Pipes used for transporting fluids such as water and natural gas are commonly made from materials such as cast or ductile iron. Over a period of time such pipes are likely to suffer corrosion as a result of chemical attack by constituents of the fluids being transported. This is undesirable, for example, in the case of mains water pipes the products of corrosion are likely to contaminate the water supply to customers.

The usual way of dealing with a corroded pipe of a small diameter is to dig it out and substitute a new one. This is an expensive operation for the pipe laying service and can be very disruptive to local residents and traffic. Although there may be evidence of corrosion, in practice the pipe can still have further useful life. Such a pipe can be reconditioned, i. e. instead of being replaced, the pipe can be scraped out and lined with a cement or plastics coating, or a tubular inner liner made of plastics material can be inserted into the pipe. To ease entry of the plastics liner, it can be swaged so as to reduce its diameter, and then allowed to expand once it is in position within the pipe.

Alternatively, the liner can be deformed to a U-shaped cross-section, then inserted in the pipe and then allowed to expand under the action of heat and/or pressure as disclosed in GB patent specification no. 2227545.

When reconditioning a pipe using an inner tubular liner, one area of concern is the provision of joints between two lengths of pipe and between two lengths of liner exposed at the ends of the lengths of pipe. GB patent specification no. 2235740 discloses joining two lengths of plastics lined metal pipes by fusion welding the liner exposed at the end of each pipe length using a heating element, and providing a coupling which is fixed to the ends of the lengths of pipe and which encloses the fusion weld and which is filled with epoxy cement grout to support the liner near the weld. US patent specification no. 5364130 discloses a coupling for connecting two pre-made plastics lined pipes. This coupling comprises an inner tubular part having a wound heating element and a diameter appropriate for receiving the exposed ends of the plastics liner and an outer tubular part which receives the ends of the pipes. The heating element is energised so as to weld the ends of the plastics liner to the inner part of the coupling. Meanwhile, the outer part of the coupling is fixed to the ends of the pipes initially by being a close frictional fit on the pipes and then by the application of adhesive to the friction joint. The inner and outer parts of the coupling may be separate items assembled to the pipe in succession or the inner part may be assembled within the outer part and held therein by shaping the outer part during manufacture of the coupling.

According to the present invention in one aspect there is provided a fluid transport pipe comprising pipe lengths arranged in line, an intermediate member being present between the adjacent pipe lengths, each pipe length having an inner lining of thin plastics material, the lining at each end of the pipe length extending beyond and having been joined by heat fusion to the intermediate member and otherwise free to be urged by the pressure of fluid towards the surrounding wall of the pipe length.

Preferably the thin plastics material is extruded polyethylene and the lining of thin plastics material is tubular with a ratio of diameter to thickness in the range of about 30: 1 to about 50: 1.

Preferably the pipe to be lined is a small diameter (75-100 mm) mains supply pipe.

However, there is no upper limit to the diameter. The intermediate member is of plastics material, preferably polyethylene. Preferably the intermediate member includes electrical heater element to generate the heat for heat fusion. Preferably the plastic lining protrudes a distance of between 100 mm and 500 mm beyond the end of each pipe length for engagement with the intermediate member.

Preferably the external diameter of the inner lining is between 92 and 98% of the internal diameter of the surrounding pipe length.

In another aspect the invention provides a method of lining aligned pipe lengths having intermediate members between the lengths, the method comprising pulling a thin plastic lining through each pipe length so that it extends beyond each end of the length to contact the adjacent intermediate member and connecting the extending portions to the intermediate member in fluid tight manner, whereby the plastics lining is anchored at its ends and is otherwise free.

Preferably the intermediate member includes an electrical heater to generate the heat for the fusion.

In order that the invention may be well understood it will now be described by way of an example only with reference to the accompanying diagrammatic drawings, in which Figure 1 is a sectional view of a fluid transport pipe of the invention before connection; Figure 2 is a plan view showing a pipe made up of pipe lengths, intermediate members and a pipe joining section, exposed to view by a suitable excavation in the ground; Figure 3 is a sectional view of a pipe length and an intermediate member prior to the heat fusion step; Figure 4 is a view of the components of Figure 2 after the heat fusion step.

Figure 5 is a sectional view of a pipe with a branch coupling; and Figures 6 and 7 are sectional views of two alternative branch couplings.

The main components of the fluid transport pipe, shown in Figure 1, are pipe lengths 1 fabricated from corrodible metal, plastic sleeves 2 between neighbouring lengths, thin polyethylene lining tubes 3 and pipe couplers 4.

Excavations are made in ground G in order to uncover both ends of the installe pipe to be lined so as to allow a length of pipe approximately 2m. long to be removed from each end, thus providing access for pipe inspection and lining. The remaining pipe is then surveyed by Closed Circuit Television and if necessary scraped and cleaned using conventional methods in order to remove products of corrosion. A thin wall polyethylene tube of external diameter equal to about 95% of the internal diameter of the first pipe length to be lined is pulled through the pipe to be lined so that 300mm. protrudes from each end of the pipe length. The tubing may be supplied cut to the necessary length or shorter lengths may be butt welded together on site. A larger diameter relatively thick- walled polyethylene sleeve having an internal diameter 2 mm. greater than the external diameter of the polyethylene lining is then fitted to each end of the pipe to be lined using known couplers in-line repair so that the tube extension and the sleeve may be secured together in fluid tight manner. The connection is made by heat fusion which is achieved by passing an electrical current through a heating coil 6 within the plastics sleeve by connecting an external power supply to the terminals of the conductor 7. The heating is arranged to generate sufficient temperature to fuse the outer surface of the lining to the inner surface of the intermediate tube, but not so high as to significantly deform their structure. This can be controlled by the temperature and/or time. Following the heat fusing step the pipes are inspected and cleaned by conventional means. The fused joints between the lining and the pipe preventing ingress of fluid into the annulus between the lining and the pipe. Because the lining is not secured along its entire length a pipe length can be lined in less than 12 hours without the need to dig out the pipe and requires no specialist equipment on site. The annular joints prevent the liner from contracting when the ambient temperature falls and hold the ends secure if the liner expands.

To replace an existing branch connection to the pipe 1, the original ferrule hole is drilled through and into the inner liner 3 and the branch service pipe (not shown) is reconnected to the lined pipe by a new ferrule 20 as shown in Figure 5. This ferrule comprises a tubular portion 21 which projects through into the inner liner 3 by about ten millimetres say to give added protection against twisting, if any, of the liner 3 within the pipe 1. The portion 21 is mounted in a member 22 forming part of a strap connector that extends round the pipe 1 and clamps the member 22 to the pipe 1 with a Neoprene seal 23 therebetween.

Figure 6 shows a modification of the Figure 5 branch connection in which a flanged cylindrical member 60 is positioned so as to extend through the aligned holes in the pipe 1 and liner 3 with the flange 61 lying inside the liner 3 and against its inner surface. The outer end of the member 60 is threaded and engaged with a matching threaded hole in a ferrule support member 62 lying outside the pipe 1. The member 62 is screwed onto the threaded end of the member 60 with a Neoprene seal 63 between member 62 and pipe 1.

Yet another branch coupling is shown in Figure 7. This comprises a grommet-like ferrule carrier member 70 having two annular flange portions 71 and 72 joined by a neck portion 73. The member 70 is made of deformable material and is able to be pushed through the aligned holes in the pipe 1 and liner 3 so that annular portion 71 of the member 70 lies within the liner 3 and overlays the periphery of the hole in the liner 3 while portion 72 lies outside the pipe 1 and overlays the periphery of the hole in the pipe. The ferrule 62 is then fixed within the member 70.