Technical field

A method of installing detection means in the form of electric conductors at the laying of heat-insulated pipe lines for detecting penetration of moisture or liquid in the heat insulation through electric transition between the conductors, which are arranged at a distance from each other and substantially parallel with and electrically insulated from the pipe lines, at which the conductors are exposed for moisture or liquid penetrating through the heat insulation.

Background of the invention

For indication of the condition of heat insulated pipelines such as distant heating pipelines one usually uses two copper conductors placed in the insulation around the steel pipe. Indication of water penetration into the insulation from the ground or from leakage through the pipe is achieved through resistance measurement between the copper conductors and the pipe. With appropriate detection methods one can locate where the leakage is within a meter or so.

In one type of warning system the copper conductors are stret¬ ched from pipe end to pipe end between the inner steel pipe and the outer plastic pipe. The copper conductors are stret¬ ched before the insulation material (usually polyurethane ) is foamed about the steel pipe. When the steel pipe becomes warm and expands there is a risk that the copper conductors are stretched to breaking, as the temperature increase of the copper conductors is negligible because of the intermediate insulation .

In case the copper conducturs are not stretched, but a sag is

is permitted in order to reduce the effects at the thermal expansion. The conductors will have varying distances to the steel tube on one hand due to tue sag and on the other hand to the forces on the copper conductors caused leg the foaming.

Furthermore, when using polyurethane insulation a high density layer adjacent to the copper conductor is formed, which is very difficult for water to decompose. This leads to an un- acceptably high water transport along the pipe before the warning system is activated.

Warning registration is accomplished by sending an impulse along the copper conductor which is returned via a possible water leakage and the steel pipe. The time of the impulse can be converted to distance. If the conductor's distance to the steel pipe varies, which is often the case with this type of warning system, then the variations will cause interference on the instrument.

Another type of warning system consists of a band of polyure¬ thane which is taped to the steel pipe before the insulation is applied foamed about the pipe. The copper conductors are placed in grooves in the band. This system can hinder the polyurethane insulation's penetration and filling all volumes in and around the band, which is turn can result in very fast and extensive spread of dampness after possible leakage and by that no distinct indication.

A warning device is also known through SE-B-375.395 comprising a moisture detecting member in the form of a textile band, into which electrically conductive wires are woven and which are connected to an alarm member. The moisture detecting textile band is intended to be placed e.g. on the floor under a carpet , where there is a risk for submersion.

The purpose of the invention and its most important characteristics

The purpose of the present invention is to achieve a method of

the type mentioned above by which: a) a constant distance to the steel pipe is provided; b) the copper conductors are not exerted to tensile strain and by that neither can be exerted to fracture; c) embedding of the copper conductors in the foaming material will not change its moisture detecting properties ; d) a cheaper product is obtained as compared to the ones available on the market; e) a considerable saving of time is obtained at the install¬ ation of the warning system.

This has been achieved according to the invention by the fact that the electric conductors in their longitudinal direction are enclosed by a strip-shaped cover comprising two surface lagers of an electrically insulating material, at least one of which is liquid-absorbing and/or liquid soluble, that one surface layers are interconnected by an adhesive layer and that the cover, which on one outer side is provided with an adhesive coating ^" is adhesively pressed against the envelope surface of the pipe line, after which the heat insulation is applied.

Description of the drawings

The invention will be described in more detail in the follo¬ wing with reference to a pair of embodiments as shown on the attached drawing.

Figures 1 shows a schematic section through a heat insula¬ ted pipe equipped with the detection means according to the invention .

Figures 2-4 show on a larger scale sections through three different modified detection means according to the invention.

Description of the embodiments

According to the embodiment shown in figure 1 the inner pipe is a steel pipe 1 outside of which heat insulation 2 is

applied, for example polyurethane, and an outer plastic pipe 3.

Directly outside on the steel pipe are placed an electrically insulating tape 4 and a pair (or three when a signalling con¬ duit is to be used) of electric conductors 5, for example of copper, which are fixed on the electrically insulating tape 4 by a water soluble adhesive layer such as a water soluble tape 6. When water penetrates the water soluble tape 6 is dissolved and the warning system gives a signal.

In the embodiment shown in fig. 2 the electric conductors 5 are arranged in a strip-shaped cover comprising two surface layers 4 and 6 of an electrically insulating material and at least the layer 6 of a liquid-absorbing material such as a textile material e.g. cotton. The surface layers 4 and 6 are interconnected by bands of an adhesive layer 8 between and/or outside the electric conductors 5. The surface layer 4 is covered by «a protective film 10, which is removed when the device is to be applied to the pipe line 1.

The embodiment shown in fig. 3 differs from the one in fig. 2 by the fact that the adhesive layer 8 between the surface layers 4 and 6 also covers the electric conductors 5 at which it is provided with perforations 11 permitting liquid penetration in case the adhesive layer 8 is not liquid soluble. The adhesive layer 8 preferably consists of a so called hotmelt adhesive film, but could of course al^o consist of a water soluble material, at which no perforations 11 are needed .

In the embodiment shown in figure 4 an additional electric conductor 7 is embedded in the adhesive layer 9 , which conductor 7 is used as a zero conductor in cases where the pipe 1 is made of a material which is not electrically conductive, for example plastic. The surface of the zero conductor 7 facing the pipe 1 should be exposed, i.e. not covered by one adhesive layer 9.

The device according to the invention has a number of advantages :

a) It is easily applied directly on the inner pipe.

b) For warning measurements the resistance is constant because the resistance of the electrically insulating tape is con¬ stant .

c) Longitudinal transport of water is limited because the system has no cavities.

d) The water soluble or water-asorbing surface lager prevents build up of a high density layer of polyurethane on the copper conductors .

e) The risk of stretching the copper conductors is eliminated because their temperature follows the temperature of the pipe, which allows reduction of the area of the copper conductors.

Of course the invention- is not limited to the embodiments shown, but rater can be varied within the scope of the follo¬ wing claim.