The present invention relates to a flexible transfer hose for a cryogenic fluid.

US patent application publication US 2012/0012221 describes a composite hose for transfer of cryogenic fluids. The composite hose can be used for example in a long floating or submerged liquefied natural gas (LNG) transfer line between two off-shore placed vessels. The composite hose described in US 2012/0012221 comprises fabrics layers that are sandwiched between an inner wire and an outer wire. Both inner and outer wires are helically wound, whereby the outer wire is located between the inner wire pitches. It appears clearly that the inner surface of the composite hose is hence not flat but corrugated and presents many obstacles to the fluid, which may induce an appreciable pressure drop in the LNG being transferred though the hose. A liner consisting of self clamping or snap-on elongated inner strip or shell has been installed on the inner wire, whereby flanges of each strip or shell overlap the adjacent one so that a flat inner surface is offered to the composite hose.

A number of drawbacks are associated with the

cryogenic transfer hose as proposed in US 2012/0012221. One of the drawbacks envisaged is that the liner

consisting strips or shells with overlapping flanges may compromise on the flexibility of the hose, making it less bendable. Moreover, the fabrication process of snapping on the liner elements may be cumbersome and the resulting inner surface is still not smooth. Another drawback lies in the fact that a fluid contact may exist between the cryogenic fluid and the fabrics layers, which may result in relatively long degassing period due to ingress of cryogenic fluid in the fabrics.

In accordance with a first aspect of the present invention, there is provided a flexible transfer hose for a cryogenic fluid, comprising:

an inner tube comprising a tube wall around a bore and arranged to contain a cryogenic fluid flowing through the bore in an axial direction, said tube wall having an inner surface facing inward to the bore and an outer surface facing away from the bore;

a first mechanical support frame configured around the tube wall; and

an external duct, said duct being bonded to the outer surface of the tube wall,

wherein the first mechanical support frame is arranged inside the external duct whereby the first mechanical support frame is moveable relative to the tube wall in axial direction.

The invention will be further illustrated hereinafter by way of example only, and with reference to the non- limiting drawing, wherein

Fig. 1 schematically shows a longitudinal cross sectional view of a first group of embodiments of the cryogenic transfer hose proposed herein;

Fig. 2 schematically shows a longitudinal cross sectional view of a second group of embodiments of the cryogenic transfer hose proposed herein; and

Fig. 2 schematically shows a longitudinal cross sectional view of a third group of embodiments of the cryogenic transfer hose proposed herein.

Same reference numbers refer to similar components. The person skilled in the art will readily understand that, while the invention is illustrated making reference to one or more specific combinations of features and measures, many of those features and measures are

functionally independent from other features and measures such that they can be equally or similarly applied independently in other embodiments or combinations.

The presently proposed transfer hose has an inner tube comprising a tube wall around a bore and arranged to contain a cryogenic fluid flowing through the bore in an axial direction. A first mechanical support frame is arranged inside a duct which is bonded to an outer surface of the inner tube wall, whereby the first

mechanical support frame is moveable relative to the tube wall in the axial direction.

The inner tube may form a lining having a continuous inner surface, which is helpful to reduce the pressure drop that the cryogenic fluid is exposed to as it flows through the bore. The mechanical support frame provides radial strength to the inner tube, guarding the inner tube against expansion as well as collapse. The latter is ensured because the duct in which the mechanical support frame is arranged is bonded to the inner tube wall and can therefore exert a radially outward pulling force on the tube wall. This configuration allows the tube wall to be formed out of a relatively deformable (flexible, low-stiffness) material with relatively low

Young's modulus. The inner tube may be in extruded form and/or formed out of a polymeric material.

Nevertheless, space for play in the axial direction is provided between the mechanical support frame and the duct, allowing for the first mechanical support frame to be moveable inside the duct relative to the inner tube wall in a direction parallel to the outer surface of the tube wall in axial direction. This helps to maintain bending flexibility of the transfer hose, despite the presence of the continuous inner tube, because as a result of the axial play axial elastic strain between the inner tube and the mechanical support frame is suspended, or even fully avoided.

The cryogenic fluid flowing through the bore may be in immediate contact with the inner surface of the tube wall. The inner surface is relatively smooth in axial direction compared to a profile in the axial direction that the first mechanical support frame forms together with the outer surface around which it is configured. In other words, it is relatively smooth compared to the inside duct of a hose where the first mechanical support frame is disposed inside the flow duct. It is also smoother than the surface in the hose as proposed in

US 2012/0012221 because the inner surface 4 of the presently proposed transfer hose is free from disruptions caused by overlapping flanges. Smooth in the present context means without surface deviations (roughness, steps or waves) in axial direction of average size and wavelength in the range of from about 1 mm to 30 cm.

The material of the inner tube wall may be

impermeable (and/or fluid tight) to the cryogenic fluid flowing through the bore compared to e.g. the fabrics layers of the hose described in US 2012/0012221, or other layers which may be provided external to the inner tube and ducts. For instance, the permeability for the cryogenic fluid (e.g. LNG) of the material of the inner tube wall may be at least a factor of ten lower than that of the fabrics or other layers that may be provided external to the inner tube and ducts.

Suitably, the tube wall may consist of a composite polymeric material, preferably a single polymer composite material. In one group of embodiments, the composite polymeric material has:

(a) a tensile Young's modulus of less than 50 GPa at ambient conditions; and

(b) a tensile strain at break of at least 5% at ambient conditions .

Such a material and its use as a fluid barrier under cryogenic conditions has been described in US patent application publication US 2010/0078439, which is

incorporated herein in its entirety. The tensile Young's modulus may be determined according to DIN EN ISO 527 at ambient conditions, that is standard atmospheric

conditions according to ISO 554, in particular the recommended atmospheric conditions i.e. at 23° C, 50% relative humidity and at a pressure between 86 and

106 kPa. The tensile strain at break may be determined according to DIN EN ISO 527 at ambient conditions.

Suitable examples include single polymer composite materials, including polypropylene (PP) fibers in a PP matrix, or based thermoplastic polymers including

polyethylene (PE) , polyamide (PA) , and polyethylene terephthalate (PET) as prominent examples.

The first mechanical support frame may suitably be a wire. The first mechanical support frame may suitably comprise, preferably be formed out of metal. Preferably, the first mechanical support frame may be provided in the form of a metal wire. The first mechanical support frame may be wound, preferably helically wound, around the tube wall of the inner tube. Alternatively, the first

mechanical support frame could be configured in the form of a plurality of individual rings around the inner tube, but this is expected to be more expensive to assemble than a (helically) wound wire or the like. Preferably, the first mechanical support frame is slidingly arranged relative to the outer surface of the tube wall. The first mechanical support frame may be in direct contact with the outer surface of the tube wall, but there may also be an auxiliary layer configured concentrically between the tube wall and the first mechanical support frame. The auxiliary layer may form part of the duct, and may be bonded to the outer surface of the tube wall.

Suitably, the first mechanical support frame

comprises, preferably essentially consists of, steel. The steel may consist of a stainless steel alloy, for instance a marine grade steel alloy. Suitably the steel is of a high-Nickel steel alloy. The alloy may contain at least 10% by weight Cr and 6% by weight Ni, and preferably less than 0.1% by weight of carbon. A

suitable example is a steel alloy of grade 316 as defined by SAE (Society of Automotive Engineers).

The term "bonded" is intended broadly - it is

intended to cover any suitable duct that is adhered to or integrated with the inner tube. Any means or method to integrate or adhere the duct to the outer surface of the tube wall or may suffice. Examples include co-extrusion, a weld joint, a groove-and-fin snap connection, adhesion by a layer of an adhesive, etc. including combinations thereof. Weld-bonded by means of a weld joint is

understood to cover bonds that involve local melting or softening in a weld-zone followed by coalescence and resolidification . Melting in this respect is not

restricted to physical melting; it may include chemical softening, for instance under influence a solvent.

Likewise, resolidification may include chemical resolidification, by a chemical reaction, for instance under influence of a hardener.

The term "bore" as used herein is not intended to be limited to bores having a circular cross section. While a circular cross section generally remains to be a preferred embodiment, as it maximizes the cross sectional area compared to the length of the circumference, non- circular cross sections may be employed if so desired. Particular an oval cross section may be selected, which has a relatively smaller open area for flow but may be beneficial in reducing the minimum bending radius of the flexible hose.

The flexible transfer hose as described herein is particularly suited for transferring a cryogenic fluid. The cryogenic fluid may be pure or blended. The

temperature of the cryogenic fluid as it flows through the hose may be below -30 °C, preferably below -100 °C, more preferably below -150 °C. Liquefied natural gas is an important example of a cryogenic fluid that can be transferred with the proposed hose, but other examples include liquefied nitrogen, liquefied oxygen, liquefied air, and liquefied petroleum gas (LPG) . The temperature of LNG at ambient pressure or slightly above (for

instance a pressure in the range of from 1.0 bar absolute to 1.5 bar absolute) is typically about -162 °C. A main area of application is envisaged in transferring the cryogenic fluid between two off-shore vessels, for instance between a floating LNG plant and/or floating LNG storage facility and a bulk LNG carrier. Another example is transfer of LNG between a bulk LNG carrier or a floating storage unit and an LNG regasification facility at or near an LNG import site. During transferring of the cryogenic fluid through the proposed hose, the hose may be floating on water or be partially or fully

submerged in the water.

The inner diameter of the bore may be selected of any suitable size, depending on the application, the required flexibility and the flow-rate and associated tolerance on pressure drop. For the transfer of LNG, any diameter in the range of from about 10 cm (4 inch) to about 50 cm (20 inch) may be technically and commercially attractive. Specific demand may exist for a 20-cm variant (8 inch) and for a 40-cm variant (16 inch) . However, the

invention is not limited to such diameters per se, and diameters outside of this range may proof to be of value for certain applications, as well.

Clearly, any suitable end fitting may be provided on the proposed hose, allowing coupling of the hose to a supply source and/or a destination of the cryogenic fluid or to another cryogenic transfer hose.

Fig. 1 in the drawing illustrates a group of

embodiments of the proposed flexible hose for transfer of a cryogenic fluid. The flexible hose comprises an inner tube 1 comprising a tube wall 2 around a bore 3.

Preferably the inner tube 2 is an extruded tube. It is arranged to contain the cryogenic fluid flowing through the bore 3 in an axial direction A. The tube wall 2 has an inner surface 4 facing inward (towards the bore 3) and an outer surface 5 facing away from the bore 3. A first mechanical support frame 6 is wound around the tube wall 2 in sliding contact with the outer surface 5. The first mechanical support frame is suitably provided in the form of a metal wire helically evolving around the inner tube wall 2.

An external duct 7 is bonded to the outer surface 5 of the tube wall 2, for instance weld-bonded by weld joints 8. The first mechanical support frame 6 is arranged inside the external duct 7. The first

mechanical support frame 6 is axially moveable relative to the tube wall 2. In the embodiment as shown in Fig. 1, the mutual axial movability is achieved by allowing a clearance 9,10 for axial play of the first mechanical support frame 6 in the duct 7. The clearance 9,10 is illustrated in Fig. 1 between the first mechanical support frame 6 within the duct 7 and the side walls 11 of the duct 7.

The inner tube 2 may be formed by extruding a polymer or a polymer composite. The weld- oints may be formed by welding, suitably by laser welding or induction welding. If induction welding is used, a thin piece of metallic mesh may be applied between the duct and the outer surface 5 of the tube wall 2 to facilitate electric conduction in the area of the anticipated weld- joint.

In the group of embodiments illustrated in Fig. 1, each duct 7 consists of two side walls 11 and a cover that is integral to the side walls. The side walls 11 are bonded to the tube wall 2. The bonds, e.g. in the form of the weld joints 8, are in the pitch in between two consecutive windings of the first mechanical support frame .

An alternative group of embodiments is illustrated in

Fig. 2, where the two consecutive side walls 11, as seen in the axial direction one on either side of one winding of the mechanical support frame 6, each individually stand out from the outer surface 5 of the tube wall 2. A non-integral cover 15 is subsequently applied to close the duct 7 over the winding of the mechanical support frame 6 between the two consecutive side walls 11. Non- integral is intended to denote that the cover is non- integral to the side walls 11 at least before it is applied to close the duct 7. Nonetheless, the non- integral cover 15 should be bonded or otherwise attached to the side walls 11 in other to be able to transmit a radial suspending force from the first mechanical support frame 6 to the tube wall 2 to protect the tube wall 2 against collapse.

Fig. 3 illustrates still another group of

embodiments, the duct is made out of a U-profile, wherein the consecutive side walls 11 are connected with a base

16. The base 16 may be bonded to the outer surface 5 of the tube wall 2, and thus form an auxiliary layer between the first mechanical support frame 6 and the outer surface 5 of the tube wall 2. In this group of

embodiments, separate weld zones may be provided on both sides of the base 16 near or under the two consecutive side walls 11. Alternatively a single weld zone 18 for the two consecutive side walls 11 may be provided on the base 16 between the two consecutive side walls 11 of each duct 7, as illustrated in Fig. 3. Similar to the group of embodiments illustrated with reference to Fig. 2, a non-integral cover 15 may subsequently be applied to close the duct 7 over the winding of the mechanical support frame 6 between the two consecutive side walls 11.

In an alternative that is not shown in the drawing, the duct may be formed out of an "Omega (Ω) profile" consisting of a duct with flanges on the side walls that can be used to bond with the outer surface 5 of the tube wall 2.

In the examples as illustrated, consecutive windings of the first mechanical support frame 6 are separated from each other as seen in the axial direction with at least one side wall 11 of the duct 7.

Regardless of the precise arrangement of the duct, the flexible hose may comprise one or more layers 12a, 12b of materials configured around the inner tube 1 and the external duct 7. A second mechanical support frame 14 (suitably provided in the form of a second metal wire, and/or formed out of the same material as the first mechanical support frame) is configured around the one or more layers 12a, 12b of materials. The one or more layers

12a, 12b of materials around the inner tube 1 are suitably held in place between and by the first mechanical support frame 6 (clearly, the duct cover is also located between the first mechanical support frame 6 and the one or more layers 12a, 12b) and the second mechanical support frame

14, without being bonded to any of these support frames. The one or more layers 12a, 12b of materials may comprise fabrics .

Suitably, the flexible hose is thermally insulated from the ambient environment. The amount of thermal insulation depends on the circumstances of the case. For instance, when the hose is for transferring LNG and expected to be in contact with sea water, the amount thermal insulation could be selected to achieve that a temperature differential of at least 155 °C between the bore and the ambient environment can be maintained in steady state. With this temperature differential

freezing of sea water can be avoided when LNG flows through the flexible hose. Material for thermal

insulation may be included amongst the one or more layers

12a, 12b, preferably sandwiched between the first

mechanical support frame 6 and the second mechanical support frame 14. A suitable thermal insulation material is capable of bearing compressive mechanical load. A micro porous material suitable for this purpose is commercially available from Microtherm N.V., under the trade name Izoflex (TM) (also known under the name

Microtherm (TM) Floppy Panel) . It is available in flexible quilted panels.

A water-tight jacket may be provided around the flexible hose, or possibly around the optional layer (s) of thermal insulation, to avoid thermal leaks caused by water infiltration.

The person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims .