Abstract:
This invention relates to a shrink sleeve ( 300 ) for joining the casing of two insulated pipes lying end-to-end, where the shrink sleeve ( 300 ) has a tubular shape comprising a first polymer-based material ( 320 ) susceptible to irradiation. The tubular shape of the shrink sleeve ( 300 ) consists of the first polymer-based material ( 320 ) and a second polymer-based material ( 322 ), where the second polymer-based material ( 322 ) is resistant to the irradiation. Further, the second polymer-based material ( 322 ) can be weldable.

Description:
FIELD OF THE INVENTION 
       [0001]    In the industry of district heating/cooling it is known to install and assemble pipelines by joining insulated pipes. In its most basic embodiment, the insulated pipe comprises an inner pipe, surrounded by a layer of insulation material, which again is covered by a casing. The inner pipe and the casing can be made of polymer-based materials and metals. Typically, the insulation pipes are though embodied with an inner pipe of metal, a closed-cell and/or solid thermal insulation layer and a polymer-based casing. 
         [0002]    The insulated pipes are manufactured in required lengths that enable transportation. The insulated pipes are manufactured such that the length of the inner pipe exceeds the length of the insulation layer and the casing. Thus at the end of the insulated pipe, the inner pipe protrudes relative to the insulation layer and the casing. At the installation site the insulated pipes are joined end-to-end, first by joining the inner pipes of the two insulated pipes lying end-to-end. Prior to welding the inner pipes, a shrink sleeve is drawn or pushed over the casing of one of the insulated pipes to be joined. After welding of the inner pipes, the shrink sleeve is moved so that it rests on the casing of the two insulated pipes. The ends of the shrink sleeve are subsequently shrunk impermeably onto the two casings of the two insulated pipes. This shrinking process is normally done by exposing the ends of the shrink sleeve to heat. Through a hole in the shrink sleeve, insulation material can be led into the cavity between the joined inner pipes and the sleeve. Through a second hole in the shrink sleeve a valve can be inserted. This valve will typically be embodied as an air valve. Hereby the joined inner pipes are insulated. The wall holes are hereafter to be impermeably closed. The impermeable closure of the wall holes is central to the functionality of the entire pipeline, as primarily the longitudinal movements of an installed pipeline can loosen or detach the plugs from the sleeve. Today it is known to weld or patch a plug onto an area in proximity to the holes. 
         [0003]    In the prior art the sleeve is a hollow shell with a tubular shape. The sleeve is normally made of polymer-based material, which after manufacturing is exposed to irradiation such as an e-beam (electron beam). After such a treatment for example polyethylene is denoted PEX or PE-Xc. The sleeve is hereby cross-linked, meaning that the polymer fibers of the material will change direction and link to other layers (molecule chains). As an effect of this treatment, the polymer-based material obtains a high mechanical strength and a high temperature resistivity. Prior to irradiation, the sleeve is normally manufactured in such a way that the diameter in the ends is smaller than the diameter of the center section there between. The sleeve can, however, also have the same diameter along the entire length of the sleeve. After irradiation, the ends of the sleeve are heated and the diameter of these is extended, such that the diameter here will be equal to or greater than the diameter of the central section. The sleeve can after irradiation also be heated and extended such that the sleeve has the same diameter along its entire length. As described, the sleeve is fastened to the casing of the two insulated pipes by heating the ends, whereby the material here will try to reach its initial size. Hence, the material in the ends shrinks as a result of the heating thereof. The casing of the two pipes will though prevent it from reaching the initial diameter, however, the sleeve will be firmly fastened to the casing of the two insulated pipes. This effect is a result of the cross linking of the material and the following extension of the diameter in the ends of the sleeve. Since the wall hole(s) of the sleeve will have to be impermeably closed or sealed off (plugged) after filling with or injecting the insulation material, the material around the wall hole cannot be fully cross-linked, as the cross-linked material has a high temperature resistivity. The process of closing the wall hole by welding a plug onto the sleeve does therefore simply not harmonize with the temperature resistivity of the sleeve material. Consequently, the welding process would be very difficult to perform, if not impossible. Hence, the cross linked material cannot melt sufficiently and thereby a complete integration with the sleeve material is not obtained, which is essential to a successful sealing of the wall hole using a welding process. 
         [0004]    It is known to solve this problem by mounting or clamping for example protective metal discs onto the wall material proximate to the wall hole. When the sleeve is exposed to irradiation, the wall material covered by the metal discs will only to a limited extent be exposed to irradiation and thereby not be completely cross linked. Hereby the material proximate to the wall hole becomes weldable in that the material has a lower temperature resistivity than the rest of the sleeve. The weldable properties of the material in proximity to the wall holes are, however, not sufficient to obtain the required welding quality and material integration. Further, the manufacturing process of mounting and dismounting the metal discs is a very time-consuming manual process, as for example one counterpart of the discs must be inserted through an end of the sleeve which at that time has a very small diameter. Consequently, this manual process contributes to very high manufacturing costs 
         [0005]    In an attempt to enhance weldability of the sleeve material in proximity to the holes, US 2001/0041235 discloses a heat shrinkable member for forming a connection between tubular sections. The member comprises a tubular section which is cross-linked. In order to be able to close the wall holes of the member, an uncross-linked or less uncrossed-linked patch is bonded to the central section of the member. A wall hole for injection of insulation material is drilled through the patch and the cross-linked material. When the wall hole is to be closed, the plug is bonded to the patch. The patch can be attached to both inside and outside of the heat shrinkable member by fusion bonding or welding or by using of a conventional adhesive agent. The patch can be attached to the heat shrinkable member before or after the whole member is exposed to irradiation. Although the welding properties might be improved by this type of shrinkable member, the manufacturing cost associated with attaching the patches is essentially undesired. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention relates to a shrink sleeve for joining the casing of two insulated pipes lying end-to-end, where the shrink sleeve has a tubular shape made of a first polymer-based material susceptible to irradiation. The tubular shape of the shrink sleeve consists of the first polymer-based material and a second polymer-based material, where the second polymer-based material is more resistant to irradiation than the first material. Further, the second polymer-based material can be weldable. In another embodiment the outer surface and/or the inner surface of the shrink sleeve are/is continuous. The shrink sleeve is advantageous in that it consists both of a material susceptible to irradiation and one resistant to irradiation in the same tubular shape. Hereby the shrink sleeve can be irradiated without changing its tubular shape or adding any parts, such as protective metal discs, prior to that treatment. In addition, the second polymer-based material of the shrink sleeve is weldable without jeopardizing the geometry of its tubular shape. The tubular shape of the shrink sleeve is essential to obtain a uniform isolation of the pipeline where shrink sleeves are placed. In addition, the continuous inner and/or outer surfaces of the shrink sleeve will enable a pipeline to extend longitudinally. 
         [0007]    In another embodiment of the shrink sleeve of the present invention, the second polymer-based material is placed in at least one delimited area of the shrink sleeve. The delimited area can be surrounded by the first polymer-based material, extend in the whole circumference of the shrink sleeve and/or extend in a part of the circumference of the shrink sleeve. The at least one delimited area of the second polymer-based material can also be approximately circular. Further, the second polymer-based material can be transparent or have a different color. Hereby a large degree of freedom is obtained in that wall holes can be placed where required. A transparent second polymer-based material enables inspection of for example the expansion process of liquid insulation material injected into the shrink sleeve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    In the following, the invention will be described referring to the figures, where 
           [0009]      FIG. 1  illustrates an insulated pipe of the prior art; 
           [0010]      FIGS. 2   a  and  2   b  illustrate a shrink sleeve of the prior art; 
           [0011]      FIG. 3  illustrates a shrink sleeve according to a first embodiment of the present invention; 
           [0012]      FIG. 4  illustrates a shrink sleeve according to a second embodiment of the present invention; 
           [0013]      FIGS. 5   a  and  5   b  illustrate a shrink sleeve according to a third and fourth embodiment of the present invention; 
           [0014]      FIG. 6  illustrates the cross-section of the shrink sleeve depicted in  FIG. 3 ; 
           [0015]      FIGS. 7   a  and  7   b  illustrate two different cross sections of two different embodiments of the shrink sleeve of the present invention, and 
           [0016]      FIG. 8  illustrates yet another embodiment of the shrink sleeve of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0017]      FIG. 1  illustrates an insulated pipe  100  known in the art, comprising an inner pipe  101  surrounded by a layer of insulation material  103 , which again is covered by a casing  102 . The inner pipe  101  and the casing  102  can be made of polymer-based materials and metals. In the context of the present invention, the insulated pipe  100  is embodied with an inner pipe  101  of metal or polymer, a closed-cell and/or solid thermal insulation layer  103  and a polymer-based casing  102 . 
         [0018]      FIG. 2   a - b  illustrate a shrink sleeve  200  of the prior art, where  FIG. 2   a  illustrates the shrink sleeve  200 , where the ends  205  of the shrink sleeve have not yet been expanded, and  FIG. 2   b  illustrates the shrink sleeve  200  after expansion of the ends  205 . The shrink sleeve  200  comprises two wall holes  210 . The shrink sleeve  200  is made of one material susceptible to irradiation. Prior to exposing the shrink sleeve  200  to irradiation, the wall material in proximity to the two wall holes  210  has been clamped with metal discs (not shown). The wall material covered by the metal discs will be exposed less to irradiation, than the rest of the shrink sleeve. Thereby the material in these less exposed areas is less cross-bonded compared to the remaining part of the shrink sleeve  200 . Although the material in proximity to the wall holes  210  has been less cross-bonded. The material in the area which has been less crosslinked is more suitable forwelding. Generally welding properties of the material are reduced as crosslinking is increased. After exposure to irradiation, the ends  205  of the shrink sleeve  200  are expanded, see  FIG. 2   b.    
         [0019]      FIG. 3   a  illustrates a shrink sleeve  300  according to a first embodiment of the present invention. The shrink sleeve  300  comprises a first polymer-based material  320  susceptible to irradiation and a second polymer-based material  322  more resistant to irradiation reducing the amount of cross binding significantly. After irradiation only the second polymer-based material  322  will be fully weldable. After irradiation, the diameter of the ends of shrink sleeve  300  has been expanded, see  FIG. 3   b . When joining the polymer-based casing  102  of the two insulated pipes  100 , the ends of the shrink sleeve  300  will be fully shrinkable, as the material here has been fully cross-bonded and subsequently expanded. In addition, the cavity between the joined inner pipes  101  and the shrink sleeve  300  can be filled or injected with e.g. expanding insulation material through wall holes positioned in the second polymer-based material  322 . Hereafter these wall holes can be plugged and closed impermeably by welding. The quality of that welding will with this embodiment not be jeopardized by the poor welding properties (high temperature resistivity) of the material in proximity to the wall holes as known in the prior art. 
         [0020]      FIG. 4  illustrates a shrink sleeve  400  according to a second embodiment of the present invention. In this embodiment the second polymer-based material  422  resistant to irradiation covers the whole circumference of the shrink sleeve  400 . 
         [0021]      FIGS. 5   a  and  5   b  illustrate a shrink sleeve  500  according to a third and fourth embodiment of the present invention. In this embodiment the second polymer-based material  522  resistant to irradiation covers an elongated area relative to the longitudinal axis of the shrink sleeve  500 . 
         [0022]      FIG. 6  illustrates the cross-section of the shrink sleeve  300  depicted in  FIG. 3 . As depicted, the outer surface of the shrink sleeve  300  is continuous. 
         [0023]      FIGS. 7   a  and  7   b  illustrate two different cross sections of two different embodiments of the shrink sleeve  700  of the present invention. In  FIG. 7   a  the shrink sleeve  700  has two areas with a second polymer-based material  722  being more resistant to irradiation than the rest of the shrink sleeve. In  FIG. 7   b  the second polymer-based material  722  being more resistant to irradiation faces only the outer surface of the shrink sleeve  700 . Thus, the inner wall of the shrink sleeve  700  is constituted only by the first polymer-based material  720  being more susceptible to irradiation. 
         [0024]      FIG. 8  illustrates another embodiment of the shrink sleeve  800  of the present invention. The shrink sleeve  800  consists of a first polymer-based material  820  susceptible to irradiation and a second polymer-based material  822  resistant to irradiation. 
         [0025]    The shrink sleeve  300 ,  400 ,  500 ,  700 ,  800  could be manufactured by a two-component blow or injection molding process. These manufacturing processes could also be combined with an in-mould technique, such that the second polymer-based material  322 ,  422 ,  522 ,  722 ,  822  is inserted in the molding tool prior to injecting or leading the first polymer-based material  320 ,  420 ,  520 ,  720 ,  820  into the tool. The wall holes in the shrink sleeve can be varied both in terms of numbers and in terms of their position on the shrink sleeve.