WO2010099795A1

WO2010099795A1 - A valve

Info

Publication number: WO2010099795A1
Application number: PCT/DK2010/050053
Authority: WO
Inventors: Krystyna Izabella LANGKJÆR
Original assignee: Nkt Flexibles I/S
Priority date: 2009-03-06
Filing date: 2010-03-04
Publication date: 2010-09-10

Abstract

The invention relates to a valve particularly for use in offshore applications. The valve comprises a house with an inlet side (I) and an outlet side (O), a seat (4) and a sealing element (5) displaceable with respect to each other to provide a substantially closed position and at least one open position. The outlet side (O) is provided by an exit passage (11) in the house, wherein the exit passage (11 ) has an exit length (L) measured as the shortest length a fluid must pass from the seat element (4) or the sea-ling element (5) to the exit of the valve. The exit passage (11 ) has a narrow length section (12), in each cross sectional cut perpendicular to the exit length (L) and along the narrow length section (12). The narrow length section (12) has a periphery (P) and a maximum gap (M) determined as the longest of shortest periphery-to-periphery straight lines through each point within the periphery (P), and an ave-rage maximum gap (M) along the narrow length section (12). The narrow length section (12) is about 2 times as long as the average maximum gap (M) or longer. The relatively small average maximum gap (M) of the narrow length section (12) prevents electrical current to reach into the part of the passage (11) closest to the seat/sealing (4, 5) and/or closer to the seat/sealing (4, 5) than the narrow length section (12) and thereby formation and precipitation of che-mical components is reduced resulting in a reduced risk of leakage.

Description

A VALVE

TECHNICAL FIELD

The present invention relates to a valve which is adapted for use in contact with electrically conducting liquids e.g. water or water containing fluids, such as for offshore use. The invention also relates to the use of such a valve as well as an offshore system comprising such a valve.

BACKGROUND ART

Valves are important components in many fluid processing industries and are frequently used in contact with electrically conducting liquids, for examples under water, such as in offshore use, e.g. an exit valve for controlling the out flow of a fluid from a container, a pipe or similar. When such a valve is in a substantially closed position it has been observed that after a certain time of use the valve has a tendency to be less effective due to an increase in leakage.

DISCLOSURE OF THE INVENTION

The inventor of the present invention believes to have found an important reason for the increase in leakage and has simultaneously found how such an increase in leakage can be minimized or even avoided.

The invention provides a novel valve in which increase in leakage is reduced compared to prior art valves. Increase in leakage over a time of use, such as several years of use may even be completely avoided.

Accordingly the objective of the invention is to provide a novel valve, preferably an exit valve, which valve has a reduced risk of undesired leakage.

This objective has been achieved by the invention as it is defined in the claims. And as it will be explained below, the invention and embodiments of the invention exhibit further beneficial properties compared with prior art valves and offshore systems. The valve of the invention comprises a house with an inlet side and an outlet side. The inlet side may have any shape and is not important for the function of the invention. The shape of the outlet side is more important and essential requirements of the outlet side as well as desired embodiments with outlet sides designed to improve the effect of the invention are described in the claims and below.

The valve of the invention comprises a seat and a sealing element displaceable with respect to each other to provide a substantially closed position and at least one open position. When the sealing element rests on the seat, the valve should preferably be substantially closed, whereas when the sealing element is displaced with respect to the seat element, a passage from the inlet side to the outlet side of the valve will be provided and accordingly the valve will be in an open position. Some valves will be either substantially closed or in open position. Other valves will have two or more open positions, for example a position which allows a first low flow through the valve and another position which allows a second larger flow or it may have several positions allowing different sizes of flows. In one embodiment the valve has a plurality of open positions from a substantially closed to a fully open position.

The house as well as the seat and the sealing element may have any shape e.g. as shaped in the prior art valves. The shape and size of the house may preferably be adapted to the expected use of the valve. In one embodiment the house comprises a hollow body with an inlet side and an outlet side opposite to each other. In another embodiment the house comprises an angled hollow body e.g. L-shaped and with an inlet side and an outlet side on respective sides of the angle. In one embodiment the size of the house is relatively small such as a house with a volume of about 25 cm³ or less, such as with a volume of about 10 cm³ or less with a volume of about 5 cm³ or less with a volume of about 2.5 cm³ or less. Valves with such relative small volumes are in particular useful for gas valves e.g. gas relief valves, but they may in certain applications also be useful in other valves involving other fluids such as mixtures of gas and liquids as well as supercritical fluids. In one embodiment the size of the house is much larger, e.g. up to about 1 m³ or even larger. The shape and the size of the seat and the sealing element are not important as long as the seat and the sealing element are adapted to each other to provide a sufficient closure of the valve when the sealing element rests on said seat, and to provide a passage from the inlet side to the outlet side of the valve when the sealing element is displaced with respect to said seat. It should be understood that the displacement of the sealing element with respect to the seat is meant to be a relative displacement, which may e.g. be caused by movements of both the seat and the sealing element or by one of the seat and the sealing element. In one embodiment the sealing element is fixed and the seat is movable. In another embodiment the seat is fixed and the sealing element is movable. In a third embodiment both the seat and the sealing element are movable. The size of the seat and the sealing element may preferably be selected in relation to the expected use of the valve. The size of the seat and the sealing element should naturally also be selected in relation to the size of the house, preferably such that the seat and the sealing element have sizes such that they fit inside the house.

The outlet side of the valve of the invention is provided by an exit passage in the house. The exit passage has an exit length measured as the shortest length a fluid must pass from the seat element or the sealing element to the exit of the valve. The exit of the valve is determined by an exit plane, which is the plane of an imaginary plate placed as close as possible against the exit passage of the valve. The exit length is determined from the one of the seat element or the sealing element which is closer to the exit plane when measuring along the exit passage.

In the valve of the invention the exit passage has a narrow length section, measured in each cross sectional cut perpendicular to the exit length and along the narrow length section, where the narrow length section in each cross sectional cut has a periphery and a maximum gap determined as the longest of shortest periphery-to-periphery straight lines through each point within said periphery. The average maximum gap along said narrow length section should be relatively small compared to the length of the narrow length section, and it has been found that if the narrow length section is about 2 times as long as the average maximum gap or longer, the valve of the invention is will have good properties with respect to reducing or even avoiding risk of undesired leakage. In particular it has been found that if the narrow length section is about 3 times as long as the average maximum gap or longer, the valve will be improved with respect to reducing or even avoiding risk of undesired leakage. In one embodiment the narrow length section is about 4 times as long as said average maximum gap or longer. In one embodiment the narrow length section is about 5 times as long as said average maximum gap or longer.

According to the invention the inventor has found that by providing the valve of the invention with an average maximum gap of the narrow length section which is relatively small compared to the length of the narrow length section, the tendency and thereby the risk of undesired leakage of the valve after a certain time of use in contact with electrically conducting liquids e.g. water or water containing fluids, will be reduced. The reason for this improvement is believed to be that this relatively small average maximum gap prevents electrical current to reach into the part of the passage closest to the seat/sealing and/or closer to the seat/sealing than the narrow length section.

The rational behind this theory is that when valves are used in contact with electrically conducting liquids under situations where the liquid is at substantially stand still within an exit passage of the valve, the liquid in the exit passage may in prior art valves be subjected to electrical current e.g. due to electrochemically reactions and/or due to applied electrical current to elements near the valve. This electrical current results in the formation and precipitation of chemical components, such as the formation and precipitation of salts of components e.g. minerals from the liquid. For example it has been found that carbonates such as MgCO3 have precipitated in exit passages of prior art valves used in offshore systems. The precipitates have shown to result in a blockage of the sealing between the sealing element and the seat, accordingly resulting in an undesired leakage of the valve. By designing the exit passage of the valve such that electrical current is prevented from reaching into the part of the passage closest to the seat/sealing and/or closer to the seat/sealing than a narrow length section, any formation and precipitation of chemical components takes place at a distance from the sealing element and the seat and thereby the risk of such precipitated chemical component being captured between the sealing element and the seat will thereby be reduced and accordingly the risk of leakage will be reduced.

It has been found that the narrow length section in principle may have any shape as long as the average maximum gap is sufficiently small relative to the length of the narrow length section as described above. However, as it will be explained below some shapes of the exit passage have shown to be even more effective.

In one embodiment the narrow length section has a minimum gap in each cross sectional cut perpendicular to the exit length and along said narrow length section. The minimum gap is determined as the shortest periphery-to- periphery straight line, where the straight line is within the circumference provided by the periphery and is perpendicular to the periphery in at least one end of said straight line. The average minimum gap along said narrow length section should preferably be relatively small and the narrow length section will in this embodiment preferably be about 3 times as long as the average minimum gap or longer. In one embodiment the narrow length section is about 4 times as long as said average maximum gap or longer, for example said narrow length section is about 5 times as long as said average maximum gap or longer.

In one embodiment where the valve is a gas valve the minimum gap is about 10 mm or less, such as about 5 mm or less, such as about 3 mm or less.

If the narrow length section has a circular, a square or a rectangular circumference the average maximum gap and the average minimum gap are identical. Also in certain other embodiments the average maximum gap and the average minimum gap will be identical, but the average minimum gap cannot be larger than the average maximum gap. In one embodiment the average maximum gap is up to 10 times larger than the average minimum gap. In one embodiment the average maximum gap is up to 5 times larger than the average minimum gap. In one embodiment the average maximum gap is up to 2 times larger than the average minimum gap. By having a narrow length section with a maximum gap which is identical to or not too much larger than the average minimum gap, a relatively large flow through the exit passage can be obtained for a selected average maximum gap.

Generally it has been observed that the largest improvement is obtained in situations where at least a part of the house providing the exit passage comprises metal or another electrically conducting material.

As indicated above the narrow length section may have any cross sectional shape. Examples of desired shapes for the narrow length section include cross-sectional shapes selected from round, oval, square, rectangular, pentagonal, hexagonal, S shaped and star shaped. The shape of the narrow length section may differ along its length. However, to optimize the potential flow through the exit passage it is often desired that the shape of the narrow length section is essentially identical along its length or alternatively that the shape of the narrow length section only differs slightly such as with a difference of up to 50 % in cross sectional area of the narrow length section.

In one embodiment the narrow length section has a substantially round cross- sectional shape, and preferably the narrow length section has an average minimum diameter along its length, which length is about 3 times as long as said average minimum diameter or longer. Preferably the narrow length section is about 4 times as long as the average minimum diameter or longer, for example the narrow length section is about 5 times as long as the average minimum diameter or longer. In one embodiment wherein the narrow length section has a substantially round cross-sectional shape, and the narrow length section has an average maximum diameter along its length, the narrow length section is about 3 times as long as the average maximum diameter or longer, preferably the narrow length section is about 4 times as long as the average maximum diameter or longer, for example the narrow length section is about 5 times as long as the average maximum diameter or longer.

In one embodiment the length section has a substantially circular cross- sectional shape, and the narrow length section has an average maximum diameter along its length which is substantially identical with its average maximum diameter.

In one embodiment the narrow length section comprises a periphery in a cross-sectional cut and a longest dimension in the cross-sectional cut determined as the longest periphery-to-periphery straight line within said perimeter. The longest dimension in at least one cross-sectional cut of the narrow length section is less than about 10 times the length of the narrow length section, such as less than about 8 times the length of the narrow length section, such as less than about 6 times the length of the narrow length section, such as less than about 3 times the length of the narrow length section, such as less than about 2 times the length of the narrow length section.

By keeping the longest dimension in at least one cross-sectional cut of the narrow length section substantially small compared with the length of the narrow length section, the risk of undesired leakage can be kept low while still allowing a large flow out of the valve.

In one embodiment the narrow length section comprises a periphery in a cross-sectional cut and a longest dimension in the cross-sectional cut determined as the longest periphery-to-periphery straight line within the periphery, and a perpendicular periphery-to-periphery straight line perpendicular to the longest periphery-to-periphery straight line, the longest periphery-to-periphery straight line has a length which is from 1 to about 10 times longer than the perpendicular periphery-to-periphery straight line, preferably the longest periphery-to-periphery straight line has a length which is up to about 5 times longer than the perpendicular periphery-to-periphery straight line.

In one embodiment the narrow length section has an average cross-sectional area and a length L, where L² > 3 ^* the average cross-sectional area, preferably L² > 4 ^* the average cross-sectional area, preferably where L² > 5 ^* the average cross-sectional area.

Based on this and the above teaching the skilled person can optimize the valve depending on its use and its requirements with respect to flow.

The house of the valve may in principle be made from any material having sufficient strength and durability for the use of the valve. For strength reasons the valve will often comprise a metal and very often it will mainly be of metal.

The precipitation of salts of components in the exit passage of prior art valves has mainly been observed in situations where the house comprised an electrical conducting material such as metal. However, since the present invention has solved this problem the valve of the invention may comprise one or more electrically conducting materials, such as metal, without this resulting in any increase in risk of undesired leakage. In one embodiment of the valve of the invention, the house of the valve is partly of a metal, such as one or more of the metals selected from steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, nickel and alloys comprising one or more of steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, chromium, molybdenum and nickel.

In one embodiment the house is totally or partly of a polymer, such as Polyvinylidene Fluoride (PVDF) and Polyetheretherketone (PEEK). The polymer valve will most often comprise minor elements of metal for strength reasons. In one embodiment the house comprises a body and a lid, wherein the exit passage is provided in the lid. This type of construction is well known in the art and is very cost effective to produce. In such a body/lid type valve the inlet side will normally be in the body of the house and the outlet side will normally be in the lid of the house. The other elements of the valve, such as sealing element(s), spring element(s) and optionally other elements are inserted into the body prior to the application of the lid. In one embodiment where the valve of the invention is of the body/lid type, the lid preferably is totally or partly of a metal, more preferably selected from steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, nickel and alloys comprising one or more of steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, chromium, molybdenum and nickel.

In one embodiment the valve is an exit valve, the outlet side of the valve being shaped such that the exit passage is adapted to lead directly out to an open space such as to a sea, when the valve is in use. In this embodiment the outlet side of the valve may preferably be free of connecting threads.

The invention is in particular effect-full in exit valves, because such valves in particular are exposed to electrical current in the fluid surrounding the valve when in use. If for example such an exit valve is used under water, there will likely be anodic/cathodic current sufficiently close to influence the immediate surroundings of the valve and resulting in precipitations which, without the invention, would have resulted in an undesired leakage of the valve over its time of use.

The valve and its operation between open (one or more open states) and close may be operated by any known methods and elements. In one embodiment the valve comprises at least one spring element which is arranged to apply a closing pressure when the valve is in its substantially closed position. In one embodiment the valve comprises one linearly operating spring element and/or at least one nonlinearly operating spring element. The house as well as the seat and the sealing element may have any shape e.g. as shaped in the prior art valves. The shape and size of the house may preferably be adapted to the expected use of the valve, e.g. with a body and a valve as described above. In one embodiment the house comprises a hollow body with an inlet side and an outlet side opposite to each other. In another embodiment the house comprises an angled hollow body inlet side and outlet side on respective sides of the angle. In one embodiment the size of the house is relatively small such as a house with a volume of about 25 cm³ or less, such as with a volume of about 10 cm³ or less with a volume of about 5 cm³ or less with a volume of about 2,5 cm³ or less. Valves with such relative small volumes are in particular useful for gas type valves, but they may in certain applications also be useful in other valves involving other fluids such as mixtures of gas and liquids as well as supercritical fluids. In one embodiment the size of the house is much larger, e.g. up to about 1 m³ or even larger. The shape and the size of the seat and the sealing element are not important, but preferably the seat and the sealing element are adapted to each other to provide a substantial closure of the valve when the sealing element rests on said seat, and to provide a passage from the inlet side to the outlet side of the valve when the sealing element is displaced with respect to said seat. It should be understood that the displacement of the sealing element with respect to the seat is meant to be a relative displacement, which may e.g. be caused by movements of both the seat and the sealing element or by one of the seat and the sealing element. In one embodiment the sealing element is fixed and the seat is movable. In another embodiment the seat is fixed and the sealing element is movable. In a third embodiment both the seat and the sealing element are movable. The size of the seat and the sealing element may preferably be selected in relation to the expected use of the valve. The size of the seat and the sealing element should naturally also be selected in relation to the size of the house, preferably such that the seat and the sealing element have sizes such that they fit inside the house.

In one embodiment the sealing element is a sealing disk member and the seat is an annular seat member. The sealing disk member may for example be connected to a valve rod. One or more spring elements may act directly on the sealing disk member, directly on the valve rod or indirectly on the sealing element and/or the valve rod e.g. via one or more additional spring elements interacting with the sealing element and/or the valve rod when the valve is in operation.

In one embodiment where both the seat and the sealing element are movable, the spring elements act directly or indirectly e.g. via one or more additional disk elements on the movable seat and/or on the movable sealing element. For example a first spring element may act directly or indirectly on the movable seat and a second spring element may act directly on the movable sealing element or visa verse, or both spring elements may act directly or indirectly on one of the movable seat and the movable sealing element, or one or more of the spring elements may act directly or indirectly on both the movable seat and the movable sealing element.

In one embodiment where only one of the seat and the sealing element is movable, the valve comprises a spring element which acts directly or indirectly e.g. via one or more additional spring elements on the movable seat or sealing element.

The valve may comprise one or more resilient sealing units, such as a sealing ring (e.g. an O-ring). In one embodiment the valve comprises a resilient sealing unit which is arranged to form a tight sealing between the sealing element and the seat when the valve is in its substantially closed position.

In one embodiment the valve of the invention is of a valve type comprising several open positions. The valve may for example comprise two open positions e.g. half opened and fully opened. In one embodiment the valve comprises several open positions, such as three, four or five opened positions with different sizes of opening through the valve. In one embodiment the valve can be gradually opened from its substantially closed position to its fully open position. In one embodiment the valve is an open - close valve with essentially one open position only. In other words - the valve is either open or substantially closed. The open position in this open - close valve may vary slightly is the size of the opening through the valve e.g. in dependence on the flow through the valve. In one embodiment the valve is an open - close valve, where the smallest passage through the valve in its open position is the passage.

In one embodiment the valve in its substantially closed position is sufficiently closed as not to allow a flow of fluid through the valve which flow is continuous for one minute or longer.

In general the term 'substantially closed position' is used to mean that the valve is either completely closed i.e. there is no fluid flow through the valve or that any possible flow of fluid through the valve is insignificant relative to a fluid flow through a valve of the given type when the valve is in its fully opened position.

In one embodiment 'substantially closed position' means that the valve is fully closed at least for a period of time.

The valve may be operated by any method, including but not limited to manually operated, mechanically operated (e.g. with one or more spring elements), semi automatically or fully automatically operated, such as electronically operated. Since the valve in most situations is adapted to be used under water, it is preferred that the valve is mechanically operated, semi automatically or fully automatically operated.

As it is clear from the above the valve may be any kind of valve which is to be used in a situation where liquid - and in particular aqueous liquid may stand substantially still in the exit passage of the valve. Examples of types of valves include, but are not limited to relief valves, safety valves, exit valves and/or dosing valves. In one embodiment where the valve construction of the present invention in particular is beneficial the valve is an exit valve and/or a gas relief valve. The exit passage may be substantially identical along its length or it may vary. In one embodiment the exit passage varies at least partly along its length. The narrow length section may be substantially identical along its length or it may vary.

In one embodiment the narrow length section is substantially identical along its length.

To provide a very high protection against precipitation within the exit passage which may result in undesired leakage of the valve, it has been found that by providing the exit passage with a shape such that the exit passage is enlarged in its outermost section a surprisingly positive effect and an additional reduction of risk of undesired leakage is provided. The outermost section of the exit passage is the section farthest from the seat or the sealing elements. It is not known why this enlarged outermost section provides this beneficial effect, but it is believed that the surfaces of the enlarged outermost section attracts any electrical current in the liquid and thereby prevents the electrical current from entering further into the exit passage and into the narrow length section which provides an additional protection. It has also been found that if the enlarged outermost section is or comprises metal, e.g. the metals mentioned above, a particularly high protection can be obtained.

In one embodiment the enlarged outermost section comprises a metal surface.

For optimal protection provided by the enlarged outermost section the cross section of the exit passage preferably is gradually increased in direction away from the seat/sealing elements in the enlarged outermost section.

In one embodiment the exit passage in its enlarged outermost section is trumpet shaped.

In one embodiment the exit passage is enlarged to provide an enlarged outermost section and the enlargement is such that the cross sectional area in the outermost end of the exit passage, away from the seat or the sealing elements, is at least about 5 times as large as the smallest cross-sectional area of the exit passage, such as at least about 8 times as large as the smallest cross-sectional area of the exit passage, such as at least about 10 times as large as the smallest cross-sectional area of the exit passage.

In one embodiment the exit passage is enlarged to provide an enlarged outermost section and the enlargement is such that the cross sectional area in the outermost end of the exit passage, away from the seat or the sealing elements, have smallest gap which is at least about 5 times the average minimum gap of the narrow length section, such as at least about 8 times the average minimum gap of the narrow length section, such as at least about 10 times the average minimum gap of the narrow length section.

In one embodiment the exit passage is enlarged to provide an enlarged outermost section and the enlargement is such that the cross sectional area in the outermost end of the exit passage, away from the seat or the sealing elements, has a smallest gap which is at least about 5 times the average maximum gap of the narrow length section, such as at least about 8 times the average maximum gap of the narrow length section, such as at least about 10 times the average maximum gap of the narrow length.

The valve may have one, two, three or more exit passages, wherein at least one and preferably all are as the exit passage described above and each comprises a narrow length section.

As indicated above the valve is adapted to be used in situations where the exit passage, when the valve is in its closed position, comprises liquid, preferably aqueous liquid.

In one embodiment the valve is a gas relief valve. The valve may for example be constructed as any one of the relief valve described in the copending DK patent application No. PA 2009 00200 and US 6,152,170, with the modification that the valve comprises an exit passage as described below.

In one embodiment the valve is an offshore valve, preferably for use in, or in combination with, an offshore pipe system. The invention also relates to a use of a valve of the invention wherein the valve is used offshore, under water.

According to the invention the use of the valve comprises fixing the valve to an offshore element such that the exit passage of the valve, when the valve is in its closed position, will be at least partly filled with sea water.

In one embodiment of the use of the invention, the use comprises that a galvanic protection and/or an impressed electrical current cathodic protection is applied to at least one offshore element, such that sea water immediately adjacent to the valve is influenced by the electrical current. The shape of the valve as described above will protect the valve from undesired leakage due to precipitates within the narrow length section of the exit passage induced by influence of electrical current.

In one embodiment of the use of the invention, the use comprises that a galvanic protection and/or an impressed electrical current cathodic protection is applied to the offshore element to which the valve is fixed.

The use of the invention may preferably be a use where the valve is a part of the offshore system of the invention as described below.

The invention also relates to a method of releasing fluid, such as gas, from a fluid comprising an offshore element of an offshore structure, e.g. from an annulus of a pipe, wherein at least one element of the offshore structure comprises a galvanic protection and/or an impressed electrical current cathodic protection. The method comprises fixing a valve of the invention directly or via one or more connecting elements, e.g. an end fitting, to the fluid comprising offshore element such that the valve is in its closed position, the outlet passage of the valve will be at least partly filled with sea water. The offshore structure may be all off or a part of the offshore system as described below.

The invention further relates to an offshore system comprising at least one offshore element and a valve. The valve comprises a house with an inlet side and an outlet side, a seat and a sealing element displaceable with respect to each other to provide a substantially closed position and at least one open position, wherein the outlet side is provided by an exit passage in the house. The valve and the offshore element each comprise a metal which metals are not in physical contact with each other. The exit passage has an exit length comprising a narrow length section, wherein the narrow length section is sufficiently narrow and sufficiently long to ensure that an electrical current provided from the metal of one of the offshore element and the valve, to the metal of the other one of the offshore element and the valve does not reach into the exit passage section between the seat/sealing and the narrow length section when the offshore system is in use.

The narrow length section of the valve will reduce the risk of undesired leakage due to precipitates within the narrow length section of the exit passage induced by influence of electrical current. The valve may preferably be as described above.

The valve of the offshore system may preferably be arranged such that the exit passage of the valve, when the valve is in its closed position, will be at least partly filled with water when the offshore system is in use. In this situation properties provided by the valve with the narrow length section and optionally other features as described above will advantageously contribute to the offshore system and the lifetime of the valve may be prolonged. In this connection it should be observed that it often will be very complicated and expensive to exchange a leaking and/or defect valve.

The offshore element may be any kind of offshore element, and the offshore system of the invention may preferably comprise two or more offshore elements which may be physically and/or operationally connected.

Examples of offshore elements include but are not limited to one of more of the elements a pillar, a pipe, an umbilical an end-fitting, a container, a wire, a cable, an anchoring element, a distribution unit, a platform and a ship hull. The offshore system of the invention could for example be as the offshore systems, disclosed in for example US 6,152,170 US 6,065,501 , US 5,813,439 and WO 01/81809 as well as in "Recommended Practice for Flexible Pipe API 17B, Mar 1 , 2002" and "Specification for Unbounded Flexible Pipe 17J, Nov 1 , 1999" or any updated versions thereof, with the modification that at least one valve of the invention as described above constitutes a part of the offshore system, either as an additional valve or in replacement of a prior art valve.

In one embodiment the metal of the at least one offshore element comprises metal of one of more of the elements a pillar, a pipe, an umbilical an end- fitting, a container, a wire, a cable, an anchoring element, a distribution unit, a platform and a ship hull.

In a preferred embodiment of the offshore system it comprises an end-fitting, such as an end-fitting for a pipe, such as a flexible pipe or an umbilical. The end fitting may comprise a sacrificial metal anode, e.g. as described below.

The one or more offshore elements of the offshore system may comprise other materials than metals, for example one or more polymers, e.g. glass fiber armed polymers or one or more polymer coated offshore elements.

In one embodiment the valve is arranged in the at least one offshore element. The valve may for example be arranged to control the outflow of an offshore element e.g. a container, a ship and other. In one embodiment the valve is arranged in an end-fitting or in an offshore element fixed to the end-fitting, the valve preferably being a relief valve.

In one embodiment the valve of the offshore system is a valve arranged to control pressure relief in an offshore pipe e.g. a flexible offshore pipe.

In one embodiment the valve of the offshore system is a valve arranged to control pressure relief in an annulus of an offshore pipe

In one embodiment where the valve is a relief valve, the relief valve is placed in an end-fitting of the offshore system. The end fitting may for example be as the end fittings described in WO04085905, US6412825 and US6923477 with the modification that at least one valve of the invention as described above is incorporated into the end fitting, either as an additional valve or in replacement of a prior art valve.

In one embodiment the offshore system comprises a flexible pipe with an annulus and an end-fitting for the flexible pipe wherein the valve is arranged to relief gas pressure in the annulus of the flexible pipe.

In one embodiment at least one offshore element comprises a metal, which metal is arranged to be in contact with water when the offshore system is in use. The one or more metal may be as the metals disclosed above.

In one embodiment of the offshore system of the invention, the metal of the at least one offshore element is more electronegative than the metal of the valve. Thereby an anode current will be established between the metal of the at least one offshore element and the metal of the valve. The more electronegative metal of the offshore element may be a sacrificial metal anode which has been fixed to the offshore element in order to protect the offshore element. Alternatively the more electronegative metal of the offshore element may be the material of an integrated part or of the whole offshore element.

In one embodiment the offshore system comprises at least one sacrificial metal anode. The sacrificial metal anode may have any shape and size. It is generally known to apply a sacrificial metal anode in electrically connection with a less electronegative metal of an offshore element in order to protect the less electronegative metal against galvanic corrosion. Such sacrificial metal anode may be fixed by any method e.g. as known in prior art.

In one embodiment the offshore system comprises at least one sacrificial metal anode placed in electrically connection with an electrically conductive element of the offshore system. In one embodiment the offshore system comprises at least one sacrificial metal anode placed in physically connection with an electrically conductive element of the offshore system. In one embodiment the offshore system comprises at least one sacrificial metal anode placed in physically connection with an electrically conductive element of the offshore system, within a distance of up to about 2 km from the valve. For example the valve may be placed in an end fitting of an offshore system, where the end fitting is connected to a pipe and a sacrificial metal anode is connected to this pipe in a distance of up to 1 or 2 km from the end-fitting.

In one embodiment the offshore system comprises at least one sacrificial metal anode which is arranged such that it is not in physical contact with the at least one offshore element. In one embodiment the offshore system comprises at least one sacrificial metal anode placed within about 10 m from an electrically conductive element of the offshore system.

In one embodiment the sacrificial metal anode is arranged such that it is in physical contact with the at least one offshore element.

In one embodiment the sacrificial metal anode is arranged such that it is in physical contact with a less electronegative metal of the at least one offshore element.

The metal of the sacrificial metal anode may in principle be any metal since it is the relative electronegativity which is relevant. Examples of useful sacrificial metal anode include but are not limited to zinc, steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, nickel and alloys comprising one or more of zinc, steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin and nickel.

In one embodiment of the offshore system of the invention the offshore system comprises a metal functioning as an anode and wherein a electrical current is arranged to be impressed over the anode and the metal of the at least one offshore element provides the metal of the at least one offshore element with a negative voltage relative to the anode and thereby protects the metal of the at least one offshore element against galvanic corrosion.

EXAMPLE 2 relief valves made from steel are applied in a test setup together with a sacrificial metal anode which is more electronegative than the steel of the relief valves. The test setup is applied under sea water for one year.

Valve A is a relief valve comprising an inlet side and an outlet side, a seat and a displaceable sealing element pre-tensioned with a coil spring. The outlet side is provided by a circular exit passage in the house of the valve, the length of the exit passage is 1 cm and the diameter of the exit passage is 1 cm.

Valve B is as the valve disclosed in Fig. 1 and comprises 3 exit passages, each with a length of 15 mm and with a narrow length section having a length of 12 mm and a diameter of 3 mm, the outermost end of the exit passage being shaped like a trumpet to provide an enlarged section.

After one month the valves are removed and examined.

In valve A, white materials are deposited on the valve in the area around the seat and sealing element.

In valve B no deposition is observed.

The white deposition from valve A is removed and analyzed and it is found that it comprises a major amount of MgO₃

BRIEF DESCRIPTION OF DRAWINGS

The invention will be explained more fully below in connection with a number of embodiments and with reference to the drawings in which:

FIG. 1 is a schematic side view of a valve of the invention.

FIG. 2 is a view in a cross sectional cut along the line A-A' of the valve shown in Fig. 1.

FIG. 3 is a view in a cross sectional cut along the line B-B' of the valve shown in Fig. 2.

FIG. 4 is a schematic drawing of another valve of the invention. FIGs. 5a-e are illustrations of examples of shapes of exit passages of the valve of Fig. 4 seen in a cross sectional cut along the line C-C of the valve shown in Fig. 4.

FIGs. 6a-b are illustrations of examples of shapes of exit passages of the valve of Fig. 4 seen in a cross sectional cut along the line D-D' of the valve shown in Figs. 4, 5a and 5c.

FIG. 7 is a schematic side view of yet another embodiment of the valve of the invention.

FIG. 8 is a view in a cross sectional cut along the line E-E' of the valve shown in Fig. 7.

FIG. 9 is a view in a cross sectional cut along the line F-F' of the valve shown in Fig. 7.

The valve shown in Figs. 1-3 comprises a house with a lid 1 and a body 2 connected to each other by pins 3. The valve comprises inlet side I and an outlet side O, a seat 4 and a sealing element 5 displaceable with respect to each other to provide a substantially closed position and at least one open position. A resilient gasket 16, such as an O-ring, is applied to seal between the seat 4 and a sealing element 5 when the valve is in its closed position as shown in Fig. 1. The resilient gasket 16 may for example be an integrated part of the sealing element 5.

The sealing element 5 is a sealing disk member and the seat 4 is an annular seat member. The sealing disk member 5 is connected to a valve rod 9. The sealing disk member 5 and the valve rod 9 in combination are also called a poppet.

The valve further comprises a first and a second spring element 6, 7, the sealing element 5 is displaced with respect to said seat 4 to provide passage from the inlet side I to said outlet side O when the relief valve is in its open position. The first and said second spring element 6, 7 are arranged to apply a closing pressure when the valve is in its closed position. The first spring element 6 is a coil spring element and the second spring element 7 is a disc spring element.

The spring elements 6, 7 act indirectly on the sealing disk member 5 via an additional element 8 which is in engagement with the valve rod 9. The additional element 8 is shaped as an annular ring with openings 8a for the flow. An annular plate 10 is arranged to protect the disc spring 7 against the fluid. In one embodiment the valve is without such annular plate 10.

The outlet side O of the valve is provided by 3 exit passages 11 in the lid 1 of the house. Each exit passage 11 has an exit length L measured as the shortest length a fluid must pass from the seat element or the sealing element to the exit of the valve. Each exit passage 11 has a narrow length section 12 and an enlarged outermost section 13 which is trumpet shaped.

In each cross sectional cut perpendicular to the exit length and along the narrow length section 12 - e.g. as the cross sectional cut shown in Fig. 3 - the narrow length section 12 has a periphery P and a maximum gap M determined as the longest of shortest periphery-to-periphery straight lines through each point within said periphery. In this embodiment maximum gap M and the average maximum gap M average are identical. In each cross sectional cut perpendicular to the exit length and along the narrow length section 12 - e.g. as the cross sectional cut shown in Fig. 3 - the narrow length section 12 also has a minimum gap M' which in this embodiment is identical with the maximum gap M.

FIG. 4 is a schematic drawing of another valve of the invention. The valve comprises a house 30, an inlet side I and an outlet side O. The valve comprises a not shown seat and sealing element for providing a closed position and at least one open position.

The outlet side O of the valve of Fig. 4 is provided by one or more exit passages. Examples thereof are shown in FIGs. 5a-e and FIGs. 6a-b. In the example shown in Figs. 5a and 6a the valve comprises 2 slit shaped exit passages 22, 23, each with a narrow length section 22 with a length L₂ and an enlarged outermost section 23. Also in this embodiment the maximum gap M and the minimum gap M' are identical in each cross sectional cut perpendicular to the exit length and along the narrow length section 22, for example in the cross sectional cut shown in Fig. 5a.

In the example shown in Fig. 5b the valve comprises a star shaped exit passage with a narrow length section 32. In this embodiment the maximum gap M is substantially larger than the minimum gap M' as shown in the cross sectional cut shown in Fig. 5b.

In the example shown in Figs. 5c and 6b the valve comprises an s-shaped slit exit passage 42, 43, with a narrow length section 42, with a length L₂ and an enlarged outermost section 43. The narrow length section 42 is slightly conical, which means that the maximum gap M and the minimum gap M' respectively, in cuts along the length of the narrow length section 42 vary. The enlarged outermost section 43 is step wise enlarging.

In the example shown in Fig. 5d the valve comprises four circular exit passages with a narrow length section 52.

In the example shown in Fig. 5e the valve comprises six slit shaped exit passages 62 arranged as an annular ring.

FIGs. 7-9 are schematic side views of yet another embodiment of the valve of the invention, wherein only a part of the valve is seen. The valve shown in Figs. 7-9 comprises a house with a lid 71 and a body 72 connected to each other by pins 73. The valve comprises inlet side I and an outlet side O, a seat 74 and a sealing element 75 displaceable with respect to each other to provide a substantially closed position and at least one open position. A resilient gasket 86, such as an O-ring, is applied to seal between the seat 74 and a sealing element 75 when the valve is in its closed position as shown in Fig. 1. The sealing element 75 is a sealing disk member and the seat 74 is an annular seat member. The sealing disk member 75 is connected to a valve rod 79 (also called a poppet), through which the movement of the displaceable sealing element 75 is controlled by not shown elements, such as one or more spring elements, manually, semi- or full-automatically adjustable element(s).

The outlet side O of the valve is provided by an exit passage 81 in the lid 71 of the house. The exit passage 81 has a narrow length section 82 and an enlarged outermost section 83 which is gradually and outwardly enlarging in cross sectional area as well as in its minimum cross sectional dimension. The narrow length section 82 is shaped like a fan shaped slit, which is outwardly expanding in width, while maintaining slit height. The narrow length section 82 has the length L₂, which in the shown embodiment is longer than 4 times the average maximum gap M.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

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.

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.

Claims

1. A valve comprising a house with an inlet side and an outlet side, a seat and a sealing element displaceable with respect to each other to provide a substantially closed position and at least one open position, said outlet side being provided by an exit passage in the house, wherein said exit passage has an exit length measured as the shortest length a fluid must pass from the seat element or the sealing element to the exit of the valve, said exit passage has a narrow length section, in each cross sectional cut perpendicular to the exit length and along the narrow length section, the narrow length section has a periphery and a maximum gap determined as the longest of shortest periphery-to-periphery straight lines through each point within said periphery, and an average maximum gap along said narrow length section, said narrow length section being about 2 times as long as the average maximum gap or longer, preferably said narrow length section being about 3 times as long as said average maximum gap or longer, for example said narrow length section being about 4 times as long as said average maximum gap or longer.

2. A valve as claimed in claim 1 , wherein said narrow length section has a minimum gap in each cross sectional cut perpendicular to the exit length and along said narrow length section, said minimum gap being determined as the shortest periphery-to-periphery straight line perpendicular to the periphery in at least one end of said line, and an average minimum gap along said narrow length section, said narrow length section being about 3 times as long as the average minimum gap or longer, preferably said narrow length section being about 4 times as long as said average maximum gap or longer, for example said narrow length section being about 5 times as long as said average maximum gap or longer.

3. A valve as claimed in any one of claims 1 and 2, wherein at least a part of the house providing said exit passage comprises metal.

4. A valve as claimed in any one of claims 1 - 3, wherein said narrow length section has a cross-sectional shape which is selected from round, oval, square, rectangular, pentagonal, hexagonal, S shaped and star shaped, said narrow length section optionally having different shapes along its length.

5. A valve as claimed in claim 4, wherein said narrow length section has a substantially round cross-sectional shape, said narrow length section has an average minimum diameter along its length, said narrow length section being about 3 times as long as said average minimum diameter or longer, preferably said narrow length section being about 4 times as long as said average minimum diameter or longer, for example said narrow length section being about 5 times as long as said average minimum diameter or longer.

6. A valve as claimed in claim 4, wherein said narrow length section has a substantially round cross-sectional shape, said narrow length section has an average maximum diameter along its length, said narrow length section being about 3 times as long as said average maximum diameter or longer, preferably said narrow length section being about 4 times as long as said average maximum diameter or longer, for example said narrow length section being about 5 times as long as said average maximum diameter or longer.

7. A valve as claimed in any one of the preceding claims, wherein said narrow length section comprises a periphery in a cross-sectional cut and a longest dimension in said cross-sectional cut determined as the longest periphery-to-periphery straight line, said longest dimension in at least one cross-sectional cut of said narrow length section being less than about 10 times the length of said narrow length section, such as less than about 8 times the length of said narrow length section, such as less than about 6 times the length of said narrow length section, such as less than about 3 times the length of said narrow length section, such as less than about 2 times the length of said narrow length section.

8. A valve as claimed in any one of the preceding claims, wherein said narrow length section comprises a periphery in a cross-sectional cut and a longest dimension in said cross-sectional cut determined as the longest periphery-to-periphery straight line, and a perpendicular periphery-to- periphery straight line perpendicular to said longest periphery-to-periphery straight line, said longest periphery-to-periphery straight line has a length which is from 1 to about 10 times longer than the perpendicular periphery-to- periphery straight line, preferably said longest periphery-to-periphery straight line has a length which up to about 5 times longer than the perpendicular periphery-to-periphery straight line.

9. A valve as claimed in any one of the preceding claims, wherein said narrow length section has an average cross-sectional area and a length L, where L² > 3 ^* the average cross-sectional area, preferably L² > 4 ^* the average cross-sectional area, preferably where L² > 5 ^* the average cross- sectional area.

10. A valve as claimed in any one of the preceding claims, wherein said house being totally or partly of a metal, preferably selected from steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, nickel and alloys comprising one or more of steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, chromium, molybdenum and nickel.

11. A valve as claimed in any one of the preceding claims, wherein said house is totally or partly of a polymer, such as Polyvinylidene Fluoride (PVDF) and Polyetheretherketone (PEEK).

12. A valve as claimed in any one of the preceding claims, wherein said house comprises a lid, said exit passage being provided in said lid, said lid preferably being totally or partly of a metal, more preferably selected from steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, nickel and alloys comprising one or more of steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, chromium, molybdenum and nickel.

13. A valve as claimed in claim 12, wherein said valve is an exit valve, the outlet side of the valve being shaped such that the exit passage is adapted to lead directly out to an open space such as to a sea, when the valve is in use.

14. A valve as claimed in any one of the preceding claims wherein said valve comprising at least one spring element is arranged to apply a closing pressure when the valve is in its substantially closed position, said at least one spring element comprising at least one linear operating spring element and/or at least one nonlinear operating spring element.

15. A valve as claimed in any one of the preceding claims wherein said sealing element rests on said seat when the valve is in its substantially closed position and said sealing element is displaced with respect to said seat to provide passage from said inlet side to said outlet side when said valve is in an open position.

16. A valve as claimed in any one of the preceding claims wherein at least one of said sealing element and said seat comprise a resilient sealing unit, such as a sealing ring, which resilient sealing unit is arranged to form a tight sealing between said sealing element and said seat when the valve is in its substantially closed position.

17. A valve as claimed in any one of the preceding claims wherein the valve is an open - close valve with essentially one open position only.

18. A valve as claimed in any one of the preceding claims 1 -16 wherein the valve comprises several open positions, preferably the valve can be gradually opened from its substantially closed position to its fully open position.

19. A valve as claimed in any one of the preceding claims wherein the valve in its substantially closed position is sufficiently closed as not to allow a flow of fluid through the valve which flow is continuous for one minute or longer.

20. A valve as claimed in any one of the preceding claims wherein the valve is semi automatically or fully automatically operated, such as electronically operated.

21. A valve as claimed in any one of the preceding claims wherein the valve is a relief valve, a safety valve, an exit valve and/or a dosing valve, preferably the valve is an exit valve and/or a gas relief valve.

22. A valve as claimed in any one of the preceding claims wherein the valve is an offshore valve, preferably for use in a, or in combination with an offshore pipe system.

23. A valve as claimed in any one of the preceding claims wherein the exit passage varies at least partly along its length, optionally the narrow length section varies at least partly along its length.

24. A valve as claimed in any one of the preceding claims wherein the narrow length section is substantially identical along its length.

25. A valve as claimed in any one of the preceding claims wherein the exit passage is enlarged in its outermost section, the cross section of the exit passage preferably being gradually increased in direction away from the seat/sealing elements in said outermost section.

26. A valve as claimed in claim 25 wherein the exit passage in its outermost section is trumpet shaped.

27. A valve as claimed in any one of the preceding claims, wherein the exit passage is enlarged to have a cross sectional area in its outermost end away from the seat or the sealing elements which is at least about 5 times as large as the smallest cross-sectional area of the exit passage, such as at least about 8 times as large as the smallest cross-sectional area of the exit passage, such as at least about 10 times as large as the smallest cross- sectional area of the exit passage.

28. A valve as claimed in any one of the preceding claims, wherein the exit passage is enlarged to have a smallest gap which is at least about 5 times the average minimum gap of the narrow length section, such as at least about 8 times the average minimum gap of the narrow length section, such as at least about 10 times the average minimum gap of the narrow length section.

29. A valve as claimed in any one of the preceding claims, wherein the exit passage is enlarged to have a smallest gap which is at least about 5 times the average maximum gap of the narrow length section, such as at least about 8 times the average maximum gap of the narrow length section, such as at least about 10 times the average maximum gap of the narrow length.

30. A valve as claimed in any one of the preceding claims, wherein the valve comprises two or more exit passages, such as at least 3 exit passages.

31. An offshore system comprising at least one offshore element and a valve, said valve comprises a house with an inlet side and an outlet side, a seat and a sealing element displaceable with respect to each other to provide a substantially closed position and at least one open position wherein the outlet side is provided by an exit passage in the house, said valve and said offshore element each comprise a metal which metals are not in physical contact with each other, wherein said exit passage has an exit length comprising a narrow length section, said narrow length section being sufficiently narrow and sufficiently long to ensure that an electrical current provided from the metal of one of the offshore element and the valve to the metal of the other one of the offshore element and the valve does not reach into the exit passage section between said seat/sealing and said narrow length section when the offshore system is in use.

32. An offshore system comprising a valve as claimed in any one of the preceding claims and at least one offshore element comprising a metal, which metal is arranged to be in contact with water when the offshore system is in use.

33. An offshore system as claimed in any one of claims 31 and 32 wherein the metal of the at least one offshore element is at least one metal selected from steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, nickel and alloys comprising one or more of steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, chromium, molybdenum and nickel.

34. An offshore system as claimed in any one of claims 31 - 33 wherein the metal of the at least one offshore element is more electronegative than the metal of the valve.

35. An offshore system as claimed in any one of claims 31 - 34 wherein the metal of the at least one offshore element comprises one of more of the elements a pillar, a pipe, an umbilical an end-fitting, a container, a wire, a cable, an anchoring element, a distribution unit, a platform and a ship hull.

36. An offshore system as claimed in any one of claims 31 -35 wherein the metal of the at least one offshore element comprises an end-fitting, the offshore system further comprises one or more polymer coated elements, the end-fitting preferably being an end-fitting for a pipe, such as a flexible pipe or an umbilical.

37. An offshore system as claimed in any one of claims 36-37 wherein the valve is arranged in the at least one offshore element, preferably the valve is arranged in an end-fitting or in an offshore element fixed to the end-fitting, the valve preferably being a relief valve.

38. An offshore system as claimed in claim 37 the offshore system comprising a flexible pipe with an annulus and an end-fitting for said flexible pipe wherein the valve is arranged to relief gas pressure in the annulus of the flexible pipe.

39. An offshore system as claimed in any one of claims 31 - 38 wherein the offshore system comprises at least one sacrificial metal anode.

40. An offshore system as claimed in claim 39 wherein the metal anode is arranged such that it is not in physical contact with the at least one offshore element.

41. An offshore system as claimed in any one of claims 39 and 40 wherein the metal anode is of or comprises a metal which is more electronegative than the metal of the at least one offshore element.

42. An offshore system as claimed in any one of claims 39-41 wherein the metal anode is of or comprises a metal selected from zinc, steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin, nickel and alloys comprising one or more of zinc, steel, aluminum, titanium, tantalum, zirconium, niobium, platinum, cobalt, tin and nickel.

43. An offshore system as claimed in any one of claims 31 -42 comprising an anode and wherein an electrical current is impressed over said anode and said metal of the at least one offshore element providing the metal of the at least one offshore element with a negative voltage relative to the anode.

44. An offshore system as claimed in any one of claims 31 -43 wherein the valve is arranged such that the exit passage of said valve, when said valve is in its closed position, will be at least partly filled with water when the offshore system is in use.

45. Use of a valve as claimed in any one of the claims 1 -30 comprising fixing the valve to an offshore element such that the exit passage of said valve, when said valve is in its closed position, will be at least partly filled with sea water, wherein a galvanic protection and/or an impressed electrical current cathodic protection is applied to at least one offshore element, such that sea water immediately adjacent to the valve is influenced by the electrical current.

46. Use of a valve as claimed in any one of the claims 1 -30 comprising fixing the valve to an offshore element such that the exit passage of said valve, when said valve is in its closed position, will be at least partly filled with sea water, wherein a galvanic protection and/or an impressed current cathodic protection is applied to said offshore element to which the valve is fixed.

47. Use of a valve as claimed in any one of the claims 45 and 46 wherein the valve is incorporated in an offshore system as claimed in any one of claims 19-30.

48. A method of releasing fluid from a fluid comprising offshore element of an offshore structure wherein at least one element of the offshore structure comprises a galvanic protection and/or an impressed current cathodic protection, the method comprising fixing a valve as claimed in any one of claims 1 -30 directly or via one or more connecting elements to said fluid comprising offshore element such that said valve is in its closed position will be at least partly filled with sea water.

49. A method according to claim 39 wherein the offshore structure is as claimed in any one of claim 31 -44.