WO1994029635A1 - A district heating pipe stretch and a method of establishing such a stretch - Google Patents

Abstract

Conventionally designed district heating pipes assembled from prefabricated heat insulated pipe elements (2, 4) are not well suited for being mounted in the underground by the so-called horizontal drilling technique, because the associated exterior sealing sleeves (16) arranged over the pipe element joints may be axially displaced if they meet with obstructions during their insertion through the subsoil bore. According to the invention, the conventional joints may still be used, if only the said sleeves, with reduced diameter, are mounted between narrowed ends (12) of the exterior mantle pipes (10) of the pipe elements (2, 4).

Description

A District Heating Pipe Stretch and a Method of Establishing such a Stretch.

The present invention relates to a subterranean district heating pipeline. Mostly, district heating pi¬ pes are mounted by laying in digged trenches, but in the field of cable and pipe laying there is increasingly used a so-called controlled horizontal drilling techni¬ que, by which a pipe is pushed or drawn into a bore through the subsoil, widely filling out the bore, such that e.g. in case of traffic load there will occur no sinking of the surface above the bore stretch.

It would be desirable to mount even district heat¬ ing pipes in this manner, but conventionally produced pipes are not well suited for such a mounting, because they are made from prefabricated pipe lengths which are joined and at the joints provided with surrounding seal¬ ing sleeves, the primary purpose of which is to provide a total seal against moisture intrusion in the insulati¬ on material, which is present between the interior con¬ ductor pipe or pipes and a surrounding mantle pipe of plastics. The sleeves are mounted about the interfacing ends of the mantle pipes at each joint, and normally they are made as crimping sleeves or welded plate wrap¬ pings of plastics, or as bolted together metal plate shells. When made conventionally, the sleeves are not suited to resist the mechanical axial displacement for¬ ces, to which they will be subjected by a laying in nar¬ row bores, where it is even desirable to mount the pipes by a relatively high insertion speed that may give rise to beat impacts on the sleeves.

According to the present invention, however, it has been found that it is in fact, as highly desirable, pos¬ sible to stick to the conventional joining techniques, including the conventional sleeves, viz. when use is made of mantle pipes shaped with narrowed end portions; it is then possible to apply sleeves of such a reduced diameter that they will not anyway be radially project¬ ing beyond the outer surface of the mantle pipes. More- over, even a strong mechanical axial anchoring of the sleeves will then be obtainable, if the ends of the sleeves abut the radial narrowing shoulders on the mant¬ le pipes.

In the following the invention is described in more detail with reference to the drawing, in which:-

Fig. 1 is a longitudinal sectional view of a pipe joint according to the invention, while

Fig. 2 is a corresponding view of an alternative embodiment.

In Fig. 1 is shown two district heating pipe ele¬ ments 2 and 4, which, in a conventional manner, comprise an inner conductor pipe 6, a surrounding insulation ma¬ terial 8 and an exterior mantle pipe 10. The ends of the conductor pipes 6 project from the ends of the surround¬ ing parts 8 and 10, and they are joined in a suitable manner, e.g. by welding or, if applicable, by some other and faster method.

Preparatory to the joining of the pipes 6 and pre¬ ferably during the production phase of the pipes the ends of the mantle pipes are prepared with narrowed outer portions 12, e.g. in that a reduction element 14 is welded to each pipe end. After the joining of the pipes 6 it will then be possible to conclude the joining work in a basically conventional manner, viz. in mount¬ ing a sleeve element 16 between and about the pipe end portions 12 and subsequently filling out the free space inside the sleeve with foam, or, respectively, by mount¬ ing an insulation material about the free ends of the pipes 6 and subsequently mounting the sleeve. When using a crimping sleeve, the same should from the beginning be large enough to be mountable in a 'ready position' on the outside of the thicker main portion of one of the pipes 2 or 4, as indicated at the top side of Fig. 1. In principle, the end portion 12 of the reduction element 14 may be long enough to hold the sleeve in its ready position, without the sleeve having to be thicker than the mantle pipe 10, but in that case the narrowed pipe length with its associated reduced heat insulation ef¬ fect will have to be lengthened noticeably.

It will be appreciated that the pipe joint thus produced will exhibit the advantage that the outside of the sleeve 16, despite the conventional design and mounting thereof, will not project beyond the outside of the mantle pipes 10, such that the joined pipes may then participate in an introduction through a narrow channel without any substantial axial influence may occur, and it can be advantageous, therefore, that the length of the narrowed end portions 12 of the mantle pipes be small enough to just accommodate the sleeve 16, inasfar as the sleeve in its mounted position will then be axi- ally stabilized between the opposed pipe shoulders at the roots of the narrowed portions 12. Optionally, the sleeve may be a sheet sleeve with semicylindrical shells that are joined at protruding edge flanges. In that case it may be tolerated that the edge flanges project beyond the periphery of the mantle pipes.

It has been found that under special circumstances there may be, anyhow, some problems in connection with the introduction of the pipes, if the sleeves 16 are made in a fully conventional manner. Such problems, however, may be counteracted quite effectively without changing the conventional character of the sleeve, viz. by adding, as shown in Fig. 2, an outer cover sleeve 18, which may be a crimping sleeve, which projects beyond the ends of the sealing sleeve 16, and which, itself, may be stabilized in the axial direction in being glued to the mantle pipe ends or in abutting the pipe shoul¬ ders at the roots of the narrowed pipe ends 12. Hereby a very efficient mechanical shielding of the sealing sleeve is achieved, but should it even be displaced a little, this would not be decisive for the efficiency of the inner sleeve 16. It could even be tolerated that the cover sleeve 18 itself has its exterior side located slightly outside the periphery of the mantle pipes.

Claims

C L A I M S :

1. A district heating pipeline made of joined, prefabricated pipe elements and preferably mounted in the ground by insertion into a drilled channel therein, said pipe elements at the joints being surrounded by joining sleeves sealingly bridging the gaps between adjacent ends of outer mantle pipes of the pipe ele¬ ments, characterized in that the surrounding joining sleeves are mounted on narrowed mantle pipe ends in such a manner that at their exterior sides they are flush with or located inside the outer periphery of the mantle pipes.

2. A pipeline according to claim 1, in which an outer cover sleeve is mounted over the joining sleeves, characterized in that also the cover sleeves are located at least partly countersunk relative to the periphery of the mantle pipes.

3. A pipeline according to claim 1, in which the joining sleeves at their ends abut the narrowing shoul¬ ders of the mantle pipes.

4. A pipe element for a pipeline according to claim 1, characterized in being provided with narrowed end portions of the mantle pipe.

5. A method of establishing a pipeline according to claim 1, characterized in that upon a preassembling of the pipeline the same is mounted in the ground by an introduction according to the horizontal drilling prin¬ ciple.