PIPELINE AND METHOD FOR MANUFACTURING A PIPELINE

Abstract: A method of manufacturing a pipeline (1) composed of several interconnected pipe sections (2). The pipe sections comprise an inner medium-holding pipe (4), a jacket pipe (5) surrounding the medium-holding pipe, and heat insulation (6) located between said pipes. In the area (7) between two neighbouring pipe sections (2) there is a joint (3). In this joint the medium-holding pipes (4) are joined together in sealing relationship at their opposing ends. The space (10) of the joint (3) around the joined-together medium-holding pipes (4) intermediate the free ends (8) of the jacket pipes (5) and the heat insulation (6) are covered by an enclosing sealing sleeve (11) and is filled with heat insulation (12) or reversely. Prior to covering and insulating the joint (3) or reversely, end protection means (13) are applied in the area of the free ends (8) of the jacket pipes (5) and the heat insulation (6). Each end protection means (13) firmly adheres to and sealingly abuts against both the heat insulation (6) of the associated pipe section (2) and the heat insulation (12) in the space (10). To increase the firm adherence, the end protection means (13), made from plastics, may be subjected to a surface treatment, such as a corona discharge treatment and/or a blazing treatment.

Description: Pipeline and method for manufacturing a pipeline TECHNICAL FIELD The present invention relates to a method of manufacturing a pipeline comprising several pipe sections, and to a pipeline of this kind. The pipeline sections are to be interconnected and each section comprises at least one inner medium-holding pipe, a jacket pipe surrounding the medium-holding pipe, and heat insulation located between the medium-holding and the jacket pipes. In the area between two neighbouring pipe sections to be interconnected there is . a joint into which the medium-holding pipe of each pipe section protrudes over a short distance away the free ends of the associated jacket pipes and heat insulation, respectively, and in which joint the opposed free ends of the medium-holding pipes are joined together in sealing relationship, the space of the joint around the joined- together medium-holding pipes intermediate the free ends of the jacket pipes and the heat insulation of the pipe sections being covered by an enclosing sealing sleeve and filled with heat insulation or reversely. Preferably but not necessarily, the pipeline sections are factory-made for particularly urban-district heating systems, in which case the medium-holding pipes may be made from a weldable material, preferably steel, and the jacket .pipe preferably from a plastics material, suitably a high-molecular ethylene plastics. The heat insulation between the medium-holding and the jacket pipes may consist of expanded urethane plastics. BACKGROUND OF THE INVENTION As a rule, the joining-together of the pipe sections in the joints is carried out when the pipe sections have been deposited in a dug-out trench, which is to be refilled once the joining operation is finished. Once the re-filling operations and any other restoration work, such as planning, asphalt surfacing and the like, are completed, the deposited pipeline is exposed to attacks from external moisture as well as to mechanical stress . To ensure long-term function of the pipeline it is of outmost importance that such moisture is prevented from coming into contact with the medium-holding pipes, since in the long run moisture will cause corrosion damage and, consequently, leakage. In turn, this leads to expensive operational interruptions and to repair work and injury hazards to the personnel. At a rough estimate, about one thousand cases of damage of this kind are reported yearly in Sweden, involving minimum costs of SEK 15,000 per damage. Despite careful execution of the joining-together work, water will sooner or later reach a considerable number of joints via the jacket-pipe joints. Once water has penetrated into the joint, the heat insulation between the jacket pipe and the medium-holding pipe is no serious bar against corrosive attacks on the medium- ' holding pipe. Water-penetration is, however, often discovered at a comparatively early stage thanks to the usually electronic alarm system installed in most pipelines, at least those intended form urban-district heating systems. OBJECT OF THE INVENTION The main object of the present invention is to reduce the risk that moisture spreads to the medium- holding pipe in case of water penetration. Another object of the invention is to reduce the risk mentioned above through simple and inexpensive measures. SUMMARY OF THE INVENTION These and other objects of the invention are efficiently achieved by means of the application, prior to covering and insulating the joint or reversely, of end protection means at the joint in the area of the free ends of the jacket pipes and the heat insulation of the pipe sections, such that each end protection means firmly adheres to and sealingly abuts against both the heat insulation of the associated pipe section and the heat insulation in the space of the joint. To reinforce the ability of the end protection means to firmly adhere to the different heat insulation means, said end protection means, which suitably are made from plastics and preferably from ethylene plastics, are subjected to a surface-treatment , e.g. a corona-discharge treatment and/or blazing. Alternatively or as a supplement the end protection means could be subjected to a surface treatment involving alteration of the surface geometry, e.g. a mechanical and/or cutting treatment. The object of all these kinds of treatments is to increase the adherence by "roughing", to coarsen the plastic surface of the protection means that is oily by nature. In addition, owing to the suggested adherence- enhancing surface treatments and/or machining treatments of the end protection means, the entire insulation (in the pipe sections and the joints) will behave like continuous and undivided insulation and thus prevent penetration of water/moisture to the medium-holding pipes . Because the end protection means are applied in position prior to the joining-together operation, suitably in conjunction with the factory-manufacture of the pipe sections, these end protection means will both cover and protect the heat insulation located between the medium-holding and the jacket pipes. For this reason, the short length of protrusion of each medium-holding pipe away from the free ends of the associated jacket pipe and heat insulation may be reduced further, down to a few centimetres, without causing any risks of excessive heat effects on the heat insulation as the medium-holding pipes are being joined together by means of welding or brazing using a naked flame. The arrangement contributes positively to minimising the space occupied by the joint. An additional advantage of factory-mounted end protection means is that the heat insulation between the medium-holding and the jacket pipes remains in dry condition during storage, transportation, and deposition at the work site prior to the interconnection of the pipe sections to form the pipeline. Similarly, the end-protection means, jointly with the jacket pipe, prevent gases, primarily carbon dioxide present in the closed cells of the expanded plastics that form the heat insulation, from escaping from the insulating material and into the surrounding atmosphere. Should such escape of diffusion of gases occur, it would cause the heat insulation to tend to shrink with consequential deterioration of its heat-insulation properties . In addition, there is a considerable advantage in that the end protection means and the jacket pipe jointly contain the gases inside the cells, since they create an excess pressure inside the cells and thereby further improve the sealing effect against and adherence to the end protection means. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in closer detail in the following with reference to the accompanying drawings illustrating a presently preferred embodiment. In the drawings : Fig 1 is a schematic and perspective view as seen obliquely from the front of a straight pipe section forming part of the pipeline in accordance with the invention and for the sake of clarity shown partly cut, Figs 2A and 2B are perspective and schematic views as seen obliquely from behind and from the front, respectively, of end protection means forming part of the pipeline in accordance with the invention, Fig 3 is a schematic and perspective view as seen obliquely from the front of a part of a pipeline prior to the joining-together, and of some of the components used to join-together two neighbouring pipe sections, Fig 4 is a schematic view as seen obliquely from the front of the part of pipeline in Fig 3 while being joined together having mounted end protection means and joined- together medium-holding pipes, and Fig 5 is a longitudinal sectional view of essentially the same pipeline part as shown in Figs 3 and 4 after completion of the joining-together operation. Fig 6 is a longitudinal sectional view essentially corresponding to Fig 5 but showing an alternative embodiment of the end protection means. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In the accompanying drawings is shown only a short part of a pipeline, generally designated by 1 and composed of several pipe sections 2. These pipe sections could be straight sections, as in the shown example, or be bent sections, T-sections, valves and the like, although these configurations are not shown herein. Irrespective of their configuration, the pipe sections 2 are to be interconnected at joints 3 to form a long pipeline intended particularly for urban-district heating systems and to be deposited in pipe trenches, not shown. As appears from Figs 1, 3, 4 and 5, the principal components of each pipe section 2 are at least one, usually one, two or four inner medium-holding pipes 4 of a preferably weldable/solderable material, preferably steel or copper, for transportation of a heating medium such as hot or superheated water or steam, in the case of urban-district heating systems, or a cooling medium or any other medium that is to be insulated from heat/cold while being transported in the pipeline 1. However, in principle there is nothing to prevent that the medium- holding pipe 4 be manufactured from some other suitable material, such as plastics, that lends itself to being joined-together with the aid of suitably configured interconnection means. Radially spaced from the medium-holding pipe(s) 4 of each pipe section 2 is disposed the second principal component of the pipe section, viz. an outer jacket 5, which encloses the medium-holding pipe 4 completely along practically the entire length thereof, as will be shown further on. Suitably, the jacket pipe 5 is made from a plastics material, preferably from a high-density ethylene plastics, PEHD. This material is stabilised with respect to thermal, chemical, and oxidising decomposition and other decomposition, and among other things it possesses high impact strength resistance and abrasive resistance also at low temperatures. Intermediate on the one hand the medium-holding pipe 4 and on the other the jacket pipe 5 is arranged the third component of the pipe section 2, viz. heat insulation 6, preferably consisting of a freon-free expanded urethane plastics possessing excellent heat- insulating properties, high mechanical strength and high ageing resistance. The pipe sections 2 including the medium-holding pipes 4, the jacket pipes 5 and the heat insulation 6 preferably are manufactured as assembled units in the factory, the heat insulation suitably being cast in place during the manufacture. Alternatively, the heat insulation 6 could be performed pipe insulations sections from the same material as the cast heat insulation or from some other material that is suitable for the purpose, such as glass wool or rockwool . Following their manufacture in the factory, the pipe sections 2 are transported for deposition in dug-out pipe trenches, not shown, wherein they are interconnected at the joints 3, see Figs 3, 4, and 5. Obviously, the joints 3 are located in the area 7 between two neighbouring pipe sections 2 to be interconnected. In each one of these joints 3 the medium-holding pipe 4 of each one of the pipe sections 2 protrudes over a short distance t from the free ends 8 of the associated jacket pipe 5 and heat insulation 6. As mentioned previously, in these joints 3 the opposing, free ends 9 of the medium-holding pipes 4 of the two pipe sections 2 are joined together in sealing relationship by means of welding, brazing or on any other way. Following the above-described joining-together of the medium-holding pipes 4 of the pipe sections 2, the still exposed, free space 10 of each joint 3 around these medium-holding pipes between the free ends 8 of the jacket pipes 5 and the heat insulation 6 of the pipe sections is covered by a sealing sleeve 11, see Figs 3 and 5. The sealing sleeve 11 could be made from the same or from similar material as the jacket pipe 5, i.e. from a plastic material, such as high density ethylene plastics. The sealing sleeve 11 is pushed onto the jacket pipe 5 of one of the pipe sections 2 prior to the joining-together of the medium-holding pipes 4 and is centred above the joint 3 after the j oining-together . Filler and ventilation bores, not shown in the drawings, are then drilled or otherwise made in the sealing sleeve 11. A required amount of a suitable expandable cellular plastics is then filled into the space 10 via the filler bores, by machine or manually, the cellular foam rising and expanding inside the space 10 so as to fill it completely, see Fig 5. The filler and ventilation bores are then sealed up. The expanded cellular plastics could be of the same type as the heat insulation 6 arranged between the medium-holding and jacket pipes 4 and 5, respectively and form a heat-insulating 12 in the space 10 in the joint 3, making the entire pipeline thermally insulated. Instead of the heat-insulation 12 made from expanded cellular urethane plastics it is possible to use preformed pipe insulation sections or the like, not shown, made from a suitable insulating material. The preformed sections are applied around the joined-together medium-holding pipes 4 in the space 10 before the sealing sleeve 11 is centred above the joint 3. Prior to the above steps of joining together the medium-hoiding pipes 4 of the pipe sections 2, covering the joint 3 with the sealing sleeve 11 and filling the space 10 with heat insulation 12, end protection means 13, see Figs 2A, 2B and 6, to be described in more detail in the following, are applied at the joint 3 in the area of the free ends 8 of the jacket pipes 5 and the heat insulation 6 of the pipe sections 2. Preferably, the end protection means 13 are manufactured from plastics, suitably ethylene plastics. If desired, the end protection means 13 preferably are applied already in conjunction with the factory- manufacture of the pipe sections 2 and thus they are so to speak part of the pipe sections as the latter are delivered to the site of use. In any case, the end protection means 13 must be applied/mounted prior to the interconnection of the medium-holding pipes 4 and the joining-together, ensuring that when positioned at the free ends 8 they are able once the joining-together operation is completed, to strongly adhere to and sealingly abut against both the heat insulation 6 of the associated pipe section 2 and the heat insulation 12 in the space 10 of the joint 3. In order to achieve or improve the strong adherence between each end protection means 13 and the heat insulations 6 and 12 on either side of the end-protection means, the end protection means 13 could and should, particularly when made from such a comparatively "oily" plastics material as ethylene plastics, be subjected to surface treatment or surface machining operations before being mounted on the pipe sections 2. Suitably, the surface treatment may consist of a corona discharge treatment, i.e. some type of spark machining treatment, or a blazing treatment, i.e. some type of naked- lame singeing, to which are subjected at least those faces, or parts thereof, of the end protection means 13 that are turned towards the heat insulation 6 and 12, so as to cause the oily ethylene plastics surface of the end protection means to "burn" and become rough in order to thus increase the adherence to the thermal insulations . Alternatively, or as a supplement, the surface treatment may consist of a mechanical or chemical alteration of the surface geometry of the end protection means, for instance in the form of channels, grooves, depressions, and so on, which also contributes to increasing the adherence to the thermal insulations 6 and 12. In purely practical terms, each end protection means 13 is formed with several through-holes the number of which corresponds to the number of medium-holding pipes 4 and any further alarm and/or communication pipes in each pipe section 2, in the present case shown in the drawing figures one hole 14. The hole has essentially the same shape and dimensions as part 15 of the medium-holding pipe 4 of the associated pipe section 2, which part protrudes a distance t into the joint space. In addition, in the embodiments shown and described herein with reference to Figs 2A, 2B and 6, each end protection means 13 has a periphery 16 that is adapted to and abut against the jacket pipe of the pipe section 2. More particularly, each end protection means 13 is formed around its periphery 16 with a peripheral flange 17 extending essentially perpendicularly to the end protection means and in parallel with the jacket pipe 5 in order to be essentially concentric with that pipe. In the embodiment shown, the flange 17 is designed for insertion into the jacket pipe 5 while sealingly abutting against the internal face of that pipe. However, there is nothing to prevent arranging the flange to be pushed onto the external face of the jacket pipe such that it sealingly abuts against the external pipe face. To complete the joining-together a contractable tape or the like 18 may as a further safety measure be applied around the ends of the sealing sleeve 11 so as to extend somewhat in over the jacket pipe 5 of the associated pipe section 2, thus preventing water/moisture from seeping into the joint 3 in the area of the interface between the sleeve and the jacket pipes. Fig 6 shows an alternative embodiment of the end protection means according to Figs 2A and 2B, which is distinguished from that embodiment principally therein that the web between the periphery 16 and the hole 14 is not straight but formed with a shoulder 20. Owing to the enlarged area provided by the provision of such a shoulder, additionally increased adherence to the heat insulations 6 and 12 interiorly and exteriorly of the end protection means 13 is achieved. In the case when the heat insulation 12 in the space 10 consists of preformed sections or the like, the shoulder 20 contributes to improving the sealing effect towards moisture penetration, since such preformed sections may be applied with their slots in staggered relationship. In addition, reversely the arrangement highly prevents heat dissipation from the medium-holding pipes 4 via the staggered slot with consequential smaller heat losses and protection against over-heating of the joint 3 itself, such that it is not, and particularly not the sealing sleeve 11 and the contractable tapes 18, damaged by the effects of heat . The invention should not be regarded as limited to the embodiments described above and illustrated in the accompanying drawings but could be modified in a number of various ways within the scope of protection as defined in the appended claims .

Claims: CLAIMS 1. A method of manufacturing a pipeline (1) comprising several pipe sections (2) , which are to be interconnected and each one of which comprises at least one inner medium-holding pipe (4) , a jacket pipe (5) surrounding the medium-holding pipe, and heat insulation (6) located between the medium-holding and the jacket pipes (4, 5), a joint (3) being arranged in the area (7) between two neighbouring pipe sections (2) to be interconnected, into which joint the medium-holding pipe (4) of each pipe section protrudes over a short distance (t) away the free ends (8) of the associated jacket pipes (5) and heat insulation (6) , respectively, and in which joint the opposed free ends (9) of the medium-holding pipes (4) are joined together in sealing relationship, the space (10) of the joint (3) around the joined- together medium-holding pipes (4) intermediate the free ends (8) of the jacket pipes (5) and the heat insulation (6) of the pipe sections being covered by an enclosing sealing sleeve (11) and filled with heat insulation (12) or reversely, c h a r a c t e r i s e d in that prior to covering and insulating the joint (3) or reversely, end protection means (13) are applied at the joint in the area of the free ends (8) of the jacket pipes (5) and the heat insulation (6) of the pipe sections (2) , such that each end protection means (13) firmly adheres to and sealingly abuts against both the heat insulation (6) of the associated pipe section (2) and the heat insulation (12) in the space (10) of the joint (3) . 2. A method as claimed in claim 1, wherein the end protection means (13) are subjected to a surface treatment and/or are treated in whole or in part in order to achieve the firm adherence to the heat insulation means (6, 12) . 3. A method as claimed in claim 1 and 2, wherein said end protection means (13) are made from plastics, preferably from ethylene plastics. 4. A method as claimed in any one of the preceding claims, wherein the surface treatment of the end protection means (13) is a corona-discharge treatment and/or a blazing treatment . 5. A method as claimed in any one of claims 1-3, wherein the surface treatment of the end protection means (13) involves alteration of the surface geometry. 6. A method as claimed in any one of the preceding claims, wherein the pipe sections (2) are factory made and the end protection means (13) are applied in conjunction with the manufacture of the pipe sections. 7. A pipe line (1) consisting of several pipe sections (2) , which are to be interconnected and each one of which comprises at least one inner medium-holding pipe (4), a jacket pipe (5) surrounding the medium-holding pipe, and heat insulation (6) located between the medium- holding and the jacket pipes (4, 5), a joint (3) being arranged in the area (7) between two neighbouring pipe sections (2) to be interconnected, into which joint the medium-holding pipe (4) of each pipe section protrudes over a short distance (t) away the free ends (8) of the associated jacket pipes (5) and heat insulation (6) , respectively, and in which joint the opposed free ends (9) of the medium-holding pipes (4) are joined together in sealing relationship, the space (10) of the joint (3) around the joined-together medium-holding pipes (4) intermediate the free ends (8) of the jacket pipes (5) and the heat insulation (6) of the pipe sections being enclosed by a sealing sleeve (11) and filled with heat insulation (12) , c h a r a c t e r i s e d in that end protection means (13) are applied at the joint (3) in the area of the free ends (8) of the jacket pipes (5) and the heat insulation (6) of the pipe sections (2) , such that said end protection means (13) firmly adhere to and sealingly abut against both the heat insulation (6) of the associated pipe section (2) and the heat insulation (12) in the space (10) of the joint (3) . 8. A pipeline as claimed in claim 7, wherein the end protection means (13) are formed with at least one through-hole (14) of essentially the same shape and dimensions as that part (15) of the medium-holding pipe (2) of the associated pipe section (2) that protrudes over the short distance (t) . 9. A pipeline as claimed in claim 7 or 8, wherein the end protection means (13) have a periphery (16) adapted to and thus in contact with the jacket pipe (5) of the associated pipe section (2) . 10. A pipeline as claimed in claim 9, wherein the end protection means (13) are formed at their periphery (16) with a peripheral flange (17) , which is essentially concentric with the jacket pipe (5) and which is arranged to be inserted into or pushed onto the jacket pipe while sealingly abutting against the internal face or the external face, respectively, of said jacket pipe.

Inventors: JOHANSSON GOERAN, LJUNGGREN LARS, JOHANSSON, GOERAN, LJUNGGREN, LARS
Applicants: JOHANSSON GOERAN, LJUNGGREN LARS, POWERPIPE SYSTEMS AB, JOHANSSON, GOERAN, LJUNGGREN, LARS
Application year: 2001
Main classification: F16L59
IPC codes: F16L59