Electrofusion fitting

1. An electrofusion fitting comprising a tubular length of thermoplastic material, of an outer diameter commensurate with the inner diameter of the ends of a compatible thermoplastic material lining of adjacent lengths of metal pipe, there being at each end of the fitting at least two heater coils on or in close proximity to the outer surface of the fitting, electrical leads from the heater coils extending through the fitting to emerge at the inner surface of the tubular length, for connection to a source of electrical power.

2. An electrofusion fitting as in claim 1 , wherein the electrical leads are of a length to allow them to be carried through a pipe length and connected to a source of electrical power.

3. An electrofusion fitting as in claim 1 , wherein electrodes are provided on the inner surface of the tubular fitting to which the electrical leads are connected and to which a source of electrical power can be connected.

4. An electrofusion fitting as in claim 3 , wherein the electrodes at the ends of the electrical leads are sited between the positions of the adjacent ends of the co-operating heater coils, at each end of the tubular length.

5. An electrofusion fitting as in claim 4 , wherein the electrodes are such as to allow the manual attachment of electrical leads to an appropriate source of electrical power.

6. An electrofusion fitting as in claim 1 , wherein the ends of the tubular fitting are straight to be a close sliding fit in the ends of or the counterbored ends of adjacent lined pipe lengths.

7. An electrofusion fitting as in claim 1 , wherein the ends of the fitting and the co-operating ends of the linings of the pipe lengths are equally tapered, such that the fitting can be pushed into contact with the ends of the linings of the pipe lengths.

8. An electrofusion fitting as in claim 1 , wherein there is, generally centrally of the fitting, a recess in its outer surface for the location of insulating material to be overlaid by the ends of the adjacent pipe lengths bridged by the fitting and from where the pipe lining is cut back.

9. An electrofusion fitting as in claim 8 , wherein the insulating material is a ceramic ring.

10. An electrofusion fitting as in claim 1 , wherein a supporting ring is provided below each coil of the fitting, of a material of a higher melting point than that of the fitting.

11. A method of forming a joint between two metal pipe lengths each provided with an inner lining of a thermoplastics material, comprising inserting into the one pipe length one end of an electrofusion sleeve with support rings as is defined in claim 1 , attaching electrical leads to the electrodes of the coils on the electrofusion sleeve at the end inserted into the pipe end, connecting the leads to a source of electrical power to heat the coils at that end of the electrofusion sleeve to fuse the sleeve to the lining of the pipe, detaching the electrical leads from the electrodes, attaching electrical leads to the electrodes at the opposite end of the electrofusion sleeve, positioning the opposite end of the electrofusion sleeve in the end of a second pipe length, passing the electrical leads along the pipe length, connecting the leads to a source of electrical power to heat the coils at the opposite end of the electrofusion sleeve to fuse the sleeve to the lining of the second pipe length, pulling the electrical leads from the electrodes and removing the leads from within the second pipe, and welding together the adjacent ends of the metal pipes.

12. A method of forming a joint between two metal pipe lengths each provided with an inner lining of a thermoplastics material employing an electrofusion fitting as in defined in claim 1 , comprising inserting into the end of one pipe length one end of an electrofusion fitting, introducing into the fitting an expandable mandrel having one or more electrodes on its surface, positioning a mandrel below the heating coils at the said one end of the fitting, expanding the mandrel into contact with the inner surface of the fitting to support the fitting and put the electrodes on the mandrel into contact with the electrodes on the inner surface of the fitting at that side, connecting the electrodes on the mandrel to a source of electrical power, to provide power to heat the at least two coils at the said one end of the fitting, to create at least two electrofused joints between the said one end of the fitting and the thermoplastics lining, locating an expandable mandrel having one or more electrodes on its surface at a position below the other side of the fitting, expanding the mandrel to support the fitting and put the electrodes on the mandrel into contact with the electrodes on the fitting at that side, positioning the fitting in the end of a second pipe length, connecting the electrodes on the mandrel to a source of electrical power to heat the at least two coils at the second end of the fitting to create at least two electrofused joints between the second end of the fitting and the thermoplastics lining of the co-operating lined pipe length, collapsing and withdrawing the mandrel and welding together the adjacent ends of the outer metal pipe lengths.

13. A method of forming a joint between two metal pipe lengths each provided with an inner lining of a thermoplastics material as in claim 12 , wherein collapsible and removable mandrels are used.

14. A method of forming a joint between two metal pipe lengths each provided with an inner lining of a thermoplastics material as in claim 12 , wherein a single mandrel is used, that can first be collapsed and inserted into the tubular length, and expanded into contact with the inner surface of the tubular fitting, and following welding at that side, the mandrel can be collapsed and withdrawn, and inserted into the other end of the tubular fitting, and re-expanded into contact with the inner surface of the tubular fitting at the end, to facilitate welding at that end, without the risk of collapse of the tubular fitting, followed by collapsing the mandrel again, and withdrawing it from the tubular fitting.

15. A method of forming a joint between two metal pipe lengths each provided with an inner lining of a thermoplastics material as in claim 12 , wherein the electrodes on the inner surface of the fitting and on the mandrel are such as to require point contact, with a consequent need for careful location of the mandrel into the fitting and of orienting the mandrel to ensure that its electrodes are aligned with those on the fitting.

16. A method of forming a joint between two metal pipe lengths each provided with an inner lining of a thermoplastics material as in claim 15 , wherein the electrodes are elongate around the periphery of the mandrel.