference sign 41 ) around the mandrel 45. Various methods can be used for winding the impregnated tape around the mandrel. A simple way, however, is that of employing a mechanical head 40 which moves back and forth one-dimensionally, i.e. along a line parallel to the mandrel, the head delivering the tape 41 as the mandrel 45 rotates. This arrangement is schematically shown in Figures 2 and 3. Preferably the winding process involves helical and hoop winding. Helical winding goes around the geodesic heads (ends) of the mandrel and around the openings. Hoop winding goes on the cylindrical section only in a circumferential direction. The hoop section may be arranged such that it accommodates approximately double the fiber amount of the heads, e.g. in terms of the thickness of the winding.

In the formation of the prior art type 3 vessel, the mandrel would take the form of the liner. However, in accordance with the embodiment of Figures 14 to 16, the mandrel instead takes the form of a disposable mandrel, i.e. a mandrel that can be eliminated or removed from the inside area of the vessel once the composite layer or composite laminate has been created thereon. That mandrel thus needs to be able to withstand the winding stresses during the winding of the tape, plus the lamination stresses as the layers build up - lamination refers to the process of growing the thickness of the composite wrap by gradually stacking layers of tape over one another by winding the tape continually, back and forth over the mandrel so as to pass over other previously wound layers of tape. The winding thus forms multiple helical or coiled (i.e. hooped) layers of tape so as to provide a substantially uniform or flat surface. In the embodiment of Figure 15, the disposable mandrel 47 is made of compacted sand. Other disposable mandrels are also anticipated to be useable here, such as expandable stent-like arrangements, or braids, or balloons, or other solid arrangements such as ice or clay shells, plus other collapsible structures. Figure 15 only shows the wound tape in loose-wind form, and prior to completing the full number of windings required, and this is for illustrating the principle of the winding only - in practice it would be wound down tight against the mandrel 47, and the tape windings would be overlayered many times so as to form the vessel's form. Once the over-layer of fibre-reinforced composite material has been fabricated over the disposable mandrel 47, so as to have formed the desired material thickness, the sand can be removed from the centre of the vessel. This can be achieved, for example, by applying vibrations to the finished component, e.g. by means of an electromechanical shaker. The vibrations produced by the shaker will break up the compacted sand, which will then be able to be removed from the inside of the vessel, e.g. by tipping or washing it out of an aperture in an end thereof. The aperture will be formed (or left) at the end of the vessel during the winding process. Indeed, an aperture would usually be left or formed at both ends thereof. Such apertures not only allow the sand to be removed, but they also will ultimately allow CNG to be loaded into and unloaded from the vessel, during use.

The ends of the vessel are formed over dome-shaped ends of the mandrel, but only to a sufficient degree so as to leave thereat the aperture(s). Figure 15 shows the general trajectory of the resin-impregnated tape 51 as it is wound around the disposable mandrel. The mandrel 47 has the shape of the internal volume of the CNG pressure vessel, in this case a cylinder with two dome-shaped ends or terminations. The resin-impregnated tape 51 is supplied onto the mandrel 47 starting from an origin or first free end 50. In Figure 15, the origin 50 of the tape is located close to the left dome of the disposable mandrel 47. While the mandrel spins around its longitudinal axis, the mechanical tape delivery head moves longitudinally (parallel to that axis) so as to create hoops or circles 53 (a coil or helix) of fibres around the mandrel 47. Those hoops or circles maintain a substantially constant angle relative to the axis along that cylindrical part of the mandrel. When the head reaches the first (right) end of the mandrel 47, the wrapping characteristics change. For example, as it reaches the right end of the mandrel 47, it slows down, and so does the rotation of the mandrel 47. The angle of the hoops or circles therefore may be changed. Further, as the winding slows down, torsional forces are generated within the mandrel, and these are in addition to the winding forces already being generated (the winding forces tend to compress the mandrel from outside in). The torsional forces result from the momentum of the mandrel, and can be considerable if the vessel is both large and the rotational speeds vary rapidly. Such additional torsional forces, however, would also have occurred in arrangements where the mandrel takes the form of a liner, and as such have been an existing problem with the known over-liner winding techniques, whereby it has been something that has contributed to the need to make those liners stronger, and thus heavier, than ultimately desirable, so as to prevent them from deforming out of shape as a result of the wrapping. However, when using the disposable mandrel of the present invention, such heavier mandrels do not cause a problem for the final product since the disposable mandrel will not remain within the finished vessel.

Another advantage of having a filled structure/mandrel or a structure with radial components is potentially a better behavioural response to torsional winding forces than a traditional liner, which is usually a thin-walled approximation and having a smaller material section.

This aspect of the present invention therefore offers a considerable advantage over the prior art. With the compacted sand solution for the mandrel, there should be little at issue in relation to handling the additional torsional forces either. That is because the compacted sand can be made to have significant robustness to such loadings. Other solutions for the mandrel can also offer such advantages. For example, a solid mandrel formed from a destructible, dissolvable or meltable material (including compacted sand, wax, ice, clay, gypsum and many other granular or dusty, yet compactable, materials) can be designed such that it cannot easily twist out of shape. Likewise, a fracturable clay liner, or collapsible structures like balloons, or braid or stent-like arrangements, or other collapsible scaffolds, can be made such that they are strong enough to survive such forces, but yet still being removable through the aperture(s). Such scaffolds can even support arrangements such as compacted sand pads or ice pads, thereby making the mandrel significantly lighter than a solid mandrel.

Returning to the process of winding the composite, once the fibre has reached the first end of the mandrel, it is wound around the dome of the mandrel at that end, albeit leaving the aperture part of the vessel, at that end, uncovered, and then it is returned towards the other end of the mandrel through a further coiled path 54 generally diagonally across the body of the mandrel 47. This path will typically have a different angle to the preceding coil, although that is optional, and it may even be sufficiently angulated so as not to form a full loop around the cylindrical section of the vessel. Preferably it loops around less than half of the vessel's circumference, and even more preferably it loops around even less than one third or perhaps one quarter of the vessel's circumference before inverting back towards line of passage back towards the first end again, usually at the same angle as the first-described passage towards that first end.

The speed of rotation of the mandrel, and the speed of movement of the head 40, will be controlled - reduced - at the second end of the mandrel too. Further, the tape is wound around the dome of the mandrel at that second end much like that at the first end, again leaving an aperture for the vessel at that second end.

When the winding operation is concluded, the tape is cut and a second free end of the tape 52 is formed. This is accommodated on the layer of fibres already wound around the mandrel. The vessel is now ready for curing (or "cooking"), where needed.

At the end of the curing, the disposable mandrel can be removed in an appropriate manner, such as by the vibration technique for compacted sand, or by dismantling the scaffold, etc.

The above process has been illustrated herein only schematically.

It should be noted that several layers of tape will need to be wound around the mandrel until a desired thickness, such as one of several mm or cm, is eventually obtained. The actual thickness that is desirable for a given vessel will depend upon the target pressure containment capacity, and also the diameter of the finished vessel. Conventional hoop-stress analysis can be used for determining these desired dimensions since the strength of the fibres, and the angles of winding, are all known.

Multiple axis filament winding machines can also be used to implement a method of the present invention. For example, 2-axes or 3-axes filament winding machines can be used. These are machines whose fibre delivery head can move respectively in a plane or in a 2- or 3-dimensional space. It is even known that winding machine heads can be shifting and turning with up to 5-axes.

Further, the number of axes around which the mandrel can spin could be two, three or more, instead of just the one (longitudinal) axis as described above. The machine used will depend on the design of the desired vessel, i.e. its size and shape.

An example of a finished product obtained with the manufacturing process illustrated above can be seen in Figure 16. In this Figure, the vessel 64 is made entirely and solely of a structural portion of fibre-reinforced composite material 62. It was wound around a disposable mandrel, presenting an inner surface 63 directly into contact with the CNG. The structural composite itself therefore is capable of containing the CNG within the vessel - no liner or internal coating is needed (although a coating may beneficially be applied if desired, from inside of the vessel). Examples:

1 . A composite pressure vessel made of carbon or graphite fibres having a strength of 3200 MPa or higher and a Young Modulus of 230 GPa or higher, with 12000, 24000 or 48000 filaments per yarn, and a thermosetting resin (epoxy-based or high-purity poly-dicyclopentadiene-based resin), the vessel being obtained by over- wrapping a disposable mandrel made of clay of generally cylindrical shape.

2. A composite pressure vessel made of carbon or graphite fibres having a strength of 3200 MPa or higher and a Young Modulus of 230 GPa or higher, with

12000, 24000 or 48000 filaments per yarn, and a thermosetting resin (epoxy-based or high-purity poly-dicyclopentadiene-based resin), the vessel being obtained by over- wrapping an disposable mandrel made of ice. 3. A composite pressure vessel made of carbon or graphite fibres having a strength of 3200 MPa or higher and a Young Modulus of 230 GPa or higher, with 12000, 24000 or 48000 filaments per yarn, and a thermosetting resin (epoxy-based or high-purity poly-dicyclopentadiene-based resin), the vessel being obtained by over- wrapping a mandrel made of a chemically etchable material.

4. A composite pressure vessel made of E-glass or S-glass fibres having a strength of 1500 Mpa or higher and a Young Modulus of 65 GPa or higher and a thermosetting resin (epoxy-based or high-purity poly-dicyclopentadiene-based resin), the vessel being obtained by over-wrapping a spherical mandrel which is made of modules which can be mechanically disassembled, and the single components or modules can be pulled out of the vessel, once disassembled, through the vessel's inlet/outlet aperture.

5. A composite pressure vessel made of E-glass or S-glass fibres having a strength of 1500 MPa or higher and a Young Modulus of 65 GPa or higher and a thermosetting resin (epoxy-based or high-purity poly-dicyclopentadiene-based resin), the vessel being obtained by over-wrapping filaments of the fibres on a disposable mandrel made of gypsum.

Various different forms of pressure vessel have therefore been described. The pressure vessels described herein can carry a variety of gases, such as raw gas straight from a bore well, including raw natural gas, e.g. when compressed - raw CNG or RCNG, or H ₂ , or C0 ₂ or processed natural gas (methane), or raw or part processed natural gas, e.g. with C0 ₂ allowances of up to 14% molar, H ₂ S allowances of up to 1 ,000 ppm, or H ₂ and C0 ₂ gas impurities, or other impurities or corrosive species. The preferred use, however, is CNG transportation, be that raw CNG, part processed CNG or clean CNG - processed to a standard deliverable to the end user, e.g. commercial, industrial or residential.

The CNG will typically be at a pressure in excess of 60bar, and potentially in excess of 10Obar, 150 bar, 200 bar or 250 bar, and potentially peaking at 300 bar or 350 bar.

CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , C ₅ H ₁₂ , C ₆ H ₁₄ , C ₇ H ₁₆ , C ₈ H ₁₈ , C ₉ + hydrocarbons, C0 ₂ and H ₂ S, plus potentially toluene, diesel and octane in a liquid state, and other impurities/species. The present invention has been described above purely by way of example. Modifications in detail may be made to the invention within the scope of the claims appended hereto.