The invention relates specifically to: A pipe structure for transporting a fluid substance in a physical environment, the pipe structure comprising a flexible pipe connected to an end fitting, the flexible pipe comprising a sealing layer, the flexible pipe having a longitudinal axis, the end fitting surrounding the sealing layer, the end fitting and the sealing layer having a common to-be- sealed interface and together defining a sealing cavity.

The present invention further relates to a method of sealing a pipe structure.

The invention may e. g. be useful in applications such as transport of pressurized liquids and gases (e. g. hydrocarbons, water, etc. ) at elevated temperatures in marine environments.

BACKGROUND ART The following account of the prior art relates to one of the areas of application of the present invention, flexible pipes for transporting oil or gas in a marine environment.

Flexible pipes are e. g. used in the off-shore industry for transporting oil, gas, water and other fluids between off-shore installations etc. Pressures in the range from 10 to 500 bar (1-50 MPa) and temperatures between-40 and 130 °C are commonplace. It is for several reasons (e. g. environmental and economic) important to avoid that significant amounts of the fluid transported

within the flexible pipe escapes to the (typically marine) environment. This puts focus on the tightness of the flexible pipe and of its connection to an end fitting for connecting the flexible pipe to an installation (at land or on a vessel at sea or on the seabed) or for connecting to another pipe, e. g. another flexible pipe or a rigid pipe.

The leakage of e. g. oil out of the pipe-end fitting joint in a marine environment is a problem. A system capable of maintaining a good sealing at high temperatures (e. g. > 100 °C) is needed.

US-6,019, 137 deals with a flexible pipe for conveying hydrocarbons, typically at temperatures > 80 °C, e. g. from offshore wellheads to the surface. The pipe is at its ends fitted with connection end-pieces. Sealing between a sealing barrier and the end-piece is provided by a metal sealing bush that is crimped on the sealing barrier and held axially in place in the end-piece by means of a ring pushing the bush in an axial direction and (in cooperation with a conical form of the annular housing) causing it to press into the sealing barrier. Other solutions comprise combinations of metal and polymer gaskets pressed together by an axial and/or radial pressure in the form of a cooperating, appropriately fastened ring.

US-5,720, 503 describes a sealing system for a rotatable fluid conduit coupling for an off-shore swivel. The sealing system comprises a sealing ring of a resilient material located in an annular recess in ring-shaped inner and outer, non-flexible (steel) parts separated by a clearance which is to be sealed by the sealing ring, the sealing ring functioning under a positive pressure difference in the clearance. The sealing ring comprises a body connected to separated, flexible legs, the annular recess comprising deformation limiting means resisting compression of the legs towards one another upon application of a negative pressure across the annular recess.

DISCLOSURE OF INVENTION The problem of the prior art is that the sealing element or elements must be subject to a compressive contact force built-into the pipe structure around

the sealing element, and that typically a substantial margin in the form of an extra large compressive force must be provided to be able to account for dimensional changes in the pipe structure (e. g. due to temperature induced creep) during installation and operation. Further, to sustain the sealing pressure between the sealing element and walls of the flexible pipe and the end fitting, these walls have to be relatively rigid (e. g. be of a relatively thick non-flexible construction (e. g. of steel) or requiring a rigid insert, a rigid carcass or the like in the flexible pipe beneath the sealing element).

The object of the present invention is to provide a pipe structure with a sealing that is relatively simple and able to be self-sealing in the sense that it relaxes the need for built-in compressive forces working on the sealing part.

The objects of the invention are achieved by the invention described in the accompanying claims and as described in the following.

An object of the invention is achieved according to the invention by A pipe structure for transporting a fluid substance in a physical environment, the pipe structure comprising a flexible pipe connected to an end fitting, the flexible pipe comprising a sealing layer, the flexible pipe having a longitudinal axis, the end fitting surrounding the sealing layer, the end fitting and the sealing layer having a common to-be-sealed interface and together defining a sealing cavity, the pipe structure further comprising a sealing part for sealing said to-be-sealed interface, said sealing part being contained totally or partly in said sealing cavity, said sealing part comprising an annular gasket surrounding said sealing layer and having an elongated curved cross section forming a first and a second flange section and with an outer face constituting a sealing face and an inner face constituting a non-sealing face of the annular gasket wherein the sealing face of said first annular flange section is sealing against said sealing layer of said flexible pipe and the sealing face of said second annular flange section is sealing against said end fitting, when said sealing part is mounted in said sealing cavity.

In an embodiment of the invention, the annular gasket forms an elongated curved part when viewed in a cross section through a longitudinal axis of the

flexible pipe. In the present context,'an elongated curved part' (referring to a cross section of an annular gasket when viewed perpendicular to an annular direction) is taken to mean a part that has a shape allowing it to be positioned in such a way that it bridges the interface to be sealed and has an edge of contact with each of the sealing layer and the end fitting. Examples of such a shape are a U-shape, a V-shape or any other like shape that bridges the interface to be sealed and conforms to the shape of the sealing cavity defined by the sealing layer and the end fitting. An elongated curved part may e. g. be constituted by an intermediate body connected to two elongated elements/legs/lips or simply two elongated elements physically connected at one of their ends. An elongated curved part may e. g. in a 'folded out'or non mounted situation have an essentially rectangular cross section (possibly with rounded corners or tapered ends), i. e. comprise two essentially parallel and relatively long edges connected by two relatively short, curved or pointed or straight, etc. , curves. When viewed in three dimensions, the gasket comprises an annular part with a sealing surface (i. e. a surface that-when mounted in its operational position-has a common surface of contact with the surfaces to be sealed) and an essentially opposing, non-sealing surface (i. e. a surface essentially facing away from the surfaces to be sealed). In the present context, the'to-be-sealed interface' is taken to mean the clearance or common surface of contact between the end fitting and the sealing surface of the flexible pipe.

In the present context, the term'sealing'is taken to mean to-during normal operating conditions-prevent significant amounts of the fluid (e. g. oil or gas or water) transported by the flexible pipe to escape to the physical environment around the pipe structure or vice versa to prevent significant amounts of the fluid (e. g. marine water) present in the immediate physical environment surrounding the pipe structure to enter and mix with the fluid transported by the flexible pipe.'Significant amounts'are in the present context taken to mean-ideally zero, but in practice-within the specifications of the flexible pipe structure under normal operating conditions.

The solution according to the invention provides an alternative to a traditional 'solid-type'sealing element (such as an O-ring or other geometrically formed

solid elements). It provides a design freedom in adapting the area and shape of the surface of contact with the to-be-sealed surfaces, in choice of materials, in combination with other functional elements, etc. Further, a sealing part according to the invention is more tolerant towards shrinkage, swelling or creep of the gasket itself and of the materials constituting the to- be-sealed surfaces, which may comprise polymeric materials, e. g. Polyamide (PA), Polyethylene (PE) or Polyvinylidene fluoride (PVDF). In particular, certain plasticized grades of polymeric materials exhibit a tendency to de- plasticize when exposed to hydrocarbon fluids (possibly accelerated by increasing temperatures). As a result the seal contact pressure may be compromised due to shrinkage and it becomes insufficient for maintaining fluid tightness. For a sealing part according to the invention, an'oversize'of the surfaces of contact may be designed in, thereby taking account of future possible effects due to hydrocarbon fluid exposure, temperature (or other) influences. The sealing properties of a gasket according to the invention are not significantly dependent on the volume of the gasket but mainly on the surface area of contact with the to-be-sealed surfaces. By eliminating the need for applying a compressive force to the sealing part, the end fitting becomes simpler and the internal support for the sealing layer may be made thinner and the mounting time reduced. Further, a sealing part according to the invention is independent of small movements of the inner liner.

Appropriate materials for a gasket include metals (e. g. stainless steel, (e. g. AISI 316), Duplex steel, Inconel (a nickel-iron-chromium alloy containing various amounts of other metals, e. g. Nb, Mo, Ti), polymers (e. g. fluor polymers, e. g. polytetrafluoroethylene (PTFE), polyetheretherketone (e. g.

PEEK)) or metals coated with polymers.

The'longitudinal axis'of the flexible pipe is taken to mean the centre axis of the flexible pipe when it is held in a straight line (un-curved) configuration.

The physical environment of the pipe structure is in an embodiment of the invention a marine environment such as a deep sea (salt water) environment, e. g. depths of typically 500-1000 m (but including several km). Alternatively or partially, the physical environment may be constituted by a

fresh water environment or by the atmosphere (e. g. in case of a use fully or partially above the sea or on land).

In an embodiment of the invention, the sealing cavity has a wedge-formed cross section when viewed in a cross section comprising the longitudinal axis of the flexible pipe. In an embodiment of the invention, the angle between the sealing layer of the flexible pipe and the part of the end fitting to be sealed in the sealing cavity (together making up the wedge-formed sealing cavity) is in the range 10-90°, such as 20-60°. In an embodiment of the invention, the tip of the wedge-formed cavity is rounded off by forming the end-fitting-part of the sealing cavity. In another embodiment of the invention the part of the sealing cavity comprising the surfaces of contact with the gasket has a U-or V-shaped cross section.

In an embodiment of the invention, the gasket has a sealing surface that describes a surface of revolution with an axis of revolution that coincides with the longitudinal axis of the flexible pipe. This has the advantage of providing a symmetric element which is relatively easy to manufacture. Alternatively, the gasket may take many other forms, e. g. more complex forms adapted to the particular form of the end fitting and the sealing layer.

In an embodiment of the invention, the sealing part exerts a minimum contact force on the sealing layer and the end fitting, where the contact force has a component in a radial direction towards and opposite to the centre of the flexible pipe, respectively.

The term'a minimum contact force'is in the present context taken to mean a contact force sufficient for maintaining the sealing part in place in the sealing cavity after mounting and during normal operating conditions of the pipe structure. In an embodiment of the invention, the minimum contact force is adapted to maintaining the sealing part in place in the sealing cavity in a situation where no internal pressure is applied to the pipe structure (e. g. during installation, before operation has commenced).

In an embodiment of the invention, the sealing part comprises pressing means for pressing the sealing faces of said first and second annular flanges against, respectively, the sealing layer and the end fitting.

When the gasket comprises pressing means in that the gasket is resilient and adapted for pressing the sealing face of said first and second flange sections of the sealing surface against, respectively, the sealing layer of the flexible pipe and the end fitting, it is further ensured that the sealing element is self-sealing because the flexibility of the gasket is able to compensate for variations in the diameter of the sealing layer (e. g. a liner) along its length.

Such a variation may be present due to the margins of the manufacturing process (e. g. an extrusion process). The self-adaptation provided by the built-in flexibility of the gasket has the advantage of easing the process of mounting the flexible pipe to the end fitting, It further has the advantage of relaxing or eliminating the need for an external force to press the sealing part against the to-be-sealed surfaces, which again relaxes or eliminates the need for a support structure (e. g. a carcass) providing an opposing force beneath the sealing layer (e. g. a liner) of the flexible pipe. This allows a pipe structure according to the invention to be used with flexible pipes without an inner carcass or other support structure. Such pipe structures are e. g. of interest in connection with the pumping of water back into an oil well to replace the extracted oil. An appropriate material for making a resilient gasket for these purposes is e. g. PTFE or other polymers or an armoured material or a metal coated with PTFE or other polymers. The material or its coating should preferably be chemically compatible or adapted (e. g. through appropriate treatment) to be chemically compatible with the fluid to be transported by the flexible pipe.

In an embodiment of the invention, the sealing part comprises pressing means in the form of a separate pressing element adapted for pressing the sealing face of said first and second flange sections of the sealing surface against, respectively, the sealing layer of the flexible pipe and the end fitting.

This has the advantage of contributing to keeping the gasket in close contact with the relevant parts of the sealing layer of the flexible pipe and the end fitting, thereby improving the self-sealing ability of the part. In an embodiment of the invention, a pressing element in the form of an annular body is

mounted to cooperate with the gasket (e. g. by press fitting, latching the pressing element and the gasket together) thereby pressing the two sections of the sealing surface of the gasket against the to-be-sealed surfaces. In an embodiment of the invention, the pressing element is itself resilient, thereby further improving the adaptability to mechanical tolerances of the pipe structure. In an embodiment of the invention, the pressing element has an essentially elliptical cross section. An appropriate material for making a pressing element is a metal or a metal coated with a polymer.

In an embodiment of the invention, the pressing element comprises an annular spring. This provides a simple and effective way of creating a force in support of keeping the gasket in contact with the to-be-sealed surfaces in the sealing cavity. In an embodiment of the invention the annular spring takes the form of a canted-coil spring (cf. e. g. US-4,655, 462 and products marketed by the company Bal Seal Engineering Inc, Foothill, California), which has the advantage of providing a constant force over a large spring deflection, thus being well suited for accommodating variations in physical dimensions of the to-be-sealed parts due to mechanical tolerances, temperature variations, creep, wear, etc. Alternatively, the spring may be a helically wound flat spring. Appropriate materials for making an annular spring are stainless steel (e. g. AISI 302) or other resilient metals or alloys. A stainless steel spring has the advantage of being mechanically strong and resistant to corrosion and aggressive chemicals. Alternatively, an O-ring type seal, which functions as a resilient spring, may be used as a pressing element.

In an embodiment of the invention, the sealing part comprises an annular gasket of a fluor polymer, e. g. PTFE, partially surrounding a canted-coil spring of stainless steel. This has the advantage of providing a part suitable for use in a large temperature range, such as-40 °C to +130 °C, and for use in a chemically aggressive environment (such as liquid acid or ammonia).

In an embodiment of the invention, a part of the non-sealing face of the annular gasket faces the direction of the pressure from the fluid possibly entering the sealing cavity from the interior or exterior of the tube. In an embodiment of the invention the surfaces of contact of the sealing cavity with

the annular gasket face the direction of the pressure from the fluid possibly entering the sealing cavity from the interior or exterior of the tube. This has the advantage of contributing to the self-sealing properties of the pipe structure, since the possible pressure from the fluid (e. g. the fluid flowing in the flexible pipe) will press the sections of the sealing surface of the gasket against the to-be-sealed parts of the sealing layer and the end fitting, respectively.

In an embodiment of the invention, the sealing cavity is in fluid contact with the inside of the flexible pipe, the fluid substance thereby exerting a compressive force on the non-sealing face of the gasket. This has the advantage of contributing to the self-sealing properties of the pipe structure, since the pressure from the fluid flowing in the flexible pipe will further press the sections of the sealing surface of the gasket against the to-be-sealed parts of the sealing layer and the end fitting, respectively (possibly in combination with a pressing element). In an embodiment of the invention the fluid substance transported in the flexible pipe is pressurized at a pressure in the range 10-1000 bar (i. e. 1-100 MPa), preferably in the range 1-520 bar (1- 52 MPa).

In an embodiment of the invention, the sealing-cavity is in fluid contact with the outside of the flexible pipe.

The term'in fluid contact'between two volumes is in the present context taken to mean that the pressure difference between one volume and the other is at least partially eliminated, e. g. fully eliminated, e. g. by a channel allowing fluid from one volume to flow to the other volume.

In an embodiment of the invention, the sealing part further comprises a blocking element adapted for limiting the movement of the sealing face of the first and second flange sections of the gasket relative to each other when subject to a pressure from the physical environment. This has the advantage of contributing to the self-sealing properties of the pipe structure, since the pressure from the physical environment surrounding the flexible pipe in combination with the blocking element will further press the sections of the sealing surface of the gasket against the to-be-sealed parts of the sealing

layer and the end fitting, respectively (possibly in combination with a pressing element). In an embodiment of the invention the physical environment in which the flexible pipe structure is situated is a marine environment allowing the water outside the flexible pipe structure to exert a compressive force on the sealing face of the gasket. At a depth of e. g. 2 km, the hydrostatic pressure is around 200 bar (20 MPa).

In an embodiment of the invention, the blocking element is an integral part of the end-fitting in that it constitutes a part of the wall of the sealing cavity. This has the advantage that the only movable part in the sealing cavity is the sealing gasket (and possibly a pressing element partially enclosed by the gasket).

In an embodiment of the invention, the pipe structure comprises several individual sealing parts located in the same sealing cavity. In an embodiment of the invention, individual sealing elements are mounted to abut each other in a direction of the longitudinal axis of the flexible pipe. In another embodiment of the invention, the pipe structure comprises several individual sealing parts located in different sealing cavities. In another embodiment of the invention, the sealing parts are arranged in individual cavities positioned along a direction of the longitudinal axis of the flexible pipe. In an embodiment of the invention, the pipe structure comprises two sealing parts each part being located in its own sealing cavity, one sealing cavity being in fluid connection with the interior of the pipe, the other sealing cavity being- at least in certain situations (e. g. in a fault situation or when the pipe is not at operational pressure, e. g. during installation) -in fluid connection with the physical environment.

In an embodiment of the invention, the sealing layer is constituted by an elastic inner liner. In the present context the term"an elastic inner liner"is taken to mean a tube made of an elastic material, e. g. PA, PE or PVDF.

In an embodiment of the invention, the flexible pipe is an un-bonded flexible pipe, preferably comprising a tube formed liquid tight inner liner and one or more armour layers, preferably two or more armour layers. Alternatively, the flexible pipe may be of a bonded type. The flexible pipe (bonded as well as

un-bonded) may further comprise one or more layers made of composite materials.

In an embodiment of the invention, the flexible pipe comprises two layers of helically wound armouring wires, the winding angles with respect to the longitudinal direction of the flexible pipe being between 50 and 60 degrees, such as between 53 and 56 degrees, the armour layers preferably comprising helically wound wires which are wound in opposite directions.

In an embodiment of the invention, the flexible pipe comprises an inner armouring layer such as a carcass.

In an embodiment of the invention, the flexible pipe comprises a pressure armouring and a tensile armouring, where the tensile armouring comprises two layers of helically wound armouring elements wound in opposite directions, the winding angles with respect to the longitudinal direction of the flexible pipe being between 25 and 40 degrees.

The present invention further provides a method of sealing an interface between a flexible pipe and an end fitting, the flexible pipe defining a longitudinal axis, the end fitting surrounding a sealing layer of the flexible pipe thereby defining a to-be-sealed interface and a sealing cavity, the method comprising the steps of a) providing a sealing part totally or partially contained in said sealing cavity, the sealing part comprising an annular gasket surrounding said sealing layer and having an elongated curved cross section forming a first and a second flange section and with an outer face constituting a sealing face and an inner face constituting a non-sealing face of the annular gasket, b) arranging that the sealing face of said first annular flange section is sealing against said sealing layer of said flexible pipe and the sealing face of said second annular flange section is sealing against said end fitting, when said sealing part is mounted in said sealing cavity, and thereby arranging that said sealing faces are pressed against, respectively, said sealing layer and said end fitting in said sealing cavity.

The method has the same advantages provided by the pipe structure according to the invention as described above and as defined in the claims.

Further embodiments are defined in the dependent claims and in the corresponding description and claims to a pipe structure.

A special sealing arrangement.

An embodiment of the invention provides a sealing arrangement between a flexible pipe and an end fitting connected to the end fitting, wherein the flexible pipe is constituted by a carcass, an inner liner, a pressure armouring, a tensile armouring and optionally an outer sheath, and wherein the sealing arrangement is provided between the inner liner and the end fitting.

When flexible pipes e. g. for offshore use is to be connected to an end fitting, it is absolutely necessary to have a tight sealing between the flexible pipe and the end fitting, not least if the flexible pipe is intended for transport of oil or gasses.

A known example of a flexible pipe connected to an end fitting is described in WO 99/19656.

In this construction, a conventional sealing ring placed around the inner liner has been used. The sealing effect is only achieved when an outer mechanical force is applied to the sealing ring to achieve a sufficient contacting force.

It is therefore an object of the present embodiment of the invention to provide a sealing between an inner liner of a flexible pipe in the area where the flexible pipe is connected to an end fitting which is self sealing in the sense that it is not necessary to apply an external force to the sealing.

The object is achieved by a sealing arrangement between a flexible pipe and

an end fitting connected to the pipe, wherein the flexible pipe is constituted by a carcass, an inner liner, a pressure armouring, a tensile armouring and optionally an outer sheath, and wherein the sealing arrangement is provided between the inner liner and the end fitting characterized in that the sealing arrangement is constituted by at least one spring, where the spring or springs is/are partly surrounded by an open gasket part.

In this way a compressive stress from the inner liner will be transferred to the gasket part which due to the presence of the spring will exert a pressure against the liner. It is in this connection noted that the sealing arrangement in the absence of compressive stresses from the fluid being transported in the pipe-due to the presence of the spring-maintains a resting pressure against the liner which has the effect that fluids cannot pass into the pipe from the exterior surroundings of the pipe.

Additionally the sealing arrangement according to the invention has a relatively large region of operation in the sense that it will function even if the inner liner is subject to creep, i. e. the wall thickness is reduced, or in case of large margins on the dimensions of the inner liner.

In an embodiment of the invention, the gasket part is constituted by a groove having 3 sides and where two of the sides are formed as flanges that are perpendicular to the third side. This has the advantage that the sealing is further strengthened, because the fluid-such as oil or gas-being transported, or fluid from the exterior surroundings exerts a pressure in the interior of the sealing arrangement causing the gasket part to be actuated against the liner both from the spring and directly from the pressure from the fluid being transported.

In an embodiment of the invention, the flanges face the fluid being transported in the pipe. This has the advantage that the pressure on the gasket part against the liner is increased because the fluid being transported exerts a pressure into the groove.

In an embodiment of the invention, the flanges face the external surroundings of the flexible pipe. This has the advantage that it is ensured that the pressure on the gasket part against the liner will always be sufficient because there will always be a fluid around the exterior surroundings of the pipe which exerts a pressure on the sealing arrangement.

In an embodiment of the invention, the sealing arrangement is constituted by two springs where the third side of the matching gasket parts abut each other. This has the advantage of ensuring a reliable sealing in all operational conditions irrespective of fluid is transported by the pipe or not.

In an embodiment of the invention, the gasket part is made of fluor polymers (Teflon@). This has the advantage of providing a sealing arrangement which can be used in a wide temperature range, such as from-40 °C to 130 °C, without deterioration of the sealing or collapse of the sealing arrangement.

Further, Teflon@ is very resistant to influences from aggressive liquids.

In an embodiment of the invention, the spring is expediently embodied as a coil or made of stainless steel, which provides some mechanical advantages and chemically resistant properties.

It should be emphasized that the term"comprises/comprising"when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other stated features, integers, steps, components or groups thereof.

BRIEF DESCRIPTION OF DRAWINGS The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

FIG. 1 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket placed in a sealing cavity according to the invention, FIG. 1. a and 1. b illustrating, respectively, a V-shaped and a U- shaped gasket, FIG. 2 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket placed in a sealing cavity with a blocking element according to the invention, FIG. 2. a illustrating a blocking element that is an integral part of a wall of the end fitting in the sealing cavity and FIG. 2. b illustrating a blocking element that is a separate part, FIG. 3 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket placed in a sealing cavity with a fixed blocking element according to the invention, illustrating a fluid contact between the sealing cavity and the interior of the flexible pipe, FIG. 4 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket placed in a sealing cavity with a separate pressing element according to the invention, illustrating a fluid contact between the sealing cavity and the interior of the flexible pipe, FIG 4. a. showing a pressing element of a solid material and FIG. 4. b a pressing element comprising a rigid core surrounded by a flexible material, FIG. 5 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket placed in a sealing cavity with a separate resilient pressing element according to the invention, the pressing element comprising a tubular elastic spring, FIG. 6 shows details of a cross section of a pipe structure with two sealing parts in separate sealing cavities, FIG. 6. a. illustrating an embodiment with a gasket and a pressing element in one sealing cavity and a gasket and a blocking element in the other, and FIG. 6. b illustrating an embodiment with a gasket and a pressing element in both sealing cavities, the gaskets being mutually mirror symmetrically arranged,

FIG. 7 shows an example e of a flexible pipe suitable e for being connected to an end fitting in a pipe structure according to the invention, FIG. 8 shows a conventional construction of a flexible pipe for offshore use, and FIG. 9 shows in an enlarged scale parts of the pipe of FIG. 8 connected to an end fitting with a sealing arrangement according to the invention.

The figures are schematic and simplified for clarity, and they just show details which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts.

MODE(S) FOR CARRYING OUT THE l Figes. 1-5 show cross sections of parts of a fl pipe structure 100 in a plane comprising a longitudinal axis (cf. axis 170 in FIG. 3) of the f pipe.

FIG. 1 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket 104 placed in a sealing cavity 103 according to the invention.

F a shows a cut out of a cross section of a flexible pipe structure 100 comprising an end fitting part and f pipe part, the end fitting comprising a housing 101 and the f pipe comprising a sealing I ayer 102. The sealing l 102 has an inner surface 1021 facing the interior of the flexible pipe (e. g. a f transported by the pipe or another interior l and an outer sealing surface 109 facing the end-fitting at least around the location of the sealing part in the sealing cavity. A sealing part comprising an annular gasket 104 is positioned around the sealing layer 102 in a sealing cavity 103 formed at the interface between the housing of the end fitting and the sealing layer. The gasket 104 has a V-profile comprising two sections or legs in the

cross section shown adapted to fit the wedge-formed profile of the sealing cavity around the location of the gasket. The two legs (i. e. constituting annular surfaces when viewed in three dimensions) bridge the clearance 111 between the housing 101 of the end fitting and the sealing layer 102 and have surfaces of contact constituted by sealing faces 108,107 with, respectively, the surface 110 of the housing of the end fitting and the surface 109 of the sealing layer. Thereby the interface or clearance 111 between the housing 101 of the end fitting and the sealing layer 102 is sealed. The gasket in FIG. 1. a is made of a resilient material to provide a basic minimum force against the surfaces of contact. It is preferred that the pressure in the sealing cavity 103 on the non-sealing face 105 of the gasket 104 is larger than or equal to the pressure in the clearance 111 on the sealing face 106 of the gasket.

FIG. 1. b shows a similar cut out as that of FIG. 1. a. In FIG. 1. b, however, the annular gasket 104 has a U-shape in the cross section of the flexible pipe including a longitudinal axis of the pipe. The sealing cavity constituted by the faces 110 and 109 of, respectively, the housing 101 of the end fitting and the sealing layer 102 is similarly shaped around the location of the gasket and adapted to appropriately accommodate the gasket thereby yielding a radial minimum force on the surfaces of contact 110 and 109 between the resilient gasket and the sealing cavity.

FIG. 2 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket 104 placed in a sealing cavity 103 with a blocking element 114 according to the invention. The blocking element cooperates with the gasket in that it limits the flexing of the legs of the gasket towards each other.

FIG. 2. a shows a blocking element 114 that is an integral part of a wall of the housing 101 of the end fitting in the sealing cavity 103. In the embodiment shown in FIG. 2. a, the protruding surface 115 of the blocking element 114 forces the sealing faces 108,107 of the legs 1041,1042 of the gasket 104 against the to-be-sealed faces of the sealing cavity 103, if the pressure in the clearance 111 is larger than the pressure in the sealing cavity 103. This may e. g. occur if the hydrostatic pressure from the physical environment is larger

the pressure in the flexible pipe (e. g. during installation of the pipe where the pipe may be un-pressurized).

FIG. 2. b shows an alternative embodiment of the invention, where the blocking element 114 is a separate part whose movement in a direction parallel to the flexible pipe is limited by a wall of the housing 111 of the end fitting, the wall having a face 116 that engages the blocking element and stops its movement in case the pressure in the clearance 111 is larger than the pressure in the sealing cavity 103, thereby forcing the sealing faces 108, 107 of the legs of the gasket 104 against the to-be-sealed faces of the sealing cavity 103.

The blocking element 114 may preferably be made of a material that is more rigid than the gasket.

FIG. 3 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket 104 placed in a sealing cavity 103 with a fixed blocking element 114 according to the invention, illustrating a fluid contact between the sealing cavity and the interior 150 of the flexible pipe. In FIG. 3, a partial cross section of the pipe structure is shown including diametrically opposite cross sections of the sealing cavity (as indicated by the longitudinal axis of symmetry 170 of the flexible pipe). The interior 150 of the flexible pipe is only partially shown in that a possible enlargement of the opening of the pipe is indicated by marks 160. Similarly, only a part of the housing of the end fitting is shown as indicated by the curved outer shape of the housing 101.

The embodiment in FIG. 3 is similar to that of FIG. 2. a but deviates in that an opening 112 between the sealing layer 102 and the end fitting housing 101 allows a fluid contact between the interior 150 of the flexible pipe and the sealing cavity 103 to ensure that the pressure from the fluid in the pipe is present in the sealing cavity (as indicated by arrows 151) and exerts a corresponding force on the non-sealing face 105 of the gasket 104, thereby improving the sealing properties of the structure. Further or alternatively, an opening 113 may be formed in the wall of the housing 101 of the end fitting

to allow a fluid contact between the interior 150 of the flexible pipe and the sealing cavity 103.

The pressure from the external environment 180 may fully or partially be present in the clearance 111 between the sealing layer and the end fitting housing as indicated by the arrow 181. However, the sealing part will ensure a proper tight sealing of the interface 1) due to the blocking element 114, and 2) because the equal pressure in the interior of the pipe and in the sealing cavity allows the sealing layer (which in a preferred embodiment is a flexible liner of the pipe, cf. layer 3 in FIG. 7) to be flexible without deforming into the sealing cavity (and thereby hampering the sealing properties of the gasket).

FIG. 4 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket 104 placed in a sealing cavity 103 with a separate pressing element 124 according to the invention. The pressing element 124 is partially enclosed by the gasket 104. The pressing element serves the purpose of forcing the sealing faces 108,107 of the legs 1041, 1042 of the gasket 104 against the to-be-sealed faces of the sealing cavity 103. The embodiments in FIGs. 4. a and 4. b are similar to those of FIG. 3 in that they include channels 112 and 111 for allowing fluid contact between the sealing cavity and, respectively, the interior of the flexible pipe and the exterior physical environment 180 as indicated by arrows 151 and 181, respectively. The pressing element 124 of FIGs. 4. a and 4. b additionally performs the function of the blocking element 114 of FIGs. 2 and 3.

FIG. 4. a shows a gasket 104 partially surrounding a pressing element 124 where the pressing element comprises a slightly wedge-shaped body of a relatively rigid material, e. g. steel or a ceramic material, the body being adapted so that it expands the distance between the legs 1041,1042 of the gasket in its resting position and additionally when moved in an axial direction of the flexible pipe towards the gasket. The part of the wall 115 of the sealing cavity facing and contacting the pressing element is formed so that it cooperates with the pressing element and thereby ensures that the pressing element remains relatively fixed in case of a'reverse pressure' (i. e. if the pressure from the external environment exceeds the pressure in the sealing cavity) and that the pressure is distributed relatively evenly over the

contacting face of the pressing element 124 with the wall 115 of the sealing cavity.

FIG. 4. b shows a gasket partially surrounding a pressing element 124 as in FIG. 4. a where the pressing element comprises a rigid core 117 surrounded by a resilient material.

FIG. 5 shows details of a cross section of a pipe structure with a sealing part comprising a sealing gasket placed in a sealing cavity with a separate pressing element according to the invention. In an embodiment of the invention, the pressing element 124 comprises a tubular elastic spring 118 partially enclosed by the annular gasket 104. In an embodiment of the invention the tubular spring takes the form of a canted-coil spring. The face 115 of the wall of the sealing cavity 103 is adapted to receive the pressing element in case of a'reverse pressure'in the sealing cavity so that sealing faces 108,107 of the gasket are forced against the walls of the sealing cavity to ensure a tight sealing thereby additionally performing the function of a blocking element (cf. 114 on FIGs. 2 and 3). The pressing element 124 may preferably comprise a rigid core 117.

FIG. 6 shows details of a cross section of a pipe structure with two sealing parts in separate sealing cavities.

FIG. 6. a. illustrates an embodiment of the invention with a gasket 1041 and a pressing element 1241 in one sealing cavity 1031 and a gasket 1042 and a blocking element 1142 in the other sealing cavity 1032.

In an embodiment of the invention, as illustrated in FIG. 6. b, the pipe structure 100 comprises two separate sealing cavities 1031 and 1032 each containing an annular gasket 1041,1042 and a pressing element 1241, 1242, the gaskets being mutually mirror symmetrically arranged in their respective sealing cavities.

In both embodiments (of FIG. 6. a and 6. b), the sealing cavity 1031 containing gasket 1041 and pressing element 1241 has the function as described for FIGs. 1-5 of sealing the interface against fluid escaping from

the interior of the pipe to the surrounding environment 180. The sealing cavity 1032 containing gasket 1042 and, respectively, blocking element 1142 (FIG. 6. a) and pressing element 1242 (FIG. 6. b), on the other hand, has the function of preventing e. g. salt water from a surrounding marine environment in penetrating into the interior of the flexible pipe. The way of functioning is as described for FIGs. 2-3 and FIGs 4-5, respectively.

FIG. 7 shows an example of a flexible pipe 1 suitable for being connected to an end fitting in a pipe structure 100 according to the invention (cf. FIGs. 1- 6).

FIG. 7 shows an ordinary structure of a flexible reinforced pipe 1 with its different layers. The flexible pipe in FIG. 7 consists of an inner liner 3 optionally surrounding one or more other layers 20 that together form an inner pipe. The inner liner 3 serves the purpose of preventing flow of fluids between the interior of the pipe and the external physical environment.

In connection with the present invention, the sealing layer may typically be the inner liner 3 (corresponding to 102 in FIGs. 1-6) which is surrounded by an end fitting and the to-be-sealed interface is the interface between the inner liner and the housing of the end fitting.

One or more layers of profiles 41,42 are helically wound externally, on the inner liner 3, said profiles forming turns of a great angle (e. g. 80-90°) relative to the longitudinal direction of the pipe. Because of the great angle, the profiles will primarily be capable of absorbing radial forces that occur because of internal or external pressures. The internal pressures occur in the operation of the pipe. The external pressures are caused partly by the hydrostatic pressure of the surroundings and partly by mechanical impacts during the laying of the pipe.

The turns thus form a pressure reinforcement which prevents the inner liner 3 from bursting because of a high pressure on the inner side of the pipeline, or from collapsing because of a high pressure on the outer side of the pipeline.

It is additionally shown in FIG. 7 that the pressure reinforcement has externally applied thereto a tensile reinforcement, which consists of one or more layers 61,62 comprising helically wound armouring wires.

An intermediate jacket may be interposed between the pressure reinforcement and the tensile reinforcement, serving the purpose of preventing fluids from migrating between the pressure reinforcement and the tensile reinforcement.

These layers may finally be surrounded by an outer sheath 7.

The tensile reinforcement 61,62 is usually composed of two helically wound layers of steel profiles with opposite winding direction. The armouring wires may alternatively be made of other materials, e. g. composite materials.

An example of a special sealing arrangement.

FIG. 8 shows a flexible pipe 1 which for example may be used for the transport of gasses and oil at large depths of the sea.

Inside the pipe temperatures in the range-40 °C to 130 °C may occur which in combination with the use at large depths of the sea of course makes heavy demands on all parts of the construction of the pipe.

As shown, the pipe comprises a carcass 2 surrounded by a tight inner liner 3. On the outside of the inner liner 3, a pressure armouring layer 4 is arranged which again is surrounded by a tensile armouring layer 6 which as shown is constituted by two layers. On the outside of the tensile armouring layer 6, an outer sheath 7 is arranged.

The construction of the pipe will not be further explained but it is noted that the construction of the individual layers and the chemical composition may be provided in a variety of different ways depending on the specific use.

With reference to FIG. 9 the carcass 2 of a flexible pipe, its inner liner 3 and

its pressure armouring layer 4 are illustrated whereas the remaining layers are omitted.

An end fitting is connected to the pipe by means of bolts, one of which is referred to as 10, the end fitting being constituted by a casing 9, a ring 5 with a gasket seat 15 and a sealing ring 12 which is deposited in a minor groove in the ring 5.

In the figure is further shown a holding member 11 on the inner liner whose function is to fix the inner liner in its axial position.

As is further seen, FIG. 9 shows a dotted line 21 and an arrow which symbolize that the area which in the direction of the arrow points into the end fitting is completely tight so that fluid cannot escape in this area.

Further with the arrow 21 and the bold solid line 19 are symbolized that fluid would be able to pass had a sealing not been provided between the inner liner 3 and the ring 5.

Finally with the arrow 22 and the bold solid line 23 are symbolized that fluid from the surroundings of the pipe will be able to pass if no sealing is provided between the inner liner 3 and the ring 5.

With a view to ensuring the tightness, a sealing arrangement is provided in the gasket seat 15, the sealing arrangement consisting of a spring 14 and a gasket part 13 which has the form of a groove 8 being defined by three sides 16,17, 18, where the sides 16 and 17 are constituted by flanges extending at right angles from the ends of the side 18.

In the groove 8, a spring 14 is placed, the spring being e. g. made of stainless steel.

The spring may expediently be manufactured as a coil running in the groove 8 along a path defined by the curvature of the inner liner.

The sealing arrangement works in the following way: When a pressure is present inside the pipe and in the end fitting, a pressure will be exerted against the inner liner since the carcass 2 is not tight. This pressure will by way of the gasket part 13 be transferred to the spring 14 whereby a sealing is created between the liner 3 and the surroundings.

Further, fluid will be able to exert a pressure against the interior of the gasket part 13 because the groove 8 is open towards the inner liner of the flexible pipe.

In this way a sealing is provided which always will be present when the pipe is pressurized. It is thus not necessary to provide an external mechanical pre-stressing to the sealing arrangement which is normally necessary if a conventional gasket ring is used.

In an especially expedient embodiment, the sealing arrangement is implemented with two gasket parts whose 3'"side abut each other thereby creating two open grooves in the gasket parts so that one groove is open towards the interior of the pipe whereas the other groove is open towards the outer surroundings whereby the sealing between the liner and the gasket parts becomes extra secure.

As appropriate materials for the manufacture of the sealing arrangement may be mentioned fluor polymer (Teflon@) for the gasket part since this material is very resistant to chemical influences.

As an appropriate material for the manufacture of the spring stainless steel may be mentioned.

The invention is defined by the features of the independent claim (s).

Preferred embodiments are defined in the dependent claims.

Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject-matter defined in the following claims.