GB2143162A

GB2143162A - A method of producing a rigid pipe system consisting of at least two co-axial metal pipes

Info

Publication number: GB2143162A
Application number: GB08417285A
Authority: GB
Inventors: Hans Martin Schmidtchen; Franz-Joseph Holtorf
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1983-07-09
Filing date: 1984-07-06
Publication date: 1985-02-06
Also published as: FR2548588A1; IT1178391B; FI84994C; NO163599C; SE8403597L; CH664809A5; FI84994B; NL8402119A; SE465914B; FI842012A0; BE900095A; NO163599B; DE3324848C2; GB8417285D0; JPH07353B2; DE3324848A1; SE8403597D0; NO842764L; JPS6021238A; FI842012A

Abstract

Two co-axial metal pipes (5, 6) with an electrically insulating layer arranged between them, particularly a supply pipeline for electrically-driven underwater pumps, are constructed by first mating a metal pipe (5) with a layer of synthetic resin material; the synthetic resin-coated metal pipe (5) is then inserted into a second metal pipe (6) which has a larger internal diameter, and the second metal pipe (6) is firmly drawn on to the synthetic resin layer by a die (13), so as to produce a compound pipe which is free from play in the direction of the longitudinal axis. A mandrel (14) supports the inner pipe. Further coating and assembling of other pipes can be carried out. <IMAGE>

Description

SPECIFICATION A method of producing a rigid pipe system consisting of at least two co-axial metal pipes The present invention relates to a method of producing a rigid pipe system comprising at least two co-axial metal pipes with an electrically insulating layer or layers arranged between them, particularly for use as a supply pipeline for electrically driven underwater pumps.

In order to supply underwater pumps with electrical energy and cooling and lubricating agents, a supply pipeline has been proposed which consists of three co-axial metal pipes electrically insulated from one another by synthetic resin layers. The three co-axial pipes form the three-phase conductors for the supply of the underwater pump with electrical energy, whilst the interior of the inner pipe serves as transport channel for a cooling and lubricating agent. The supply pipeline is installed inside a pipe of somewhat larger diameter, the annular space between the supply pipeline and the inner wall of the larger diameter pipe serving as the return transport channel for the cooling and lubricating agent.

Supply pipelines of this kind are subject to a number of requirements which it has not yet been possible to fulfill to full satisfaction.

Since such supply pipelines represent rigid systems, if a long length is to be provided, the system must be assembled at the location of use. This renders it necessary that the position of the pipes, at least at the end of each individual supply pipeline section, should always be the same in order that a troublefree electrical connection between the individual parts of the supply pipeline can be effected. In order to prevent the individual pipes from becoming displaced relative to one another in the direction of the longitudinal axis, both during the establishment of the electrical connection and after the installation of the supply pipeline (which is normally installed in a vertical position), it is vitally necessary that the metal pipes should be force4itted to the adjoining synthetic layers.

It is an object of the present invention to provide a method of producing a rigid pipe system which makes possible an economic production whilst adhering to dimensions laid down for the position and wall thickness of the pipes, and which ensures a force-fitting joint between the individual pipes whilst retaining the electrically-insulating layer.

According to the invention, there is provided a method of producing a rigid pipe system which consists of at least two co-axial metal pipes with an insulating layer arranged between adjacent metal pipes, comprising the steps of first coating a first metal pipe with a layer of synthetic resin material, inserting the coated metal pipe into a second metal pipe having a larger internal diameter, and drawing the second metal pipe on to the synthetic resin layer, so as to produce a compound pipe substantially without play in the direction of the longitudinal axis. The drawing-on of the second metal pipe will usually be carried out by cold drawing, since, otherwise, the synthetic resin layer would be adversely affected by the increased temperature.The synthetic resin layer should desirably be slightly deformed during drawing, in order to ensure that a strong joint is produced between the two pipes.

Advantageously, after the second metal pipe has been drawn on, this second metal pipe is also coated with a layer of synthetic resin material and the compound pipe so produced is introduced into a third metal pipe, the third metal pipe thereupon being firmly drawn on to the synthetic resin layer on the second metal pipe. In this way, an article is obtained which comprises three metal pipes which are electrically-insulated from one another and which can be used as electrical conductors.

The drawing operation is advantageously effected by drawing the pipe through a drawing die, a mandrel, mounted in the region of the drawing die, supporting the inner pipe during the drawing operation. Since considerable force is required to produce the forcelocking between the pipe which is to be drawn and the synthetic resin layer, the mandrel counteracts any deformation of the inner pipe.

In order that the synthetic resin layer arranged between the pipes should have a constant wall thickness, this layer is advantageously applied by extrusion.

In a particularly economical way of producing the compound pipe, a plurality of metal pipes are connected to one another end to end and are conveyed through an extruder, where a synthetic resin layer is applied to the outer surfaces of the pipes. After the cooling and hardening of the synthetic resin, the pipes are separated at the connection points and each separated pipe is inserted into a respective outer metal pipe and the outer metal pipe drawn down on to the synthetic resin layer, the inner pipe being supported by a mandrel. The compound pipes so produced are again connected to one another end to end and are conveyed through a further extruder which produces a further synthetic resin layer on the outer surfaces of the second pipes.After the cooling and hardening of this synthetic resin layer, the compound pipes are separated at the connection points and each individual compound pipe is inserted into a third metal pipe which is again drawn on to the synthetic layer of the compound pipe, the inner pipe again being supported by a mandrel.

The metal pipe, or compound pipe, coated with a layer of synthetic resin material, is inserted into the respective larger diameter metal pipe with a slight play, possibly with the aid of a lubricating agent. It is essential that the outer diameter of the synthetic resin layer and the inner diameter of the larger pipe should not differ appreciably from one another in order to avoid serious difficulties during the subsequent drawing-on of the outer pipe. A play (or diameter difference) of about 1 mm is therefore preferred. In order to improve the sliding operation, the surface of the synthetic resin layer is expediently coated with a lubricating agent, preferably a paraffin oil.To prevent the synthetic resin layer from becoming damaged during the insertion process, the inner edge of the outer pipe in question is preferably chamfered, prior to the insertion of the synthetic resin-coated metal pipe, or compound pipe.

The invention will now be further described with reference to the drawings, in which:~ Figure 1 is a schematic side-sectional view of a supply pipeline produced in accordance with the invention, in the installed state; Figures 2 to 5 are schematic views illustrating sequential steps in a method according to the invention.

Referring to Fig. 1, the supply pipeline 1 illustrated is accommodated co-axially within a pipe 2 in a vertical arrangement. The interior of the pipeline 1 forms a channel 3 which serves for the supply of a lubricating and cooling agent to an underwater pump (not shwn). The pipe 2 is of appreciably larger internal diameter than the external diameter of the pipeline 1, so as to leave an annular space 4 between the outer wall of the pipeline 1 and the inner wall of the pipe 2. This annular space 4 serves for the return transport of the cooling and lubricating agent.

The supply.pipeline 1 also serves to supply the underwater pump with electrical energy.

for this purpose, three concentric copper pipes 5, 6 and 7 are provided in the supply pipeline, which are electrically insulated from one another by means of synthetic resin layers 8 and 9 which preferably consist of polyethylene. The copper conductors 5, 6 and 7 carry the respective phases of three-phase alternative current. The copper pipes 5, 6 and 7 and the polyethylene layers 8 and 9 are forcefitted to one another, so that in the case of a vertical arrangement a displacement of the pipes 5, 6 and 7 relative to one another in the direction of the longitudinal axis is prevented.

The copper pipes 5, 6 and 7 are seamless pipes.

In a specific example, the dimensions of the inner pipe are 19 X 1.5, (i.e. 19 mm outer diameter and 1.5 mm wall thickness). The adjoining polyethylene layer 8 has a thickness of 1.5 mm. The dimensions of the central copper pipe 6 are 25 X 1.5. The adjacent polyethylene layer 9 again has a thickness of 1.5 mm. The dimensions of the outer copper pipe 7 are 31 x 1.5 mm. Alternatively, the wall thickness of the individual copper pipes 5, 6 and 7 may decrease from the interior towards the exterior, to be endeavoured that the pipeline cross-section of the pipes 5, 6 and 7 is identical.

In certain cases it may be advantageous to apply an additional synthetic resin layer to the outside of the copper pipe 7.

For the production of the supply pipeline 1, as illustrated in Fig. 2, a plurality of individual copper pipes 5 are joined to one another end to end by means of known connectors 10 and are passed through an extruder 11 which produces the polyethylene layer 8 on the outside of the copper pipe 5. By means of a separating device 12 the polyethylene-coated copper pipes 5 are separated in the region of the connectors 10. An individual polyethylene-coated copper pipe 5 is indicated at 5a.

In the next operating step, as shown in Fig.

3, the polyethylene-coated copper pipe 5a is inserted into a copper pipe 6. The outer diameter of the pipe 5a and the inner diameter of the pipe 6 should not differ too greatly. In order to facilitate the fitting of the pipes 5a and 6 into one another, the outer surface of the pipe 5a may be coated with a lubricating agent, for example a paraffin oil.

In order to prevent the surface of the polyethylene layer 8 becoming damaged during the insertion, it is expedient to chamfer the inner edge of the end face of the pipe 6.

When the pipes 5a and 6 have been fitted into one another, this double pipe is introduced into a die 13 and the pipe 6 is drawn tightly on to the pipe 5a. As a result, the polyethylene layer 8 is slightly deformed. In order to prevent the inner pipe 5 from being deformed by the deformation forces, it is supported by a mandrel 14 which is held by a mandrel rod 15, or in other known manner in the vicinity of the die 13. As shown in Fig. 4, compound pipes produced in this way are again joined end to end by means of known pipe connectors and are fed through a further extruder 16 which produces the polyethylene layer 9 on the compound pipe. The compound pipe provided with the poyethylene layer 9 is indicated hereafter at 6a. In the region of the connectors, the compound pipe 6a is again divided into individual lengths by means of a separating device 17. As shown in Fig. 5, each individual length 6a is introduced into a further copper pipe 7, the use of a lubricating agent, and the chamfering of the edge of the outer pipe again being applied, and also diameter conditions corresponding to the assembly of the pipes 5a and 6. The compound pipe, made up of the pipe 6a and the pipe 7 is introduced into a further die 18 and the pipe 7 is tightly drawn on to the polyethylene layer 9 of the pipe 6a, a mandrel 19 again serving to support the inner pipe 5.

In a final operating step the individual lengths of the supply pipeline 1 are levelled at the ends, i.e. the drawing equipment is removed and the drawing ends are cut off and cut to a length of e.g. 6 m.

The supply pipeline 1 produced in accordance with the invention is characterised by a force-fitted joint between the individual copper pipes 5, 6 and 7 and the polyethylene layers 8 and 9, and by a precisely concentric arrangement of these layers.

Claims

1. A method of producing a rigid pipe system which consists of at least two co-axial metal pipes with an insulating layer arranged between adjacent metal pipes, comprising the steps of first coating a first metal pipe with a layer of synthetic resin material, inserting the coated metal pipe into a second metal pipe having a larger internal diameter, and drawing the second metal pipe on to the synthetic resin layer, so as to produce a compound pipe substantially without play in the direction of the longitudinal axis.

2. A method as claimed in Claim 1, wherein after the drawing-on of the second metal pipe, the second metal pipe is also coated with a layer of synthetic resin material and the compound pipe so produced is introduced into a third metal pipe, whereupon the third metal pipe is firmly drawn on to the synthetic resin layer on the second metal pipe.

3. A method as claimed in Claim 1 or Claim 2, wherein the or each drawing-on operation is effected by drawing the pipe, or the compound pipe, through a drawing die, the inner pipe being supported during the drawing operation on a mandrel located in the region of the drawing die.

4. A method as claimed in any one of the preceding Claims, wherein the coating of the pipe, or of the compound pipe with synthetic resin material is carried out by extrusion.

5. A method as claimed in any one of the preceding Claims, wherein a plurality of metal pipes are connected to one another end to end and are fed through an extruder, a layer of synthetic resin material is applied to the outer surface of the pipe, after hardening of the synthetic resin material the pipes are separated at the connection points, each individual pipe is inserted into a second metal pipe having a larger diameter, the second metal pipe is drawn on to the synthetic resin layer whilst the inner pipe is supported by a mandrel, a plurality of compound pipes so formed are connected to one another end to end and are fed through a further extruder which produces a further synthetic resin layer on the outer surface of the second pipe, after harden- ing of this synthetic resin layer the compound pipes are parted at the connection points, and that each individual compound pipe is inserted into a larger diameter metal pipe which is drawn on to the synethetic resin layer of the compound pipe, the inner pipe again being supported by a mandrel.

6. A method as claimed in any one of the preceding Claims, wherein the metal pipe, or compound pipe, coated with a layer of synthetic resin material is inserted into the larger diameter metal pipe with only a slight degree of play.

7. A method as claimed in Claim 6, wherein the insertion of the metal pipe, or the compound pipe, into the larger diameter pipe, is effected with the aid of a lubricating agent.

8. A method as claimed in any one of the preceding Claims, wherein the inner edge of the respective outer pipe is chamfered prior to the insertion of the synthetic resin-coated metal pipe, or compound pipe, therein.

9. A method of producing a rigid pipe system substantially as hereinbefore described with reference to and as illustrated in the drawings.

10. A rigid pipe system produced by a method as claimed in any one of Claims 1 to 9.

11. A supply pipeline for an electricallydriven underwater pump comprising a rigid pipe system as claimed in Claim 10.