WO2004065840A1

WO2004065840A1 - District heating pipe having a conductor pipe covered by a rubber material

Info

Publication number: WO2004065840A1
Application number: PCT/DK2004/000034
Authority: WO
Inventors: Jan Rasmussen
Original assignee: A/S Star Pipe
Priority date: 2003-01-21
Filing date: 2004-01-21
Publication date: 2004-08-05
Also published as: EP1642060A1

Abstract

A district heating pipe (1) comprising a conductor pipe (2) of plastic material, a surrounding insulating material (4), and an outer protective casing (3), wherein the characterizing feature is a diffusion barrier layer (5) of a rubber material, which is provided between the conductor pipe (2) and the insulating material (4).This structure provides an insulated district heating pipe, which is lightweight, pliable and repels diffusion of gasses and water vapor out through the conductor pipe, offering cost as well as weight advantages.

Description

DISTRICT HEATING PIPE HAVING A CONDUCTOR PIPE COVERED BY A RUBBER MATERIAL

TECHNICAL FIELD OF THE INVENTION

The invention relates to an insulated district heating pipe having a conductor pipe covered by a rubber material.

BACKGROUND OF THE INVENTION

According to the state of the art it is common knowledge to manufacture pre- insulated district heating pipes having a conductor pipe of steel surrounded by insulating material and an outer protective casing. This is also reflected in the European standardization work in the CEN TC107 Committee, which in its objectives is still making use of a definition of district heating systems as systems comprised of "rigid PU cellular plastic bonded to a rigid steel pipe and to a PE casing ....".

However, the industry has long ago recognized that conductor pipes could also consist of other types of material, such as metals e.g. aluminum and copper, and polymer materials, where these are suitable.

The reasons for choosing materials other than steel could be parameters like e.g. weight, price and pliability. On the other hand, it has been a requirement to adapt the use of different types of conductor pipes to the anticipated applications, since steel is capable of dealing with high operational temperatures, typically 140°C, while e.g. copper is recommended for temperatures up to 110°C and for plastic pipes a maximum of 95°C prevails.

Typically, conductor pipes of steel are used for the main piping in district heating systems, while the other types of material could be applied on branch piping situated in such distance from the very hot water flowing in the main pipeline that the temperature could not become detrimental to them. A disadvantage of using a conductor pipe of metal might be the risk of galvanic corrosion at the interface between steel and metal, which instigates the use of plastic materials for conductor pipes.

WO 94/19641 describes a district heating pipe having a conductor pipe of aluminum, which is inexpensive and capable of being coiled up. Aluminum is well suited to create a not only physical but also steam impervious layer between the district heating water and the insulating material, but due to the risk of galvanic corrosion in the district heating system, the conductor pipes are being coated, on the inside and the outside, with a plastic material. This is done due to the need for pipe joints of a stronger material such as iron or steel, whereby the perfect conditions for galvanic corrosion emerge. Accordingly, it is also required to pay much attention to how said joints are tightened so that bolts or the like do not establish electric conductive connection to the aluminum of the conductor pipe, whereby the galvanic corrosion would become a reality. Paying this special attention would be an undesirable cost- increasing process step.

From e.g. EP 0 806 600 it is known to have a pre-insulated pipe for district heating water, steam or domestic water, provided with a conductor pipe of copper in order to have a bendable pre-insulated pipe, and furthermore the choice of insulating foam mixture is taking into account that the foam becomes reasonably pliable, thus not creating cracks or fissures if the pipe is being bent.

A significant parameter for the required long-term durability of the insulating material surrounding the conductor pipe is to the greatest possible extent avoiding penetration by ambient gasses such as oxygen and nitrogen, because otherwise the insulating efficiency is reduced.

Moreover, the above-mentioned WO 94/19641 describes experiences with plastic conductor pipes, whereby oxygen penetration through the outer casing surrounding the insulating foam would partly reduce the insulating power of the foam, partly increase aging of the plastic pipe, and finally the oxygen content of the district heating water increases and thus the corrosive aggressiveness therein. It is stated that hitherto a suitable diffusion barrier for the plastic pipe has not been found, so the choice of aluminum for the conductor pipe is a good alternative, but it requires a complete sealing thereof by the plastic coating.

Steel and metal pipes offer an efficient protection against diffusion, while plastic pipes would typically require a supplementary protection by e.g. enveloping the pipe by a metal foil, which immediately reduces the pliability of the pipe. Moreover, it is also desired to avoid the occurrence of condensation due to water vapor penetrating from inside the plastic pipe.

From said patent EP 0 806 600 it is also known to provide a layer interleaved between the conductor pipe and the insulating foam, but the object is not to serve as a barrier layer. Its sole purpose is to deliberately reduce the adherence of the foam to the conductor pipe in order to make it easy to remove the foam at selected areas.

From PCT/DK 02/00432 it is known to let a gas diffusion barrier layer (EVOH) be attached to the outside of the steel conductor pipe, but it is not capable of barring the water vapor, which might penetrate from inside a plastic pipe.

DISCLOSURE OF THE INVENTION

Object of the present invention is to manufacture an insulated district heating pipe which is lightweight, pliable and bars diffusion of gasses and water vapor through the conductor pipe, while the cost and weight gains are maintained and the galvanic corrosion is avoided.

According to the invention this is achieved by a district heating pipe comprising a conductor pipe of plastic material, a surrounding insulation material and an outer protective casing, which is characterized by a diffusion barrier layer of rubber material being provided between the conductor pipe and the insulating material.

Preferably, the conductor pipe comprises a PEX (cross-linked polyethylene) or PB (polybuten) material, and the diffusion layer could preferably consist of butyl rubber or latex. Preferred embodiments of the invention are revealed in the subordinate claims and the advantages thereof are revealed in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWING

In the following detailed part of the present description, the invention will be explained in more detail with reference to the exemplary embodiments of a district heating pipe according to the invention shown in the drawing, in which

Figure 1 is an end view of a district heating pipe according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment, the rubber material is sprayed onto the conductor pipe.

In another preferred embodiment, the rubber material is comprised of a rubber film adhering to the surface of the conductor pipe.

In a further preferred embodiment, the rubber material is co-extruded with the plastic conductor pipe.

In yet another preferred embodiment, the rubber material is comprised of a material, which maintains its plasticity throughout the lifetime of the pipe.

In the following, an embodiment of the invention is explained in more detail with reference to the drawing, in which is shown a district heating pipe (1), which in a known manner comprises an inner conductor pipe (2) of a plastic material and surrounded by a protective casing (3) of PEH material, and the space between the conductor pipe (2) and the casing (3) is filled with an insulating layer (4) of PUR foam.

On the external surface of the conductor pipe and inside of the PUR foam (4) is provided a diffusion barrier layer (5) of a rubber material, e.g. butyl rubber or latex, which will effectively prevent water vapor and other gasses from diffusing out into the PUR foam (4) or into the conductor pipe (2).

In a modified embodiment of the invention, which honos the wish to exploit the pliability of the conductor pipe, the rubber layer (5) is made of a rubber type, which maintains its plasticity throughout the lifetime of the pipe such that it stays tight without cracks.

In another modified embodiment of the invention the rubber material is a non- hardening material.

Claims

1. District heating pipe (1) comprising a conductor pipe (2) of plastic material, a surrounding insulating material (4), and an outer protective casing (3), characterized by a diffusion barrier layer (5) of a rubber material being provided between the conductor pipe (2) and the insulating material (4).

2. District heating pipe according to claim 1 , characterized by the conductor pipe (2) substantially consisting of a PEX (cross-linked polyethylene) or PB (polybutyl) material.

3. District heating pipe according to claim 1 or 2, characterized by the diffusion barrier layer (5) substantially consisting of butyl rubber or latex.

4. District heating pipe according to any preceding claim, characterized by the rubber material (5) being sprayed onto the conductor pipe (2).

5. District heating pipe according any of the claims 1-3, characterized by the rubber material (5) consisting of a rubber film adhering to the surface of the conductor pipe (2).

6. District heating pipe according any of the claims 1-3, characterized by the rubber material (5) being co-extruded with the plastic conductor pipe (2).

7. District heating pipe according to any preceding claim, characterized by the rubber material (5) consisting of a non-hardening material.