JPS6337568B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for reducing or stopping fluid leakage into or from a fluid conduit, and to a fluid flow modification device for implementing this method.
However, this invention is limited to conduits filled with a fluid having a pressure approximately equal to the external pressure at least downstream of the point where the leak occurs, but where the specific gravities of the fluid inside and outside the conduit are slightly different. . The present invention relates specifically to apparatus and methods for use in connection with fluid-filled electrical cables, but is not limited to such applications. That is,
The fluid conduit does not necessarily have to be incorporated into the electrical cable, but can be incorporated into different structures and even be of a structure intended primarily for use as a fluid conduit. Electrical cables having an insulation consisting of a spirally applied tape and filled with a low viscosity oil or gas (for example SF ₆ ) so as to penetrate the entire thickness of the tape are known heretofore. The filled fluid is allowed to flow in the axial direction of the cable;
Voids do not form when the cable is subjected to temperature changes that cause fluid expansion or contraction. In the case of a single conductive cable, the fluid conduit is typically located in a recess or channel located along the center of the centrally located conductive wire or along the inner surface of the outer jacket. In contrast, in the case of multi-conductor cables, fluid conduits are usually created by gaps between the conductive wires and between the conductive wires and the outer jacket. When such cables are submerged in the sea and subjected to external mechanical stresses caused by ship drafts or fishing equipment, etc., severe damage occurs, the fill fluid leaks out, and water enters to replace the lost fluid. do. Naturally, the cables are thus damaged and the environment is adversely affected by contamination. In the worst case scenario, the cable will tear completely. At that time, filling fluid flows from both ends of the damaged cable.
For example, oil leaks into the ocean. All cables contaminated with seawater must be replaced. In conventional cable construction, maintaining an overpressure condition within the cable with respect to external water pressure prevents water from entering through the cable until the cable end is repaired. However, such measures increase gas or oil pollution, are expensive, and require large amounts of oil. A blocking restrictor is a system in which oil ducts are inserted into the underwater cable at certain intervals.
A device called a restrictor has been known for a long time. Such a device makes it possible to reduce the amount of contaminated oil during the damage period. Such a restrictor is disclosed in US Pat. No. 3,798,345 (corresponding to Norwegian Patent No. 134,475). Such known restrictors are inserted into the cable at intervals of several hundred meters. The principle behind this restrictor is that the invading water forms droplets whose maximum dimensions are determined by the surface tension between the water and the oil. A small opening in the restrictor is designed to stop water but allow oil to pass through.
The size of the pores is determined by the properties of the oil and water. However, it is clear that this known restrictor does not provide a completely reliable barrier to water ingress when the fluid flow rate is zero, ie when the external and internal pressures are equal at the point of damage. if,
If the cable were submerged in water and the cable path was not level, and the breakage occurred, the water would slowly enter the cable and push out the oil that had filled the lowest part of the cable. The reason for this is, of course,
This is because the specific gravity of water is greater than that of oil (or gas). When the water level reaches the aperture of the restrictor (which has a diameter of 4 to 12 mm in the above-mentioned US patent), the water does not form any droplets and the water level rises quietly until the water flows out of the aperture. This results in a situation where the water flows out and passes through the restrictor, and it no longer becomes an obstacle to water intrusion. If the cable were placed more or less vertically, water would pass through the restrictor more easily. For the above-mentioned known restrictors to work satisfactorily, it is therefore necessary that there is a reliable flow of oil from the restrictor. This flow rate must create a pressure that at least balances the difference in specific gravity 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 less than that of water at the same depth, requiring overpressure to be created by a pumping device or pressure reservoir, and a large amount of oil must be stored to prevent water ingress during recovery repairs. It is also known to space tubular members around the cable to limit the movement of water along the oil duct. This is a British patent no.
See No. 1435592 (corresponding to Norwegian Patent No. 136866). However, this patent only works when the cable system is straight and close to the water. Even small localized irregularities in the ocean floor would invalidate the precautions of this patent. Also, in the case of a smoothly sloping seabed, the entire series of such tubular members cannot be used. As soon as the cable is repaired and the cable end is lifted out of the sea, the water that was in the cable with such tubular members and that had migrated down to the nearest tubular member will further damage the core of the cable. It can be moved freely downwards. The tubular member does not provide protection against further ingress of water when the cable is arranged vertically. It is an object of the present invention to provide a method or device (hereinafter referred to as deflector) which acts as an impediment to water ingress even when the pressure is equal on both sides of the device, i.e. in the absence of flow, and which also works at more than one specific location or direction of a cable or conduit. ). The preferred embodiment aims to provide a deflector structure that has the same water blocking performance regardless of the orientation of the cable itself. Another object is to provide a method and apparatus that work independently of the slope or irregularities of the seabed. Yet another object is to provide a method and apparatus that can maintain operation during a cable recovery operation even if the cable axis is tilted. A preferred embodiment aims to obtain a cable with the above-mentioned advantages without increasing the diameter or without auxiliary measures. These objects and advantages are realized by the method and apparatus of the present invention. In order to facilitate understanding of the present invention, embodiments will be described below with reference to the drawings. 1 to 4 are designed as inserts to be placed in conduits or oil channels. However, it is equally possible to arrange it as a complete conduit itself along a curved path that can be supported on an external support. The idea is to provide a flow path deflection similar to conventional water traps or water seals. In other words, the flow must be guided so that all the particles in it pass through different height levels. More specifically, each particle must rise to a high level and then fall back down to a low level, or vice versa. A particle has no possibility of passing through the deflector without changing height twice each time in the opposite direction. In Figures 1-4, several deflector principles are shown, all of which serve as water traps at one or more locations in a conduit. In Figures 1a, b and c, a simple two-sided water trap is illustrated from three different points. In FIG. 1, a is a front view of the deflector, b is a top view, and c is an end view. 1 is a conduit, 2 and 3 are water trap bends in two vertical planes, 4 is a crack in the conduit, 5 is oil (or other fluid) in the conduit, 6 is intruded water (or other fluid from the outside world) fluid). When a conduit with such a structure is placed on the seabed, one of the bends 2 or 3 tends to point upwards. The upwardly oriented part acts as a water trap, while the other curved part is attractive. Therefore, if the curved part 2 extends upward as shown in the figure,
The invading water 6 moves until its surface reaches the level 7 shown. If the pressure of the now invading water is equal to the pressure of the internal fluid 5, the invading fluid is effectively stopped at this point. If the pressure of the internal fluid 5 exceeds the pressure of the intruding fluid 6, some internal fluid will flow out of the rupture point, but the intruding fluid will not exceed level 7 in the figure. The left-hand part of the conduit 1 is effectively protected against water ingress. Water can only overcome the barrier and enter the left-hand part of the conduit when the pressure of the internal fluid 5 is lower than the pressure of the invading fluid such that the height of the bend 2 (or 3) is balanced.
Therefore, the internal pressure must be maintained and controlled so that it never falls below the external pressure. The efficiency of this water trap is determined by the two slopes 10, 1
1 is maximum when the slope is the same in the opposite direction. If the conduit is tilted so that one dotted line is horizontal or both lines slope in the same direction, no water trapping effect will be obtained. (The dashed lines represent actual streamlines that are close to straight lines.) The embodiment of FIG. 1 shows a simple embodiment of the invention. The deflector in this structure is such that when the deflector is in an angular position that can be distinguished from the two edges,
In other words, the trapping efficiency is maximum when the curved portion 2 or 3 faces upward. Figure 1d shows another embodiment. A water disc is inserted which partially fills the cross section of the conduit. The angular position of each disk is illustrated. The disk imparts vertical and horizontal movement to the flow within the conduit. FIG. 2 shows a different solution. In the figure, a is an end view, and b is a side view. The conduit is arranged helically, only its ends 9, 10 being guided somewhat towards the helical axis. The trap effect does not have two distinct maximum values, but has the same value no matter what angular position the helix is in around its own axis. Therefore, this type of "water trap" can operate as a water trap even in the absence of a pressure difference. The only thing required is the dotted line 10,
11, that the helix must be substantially horizontal. At this point, the following will be understood. That is, even if the entire fluid conduit or cable is biased, or if a deflector is inserted into the fluid flow path such that only that flow path is biased within a small cross section of the fluid flow channel itself. A similar "water trap" effect can be obtained. Therefore, the oil flow path 1 in FIG. 1 can be the entire installed cable or pipe. However, the flow path 2 can be a small part of the oil duct itself, the upper/lower, left/right bends being taken within the limits dictated by the dimensions of the oil channel. Several dry tracks can be used instead of a single track. It can thus be seen that such a device, upon subsequent ingress, provides an effective barrier against further ingress of water at pressure equilibrium. In such a situation, no flow of fluid is necessary and therefore no contamination occurs. However, the embodiments of FIGS. 1 and 2 suffer from inherent disadvantages. If one of the deflectors is lifted and the dotted lines 10, 11 assume a horizontal or different slope than shown, the water trapping effect will be impaired. Therefore, when the deflector of FIG. 1 or FIG. It passes through a deflector at the moment it ascends. With such a solution, the oil pressure or fluid flow must be increased significantly during repeated operations since a positive oil flow is required to prevent further water ingress. It should be noted that this solution is within the scope of the invention since oil flow is only required during the recovery step, which is of relatively short duration. To maintain the water trapping effect even during horizontal to vertical and back to vertical tilting steps, the bend must include a bend of at least 270°.
This is because the static water trap creates a 180° bend and the horizontal-vertical-horizontal tilt step represents an additional 90°. Figure 3 has a 360° bend in the conduit, therefore
A solution is presented which makes it possible to effectively protect against water intrusion even during tilting processes (e.g. recovery) of more than 90°. If a one-plane water trap effect is sufficient, only one bend 16 (or 17) is needed.
Accordingly, conduits having only one such bend are also within the scope of the present invention. However, Figure 3 a (from the front), b (from the top) and c (from one side)
A two-plane deflector can be easily obtained as shown in FIG. It is also possible to obtain an omnidirectional water trap effect with a relatively simple arrangement, ie, a water trap that operates whatever its spatial or angular position. The embodiment of FIG. 4 shows a tied pipe or conduit. No matter which way you look at that simple knot,
Can undergo 360° bending. The simple knot-shaped conduit thus becomes an effective omnidirectional water trap. If such a water trap is intended as a limited insert placed in a fluid conduit, a small pipe section arranged as shown, for example, may be inserted only in at least one channel of the shape shown. It can be formed into an open solid body.
This shaped (or otherwise fabricated) insert has an outer shape that matches the inner diameter of the conduit itself. Such a solution is shown in the transparent body of FIG. 4c. As another option, an external, stiffened structure can be used to maintain the desired shape of the entire conduit. However, if the conduit is sufficiently flexible and pressure resistant, the configuration of FIG. 4 alone does not require any support structure. However, since in many cases the conduit is not very rigid, the knot should be somewhat open and therefore preferably supported by external means. The principles shown in Figs. 1 to 4 are realized by various embodiments, and various preferred ones are shown in Figs.
Shown in Figure 3. However, a number of related solutions can be used according to the above principles. The only essential feature is that there is a device for biasing the passing flow in different alternating directions. For example, a helically twisted length of tape, the width of which corresponds to the channel diameter, will in some cases achieve sufficient deflection. In FIG. 5, the deflector is considered to be formed as a spaced apart insert within the circular oil duct. Insertable deflector 20 may be made of metal, synthetic material such as plastic, rubber, or the like. Its shape is simply that of a substantially cylindrical body with helical recesses 21, 22, 23 on its outer surface. Length L of main body 20 and spiral grooves 21, 22
The pitches of and 23 are mutually determined so that each helical recess makes one or more turns. A value of about 1.5 turns is preferable; in other words, L should be at the pitch of the groove.
It is multiplied by 1.5. The grooves or recesses 21, 22, 23 are open towards the periphery so that the insert is placed within a smooth-walled conduit that conforms to the contour of the insert. The depth of the grooves 21, 22, 23, together with the length of the helical pitch, determines the maximum permissible slope without losing the water trapping effect of the insert. This is the first
2 has already been explained. (See the slope of dashed lines 10 and 11.) The results of tests performed on different dimensions of the insert in this example are shown in the table below.

[Table] From this test, 112 has three recesses with an equivalent diameter of 7.1 mm and a pitch (pitch turn length) of 75 mm.
An insert of mm length and 30 mm φ presents an additional flow resistance corresponding to a 19.1 m long conduit (30 mm φ).
Here The flow resistance added by each such insert can be critical since the flow resistance in the entire channel must be kept within certain limits. If the inner surface of the conduit is not very smooth, the embodiment of FIG. 6 is preferred. Here, the helical opening along the insert is not open to the surface.
A sealing comparand or gasket facilitates sealing between the insert and the inner surface of the conduit. The helical openings 21', 22', 23' have a circular cross-section or, as shown, a shape which does not extend much in the radial direction as well as the circumferential direction. In such a variant, used with apertures of relatively small radial extent or depth, the effective water trap value increases somewhat, as again indicated by dotted lines 5 or 6 in FIGS. With the embodiment of FIG. 5 or 6, a water trapping effect is obtained at all angular positions, but if the slope increases, the water trapping effect decreases and is eventually lost as described above. However, if an end bypass is placed from channels 21-22 on the left end of the insert and from channels 22-23 on the right end, backflow movement of the fluid is also obtained.
The course of the fluid at this time is the left end 23, the right end 23,
It returns to the left end 22 and goes in the order of the right end channel 21 (or vice versa). such external (or internal)
Omnidirectional water trapping effects can be obtained even with this structure due to the feedback creep of the arrangement. A different solution is shown in FIG. This modification may also be referred to as a maze embodiment. Here, the fluid flow is guided through a spatial labyrinth as shown in the figure. In FIG. 7 a very simple embodiment is shown having three labyrinth chambers with openings 24, 25, 26 and 27 in their partitions. The flow is guided through these openings one after another, the flow being biased in different directions. In this way, the flow changes direction many times, creating an omnidirectional water trapping effect. The solution shown in FIG. 8 is similar in principle to those shown in FIGS. 2 and 5 because the flow paths are similar. The insertion deflector has a centrally located compact body 30 with projecting fins 31, 32, 33, 34. The number of protruding fins is not essential and can be selected depending on the actual structure. The fins are in a helical arrangement as shown, and the pitch of the helix varies slowly along the deflector to ensure uniform laminar flow conditions. Preferably, the direction of twist of the fins is the same as that of the inner layer of the conductor (if twisted conductors are used). The twist of the fins can be the same as that of the inner layer at the beginning and end. The centrally located compact body has a torpedo shape as shown, which reduces flow resistance and allows for some slope. A particular solution based on this principle is a single, light but rigid tape section twisted longitudinally but inserted into the channel. The thickness of such tape determines the minimum thickness and level change taken by the streamlines. The tape is then placed along the diameter of the channel in each of its cross sections. The tape is as wide as the channel diameter and the apex. Of course, polygonal shapes on twisted inserted elements are also possible. This is because a narrow channel is obtained between the sides of the polygon and the channel wall.
Otherwise, a channel is obtained between the circular cylindrical insert and the channel wall, if the channel wall is helically corrugated. FIG. 9 shows a rather complex embodiment, which is labyrinthine as described above. However, even if only one fin is used, the same effect as in FIG. 4 can be obtained. Assume that the entrance is at the top. The flow enters the inlet opening 35 and passes axially through the semi-cylindrical tube 36. From the bottom of this tube the flow flows outwardly through the tube wall openings as indicated by arrow 37 and then through the manifold chamber 43 (and possibly another chamber if several fins are provided) to the upper surface 39. and then back to the parallel spiral passage(s) 38 surrounding the central cylinder. This upper flange surface is closed;
The flow is re-energized into another semi-circular tube 41 arranged complementary to the first one 36, now redirecting as shown by arrow 40. This spatial maze is placed in the oil duct of the cable and forms an omnidirectional water trap. The outer surface 44 can be a rigid cylindrical wall, but can also be omitted since the inner surface of the flow channel or fluid conduit also behaves as a rigid cylinder itself. The total cross-sectional area of the helix 38 can be equal to the cross-section of each of the semi-cylinders 35, 42. At that time, the cross-sectional area of the flow is approximately 1/3 of the total cross-sectional area of the conduit.
becomes. FIG. 10 shows a labyrinth or protruding fin type variant in its unfolded state. The walls of the tube or channel are themselves used as part of the labyrinth or its outer envelope. The placement of the partitions can be somewhat flexible here as well. On the other hand, FIG. 8 recommends a helical arrangement, while FIG. 10 proposes a more complex arrangement that provides an omnidirectional water trapping effect. The length dimensions of sections A and B can be chosen somewhat freely, but should preferably be at least equal to the channel diameter. Several different embodiments of the application of the principles of the invention to a conventional (three-phase) three-conductor oil-filled cable are shown in FIG. Here 45,
46 and 47 indicate three circular insulated conductors embedded in an impermeable covering 48. The insulated electrical conductors are typically arranged in a spiral. The four helical channels are thus effective as axial oleodites within the cable jacket. three outer ducts 52
is smaller and has a straight axis but is twisted in a spiral. If the central duct 52 is locally closed at intervals by fitted members, the oil transmission along the three cable sections will occur in a helical manner as in the peripheral channel, as shown in FIG. An effect similar to that shown in FIG. 2 can be easily obtained by simply using three parallel spiral passages. The innermost part of the helical channel can also be filled to increase the water trapping effect. A suitable filter structure 53 for achieving such an effect is shown in FIG. 11b. The alternating up-valve downward movement of all flow elements obtains large height oscillations, so the water trapping effect is better and a more sloping placement path can be used. This can be modified.
That is, the previously mentioned deflectors can be integrated into each channel, or the channels can also be partially filled by an adapted filter arrangement. In multiconductor cables, the pitch of the wires affects the angle of inclination that can be tolerated in the same way that the pitch of the helix does in FIG. The pitch of the wires can thus be reduced locally or along the entire cable. Deflectors of any of the solutions shown above can be inserted into the holes 54, 55, 56 in the filter of FIG. 11c. If these filters or stops are made of elastic material, the water trap insert can be metallic and resist swelling forces. Also, using two separate filters in these examples,
A water trap member can be placed between these. When the insulation is too densely packed to allow sufficient oil flow to and from the centrally located duct between the duct closure intervals, one of the surrounding ducts may A secondary flux passage can be arranged radially therebetween. For example, secondary flow connections can be arranged at axially spaced intervals between the central duct and a particular one of the peripheral ducts. By arranging such secondary radial flux passages with such spacing that they are parallel, coplanar, and in the same peripheral duct, the central flux passages can be separated from one level in the same helical duct. You can prevent the risk of having to bypass connection for water to lower levels. There are advanced variations of the invention within a wide variety of this structure. Therefore, the water trap effect exists only in one plane, two orthogonal planes, or three orthogonal arranged planes. More than one throughlet can be employed. The structure shown in Figure 2 can be obtained by fixing a straight tube between two flanges and then twisting them together, in this case perhaps to avoid internal rings within the tube as they are twisted into a helix. A spacer is placed in the center. The material can be made of an electrical conductor, such as a metal, or an insulator, such as a plastic. To reduce flow resistance, each opening has a streamlined outlet and inlet as shown in Figure 4c. The threaded fins of the torpedo-shaped book of FIG. 8 can have a slowly varying pitch to reduce the risk of turbulence. In FIG. 12, the deflector of the present invention can be assembled from modules. Each module 57, 58 can, for example, change the flow path in only one plane (or two planes 59). When the modules are assembled into a working deflector, their mutual arrangement provides a multidirectional or omnidirectional water trap. In Figure 12, module 58 is biased horizontally, module 57 is biased vertically, and module 59 sees vertical bias and tilt effects. Assembling the modules, each of which is a planar deflector, creates one combined omnidirectional deflector. With regard to the flow area, it is advantageous if the flow channel cross section is constant throughout the deflector. This is obtained, for example, in the embodiment of FIG. 9 when the semi-cylindrical channel has a cross section equal to the sum of the parallel spiral channels. Additionally, the entire cable can be bent and secured to an external clamping device to maintain its shape. This outer equipment can be placed under the cable on the seabed prior to installation, or it can be fixed to and laid out with the cable. Other solutions are applicable within the scope of the invention. For example, a pre-manufactured deflector is installed inside the cable oil duct during cable manufacturing.
It can be joined to the cable at each regular cable joint. In larger plants, it may be possible to enclose the conduit or cable at least at the point of excursion in a drainage pipe system, which is likely to be maintained at low pressure. The unwanted fluid can then be diverted at the point of excursion and removed via the drainage system. Such a drainage system provides continuous control management of leaks. The plant should preferably be equipped with a system to achieve pressure equilibrium or a slight overpressure of the oil at the point of rupture. This, however, is not part of the invention and therefore will not be described further. However, referring to one particular use of the invention, the deflector is also useful in high pressure plants. If the deflector of the present invention is inserted at intervals into a high-pressure subsea oil pipe, the amount of leakage oil due to tube rupture can be significantly reduced. If the oil supply flow is stopped at the moment of discovery of the break, any oil that remains in the tube beyond the deflector will be retained there. Therefore, contamination and oil losses are reduced and, considering elastic cables, cable damage is also reduced since water ingress is also completely avoided between the deflectors.

[Brief explanation of the drawing]

FIG. 1 shows the principle of a simple two-sided water trap according to the invention. FIG. 2 shows an embodiment that works in all angular directions of the conduit, and FIG. 3 shows an arrangement that is effective even when tilted. FIG. 4 shows an omnidirectional water trap member as a pipe knot, FIG. 5 shows a practical water trap working on the same principle as FIG. 2, and FIG. 6 shows cross-sectional views of different embodiments of a spiral water trap.
FIG. 7 is a curved, multiplanar deflector maze structure; FIG. 8 is a streamlined helical deflector that produces low resistance to flow; FIG. 9 is a specific embodiment of a labyrinth structure with an omnidirectional effect; FIG. The figure shows a specific omnidirectional shape of a torpedo shape shown in the unfolded state, Figure 11 shows the arrangement in a multi-conductor, and Figure 12 shows a standardized deflector in which the individual modules impart a flow path deflection in one plane. . 2, 3... Bend part of conduit, 4... Rupture part, 5... Oil, 6... Water, 12, 13, 14, 15... Disk, 21, 22, 23... Spiral recess, 21', 2
2', 23'...Spiral opening, 24, 25, 26, 2
7...Opening, 31, 32, 33, 34...Fin.

Claims (1)

[Scope of Claims] 1. Reduction of fluid leakage into or from oil or gas pipes or oil or gas ducts in composite structures such as electric wires by means of local flow actuators that locally change the properties of the fluid flow path. or stopping method, each flow actuator comprises a deflector for regulating or guiding the flow path to change as the fluid passes; the deflector controls the flow direction of the fluid, and Fluid leakage reduction characterized in that the height level of all particles is varied in at least two different orientations of the fluid conduit (different angular or different axial orientations) and preferably in all spatial orientations. Or how to stop it. 2 The flow path deflector has a projection of the flow path of at least
2. A method according to claim 1, characterized in that the flow path is deflected so as to curve through 180°, preferably 360°, in at least one projection plane, preferably three orthogonal projection planes. 3. A device for reducing or stopping the leakage of fluid into or from a fluid conduit, comprising a flow direction deflector configured as a multi-curved water trap, the deflector being one or more curved water traps disposed within a solid body. Further openings or holes 21', 22', 23'
and/or one or more curved points 21, 22, 23 arranged on the surface of the solid body 20, characterized in that it has a maximum water trapping effect in at least two channel orientations. Directional deflector device. 4. The deflector has a torpedo-shaped body centered within the fluid conduit, the body being secured to the conduit by outwardly projecting fins preferably arranged in a regular pattern. Device. 5 The flow path deflector is disk 12, 13, 1
4, 15, 18, 19 and/or holes 24, 25, 26, 2 for guiding fluid flow in different spatial directions.
3. The device of claim 3, comprising a partition with 7. 6. Device according to claim 3, in which the fluid conduit is itself located in a predetermined curvature and is preferably guided by a rigid external structure. 7. The channel preferably consists of at least one cylindrical helix with at least 11/2 turns, the inlet/outlet to this helix being arranged axially through the helix, preferably in a "knot" configuration. Claims 3 and 5 that intersect with each other
or the apparatus of paragraph 6. 8. The deflector comprises one or several pipes or tubes, which are bent or twisted in a predetermined manner, and the pipes are cast in such a way that they form throughlets in the solid body. Apparatus according to paragraph 3 or paragraph 7. 9 used in multi-conductor cables in which there is a flow of insulating fluid between the conductors and/or between the conductors and the external covering, where at least the central duct 52 of the conductor is locally or continuously filled with blocking material 53, while the conductor 9. A device according to any one of claims 3 to 8, wherein all or some of the peripheral ducts between the duct and the outer covering are at least partially open and constitute biased flow paths. 10. The device of claim 9, wherein the flow path deflector is arranged sealingly in at least one peripheral duct 54, 55, 56. 11. The device of any one of claims 3 to 9, wherein the biased fluid passageway is made of or reinforced with a rigid support structure and maintains its shape substantially unundulating under normal handling or operating stresses. .