The present invention relates to an insulated pipe and use thereof in systems that require insulated pipes, such as heating systems. Introduction

In the field of thermal insulation techniques insu lated pipes are commonly used to transport a hot or cold medium, such as water, to the place of need thereof.

For instance, insulated pipes are used in heat dis- tribution systems, such as district heat distribution net works in order to transport heat to secondary distribution networks, for instance heat networks of houses or other buildings .

In order to avoid heat loss during transfer of the heating medium to the eventual destination it is important that the pipes used are well insulated.

Various insulation techniques are known in the art of thermal insulation. One of these techniques is vacuum in sulation. This technique makes use of vacuum insulation panels. Use of vacuum insulation panels for thermal insu lation purposes has recently gained increased interest. The thermal conductivity of vacuum insulation panels is in general lower than that of conventional insulation materi als. Therefore, if vacuum insulation panels are used as pipe insulation this can lead to improved insulation com pared to conventional insulation materials. Thus, when vacuum insulation panels are used as pipe insulation in a heating network this may lead to a decreased loss of heat during transport of the heating medium.

The use of vacuum insulation panels as pipe insula tion has been described for instance in WO 2017/144609 A1. This patent application discloses insulated pipes for use in district heating networks which have an inner pipe sur rounded by a vacuum insulation panel.

Summary of the invention

Heating networks such as district heating networks often require transport of heating medium (such as hot wa ter) with a temperature of up to 90-95°C. The inventors have found that exposure of a vacuum insulation panel to such high temperatures has an adverse effect on the life time of the vacuum insulation panel. These high tempera tures cause accelerated aging of the materials of the vac uum insulation panel, which is accompanied with brittle ness of said materials. This eventually leads to leakage, loss of vacuum and consequently loss of insulation capaci ty.

Therefore, if insulated pipe systems as disclosed for instance WO 2017/144609 A1 are used in the abovementioned heating networks the vacuum insulation panels surrounding the inner pipes are exposed to high temperatures of up to 90-95°C, leading to the abovementioned adverse effects.

With the present invention the inventors have found a way to improve the lifetime of vacuum insulation panels in insulated pipes and therewith the lifetime of the insulat ed pipes.

The present invention therefore relates in one aspect to an insulated pipe, comprising one or more inner pipes surrounded by a first foam layer and a flexible vacuum in sulation panel wrapped around said first foam layer.

In a second aspect the invention relates to a heating system comprising one or more insulated pipes according to the first aspect in connection with a heat source.

The inventors have surprisingly found that the use of a foam layer between the outer surface of an inner pipe and a vacuum insulation panel surrounding said inner pipe leads to increased lifetime of the vacuum insulation panel and therewith the lifetime of the insulated pipes, with stable and non-decreasing insulation properties in time. Namely, by the provision of this foam layer between the vacuum insulation panel and the inner pipe containing hot medium with a temperature of 90-95 °C, a slight decrease in the temperature is realized at the surface of the vacu um insulation panel facing said inner pipe, so that the vacuum insulation panel is only exposed to temperatures of maximal 60-70 °C. At these lower temperatures, aging of the vacuum insulation panel is almost completely prevent ed. With the provision of the present invention insulated pipes with a lifetime of up to 40 years are realized.

Short description of the drawings

Fig. 1 shows a cross section of an embodiment of an insulated pipe according to the invention.

Fig. 2 shows a cross section of another embodiment of an insulated pipe according to the invention.

Fig. 3A shows a cross section of another embodiment of an insulated pipe according to the invention.

Fig. 3B shows a perspective view of the insulated pipe of Fig. 3A.

Fig. 4 shows a cross section of an embodiment of an insulated pipe according to the invention having two inner pipes .

Fig. 5 shows a cross section of another embodiment of an insulated pipe according to the invention having two inner pipes .

Detailed description of the invention

The present invention is based on the use, in an in sulated pipe, of a foam layer between an inner pipe of said insulated pipe and a vacuum insulation panel sur rounding said inner pipe for conferring extended lifetime of the vacuum insulation panel and therewith maintenance of stable insulation values of said insulated pipe in time .

The insulated pipe may contain one or more inner pipes. The one or more inner pipes may be composed of any material suitable for use of the intended purpose. For purposes of use in a heating system it is preferred that the one or more inner pipes are plastic pipes, because these materials are corrosion and temperature resistant and in general flexible to a certain extent while provid ing enough strength for the intended use. Suitable plas tics in this regard are for instance polyolefine plastics. For instance it is possible to use non-crosslinked poly olefines. Such non-crosslinked polyolefines may include selected polyethylene, such as PE-RT (polyethylene of raised temperature resistance), polypropylene, such as PPR, polybutylene terephthalate (PBT) , polybutene and mix tures thereof. A very suitable material is polybutene, a polymer made from a mixture of 1-butene, 2-butene and iso butylene. The advantage of using non-crosslinked polyole fines is that these are recyclable. It is also possible to use a cross-linked polyolefine as basis material for the one or more inner pipes, for instance cross-linked poly ethylene (PEX) which may for instance be high density pol yethylene (HDPE), which has high flexibility and high- temperature resistance.

Suitable inner pipes may be provided with a so-called diffusion barrier, for instance in the form of an EVOH foil glued to the outer surface of the one or more inner pipes. Such a diffusion barrier is resistant to humidity and prevents oxygen from entering the medium in the insu lated pipes, which on its turn decreases the risk of oxi dation of heating network components.

Vacuum insulation panels as used in the present in vention are sheets in which insulating materials or inert fillers are completely encapsulated in an envelope, which is impermeable to gases. The envelope is evacuated to cre ate a vacuum core. Once the vacuum has been applied it is retained for a long time, provided that the envelope is intact .

In accordance with the present invention, a flexible vacuum insulation panel is used. This allows the vacuum insulation panel to be wrapped around the foam layer (first foam layer) surrounding the one or more inner pipes. Such a flexible vacuum insulation panel has a high er flexibility than a vacuum insulation panel having a core comprising prepressed silica. An example of a flexi ble vacuum insulation panel has a core comprising a pow dery material, for instance powder of inorganic oxides.

The flexible vacuum insulation panels for use in the present invention preferably have a thickness from 3 to 40 mm, more preferably 3 to 35 mm, most preferred 3 to 10 mm. In a suitable exemplary embodiment the flexible vacuum in sulation panel has a thickness of approximately 5 mm.

Suitable flexible vacuum insulation panels for pur poses of the present invention and the production thereof are for instance described in above mentioned WO 2017/144609 A1. Suitable flexible vacuum insulation panels for use in the present invention are commercially availa ble, for instance from VA-Q-TEC AG (DE) .

The flexible vacuum insulation panel is wrapped around the first foam layer. The first foam layer is formed as a discrete foam layer between a vacuum insula tion panel and one or more inner pipe(s) . This way the vacuum insulation fittingly surrounds the foam layer with out the risk of damaging the panel during construction of the pipe. This can be done by wrapping a rectangular sheet of vacuum insulation panel around the first foam layer and fixing (e.g. with glue) the ends to each other so that there is no gap or cleft in the longitudinal direction of the pipe between the ends of the vacuum insulation panel . Fixing the one end of the vacuum insulation panel to the other may be done before or after wrapping the vacuum in sulation panel around said first foam layer, for practical purposes preferably after. It is also possible that one end of the vacuum insulation panel overlaps the other end and that the vacuum insulation panel is fixed in a desired position. In this respect it is also envisaged that the vacuum insulation panel is wrapped more than once around one or more inner pipes.

In order to maintain insulation properties in case of cutting a pipe according to the invention to size, it is possible that barriers are provided in the vacuum insula tion panel avoid loss of vacuum as much as possible. These barriers are preferably provided in the vacuum insulation panel orthogonal to the longitudinal axis of the pipe. Al ternatively, multiple vacuum insulation panels may be abutted, preferably sealingly, to each other in longitudi nal direction of the pipe. This way an insulation pipe ac cording to the invention can be sized to the desired length without loss of vacuum and thus insulation proper ties.

The foam between the one or more inner pipes and the vacuum insulation panel, i.e. the first foam layer, may be made of a flexible or non-flexible foam as long as it is able to realize the temperature drop from 90-95°C at the outer surface of an inner pipe to 60-70°C on the surface of the vacuum insulation panel facing the inner pipe.

In a preferred embodiment the first foam layer is a flexible foam. This allows bending of the insulation pipe of the invention without the risk of damages such as cracks. Moreover, it also lowers the risk of damage of the vacuum insulation panel due to possible uneven surfaces.

Without limitation, suitable materials for the first foam layer may include foams common in the field of ther mal insulation such as polyolefine foams, such as polyeth ylene foams (crosslinked or non-crosslinked) , polyurethane foams, or phenolic foams. Foams may be open or closed cell foams depending on the desired insulation properties or anything in between.

Very suitable polyolefine insulation foams are the foams disclosed in WO 01/94092 Al, WO 02/42679 A1 or WO 2019/050402 Al of the present applicant. These foams are flexible, recyclable and have excellent insulation proper ties. In a preferred embodiment the foam of the first foam layer may be based on a non-crosslinked polyolefine foam. Such a foam is flexible, recyclable and has excellent in sulation properties. Such foams are described and claimed for instance in WO 2019/050402 A1 of the present appli cant .

The thickness of the first foam layer may depend on its thermal insulation properties. The thickness should be chosen such that it allows a temperature drop from 90-95°C on the outer surface of the one or more inner tubes to 60- 70°C on the surface of the vacuum insulation panel facing the inner pipe. For instance, if a foam as described in the example of WO 2019/050402 A1 is used a thickness of the first foam layer between 5 to 10 mm, such as 7,5 mm, would be suitable to realize this temperature drop.

In a preferred embodiment the insulated pipe accord ing to the invention further comprises a second foam layer surrounding said vacuum insulation panel. This second foam layer protects the vacuum insulation panel from the envi ronment surrounding it on one hand, while increasing ther mal insulation on the other hand. The material of the sec ond foam layer may be selected from the same materials and have the same properties as described above for the first foam layer.

The first foam layer and optional second foam layer are applied as discrete, separate foam layers. This allows flexibility in construction of the insulated pipe of the invention, because insulated pipes of various configura tions can be made without necessitating substantial adap tations in the production line.

In a preferred embodiment the first and second foam layer are the same material. The thickness of the second foam layer may be chosen depending on the desired total thickness of the insulated pipe of the invention and the desired insulation and/or protection properties. In a suitable embodiment wherein the second foam layer is a foam as described in the example of WO 2019/050402 A1 of the present applicant a thickness of the second foam layer may be between 10 to 40 mm, such as 20 mm.

In a further preferred embodiment the insulated pipe according to the invention further comprises an outer cas ing. This is also for protection of the vacuum insulation panel. The outer casing may be of the same material as the one or more inner pipes and may therefore suitably be a plastic casing. The outer casing may be a smooth film or an outer pipe, for instance a plastic outer pipe. It is preferred that said outer casing is a corrugated outer casing. Such a corrugated or ribbed casing has ribs ex tending over the circumference of the casing, which pro vides additional strength and thus protection from the en vironment surrounding it. A corrugated casing may be real ized for instance as described in WO 02/31400 A1 of the present applicant.

The insulated pipes of the invention may suitably contain more layers of material except for the above men tioned layers, such as coatings and the like. For instance the inner pipe may consist of multiple layers and/or the vacuum insulation panel may comprise a coating layer and/or the foam layers may consist of multiple sublayers of foam.

As mentioned above the insulated pipe of the inven tion may comprise one or more inner pipes.

In a suitable embodiment the insulated pipe according to the invention comprises only one inner pipe arranged in a concentric manner with respect to the first foam layer, the vacuum insulation panel, the optional second foam lay er and the optional outer casing.

In a further embodiment the insulated pipe according to the invention comprises multiple inner pipes. For in stance, it is very common to use an insulated pipe with two inner pipes.

In this embodiment each pipe may be surrounded by a separate flexible vacuum insulation panel, and first foam layers are provided between the outer surface of the pipes and said flexible vacuum insulation panels. In this case each inner pipe is surrounded by a separate first foam layer and a separate vacuum insulation panel. If a second foam layer is used herein this may be a single second foam layer surrounding all vacuum insulation panels. This ap plies also for the optional outer casing.

Another possibility is that said multiple pipes are surrounded by a common flexible vacuum insulation panel. In this case a first foam layer is provided between the outer surface of said pipes and said common flexible vacu um insulation panel. The first foam layer may here be a single entity covering all inner pipes, thus filling the space between the inner pipes and the space between the inner pipes and the common vacuum insulation panel.

The insulated pipe can be made via various ways known in the art and may for instance involve wrapping the lay ers over each other or involve an extrusion process as de scribed in WO 02/31400 A1 to apply the first foam layer around the one or more inner pipes. In preferred embodi ment, the first foam layer, the vacuum insulation panel, and the optional second foam layer are applied in this re spective sequence. The optional outer casing can be ap plied after this. It is preferred that the first foam lay er, the vacuum insulation panel, the optional second foam layer and the optional outer casing are arranged in a non- bonded fashion. This facilitates production of the insu lated pipes according to the invention and glue is not necessary as all layers preferably fit tight into each other. Moreover, this ensures uniform insulation proper ties over the full length of the pipe of the invention.

The insulated pipes of the invention can be used of any thermal insulation purpose, including cold insulation systems. However, as explained above the insulated pipes according to the invention are in particular suitable for heat insulation. Therefore the invention relates also to a heating system comprising one or more insulated pipes ac- cording to the invention in connection with a heat source, for instance a district heating system.

Detailed description of the drawings

The invention will now be further elucidated in the attached drawings. The following explanation is meant to illustrate and explain the invention and not to limit the claims. The scale and size ratio of the components shown in the drawings may deviate from the actual scales and ra tios.

Fig. 1 shows a cross sectional view of a first embod iment of the insulated pipe of the invention which com prises a single inner pipe 1 surrounded by a first foam layer 2 and a flexible vacuum insulation panel 3 wrapped around said first foam layer 2. The ends of the vacuum in sulation panel 3 are glued to each other to provide full covering of the foam layer 2. An embodiment like this pro vides excellent insulation properties and lifetime of the vacuum insulation panel. However, this embodiment is in particular suitable if the insulated pipe is used for ap plications above the ground or in protected environment, such as for instance within casings and the like.

In general, if the insulated pipe of the invention is not used in a protected environment it will therefore be more preferable to have a protection around the vacuum in sulation panel 3. Fig. 2 shows in a cross sectional view that a second foam layer 4 surrounds the vacuum insulation panel 3. This confers protection to the vacuum insulation panel and contributed to the isolation properties. Further protection can be provided in the form of an outer casing 5 as shown in the cross sectional view of Fig.3A and the perspective view of Fig. 3B. In the situation depicted in Fig. 3 the outer casing 5 is a corrugated plastic outer casing as shown in the perspective view represented by Fig.3B. The ribs of the corrugated outer casing 5 provide further strength. As mentioned above the insulated pipe of the inven tion may also be designed as an embodiment comprising mul tiple inner pipes. Such embodiments are shown in the cross sectional views of Fig. 4 and Fig. 5.

In the embodiment in Fig. 4 two inner pipes 1 are each provided with a separate first foam layer 2 and vacu um insulation panel 3 surrounding it. In this embodiment a single second foam layer 4 surrounds both vacuum insula tion panels 3. The second foam layer is surrounded by an outer casing 5, such as a corrugated plastic outer casing.

In the embodiment in Fig. 5 two inner pipes 1 are provided with a shared first foam layer 2 and a single vacuum insulation panel 3 surrounding it. The second foam layer 4 surrounds the vacuum insulation panel 3. The sec- ond foam layer is surrounded by an outer casing 5, such as a corrugated plastic outer casing.

The principle shown in the embodiments shown in Fig. 4 and 5 is also applicable to insulated pipes comprising more than two inner pipes.