GB2106702A - Reducing fluid leakage - Google Patents

Abstract

A conduit (1) forming, for example, part of an oil filled under-water power cable has two water trap bends (2 & 3) in mutually perpendicular planes which prevent oil (5) from contacting water (6) as a result of damage (4) to the cable. Alternative means of forcing flow to be displaced in two orthogonal directions include helical conduit sections (Figure 2), knots in the conduit (Figure 4) and internal baffles. <IMAGE>

Description

SPECIFICATION Reducing fluid leakage This invention relates to a method for reducing or stopping fluid leakages into and/or out from a fluid conduit such as an oil or gas pipe, and it also relates to a fluid flow modifying device for realising this method.

However, the invention is limited in its application to conduits filled with a fluid having approximately the same pressure, at least after a leak has occurred, as the ambient pressure, and to cases where the specific gravity values of the fluids within the conduit and outside the conduit are somewhat different.

The invention is particularly applicable to a method and means for use in connection with an electrical cable impregnated with a fluid, but is not limited to such applications. Thus the fluid conduit need not necessarily be incorporated in an electrical cable, but may be incorporated in a different structure or may be of a design whose main purpose is that of being a fluid conduit.

There are already known electrical cables with an insulation consisting of helically applied tapes impregnated with a low-viscosity oil or gas (e.g. SF6) which penetrates all the tape layers. The impregnating fluid is allowed to flow axially through the cable to avoid the formation of voids when the cable is subjected to temperature variations, which cause expansion/contraction of the fluid.

If a single conductor cable is considered, the fluid conduit(s) is (are) usually arranged in the centre of the centrally arranged conductor and/or in recesses or channels arranged along the inner surface of the outer sheath. If on the contrary a multi-conductor cable is concerned, the fluid conduits are usually made up by the interstices between the conductors and the outer sheath.

If such cables, when used submerged in a marine environment, are subjected to an external, mechanical stress, e.g. caused by ship anchors or fishing equipment, they may be so severely damaged that impregnating fluid will leak out, and water may enter the cables to replace the fluid lost. This is, of course, detrimental to the cables, and the pollution may also have undesirable effects on the environment. The cable may at worst be completely torn apart. Then two damaged cable ends will be leaking impregnated fluid, which e.g. may be oil, into the sea. Moreover, all the cable contaminated by sea water has to be replaced.

With conventional cable design it has been possible to avoid water ingress through the cable ends until the ends are recovered, by maintaining a certain overpressure within the cable related to the external water pressure. However, such measures will increase the pollution of gas or oil, will cause large expense, and require large oil quantities to be available.

A device is already known, named a blocking restrictor, for insertion into the oil duct in a submarine cable at certain intervals. Due to such a device the amount of polluted oil during a period of damage will be reduced. Such restrictors are known from US pat. No. 3,798,345.

Such known restrictors are to be inserted in the cable at intervals of several hundred metres.

The principle on which this restrictor is based, is that intruding water will form droplets, the maximum dimension of which is determined by surface tension forces between water and oil. A small opening in the restrictor will therefore stop water but will allow oil to pass. The size of the hole is determined by the oil and water characteristics.

It is, however, clear that the known restrictor does not represent a completely tight barrier to water intrusion if the flow rate is zero, that is, if the external and internal pressures are equal at the damaged spot. If the cable is submerged in water and a rupture takes place where the cable route is horizontal, water will slowly enter the cable and fill up the lowermost portions of same while oil is forced out. The reason for this is of course that water has a higher specific gravity than oil (or gas). When the water level reaches the opening in the restrictor, which opening according to the above mentioned US patent preferably has a diameter between 4 and 12 mm, the water will not form droplets at all, but its level will gradually rise until water runs through the opening and passes the restrictor which does not then represent a block to water intrusion.If the cable runs more or less vertically, water will pass the restrictors even more easily.

For this earlier known restrictor to work satisfactorily, it is therefore necessary for there to be a positive oil flow out of the restrictor. This flow must be so fast that it develops a pressure at least balancing the specific gravity difference between water and oil at the cross-section of the restrictor.

Since oil has a lower specific gravity than water, the gravitational pressure of oil will be lower than that of water at the same depth, and the excess pressure has to be provided from a pumping plant or from a pressure reservoir, and a large amount of oil must be stored to prevent water intrusion during recovery and repair.

It also known to arrange tubular members around a cable at intervals to limit the migration of water along the oil ducts, for example UK pat. No. 1 435 592.

The solution proposed in this patent specification will, however, only work if the cable arrangement is linear and close to horizontal. Even small, local, irregularities in the sea bed may nullify the precautions taken according to the patent specification. A smoothly inclined sea bed will put a whole series of such tubular members out of use.

It should also be mentioned that as soon as the cable is to be recovered and the cable end therefore is raised towards the surface of the sea, water which has entered a cable equipped with such tubular members and has migrated down to the nearest tubular member, will pass freely further down the cable core. The tubular members will certainly not represent a bar to further water intrusion when the cable goes vertical.

The object of the present invention is to obtain a method and a device (below called a deflector) which presents a hindrance to the intrusion of water even when the pressures are equal on both sides of the deflector, i.e. when no flow exists, and which also works for more than one specific position or direction of the cable or conduit. In a preferred embodiment it is also an object to design a deflector having the same water blocking effect notwithstanding the spatial orientation of the cable itself.

A further object is to provide a method and a device each of which is independant of the inclination and irregularities on the sea bed.

A further object is to provide a method and a means which will continue to work during cable recovery operations when the cable axis is tilted.

For a preferred embodiment it is also an object to obtain a cable having the above listed advantages without having an increased diameter or outer auxiliary means.

According to one aspect of the invention, there is provided a method for reducing or stopping fluid leakages into and/or out from a fluid conduit such as an oil or gas pipe, or an oil or gas duct in a complex structure such as an electric cable, by introducing local flow actuators which each locally changes the fluid flow path properties, characterised in this that each flow actuator consists of a flow path direction deflector which has such a design that it will force or guide each and every element of the fluid flow to change height level at least twice, and in alternating directions, as it passes through the flow deflector.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows the principle of the invention in a simple two plane water trap according to the invention.

Figure 2 shows an embodiment acting for all possible angular conduit orientations.

Figure 3 shows an arrangement which in addition to a two plane embodiment also represents an effective block against further water intrusion during tilting.

Figure 4 shows an omnidirectional water trap element arranged as a pipe-knot.

The solutions according to Figures 1-4 may be designed as insertions to be arranged in the conduit or in the oil channel(s). However, the solutions may also be obtained by arranging the complete conduit itself along a curved path, possibly supported by an external structure.

Figure 5 represents a practical helical water trap acting according to the same principle as that illustrated in Figure 2.

Figure 6 shows a cross-section of a different version of a helical water trap.

Figure 7shows a labyrinth version of a curved, multi plane deflector.

Figure 8 shows a streamlined type of a helical deflector yielding low resistance against the flow.

Figure 9 shows a special version of a labyrinth embodiment having an omnidirectional effect.

Figure 10 shows a specific omnidirectional shape of the "torpedo-type" in unfolded view.

Figure 11 shows some arrangement in a multiconductor cable, and Figure 12 shows a module deflector where each single module substantially gives a flow path deflection in one plane.

The idea is to introduce a deflection of the flow path similar to that of a conventional water trap or water seal. The flow should in other words be guided so that every particle therein has to pass different height levels; or still more precisely, each particle has to move up to a higher level, then back again to a lower level or vice versa. No particle should have the possibility of passing through the deflector without changing height level twice, each time in the opposite direction.

In Figures 1 - 4 some principles of deflectors, all acting as water-traps in more than one conduit position, are shown.

In Figures la, band ca simple two-plane water trap is shown from three different points of view. Figure la shows the deflector in a front view, 1 b from above and 1 c is the deflector seen from its end face.

In these figures 1 represents the conduit, 2 and 3 the water trap bend in two perpendicular planes, 4 is a rupture in the conduit, 5 is oil (or a different fluid) in the conduit, 6 is intruding water (or other fluid from the environment).

If a conduit having such a design is arranged on the sea bed, one of the bent portions (2 or 3) will tend to point upwards and the upwardly directed portion will act as a water trap while the other bend may be neglected. If therefore the bent portion 2 is stretching upwards as shown, introducing water 6 will move until its surface reaches the shown level 7. If now the pressure of the intruding fluid equals that of the internal fluid 5, the intruding fluid will be effectively stopped at this point. If the pressure of the internal fluid 5 exceeds that of the intruding fluid 6, a small flow of the internal fluid will move out of the ruptured place, but the intruding fluid will not move above the shown level 7. And the left-hand portion of the conduit 1 will be effectively protected against water ingress. Only if the pressure of the internal fluid 5 is so much less than the pressure of the intruding fluid that the height of the bent portion 2 (or 3) is balanced, will water pass the barrier and enter the left portion of the conduit. The internal pressure should therefore be maintained and controlled so that it never falls below the external pressure.

The efficiency of this water trap is at its maximum when the two dotted lines 10, 11 have the same inclination, but in opposite directions. If the conduit is tilted so much that one of the dotted lines becomes horizontal, or the two lines are both inclined in the same direction, no water trap effect will be obtained. (The dotted lines represent the practical flow line which is closest to a straight line).

The embodiment shown in Figure 1 is a simple representation of the mentioned invention. The deflector according to this design will have a maximum water trap effect for two distinctly different angular orientations of the deflector, namely when the bend 2 or the bend 3 points directly upwards.

In Figure 1 da different embodiment is shown. Small discs 12, 13, 14, 15 which partly fill-up the conduit cross-sections are inserted. The angular position of each disc is shown. The discs will force the flow to undertake up/down right/left movements within the conduit.

A different solution is shown in Figure 2. Here Figure 2a is an end view while Figure 2b shows a side view.

Here the conduit is arranged in a helical shape except that the end portions (9, 10) of the conduit are guided somewhat towards the helix axis. However, the end portions may also be arranged at the periphery, so that the deflector obtains a helical shape from end to end. The water trap effect will not exhibit two distinct maxima, but will have the same value no matter in which angular position the helix is turned around its own axis.

This type of "water trap" will therefore act as a water barrier even when no differential pressure is present.

The only requirement is that the helix is substantially horizontal as explained above in connection with the dotted lines 10,11.

It is understood that the same "water trap" effect will be obtained both if the whole fluid conduit or cable is deflected, and also if a deflector as shown is inserted in the fluid flow path, so that the flow path only is deflected within the small dimensions of the fluid flow channel itself. Thus the oil flow path 1 in Figure 1 may be the total cable or pipe channel as laid. However, the flow path 2 may also represent a small part of the oil duct itself, and the up/down right/left bends then have to be undertaken within the limits set forth by the oil channel dimensions. Several parallel paths may be used instead of one single path.

It is understood that such a design when exposed to water intrusion, will represent an effective barrier for further water intrusion when the pressures are equalised. It is in such circumstances not necessary to have any flow of the fluid at all. Therefore, no pollution will occur.

However, both the Figure 1 and the Figure 2 embodiments have one inherent disadvantage. If one end of the deflector is lifted so much that one of the dotted lines 10, 11 becomes horizontal or even obtains an inclination in a different direction from that shown in the figures, the water trap effect will be jeopardized.

Therefore, if a deflector according to Figure 1 or Figure 2 is arranged in a conduit laid on the sea bed, water which has entered the conduit down to the right side portion of the deflector will pass the deflector as shown as the right side portion of the deflector is raised above the inclination mentioned. With such solutions the oil pressure or fluid flow has to be increased considerably during a recovery operation, as a positive oil flow is required to prevent further water ingress. However, this solution also is within the scope of the present invention, as an oil flow is only required during the relatively short lasting recovery procedure.

To ensure that the water trap effect will be maintained even during a tilting process from horizontal to vertical and finally back to a horizontal position again, it is required that the bent portion include a turn of at least 270'. This is because a static water trap should make a 180' turn, and the horizontal-vertical-horizontal tilting process represents an additional 90 angle.

In Figure 3 is shown a solution which includes a 360 turn of the conduit and therefore effectively protects against water intrustion even during a tilting process (e.g. during recovery) of more than 909 If it is sufficient with a one plane water trap effect, only one turn such as 16 (or 17) would be required. Therefore a conduit having only one such turn is also within the scope of the present invention. However, a two plane deflector may easily be obtained also here as shown in Figure 3a (from front), 3b (from above) and Figure 3e from one side.

It is also possible, in a relatively simple arrangement, to obtain an omnidirectional water trap effect, i.e. a water trap which is operative no matter in which spatial or angular position it is arranged. The Figure 4 embodiment is represented by a knotted pipe or conduit 1. Regardless from which direction such a simple knot is regarded, it will in all and every projection undergo a turn of 360 . Thus a conduit shaped as such a simple knot will represent an effective ominidirectional water trap.

If such water traps are designed as restrictive insertions arranged within a fluid conduit, a smaller pipe section, arranged as shown, may e.g. be moulded into a solid body only leaving open at least one channel with the shape shown. This moulded (or otherwise manufactured) insertion may then have outer dimensions adapted to the inner dimensions of the conduit itself. Such a solution is shown as a transparent body in Figure 4c.

As a second alternative, an external, stiffening structure may be used to keep the desired shape of the whole conduit. Such an external supporting structure may be moulded or shaped as a stiff framework. If the conduit is sufficiently flexible and pressure resistant, however, a shape such as that of Figure 4 needs no supporting structure at all. In many cases the conduit is, however, so stiff that the knot must be rather open and therefore is preferably supported by external means.

The principles shown in Figures 1 - 4 may be realised in various embodiments, of which some preferred versions are shown in Figures 5 - 13, but a number of related solutions may be used according to the principles shown above. The only eseential feature is that there be arrangements which subsequently force the passing flow in different, alternating directions. E.g. a helically twisted tape length, with a tape width corresponding to the channel diameter, will in some cases perform a sufficient deflection.

In Figure 5 the deflector is shaped as an insertion to be arranged at intervals in a circular oil duct. The insertable deflector 20 may consist of metal or a synthetic material such as plastics, rubber or the like. The shape is simply a substantially cylindrical body with helical recesses 21, 22, 23 in its outer surface. The length L of the body 20 and the pitch of the helical grooves 21,22 and 23 may be determined in dependence on each other so that more than one turn of each helical recess is obtained. Avalue of approximately 1,5 turn is preferred or, in other words, L = 1,5 x length of lay of the grooves.

As the grooves or recesses 21, 22, 23 are open towards the surroundings it is assumed that the insertion is arranged within a smooth-walled conduit adapted to the outer shape of the insertion.

The depth of the grooves 21, 22, 23 together with the length of lay of the helixes, determines the allowed maximum inclination without nullifying the water trap effect of the insertion. This is already explained in connection with Figures 1 and 2, in relation to the inclination of dotted lines 10-11.

Some results obtained during a test made with different dimensional values of an insertion according to this embodiment are shown in the table below.

Sample Sample Sample 11 III Number n recesses 3 3 4 D Diameter of insertion (mm) 30 30 30 S Length of lay (mm) 72 75 140 L Length of insertion (mm) 108 112 210 deq Equivalent diameter (mm) per recess 9,5 7,1 9,1 Flow resistance corresponds to additional channel 1k length (m) 6,0 19,1 7,4 From this test it is found e.g. that one 112 mm long and 30 mm 0 insertion having 3 recesses, each of an equivalent diameter of 7,1 mm and having a length of lay (pitch turn length) of 75 mm represents an additional flow resistance according to 19,1 m length of the conduit (of 30 mm p), where

The flow resistance added by each such insertion may be critical as the flow resistance in the total channel must lie within certain limits.

If the inner surface of the conduit is not quite smooth, an embodiment according to Figure 6 may be preferred. Here the helical openings along the insertion are not open at the surface. It would then be easier to seal between the insertion and the inner surface of the conduit by using a sealing compound or a gasket. The helical openings 21 22', 23' may have a circular cross-section or may have a shape as shown, which does not extend so far in a radial as in a peripheral direction. With such a modification using a relatively small radial extension or depth of each opening, the effective water tape value may be somewhat increased, again as indicated by the dotted lines 10-11 in Figure 1 and Figure 2.

By embodiments according to Figures 5 or 6 a water trap effect is obtained for all angular positions, but if the inclination increases, the water trap effect will be reduced and finally lost as explained above. If, however, end by-passes are arranged e.g. from channel 21-22 on the left-hand end of the insertion and from channel 22-23 on the right-hand end, a back-forth movement of the fluid is also obtained. The fluid flow path will then be: Left-hand end 23, right-hand end 23, back to left-hand 22 and out from right-hand end channel 21 (or vice versa). With such externally (or internally) arranged feed back loops an omnidirectional water trap effect is easily obtained also with this design.

A different solution is indicated in Figure 7. This version may be named the labyrinth embodiment. Here the fluid flow is guided through a spatial labyrinth as shown. In Figure 7 there is shown a relatively simple embodiment comprising three labyrinth compartments with partitions provided with openings 24, 25, 26, and 27 as indicated. The flow will then be guided through these openings in succession while the flow is forced in different directions. In this manner the flow changes directions so many times that an omnidirectional water trap effect is obtained.

The solution shown in Figure 8 is in principle similar to that shown in Figures 2 and 5 as the flow paths are similar. Here the inserted deflector comprises a centrally arranged compact body 30 with protruding fins 31, 32,33,34. The mumber of the protruding fins is not essential and may be chosen according to practical design. The fins are helically arranged as shown, and the pitch of the helixes may vary slowly along the deflector to ensure even and laminary flow conditions. Preferably the lay direction of the fins is the same as that of the inner layer of the conductor (if a twisted conductor is used). And the lay of the fins, at start and finish, may be equal to that of the inner layer. The centrally arranged compact body may have a torpedo-shape as shown to represent a low flow resistance and also allow a certain tilting.

A specific solution based on this principle is a single, light, but stiff tape section, longitudinally twisted and inserted in the channel. The thickness of such a tape will determine the minimum height and level changes undertaken by the flow lines. The tape will then, in each cross-section, be arranged along a diameter of the channel. And the tape is just a broad as the channel diameter. Of course a polygonal shape of the twisted, inserted element is also possible, as narrow channels will then be obtained between the side faces of the polygon and the channel wall. Alternatively the channels may be obtained between a circular cylindrical insertion and the channel wall if the latter is helically corrugated.

Figure 9 shows a still more complex embodiment, this being also of the labyrinth type discussed above.

Here, however, if only one fin is used, a similar flow path is obtained as that of Figure 4. Let us assume that the inlet is at the upper end. Then the flow enters the inlet opening 35 and passes axially through a semi-cylindrical tube 36. From the lower side of said tube the flow passes outwards through tube wall openings as shown by the arrows 37, and via a manifold chamber 43 (or possibly separate chambers if several fins are used) enters parallel helical pathway(s) 38 (only one being shown) enveloping the central cylinder back to the upper face 39. This upper flange face is closed and the flow is forced to turn again, this time as shown by the arrows 40, to another semi-cylindrical tube 41, complementary arranged with the first one 36, and then the flow passes axially to the lower outlet 42.This spatial labyrinth is arranged within the oil duct of the cable and represents an omnidirectional water trap. The outer surface 44 may be a tight, cylindrical wall, but this may also be omitted, as the inner surface of the flow channel or fluid conduit will act as such a tight cylinder itself. The total cross-section of all the helixes 38 may equal the cross-sectional area of each of the semi-cylinders 35, 42. Then the cross-sectional area of the flow will be approx. 1/3 of the total conduit cross-section.

In Figure 10 is shown in unfolded representation a modified embodiment of the labyrinth or the protruding fin type. Here the wall of the tube or the channel itself is used as part of the labyrinth wall or the outer envelope of the latter. The configuration of the partitions may also here be rather freely arranged, and whereas in Figure 8 a helical arrangement is proposed, there is in Figure 10 suggested a more complex arrangement giving an omnidirectional water trap effect. The length dimensions of sections A and B may be chosen rather freely, but they should preferably at least equal the channel diameter.

If the principle of the invention is to be used in a conventional (3-phase) three conductor oil impregnated cable, some appropriate different embodiment are shown in Figure 11. Here 45, 56 and 47 represent three circular insulated conductors embedded in an impervious sheath 48. The insulated conductors are usually arranged helically. Then four helical channels are available as axial oil ducts within the cable sheath. The three outer ducts 49,50,51 have identical cross-sections, while the central duct 52 is much smaller and has a straight axis, but is helically twisted.

If now the central duct 52 is locally closed at intervals by an adapted member, all the oil transport along these cable portions has to take place in the helical, identical peripheral channels, and in this simple manner a similar effect to that in the Figure 2 version is obtained, but only three parallel helical passageways are used.

To improve the water trap effect, the innermost parts of the helical channels may also be filled. A proper filler design 53 to obtain such an effect is shown in Figure 1 ib. Then the alternating ascending/descending movements of all flow elements receive a larger height variation and therefore the water trap effect will be better and a more inclined layer path may be used. Modifications may be introduced. Thus deflectors as earlier mentioned may be built into each of the channels, or the channels may be partly filled be an adapted filler configuration. Figure 1 inc is also referred to. In a multiconductor cable the conductors' length of lay will affect the tolerable tilting angle in a similar way of the pitch of the helix does in Figure 2. Therefore the length of lay may be reduced, locally or along the whole cable.A deflector according to any of the above shown solutions may be inserted in holes 54,55,56 in the filler according to Figure 1 Ic. If these fillers or stoppers are made of an elastomer, the water trap insertions may be metallic to resist swelling forces. Also in these embodiments there may be used two spaced apart fillers with a water trap element arranged therebetween.

If the insulation is too dense to allow a sufficient oil flow to and from the centrally arranged duct between the duct closure intervals, a minor flux path may be radially arranged between the central duct and one of the peripheral ducts at intervals between the inserted fillers. E.g. there may at axial intervals be arranged a minor flow connection between the central duct and one specific of the peripheral ducts. If these minor radial flux paths are arranged at such intervals that they all are parallel, coplanar, and connected to the same peripheral duct, there is no risk that the central flux path will represent a pass-by connection for the water from one level to a lower level in the same helical duct.

There may be developed different modifications of this invention within a wide variety of designs. Thus the water trap effect may only be present in one plane, in two perpendicular planes, or in three orthogonally arranged planes. More than one single throughpath may be adopted. The design shown in Figure 2 may be obtained by fastening straight tubes between two flanges and then twisting the unit, possibly with a centrally arranged spacer to avoid internal kinks in the tubes as they are helically twisted. The material may be conducting, e.g. metal; or insulating, e.g. plastics. To reduce the flow resistance each opening may have a streamline-shaped outlet and inlet zone, as suggested in Figure 4c. The threaded finds of the torpedo-shaped body of Figure 8 may also have a slowly or gradually variable pitch to reduce the risk of turbulent flow.

In Figure 12 it is assumed that a deflector according to the present invention may be built up from modules. Each module 57, 58 may e.g. deflect the flow path in only one plane (or in two planes 59). When the modules are assembled to a working deflector the mutual arrangement ascertains that a multidirectional or omnidirectional water trap is obtained. In the Figure 12 module 58 deflects horizontally, module 57 deflects vertically, and module 59 takes care of vertical deflection and of the tilting effect. Assembled, the modules, which each represent a plane deflector, therefore made up one combined omnidirectional deflector.

As to the flow area it is deemed to be advantageous if the flow path cross-section is constant through the deflector. This will, e.g. in the embodiment shown in Figure 9 be obtained if the semicylindrical flow paths have a cross-sectional area equal to the sum of the parallel helical passageways.

Further, the whole cable may be curved and fastened to an outer clamping device to maintain its shape.

This outer device may be arranged below the cable on the sea bottom before laying, or may be fastened to the cable and laid out together with it.

Other solutions are also applicable within the scope of this invention. E.g. pre-manufactured deflectors may be installed in the oil duct of a cable during cable manufacture, orthey may be jointed into the cable at each regular cable joint.

In large plants it should also be possible to enclose the conduit or cable, at least at the deflecting places, in a drainage tube system, possibly maintained at lower pressure. Then the undesirable fluid may be tapped off at each deflecting point and guided away through the drainage system. With such a drainage system possible leakages may be controlled and supervised continuously.

The plant preferably should be equipped with a system for establishing pressure equalisation or a minor oil over-pressure at the rupture place. This, however, is not a part of this invention, and therefore it is not further described here.

However, one specific use of the invention should be mentioned to explain that the deflector is also useful in high pressure plants.

If a deflector according to the invention is inserted at intervals in a high pressure submarine oil tube, the amount of leaked out oil, due to a tube rupture, may be reduced considerably.

If the supply flow of oil is stopped as soon as the rupture is detected, the large amount of oil which still remains in the tube portions beyond the deflectors, shall be maintained there. Therefore the pollution will be reduced, and also the loss of oil. When an elastic cable is considered, damages of the cable will also be reduced as water ingress is completely avoided between the deflectors.

Claims (15)

1. Method for reducing or stopping fluid leakages into and/or out from a fluid conduit such as an oil or gas pipe, or an oil or gas duct in a complex structure such as an electric cable, by introducing local flow actuators which each locally changes the fluid flow path properties, characterised in that each flow actuator consists of a flow path direction deflector which has such a design that it will force or guide each and every element of the fluid flow to change height level at least twice, and in alternating directions, as it passes through the flow deflector.

2. Method according to claim 1, characterised in that the flow path deflector deflects the fluid flow in different directions so that height level changes of all the particles in the fluid flow are obtained at least for two different orientations (different angular or different axial orientations) of the fluid conduit, and preferably for each and every spatial orientation of same.

3. Method according to claim 1 or 2, characterised in that the flow path deflector deflects the flow path in such a manner that the projection of the flow path is curved at least 180', and preferably 360 , in at least one projection plane, and preferably in three, orthogonally arranged projection planes.

4. Flow path direction deflector for realising the method according to claim 1, 2 or 3, characterised in that the deflector is designed as a multiple curved water trap which has a maximal water trap effect for at least two different flow path orientations.

5. Flow direction deflector according to claim 4, characterised in that the deflector comprises one or more curved openings or holes (21', 22', 23') arranged in an otherwise solid body, and/or one or more curved recesses (21,22,23) arranged atthe surface of a solid body (20).

6. Flow direction deflector according to claim 4 or 5, characterised in that the deflector comprises a torpedo-shaped body (Figure 8) centrally arranged in the fluid conduit and fastened to the latter by outwardly protruding fins (31,32,33,34) preferably arranged in a regular pattern.

7. Flow direction deflector according to claim 4 or 5, characterised in that the flow path deflector comprises a spatial labyringth built up from discs (12, 13, 14, 15, 18, 19) and/or partitions equipped with holes (24,25,26,27, Figure 7) guiding the fluid flow in different spatial directions.

8. Flow direction deflector according to claim 4, characterised in that the fluid conduit itself is laid in a predetermined curved arrangement, preferably guided by and supported by a stiff external structure.

9. Flow direction deflector according to claim 4, 5, 7 or 8, characterised in that the flow path comprises at least one peripherally arranged cylindrical helix, preferably comprising at least 11/2 turns, and that the inlet(s)/outlet(s) to this (these) helix(es) is (are) arranged axially through said helix(es), and preferably in a mutually crossing manner, so that a "knotted" structure is obtained (Figure 4).

10. Local flow path deflector according to claim 4, 5 or 9, characterised in that the deflector comprises one or several tubes or pipes which either are curved or twisted in a predetermined manner and then are subjected to a casting process so that the pipes will represent throughlets in an otherwise solid body (Figure 4a).

11. Flow direction deflector according to claim 4,5,6,7,8,9 or 10, and used in a multiconductor cable having insulating fluid flowing in the free space between the conductor and an external sheath, characterised in that at least the central duct(s) (52) between the conductors is (are) locally or continuously filled by a blocking material (53) while all or some of the peripheral ducts between the conductors and the outer sheath are at least partly left open and constitute the deflected flow paths.

12. Flow direction deflector according to claim 11, characterised in that a flow deflector according to any of claims 4 - 10 is arranged in a sealing manner, within at least one of the peripheral ducts (e.g. at 54, 55, 56).

13. Flow direction deflector according to any of claims 4 - 12, characterised in that the deflector path is built up from or stiffened with a supporting structure which is so rigid that it will substantially maintain its shape unaltered during normal handling and working stresses.

14. Method for reducing or stopping fluid leakages substantially as described with reference to the accompanying drawings.

15. Flow direction deflector substantially as described with reference to the accompanying drawings.