The present invention relates to an article that incorporates an electrical element of a strain gauge, a method of holding a strain gauge fast to an article, a pipe system including a plurality of pipes attached together by connectors and a method of monitoring such a pipe system. The invention is particularly, although not exclusively, applicable to gas and water supply pipes•

In a known pipe supply system pipes are attached together in a line by connectors into which aligned ends of adjacent pipes extend. The pipes are sealed within these connectors. Failure of the pipeline is most likely to occur at the ends of the pipes in the region of the connectors. It frequently happens that the first sign that the pipeline has a fault is that gas or water no longer exits the pipeline at the same rate that it is supplied. Obviously, in the case of gas, this can be extremely dangerous. Furthermore, as the pipelines can have a considerable length, and as the pipeline may be relatively inaccessible, it can take a very considerable amount of time to check the pipeline in the region of each connection to find the failure.

Where it is desired to monitor the stress on an article a strain gauge is adhered to the article. The adhesive has to be rigid enough to transfer all movement or change in dimension to the gauge from the article and yet flexible enough not to fracture. Clearly there is a conflict in the design parameters of the adhesive that cannot be completely resolved and must necessarily involve a compromise. Furthermore the gauge is exposed and subject to damage through impact or the effects of a harsh environment.

GB 2 155 183A (Strain Measurement Devices Limited) shows strain gauges 4 that are mounted on a base 2 that is fixed to a surface S by stud welding. However, it is the surface S that is to be monitored by the strain gauge and the strain gauge is not directly in contact with the article to be monitored.

GB 1 456 403 (Welwyn Electric Limited) discloses an

S shaped metal strip which is welded or mechanically secured to a mechanical structure that is to be stressed.

However, the gauge is required to be fixed at separate spaced locations.

US 4 706501 (Imperial Chemical Industries PLC) shows a pipe that is surrounded by four strain gauges 2, 3, 4 and 5. These gauges are bonded to the pipe 1 by adhesive.

According to one aspect of the present invention an article that incorporates a strain gauge which strain gauge, in use, is arranged to monitor the article is characterised in that a part of the article has been melted in order to hold the strain gauge fast with the article.

Part of the article may have been melted by passing current through and heating the strain gauge. Such a means of holding the strain gauge fast with the article provides an extremely accurate and simple way of attaching the strain gauge.

The heating may have been arranged to cause the article to bond with a further article.

The strain gauge may be integral with the article.

The strain gauge may be embedded in the article.

The electrical element of the strain gauge may comprise a wire.

The electrical element of the strain gauge may extend through more than 360° and may be helically wound. The electrical element may surround an opening.

The article may comprise a plastics article and may comprise a pipe connector.

Only the part of the article in the region of the strain gauge or that surrounds the strain gauge may have been melted.

According to another aspect of the present invention a method of holding a strain gauge fast to an article such that, in use, the strain gauge can monitor the article is characterised in that a part of the article is melted and then allowed to solidify in order to hold the strain gauge fast with the article.

The part of the article that is melted may be melted by passing current through and heating the strain gauge.

The method may comprise melting a part of the article and fusing the article with a further article.

The method may comprise melting the article only in the region of the strain gauge. The method may comprise melting the article around the strain gauge.

According to another aspect of the present invention a pipe system includes a plurality of pipes attached

together by connectors, the system being characterised in that a plurality of the connections between the pipes and the connectors are monitored by means of a strain gauge.

The strain gauge may be bonded to at least part of the connection between the pipes and the connectors.

According to a further aspect of the present invention a method of monitoring a pipe system that includes a plurality of pipes attached together by connectors in which a plurality of the connections between the pipes and the connectors include a strain gauge is characterised in that information is received from each strain gauge and that information is monitored.

The method may comprise monitoring pipe system failure or fluid pressure within the pipe system, for instance.

The present invention includes any combination of the herein referred to features or limitations.

The present invention may be carried into practice in various ways and several embodiments will now be described by way of example and with reference to the accompanying drawings, in which:-

Figure 1 is a schematic exploded view of a connector 10 with associated pipes 11 and 12 being aligned either side.

Figure 2 is a plan sectional view taken along the line II-II of Figure 1;

Figure 3 is a side view of a pipeline 13 including a succession of connectors 10A, 10B, IOC and 10D that attach pipes 14, 15, 16, 17 and 18 together; and

Figure 4 is a cross-sectional view of a further embodiment of a connector showing pipes connected thereto.

As shown in Figure 1 the connector 10 comprises a hollow tubular member into which the ends of the pipes 11 and 12 are arranged to be located. The pipes 11 and 12 are a close sliding fit with the internal cylindrical wall of the connector. Movement of the pipes into the connector is restricted by a projection (not shown in Figure 1 but shown as 22 in Figure 4) that extends into the bore of the connector at a central region thereof.

The internal surface of the connector includes a helically wound wire 19 and 20 towards each end of the connector. The wires are laid in grooves in the internal wall of the connector and the two ends of each wire lead to a terminal post 21.

When attaching the pipes to the connector, the pipes are first located in the connector. Then current is supplied through each wire via the connections at the terminal post 21. The current causes the wire to heat up and melt the immediately adjacent plastic of the connector and the adjacent outer surface region of the pipes and thereby cause the plastic from both parts to fuse together.

When the plastic components are connected together traditionally the wires have served no further purpose. The present invention, however, aims to use the wires as a strain gauge.

It will be appreciated that the wires themselves are bonded with or embedded in or fast with or integral with the very material that it is designed to monitor the stress of. Furthermore the wires are protected from the environment both externally to the pipeline and, when the wires are enclosed within plastics from the connector or plastics from both the pipe and connector. The terminal posts 21 that have previously been used to supply current through the wires are now used to provide a connection whereby a change in resistance occasioned by stress in the pipe can be monitored.

Figure 3 illustrates how the terminal posts of a pipeline are accessible in order that both wires at each of the joints 10A, 10B, IOC and 10D may be monitored.

The wires 19 and 20 at each connector may be able to monitor many strains and stresses including:-

l) radial pressure exerted both externally and internally (for example as a consequence of the fluid pressure within the pipe) ;

2) bending stresses occurring at the connectors, and

3) extension and compression forces exerted in line with the extent of the pipeline.

There may be a significant amount of background electrical noise picked up by the strain gauge which may render precise changes in strain difficult to monitor. Furthermore, the sensors may provide low signal-noise ratios. However, it may be sufficient to be able to

monitor when this stress has been sufficient to break or damage the pipe or connection.

As shown in Figure 4, the connector in the region where the fusion occurs need not be as thick as the intermediate portion of the connector. This is because the overall width of the integral structure at the fusion zone is made up of the thickness of the connector and the thickness of the pipe wall. Indeed the wire 19 may be more sensitive in such a connection as they may pick up changes in stress more readily than in a structure of greater thickness or rigidity.

In an alternative embodiment (not shown) the sensor could be fixed to the pipe or connector separately from the electro-fusion of the pipes and connectors.

It will be appreciated that, although the illustrated embodiments have been described in relation to strain gauges for pipe connection for water or gas, for instance, the concept may have a wider application. For example, strain gauges could be an integral part of an article to be tested, or monitored, which article is not a pipe or a connector, rather than being adhered to the part to be tested. The wire of the gauge could be surrounded by the part to be tested by casting or moulding the part (which may be plastic) around the wire or by heating the wire to cause localised melting of the article around the wire.

The pipes and connectors may be plastics such as Polyethylene.

The present invention also includes monitoring a sveel pipe, for instance when a localised repair is made, by fitting a short section of plastics pipe with a sensor.

The monitoring device could, for example, be a transponder which lies inactive and draws only residual power until activated by an external signal.