WO2004090520A1

WO2004090520A1 - Wear detection

Info

Publication number: WO2004090520A1
Application number: PCT/GB2004/001489
Authority: WO
Inventors: Andrew Loveridge; Andrian R. Bowles
Original assignee: Qinetiq Limited
Priority date: 2003-04-07
Filing date: 2004-04-06
Publication date: 2004-10-21
Also published as: GB2400434A; GB0307984D0

Abstract

A fluid-conducting tubular article such as a pinch valve sleeve (1) is equipped with wear detecting apparatus including an optical fibre (7) embedded within the sleeve and light generating and detecting means (not shown) coupled to its respective ends (9) and (11). The fibre is wound to define a plurality of successive portions (13) spaced in the circumferential direction of the sleeve and extending parallel to its longitudinal axis along its centre section. Internal wearing of the sleeve anywhere around its circumference due for example to the action of abrasive fluids can be detected by monitoring for breaks in the transmission of light through the fibre (7), without however subjecting the portions (13) to excessive bending when the centre section of the sleeve is clamped in use of the valve.

Description

WEAR DETECTIO

This invention relates to the field of wear detection and more specifically to the detection of wear in fluid-conducting tubular articles such as pipes, conduits and hoses.

Many systems and articles will experience wear during the course of their normal operation. For example, fluid-conducting conduits can experience wear both externally (from the environment in which they are located) and internally (from, for example, abrasive fluids) that can potentially compromise the structural integrity of the conduit. Failure to detect wear can result in system failure, financial losses and a reduction in operational efficiency.

Many industrial processes use rubber (elastomer) hosing to transport fluids. In some instances the fluids are abrasive resulting in degradation of the internal surfaces of the hosing. Often it is impossible to see abrasion from an external inspection of the hosing and the first indication that something is wrong is when the hosing catastrophically fails. There are two ways in which the possibility of the hosing being breached can be minimised. Either the hosing can be replaced after a given length of time regardless of the level of wear or a wear detection system can be used.

The detection of wear can however be a time consuming task. For example, manual checking of a pipe can be difficult. It is therefore desirable to provide automated systems for the detection of wear.

One type of article for which the invention may be particularly useful is the so-called pinch valve, such as may be used in industrial processes in the ceramics, waste processing and mining industries for example. Pinch valves comprise a sleeve of compliant (usually rubber) material located within a piping structure. To close off the valve the compliant sleeve is clamped (or "pinched") to constrict its cross-sectional area available for fluid flow. Wear and plastic deformation therefore occurs as a result of repeated cycling of the valve and also potentially as a result of the abrasive effects of the fluids which pass through the valve.

Examples of wear detection systems already exist for industrial pinch valves. Current such systems either (i) utilise embedded copper wires within the rubber structure whose electrical continuity is monitored for the detection of wear or (ii) utilise a pair of spaced electrical conductors within the rubber structure which become exposed when the rubber wears and a conductive path is formed between them by the fluid passing through the valve or (iii) require the rubber to be doped to make it electrically conductive and its resistance is monitored for the detection of wear. However, the copper wires used in the first solution are ductile and are therefore prone to plastic deformation and premature failure; if used with an electrically conductive fluid within the valve there is also the risk that wear will not be detected even when the wire broken if it is exposed to the fluid. On the other hand, the second solution will only function with conductive fluids such as aqueous solutions and will not work with many oils and solvents. The third solution is incapable of distinguishing between general low levels of wear occurring over a substantial portion of the internal valve surface and a high level of localised wear (e.g. a deep crack within the rubber structure); this therefore leads to the early replacement of valves with a tolerable level of general wear on the assumption that there is more serious localised wear.

It is therefore an object of the present invention to provide for a wear detection system which mitigates the problems with prior art wear detection systems described above.

Accordingly this invention provides a fluid-conducting tubular article equipped with apparatus for use in detecting wear within the article comprising an optical fibre embedded within the article where wear is to be detected, the fibre being configured to define a plurality of successive portions spaced in the circumferential direction of the article and extending generally parallel to the longitudinal axis of the article along a significant length of the article.

In use of the wear detecting apparatus light generating means can be optically coupled to a first end of said fibre and light detection means can be optically coupled to a second end of said fibre to monitor the passage of light through it.

The invention thus provides an optical fibre which is embedded in the article which will experience wear, typically between the inner and outer surfaces of the tubular structure. In the usual case, when wear reaches the fibre the fibre itself begins to wear and eventually breaks, the resultant discontinuity in the passage of light through the fibre can be detected and the onset of wear can therefore be inferred. It is preferable in this respect that the fibre wears at a similar rate to the material of the article in which it is embedded. Even if this is not the case, wearing away of the surrounding material to leave the fibre unsupported is liable to result in breakage of the fibre when the article is subject to a mechanical load, especially in the case of a pinch valve sleeve or flexible hose for example. It is, however, also within the scope of the invention to detect wear of the article by monitoring the change of light transmission through the optical fibre as it wears but prior to breakage. In any case, the use of optical fibres means that the wear detection apparatus is independent of the electrical properties of either the article or the fluids passing through the article.

When the light detection means detects that the passage of light through the fibre is impeded or ceases this information may be communicated in any convenient way, e.g. by displaying it visually or by electronic communication to a monitoring system.

Although the term "light" is used it should be appreciated that this includes not only wavelengths within the visible part of the electromagnetic spectrum but also neighbouring parts of the infra red and ultra violet wavebands. Conveniently an inexpensive pulsed infra red light emitting diode can be used as the light source and a complementary photodiode can be used as the light detector. A simple electrical circuit can then indicate when wear occurs.

The orientation of the optical fibre within the article is important. For flexible articles such as the rubber sleeve structure of a pinch valve a helical winding of the fibre throughout the article would not be suitable. In the case of a pinch valve parts of the sleeve wall will be deformed to a relatively small radius of curvature when it is clamped in the closed position. This would place a helically wound fibre under a high degree of strain which could result in the fibre breaking and a false wear detection result.

In contrast if the fibre is generally parallel to the longitudinal axis of the article where it is laible to be deformed then the high strain can be avoided. Strict parallelism to the longitudinal axis of the article may not always be required, however, and departures of, say, 20 or 30° from parallelism or possibly even more may be permissible in some embodiments. Conveniently if the fibre is wound with a suitable number of loops back and forth along the article then the aforementioned generally parallel portions of the fibre can permit monitoring for wear of the corresponding length of the article around its entire circumference.

Conveniently the fibre should be located close to a critical wear point. For the case of pinch valves the fibre may be embedded just inside of the usual sleeve reinforcement. As wear abrades the inside of the sleeve the fibre will be broken before the reinforcement is breached and replacement of the valve can be effected before any failure of the article.

A further advantage of the fibre orientation is that its two ends may be located adjacent to one another, for example at the same end of the article. This would allow the associated light generating means and detection means to be located together.

A preferred embodiment of the invention will now described by way of example only with reference to the accompanying drawing which shows a pinch valve sleeve, partially broken away, having embedded therein an optical fibre in accordance with the present invention.

Turning to the Figure a pinch valve sleeve 1 comprises a flexible rubber pipe section 3 having end flanges 5. The flanges 5 are used to connect the valve into a piping structure (not shown). Embedded within the sleeve 1 is a single continuous optical fibre 7. The fibre 7 is wound back and forth through the length of the section 3 many times.

The fibre 7 is wound such that its two ends 9 and 11 enter and exit the sleeve in close proximity to one another. This allows the light generating and detection means (not shown) which are coupled to respective ends of the fibre to be located next to one another instead of at opposite ends of the sleeve.

As will be seen, the fibre 7 is wound to define a plurality of successive portions such as 13 which extend substantially parallel to the longitudinal axis of the article in the centre section of the sleeve. These portions are equi-spaced in the circumferential direction of the sleeve so that internal wear can be monitored around the entire circumference of its centre section without, however, subjecting the fibre to excessive bending when that section is clamped to close off fluid flow in use of the valve.

Claims

1. A fluid-conducting tubular article equipped with apparatus for use in detecting wear within the article comprising an optical fibre embedded in the article where wear is to be detected, the fibre being configured to define a plurality of successive portions spaced in the circumferential direction of the article and extending generally parallel to the longitudinal axis of the article along a significant length of the article,

2. An article according to claim 1 wherein said portions of the optical fibre extend in directions less than 30° from parallelism to the longitudinal axis of the article.

3. An article according to claim 2 wherein said portions of the optical fibre extend in directions less than 20° from parallelism to the longitudinal axis of the article.

4. An article according to claim 3 wherein said portions of the optical fibre extend substantially parallel to the longitudinal axis of the article.

5. An article according to any preceding claim wherein said first and second ends of the optical fibre are located adjacent to one another.

6. An article according to claim 5 wherein said first and second ends of the optical fibre are located adjacent to an end of the article.

7. An article according to any preceding claim wherein the optical fibre is located within the article such that in use it is between a critical wear point and a surface of the article that is subject to wear.

8. An article according to any preceding claim further equipped with light generating means optically coupled to a first end of said fibre and light detection means optically coupled to a second end of said fibre.

9. An article according to claim 8 wherein the light generating means is a light emitting diode and the light detection means is a photodiode.

10. A pinch valve sleeve equipped with apparatus for use in detecting wear as defined in any preceding claim.

11. A pinch valve comprising a sleeve according to claim 10 and means for clamping the sleeve to constrict the cross-sectional area thereof available for fluid flow.