Hydrogen pressure vessel

Abstract

A hydrogen pressure vessel 10 comprises a liner 12 defining a chamber for containing hydrogen, a valve for sealing and opening the chamber and a fibre composite layer 16 formed around the liner. It fu

Description

Background Hydrogen storage pressure vessels are used to transport and store hydrogen for use as an energy source in a variety of applications such as fuel cell vehicles and hydrogen power production systems. Such vessels can comprise an inner liner around which a layer of carbon fibre is formed for reacting pressure from hydrogen stored within the vessel. The vessel can be coated with a glass coating to protect the carbon fibre layer. In type 3 vessels, the liner can be formed from a metal such as aluminium, whereas in type 4 vessels, the liner can be formed from a polymer. In both cases, the primary purpose of the liner is to provide a gas impermeable container for inhibiting the escape of hydrogen from within the vessel, whereas the primary purpose of the carbon fibre layer is to inhibit the liner from expanding beyond a boundary defined by the carbon fibre layer. If a crack or other opening forms In the liner of a pressure vessel, hydrogen can escape from the vessel. The present inventors have devised a new type of Hydrogen pressure vessel which can have one or more of the following advantages relative to known Hydrogen pressure vessels: • less prone to failure • simpler to manufacture Summary In accordance with a first aspect of the present invention there is provided a hydrogen pressure vessel comprising: a liner defining a chamber for containing hydrogen and a valve for sealing and opening the chamber; a fibre composite layer formed around the liner; and one or more ultrasound transducers mounted on an outer surface of the liner, each ultrasound transducer being electrically coupled to a respective induction coil to define a non-destructive testing sensor, each non-destructive testing sensor being arranged and configured for guided wave testing of the liner. Thus, the hydrogen pressure vessel according to the first aspect of the invention includes guided wave NDT sensors which each comprises an ultrasound transducer mounted on the liner, under the composite layer. The thin, battery-free sensors can be activated wirelessly by a remote energisation device and data collector to provide accurate, reproducible liner ultrasonic readings from the exact same location each time. The induction coil of each sensor can be positioned in or on the fibre composite layer. Thus, embodiments of the invention can include sensors with an induction coil which is either within the composite layer or at the outer surface of the composite layer and electrically coupled to the transducer. The present inventors have recognised that, due to the winding patterns employed for the outer composite layer, it can be challenging or impossible to inductively couple with the sensors through the entire thickness of the composite layer for certain non-transparent materials such as carbon fibre. Embodiments of the invention place the induction coils within, or at the surface of the composite layer to enable the passive sensors to be inductively energised with power and NDT signal via a remote energisation device for guided wave testing. The liner can comprise a neck at which the valve is located, wherein the electrical conductor for each sensor extends from the respective transducer along the liner under the composite layer to the neck and extends from the neck to the respective induction coil along the outer surface of the composite layer. Advantageously, this enables the composite layer to be formed in a conventional manner without having to work around the wiring. The fibre composite layer can be formed of glass fibre and the induction coil of each sensor can be positioned between the liner and the fibre composite layer, such as on the liner. The fibre composite layer can have a first region having a first thickness and one or more second regions having a second thickness which is less than the first thickness and the induction coil of each sensor can be positioned between the liner and the fibre composite layer at one or the second regions. The second thickness can be the same or different for the second regions. n pressure vessel can comprise a plurality of sensors, each sensor comprising a dedicated electrical conductor between the transducer and the coil of the sensor. The coil of each sensor can be generally coaxial with the transducer. The coil of each sensor can be non-coaxial with the transducer; for example, spaced from the transducer by a distance greater than 5cm and / or less than lm. The induction coil of a sensor can be directly electrically coupled to the transducer by electrical conductor. Thus, the electrical conductor can be a wire having one end coupled to the coil and another end coupled to the transducer. Alternatively, the induction coil of a sensor can be indirectly electrically coupled to the respective transducer by: a first portion of the electrical conductor which directly electrically couples the coil to a first intermediate induction coil; and a second intermediate induction coil directly electrically coupled to the transducer by a second portion of the electrical conductor, wherein the first intermediate induction coil is mounted relative to the second intermediate induction coil to enable inductive coupling therebetween. Advantageously, a portion of the electrical conductor in such embodiments acts as an 'extension cable' that enables a conventional inductively powered ultrasound sensor placed on the liner to be energised from a remote location, with an inductive coupling between the extension cable and the sensor. The electrical conductor can have a cross section with a width which is greater than a height. The electrical conductor can for example comprises a flexible printed circuit board. Thus, the electrical conductor can have a low profile. The electrical conductor can be no greater than 5m in length, in some embodiments no greater than 3m and in some embodiments no greater than lm. The liner can be formed from metal or a plastics material. iposite layer can comprise at least 30 layers and / or no more than 300 layers. The fibre composite layer can have a thickness of at least 10mm and / or no greater than 50mm. This can be the first thickness at a first region. Each sensor can comprise a unique RFID for traceability and automated data management. Each non-destructive testing sensor can be a passive device. Brief Description of the Drawings By way of example only, certain embodiments of the invention will now be described by reference to the accompanying drawings, in which: Figures la to 1c are diagrams of a hydrogen pressure vessel according to an embodiment of the invention; Figure 2 is a diagram of a sensor arrangement of an embodiment, with the coil embedded in the composite layer and wiring through the composite layer; Figure 3 is a diagram of a sensor arrangement of an embodiment, with the coil at the outer surface of the composite layer and wiring through the composite layer; Figure 4 is a diagram of a sensor arrangement of an embodiment, with the coil at the outer surface of the composite layer and wiring extending under the composite layer to the neck; Figures 5a to 5c show stages of a method of forming a pressure vessel with the sensor arrangement of Figure 4; Figure 6 is a diagram of an electrical conductor including an inductive extension cable which can be applied to any embodiment where the coil is remote from the transducer; Figure 7 is a diagram of a sensor arrangement which can be used with electromagnetically transparent composite layers such as glass fibre; diagram of a sensor and energisation tool which can be employed In embodiments of the invention; and Figure 9 is circuit diagram of a wireless ultrasound sensor which can be employed in embodiments of the invention. Detailed Description Figures la to 1c shows a hydrogen pressure vessel according to an embodiment of the invention generally at 10. As shown in Figure la, the vessel 10 has an internal liner 12 which defines a gas impermeable container for storing hydrogen H. The liner 12 has a cylindrical sidewall 12a closed at one end with a first domed end wall 12b and dosed at the opposite end by a second domed end wall 12c. The second domed end wall 12c includes an axially extending neck 14 provided with a valve V which can be dosed in order to confine hydrogen H within the liner 12 and opened to permit hydrogen H to be dispensed from the liner 12. In other embodiments, the liner 12 can take any suitable form; for example, a valve can also be provided in the first domed end wall 12b and / or the valve V can be placed axially in the second domed end wall 12c without a neck 14. Hydrogen pressure vessels are subject to high internal pressures that over time and refilling cycles can cause cracking in the liner 12. As shown In Figure lb, ultrasound transducers T are coupled to the outer surface of the liner 12. The transducers T can for example each comprise a piezoelectric transducer. As shown in Figure lc, a carbon fibre layer 16 is then formed around the liner 12 and transducers T to define a maximum volume of the pressure vessel 10. Each of the ultrasound transducers T forms part of a passive non-destructive testing sensor, each having at least one induction coil C electrically coupled to the respective transducer T such that the transducer T can be inductively powered. The induction coil(s) C and the transducer T of each sensor together form an LC circuit with a particular resonant frequency. In use, an energisation tool (not shown) can be used to ivate and then collect an ultrasonic reading by inducing a current in the LC circuit at the resonant frequency. This causes the transducer T to output an ultrasound pulse. The ultrasound pulse can reflect off a defect of the liner 12 and / or defects in composite layer and the reflected signal is received by the transducer T, producing a current in the sensor S that can be transmitted to the energisation tool via inductive coupling. The present inventors have identified that filament winding patters utilised to form the composite layer 12 of a hydrogen pressure vessel 10 severely impact the ability to inductively couple with an induction coil through the entirety of the composite layer 12, especially when a conductive material such as carbon fibre is used. This problem has been solved by positioning the coil within or on top of the composite layer 12 such that the coil is not in the same plane as the transducer i.e. the coil is not positioned on the liner. Figure 2 is a diagram of a sensor arrangement that can be used in the pressure vessel 10 of Figures la to lc. In this embodiment, the induction coil C is embedded within the composite layer 12 and electrically coupled to the transducer T by wiring which extends through some but not all the thickness of the composite layer 12. This can be achieved by securing the transducer to the liner 12 with the wiring extending away from the liner 12 and filament winding a base level of the composite layer 16. The induction coil C can then be electrically coupled to the transducer T via the wiring, and the filament winding process can then continue to cover the coil C and build up the remaining portion of the composite layer 16. Figure 3 is a diagram of an alternative sensor arrangement that can be used in the pressure vessel 10 of Figures la to lc. In this embodiment, the induction coil C is provided at the outer surface of the composite layer 12 and electrically coupled to the transducer T by wiring which extends through all the thickness of the composite layer 12. This can be achieved by securing the transducer to the liner 12 with the wiring extending away from the liner 12 and filament winding the composite layer 16. The induction coil C can then be electrically coupled to the transducer T via the wiring. An outer glass layer (not shown) can be applied to protect the composite layer 16 and secure the coil C in place. Figure 4 is a diagram of an alternative sensor arrangement that can be used in the pressure vessel 10 of Figures la to lc. In this embodiment, the induction coil C is provided at the outer surface of the composite layer 12 and electrically coupled to the by wiring which extends along the outer surface of the liner 12, under composite layer 16. At the neck region 14, the wiring folds back on itself and extends on top of the composite layer 16 to reach the coil C. The coll C can be mounted at any suitable location on the outer surface of the composite layer 16. Optionally, a glass coating 15 (only part of which is shown) can be formed around the composite layer 16 with the coil C held in place between the composite layer 16 and the glass layer 18. Figures 5a to 5c illustrate how the hydrogen pressure vessel 10 can be formed with the sensor arrangement of Figure 4. As shown in Figure 5a, a plurality of transducers T are coupled to the liner 12. Wiring W is then electrically coupled to each transducer and positioned to extend along the vessel 12 axially to the neck 14. The wiring W extends beyond the neck 14. As illustrated, each transducer T can have a dedicated wire W. As shown in Figure 5c, the composite layer 16 can then be formed over the vessel 12 and transducers T. Advantageously, the sensor arrangement of Figure 4 enables the composite layer 16 to be formed over the portions of the wiring W adjacent to the liner 12 so as not to restrict the fibre winding process. Once the composite layer 16 has been formed, the coils C can be positioned on the outer surface of the composite layer 16. In this embodiment, each coil C is positioned over the underlying transducer T to which the coil C will be electrically coupled by the wiring W, but in other embodiments the coils C can be positioned at any location on the composite layer 16 or on the exposed neck 14 of the liner 12. The free ends of the wiring W are coupled to the coils C. Optionally, a glass coating 18 (not shown) can be formed around the composite layer 16 with the coils C held in place between the composite layer 16 and the glass layer 18. Figure 6 is a diagram of an alternative sensor arrangement that can be used in the pressure vessel 10 of Figures la to 1c. In this embodiment, the fibre composite layer 16 has a first region 16a having a first thickness T1 and one or more second regions 16b each having a second thickness T2 which is less than the first thickness Tl. The induction coil Cl of the sensor is positioned between the liner 12 and the fibre composite layer 16 at one or the second regions 16b. Thus, in such embodiments, the induction coil Cl can be mounted prior to the composite layer 16 being formed, but at a location which it will be possible to energise the sensor from the exterior of the composite layer 16. This embodiment also shows the Induction coil Cl indirectly electrically coupled to the transducer T. A first portion W1 of the electrical conductor directly electrically couples the coil Cl to a first intermediate induction coil C2. A second Intermediate induction 3ctly electrically coupled to the transducer T by a second portion W2 of the electrical conductor. The first intermediate induction coil C2 is mounted relative to the second Intermediate induction coil C3 to enable inductive coupling therebetween. In other embodiments, the induction coll Cl can be located at a second region 16b and directly coupled to the transducer T by an electrical conductor. Figure 7 is a diagram of a sensor arrangement which can be used with electromagnetically transparent composite layers such as glass fibre. In this embodiment, the coil C is located between the liner 12 and composite layer 16 in a coaxial or non-coaxial manner with respect to the transducer T. The present inventors have found that such composite layers enable the sensor to be inductively operated from the exterior of the composite layer 16. In any embodiment, the transducers T can be coupled to the liner 12 by, for example, acrylic adhesive, epoxy, cyanoacrylate, silicone, polyurethane adhesive, or a thin piece of metal. In any embodiment, the coil(s) C can be coupled to the composite layer 16 by adhesive, as for the transducers T mentioned in the preceding paragraph, or by mechanical fixing. In any embodiment, the liner 12 can be formed from a metal such as aluminium, stainless steel, titanium, or nickel alloy, or a polymer such as high density polyethylene, polyamide, or polytetrafluoroethylene. The liner 12 can have any suitable shape and size, for example a small cylinder of 0.5-10 Liters, as typically used in a lab environment, a medium cylinder or 10-50 Liters, as typically used in industrial settings, or a large cylinder of 50-500 Liters, as typically used for transportation. In any embodiment, the composite layer 16 can be formed from carbon fibre reinforced polymer, glass fibre reinforced polymer, or hybrid composites and can be formed by a filament winding process. Figure 8 is a diagram illustrating an embodiment of a non-destructive testing system 20 comprising a sensor S installed on the pressure vessel 10 of Figures la to 1c and an energisation device 18. The NDT system 20 is arranged and configured for guided wave testing of the liner 12 of the hydrogen pressure vessel 10. The wireless ultrasound sensor S comprises a piezoelectric ultrasound transducer T, electrically coupled to an induction coil C. The induction coll C enables the wireless ultrasound sensor S to be remotely powered by the energisation device 18 by inductive coupling. The induction coil C is connected to a negative electrode of the transducer T by a first connection Wa and to a positive electrode of the transducer T by a second connection Wb. Although in this example the transducer is shown as being mounted coaxially with respect to the coil C, it will be appreciated that the wiring W comprising the first connection Wa and the second connection Wb enable the coil C to be located remote from the transducer T. The induction coil C and the ultrasound transducer T together form an LC circuit with a particular resonant frequency. For guided wave NDT applications using an ultrasound transducer, this frequency is generally in the range of 50khz to 1 MHz. In use, the energisation device 18 is brought towards the sensor S which induces a current In the LC circuit at the resonant frequency. This causes the transducer T to output an ultrasound pulse. The ultrasound pulse can reflect off a defect of the liner 12 and the reflected signal Is received by the transducer T, producing a current in the sensor S that can be transmitted to the energisation device 18via inductive coupling. In order for inductive coupling to take place between the energisation device 18 and the sensor S, the energisation device 18 must be held within a distance of less 100mm of the coil C of the ultrasound sensor S. Outside of this range, the inductive coupling Is too weak to enable the energisation device 18 to operate. In one example, operation means 'pulse echo' operation in which a signal is sent from the energisation device 18 to the transducer T for emission into the liner 12 and the received echo is sent back to the energisation device 18. The maximum operating distance is determined by a number of factors including the resonant frequency of sensor S, the resonant frequency of the energisation device 18, material between the inspection wand and sensor and the outer diameter d of the coil. Figure 9 shows a circuit diagram of the wireless NDT sensor S of Figure 8. The induction coil C can be represented as an inductance L parasitic resistance Rd and capacitance Cd, which are electrically coupled in parallel with the piezoelectric ultrasound transducer T, which can be represented as an impedance Zpz. For guided wave applications, a coil with a small number of turns (generally 10 to 50) can be used and therefore the perfect inductor assumption may be made and the stance and capacitance of the induction coil C can be neglected. Therefore, the electrical circuit can be simplified to an inductance associated with the coil L, and a capacitance associated with the transducer Cpz. The frequency f0 is then given by: 4 = 1 / (2^2^) and the required inductance of an induction coil can be estimated as: It is known to design a coil to achieve this value of inductance by adjusting the parameters of the coil such as coll diameter, number of turns and turn density. An equation for inductance of a circular loop of number of turns N and circle radius R, with wire radius a, and medium relative permeability pr is given by: As noted above, the sensors S are arranged for guided wave testing of the pressure vessel 10. The applied voltage Induces mechanical vibration in the piezoelectric transducer T. The mechanical vibration is transferred to the materials or structure to which the transducer is bonded. In one example, the transducer T can be a piezoelectric transducer of 20mm diameter and 1mm thickness with an operating frequency of 165khz. In another example, the transducer T can be a piezoelectric transducer of 23 mm diameter and 0.5mm thickness with an operating frequency of 150khz. It should be noted that various types of passive NDT sensors S can be used in embodiments of the invention, such as single coil designs as described in EP3614137 or dual coll designs as described in EP3311154. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parenthesis shall ued as limiting the claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in any claim or the specification. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. Parts of the invention can be implemented by means of 5 hardware comprising several distinct elements. In a device claim enumerating several parts, several of these parts can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 10

Claims

1. A hydrogen pressure vessel comprising:a liner defining a chamber for containing hydrogen and a valve for sealing and opening the chamber;a fibre composite layer formed around the liner; andone or more ultrasound transducers mounted on an outer surface of the liner, each ultrasound transducer being electrically coupled to a respective induction coil by a respective electrical conductor to define a non-destructive testing sensor, each non-destructive testing sensor being arranged and configured for guided wave testing of the liner.

2. The hydrogen pressure vessel according to claim 1, wherein the induction coil of each sensor is positioned in or on the fibre composite layer.

3. The hydrogen pressure vessel according to claim 2, wherein the liner comprises a neck at which the valve is located, wherein the electrical conductor for each sensor extends from the respective transducer along the liner under the composite layer to the neck and extends from the neck to the respective induction coil along the outer surface of the composite layer.

4. The hydrogen pressure vessel according to claim 1, wherein the fibre composite layer is formed of glass fibre and the induction coil of each sensor is positioned between the liner and the fibre composite layer.

5. The hydrogen pressure vessel according to claim 1, wherein the fibre composite layer has a first region having a first thickness and one or more second regions having a second thickness which is less than the first thickness and the induction coil of each sensor is positioned between the liner and the fibre composite layer at one or the second regions.

6. The hydrogen pressure vessel according to any preceding claim, wherein the coil of each sensor is generally coaxial with the transducer.

7. The hydrogen pressure vessel according to any of claims 1 to 5, wherein the coil of each sensor is non-coaxial with the transducer.

8. The hydrogen pressure vessel according to claim 7, wherein the induction coil of one or more of the sensors Is directly electrically coupled to the respective transducer by the respective electrical conductor.

9. The hydrogen pressure vessel according to claim 7 or claim 8, wherein the induction coil of one or more of the sensors is each indirectly electrically coupled to the respective transducer by: a first portion of the electrical conductor which directly electrically couples the coil to a first intermediate induction coil; and a second Intermediate induction coil directly electrically coupled to the transducer by a second portion of the electrical conductor, wherein the first intermediate induction coil is mounted relative to the second intermediate induction coil to enable inductive coupling therebetween.10.The hydrogen pressure vessel according to any of claims 8 and 9, wherein some or all of the electrical conductor has a cross sectional width which is greater than cross sectional height.

11. The hydrogen pressure vessel according to claim 10, wherein the electrical conductor comprises a flexible printed circuit board.

12. The hydrogen pressure vessel according to claim 11, wherein the electrical conductor is no greater than 5 m in length.13.The hydrogen pressure vessel according to any preceding claim, wherein the liner is formed from metal or a plastics material.14.The hydrogen pressure vessel according to any preceding claim, wherein the fibre composite layer comprises at least 30 layers.15.The hydrogen pressure vessel according to any preceding claim, wherein the fibre composite layer has a thickness of at least 10 mm and / or not greater than 50mm.16.The hydrogen pressure vessel according to any preceding claim, wherein each sensor comprises a unique RFID.17.The hydrogen pressure vessel according to any preceding claim, where each non-destructive testing sensor is a passive device.14

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