CA1199853A - Method for reducing fluid leakages, and deflector to obtain such reduction - Google Patents

Abstract

Abstract This invention relates to a method for reducing or stopping fluid leakages into or out from a fluid conduit (1). In particular leakages due to differences in specific gravity of the internal and external fluid are prevented, and not leakages due to high differential pressures. It also concerns a fluid flow deflector arranged at intervals along the conduit to implement this method.
Fluid leakages may occur e.g. from submerged fluid flow conduits due to damages caused by external strain.
As fluid leaks out, water will penetrate into the conduit and replace the leaked out fluid. The polluted fluid is expensive, has an adverse effect on the environ-ments, and later on it has to be replaced. The ingressed water may have a detrimental effect on the conduit in particular if the conduit is included in a paper insulated electric cable.
To avoid or limit both fluid pollution and water ingress, it is proposed to arrange a "water trap" shaped disalignment of the fluid conduit at intervals.
The "water trap" may be arranged internally in the conduit or may be obtained by laying the conduit itself in a curled manner.
The main application field is in ducts for an insulating agent in electrical cables, and in particu-lar in paper- and oil-insulated power cables.
By introducing a flow path disalignment in several or all spatial directions a multi-directional or omni-directional "water trap" is obtained.

Description

1 . 5036-108 Method for reducing fluid leakages, and deflector to obtain such reduction 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 reali~ing this method. However, the case is limited 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.
This invention in particular relates to a method and means for use in connection with an electrical cable impregnated with a fluid.
There are earlier known electrical cables with an insulation con-sisting 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 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 conduc-tor 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 Eluid conduits are usually made up by the interstices between the conductors and 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 wlll 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 environments. The cable may at worst be com-pletely toxn off. Then two damaged cable ends will be leakingimpregnated fluid, which e.g. may be oil, into the sea. And all of the cable contaminated by sea water has to be replaced.
With conventional cable design it has been possible to S avoid water ingress through the cable ends un~il the ends may be recovered, by maintaining a certain overpressure within the cable r~lated to the external water pressure. However, such measures will increase the pollution of gas or oil, and will cause large expenses, and large oil quantities must be available.
It is ealier known a device, 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, which corresponds to Norwegian Pat. No. 134.475~
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 m~1mum 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 si~e of the hole is determined by ~he 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 i 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 i5 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 preerably has a diameter between 4 and 12 mm, the wat~ wlli not form droplets at all, but its level will ~uietly rise until water runs through the opening and passes the restrictor which does not then represent a block to water in-trusion. And if the cable goes more or less vertically, water will pass the restrictors even more easily.

For the earlier known res~rictor to work satisfactorily, it is therefore necessary that there is a positive oil flow out of the restrictor. This flow must be so fast that it developes 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 ~o be provided from a pumping plant or from a pressure reservoir, and a large amount of oil must be stored to prevent water in~rusion during recovery and repair7 It is also known to arrange tubular members around a cable at intervals to limit the migration of water along the oil ducts, ref. UK pat. No. 1 435 592 (which corresponds to Norwegian pat. No. 136.866).
The solution proposed in this patent 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 mentioned patent. And a smoothly inclined sea bed will put a whole series of such tubular members out of use.
It shou~d 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 entare~ a cable equipped with such tubular members and has migrated down to the nearest tubular member, will pass freely further down the cable core. ~he tubu-lar members will certainly not represent a bar to further water intrusion when the cable goes ver~ically.
The object of the present invention is to obtain a method and a device (below called a deflector) which presents a hin~
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 it ~ f.
A further object is to provide a method and a device which each is independent of the inclination and irregularities on the sea bed.
A further object is to provide a method and a means which 985~
will continue to work during cable recovery operations when the cable axis is tilted.
The invention provides an elec-tric cable having a conductor and a duct for the flow of an insulating fluid, a flow path direction deflector in said duct for guiding fluid through said deflector and changing its height level a-t least twice and in alternating directions.
To give a clearer and more unambiguous understanding of the present invention, reference is made to the detailed description below of different embodiments and to the accompany-ing drawings, in which:
- Figure 1 shows the principle of the invention in a simple two plane water trap according to the present inven-tion - 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 plpe-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 i-tself 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 illustrated in Figure

2.
- Figure 6 shows cross section of a differen-t version of a helical water trap.
- Figure 7 shows a labyrinth version of a curved, rnulti plane deflector.

;'~

- Yigure 8 shows a streamlined type of a helieal defleetor yielding low resistance against the flow.

- Figure 9 shows a speeial version of a labyrinth embodiment having omnidirectional effect.

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

- Figure 11 shows some arrangements in a multiconductor cable, and .~ ~a - Fig. 12 shows a module deflectox where each single module substantially gives a flow path deflection in one plane.
The idea is to introduce a defl ction 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 to pass through ~he deflector without changing height level twice, each time in opposite directions.
In the Figures 1 - 4 some principles of deflec~ors, all acting as water-traps in more than one conduit position, are shown.
In Figure 1 a, ~, and c a simple two-plane water trap is shown from three different points of view. Fig. la shows the deflector in a front view, lb from above and lc is the deflector seen from its end face.
~ere 1 represents the conduit, 2 and 3 the water trap bends in two perpendicular planes, 4 is a rupture in the conduit, 5 is oil (or a different fluid) in the conduit, 6 is intruded water (or other fluid from the environments).
If a conduit having such a design is arranged on the sea bed, one of the bent portions t2 or 3) will tend to point up-wards. And the upwardly dir~cted portion will act as a watertrap while the other bend may be neglected. If therefore the bent portion 2 is stretching upwards as shown, i~truded 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 S exc~eds 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 poxtion 2 (or 3) is balanced, water shall pass the barrier and enter the left portion of the conduit. The internal pressure therefore should be maintained and controlled so that it never ~19~B53 will fall below the external pressure.
The efficiency of this water trap is maximum when the two dotted lines 10, ll have ~he same inclination, but in opposite directions~ If the conduit is til~ed so much that one of ~he dotted lines becomes horizontal, or the two lines both are in-clined in 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 Fiy. 1 is a simple representation of the mentioned invention. The deflector according to this design will have a m~;rllm water trap effect for two distinctly differ-ent angular orientations of the deflector, namely when the bend 2 or the bend 3 points direct upwards.
In Fig. ld still a different embodiment is shown. Small discs 12, 13, 14, 15 which partly fill-up ~he 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 Fig. 2. Here Fig. 2a is an end view while Fig. 2b shows a side view. Here the conduit is arranged ln a helical shape except for the end portions (9, lO) 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 shall not exhibit two distinct maxLma, but will have the same value no matter in which angular position the helix is turned around its own axis.
This type of a "water trap" therefore will 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.
We now understand 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 l in Fig. 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 seth for~h by the oil chlnnPl . ..

dimensions. Several parallel paths may be used inskead of one single path.
We now understand that such a design, when exposed to water intrusion, will repxesent an effective barrier for further water intrusion when the pressures are equalized. It is in such cir-cumstances not necessary to have any flow of the fluid at all.
Therefore, no pollution will occur.
However, both the Fig. 1 and the Fig. 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 different direction than shown on the figures, the water trap effect will be jeopardized. There-fore, if a deflector according to Fig. 1 ox Fig. ~ 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 soon as the right side portion of the deflector is raised above the mentioned inclination. With such solutions the oil pressure or fluid flow has to be increased considerably during a r~covery operation, as a positive oil flow is required to prevent further water ingress. However, thls solution also is within the scope of the pres,ent invention, as an oil flow only is required during the re'latively short lasting recovery procedure.
To ensure that the water l:rap effec~ shall be maintained even during a tilting process from horizontal to vertical and finally back to horizontal position again, it is required that the bent portion must include a turn of at least 270. This because a static water trap should make a 180 turn, and the horiæontal-vertical-horizontal tilting process represents an additional 90 angle.
In Fig. 3 is shown a solution which includes a 360 turn of the conduit and therefore ef~ectively protects against water intrusion even during a tiltiny process (e.g. during recovery) of more than 90. 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 o the present invention. However, a two plane deflector may easily be obtained also here as shown in Fig. 3a (from front), 3b (from above) and Fig. 3c from one side.
It i5 also possible, in a relatively simpla 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 Fig. 4 embodLment 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 omnidirectional water trap.
If such water traps shall be designed as restrictive in-sertions 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 ch~nnel with the shown shape. This moulded (or otherwise manufactured) inser~ion then may have outer dimensions adapted to the inner dimensions of the conduit itself.
Such a solution is shown as a transparent body in Fig. 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 as that of Fig. 4 needs no supportiny structure at all. In many cases the conduit is~
however, so stiff that the knot must be rather open and therefore preferably may be supp~rted by external means.
The principles shown in Figs 1-4 may be realized in various embodiments, some preferred versions are shown in Figs 5-13, but a number of related solutions may be used according to the prin-ciples sho~n above. The only essential feature is that there shall 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 Fig. 5 the deflector is thought to be shaped as an in-sertion to be arranged at intervals in a circular oil duct. The insertable deflector 20 may consist o metal, a synthetic material as plastics, xubber or the like. The shape is simply a sub~
stantially cylincrical body with halical recesses 21, 22, 23 in its outer surface. The length L o~ the body 20 and the pitch o the helical grooves 21, 22, and 23 may be determined in depend-ence of each other 50 that more than one turn of each helical recess is obtained. A value of approximately 1,5 turn is pre-ferred or, in other words, L ~ 1,5 x length o 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 in~ertion.
The depth of ~he grooves 21, 22, 23 together with the length of lay o~ the helixes, decides allowed ~x;~llm inclination with-out nullifying the water trap effect of said insertion. This is already explained in connection with Figs 1 and 2. (Re 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 1 Sample II Sample III
Number of 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 d Equivalent diameter (mm) eq per recess 9,5 7,1 9,1 1 Flow resistance corresponds to k additi~nal channel length (m) 6,0 19,1 7,4 From this test it is e.g. found that one 112 mm long and 30 mm 0 insertion ha~ing 3 recesses, each of an equivalent dia-meter 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 0), where u d de~ -V~-d and lk = e-2~- L

The flow resi~tance added by each such insertion may be critical as the flow resistance in the total channel must lie within certain limlts.
If the inller surface of the conduit is not quite smooth, an embodiment according to Fig. 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 radial as in peripherial direction. With such a modifi-cation using a relatively small radial extension or depth of each opening, the ef~ective water tape ~alue may be somewhat increased, again as indicated by the dotted lines 10-11 in Fig. 1 and Fig. 27 By embodiments according to Figs 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 expl~1ne~ above. If, however, end by-passes are arranged e.g.
from ch~nnel 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 loop~ an omnidirectional water trap effect is easi.ly obtained also with this design.
A different solution is indicated in Fig. 7. This version may be named the labyrinth embodiment. Here the fluid flow is guided through a spatial labyrinth as shown. In Fig. 7 there is shown a quite simple embodiment comprising three labyrinth com-part~ents with partitions provide!d with openings 24, 25, 26, and 27 as indicated. The 10w 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 ~mn;~;rectional water trap effect is obtained.
The solution shown in Fig. 8 i5 in principle similar to Fig. 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 number of the protruding 3D 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 10w conditions. Preferably the lay direction of the fins should be the same as that of the inner layer of the conductor (if a twisted conductor is used)D And the lay o 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, B~

light, but stiff tape section, bsing longitu~;n~lly twisted and inserted in the channel. The thickness of such a tape will de-termine the minimllm height and level changes undertaken by the flow lines. The tape will then, in each cross section, be arranged along a diameter o the channel. And the tape is just as broad as the channel diameter~ Of course a polygonial shape on the twisted, inserted element is also possible, as narrow channels then will be obtainea be~ween the side faces of the polygon and the ch~nn~l wall. Or the channels may be obtained between a circular cylindrical insertion and the channel wall if the latter is helically corrugated.
Fig. 9 shows a still more complex embodiment, this also of the labyrinth type discussed above. Here, however, if only one fin is used, a s~mll~r flow path is obt~1ne~ as that of Fig. 4.
Let us assume ~hat 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 lowex side of said tube the flow passes outwards through tube wall openings as shown by the arrows 37, and via a manifold chc~mber 43 (or possibly separate ch~nhers if several fins are usecl) enters parallel helical path-way(s) 38 (only one shown) enveloping the central cylinder back to the upper face 39. This upper 1ange face is closed and the flow is forced to turn again, this time as shown by the arrows 40, to another semicylindrical tube 41, complementary arranged with the first one 36, and then the flow passes axially to the lower outlet 42. ~his spatial labyrinth is arranged within the oil duct of the cable and represents an omnidirectional water trap. The outer surface 44 may ~e a tight, cylindric walll but this may also be omitted, as the inner surface of the flow channel or fluid conduit will act as such a tight cylinder it-sel. The total cross sections of all the helixes 38 may equal the cross sectional area of each of the semicylinders 35, 42.
Then the cross sectional area of the flow will be approx. 1/3 of the total conduit cross se~tion.
In Fig. 10 ii shown in unfolded representation a modified embodiment of the labyrlnth or the protrudlng fin type. Here the wall of the tube or channel itself is used as part of the laby-rinth wall or the outer envelope of same~ The configuration of the partitions may also here be rather reely arranged, and whereas in Fig. 8 a helical arrangement is proposed, there is in Fig. 10 suggested a more complex arrangement giving an omni-directional water trap effect. The length dim~nsions of sections A and B may be chosen rather freely, but they preferably should at least equal the channel diameter.
If the principle o this invention is to be used in a con-ventional (3-phase) three co~ductor oil impregnated cable, some different embodiments are sho~ in FigO 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 ch~nnel 5 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 ~mher~ all the oil transport along these cable portions has to take place in the helical, identical peripher channels, and in this simple manner a similar efect as in the Fig. 2 version is ob~A; nefl, only that three parallel helical passageways are used.
To improve the water trap effect, also the innermost parts of the helical ch~nnel s may be filled. A proper filler design 53 to obtain such an effect is sho~l in Fig. llb. Then the alter-nating ascendingJdescending movemen~s of all flow elements get a larger height variation and therefore the water trap effect will be better and a more inclined laying path may be used. Modifica-tions may be introduced. Thus deflectoxs as earlier mentioned may be built into each of the chAnnels~ or the channels may be partly filled by an adapted filler configuration. Fig. llc is also referred to. In a multiconductor cable the conductors' length of lay will affect the tolerable tilting angle in a similar way as the pitch of the helix does in Fig. 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 in~erted in holes 54, 55, 56 in the filler according to Fig. llc.
If these fillers or stoppers are made of an elastomer, the water trap lnsertions may be metallic to resist swelling forces. Also in these embodim~nts there may be used two spaced apart fillers with a water trap element arranged therebetw~en.

5~3 If the insulation is too dense to allow a sufficient oil flow to and from the centrally arranged duct between the duct closur~ intervals, a minor flux path may be radially axranged ~etween the central duct and one of the peripherial ducts at intervals be~ween the inser~ed fillers. E.g. there may at axial intervals be arranged a minor flow connection between the central duct and one spscific of the peripherial ducts. If these minor radial flux paths are arranged at such intervals that they all are parallel, coplanar, and connec~ed to the same peripherial duct, there is no risk that the central flux path shall represent a pass-by connection for the water from one level to a lower level in same helical duct.
There may be developed different modifications o this invention within a wide variety of designs. Thus the water trap effect may onl~ be present in one plane, in two perpenclicular planes, or in three orthogonally arranged planes~ More than one single throughlet may be adopted. The design shown in Fig. 2 may be obtained by fastening straight tubes between two flanges and then twist the unit, possibly with a centrally arrangecl 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 FigO 4c.
And the threaded ~ins of the torpedo-shaped body of Fig. 8 may also have a 510wly or gxadually variable pitch to reduce the risk of turbulent flow.
In Fig. 12 there is assumed that a deflector according to the present invention may be built up from modules. Each module 57, 58 may 2.g. deflect the flow path in only one plane (or in two planes 591. When the modules are assembled to a working deflector the mutual arrangement ascertains that a multi-directional or omni-di~ectional water trap is obtained. In the Fig. 12 module 58 deflects horizontally, module 57 deflects vertically, and module 59 takes care of vertical deflection and of the tilting efect. Assembled the modules, which each re-presents a plane deflector, therefore make up one combined omni-directional 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 Fig. 9 be obtained if the semi-cylindrical 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 fastented to the cable and laid out together with same.
Other solutions are also applicable within the scope of this invention. E.g. premanufactured deflectors may be installed in the oil duct of a cable during cable manufacturing, or they 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 a lower pressure. Then the not desirable fluid may be tapped out at each deflecting point and guided away through the drainage system. With such a drainage system possible leakages may be controlled and supervised con-tinuously.
The plant preferably should be equipped with a system for establishing pressure equalization or a minor oil overpressure at the rupture place. This, however, is not a part of this in-vention, and therefore it is not further described here.
However, one specific use of the invention should be mentioned to explain that the deflector also is 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 consider-ably.
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 aslo 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 (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electric cable having a conductor and a duct for the flow of an insulating fluid, a flow path direction deflector in said duct for guiding fluid through said deflector and changing its height level at least twice and in alternating directions.

2. An electric cable as recited in claim 1 wherein said deflector comprises a solid generally cylindrical body member having at least one generally helical recess formed in its outer surface.

3. An electric cable as recited in claim 1 wherein said deflector comprises a solid generally cylindrical body member having at least one generally helical passageway formed there-through.

4. An electric cable as recited in claim 1 wherein said deflector comprises a generally cylindrical hollow body member having a plurality of axially extending partitions dividing the interior thereof into a plurality of compartments, some of said partitions being formed with an opening adjacent one end such that the openings in adjacent partitions are at opposite ends of said body member whereby a spatial labyrinth is formed for the flow of fluid.

5. An electric cable as recited in claim 1 wherein said deflector includes a plurality of discs arranged in said duct, each of said discs being formed with an opening such that each opening is at a different height within said duct.

6. An electric cable as recited in claim 1 wherein said deflector comprises a torpedo shaped body member formed with radially extending fins on the outer surface thereof, said fins extending helically along said body member.

7. An electric cable as recited in claim 1 wherein said deflector comprises a generally cylindrical body member formed with a first axially extending internal passage open at one end of said body member and a second axially extending internal passage open at the other end of said body member, a third passageway around said first and second passages, said first passage communicating with said third passageway adjacent said other end of said body member and said second passage communi-cating with said third passageway adjacent said one end of said body member.

8. An electric cable as recited in claim 1 wherein said third passageway is helical.

9. An electric cable as recited in claim 1 wherein said deflector changes 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 of the fluid.

10. An electric cable as recited in claim 1 wherein said deflector changes the flow path such that the projection of the flow path is curved at least about 360° in three orthogonally arranged projection planes.

11. An electric cable as recited in claim 1 wherein said deflector includes at least one helical passage extending through at least 1-1/2 turns.

12. An electric cable as recited in claim 1 wherein said deflector comprises tubes twisted and set in a predetermined manner.

13. An electric cable having a conductor and a duct for the flow of an insulating fluid, said cable having a portion twisted around itself to cause the fluid in said duct to change its height level at least twice and in alternating directions, and a stiff support structure around said portion of said cable.