TUBE FOR LINING OF PRESSURE WATER PIPES

Abstract: A pipe of thermoplastic material for relining of pressure water pipelines is made as a finned pipe wherein the tensile strength of the pipe wall (1) is greater than the shear strength of the fins (2).

Description: TUBE FOR LINING OF PRESSURE WATER PIPES The invention relates to. a pipe for relining pressure water pipelines and more particularly to a relining pipe which shall be drawn into the pipeline to be restored. This type of relining is termed slip- lining. In pressure water pipelines which often comprise cast-iron or nodular-iron pipes or steel pipes de¬ posits eventually build up on the inner side of the pipe wall, which necessitate repeated cleaning of the pressure water pipeline. However, by such cleaning the material of the iron pipes will be uncovered, which in turn causes increased corrosion so that the pipe wall after repeated cleaning will be thinner and thinner and finally will not satisfy the established requirements as to the strength. The reduction of the strength of the pipe caused by corrosion can give rise to damages such as perforation of the pipe wall. Damages can also arise due to shocks. In those cases wherein a reduction of the dimension of the pressure water pipeline can be accepted, the pipeline can be restored by drawing a relining pipe thereinto. The pipes which are used today in restoring pipelines in this manner consist of smooth polyethylene or poly¬ propylene pipes which are drawn into the pressure water pipeline either as a major continuous length of pipe which is wound up to form a coil, or as lengths of about 12 m which are interconnected by butt weld¬ ing in the field. When the pipe is introduced into the pressure water pipeline from the ground level the pipe often will be tightly bent, e.g. at the transi¬ tion from a vertical well to a horizontal pipeline and in bends in the pipeline. In order that the re¬ lining pipe can be drawn into the pipeline from the ground level through a shaf the pipe accordingly- must have some flexibility in the longitudinal direc¬ tion thereof, which is of course also required in order that the relining pipe can follow existing bends or irregularities in the pipeline. At the same time it is required that the pipe has a strength which is so great that the pipe resists the positive and negative pressures which can appear in the pipe¬ lines. These two requirements are in conflict with each other and therefore it is not unusual that a pipe which is sufficiently flexible will be deformed during the relining or at great negative pressures. Moreover, the relining pipe must have an outside diameter which is sufficiently smaller than the in- side diameter of the pipeline in order that the pipe can slide unobstructedly through the pipeline when it is drawn thereinto. Due to the gap between the re¬ lining pipe and the pipeline there will be obtained, however, a movement of the relining pipe at existing pressure shocks in the relined pressure water pipe¬ line, which can result in damages on the relining pipe at existing irregularities or sharp edges in the pipeline so that the relining pipe eventually will break due to such mechanical damages. The movement of the relining pipe as such can be eliminated by in¬ jecting between the relining pipe and the pipeline a setting filler, but this measure makes the relining substantially more expensive and, therefore, it is desired to avoid such measure. The joints between the pipe lengths provided by mirror welding or induction welding moreover provide risk zones because they can be of poor quality, which cannot be detected by ex¬ ternal visual inspection, and because there is ob¬ tained at the joints a bead on the outside of the re- lining pipe, which can engage with the pipes of the pipeline when the relining pipe is drawn thereinto. The purpose of the invention is to provide a pipe which is more suitable for sliplining than the smooth polyethylene or polypropylene pipe and elim¬ inates the drawbacks accounted for above, and which at the same time is flexible in the longitudinal direction thereof and is stiff in the radial direc¬ tion and can easily be secured in position in the pipeline. The pipe according to the invention is characterized in that the pipe is a finned pipe wherein the tensile strength of the pipe wall is greater than the shearing strength of the fins. Due to the fact that the relining pipe comprises a finned pipe having the properties mentioned above it is possible to successfully use the pipe as a re¬ lining pipe. Owing to the fins the pipe wall can be made thinner than in smooth pipes, which improves the flexibility of the pipe, and at the same time the fins reduce the risk of deformation in the direction of the pipe radius. The relationships between the strengths of the pipe wall and- the fins make possible that the finned pipe is used as a relining pipe be¬ cause said relationships guarantee that the fins and not the pipe wall yield when the fins encounter a resistance in the pressure water pipeline. The lower shear strength of the fins can be ob¬ tained in a simple manner by making the fins of a softer material than the pipe wall. As an alternative the total volume of the fins is at the most half the volume of the pipe wall, and the height of the fins is at least double the size of the average width of the fins. In order to facilitate the introduction of a finned pipe into the pipeline it may be advantageous that the fin or fins extend helically around the pipe, the rotation of the pipe as a consequence thereof can facilitate the insertion of the pipe into the pipeline. An advantageous embodiment of the pipe of the invention is characterized in that the pipe is pro¬ vided with alternating higher thinner fins and lower thicker fins. In a pipe thus finned the fins stiffen the pipe wall so that this wall between the fins can have a smaller wall thickness than the smooth pipe, which in turn means that the pipe will be more flexible in the longitudinal direction thereof. The higher fins sta¬ bilize and center the relining pipe in the pipeline, the pipe as a consequence thereof will be prevented from movement under the influence of pressure shocks. At the same time a better and safer joint can be pro¬ vided between the pipe lengths at the low fins where the joint moreover is protected between adjacent higher fins and is prevented from engaging the pipe- line pipes when the relining pipe is drawn into the pressure water pipeline. The invention also relates to the use of a finned pipe, wherein the tensile strength of the pipe wall is greater than the shear strength of the fins, as a relining pipe in pressure water pipelines. The pipe of the invention will be described in more detail below reference being made to the accom¬ panying drawings wherein Figure 1 discloses a first embodiment of the pipe of the invention in a longitudinal cross- sectional view, Figure 2 discloses a second embodiment in longi¬ tudinal cross-sectional view, Figure 3 is a longitudinal cross-sectional view of a mirror welded joint between two pipe lengths, Figure 4 is a longitudinal cross-sectional view of a joint obtained by induction welding, Figure 5 discloses a joint obtained by resis¬ tance welding and Figure 6 discloses a mechanical joint between pipe lengths. Figure" 1 discloses a pipe of the present inven¬ tion. The pipe is made of thermoplastics, e.g. poly¬ ethylene or polypropylene. The pipe wall is indicated at 1 and the fins at 2. The pipe wall and the fins are dimensioned in relation to each other such that the tensile strength or compression strength of the pipe wall is greater than the shear strength of -the fins 2. Preferably, the fins 2 are made of a softer material than the pipe wall. From the figure it can also be seen that the total volume of the fins 2 per unit length of the pipe is at the most half the volume of the pipe wall, and that the height of the fins is at least double the size of the average width of the fins. The fins shown in Figure 1 encircle the pipe wall in the peripheral direction but the fins can also extend helically around the pipe. According to Figure 2 the relining pipe of the invention is constructed as a finned pipe having alternating higher thinner fins 10 and ' lower thicker fins 11, the higher and lower fins alternating with each other in such manner that there is provided between each two adjacent fins of one kind a fin of the other kind. The pipe should be made of thermo¬ plastics, and a suitable material is polyethylene, but also polypropylene can be used. The higher thinner fins preferably are dimensioned such that they are elastically flexible to some extent. The fins stiffen the pipe wall 12 so that this can be given a smaller thickness than in a corresponding smooth pipe for the same external pressure. Due to the fact that the wall thickness is smaller the pipe will also be more easily flexed, the introduction of the pipe in the pipeline to be relined being facili¬ tated as a consequence thereof. Owing to the flexi¬ bility of the higher thinner fins these fins can yield at the introduction. These fins guide the pipe when it slides through the pipeline and serve to sta¬ bilize the inserted pipe and to keep it centered in the pipeline. At the lower thicker fins 11 lengths of the pipe of the invention can be joined in different manners, and the most important ones thereof are disclosed in Figures 3 to 6. In Figure 3 there is shown a butt joint 13 obtained by mirror welding after the two joint pipe ends having been cut substantially cen¬ trally through a terminating lower thicker fin 11. It will be seen that the joint is well protected between the adjacent higher thinner fins 10, which is an ad¬ vantage particularly when the pipe is drawn into the pipeline to be relined, because the joint which may have a bead or other irregularity on the outside of the pipe will be prevented from engaging existing ir¬ regularities in the pipeline at this bead or irregu¬ larity. A similar joint as that in Figure 3 can be ob¬ tained by induction welding in the manner disclosed in Figure 4 wherein a metal ring 15 is provided be¬ tween the end surfaces of the pipes to be intercon¬ nected and this ring is heated by generating eddy currents therein by means of a magnetic field gener¬ ator 16 the two pipe ends being fused to opposite sides of the ring. The oint in Figure 5 has been obtained by resistance welding. A ring 17 of the same material as that of the pipe is welded to the lower thicker fins 11 abutting each other, by fusing the plastic ma¬ terial by means of electric heating wires 18 located between the ring and the fins. Finally, a purely mechanical connection is dis¬ closed in Figure 6, wherein the two pipe ends are kept together by means of an external metal ring 19 which engages at hook-shaped edge portions the two adjacent lower thicker fins 11 between which there is provided a sealing ring 20. In order that the relining pipe will not move at the position thereof in the pipeline, e.g. at exist¬ ing pressure shocks, it should be anchored so that it cannot move axially. At smooth relining pipes this is achieved by means of a clamp shackle consisting of two halves which are clamped around the relining pipe by means of screw connections and are fixedly anchor¬ ed in a suitable way. The clamp shackle is kept in position on the relining pipe solely by friction, which means that it may be necessary to clamp the shackle so tightly around the relining pipe that this pipe will be deformed, and that the relining pipe may be exposed to wear at existing movement between the relining pipe and the shackle. The invention allows this force engagement be¬ tween the relining pipe and the shackle to be re¬ placed by a positive engagement. In Figure 2 there is shown a shackle 21 which in a conventional manner comprises two halves which are clamped by means of screw connections around the relining pipe and which on the inside thereof are profiled to receive the fins 10 and 11 in corresponding annular grooves. It is not necessary to clamp this shackle so tightly around the relining pipe that this will be deformed because the engagement between the relining pipe and the shackle is a positive engagement and is not de¬ pending on the abutting pressure against the relining pipe. The shackle can keep the relining pipe in po¬ sition by engaging the end edge of a pipeline 22 wherein the relining pipe has been inserted, as is shown in Figure 2, or can be anchored in an existing valve or pipe bend or in stationary anchoring means in the ground.

Claims: CLAIMS 1. Pipe of thermoplastic material for relining pressure water pipelines, c h a r a c t e r i z e d in that the pipe, is a finned pipe wherein the tensile 5 strength of the pipe wall (1, 12) is greater than the shear strength of the fins (2, 10, 11). 2. Pipe as in claim 1 wherein the fins (2, 10, 11) are made of a softer material than the pipe wall (1, 12) . 0 3. Pipe as in claim 1 wherein the total volume of the fins (2) is at the most half the volume of the pipe wall (1) and wherein the height of the fins is at least double the size of the average width of the fins. 5 4. Pipe as in claim 1 wherein the fin or fins extend helically around the pipe. 5. Pipe as in claim 1 wherein the pipe is pro¬ vided with alternating higher thinner fins (10) and lower thicker fins (11) . 0 β• Pipe as in claim 5 wherein each fin of one type is located between two fins of the other type. 7. Pipe as in claim 5 or 6 wherein the higher thinner fins (10) are made elastically flexible. 8. Pipe as in claim 5 wherein an encircling 5 anchoring shackle (21) is provided on the pipe in positive engagement with the fins (10, 11). 9. The use of a finned pipe wherein the tensile strength of the pipe wall is greater than the shear strength of the fins, as a relining pipe in pressure U water pipe lines. 5

Inventors: JAERVENKYLAE JYRI, JOHANSSON THOMAS, JAERVENKYLAE, JYRI, JOHANSSON, THOMAS
Applicants: UPONOR NV, UPONOR N.V.
Application year: 1988
Main classification: F16L55
IPC codes: F16L55