METHOD AND APPARATUS FOR FITTING AN INNER TUBE IN AN EXISTING PIPELINE WHILE CONTINUOUSLY SUPPLYING HEAT, AND A PIPELINE OBTAINED IN THIS WAY

Abstract: Lining of a pipeline (1) by stretching therein a plastic inner tube (2) by means of a recirculating medium maintained at stretching temperature. An apparatus for stretching the inner tube (2) comprises pressure raising means (14) for a conveyed medium, medium heating means (3) for maintaining the medium continuously at stretching temperature, and a recirculation pipe (9, 22, 23, 24).

Description: Method and apparatus for fitting an inner tube in an exist¬ ing pipeline while continuously supplying heat, and a pipeline obtained in this way The invention relates to a method for fitting a close-fitting inner tube against the inside wall of an existing pipeline by introducing an inner tube of thermoplastic plastic with a smaller external diameter than the internal diameter of the pipeline, followed by radial stretching of the inner tube until the outside wall of the inner tube rests against the inside wall of the pipeline, using heat by means of a hot medium, and using internal pressure, and cooling down under internal pressure. Such a method for the protection of an existing pipeline from erosion, corrosion and deposits of solids on the surface, and for making walls of such a pipeline impervious, is described in the PCT Application PCT/NL92/00038, which is not a prior publication. In this application an inner tube is introduced into a pipeline, following which a hot medium, such as steam, is fed through the inner tube until the latter is heated sufficiently. Hereafter, one of the two ends of the pipeline is shut off, and compressed air is admitted at the other end, so that the inner tube is stretched until it rests against the inside of the pipeline. However, the pipelines in which the inner tubes are situated can be very cold, such as pipelines lying in the groundwater. This coldness of the pipelines will lead to rapid cooling down of the heated-up inner tubes when the supply of hot medium ' is stopped in order to admit compressed air. Since a cooled-down inner tube is impossible or just difficult to stretch, only the warmest parts, which are generally situated close to the inlet opening at the end of the inner tube, are stretched. Accordingly, in this case it is not readily possible to provide the pipeline with an internal lining layer over the entire axial length. The object of the present invention is to obviate this disadvantage and to provide a method in which cold pipelines can also be lined with a stretched inner tube, irrespective of their length. This object is achieved according to the present invention in that the heat and internal pressure are supplied by the same medium and in that there is a continuous supply of heat to the medium during the radial stretching of the inner tube, in order to bring the temperature of the inner tube to stretching temperature over the entire axial length to be stretched. By not stopping the supply of hot medium at stretching temperature during the stretching, all parts of the inner tube are heated sufficiently - even under the influence of the coldness of the pipeline - for efficient stretching thereof. The entire axial length of the inner tube to be stretched is understood to mean at least the length along which the inner tube has to be brought into contact with the pipeline. In particular, the medium used for stretching the inner tube is recirculated while raising the temperature of the medium after it has passed through the inner tube, and before it is returned to the inner tube, to the temperature required for the stretching. When the medium flows into the inner tube at a certain raised temperature, by the method according to the present invention, cooling off will cause the medium to be at a lower temperature when it flows out of said inner tube. This temperature difference can go up to about 10°C, depending on the coldness and the length of the pipeline, so long as the inner tube is not resting against the pipe¬ line. By now making a medium flow constantly through the inner tube, even during the stretching, at a temperature which is higher than or equal to the required stretching temperature, it is ensured that the inner tube over the entire axial length is at a temperature at which stretching can take place. As soon as the inner tube rests against the cold pipeline, the medium will be cooled down more strongly, for example 15° or more. The thin stretched inner tube in fact gives virtually no insulation, so that the cold pipeline causes very strong cooling. As long as the inner tube is at a distance from the pipeline, said effect is much less. Of course, said temperature differences depend strongly on the thickness of the diameter and materials of the pipeline and inner tube, as well as on the ambient temperature of the pipeline. Preferably, the medium is hot water. Advantageoulsy, the inner tube is made of a thermoplastic polyester, preferably polyethylene tereph- thalate. In the case of a pipeline of polyethylene tereph- thalate to be stretched, having a length of 10 m, the temperature of the medium at the inflow into the inner tube is advantageously just under 100°C, preferably 95°C, a temperature at which stretching can take place. The temperature will then be 85°C after passing through the inner tube, which is just high enough to make the inner tube stretch. In particular, gas discharge-promoting means are fitted between the inside of the pipeline and the outside of the inner tube, for the discharge of gases present here. These gas discharge-promoting means may be in the form of thread-type elements extruded on the inner tube. When the inner tube is radially stretched, air which is present can escape through these elements. For the discharge of gases which are present here, the space between the inside of the pipeline and the outside of the inner tube is de-aerated by means of an underpressure, prior to and/or during the radial stretching of the inner tube. When an underpressure is used, the inner tube can be stretched more easily, since during the stretching less counterpressure is experienced and, moreover, the inner tube can make good contact against the inside wall of the pipeline. Preferably, the cooling down under internal pressure takes place by conveying compressed air through the radially stretched inner tube. It is particularly advantageous if the ratio of the external diameter of the inner tube to the internal diameter of the pipeline before the radial " stretching is less than 0.6 and greater than 0.2, and it preferably is between 0.52 and 0.56. When an inner tube of the type described above is used, one can work with an inner tube which is easily introduced into an existing pipeline, and which is subsequently pressed against the inside wall of the pipeline by means of a pressure medium. In order to simplify the introduction of the inner tube, it is also possible to press it to a greater or lesser extent into an oval or flat shape. This has great advantages for storing the inner tube on a reel, since it means that more tube can be wound up a reel and the forces are not so great during the reeling. The radially stretched inner tube is in particular resistant to external pressure of more than 1 bar. The method according to the present invention has advantages in particular for the lining of existing pipelines comprising 'material which can be released into a medium being conveyed through said pipeline. This applies in particular to lead water pipelines which are still mechanically in good condition, but have the drawback of the undesirable release of lead into the drinking water. In the case of service pipes in particular, namely from the main pipeline to the private property or the user's water meter, it is very difficult to dig up these pipes, since this generally leads to serious damage to the footpath, plants and the paving. With the use of the abovementioned thin-walled inner tube, this inner covering is mainly only a sort of lining of the inside wall of the existing pipeline and generally makes little or no contribution to the mechanical strength of the pipeline. The stretching does take advan¬ tage of the improved physical properties, for example the resistance to stress corrosion. Of course, it is also possible to use the method in pipes with mechanical defects, such as leaky connections, steel pipes affected by corrosion and sewers etc. In that case an inner tube of greater wall thickness must be used, so that after stretching the inner tube can withstand the full internal pressure of the medium being conveyed through the pipeline or external loads, such as ground and traffic loads. In this case optimum use is made of the mechanical properties of the material of the inner tube, which are greatly improved by the stretching. It is pointed out that it is known that many physical and mechanical properties of tubes made of thermoplastic materials are considerably improved by stretching, but such methods serve only in industrial circumstances for making stretched tubes in accurately controlled conditions, and not for the lining of existing pipelines. The invention also relates to an apparatus according to the introductory part of claim 11. In such a known apparatus, a hot medium is first conveyed into the inner tube, in order to increase the temperature of the inner tube. The medium supply is then stopped, and the pressure is raised in order to stretch the inner tube. However, if the pipeline is cold, the medium in the inner tube will cool down very strongly and rapidly, with the result that only a short axial length of the inner tube can be radially stretched, and the remaining length can no longer be stretched because the stretching temperature has not been reached. These drawbacks are cancelled out with the use of the measures according to the characterizing part of claim 11. With the use of such an apparatus, the heat and internal pressure for the stretching of the inner tube are supplied by means of the same medium, and said medium is also maintained at stretching temperature during the stretching of the inner tube. In particular, the measures according to the characterizing part of claim 12 are used. The last-mentioned measures make it possible to circulate a heated medium through the apparatus under raised pressure, in which after passing through the inner tube the medium is reheated to the required stretching temperature, so that the entire axial length of the inner tube is brought to stretching temperature. By raising the pressure, which is supplied by the same medium, the inner tube can be stretched over the entire axial length at stretching temperature. The pressure-raising means in particular comprise a pressure regulating valve. In a suitable embodiment, a return pipe connects the recirculation pipe after the medium heating means to the recirculation pipe for said medium heating means, preferably to the medium storage tank. Medium can then flow out of the medium stqrage tank by means of the medium conveyance element to the medium heating means and back again to the medium storage tank, as a result of which said medium is brought to the desired temperature. In an advantageous embodiment, the cooling means can force a gas under raised pressure through the inner tube, and a cooling medium outlet is provided, preferably on the medium storage tank. After the inner tube has been radially stretched, compressed air is conveyed through the inner tube, which compressed air can then escape from the apparatus through the cooling medium outlet. Cooling with cold water is, of course, also possible. Advantageously, a gas suction element which can be connected to the space present between an inner tube and an existing pipeline, and which provides for an easy escape of air present between the outside of the inner tube and the inside of the pipeline during the stretching of the inner tube, and for lowering of the counter pressure during stretching, is present. A control element can be present for controlling valves and flow regulating element. The invention will now be explained in greater detail by means of the appended drawing, in which: Fig. 1 shows a cross-section of an existing underground pipeline, in which an unexpanded inner tube is present; Fig. 2 shows a similar pipeline in which the inner tube is only partially expanded; Fig. 3 shows a cross-section of the pipeline according to Fig. 2 , with fully expanded inner tube; and Fig. 4 shows an apparatus for application of the method according to the invention. Fig. 1 shows an existing underground lead pipeline 1, e.g. lying 1 m below a road surface 27. Said pipeline 1 may be situated underground in the groundwater and may therefore be relatively cold. An inner tube 2 of thermoplastic plastic, in this case polyethylene tereph- thalate, is provided over the entire axial length of the pipeline 1. In the space 17 between the inside wall l 1 of the pipeline 1 and the outside wall 2a of the inner tube 2 gas discharge-promoting means in the form of ribs 3, which are formed directly on the outside wall 2a of the inner tube 2 during the extrusion of the inner tube 2, are present. Fig. 2 shows the inner tube 2 after stretching achieved by first heating it with hot water, supplied in the direction of arrow 28, then stopping the supply of hot water, and thereafter raising the pressure. However, because of the cold groundwater in zone A, heat loss from supplied hot medium means that the inner tube is not heated to the stretching temperature over its entire length. Consequently the inner tube over the length of zone A, unlike the preceding part of the inner tube, cannot be fully stretched. A solution to this problem is provided by supplying heat and internal pressure by means of the same medium, hot water, and also supplying continuously heat to the medium during the radial stretching of the inner tube, in order to bring the temperature in the inner tube over the entire axial length to stretching temperature during the stretching. This produces a pipeline 1 which is lined over its entire length on its inside wall l 1 with a stretched inner tube 2• , as shown in Fig. 3. An apparatus of the type shown in Fig. 4 can be used for this purpose. This apparatus comprises a medium storage tank 10, for receiving a heated medium, such as hot water, which is pumped by means of a pump 11 through medium heating means 3. The medium heating means heat the medium to a predetermined temperature. Pressure and temperature are checked by meter 4. The water can flow back out of the medium heating means 3 through return pipe 16 to the medium storage tank 10 when the flow regulating valve 5 is open. Medium storage tank 10, pump 11 and medium heating means 3 can be connected by means of connector 15 to the recirculation pipe 9, 22, 23, 24, which pipe comprises a medium inlet 20 which can be connected to an inner tube 2, as well as a medium outlet 21. A gas discharge element 18 can also be connected to the space 17 between an inner tube 2 and an existing pipeline 1. The flowrates through the recirculation pipe 9, 22, 23, 24 and through the return pipe 16 are regulated by means of flow regulating valve 5. Meter 12 measures the temperature and the pressure of the medium which has passed through the inner tube. The medium can be guided by means of shut-off element 13 through a bypass 26 which can be connected to the recirculation pipe and contains a pressure regulating valve 14, which together with pump 11 forms pressure-raising means. It will be clear that the pressure regulating valve 14 can also be placed directly in the recirculation pipe part 22, and bypass 26 need not be used. By means of three-way valve 6, gas under raised pressure from compressor 8 can be forced by way of an air tank 7 through the stretched inner tube 2 ' and cooled in the process. Medium storage tank 10 is provided with a compressed air outlet 19. Flow regulating element 5 and the shut-off valves 6 and 13 can be controlled by control element 25. The method for stretching an inner tube is as follows. An inner tube 2, situated in an underground pipeline 1, is connected to the apparatus by means of the medium inlet 20 and medium outlet 21, which can be connected to the inner tube 2. Since in the case of larger diameters of the pipeline, such as 75 mm, air extraction by means of ribs 3 is not always guaranteed, the apparatus suitably comprises a gas suction element 18, which is connected to the space 17 between the inner tube 2 and the pipeline 1. Hot water is circulated by pump 11 from medium storage tank 10 through return pipe 16 and through the medium heating means 3 until it has reached a temperature at which the inner tube can be stretched, suitably a tem¬ perature of just below 100°C, preferably 96°C for a polyethylene terephthalate inner tube 2 with a length of 10 m. Flow regulating valve 5 is then set in such a way that when connector 15 is opened a suitable flow of the medium can pass through the inner tube 2 via recirculation pipe 9, 22, 23, 24. The measured overpressure is virtually zero at the position of meter 12. When the temperature of the water after passing the inner tube, measured with meter 12, is approximately 85°C, valve 13 is closed and the hot water is conveyed through bypass 24 with pressure regulating valve 14 disposed therein. Pump 11, together with pressure regulating valve 14, raises the pressure of the water, and thus the pressure in the inner tube 2, while the medium heating means 3 reheat this water coming out of the inner tube to 95°C, with the result that the inner tube can be stretched properly over its entire axial length. During the pressure increase the medium conveyance is maintained, so that a temperature which is raised for stretching is constantly maintained in the inner tube. The pressure raising means 14 can provide a pressure of 4 to 5.5 bar of this hot water. During the stretching of the inner tube 2, air present in the space between the outside wall 2a of the inner tube 2 and the inside wall 1' of the pipeline 1 is extracted by means of gas suction element 18. As soon as the inner tube rests against the cold pipeline, a particularly strong cooling of the throughflowing hot water occurs, and its temperature falls to 80° at outlet 21. When the inner tube 2 is fully stretched and rests against the inside wall 1' of the pipeline 1, valve 5 is again set in such a way that the hot water flows from the medium heating means 3 by way of return pipe 16 to the medium storage tank 10. No further medium then flows through the recirculation pipe. Valve 13 is then also opened. Thereafter, three-way valve 6 is opened, in order to blow compressed air as a cooling medium through the inner tube 2. Said compressed air can escape from the apparatus through cooling medium outlet 19 on storage tank 10. The valves 6 and 13 as well as flow regulating valve 5 can be controlled by means of control element 25, which receives information from meters 4 and 12.

Claims: CLAIMS 1. Method for fitting a close-fitting inner tube against the inside wall of an existing pipeline by introducing an inner tube of thermoplastic plastic with a smaller external diameter than the internal diameter of the pipeline, followed by radial stretching of the inner tube until the outside wall of the inner tube rests against the inside wall of the pipeline, using heat by means of a hot medium, and using internal pressure, and cooling down under internal pressure, characterized in that the heat and internal pressure are supplied by the same medium and in that there is a continuous supply of heat to the medium during the radial stretching of the inner tube, in order to bring the temperature in the inner tube to stretching temperature over the entire axial length to be stretched. 2. Method according to claim 1, characterized in that the medium used for stretching the inner tube is recirculated while raising the temperature of the medium after it has passed through the inner tube, and before it is returned to the inner tube, to the temperature required for the stretching. 3. Method according to claims 1 and 2, characterized in that the medium is hot water. 4. Method according to one or more of claims 1 - 3, characterized in that the inner tube is made of a thermoplastic polyester, preferably polyethylene tereph- thalate. 5. Method according to claim 4, characterized in that the temperature of the medium during its inflow into the inner tube is at least 95°C. 6. Method according to one or more of the preceding claims, characterized in that gas discharge-promoting means are fitted between the inside of the pipeline and the outside of the inner tube. 7. Method according to one or more of the preceding claims, characterized in that the space between the inside of the pipeline and the outside of the inner tube is de-aerated by means of an underpressure, at least during the radial stretching of the inner tube. 8. Method according to claims 1 - 4, characterized in that the cooling down under internal pressure is achieved by conveying compressed air through the radially stretched inner tube. 9. Method according to one or more of claims 1 - 8, characterized in that the radially stretched inner tube has a wall thickness which is resistant to an external pressure of more than 1 bar. 10. Method according to one or more of the preceding claims, characterized in that the existing pipeline comprises material, in particular lead, which can be released to a medium conveyed through said pipeline. 11. Apparatus for fitting a close-fitting inner tube (2') against the inside wall (l 1 ) of an existing pipeline (1) by means of stretching of an inner tube (2) made of thermoplastic material using a heated medium and under pressure, and subsequent cooling down of the inner tube (2•) , comprising a medium storage tank (10) for receiving a heated medium; - a medium inlet (20) ; - a medium outlet (21) ; a medium conveyance element (11) for conveying a heated medium through an inner tube; pressure raising means (14) for subjecting at least the heated inner tube internally to a raised pressure; cooling means (7) with a cooling means inlet which can be connected to an inner tube; characterized in that - the pressure raising means (14) can act upon the heated medium conveyed through an inner tube (2) ; and medium heating means (3) are present for maintaining the medium at a temperature necessary for the stretching both during the heating and during the stretching of the inner tube under internal pressure. 12. Apparatus according to claim 11, characterized in that the apparatus comprises a recirculation pipe (9, 22, 23, 24) with a medium inlet (20) and medium outlet (21) which can be connected to the inner tube (2) , in which recirculation pipe (9, 22, 23, 24) at least one medium storage tank (10) , a medium conveyance element (11) , and heating means (3) are provided; pressure raising means (11, 14) ; and at least one shut-off element (13) for the purpose of guiding heated medium through the inner tube, with or without passing through the pressure raising means, at the temperature required for stretching the inner tube. 13. Apparatus according to claim 11, 12, characterized in that a pressure raising means part (14) is provided in a bypass (26) which can be connected to the recirculation pipe. 14. Apparatus according to one or more of claims 11 - 13, characterized in that the pressure raising means comprise a pressure regulating valve (14) . 15. Apparatus according to one or more of claims 11 - 14, characterized in that a return pipe (16) connects recirculation pipe (9) after the medium heating means (3) to the recirculation pipe for said medium heating means (3) , preferably to the storage tank (10) . 16. Apparatus according to one or more of claims 11 - 15, characterized in that the cooling means (7, 8) can force a gas through an inner tube at raised pressure. 17. Apparatus according to claim 16, characterized in that a cooling means outlet (19) is provided, preferably on the medium storage tank (10) . 18. Apparatus according to one or more of claims 11 - 17, characterized in that it comprises a gas suction element (18) which can be connected to the space (17) present between an inner tube (2) and an existing pipeline (1). 19. Apparatus according to one or more of claims 11 - 18, characterized in that a control element (25) is present to control shut-off valves (6, 13) and flow regulating element (5) . 20. Pipeline with lined inside wall obtained using the method and/or apparatus according to one or more of the preceding claims.

Inventors: VAN DIJK BEREND JAN, VAN DIJK, BEREND, JAN
Applicants: DIJK BEREND JAN VAN, WAVIN BV, WAVIN B.V.
Application year: 1993
Main classification: F16L55
IPC codes: B29C55, B29C63, F16L55