GB2368377A

GB2368377A - Hose having improved axial strength

Info

Publication number: GB2368377A
Application number: GB0111022A
Authority: GB
Inventors: Matthew Vernon Ridolfi; Eric Joseph Davis; Gerard Anthony Hall; Simon Peter Alexander Thorp; Joel Aaron Witz; Raymond Nicholas Burke
Original assignee: BHP Petroleum Pty Ltd
Current assignee: BHP Petroleum Pty Ltd
Priority date: 2000-06-12
Filing date: 2001-05-04
Publication date: 2002-05-01
Anticipated expiration: 2021-05-04
Also published as: GB2368377B; CN100585248C; ES2351548T3; GB0014354D0; GB0111022D0; CN1818446A

Abstract

A hose 10 comprises a flexible tubular body 12 having a sealing layer 18 sandwiched between two reinforcing layers 14,16 arranged between an inner and an outer helically wound wire 22, 24. The hose 10 further comprises an axial strengthening means 20, preferably in the form of a tubular braid (figures 4A,4B), adapted to reduce deformation of the tubular body 12 when the tubular body 12 is subjected to axial tension, the axial strengthening means 20 being adapted to exert a radially inward force on at least part of the tubular body 12 when it is subjected to axial tension. Failure of the tubular body 12 and axial strengthening means 20 occurs when the strain is between 1 and 10%, preferably greater than 5%.

Description

HOSE HAVING IMPROVED AXIAL STRENGTH This invention relates to hose, and more particularly relates to hose having improved axial strength. The invention is especially concerned with hose which can be used in cryogenic conditions.

Typical applications for hose involve the pumping of fluids from a fluid reservoir under pressure. Examples include supplying of domestic heating oil or LPG to a boiler ; transporting produced oilfield liquids and/or gases from a fixed or floating production platform to the cargo hold of a ship, or from a ship cargo hold to a land-based storage unit; delivering of fuel to racing cars, especially during refuelling in formula 1; and conveying corrosive fluids, such as sulphuric acid.

It is well known to use hose for the transport of fluids, such as liquefied gases, at low temperature. Such hose is commonly used to transport liquefied gases such as liquefied natural gas (LNG) and liquefied propane gas (LPG).

In order for the hose to be sufficiently flexible, any given length must be at least partially constructed of flexible materials, i. e., non-rigid materials.

The structure of such hose generally comprises a tubular body of flexible material arranged between an inner and outer helically wound retaining wires. It is conventional for the two wires to be wound at the same pitch, but to have the windings displaced by half a pitch width from one another. The tubular body typically comprises inner and outer layers with an intermediate sealing layer. The inner and outer layers provide the structure with the strength to carry the fluid therein. Conventionally, the inner and outer layers of the tubular body comprise fabric layers formed of a polyester such as polyethylene terephtalate. The intermediate sealing layer provides a seal to prevent the fluid from penetrating the hose, and is typically a polymeric film.

The retaining wires are typically applied under tension around the inside and outside surfaces of the tubular body. The retaining wires act primarily to preserve the geometry of the tubular body. Furthermore, the outer wire may act to restrain excessive hoop deformation of the hose under high pressure. The inner and outer wires may also act to resist crushing of the hose.

A hose of this general type is described in European patent publication no.

0076540A1. The hose described in this specification includes an intermediate layer of biaxially oriented polypropylene, which is said to improve the ability of the hose to resist the fatigue caused by repeated flexing.

Another hose is described in GB-2223817A. The hose described in this publication is a composite hose comprising an inner helical metallic core, a plurality of layers of plastics material fibres and films wound on the core, at least one layer of glass cloth and at least one layer of aluminium foil disposed adjacent one another and wound onto the plastics material, and an outer helical metallic former. This hose is said to be suitable for transporting flammable fuels and oils.

Another hose is described in GB-1034956A. The hose described in this application is an electrical hose or conduit, i. e. , it is intended for carrying electrical wires rather than for the transport of fluids. As a result of this, the considerations involved in the design of this hose are completely different from the considerations involved in the hose described in EP-0076540A1 and GB-2223817A. The hose described in GB1034956A comprises: (i) an internally arranged helically wound wire; (ii) an extruded neoprene hose surrounding the internal wire; (iii) a braided metal sheath surrounding the neoprene hose; (iv) a nylon cord applied helically to the sheath; (v) a canvas wrapping around the nylon cord and the sheath; and (vi) an outer helically wound wire arranged around the canvas wrapping.

The braided metal sheath is made to follow the convolutions of the inner wire by temporarily winding a further wire around the sheath during manufacture of the hose.

Many applications of hose require the hose to be supported along its length. This especially applies to the transport of the produced liquids and/or gases mentioned above. Without additional support, conventional hose is often incapable of supporting its own weight, or the weight of the fluid contained therein.

We have now found a way to improve the load carrying capabilities of hose, especially the type of hose described in EP-0076540A1, so that it can be used to carry fluids either without the need for any support at all, or with a much reduced requirement for support. The hose is suitable for both cryogenic and non-cryogenic applications.

Broadly, we provide an axial strengthening means for hose, whereby the hose can withstand greater axial tension than has previously been possible, without impairing the other properties of the hose..

According to one aspect of the invention there is provided a hose comprising a tubular body of flexible material arranged between inner and outer gripping members, wherein the hose further comprises an axial strengthening means adapted to reduce deformation of the tubular body when the tubular body is subjected to axial tension, and the axial strengthening means is further adapted to exert a radially inward force on at least part of the tubular body when axial strengthening means is subjected to axial tensioning, and wherein the failure strain of the tubular body and the axial strengthening means are within the range of 1 to 10%. Preferably the failure strain is in excess of 5% at ambient and cryogenic temperatures By means of this arrangement, the axial strengthening means improves the ability of the hose to cope with axial stresses, and at the same time can contribute to the structural integrity of the hose during axial tensioning by pressing against at least part of the tubular body. In addition, the materials of the tubular body and the axial strengthening means are compatible so that the each perform in a similar manner when in operation, so that no single component is subjected to excessive stresses and strains. This means that the materials of the tubular body and the axial strengthening means respond to strain in a similar manner A bend stain (for a cylindrical component) of at least 3% is generally needed for the type of hose applications primarily envisaged by the present invention. While, inter-layer slip and the straightening of helically oriented components will account for some of this slip, there will still be a resultant strain in the order of 1 % acting on the structural components of the hose wall. This compares to a typical yield strain of 0.2% for metals.

It is preferred that the tubular body and the axial strengthening means comprise the same material, most preferably ultra high molecular weight polyethylene (UHMWPE), as described in further detail below.

Preferably, a reinforcing layer is provided between the outer gripping member and the axial strengthening means, the ultimate strength of the reinforcing layer being between 100 and 700 kN for an 8" (200 mm) diameter hose. It is preferable that the bend strain at failure of the reinforcing layer is in the range 2% to 15%. Desirably, the reinforcing layer is the same material as the tubular body and the axial strengthening means, most preferably UHMWPE.

Preferably the axial strengthening means comprises a generally tubular sheath formed of a sheet of material provided in a tubular shape, such that the sheath can maintain the integrity of its tubular shape when subjected to axial tension. The hose may be provided with two or more tubular sheaths in order to further improve the performance of the hose under axial tension.

In a particularly advantageous embodiment the axial strengthening means is provided in the form of a generally tubular braid. In this specification the term"braid" refers to a material which is formed of two or more fibres or yarns which have been intertwined to form an elongated structure. It is a feature of braid that it can elongate when subjected to an axial tension. It is a further feature of braid that, when provided in a tubular form, its diameter will reduce when the braid is subjected to axial tension.

Thus by providing a tubular braid around the tubular body, or within the structure of the tubular body, the braid will exert a radially inward force on at least part of the tubular body when subjected to axial tension.

It is preferred that the entire tubular sheath is provided in the form of the braid.

However, it is possible for only one or more parts of the length of the tubular sheath to be provided in the form of the braid.

It is also preferred that the braid extends all the way around the circumference of the tubular sheath. However, it is possible for only part of the circumference of the tubular sheath to be provided in the form of the braid.

The braid may be provided in a biaxial form (i. e. in which the braid is formed of only two intertwining fibres or yarns) or in a triaxial form (i. e. in which there are also longitudinally extending fibres or yarns, for increased axial strength).

Although it is preferred to provide the axial strengthening means in the form of a braid, it may be provided in other forms which meet the functional requirements specified above. Thus, the axial strengthening means may be provided as a suitable arrangement of cords or ropes helically wrapped around the tubular body.

The materials of construction of the hose should be selected to enable the hose to perform in the environment for which it is intended. Thus, there is a need for the hose to be able to transport pressurised fluids therethrough without leakage of the fluid through the walls of the hose. There is also a need for the hose to withstand repeated flexing, and to withstand the axial stresses caused by the combination of the hose and fluid weight. Also, if the hose is intended for use in transporting cryogenic fluids, the materials should be capable of operating at extremely cold temperatures without any significant reduction in performance. The tubular body preferably comprises at least one reinforcing layer and at least one sealing layer. More preferably, there are at least two reinforcing layers with the sealing layer sandwiched therebetween.

The main purpose of the or each reinforcing layer is to withstand the hoop stresses which the hose is subjected to during transport of fluids therethrough. Thus, any reinforcing layer which has the required degree of flexibility, and which can withstand the necessary stresses, will be adequate. Also, if the hose is intended for transporting cryogenic fluids, then the or each reinforcing layer must be able to withstand cryogenic temperatures.

We prefer that the or each reinforcing layer is formed of a sheet of material which has been wound into a tubular form by winding the sheet material in a helical manner.

This means that the or each reinforcing layer does not have much resistance to axial tension, as the application of an axial force will tend to pull the windings apart. The or each reinforcing layer may comprise a single continuous layer of the sheet material, or may comprise two or more single continuous layers of the sheet material. However, more usually (and depending on the length of the hose) the or each layer of the sheet material would be formed of a plurality of separate lengths of sheet material arranged along the length of the hose.

In the preferred embodiment each reinforcing layer comprises a fabric, most preferably a woven fabric. The or each reinforcing layer may be a natural or synthetic material. The or each reinforcing layer is conveniently formed of a synthetic polymer, such as a polyester, a polyamide or a polyolefin. The synthetic polymer may be provided in the form of fibres, or a yarn, from which the fabric is created.

When the or each reinforcing layer comprises a polyester, then it is preferably polyethylene terephtalate.

When the or each reinforcing layer comprises a polyamide, then it may be an aliphatic polyamide, such as a nylon, or it may be an aromatic polyamide, such as an aramid compound. For example, the or each reinforcing layer may be a poly- (p- phenyleneterephthalamide) such as KEVLAR (registered trade mark).

When the or each reinforcing layer comprises a polyolefin, then it may be a polyethylene, polypropylene or polybutylen homopolymer, or a copolymer or terpolymer thereof, and is preferably monoaxially or biaxially oriented. More preferably, the polyolefin is a polyethylene, and most preferably the polyethylene is a high molecular weight polyethylene, especially UHMWPE.

The UHMWPE used in the present invention would generally have a weight average molecular weight above 400,000, typically above 800,000, and usually above 1,000, 000. The weight average molecular weight would not usually exceed about 15,000, 000. The UHMWPE is preferably characterised by a molecular weight from about 1,000, 000 to 6,000, 000. The UHMWPE most useful in the present invention is highly oriented and would usually have been stretched at least 2-5 times in one direction and at least 10-15 times in the other direction.

The UHMWPE most useful in the present invention will generally have a parallel orientation greater than 80%, more usually greater than 90%, and preferably greater than 95%. The crystallinity will generally be greater than 50%, more usually greater than 70%. A crystallinity up to 85-90% is possible.

UHMWPE is described in, for example, US-A-4344908, US-A-4411845, US-A4422993, US-A-4430383, US-A-4436689, EP-A-183285, EP-A-0438831, and EP-A0215507.

It is particularly advantageous that the or each reinforcing layer comprises a highly oriented UHMWPE, such as that available from DSM High Performance Fibres - fx-tm) BV (a Netherlands company) under the trade name DYNEEM or that available from (n..-r ) the US corporation AlliedSignal Inc. under the trade name SPECTRA K) Additional details about DYNEEMA\are disclosed in a trade brochure entitled "DYNEEMA ; the top performance in fibers ; properties and application"issued by DSM (qu) High Performance Fibers BV, edition 02/98. Additional details about SPECTRAJ. are disclosed in a trade brochure entitled"Spectra Performance Materials"issued by

AlliedSignal Inc., edition 5/96. These materials have been available since the 1980s.

In the preferred embodiment, the or each reinforcing layer comprises a woven fabric formed of fibres arranged in a weft and warp direction. We have found that it is particularly advantageous if the or each reinforcing layer is arranged such that the fabric warp direction is at an angle of less than 200 to the axial direction of the hose; we also prefer that this angle is greater than 50. In the preferred embodiment, the or each reinforcing layer is arranged such that the fabric warp direction is at an angle of from 10'to 20', most preferably about 150, to the axial direction of the hose.

The purpose of the sealing layer is primarily to prevent the leakage of transported fluids through the tubular body. Thus, any sealing layer which has the required degree of flexibility, and which can provide the desired sealing function, will be adequate. Also, if the hose is intended for transporting cryogenic fluids, then the sealing layer must be able to withstand cryogenic temperatures.

The sealing layer may be made from the same basic materials as the or each reinforcing layer. As an alternative, the sealing layer may be a fluoropolymer, such as: polytetrafluoroethylene (PFTE); a fluorinated ethylene propylene copolymer, such as a copolymer of hexafluoropropylene and tetrafluoroethylene (tetrafluoroethyleneperfluoropropylene) available from DuPont Fluoroproducts under the trade name Teflon FEP; or a fluorinated hydrocarbon-perfluoralkoxy-available from DuPont Fluoroproducts under the trade name Teflon PFA. These films may be made by extrusion or by blowing.

We prefer that the sealing layer is formed of a sheet of material which has been wound into a tubular form by winding the sheet material in a helical manner. As with the reinforcing layers, this means that the or each sealing layer does not have much resistance to axial tension, as the application of an axial force will tend to pull the windings apart. The sealing layer may comprise a single continuous layer of the sheet material, or may comprise two or more single continuous layers of the sheet material. However, more usually (and depending on the length of the hose) the or each layer of the sheet material would be formed of a plurality of separate lengths of sheet material arranged along the length of the hose. If desired the sealing layer may comprise one or more heat shrinkable sealing sleeves (i. e. tubular in form) which are arranged over the inner reinforcing layer.

We prefer that the sealing layer comprises a plurality of overlapping layers of film. Preferably there would be at least 2 layers, more preferably at least 5 layers, and still more preferably at least 10 layers. In practice, the sealing layer may comprise 20, 30,40, 50, or more layers of film. The upper limit for the number of layers depends upon the overall size of the hose, but it is unlikely that more than 100 layers would be required. Usually, 50 layers, at most, will be sufficient. The thickness of each layer of film would typically be in the range 50 to 100 micrometres.

It will, of course, be appreciated that more than one sealing layer may be provided.

One suitable sealing layer is described in our copending UK patent application of even date entitled"Hose incorporating an improved Sealing Layer".

The axial strengthening means may also be formed of the same material as the or each reinforcing layer. Thus, it will be clear that the axial strengthening means, the or each reinforcing layer and the sealing layer may all be formed from the same basic compound. However, the form of the compound must be different in order to provide the required function, i. e., the axial strengthening means provides an axial reinforcement

function, the or each reinforcing layer provides reinforcement against hoop stresses,

and the sealing layer provides a sealing function. We have found that the UHMWPE uca c < M) materials are most suitable, particularly the DYNEEMAjand SPECTRAproducts. These material have also been found to work well in cryogenic conditions.

It would be possible for the axial strengthening means to be provided within the layers of the tubular body. However we prefer than the axial strengthening means is positioned between the tubular body and the outer gripping member. In an another preferred embodiment, the axial strengthening means is provided within the layers of the tubular body, and is also provided between the tubular body and the outer gripping member.

The gripping members typically each comprise a helically wound wire. The helices of the wires are typically arranged such that they are offset from one another by a distance corresponding to half the pitch of the helices. The purpose of the wires is to grip the tubular body firmly therebetween to keep the layers of the tubular body intact and to provide structural integrity for the hose. The inner and outer wires may be, for example, mild steel, austenitic stainless steel or aluminium. If desired, the wires may be galvanised or coated with a polymer.

It will be appreciated that although the wires making up the gripping members may have a considerable tensile strength, the arrangement of the wires in coils means that the gripping members can deform when subjected to relatively small axial tension.

Any significant deformation in the coils will quickly destroy the structural integrity of the hose.

When the hose is intended for cryogenic applications, then it is desirable to provide insulation over the tubular body. The insulation could be provided between the outer wire and the tubular sheath and/or outside the outer wire. The insulation may comprise material conventionally used to provided insulation in cryogenic equipment, such as a synthetic foam material. One suitable form of insulation is described in our copending United Kingdom patent application of even date entitled"Hose Having Improved Flexing Capabilites". It is preferred that the axial strengthening means is also provided around the insulating layer to compress the insulation layers and maintain their structural integrity. The axial strengthening means around the insulation layer is preferably provided in addition to the axial strengthening means between the outer gripping member and the tubular body.

The hose according to the invention can be provided for use in a wide variety of conditions, such as temperatures above 100oC, temperatures from OOC to 100C and temperatures below OOC. With a suitable choice of material, the hose can be used at temperatures betow-20 C, betow-50 C or even below-1 OOOC. For example, for LNG transport, the hose may have to operate at temperatures down to-170 C, or even lower. Furthermore, it is also contemplated that the hose may be used to transport liquid

oxygen (bp-183 OC) or liquid nitrogen (bp-196 OC), in which case the hose may need to operate at temperatures ouf-200 C or lower.

The hose according to the invention can also be provided for use at a variety of different duties. Typically, the inner diameter of the hose would range from about 2 inches (51 mm) to about 24 inches (610 mm), more typically from about 8 inches (203 mm) to about 16 inches (406 mm). In general, the operating pressure of the hose would be in the range from about 500 kPa gauge up to about 2000 kPa gauge, or possibly up to about 2500 kPa gauge. These pressures relate to the operating pressure of the hose, not the burst pressure (which must be several times greater). The volumetric flow rate depends upon the fluid medium, the pressure and the inner diameter. Flowrates from 1000 m3/h up to 12000 m3/h are typical.

The hose according to the invention can also be provided for use with corrosive materials, such as strong acids, According to another aspect of the invention there is provided a hose comprising a tubular body of flexible material arranged between inner and outer gripping members, wherein the tubular body comprises at least one reinforcing layer of a woven fabric formed of fibres arranged in a weft and warp direction, characterised in that the or each reinforcing layer is arranged such that the fabric warp direction is at an angle of less than 20 , more preferably less than 150, and most preferably less than 100, to the axial direction of the hose. The hose according to this aspect of the invention may be provided with any desired combination of the additional features described in relation to the hose according to the first aspect of the invention.

According to another aspect of the invention there is provided a method of making a hose comprising: (a) wrapping a wire around a tubular mandrel to form an inner coil ; (b) wrapping a sheet material around the tubular mandrel and the inner coil order to provide a tubular body formed of the sheet material ; (c) pulling a tubular axial strengthening sheath over a free end of the mandrel, so that the mandrel extends within the axial strengthening sheath, then pulling the axial strengthening sheath along the mandrel so that it at least partially covers the tubular body; (d) wrapping a wire around the axial strengthening sheath to form an outer coil ; (e) securing the ends of the hose produced in step (d); and (f) removing the hose from the mandrel.

Preferably the coils and the sheet material are applied under tension in order to provide the hose with good structural integrity.

Preferably the sheet material in step (b) comprises two reinforcing layers sandwiching a sealing layer, as described above. In the preferred embodiment, an inner reinforcing layer, in sheet form, is wrapped helically around the inner coil and the mandrel ; then the sealing layer, in sheet form, is wrapped helically around the inner reinforcing layer ; then the outer reinforcing layer, in sheet form, is wrapped around the sealing layer. Usually a plurality of sealing layers would be applied.

The tubular axial strengthening sheath may be the same as the axial strengthening sheath described above, and is preferably a braid.

Preferably the inner and outer coils are applied in a helical configuration having the same pitch, and the position of the coils of the outer coil are positioned half a pitch length offset from the position of the coils of the inner coil.

According to another aspect of the invention there is provided a hose comprising a tubular body of flexible material arranged between an inner and an outer gripping members, the tubular body serving to transport fluid through the hose and to prevent fluid leakage through the body, characterised in that the hose further comprises a generally tubular braid disposed around the tubular body.

Reference is now made to the accompanying drawings, in which: Figure 1 is a schematic diagram showing the principle stresses to which the hose according to the invention may be subjected in operation; Figure 2 is a schematic cross-sectional view of a hose according to the invention; Figure 3 is a sectional view showing the arrangement of a reinforcing layer of the hose according to the invention; Figure 4A is a sectional view showing the arrangement of a tubular axial strengthening sheath of the hose according to the invention, the axial strengthening sheath being in a relaxed condition; Figure 4B is a sectional view showing the arrangement of a tubular axial strengthening sheath of the hose according to the invention, the axial strengthening sheath being in a tightened condition; and Figures 5A, 5B, 5C and 5D show four applications of hose according to the present invention.

Figure 1 shows the stresses to which a hose H is normally subjected to during use. The hoop stress is designated by the arrows HS and is the stress that acts tangentially to the periphery of the hose H. The axial stress is designated by the arrows AS and is the stress which acts axially along the length of the hose H. The flexing stress is designated FS and is the stress which acts transverse to the longitudinal axis of the hose H when it is flexed. The torsional stress is designated TS and is a twisting stress which acts about the longitudinal axis of the hose. The crushing stress is designated CS and results from loads applied radially to the exterior of the hose H.

The hoop stress HS is generated by the pressure of the fluid in the hose H. The axial stress AS is generated by the pressure of the fluid in the hose and also by the combination of the weight of the fluid in the hose H and by the weight of the hose H itself. The flexing stress FS is caused by the requirement to bend the hose H in order to position it properly, and by movement of the hose H during use. The torsional stress TS is caused by twisting of the hose. Prior art hose is generally capable of withstanding the hoop stresses HS, the flexing stresses FS and the torsional stresses TS, but is less capable of withstanding the axial stresses AS. For this reason, when prior art hoses were subjected to large axial stresses AS they generally had to be supported, to minimise the axial stresses AS.

The problem of withstanding the axial stresses AS has been solved by the present invention. In Figure 2 a hose in accordance with the invention is generally designated 10. In order to improve the clarity the winding of the various layers in Figure 2, and in the other Figures, has not been shown.

The hose 10 comprises a tubular body 12 which comprises an inner reinforcing layer 14, an outer reinforcing layer 16, and a sealing layer 18 sandwiched between the layers 14 and 16. A generally tubular sheath 20, which provides axial strengthening, is disposed around the outer surface of the outer reinforcing layer 16.

The tubular body 12 and the tubular sheath 20 are disposed between an inner helically coiled wire 22 and an outer helically coiled wire 24. The inner and outer wires 22 and 24 are disposed so that they are offset from one another by a distance corresponding to half the pitch length of the helix of the coils.

An insulation layer 26 is disposed around the outer wire 24. The insulation layer may be a conventional insulating material, such as a plastics foam, or may be a material described in our copending United Kingdom patent application entitled 11 Hose Having Improved Flexing Capabilities".

The reinforcing layers 14 and 16 comprise woven fabrics of a synthetic material, such as aramid fibres. Figure 3 illustrates the inner reinforcing layer 14, from which it will be clear that the inner reinforcing layer 14 comprises fibres 14a arranged in a warp direction W, and fibres 14b arranged in a weft direction F. In Figure 3 only the layer 14 has been shown, in order to improve the clarity. We have unexpectedly found that the axial strength of the hose 10 can be improved by arranging the inner reinforcing layer 14 such that the warp direction W is at a low angle, of less than 200 and typically around 150 to the longitudinal axis of the hose 10. This angle is indicated by the symbol a in Figure 3. The structure and orientation of the outer reinforcing layer 16 is substantially identical to the inner reinforcing layer 14; the angle a for the outer reinforcing layer 16 may be the same as, or different from, the angle a for the inner reinforcing layer 14.

The sealing layer 18 comprises a plurality of layers of plastics film which are wrapped around the outer surface of the inner reinforcing layer 14 to provide a fluid tight seal between the inner and outer reinforcing layers 14 and 16.

The hose 10 may further include a reinforcing layer (not shown) disposed between the sheath 20 and the outer wires 24. The reinforcing layer may have similar characteristics to the sheath 20 and the tubular body 12.

The tubular sheath 20 is formed of two sets of fibres 20a and 20b which are braided to form a tubular braid. This is shown in Figures 4A and 4B-in these Figures only the tubular sheath 20 has been shown, in order to improve the clarity. There are spaces 28 between the sets of fibres 20a and 20b, so that when the tubular sheath 20 is subjected to axial tensioning the fibres 20a and 20b can contract moving into the spaces 28. This acts in a way to try to reduce the diameter of the tubular sheath 20, which causes it to tighten around the tubular body 12, thereby increasing the structural integrity and burst pressure of the hose 10. Figure 4B shows the tubular sheath 20 in the tightened condition.

The hose 10 can be manufactured by the following technique. As a first step the inner wire 22 is wound around a support mandrel (not shown), in order to provide a helical arrangement having a desired pitch. The diameter of the support mandrel corresponds to the desired internal diameter of the hose 10. The inner reinforcing layer 14 is then wrapped around the inner wire 22 and the support mandrel, such that warp direction W is set at the desired angle a. A plurality of layers of the plastics film making up the sealing layer 18 are then wrapped around the outer surface of the inner reinforcing layer 14. The outer reinforcing layer 16 is then wrapped around the sealing layer 18, such that the warp direction W is set at the desired angle (which may be a, or may be some other angle close to a). The tubular axial strengthening sheath 20 is drawn over the outside of the outer reinforcing layer 16. The outer wire 24 is then wrapped around the tubular sheath 20, in order to provide a helical arrangement having a desired pitch. The pitch of the outer wire 24 would normally be the same as the pitch of the inner wire 22, and the position of the wire 24 would normally be such that the coils of the wire 24 are offset from the coils of the wire 22 by a distance corresponding to half a pitch length; this is illustrated in Figure 2, where the pitch length is designated p. The insulation layer 26 may then be applied around the outer wire 24 and the tubular sheath 20.

The ends of the hose 10 may be sealed by crimping a sleeve onto an insert inside the hose 10. This termination is generally applied after the hose 10 as been removed from the mandrel. An improved technique for sealing the ends of the hose 10 is disclosed in our copending United Kingdom patent applications of even date entitled "End Fitting for a Hose"and"End Fitting Having Improved Sealing Capabilities".

Figures 5A to 5D show three applications for the hose 10. In each of Figures 5A to 5C a floating production, storage and offloading vessel (FPSO) 102 is linked to a LNG carrier 104 by means of a hose 10 according to the invention. The hose 10 carries LNG from a storage tank of the FPSO 102 to a storage tank of the LNG carrier 104. In Figure 5A, the hose 10 lies above the sea level 106. In Figure 5B, the hose 10 is submerged below the sea level 106. In Figure 5C, the hose 10 floats near the surface of the sea. In each case the hose 10 carries the LNG without any intermediate support. In Fig 5D the LNG carrier is linked to a land-based storage facility 108 via the hose 10.

The hose 10 may be used for many other applications apart from the applications shown in figures 5A to 5C. The hose may be used in cryogenic and non-cryogenic conditions.

It will be appreciated that the invention described above may be modified. For example, the tubular sheath 20 could be located outside the outer wire 24. Also, the hose 10 may include additional reinforcing layers 14,18, sealing layers 16 and/or tubular sheaths 20.

Claims

CLAIMS : 1. A hose comprising a tubular body of flexible material arranged between an inner and an outer helically wound wire, the tubular body serving to transport fluid through the hose and to prevent fluid leakage through the body, the tubular body comprising two reinforcing layers having a sealing layer sandwiched therebetween, wherein the hose further comprises an axial strengthening means adapted to reduce deformation of the tubular body when the tubular body is subjected to axial tension, and the axial strengthening means is further adapted to exert a radially inward force on at least part of the tubular body when axial strengthening means is subjected to axial tension, and wherein the strain at failure of the tubular body and the axial strengthening means are within the range 1% to 10%.
2. A hose according to claim 1, wherein the axial strengthening means comprises a generally tubular sheath formed of a sheet of material provided in a tubular shape, such that the tubular sheath can maintain the integrity of its tubular shape when subjected to axial tension.
3. A hose according to claim 2, comprising two or more of said tubular sheaths
4. A hose according to claim 1,2 or 3, wherein the axial strengthening means is provided in the form of a generally tubular braid.
5. A hose according to claim 4, wherein the braid is provided in a triaxial form.
6. A hose according to any preceding claim, further comprising a reinforcing layer between the axial strengthening means and the outer gripping member.
7. A hose according to claim 6, whereinthe tubular body, the axial strengthening means and the reinforcing layer are all made of the same polymeric material.
8. A hose according to any preceding claim, wherein the or each reinforcing layer comprises a woven fabric formed of fibres arranged in a warp and a weft direction, and wherein the or each reinforcing layer is disposed such that the warp direction is at an angle of less than 200 to the longitudinal axis of the hose.
9. A hose according to claim 9, wherein the reinforcing layer is disposed such that the warp direction is at an angle of less than 10 to the longitudinal axis of the hose.
10. A hose according to claim 6,7 8 or 9, wherein the or each reinforcing layer comprises an ultra high molecular weight polyethylene.
11. A hose according to claim 6, 7 8, 9 or 10, wherein the sealing layer comprises an ultra high molecular weight polyethylene or a copolymer of hexafluoropropylene and tetrafluoroethylene.
12. A hose according to any preceding claim, wherein the axial strengthening means comprises an ultra high molecular weight polyethylene, aramid fibres or polyester fibres.
13. A hose according to any preceding claim, further comprising an insulating layer.
14. A method of making a hose comprising: (a) wrapping a wire around a tubular mandrel to form an inner coil ; (b) wrapping a sheet material around the tubular mandrel and the inner coil order to provide a tubular body formed of the sheet material; (c) pulling a tubular axial strengthening sheath over a free end of the mandrel, so that the mandrel extends within the axial strengthening sheath, then pulling the axial strengthening sheath along the mandrel so that it at least partially covers the tubular body, wherein the axial strengthening sheath is adapted to reduce deformation of the tubular body when the tubular body is subjected to axial tension, and is adapted to exert a radially inward force on at least part of the tubular body when axial strengthening sheath is subjected to axial tension; (d) wrapping a wire around the axial strengthening sheath to form an outer coil ; (e) securing the ends of the hose produced in step (d); and (f) removing the hose from the mandrel.
15. A method according to claim 14, wherein the coils and the sheet material are applied under tension.
16. A method according to claim 14 or 15, wherein the sheet material in step (b) comprises two reinforcing layers and a sealing layer sandwiched therebetween
17. A method according to claim 16, wherein an inner reinforcing layer, in sheet form, is wrapped helically around the inner coil and the mandrel ; then the sealing layer, in sheet form, is wrapped helically around the inner reinforcing layer ; then an outer reinforcing layer, in sheet form, is wrapped around the sealing layer.
18. A method according to any one of claims 14 to 17, wherein the inner and outer coils are applied in a helical configuration having substantially the same pitch, and the position of the coils of the outer coil are positioned half a pitch length offset from the position of the coils of the inner coil.
19. The use of a hose according to any one of claims 1 to 13 to transport fluids at cryogenic temperatures therethrough.
20. A hose substantially as herein described with reference to and as shown in the accompanying drawings.
21. A method of making a hose substantially as herein described with reference to and as shown in the accompanying drawings.