PIPES AND COUPLINGS

FIELD OF THE INVENTION

The invention relates to a method of making a pipe, in particular a pipe for use with couplings secured at its ends. The invention extends to such a pipe and to the couplings.

BACKGROUND TO THE INVENTION

Pipes are used to convey fluids or particulate suspensions or slurries in a number of different applications. The pipes are connected to provide a pipeline. It is desirable that connection be convenient. This facilitates the laying of a pipeline.

Easy connection also helps where repair work is required. To this end, pipes are often supplied with connectors already fitted. Properly securing connectors to a pipe can be difficult and adds to the expense of the pipes. The leaks that arise in a pipeline are usually associated with the couplings.

A number of couplings for rigid pipes are known. One type of coupling includes a pair of connectors, each of which can engage over the end of a pipe. Once secured to adjacent ends of a pair of pipes, the connectors can be engaged with each other to provide the coupling. Securing a connector to a plastics pipe can be difficult. With a steel pipe this is normally done by welding.

A large part of the effectiveness of a pipeline, especially one that has a relatively high operational pressure, depends on the couplings. All of the usual difficulties are compounded when pipes are to be used at high pressures and under harsh conditions. It is also desirable to have pipes which are suited to operate under harsh conditions. Conveying backfill, particularly in underground mines, requires pipes and connections that are suited to such use. Resistance to abrasion within the line is essential.

OBJECT OF THE INVENTION

It is an object of this invention to provide a pipe that is reliably connected to couplings at its ends.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a method of making a composite pipe having a steel sleeve with a plastic lining, comprising heating a plastic lining, drawing the heated lining into a steel sleeve having an inner circumference smaller than the outer circumference of the lining, and allowing the lining in the assembled pipe to cool to ambient temperature.

The invention further provides for the assembled pipe at ambient temperature to be cooled to below ambient temperature. The lining will initially be heated to between 55 and 85 degrees Celsius, preferably about 70 degrees Celsius; and the assembled pipe cooled to about minus 30 degrees Celsius.

Further features of the invention provide for the assembled pipe to be cooled to below ambient temperature a plurality of times; and for the lining to be drawn to extend beyond the ends of the sleeve and subsequently cut in line with the ends of the sleeve after the pipe assembly has been cooled.

Further features of the invention provide for the lining to be Ultra High Molecular Weight Polyethylene (UHMW-PE); or selected from the group comprising Polytetrafluroethylene (PTFE), High Molecular Weight Polyethylene (HMW-PE), High Density Polyethylene (HDPE) and Polypropylene.

In accordance with another aspect of this invention there is provided a pipe comprising a steel sleeve with an inner plastics material lining, the sleeve externally screw-threaded at its ends to engage a pair of internally screw- threaded connectors, each connector including a plastics material bush having the same internal diameter as the lining and extending between a face provided in the connector and the end of the pipe.

The invention further provides for the connectors to be inwardly stepped adjacent their free ends and for the bushes to extend over the step with lips on the bushes located between the steps and ends of the pipe.

In accordance with another aspect of this invention there is provided a pipe connector for rigid pipes having a longitudinal bore between a first end and a second end, an outer coupling formation at the first end and the bore screw- threaded at the other end to engage on a pipe, the bore inwardly stepped at the first end and a plastics material bush located in the first end with a lip locatable against the step to abut the end of a pipe when engaged in the screw-thread.

The invention further provides for the bush to protrude past the first end of the connector to resiliently contact the end of a similar bush on a contiguous connector in use; and for the connector to have a transverse face at the first end including a groove to receive an annular locating ring in the face.

A further aspect of this invention provides a coupling comprising a pair of connectors as defined.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will become apparent from the following description of one example described below with reference to the accompanying drawings in which:

Figure 1 shows a part cutaway cross-sectional side elevation of a pipe and connector; and Figure 2 shows a coupling between two pipes.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, an end of a pipe (1 ) is shown fitted with a connector (2). The other end will have an oppositely facing connector (2) fitted in the same manner. A pair of these connectors (2) provides a coupling (3) for end to end connection of the pipes (1 ).

The coupling (3) is of the type sometimes referred to as a "tapered end" coupling. This name derives from the feature of an annular flange on each abutting connecter (2) which tapers outwardly towards the other connector. An annular clamp (4) is bolted together over the flanges (5). The tapered flanges (5) of two connectors (2) provide engaging surfaces for a channel (not shown) with correspondingly inclined sidewalls formed inside the clamp (4).

The flange (5) of each connector (2) provides an outer coupling formation at a first end (7). The second end (8) of the connector (2) is adapted to engage over the end of the pipe (1 ). In this embodiment, an internal screw-threaded portion (9) is provided to engage the end of a pipe (1 ).

The screw-threads (9) are provided in a longitudinal bore (10) through the connector (2). The bore (10) has a reduced diameter at the first end (7). The reduced diameter of the bore (10) is provided by an inward step (1 1 ). An annular groove (12) is provided in the face (13) of the connector (2), at the first end (7).

An annular bush (14) fits into the connector (2) from the second end (8) and has an outwardly extending lip (15) that abuts against the step (1 1 ). The bush (14) extends over the step (1 1 ) to the first end of the connector (2) and is a close fit to the bore (10). The bush (14) is oversized to extend a small amount past the first end (7) of the connector (2) at its narrow side (16) and slightly into the threaded portion (9) of the bore (10) at its lipped side (17). The significance of this will be described below.

The pipe (1 ) is of a composite nature having an inner plastics lining (18) fitted within a steel sleeve (19). The sleeve (19) is screw-threaded at (20) adjacent its ends to engage the corresponding screw-threads (9) in the ends of the connectors (2).

The lining (18) is preferably made from Ultra High Molecular Weight Polyethylene (UHMW-PE). The bushes (14) will be made of the same material in this embodiment.

In manufacture of the composite pipe (1 ), the lining (18) is placed in a heating bath with water at a temperature somewhere between 55 and 85 degrees Celsius. The water is preferably maintained at about 70 degrees Celsius.

The steel sleeve (19) is at this stage already fitted with the screw-threaded connectors (2) at each end. The heated lining (18) is then engaged with suitable machinery and drawn into the sleeve (19), which is held fast. The connectors (2) serve to protect the screw-threads (20) at the pipe ends during this operation.

The outer diameter (OD) of inner lining (18) is about 1.5 mm larger than inner diameter (ID) of steel sleeve (19). Heating of the lining (18) makes it pliable, which allows the necessary elastic deformation during the drawing operation. Once it is in place, the lining (18) expands as it cools to the ambient temperature. This locks the lining within the sleeve (19). The ends of the lining (18) are cut at the free ends of the sleeves (19).

Selecting suitable lining OD and sleeve ID is within the competence of a person skilled in the art. This will depend on overall diameter, materials and the pipe's application.

The pipe (1 ) is then cooled to a temperature of about -30 degrees Celsius. Liquid Nitrogen is used to bring the pipe (1 ) to this temperature. The lining (18) shrinks within the sleeve (19). This may be accompanied by drawing the lining (18) into the sleeve (19) at its ends. The complete pipe (1 ) is then removed and the connectors (2) are unscrewed. The pipe is allowed to warm to ambient temperature.

The pipe (1 ) without couplings is then cooled to the same minus temperature again. The lining is once more subjected to the shrinking effect of the cold. The ends of the lining (18) are cut to line up with the sleeve (19) ends. The connectors (2) are refitted and tightened up with the bushes (14) in place.

Once assembled, the pipe is cooled once more to test against further shrinking. Basically, the lining can only expand.

The connectors (2) can then be secured together to establish a coupling between contiguous pipes. This is done with the assistance of an annular locating ring (21 ) which fits into corresponding grooves (21 ) in the faces of two connectors. Once the connectors (2) are lined up and abutting each other, the clamp (4) can be fitted and tightened. The ring (21 ) is also made of UHMW-PE.

Because each bush (14) is oversized as referred to, the pipe (1 ) compresses the bush from the one side when the connector (2) is tightened onto the sleeve (19) and a corresponding bush (14) similarly does the same from the opposite side (16) as the clamp (4) is tightened to form a coupling (3) between two pipes (1 ).

A smooth transition through the coupling from one pipe to another is thus provided. This is generally desirable for unobstructed flow and very important when conveying slurries or suspensions of particulate material. The compression of the bushes (14) between the pipes (1 ) and connectors (2) deters the formation of gaps between the pipes and bushes. Any such gaps will normally be highly susceptible to forming an abrasion site.

The coupling formation (5) of each connector (2) may, instead of a tapered flange for a clamp, be a perforated flange for bolting the connectors together.

The plastics material for the lining may be selected from Polytetrafluroethylene (PTFE), High Molecular Weight Polyethylene (HMW-PE), High Density Polyethylene (HDPE) and Polypropylene, or any other suitable kind.

A suitably skilled person will appreciate that a number of other variations may be made to details of the features described without departing from the scope of the current invention.