"SOCKET AND SPIGOT PIPE"

FIELD OF THE INVENTION

This invention relates to a socket and spigot pipe.

BACKGROUND TO THE INVENTION

Plastic socket and spigot pipes are well known. A socket is formed at one of the ends of the pipe. The socket includes a groove for a pressure activated seal. Examples of these seals are Forsheda, Anger and Lyng seals. The spigot of one pipe is inserted through the seal and located in the socket of another similar pipe to form a sealed joint between the two pipes.

Commercially available steel pipes are not compatible with plastic socket and spigot pipes. This is because the external or outside diameters of the steel pipes are different to the external diameters of the plastic socket and spigot pipes.

It is possible to manufacture steel pipes having the same external diameter as plastic socket and spigot pipes, as suggested in ZA 2005/05712. However a disadvantage of this is the cost associated with setting up the equipment to manufacture the steel pipes, as the existing steel pipe production equipment cannot be utilized.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a socket and spigot pipe comprising a first end and a second end, with an intermediate section located intermediate the first and second ends, the first end having a socket with a groove for a seal, the second end having a spigot, the spigot including a circular cylindrical section having an enlarged or reduced external diameter relative to the external diameter of the intermediate section of the pipe with the external diameter of the circular cylindrical section of the spigot being slightly less than the internal diameter of the socket so that in use the spigot of one pipe can be inserted through the seal and be located in the socket of another pipe to form a sealed joint between the two pipes.

In some cases, the internal diameter of the socket is greater than the internal diameter of the intermediate section, and the external diameter of the cylindrical section of the spigot is less than the external diameter of the intermediate section. In other cases, the internal diameter of the socket is less than the internal diameter of the intermediate section and the external diameter of the cylindrical section of the spigot is greater than the external diameter of the intermediate section.

It is preferred that the spigot have an inwardly tapering free end to facilitate insertion of the spigot into a socket.

The internal surface of the pipe may be lined for example with a polymeric. The external surface may be similarly lined at least at the spigot.

The pipe will typically be made of a ductile material such as steel, with a wall thickness of 4 mm or less, typically 3mm or less.

According to another aspect of the invention there is provided a method of manufacturing a socket and spigot pipe comprising the steps of:

providing a pipe of ductile material having a first end and a second end and having a constant diameter throughout;

modifying the first end of the pipe to form a socket having a groove for a seal;

modifying the second end of the pipe by increasing or reducing its diameter to form a spigot having an external diameter slightly less than the internal diameter of the socket so that in use the spigot of one pipe can be inserted through the seal and into the socket of another similar pipe to form a sealed joint between the two pipes; and

leaving an intermediate section of the pipe, between the first and second ends, unmodified.

Other features of the invention are set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings.

In the drawings:

Figure 1 shows a cross-sectional side view of pipe according to the invention;

Figure 2 shows a cross-sectional side view of two pipes as shown in Figure 1 connected end to end; and

Figure 3 shows a cross-sectional side view of a pipe according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring firstly to Figures 1 and 2, a steel socket and spigot pipe 10 formed from a standard steel pipe includes a socket 12, an intermediate section 14 and a spigot 16. The socket 12 has a circumferentially extending groove 18 for an elastomeric seal 20 seen in Figure 2.

The spigot 16 has a circular cylindrical section 17 with an external diameter indicated by arrows 22 which is reduced relative to the external diameter, indicated by arrows 24, of the intermediate section 14.

The external diameter 22 of the circular cylindrical section of the spigot 16 is slightly less than the internal diameter, indicated by arrows 26, of the socket 12. This is so that the spigot 16 of one pipe can be inserted through the seal 20 and into the socket of another pipe to form a sealed joint between the two pipes. Initially a low pressure seal is formed by slight compression of the seal by the spigot. Thereafter, when pressurized fluid is introduced into the pipes, the seal is pressure activated and a higher pressure seal is obtained.

The internal diameter, indicated by arrow 28, of the intermediate section 14 is less than the internal diameter, indicated by arrow 26, of the socket 12.

The free end 30 of the spigot 16 tapers inwardly to facilitate insertion of the spigot 16 into a socket 12.

As can be seen in Figure 2, two pipes can be connected end to end with the spigot 16 of one pipe inserted through the seal 20 and located within the socket 12 of the other pipe.

The external diameter of the spigot 16 and the internal diameter of the socket 12 correspond to those of conventional plastic socket and spigot pipes. Thus the steel pipe 10 can be used interchangeably with conventional plastic socket and spigot pipes. By way of example, certain conventional plastic socket and spigot pipe is provided with an external diameter of 63 mm.

Nominally corresponding structural steel pipe has an external diameter of 63,5 mm and an internal diameter of 57,3 mm, and nominally corresponding conveyance steel pipe has an external diameter of 60,3 mm and an internal diameter of 57,3 mm.

In accordance with the invention, if the structural steel pipe is to be used, the spigot end of the steel pipe would be reduced by 0,5 mm in external diameter to correspond to the outside diameter of the plastic pipe and, in forming the socket, the internal diameter of the socket would be increased to slightly greater than 63 mm. If conveyance steel pipe is to be used the spigot end of the steel pipe would be enlarged by 2.7 mm in external diameter to correspond to the external diameter of the plastic pipe and the internal diameter of the socket end would be increased to slightly greater than 63 mm. With these modifications of their spigot and socket ends the socket of both the structural steel pipe and the conveyance steel pipe would be able to receive a 63 mm external diameter spigot of another pipe whether it be a plastic or a steel pipe.

Referring now to Figure 3 a steel spigot and socket pipe 10.1 , formed from a standard steel pipe, is similar to pipe 10 except that the external diameter 22.1 of the circular cylindrical portion 17.1 of the spigot 16.1 is enlarged relative to the external diameter 24.1 of the intermediate section 14.1.

The internal surface of the pipe 10, 10.1 could be lined, typically with a polymeric lining, for abrasion or corrosion resistance. As the external surface of that portion of the spigot 16 which extends beyond the seal 20 in a pipe connection will also be exposed to fluid conveyed in the pipes, such external surface may similarly be lined, with the lining extending the end surface of the pipe at the spigot end so that the steel surfaces at this end are fully lined.

As an alternative to a polymeric lining, other forms of corrosion protection, for example epoxy coating, painting or galvanising could be applied to the internal surface of the pipe and/or at least to the external surface of the spigot.

It will be appreciated that many modifications or variations of the invention are possible without departing from the spirit or scope of the invention. For example the scope of the invention extends to fittings such as bends, T-pieces, crosses and laterals having sockets and spigots as described above. The term "pipe" should accordingly be interpreted to include to such fittings.