WO1995000797A1

WO1995000797A1 - Insulated pipe

Info

Publication number: WO1995000797A1
Application number: PCT/SE1994/000628
Authority: WO
Inventors: Heimo Zinko; Hans Torstensson; Stefan Swebilius
Original assignee: Fjarrvarmeutveckling Fvu AB
Current assignee: Fjarrvarmeutveckling Fvu AB
Priority date: 1993-06-24
Filing date: 1994-06-22
Publication date: 1995-01-05
Anticipated expiration: 1995-12-24
Also published as: SE501471C2; AU7090094A; SE9302205L; SE9302205D0

Abstract

An insulated pipe comprises an inner fluid pipe (1), an outer jacket pipe (3), as well as an insulation (5, 6, 7) arranged therebetween. The insulation consists of a plurality of insulating bag units (5, 6), each having a flexible bag wrapping enclosing a high-insulating, fine-grained powder material in a moisture- and vacuum-proof manner, the insulating bag units substantially filling the space between the fluid pipe and the jacket pipe, and of an insulating foam (7) filling the interspaces (9, 10, 11) between the insulating bag units as well as between the latter and the two pipes.

Description

INSULATED PIPE

Technical Field

The present invention relates to an insulated pipe, especially a so-called culvert pipe, comprising an inner fluid pipe and an outer, concentric jacket pipe, as well as an insulation arranged therebetween.

Technical Background

Pipes of the above-mentioned type are used to a large extent for distributing process heat and in dis¬ trict heating. The insulation used primarily is polyure- thane foam, which is foamed between the inner and outer pipes, where the foam is left to solidify. Previously, Freon was generally used as propellant. Because of the environmental problems linked with Freon, attempts have lately been made involving other propellants, for example carbon dioxide, which however results in impaired insu¬ lating properties.

Object of the Invention

One object of the invention is to provide a new pipe design which makes it possible to use environmentally- friendly, Freon-free insulation having improved insulat¬ ing properties as compared with conventional techniques. Another object of the invention is to provide a new pipe design which makes it possible substantially to use as insulation an insulating material that can be produced in advance by means of fully automatic machines.

Yet another object of the invention is to provide a new pipe design which makes it possible to use insulat¬ ing material produced in advance in one or a few standard sizes for insulating pipes of different dimensions, while preserving the technique established for pipes of this type, which consists in using insulating foam as a fixing and load-transmitting joint between the inner and outer pipes.

Summary of the Invention The above-mentioned objects are achieved by the pipe according to the invention having the features recited 'in the appended claims.

The invention is thus based on the principle that the insulation substantially consists of a plurality of specially-manufactured insulating bag units, the inter¬ spaces remaining between the insulating bag units as well as between these and the two concentric pipes being filled with an insulating foam.

The insulating bag units have very high insulating capacity and consist of a flexible bag wrapping which encloses in a moisture- and vacuum-proof manner a high- insulating, fine-grained powder material, preferably silica aerogel, especially blackened such aerogel, or kieselguhr. The insulating bag units are advantageously compact¬ ed and/or evacuated to a suitable extent. In other words, they may be of a design similar to that of vacuum-packed coffee packages. As those skilled in the art will readily realise, an insulating bag unit of this type can be easi- ly and efficiently manufactured fully automatically in suitable machines.

As mentioned above, the insulating bag units sub¬ stantially fill the space between the two pipes, typi¬ cally by at least about 70%, preferably by at least about 80-85%. This means that the remaining volume to be filled with insulating foam is relatively small, and so the demands placed on the insulating foam, having higher heat conductivity, need not be equally high. In other words, the foam may, for example, be carbon-dioxide-blown load- transmitting polyurethane foam, without adversely affect¬ ing the overall insulating capacity to any appreciable extent. Advantageously, the insulating bag units are arrang¬ ed overlappingly, so that paths extending from the inner fluid pipe to the outer jacket pipe outside the insulating bag units will have a length which essentially exceeds the radial distance between the fluid pipe and the jacket pipe. In this manner, heat insulation will be improved by the foam.

The insulating bag units may have an elongate, gen¬ erally flattened configuration. Their length may be equal to the length of the pipe or, if the pipe length is con¬ siderable, for example half the pipe length. As will be understood, this means that, when manufacturing the pipe, the insulating bag units can easily be inserted longitu¬ dinally in the space between the inner and the outer pipe from one end and/or from both ends, optionally by using spacer or support elements, before the subsequent foam blowing takes place.

In a first preferred design, the insulating bag units have in cross-section a thin side portion and a thick side portion, the thin side portions of the insu¬ lating bag units connecting with the fluid pipe and the thick side portions of the insulating bag units connect¬ ing with the jacket pipe, and the insulating bag units generally extending, as seen in cross-section, in a direction essentially deviating from the radial direc¬ tion. The insulating bag units may then have a wing-like profile in cross-section.

The above-mentioned design means that the insulating bag units may be of a standard size usable for a number of pipe dimensions, the inclination of the insulating bag units relative to the radial direction being adapted to the radial distance between the fluid pipe and the jacket pipe.

According to a second preferred design, the insulat- ing bag units, as seen in cross-section, are arranged in two or more concentric ring layers, the succeeding insu¬ lating bag units in one ring layer being so offset rela- tive to the succeeding insulating bag units in adjacent ring layers that gaps between succeeding insulating bag units in one ring layer are offset in the circumferential direction relative to the corresponding gaps in adjacent ring layers. These gaps may, as seen in cross-section, be inclined relative to the radial direction. The insulating bag units may have a domed or curved configuration to conform to a cylindrical pipe shape, which is however not compulsory. As a person skilled in the art will readily under¬ stand, this design makes it possible to build up insulat¬ ing layers of different thicknesses between the inner and the outer pipes by using only one or optionally two dif¬ ferent sizes of the insulating bag units manufactured in advance.

Further, it has been found that the powder material used should be at least so fine-grained that the heat conduction decreases with decreasing gas pressure, and preferably so fine-grained that maximum heat insulation is achieved even at a relatively moderate vacuum. The powder grains should exhibit high resistance to pressure load but at the same time have low density. The powder must not be appreciably impaired by high temperatures or temperature cyclings. It has been found that suitable powder materials are based on silicon dioxide. As previously mentioned, silica aerogel and fine-grained kieselguhr are suitable mate¬ rials.

The grain size of the kieselguhr suitably is micro- meter size (less than 0.1 mm). Its bulk density may be a few hundred kg/m^, typically about 250 kg/m^.

When using kieselguhr, the insulating bag units are suitably evacuated to a pressure below about 10 mbar, pre¬ ferably to a pressure below one or some mbar. The silica aerogel generally consists of 3-4-mm granules. It is preferred to have the granules ground so as to obtain a maximum particle size of about 1 mm. The bulk density suitably is between about 100 and about 250 kg/m-3. It is preferred to be closer to the lower limit.

The aerogel may be translucent or pigmented (blacken- ed). The latter alternative is preferred, since it improve the heat insulation.

The silica aerogel is suitably evacuated to a pres¬ sure below about 100 mbar. Especially good insulating values are obtained at a pressure below about 1 mbar. After optional evacuation of the insulating bag units, a certain amount of residual or background gas may remain. It is advantageous if this residual gas has a lower heat conductivity than air (such as argon) and/or is the same as the propellant for the surrounding, load- transmitting foam (such as carbon dioxide). It is under¬ stood that to achieve a residual gas of the above-men¬ tioned type the evacuation may take place in an environ¬ ment with such a gas.

If the heat conductivity in the residual gas is lower than in air, a lower total heat conductivity is obtained. If the gas is the same as the propellant for the surrounding foam, the pressure difference over the bag wrapping decreases, like the gas diffusion. This is especially so if a higher residual pressure of the order of, say, 10-100 mbar, is permissible in the insulating bag units.

As to the bag wrapping, high demands are placed on moisture- and vacuum-barrier quality, strength, resis¬ tance, low temperature sensitivity, capability of with- standing shear stresses, as well as on jointing capacity. In view hereof, it has been found that the wrapping material suitably consists of laminated plastic-metal foil or pure plastic foil.

A typical laminated foil has from 3 to 5 different layers. The outermost stratum consists of one or two plastic layers, for example polyethylene, polypropylene and/or polyester. The central stratum is a layer of metal foil, for example aluminium foil. The innermost stratum again consists of one or two polymer plastic layers. Typically, the total foil thickness may be about 150 μm. The bag wrapping can easily be heat seam welded, for example with the aid of electrically heated jaws.

A homogeneous plastic foil may, for example, be a ' high-temperature polymer having low oxygen diffusion and a thickness of the order of about a tenth of a millime¬ tre. Finished bag wrappings can be filled with powder and thereafter be evacuated and sealed in a vacuum chamber. A person skilled in the art will realise that fully automa¬ tic evacuation and welding machines permit a rational manufacturing process. In order to improve the frictional fixation in the finished pipe, the bag wrappings may have an external friction-fixing structure. For example, they may be grooved, folded or otherwise structured to improve the engagement with the insulating foam. Embodiments of the invention will be described here¬ inafter with reference to the accompanying drawings.

Brief Description of the Drawings

Fig. 1 is a schematic perspective view showing one example of an insulated pipe according to the invention, the configuration of the insulation being shown in a sim¬ plified manner in the pipe end surface.

Fig. 2 is a schematic cross-sectional view of another example of an insulated pipe according to the invention.

Figs 3 and 4 are schematic cross-sectional views of the same type as Fig. 2, illustrating two further exam¬ ples of the design of the insulation in the pipe.

Fig. 5 is a schematic cross-sectional view of an example of an insulating bag unit for use according to the present invention. In the Figures, the same or corresponding parts bear the same reference numerals. Description of Embodiments

Fig. 1 schematically illustrates the design of an embodiment of an insulated pipe according to the inven¬ tion. The straight pipe comprises an inner fluid pipe 1^{" "} of metal and an outer jacket pipe 3 of plastic which is concentric with the pipe 1. Between the two pipes, there is accommodated an insulation which fills the entire space and which consists of insulating bag units 5, 6 and an intermediate insulating foam (PUR) 7. The insulating bag units 5, 6 are elongate, flattened and slightly domed units, which are inserted in the pipe space in its longi¬ tudinal direction. Typically, the units may have a width of the order of 5-10 cm, a thickness of the order of one or some centimetres and a length of up to several metres. When, for example, the pipes have a standard length of 12 m, insulating bag units having a length of 6 m prior to foaming can be inserted towards each other from the respective pipe ends. As a person skilled in the art will readily realise, suitable spacer and support elements.for the ends of the insulating bag units can be provided, such that the insulating bag units are positioned during foaming. The insulating bag units 5, 6 are arranged in suc¬ cession in two concentric rings (as seen in cross-sec¬ tion) . The inner ring comprises six narrow units 5 and the outer ring six broader units 6. It is understood that the units are disposed close together and close to the pipes so as to substantially fill the insulating space.

The gaps 9', 9", 10, 11', 11" filled with insulating foam and defined between adjacent units and between the units and the pipes thus have a small size in actual practice. The units 5, 6 of the respective rings are offset in relation to each other, so that a gap 9' between the units 5 in the inner ring is offset in relation to (here located about midway between) adjacent gaps 9" between the units 6 in the outer ring. In this way, the heat leak path through the insulating foam 7 becomes substantially longer than the radial distance between the inner and outer pipes 1, 3, as indicated by the dashed line 13. The side surfaces of the units 5, 6 might be inclin¬ ed in relation to, i.e. make an angle with the radial direction, whereby the heat leak path will apparently be further lengthened. In this case, the units will have the cross-section of a flattened rhombus. One example of this is illustrated in Fig. 5, showing an enlarged cross-sec¬ tion of such an insulating bag unit 55. The unit has a bag wrapping 57 enclosing in a moisture- and vacuum-proof manner compacted and evacuated blackened silica aerogel 59. The bag wrapping is longitudinally heat-sealed at the upper longitudinal right-hand edge 61. The outer surface of the bag wrapping is provided with small projections or pimples 63 cooperating with the insulating foam 7 to provide better frictional fixation.

Fig. 2 schematically illustrates the design of another embodiment of an insulated pipe according to the invention. The design is similar to that of Fig. 1, although the insulating bag units 15 here have a differ¬ ent shape and location. The insulating bag units have wing-like cross-section with a narrow inner side 17 and a broad outer side 19. The narrow side 17 of the units 15 connects with the inner pipe 1 and the broad side 19 of the units 15 connects with the outer pipe 3. The general extent of the units, as seen in cross-section, is essen¬ tially inclined relative to the radial direction of the pipe, as indicated by the dashed line 21. It is under¬ stood that by suitably adapting the inclination of the units 15, it is possible to use units of a single stan¬ dard design for insulating pipes with highly varying requirements as to insulating thickness, i.e. different distances between the inner and outer tubes. A consider¬ able inclination means that the heat leak path through the insulating foam 7 will also here be lengthened in an advantageous manner.

Fig. 3 shows an example of a design of the insulat¬ ing bag units which is modified in relation to Fig. 2. In order to further improve the adaptation to the larger circumference of the jacket pipe 3, the broad ends 29 of^" the insulating bag units 25 have here been further broadened. The units 25 will thus have an almost triangu¬ lar shape as seen in cross-section. Fig. 4 schematically shows another modified design of the insulating bag units 35. Here, the units have the cross-section of an approximately rhombic, high shape, in that the inwardly facing surfaces of the units which extend from the inner end edge 37 have a first portion 39 extending substantially along the inner pipe 1. The corresponding outwardly facing surface 41 is longer in the circumferential direction so as to be adapted to the larger diameter of the outer pipe 3 and terminates in a stretched pointed side edge 43. As a result, the heat leak path through the insulating foam from the inner pipe 1 to the outer pipe 3 will again be lengthened. .

A design using a pointed stretched inner and/or outer side edge, which in principle is applicable to all the embodiments illustrated, may be advantageous also from manufacturing standpoints, since such a side edge may advantageously be provided in connection with the sealing of the respective insulating bag units after the evacuation thereof.

As is readily understood, the embodiments shown in Figs 1-5 of the insulating bag units according to the invention are arranged in a manner to enable adaptation to most pipe dimensions currently on the market. It is of course also possible to combine insulating bag units, especially of the designs shown in Figs 3 and 4, with insulating bag units of the designs shown in Figs 1 and 5, in order to obtain a pipe insulation of combined design and of a larger radial dimension.

Claims

1. An insulated pipe, especially a so-called culvert pipe, comprising an inner fluid pipe (1), and outer jacket pipe (3), as well as an insulation arranged there¬ between, c h a r a c t e r i s e d in that the insulation consists of a plurality of insulating bag units (5, 6; 15; 25; 35), each of which has a flexible bag wrapping enclosing a high-insulating, fine-grained powder material in a moisture- and vacuum-proof manner, said insulating bag units substantially filling the space between the fluid pipe and the jacket pipe, and of an insulating foam ( 7 ) which fills the interspaces between the insulating bag units as well as between the latter and the two pipes and which preferably is a solid, load-transmitting foam, such as polyurethane foam.

2. A pipe as claimed in claim 1, c h a r a c t e r ¬ i s e in that the insulating bag units (5, 6; 15; 25; 35) are arranged in overlapping relationship, such that paths (13) passing from the fluid pipe (1) to the jacket pipe (3 ) outside the insulating bag units have a length substantially exceeding the radial distance between the fluid pipe and the jacket pipe.

3. A pipe as claimed in claim 1 or 2, c h a r a c ¬ t e r i s e d in that the insulating bag units (5, 6; 15; 25; 35) have an elongate, generally flattened configura¬ tion.

4. A pipe as claimed in claim 3, c h a r a c t e r - i s e d in that the insulating bag units (15; 25; 35) have in cross-section a thin side portion and a thick side portion, the thin side portions of the insulating bag units connecting with the fluid pipe ( 1 ) and the thick side portions of the insulating bag units connect- ing with the jacket pipe (3), and the insulating bag units generally extending, as seen in cross-section, in a direction substantially deviating from the radial direction.

5. A pipe as claimed in claim 4, c h a r a c t e r ¬ i s e in that the insulating bag units (15) have a wing-like profile in cross-section.

6. A pipe as claimed in claim 4 or 5, c h a r a c¬ t e r i s e d in that the insulating bag units (15; 25) are of a standard size usable for a number of pipe dimen¬ sions, the inclination of the insulating bag units rela- tive to the radial direction being adapted to the radial distance between the fluid pipe (1) and the jacket pipe (3).

7. A pipe as claimed in claim 3, c h a r a c t e r ¬ i s e in that the insulating bag units (5, 6), as seen in cross-section, are arranged in at least two concentric ring layers, the succeeding insulating bag units (5) in one ring layer being so offset relative to the succeeding insulating bag units (6) in the other ring layer that gaps (9' ) between succeeding insulating bag units (5) in one ring layer are offset in the circumferential direc¬ tion relative to corresponding gaps (9") in an adjacent ring layer (6) .

8. A pipe as claimed in claim 7, c h a r a c t e r ¬ i s e d in that the gaps, as seen in cross-section, are inclined relative to the radial direction.

9. A pipe as claimed in claim 7 or 8, c h a r a c ¬ t e r i s e d in that the insulating bag units (5, 6) have a domed configuration.

10. A pipe as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the bag wrap¬ pings (57) have an outer friction-fixing structure (63).

11. A pipe as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the insulating bag units (5, 6; 15; 25; 35) are compacted and/or evacu- ated.

12. A pipe as claimed in claim 11, c h a r a c ¬ t e r i s e d in that the insulating bag units (5, 6; 15; 25; 35) are evacuated in such a manner that remaining residual gas has a lower heat conductivity than air and/ or is the same as the propellant of the load-transmitting foam.

13. A pipe as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the powder material (59) is silica aerogel, the insulating bag units preferably being evacuated to a pressure below about 100 mbar, especially below one or a few mbar, or kiesel- guhr, and the insulating bag units preferably being eva¬ cuated to a pressure below 10 mbar, especially below about 1 mbar.

14. A pipe as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the insulating bag units (5, 6; 15; 25; 35) fill the space between the fluid pipe and the jacket pipe by at least about 70%, preferably at least about 80-85%.