CA1225043A

CA1225043A - Thermally insulated conduction of fluid

Info

Publication number: CA1225043A
Application number: CA000452775A
Authority: CA
Inventors: Juergen Friessner; Peter Huber; Gerhard Ziemek
Original assignee: Kabelmetal Electro GmbH
Current assignee: Kabelmetal Electro GmbH
Priority date: 1983-03-05
Filing date: 1984-04-25
Publication date: 1987-08-04
Also published as: GB8405484D0; NL8400402A; FI833333A; SE8401168L; SE8401168D0; IT1169076B; CH660907A5; DK362483A; DE3307865A1; DK362483D0; IT8349095A0; ATA270683A; FI833333A0; GB2136528A; FR2542060B1; GB2136528B; JPS59164128A; FR2542060A1

Abstract

THERMALLY INSULATED CONDUCTION OF FLUID

ABSTRACT OF THE DISCLOSURE
A corrugated metal inner tube is provided with a helical spacer and an outer jacket of an extruded synthetic, there being a metal foil with overlapping edges provided as lining along the inside wall of the outer tube and being seated on a helical spacer on the inner tube; the otherwise unoccupied space between the tubes is filled with foam, preferably bonded to the metal foil,- overlapping edges of the foil are bonded to each other;
the metal foil prevents ingress of moisture from the outside by diffusion, as well as escape of pore-sustaining gas filling from the foam.

Description

5 the present invention relates -to a thermally insulated 6 ¦ conduit, and more particularly the invention relates to a 7 ¦ thermally insulated conduit system which includes a metallic 8 ¦ inner tube for the fluid to be conducted and being provided with 9¦ a helically or annularly corrugated wall, an outer tube 10¦ surrounding the inner tube and being made of a synthetic 11¦ material, the space between the inner and outer tubes being - 12¦ filled with a thermally insulating material such as a foam 131 synthetic on polyurethane basis.

151 A tube of the type to which the invention pertains is 16¦ for example suggested in German , Petty Patent 7,816,809.
17¦ Such a tubing is usually provided with connection or joint 18¦ elements for connection to appropriate fitting or for connecting 201 one string of tubing to another one because the strings of tubing l as they are furnished to the installation site have a limited 21¦ length, usually from six to fourteen meters. The tubing of this ~21 variety is particularly suitable for branch conduits leading from 231 a trunk conduit in remote heating facilities to the individual 24 ¦ users.
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28 l lZZ5043

2 .

3 It is an object of the present invention to improve the

4 known conduit system of the type referred to above in such a manner that the interference of the foam layer through moisture 6 and gases can be avoided without, however, limiting the 7 flexibility of this rather flexible conduit system.

It is therefore a specific object of the present invention to improve conduit systems which are comprised of an 11 inner, metal, corrugated tubing and an outer synthetic tubing 13 with polyurethane foam interposed between the two tubes.
14 In accordance with the preferred embodiment of the present invention it is suggested to provide a metal between the 16 synthetic foam filling the gap in the system as per the 17 specific object, and the outer synthetic tubing, particularly 18 along the inside Hall thereof, whereby this metal foil provides a tabularly closed hose which is bonded adhesively either with the respective outside layer (the synthetic tube) or with the foam on 21 the inside, or both. this metal foil is preferably an aluminum 23 foil coated with adhesive copolymer, and its overlapping edges are bonded together to obtain indeed a closed tube, being, so to 24 speak, the third tube in the two tube system as per the specific 26 object.

28 The closed foil as per the preferred embodiment of the , l~Z5043 1¦ present invention provides a barrier against water vapor 2 diffusion through the outer synthetic tuning into the 3 polyurethane foam. Due to the closed nature of this foil-hose, 4 such penetration of moisture is prevented with certainty. This way it is avoided that the foam will decompose on account of any 6 moisture.

8 The foil fulfills a double function, namely, it prevents 9 also the diffusion of any gas that may develop in its interior toward the outside. It should be noted that the formation of 2 foam is of course accompanied by the presence or development of 1 gas in the foaming material so as to form the pores and cells.
13 The particular gas used in cases is known under the trade name 14 Frigen. This gas is in effect necessary because it maintains to some extent the cell structure and avoids any collapse, 16 particularly if the foam happens to be rather soft. The escape 18 of such gas from the foam slayer will in fact cause a deterioration in the thermal insulating property of the foam layer; in other words, a foam layer from which this particular 2 gas has escaped to some extent will provide enhanced conduction 1 of thermal energy. The gas will in time diffuse from out of the 22 pores through the wall structure of the cells and pores, and 23 leave the system unless such diffusion is prevented.

Now in accordance with the preferred embodiment of the 27 invention, this gas is maintained within the system as a whole, 28 and since diffusion depends on a concentration gradient, the 1~250~3 2 prevention of an escape of gas from the outer areas of the polyurethane layer is directly instrumental in avoiding the 3 setting up of a concentration gradient in the interior of the 4 foam so that the mechanism of diffusion in radial out direction will not develop. Therefore, the metal hose which surrounds in a 6 closed fashion the polyurethane foam maintains the gas content in 8 the foam so that the thermal insulating property of that layer is maintained.

The bonding of the foil of which the hose is made either 11 to the adjoining foam layer, or to the outer tube or both, 12 insures a good flexibility on part of the system as a whole 13 without endangering the foil with regard to any tearing.
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The inventive improvement offers the additional 16 advantage that a migration and a diffusion ox the softening and 17 plasticizing agent from a thermoplastic outer tube into the 18 thermally insulating polyurethane layer is avoided. Again, this 29 ¦ is an important feature because such a diffusion and migration ¦ into the polyurethane foam would tend to render the outer tube 21 ¦ brittle. The bonding of the hose in a metal foil to the 22 ¦ adjoining layers finally provides for a sealing of the conduit I against longitudinal migration of water along interfaces between various layers, such as the outer tubing and the adjoining foam.

27 The inventive concept can be realized primarily in a 28 concentric tube system; such a configuration however is not

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~LZ25043 1 mandatory as far as practicing the inventive concept is 2 concerned. Conceivably several inner tubes are provided in a 3 bundle-like fashion, or otherwise and are thermally isolated with 4 respect to each other, and that assembly as a whole is enveloped by and in an outer tubing, all the various gaps and interfaces

6 are filled with foam. For practical reasons, one may provide two

7 internal tubes and envelope them by a single outer jacket with

8 foam filling the interior ox the outer jacket to the extent the

9 interior is not occupied by the two inner tubes.

11 Branches according to this system, leaving from a remote 12 heating trunk line to individual users, such as single-family 13 dwelling or the like, provide in effect a conduit system wherein 14 these branch lines are relatively short. Thus, the heat exchange between the feeder conduit and the return path is relatively 16 small. Therefore, the utilization of a conduit system in which 17 feed and return path conduits are maintained within one system 18 and thermally isolated with respect to each other, but primarily 19 with respect to the exterior through a common foam layer and a surrounding synthetic jacket is a very practical approach for 21 constructing such branch lines. If one uses the branch lines in 22 this configuration, only this type of conduit system is needed, 23 which is highly advantageous from the point of view of inventory.

In order to optimize matching of the insulation 26 requirement to the conditions under which the conduit system is 27 expected to be used, one may in cases provide an outer tubing 1 which does not have a circular cross section. In particular, in the aforementioned two tube arrangement with a common outer 3 jacket, the latter is preferably made with elliptical cross 4 section.

6 The outer jacket is preferably made from low pressure 7 polyethylene which has cross linked and thermoses This kind of 8 material has a high mechanical strength so that damage to the 9 outer tube and jacket, particularly during installation and other handling, is avoided to a considerable extent. It was found to 11 be of significant advantage if a polyethylene is used which has 12 cross-linked in the presence of moisture selection cross linking).

14 As far as the inner tube or tubes are concerned, they are preferably made from longitudinally molded and longitudinally 16 seam-welded strip which has been provided subsequently with a 17 helical or an annular corrugation pattern, the peak to peak 18 distance of the corrugation being between lo and 60 mm. The 19 advantage of using an annularly corrugated tubing configuration is to be seen in that connection to fittings or to other tube 21 lines is considerably simpler for annular corrugation as 22 compared with helically corrugate tubing. In cases such a 24 corrugated tubing is provided at its end with an uncorrugated portion. This then permits connecting techniques as are customarily used for uncorrugated tubing generally. Moreover, a 26 distance of the corrugation peaks or valleys by 10 to 60 mm does 27 not limit the flexibility of the tube system, and particularly the ..

l;~Z5043 1 inner tube remains capable of providing the requisite 2 compensation against thermal lengths extension.

4 The tubular system in accordance with the preferred embodiment of the present invention is established through a 6 commensurately novel method for making thermally insulated 7 tubing. By way of preferred practicing the invention, it is assumed that corrugated metal tubing is provided on suitable spools or drums, and has been made, for example, in continuous fashion through earlier procedure. This metal tubing is unreeled 11 and provided with certain spacers, such as a spacer hellos made 12 on the basis of polyurethane foam. pharaoh this spacer has been 13 helically looped around the annularly corrugated tubing, a metal 14 foil is run longitudinally along this assembly, and is tabularly shaped around this assembly with overlapping edges, whereby it is 16 assumed that at least one of the surfaces now in engagement are 17 coated with a copolymer that may serve as an adhesive. But prior 18 to forming the foil into a hose, or more particularly prior to 19 closing the folded foil by means of bonding, a formable synthetic blend on the basis of polyurethane or polyisosyanurate is placed 21 upon the metal foil-to be-closed, after closing the metal foil 22 into a tube this blend will foam to fill the space between the 23 now tubular toil and the metal tubing serving as a substrate;
24 subsequently, a synthetic jacket is extruded upon the metal foil hose, and through the extrusion heat the foil is either bonded to 26 the foam layer underneath or to the now produced outer jacket and 27 simultaneously the overlapping foil edges are caused to be bonded lZ25~43 1 together.

3 It can thus be seen that this particular method utilizes 4 the metal foil, such as an aluminum foil, as an additional element, namely as an element that carries out a function within 6 the method as such namely, the foil is used as a transport 7 ribbon for the material that will be foamed. Moreover, the 8 particular metal foil as it is formed into a tube is used as a 9 mold or the foam that is being made and is generated in the process. The bonding of the foil with one, but preferably both 11 of the adjoining layers, is carried out under immediate and 12 direct utilization of the heat content that results from the 13 extrusion process of the outer jacket. Moreover, this extrusion 14 heat is used to cause the overlapping foil edges to be bonded together. The heckle spacer that was initially wound around 16 the inner tube makes sure that the resulting insulation layer has 17 a uniform wall (radial) thickness.

19 In accordance with a further feature of the invention t and particularly the inventive method, it is advisable to loop 21 one or several signaling lines around the inner tube together 22 with the helical spacer These signal lines are in effect 23 sensors which will respond to any accident and unforeseen 24 penetration ox moisture into the foam layer, and will provide a signal representative ox such penetration so as to permit better 2267 localization of such a potential danger source.

l~Z~043 1 The conduit system made in accordance with the method 2 outlined above remains flexible so that it can be reeled onto the 3 usual cables drums. However, for reasons of transport generally 4 and inventory and storage, it was found to be of advantage to provide this kind of a conduit system in length between 6 and 14 6 meters (about 20 to 50 feet. On the other hand, the method 7 outlined above is basically a continuous one which produces 8 tubing of endless length or a length that is merely limited by 9 the length of the corrugated inner tubing, and this method is supplemented to provide for the continuous connection of strings 11 of such tubing. However, the desirable length for tubing 12 mentioned a little earlier mazes it advisable to cut the endless 13 string within this range for length, and the cutting should be 14 carried out particularly after curing and full development of the foam within the system. Having produced individual lengths of 16 tubing in this fashion, the jacket and the foam layer is stripped 17 for a very short length from the respective ends to thereby 18 expose the end portion of the inner tube, and that end can now be 19 prepared for suitable connection to fittings or other length of tubing, and the resulting gap of course will have to be 22 insulated thereafter by convenient methods.

I

-10-In summary form, the present invention provides, according to a broad aspect, a thermally insulated conduit soys-them comprising: an inner metal tube with looped around cargo-lion of helical or annular configuration; an outer tube made of a synthetic material and being disposed around said inner tube;
a metal hose lining the inner surface of said outer tube and being bonded thereto, said hose lining being made of metal foil and carrying an adhesive bonding layer on at least the surface facing the outer tube and being closed as a hose through over-lapping edges; a foam filling space between said inner tube anodized hose and being adhesively bonded to said hose; and said outer tube being an extruded-on jacket, the latent heat content of the extradite having caused the metal foil to be bonded to the outer tube and to the foam and the edges of the hose strip to be bonded together.
According to another aspect, the invention provides a method of making a thermally insulated conduit system comprise in the steps of: providing a corrugated metal tube with a helical spacer; forming a longitudinally paid metal foil around the corrugated metal tube with spacer to obtain a split tube with overlapping foil edges; depositing, just prior to closing the split tube a formable synthetic blend onto the metal foil which after closing of the tape edges will occupy the space between the metal tube and tubular metal foil; and extruding a synthetic jacket on top of the split tube.

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~2~i043 3 While the specification concludes with claims, 4 particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that 6 the invention, the objects and features of the invention, and 7 further objects, features and advantages thereof will be better 8 understood from the following description taken in connection 9 with the accompanying drawings in which:

11 figure 1 is a longitudinal section through a thermally

12 insulated conduit and tube system in accordance with the

13 preferred embodiment of the present invention for practicing the

14 best mode thereof;

16 ¦ Figure 2 is a section view through the conduit system 17 ¦ shown in Figure l;
18 l 19 Figure 3 is a modified section view through a conduit ¦ system with two internal tubes but being constructed otherwise 21 ¦ similar to the embodiment shown in Figure l and 2;
22 I .
3 ¦ Figure 4 is a schematic view for equipment used for 24 ¦ practicing the inventive method in order to obtain thermally 25 ¦ insulated conduit systems in accordance with the preferred 27 embodiment of the invention; and aye 1 Figures 5 and 6 illustrate various joints and 2 connections of inner tubing of conduit systems made in accordance 3 with the invention.

Proceeding now to the detailed description of the 6 drawings, reference is made to Figures l and 2 showing corrugated 7 inner tube 1 made of metal, for example, copper or aluminum, and 8 being provided with annular corrugation grooves and ridges. This 9 particular tube l is concentrically received by and in an outer tube 3 made of, for example, polyethylene of low pressure variety 11 and exhibiting moisture type cross linking. The inner tube l 12 carries a helical spacer 4 made of polyurethane foam but having 13 fairly rigid properties so that this kind of spacer is 14 sufficiently stiff and rigid because it must be able to support an outer tube 3 on the inner tube l (or vice versa) without local 16 compression and deviation from concentricity throughout.

18 The space between the inner and the outer tubes l and 3, I respectively, is filled in a two-fold manner. First of all, there is a filling of polyurethane foam 2, essentially filling 21 the space above and around tube l and between the spacer 4. An 22 aluminum foil 5 is configured as a hose, and is interposed 23 between the outer tube 3 on one hand and the spacer 4 and the 24 foam layer 2 on the other hand. This particular foil 5 is established as a tube through overlapping edges 6 which are 26 adhesively interconnected. Moreover, this hose 5 is bonded and 27 adhesively connected to the internal wall surface f the outer 1 jacket or tube 3 of the assembly, and the foil is also hounded to 21 the inside to the foam layer 2. Additional bonding may ye 31 provided for to the helix 4.

51 In order to obtain this particular bonding the metal 61 layer 5 prior to the assembly may be coated on both sides with a 7¦ suitable adhesive copolymer such as ethylene-vinylacetate or 81 ethylene-ethylacrylate which upon heating will adhesively bond 9¦ that particular foil 5 to whatever layer it is adjacent to. If 10¦ in fact the foil ribbon of which the hose 5 is jade is provided 11¦ with this kind of an adhesive coating on both sides, then 12¦ ¦ overlapping edges will automatically face each other through 13 ¦ bondable and adhesive layers. Accordingly, the tube 5 is indeed 14 ¦ closed as a result of folding a longitudinal ribbon around the

15 ¦ assembly 1-4, which will be explained more fully below.

16 l

17 ¦ It can thus be seen that the foam layer, which in fact

18 ¦ is a composite layer consisting of the layer 2 and of the spacer

19 ¦ 4, is completely enveloped in an aluminum foil hose-like cover

20 ¦ which has been bonded to establish indeed a closed configuration

21 ¦ and firm adherence to any part it adjoins. This foil

22 establishes a barrier against any ingress of water vapor

23 molecules that may tend to diffuse through the outer tube 3 into

24 the interior of the system. Moreover, any gas within the layer that may tend 2 to diffuse in one direction or the other will 26 find the aluminum toil to be an impenetrable barrier so that a 227 diffusion gradient necessary for obtaining diffusion of gas out 21 of the layer 2 cannot develop, and the diffusion will in fact not take place. In particular, the layer portions of layer 3 directly adjoining the aluminum foil will for no reason be 4 depleted of their gas content in the pores ox the foam, so that in fact a diffusion mechanism for the gas in the pores out of the 6 layer 2 and 4 the gas will not begin.

8 Tubing system of the type shown in Figure l is 9 preferably made in length from 6 to 14 meters (20 to 50 feet) and is delivered as such to the respective installation site to be 11 connected Jo other portions of like configuration or to suitable 12 I fittings which may generally qualify as source and/or destination 13 of the medium to be transmitted through the internal tube of a I ¦ particular type of conductor as explained.

16 Figure 3 illustrates that a pair of internal tubes l and 17 l' can be included within a conduit system, the outer tubing 3' 181 in this case being of elliptical cross section. The helical 191 spacer may in this case be interwoven between the two tubes l and 20¦ l' in an up and down pattern so that it serves on one hand as a 21 ¦ spacer between the two tubes l and 1', but provides also the 22 ¦ requisite outer support for the enveloping outer jacket 3'.

¦ The insulating tubular system of the kind illustrated

25 ¦ and ascribed thus far is sufficiently flexible so that it can be 27 ¦ reeled on usual and conventional cable drums, and can be 28 ¦ installed and unreeled quite analogously to the unreeling and 2504~

2 installation of an electrical cable into suitable ditches, grooves, etc. The outer jacket 3 is illustrated as a smooth wall 3 synthetic tube and, as will be described more fully below, is 4 preferably the result of an extrusion process by means of which the synthetic is extruded on top of the hose 5. However, in lieu 6 of the smooth wall jacket 3, one may use a corrugated synthetic 7 outer tube. Using a synthetic tube with corrugation as the outer 8 jacket will in fact enhance the flexibility of the conduit system 9 and the corrugation will serve as an improved anchoring facility for maintaining the conduit system within the soil after 11 installation has been completed.

13 In order to provide an outer tube of a corrugated 14 configuration, one has to proceed somewhat differently. The inner tube l is provided at a particular length, such as 6 meter, 16 i.e., about 20 feet, and carries a suitable spacer such as 4.
17 Such a short tube 1 with spacer 4 is then inserted into a 18 corrugated synthetic tube 3 which has been previously lined internally with a metal foil. The tube l with spacer 4 is 21 therefore, strictly speaking, shifted into the foil lining 5 of 22 such a tube 3. The foam components, i.e., the components which will cause foam to be generated of an inserted into the gap 223 between the tube l and the lined tube 3 in order to obtain the insulating coating and layer 2.

26 For the continuous manufacture of the conduit system in 228 accordance with the present invention, including particularly a lZ25~ 3 1 corrugated outer tube, it may be advisable that a synthetic tube 2 with corrugation of indefinite length is provided with an 3 internal metal coating meeting the requirements for the hose 5.
4 Such a remanufactured outer synthetic tube with internal metal lining is then longitudinally slithered, and the thus opened-up 6 synthetic corrugated tube will then receive the inner tube with 7 spacer, and it will also receive the materials needed for 8 roaming. Subsequently, the longitudinal slot and slit in the 9 outer tube is closed through bonding and/or welding This approach however is disadvantaged by the fact that the metal hose 11 is also slithered. Therefore the inner tube spacer assembly 12 should be covered by a metal hose before being inserted in the 13 slithered outer tube.

The Figure 4 illustrates a more economical and 16 definitely more reliable manner of manufacturing and making the 17 system a conduit system in accordance with the preferred 18 embodiment. It is assumed that corrugated inner tubing 1 is 19 reeled on a fairly large supply drum 7, and for purposes of making the conduit system it is unreeled therefrom. A rotating 21 wrapping device 8 will provide a helical spacer 4 around this 22 inner tube 1. Reference numeral 9 depicts a supply spool or 23 drum which carries an aluminum foil 5 which has been coated on 24 both sides with an adhesive copolymer. This aluminum foil is drawn from the spool 9 and run towards and below the horizontally 26 propagating inner tube 1. Through suitable and well-known tools, 28 ribbon 5 is formed into a split tube with overlapping edges 1 around the assembly 1-4. Prior to closing ribbon 5 into a tube, 2 a tamable blend of synthetic is deposited from a suitable storage bin 10 onto the ribbon 5. Due to the overlapping 4 configuration of the ribbon, the tube appears in fact to be 5 closed with a formable substance trapped on the inside. I
6 I, 7 The assembly as produced thus far is now past into and 8 through an extrular 11 by means of which the outer jacket 3 is extruded on top of the hose 5. The extrusion heat content is imparted from the layer 3 upon the component it encloses, and 12 this involves first of all the adhesive on the ribbon 5 that 13 immediately adjoins the freshly extruded layer 3, and will therefore cause an immediate bonding of the now-produced 14 synthetic jacket 3 to the aluminum foil and hose 5.

16 The blend that has been deposited from the storage 17 facility 10 onto the ribbon 5 may be adjusted so that it has 18 filled the gap with foam between the inner tube 1 and the foil 5 as the assembly passes through the extrude. In other words, the 21 foaming process exerts a radially outwardly oriented pressure 22 upon the hose, but the hose is maintained in a tubular 23 I configuration by the extrude 11 while the edges of the foil remain overlapping. The heat content of the extrusion process 225 ¦ can therefore be used also and is effective immediately and I directly in order to obtain bonding of the overlapping edges 226 through the adjoining adhesive This then stabilizes the 28 internal assembly, and the heat of the extrusion process as it 'I Z~5043 1 migrates towards the interior of the system will also be 2 effective to bond the inside surface of the hose 5 to the 3 developing foam.

Downstream from the extrude 11 is provided a water 6 cooling tank 12 in which the extruded jacket 3 is cooled.

7 Moreover, it was mentioned above that the material out of which 8 the jacket 3 is formed may be polyethylene which through the 9 addition of Solon can be cross linked in the presence of moisture. For this of course it is necessary to obtain Solon 11 grafting within the extrude, a process that is described for 12 example in U.S. Patent 4,333,898 or 4,289,860. The water tank 12 13 in this case has therefore not only the function of cooling the 14 jacket 3, but it will also expose the material thereof directly with the moisture to obtain a cross-linking process.

17 Reference numeral 13 denotes schematically a saw or 18 cutter by means of which suitable lengths are cut from the string 19 of tubing that emerges basically on a continuous basis from the cooling facility 12. The cut lengths 15 are then transported by 21 means of a roller track 14 out of the system to be stored in a 22 suitable fashion. However, it should be mentioned that the saw 23 13 does not have to be provided for or can be maintained idle in 24 those cases in which a more or less continuous string of a conduit system is to be extracted from the manufacturing system, 26 which string of tubing is then reeled onto drums of the cable

27 type. Of course, the capacity of such a drum is finite and .

1 limited, and that it may well be necessary to employ a saw in 2 this capacity in order to obtain the suitable length. On the 3 other hand, the capacity of the drum for the inner tub no l is 4 likewise limited and it may well be that the quantity of inner tubing l that is unreeled from the drum 7 is in fact sufficient 6 in order to fill a storage drum for a finite length of the final 7 system of tubing.

9 The inner tubing l is illustrated with an annular corrugation which is normally fully covered by the insulation if layer 2 and the outer jacket 3 as well as the aluminum foil and 12 hose 5. However, before obtaining a requisite connection, to 13 fittings or for a string of tubing of like configuration a 14 certain end portion of the compound tubing is stripped off the tubing 1, i.e., the insulation and hose 5 and jacket 3 is 16 removed, as is illustrated in Figures 4 and 5. This then serves 17 as a preparation for making a connection of the tubing 1. In 18 further preparation, the corrugation is removed in the end 19 portion lo of such tubing, or the corrugation process has been interrupted at -that point.

22 In order to interconnect two inner tunings l they are 23 prepared in this fashion in order obtain sooth wall tube 24 endings, and these endings are then inserted into a sleeve 16.
The sleeve 16 is soldered or welded onto the tube ends lay In 26 order to obtain this kind of connection it was found to be of

28 advantage to make sure that the distance between adjacent :, -19-11 2250~3 1 ¦ corrugation valleys in axial direction is at least 30 mm.

3 ¦ Figure 5 illustrates a connecting method between 41 adjoining tubes 1 if they are provided with a helical 5 ¦ corrugation. In this case a flattening of the end two portions Al of the tubes would be impractical. Rather, one makes use of the 71 fact that a helical corrugation is akin to a threading.
81 Therefore, one will proceed in this manner by inserting into the 9¦ tubes ends short sleeves with outer threading matching the 10¦ corrugation. Reference numeral 17 and 17' denotes such separate 11¦ sleeves. Subsequently, a common sleeve 13 with internal 12 threading is threaded on top of one of the tubes 1, thereby l sandwiching the respective tube 1 between the threaded in sleeve 14 ¦ 17 and the sleeve 18. Next the tube ends are brought into proximity and the sleeve 18 is now threaded with its other end 16 ¦ on top of the other tube 1 again radially adjacent to the 17¦ internally threaded sleeve 17'. -I Tyke ends of the two tubes are 18 ¦ now firmly clamped in between the sleeves 17 and the sleeve 18.
201 In order to obtain the requisite threading, sleeve 18 is provided l with a hexagonally swapped keying portion 19 for application of a 21 ¦ suitable wrench. After the threading has been completed, the 22 ¦ sleeve 18 is soldered with the inner tubes 1 or welded thereto.
23 l ¦ In either case, i.e., in either of the examples shown in 25 Figures 4 and 5, it is necessary to reinsulate the previously 27 I exposed portion ox the tube 1. For this one may provide known 28 techniques such as providing a sleeve on top of the two outer assay 1 coatings and jackets 3 and covering the gap space of the joint 2 which is then filled with foaming material. The slipped on 3 sleeve covering the adjoining the outer tubes 3 is in addition 4 sealed against these tubes under utilization of a shrink hose in a manner known per so.

7 The invention is not limited to the embodiments 8 described above, but all changes and modifications thereof not 9 constituting departures from the spirit and scope of the invention are intended to be included.

It

Claims

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

I A thermally insulated conduit system comprising: an inner metal tube with looped around corrugation of helical or annular configuration; an outer tube made of a synthetic material and being disposed around said inner tube; a metal hose lining the inner surface of said outer tube and being bonded thereto, said hose lining being made of metal foil and carrying an adhesive bonding layer on at least the surface facing the outer tube and being closed as a hose through overlapping edges; a foam filling space between said inner tube and said hose and being adhesively bonded to said hose; and said outer tube being an extruded-on jacket, the latent heat content of the extradite having caused the metal foil to be bonded to the outer tube and to the foam and the edges of the hose strip to be bonded together.
2. A conduit system as in claim 1, there being a helical spacer looping around the inner tube for supporting the outer tube thereon, the foam occupying space between the helical spacer.
3. A conduit system as in claim 1 wherein said inner tube is concentrically disposed to said outer tube.
4. A conduit system as in claim 1 wherein a plurality of inner tubes are disposed and surrounded by the outer tube.
5. A conduit system as in claim 4 wherein said outer tube has a non-circular cross section.
6. A conduit system as in claim 1 wherein said outer tube is made of a cross-linked low-pressure polyethylene.
I A conduit system as in claim 1 wherein said outer tube is also corrugated.
8. A conduit system as in claim 1 wherein said metal foil hose is a longitudinally folded metal strip with overlapping and bonded together edges.
9. A method of making a thermally insulated conduit system comprising the steps of: providing a corrugated metal tube with a helical spacer; forming a longitudinally paid metal foil around the corrugated metal tube with spacer to obtain a split tube with overlapping foil edges; depositing, just prior to closing the split tube a formable synthetic blend onto the metal foil which after closing of the tape edges will occupy the space between the metal tube and tubular metal foil; and extruding a synthetic jacket on top of the split tube.
10. A method as in claim 9 wherein said metal foil is pro-voided with an adhesive coating causing bonding of the split tube to the foam as well as to the synthetic jacket and also causing bonding of the overlapping edges of the foil to each other.
11. A method as in claim 10 including the step, prior to the step of forming the metal foil around the corrugated tube, of looping several signal lines around the corrugated metal tube and spacer at a certain spacing to the corrugated metal tube.