TUBE SYSTEM FOR TRANSPORT OF FLUIDS THERMALLY ISOLATED FROM THE AMBIENT

Abstract: The invention relates to a tube system for transporting fluids thermally insulated from the ambient, comprising: an inner casing (12) adapted to guide fluids, an insulating layer (3) arranged therearound, and an outer casing imparting strength to the tube system, wherein the inner casing is connected to the outer casing (4) at least for transferring longitudinal forces. The inner casing, which will of course fluctuate in temperature of the fluid flowing through the tube, will thus generate only small forces in longitudinal direction due to its small thickness. According to a preferred embodiment the insulating layer is fixed to the inner casing and the outer casing such that longitudinal forces exerted by the inner casing are transferred by the insulating layer to the outer casing.

Description: TUBE SYSTEM FOR TRANSPORT OF FLUIDS THERMALLY ISOLATED FROM THE AMBIENT The present invention relates to a tube for trans¬ porting fluids thermally insulated from the ambient, comprising an inner casing adapted to guide fluids, an insulating layer arranged therearound and a casing im- parting strength to the tube. Such tubes are generally known, for instance in the form of tubes which are applied in for instance district heating. In these prior art tubes the inner casing has a relatively great thickness; the inner casing is dimen¬ sioned to contain the fluids for transporting, to absorb the pressure at which the fluid is transported, to absorb mechanical loads during fitting of the tube and to absorb mechanical loads while the tube is in place, which mechanical loads are largely generated by the thermal stresses generated as a result of the heat of the fluid for transporting. It is also possible that mechanical forces are exerted on the inner casing by the ambient, for instance the soil in which the tube is placed. In short, the inner casing is adapted to impart strength to the tube. The function of the insulating layer requires no further explanation in this case. Further arranged is a relatively thin outer casing which is usually manu- factured from plastic and which only serves to seal the insulating layer from influences from the environment. These prior art tubes result in a number of draw¬ backs, wherein one of the most important is the fact that as a result of changes in the temperature of the trans- ported fluid the inner casing is exposed to mechanical stresses of thermal origin. These stresses cause ex¬ pansion or shrinkage in different directions, wherein the radial direction does not generally represent a problem because this can be absorbed by the insulating layer. However, expansion and shrinkage in the longitudinal direction do often result in undesirably high stresses in the outer casing, for which purpose special compensation devices must be arranged, for instance in the form of U- or Z-shaped bulges. At the position of the bulges foam cushions must enable the expansion and shrinkage over a determined length without the outer casing having to cope with excessive stresses. The compensation devices require much space, increase the construction time and are ex¬ pensive. Another drawback of the stresses generated by the thermal variations lies in the fact that when such pipes are laid a pre-heating process must be applied to provide the internal tube with a pre-stress prior to fixing of the pipes, for instance by closing the trench in which the pipes are laid. This pre-stress is usually provided by the internal tube. Fixing can take place thereafter and the work can be finished. It will be apparent that this results in great problems during laying; provisions must be arranged to temporarily heat the pipe to the mounting temperature, which provisions are not in¬ considerable. The normal process of burying district heating pipes is also greatly delayed herein. Another drawback of the prior art tubes which can also be mentioned is the limitation of the diameter. The internal diameter usually amounts to a maximum of 800 mm. The object of the present invention is to provide a tube wherein the above stated drawbacks are avoided. From DE-C-40 16 048 is known a tube system for transport of fluids thermally insulated from the ambient comprising: an inner casing adapted to guide fluids, an insulating layer arranged therearound and an outer casing imparting strength to the tube system. This however relates to a tube system which is only suitable for laboratory applications. The object of the invention is to provide such a tube system which is suitable for transport over long distances without much flow loss. This object is achieved by such a tube system, wherein the inner casing is connected to the outer casing at least for transferring longitudinal forces. As a result of these steps a long continuous inner casing can be used because the longitudinal mechanical stresses generated in the inner casing by temperature gradients can be transferred to the outer casing. Forces in the longitudinal direction are however much smaller in magnitude as a result of the relatively small thickness. They can therefore be absorbed easily without making special provisions. According to a preferred embodiment the insulating layer is fixed to the inner casing and the outer casing such that longitudinal forces exerted by the inner casing are transferred by the insulating layer to the outer casing. This means that possible forces in the inner casing will not result in expansion, or hardly so they are transferred to the outer casing which on account of its thickness is more than sufficiently large enough to absorb these forces and consequently only has to absorb slight stresses. It is noted here that the outer casing is not or hardly subject to temperature changes relative to the surrounding ground due to its insulated arrangement, which likewise brings about only small stresses. A further advantage of the present invention lies in the fact that the outer casing is the most robust com¬ ponent, so that handling of such tubes takes place more easily than handling of prior art tubes and the danger of pipe fracture due to excavation operations is also significantly lower. Yet another advantage of the invention lies in the fact that a greater freedom of dimensioning results from the wide availability of tubes of different diameter and thickness. The present invention also relates to a sleeve for mutually connecting tube pieces according to the in¬ vention, wherein a particularly attractive form of the outer casing can be obtained by applying internal rings in the sleeve and external rings on the tube pieces. The invention further relates to a method for laying a pipe consisting of pieces of tube according to the invention, wherein the tube pieces are placed in their position in a trench and mutually connected, whereafter the trench is filled without interposing of heating. Other attractive preferred embodiment are designated in the remaining sub-claims. The present invention will now be elucidated with reference to the annexed drawings, in which: figure 1 shows a partly broken away perspective view of a tube according to the invention; figure 2 shows a sectional view of a weld of tubes according to the present invention,- figure 3 is a detailed sectional view of the weld of an inner tube according to a first embodiment; figure 4 is a detailed sectional view of the weld of the inner casing according to a second embodiment; figure 5 shows a sectional view of a transition element between prior art tubes and tubes forming part of the invention according to the first embodiment; figure 6 is a view corresponding with figure 5 of a further embodiment of such a transition piece; and figure 7 shows a partly broken away perspective view of pipes forming part of a district heating system. Shown in figure 1 is a tube piece 1 formed by an inner casing 2 manufactured from a thin material, around which an insulating layer 3 is arranged which is sealed on its outside by an outer casing 4. The inner casing 2 is manufactured from thin plastic, for instance polyetherimide, while it is also possible for inner casing 2 to be manufactured from a metal, for instance steel, stainless steel or aluminium. The insulating layer 3 is manuf tured from known insulating material, for instance PUR foam. When use is made of a plastic inner casing 2, an insulating layer with an increased density, for instance a PUR foam with an increased density, is preferably used to be able to absorb the in this case extra-great internal pressures due to the transport of fluids. The plastic inner casing mainly performs the function of watertight seal. In order to prevent moisture or other material from outside penetrating between tube pieces into the in- sulating layer 3 during welding, collars 5 are arranged with a U-shaped cross section. These also serve during manufacture of the tubes as fixation elements for mutual fixing of inner casing 2 and outer casing 4. These collars 5 can for instance be manufactured from plastic or from the same material as the inner or outer casing. They can be connected to the relevant casings for instance by means of a glue connection. These collars 5 can be adapted to transfer longitudinal forces. It is noted here that in figure 1 the inner casing 2 protrudes in axial sense relative to collar 5 and outer casing 4. The outer casing is optionally provided with a coating to prevent corrosion. After installation of the tube system at its final location, a glass fibre cable is arranged on the top of each tube and/or elsewhere on each tube and is connected to a measuring unit for recording temperatures. Leakages are traced herewith on the one hand and "on-line" recording of heat losses of the tubes is effected on the other. In figure 2 is shown a weld between two such tube pieces according to the invention. Going from inside to outside, which also designates the working sequence, the inner casings 2 are first mutually connected, for in¬ stance as in the present case of metal inner casings 2 , by a weld 6. Thereafter the space between collars 5 and outer casings 4 are filled with an insulating material, for instance mineral wool, an insulating plastic or filling pieces of other insulating material. A sleeve 8 is subsequently placed round the thus manufactured weld. This sleeve is preferably manufactured from steel, wherein it is possible that sleeve 8 cane be divided so that it consists of two halves which are mutually connected for instance by means of hinges, although it is also possible for sleeve 8 to be formed is integrally and be pushed round one of the tubes before the tube pieces are mutually attached. Sleeve 8 is then placed in its position, wherein the space between the sleeve and the relevant parts of outer casing 4 are filled by a curing mass 9. This curing mass 9 can once again be formed by a curing plastic, but can also be formed by for instance concrete. In order to improve the transfer of forces from curing mass 9 to casing 4 a peripherally extending ring 10 is fixed to the outside of each of the casings 4. This ring 10 can be continuous as in the present case but may also be dis¬ continuous and formed for instance by separate pieces. In similar manner the inside of sleeve 8 is provided with corresponding rings 11. Here also the rings 11 serve to increase the transfer of forces. In the shown preferred embodiment the r ^ ngs 11 are placed outward relative to rings 10. This has the advantage that when concrete is used as mass 9 particularly good use is made of the properties of concrete, since in that case the concrete is mainly under strain of pressure between rings 10 and 11. It will be apparent that the above described sleeve construction for connecting tube pieces is not only applicable with tubes according to the invention but is also applicable in the case of tubes provided with a single casing, for instance water pipes or gas pipes. It is of course also possible to make use of sleeves wherein the internal diameter equals that of the outer casing. Figure 3 shows a preferred embodiment of a connection between the internal casing 2 of different tube pieces. One of the internal casings 2 is herein provided with a connecting sleeve 12 of the first embodiment which is fixed thereto, for instance by means of a weld 6, while the inner casing associated with the other tube piece is connected to a connecting sleeve 13 of the second type. Both connecting sleeves 12,13 are formed at their free end such that they fit mutually. They can herein be mutually fixed by for instance a glued seam 35. It is pointed out here that said embodiment can be applied with plastic inner casings as well as metal inner casings . The embodiment shown in figure 4 is however only applicable with plastic inner casings 2. Use is made herein of a sleeve 15 which is provided with a heating wire 14 and which is pushed round the two inner casings 2 for mutual connection and wherein a connection is formed by feeding a current through the heating wire 14, whereby the relevant part of sleeve 15 and a corresponding part of the outside of inner casing 2 melt and a joint is formed. The invention is however most certainly not limited to said forms of mutual connection; it is very well possible to apply other forms of connection, for instance by mechanical connecting means such as clamps, bolts or glues. Shown in figure 5 is a transition piece 16 which is suitable to form a connection between a tube piece according to the present invention 1 with a metal inner tube and a prior art tube piece 17 and for connecting accessories such as valves or manifolds, which initially will certainly be more easily obtainable generally than valves or accessories for the system described in the present application. The prior art tube piece 17 com¬ prises an inner tube 18 of substantial thickness, an insulating layer 19 and an outer tube 20 of substantial thickness. In many situation this outer tube 20 is manufactured from plastic. The transition piece 16 is formed by an inner casing 21 of a first small thickness, which thickness sub¬ stantially corresponds with that of the inner casing 2 and a casing piece 22 welded thereto of greater thickness, for instance a thickness lying between the thickness of inner casing 2 and that of inner casing 18. It is possible to make use of a larger number of intermediate steps. The casing pieces 21,22 are mutually connected by welds 23 and also connected by welds 23 to the relevant inner casings 2 respectively 18. Here also use is made of a separate insulating layer 7 to fill the space between the inner casing and the outer casing, while a separate outer casing 24 is applied which consists for instance of two parts and which is connectable by means of welding, shrinking or glueing to outer casing 2 respectively 20. By gradually increasing the thickness of the inner casing it is possible to absorb in the correct manner the mechanical stresses occurring therein which are caused by temperature. Figure 6 shows an embodiment wherein a flange connection 36 is applied as connection between a tube piece 1 with plastic inner tube 2 according to the invention and a prior art tube piece 17 and for connecting accessories such as valves or manifolds, which initially will certainly be more easily obtainable generally than valves or accessories for the system described in the present application. Use is made for this purpose of a transition piece 25 which comprises a metal inner casing 26, the diameter and thickness of which correspond with those of the prior art tube pie 17 and which is connected thereto by means of a weld 13. The transition piece contains a metal outer casing 27 over a part of its length. Inner casing 26 and outer casing 27 are connected via welds to flange 28. The space between inner casing 26, outer casing 27 and flange 28 is provided with an insulation material 3. The connection between the outer casing 27 of the transition piece according to the invention and the outer casing 20 of the prior art tube piece is effected by means of the outer casing 24 under which is situated an insulating filling piece 7. The inner casing 2 of the tube piece according to the invention is provided with a plastic flange 29, while outer casing 4 is provided with a metal flange 30. Flanges 28,29 and 30 are connectable by means of a bolt connection 31. The embodiment wherein a flange connection is used as connection between a tube part 1 with an aluminium inner tube 2 according to the invention and a prior art tube piece 17 likewise comprises a transition piece 25. The inner casing 2 of the tube piece according to the invention is now provided however with an aluminium flange 29. Between flanges 28,29 and 29,30 are applied gaskets 32 which electrically separate the contact potentials of the materials. This latter embodiment is more particularly suitable for connecting accessories such as valves or manifolds, which initially will certainly be more easily obtainable generally than valves or accessories for the system described in the present application. The embodiment is not however limited thereto. Finally, figure 7 shows a portion of a district heating system which is formed by two tubes 33,34 which are used for feed respectively as return pipe for a fluid, for instance water or steam for a district heating system. It is pointed out here that the pressures applied herein generally lie in the order of magnitude of 10 to 15 bar, so that the inner tube must also be dimensioned for this purpose. In this configuration it is particularly important that in the case of the feed pipe the inner casing is manufactured from metal, for instance steel, since steel has a better resistance to a relatively high temperature than plastic, while for the return pipe 34 plastic can suffice; this results in a cost saving. Another advantage of the present invention lies in the fact that, as a result of the strength-imparting construction being present on the outside, said tube construction can be easily pressed, for instance when making tunnel pressings and borings under roads or under waterways. This results in a considerable cost saving since fewer excavation operations then have to be carried out or pressing or drilling of the casing tubes is no longer necessary. Another advantage lies in the fact that the tube pieces can be placed more easily; welding of the thin inner tube can be performed more easily and rapidly than welding of the thick inner tube which was heretofore customary and which also had to be examined with an X-ray device for checking purposes. The application of modern techniques, for instance glueing and the robust concrete sleeve connection, results in even more attractive embodiments. The option is herewith also formed of mutually connecting a plurality of such tube pieces, which are normally supplied in lengths of about 16 m, before they are placed in position,- it is after all easier to process the tube pieces when they are lying free than when they are placed in a trench and access is usually more difficult. Another advantage lies in the fact that the diameter of the thin inner tube and the insulation thickness can be chosen in optimum manner. It can be envisaged that transport of hot fluids over large distances can best take place in a manner where the diameter and degree of insulation are properly geared to each other. This in contrast to the prior art tubes wherein standardized tube dimensions are used. Another advantage lies in the fact that the glass fibre cable 38 with associated measuring unit forming part of the tube system of the invention enables heat loss measurement in the tube system during operation and also serves as leakage detection. It will be apparent that the invention is not limited to the shown embodiments.

Claims: CLAIMS 1. Tube system for transporting fluids thermally insulated from the ambient, comprising: - an inner casing adapted to guide fluids, - an insulating layer arranged therearound, and - an outer casing imparting strength to the tube system, characterized in that the inner casing is connected to the outer casing at least for transferring longitudinal forces. 2. Tube system as claimed in claim 1, characterized in that the insulating layer is fixed to the inner casing and the outer casing such that longitudinal forces exerted by the inner casing are transferred by the insulating layer to the outer casing. 3. Tube system as claimed in claim 1, characterized in that the longitudinal forces exerted by the inner casing are transferred to the outer casing by means of a wall placed close to one or both tube ends . 4. Tube system as claimed in claim 1, 2 or 3 , where¬ in the tube system is formed from tube pieces, characterized in that the inner casings of the tube pieces of the tube system connect smoothly onto each other. 5. Tube system as claimed in claim 1, 2, 3 or 4, characterized in that the inner casing is manufactured from metal, for instance aluminium or steel. 6. Tube system as claimed in claim 1, 2, 3 or 4, characterized in that the inner casing is manufactured from plastic, for instance polyetherimide. 7. Tube system as claimed in claim 6, characterized in that the wall is manufactured from the same material as the inner and outer casing and is adapted to be connected by means of liquid-tight welds to the inner and outer casing. 8. Tube system as claimed in claim 5, characterized in that the insulating layer is manufactured from reinforced insulation material, for instance PUR foam with an increased density. 9. Method for manufacturing a piece of tube as claimed in any of the foregoing claims, characterized by placing the inner casing and the outer casing concentrically, placing spacing rings between the casings and subsequently arranging the insulating layer. 10. Method as claimed in claim 9, characterized in that the insulating layer is arranged by arranging insulating foam for instance by means of jet sprays. 11. Piece of a tube system as claimed in any of the foregoing claims 1-8, characterized in that the inner casing protrudes further outward in axial direction than the outer casing and the insulating layer. 12. Tube piece as claimed in claim 11, characterized in that the outer casing is provided on its periphery in the vicinity of its ends with at least one ring extending all around. 13. Sleeve for mutually connecting tube pieces as claimed in claim 11, characterized in that the sleeve has an internal diameter corresponding with the internal diameter of the outer casing. 14. Sleeve for mutually connecting tube pieces as claimed in claim 12, characterized in that the sleeve has an internal diameter greater than the external diameter of the at least one ring. 15. Sleeve as claimed in claim 14, characterized in that the sleeve is provided on its inside with at least two rings, the internal diameter of which is greater than the external diameter of the tube pieces and the mutual distance of which is greater than the distance between the rings fixed to two adjacent tube pieces. 16. Sleeve as claimed in claim 13, 14 or 15, characterized in that the sleeve is divisible. 17. Sleeve as claimed in claim 13, 14, 15 or 16, characterized in that the sleeve is manufactured from material with the same coefficient of expansion as the material from which the outer casing is manufactured. 18. Sleeve as claimed in claim 13 or 14, characterized in that the sleeve is adapted to be connected to the outer casing by means of welding. 19. Sleeve as claimed in claim 14, characterized in that the sleeve is adapted to be connected to the outer casing by means of shrinkage. 20. Method for laying pipe consisting of pieces of pieces of tube as claimed in any of the claims 1-8, characterized in that the tube pieces are placed in their position in a trench and mutually connected, whereafter the trench is filled without interposing of thermal or mechanical length increase. 21. Method as claimed in claim 20, characterized in that the tube pieces are mutually connected at least partly in groups and subsequently placed integrally in their position. 22. Method as claimed in claim 20 or 21, characterized in that the pieces of tube are mutually connected by first mutually connecting the inner casing, subsequently adding the insulation and by finally mutually connecting the outer casing of the tube pieces. 23. Method as claimed in claim 22, characterized in that the inner casings are mutually connected by welding or glueing. 24. Method as claimed in claim 22 or 23, characterized in that the outer casing of adjacent pieces of tube are mutually connected by placing a sleeve as claimed in any of the claims 10-12, and filling the space between the sleeve and the tube pieces. 25. Method as claimed in claim 24, characterized in that the space between the sleeve and the tube pieces is filled with a material having substantially the same coefficient of expansion as the outer casing. 26. Method as claimed in claim 24 or 25, characterized in that the outer casing is provided with external rings, the sleeve is provided with internal rings and the space between the sleeve and the tube pieces is filled with concrete. 27. Piping system for a district heating system comprising tubes as claimed in any of the claims 1-9, wherein the heat-transporting pipes each have a metal inner casing and the return pipes have a plastic inner casing. 28. Tube system as claimed in any of the claims 1-8, characterized in that a longitudinally extending thermal sensor is arranged on the outside of the outer casing. 29. Tube system as claimed in claim 28, characterized in that a longitudinally extending moisture sensor is arranged on the outside of the outer casing. 30. Tube system as claimed in claim 28 or 29, characterized in that the sensors are formed by a glass fibre cable. 31. Piping system comprising tubes as claimed in any of the claims 28, 29 or 30, characterized by central reading devices for the sensors.

Inventors: RIKKEN JACOBUS FREDERICUS, VAN SCHAIK MARINUS ADRIANUS WI, RIKKEN, JACOBUS, FREDERICUS, VAN SCHAIK, MARINUS, ADRIANUS, WILHELMUS
Applicants: KEMA NV, RIKKEN JACOBUS FREDERICUS, SCHAIK MARINUS ADRIANUS WILHEL, N.V. KEMA, RIKKEN, JACOBUS, FREDERICUS, VAN SCHAIK, MARINUS, ADRIANUS, WILHELMUS
Application year: 1997
Main classification: F16L59
IPC codes: F16L59