GB2496890A - Corrosion detector - Google Patents

Abstract

Apparatus for corrosion detection within a fluid handling system containing a fluid comprises an element that is sensitive to corrosion, in contact with the fluid and arranged to break in response to a predetermined level of corrosion, an electrical readout circuit arranged to monitor the electrical continuity of the element, indication means for providing an indication that the readout circuit has detected a break in continuity of the element, a sensor housing to protect the element from particles and hydrodynamic forces while allowing sufficient fluid communication for corrosion of the element to be representative of corrosion in the fluid handling system. The sensor housing is provided with a purge hole through which, in use, air is expelled from the sensor housing to ensure that the element is fully wetted by the fluid. Also, the housing may include a low friction and/or non stick material to improve fluid flow.

Description

Improved corrosion detector The present invention relates to an improved corrosion detector for corrosion monitoring, for example to permit sensing of the occurrence of a predetermined level of corrosion.

Corrosion, for example electrolytic corrosion, is a major cause of failure in systems of pipes for handling fluid, for example in wet central heating systems. Over time corrosion can damage the structure of the fluid system leading to failure. For example a pipe wall or radiator may be thinned by corrosion until it mechanically fails under pressure or structural load. Deposits of corrosion can accelerate wear of mechanical components and reduce overall system efficiency, for example by increasing energy consumption, and may result in increased CO2 emissions.

Central heating systems frequently employ water as a working fluid for the transport of heat. Such heating systems frequently comprise a number of different metals for example copper, aluminium, brass and steel, comprising for example pipes, heat exchangers, pumps, fittings and radiators. Electrolytic corrosion occurs due to the dissimilar metals and the presence of water which acts as an electrolyte, resulting in accelerated corrosipn of less noble materials, for example steel.

The corrosion of metal parts may lead to the build-up of sludge typically comprising iron oxide or rust. Removal of the sludge can be achieved, at least to some degree, for exampLe, by power flushing and/or by the use of a magnetic separation technique.

Corrosion may further damage parts or reduce their efficiency. To reduce corrosion it is known to add a corrosion inhibitor to the working fluid. This is typically a liquid comprising various chemicals that is added to the working fluid. The effect of such corrosion inhibitors may diminish over time due to degradation of the chemicals. The addition of fresh working fluid to the system, which may take place as a result of maintenance, will also tend to dilute the concentration of the corrosion inhibitor and reduce its effectiveness. It is known that damage resulting from corrosion can result in reductions in overall central heating system efficiency and can damage components and prevent them from working.

A known technique for measuring the rate of corrosion within fluid systems is to measure the electrical resistance or electrical continuity of a metallic element immersed in the fluid. Changes in the resistance of the metaLlic element in contact with the fluid are attributable to metal loss from the exposed element. An incremental change in resistance is proportional to an increment of corrosion. A reference resistor eLement which is not exposed to the fluid is typically incorporated into the probe comprising the metallic element in contact with the fluid, and the ratio of resistance of the reference and exposed element is typicaLly measured to eliminate changes in resistance due to temperature. An example of a resistance based corrosion monitoring system is described in US3094865. Such prior art resistance based corrosion monitoring devices are directed towards providing a measurement of the rate of corrosion over a relatively short period of time.

It is known to carry out a chemical analysis of the working fluid to detect the presence of a corrosion inhibitor. Such testing cannot be used on a continuous basis, and is relatively tithe consuming and inconvenient to carry out. Furthermore, the chemicals used typicalLy have a relatively short shelf life and tests carried out with degraded reagents can give inaccurate results.

US61 31443 discLoses a corrosion monitor that indicates when a threshold level of corrosion has taken place. A corrodible interior wall excludes fluid from an interior cavity of the monitor. The interior cavity includes a material that reacts with the fluid to indicate penetration of the corrodible wall by the fluid. An optical indication means is disclosed in which a transparent window of the interior cavity is coated with a material that changes colour when the corrodible interior wall has been penetrated by the fluid.

This invention requires that the corrodible eLement be of sufficient thickness to survive the pressure of the fluid and this limits the minimum threshold that the device is responsive to. In addition the indication by means of a colour change could easily not be noticed due to difficult viewing conditions or a failure to actively inspect a device for colour change.

The present applicant has identified a need for a sensitive, low cost method of detecting corrosion within fluid systems. Detection of corrosion, or of the fluid becoming corrosive, can reduce the formation of the aforementioned sludge and so negate the disadvantages associated with the build up of such sludge and also negate need to perform sludge removal operations. A further need has been identified by the present applicant for a more sensitive method of indicating when a predetermined threshold level of corrosion has taken place, and of providing a more obvious warning by the provision of an indicator light and audible sound. Copending British Patent Application Number 1108753.3 describes a method and apparatus suitable for detecting and providing a warning when the fluid in the system has become corrosive. The present invention relates to improvements and enhancements of that type of arrangement.

According to the present invention there is provided an apparatus as defined in either Claim 1 or Claim 3. Optional features are set out in the dependent claims.

Reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 a, lb and 1 c are schematic diagrams of a sensor assembly lid according to an embodiment of the invention; Figure 2 is a schematic diagram of a sensor assembly body according to an embodiment of the invention and with which the lid of Figures la and lb may be used; Figure 3 is a schematic diagram of an output device according to an embodiment of the invention; and Figure 4 is a schematic diagram of an installation arrangement according to an embodiment of the invention; Figure 1 and 2 are schematic diagrams of a sensor assembly according to an embodiment of the present invention. The sensor assembly comprises a lid or end cap 1 serving, in use, in this embodiment. as one or more of a flow rate trimmer, a particulate separator and/or means by which air can be purged or bled from the assembly, as detailed below, and a body 2 to which the cap 1 is fitted, in use.

The cap 1 has a circular cross section, comprises a substantially fnisto-conical region, an annular lip or protrusion 12 on the base side thereof and three bleed holes 11. The three bleed holes 11 exit the cap through the tapering face of the substantially frusto conical cap-The interior of the frusto-conical region and the protrusion 12 together define a recess 13 within the cap 1.

The body 2 has a circular cross section, and is provided with a recess 24 of circular cross section and of stepped form so as to define a shoulder, and a larger diameter part or shoulder recess 26 around its free edge for receiving the protrusion 12 of the cap 1. The body 2 further comprises an entry hole 22 and an exit hole 23 through which fluid passes to enter and leave the recess 24 in use.

Two conducting sensor elements 21 are disposed across the recess 24, substantially perpendicular to the circular cross section of the body 2. The sensor elements rest on the shoulder and are connected at junctions 27 to conductors 25 which are integrated into the body 2. The conductors 25 are in turn are connected to an electrical readout circuit via wires or pins (schematically indicated by 28).

The sensor housing, comprising the body 2 and the cap 1, is arranged to support the sensor elements 21 in use, and to protect the elements 21 from hydrodynamic forces and water or fluid borne particles or particulates while allowing fluid communication with the sensor elements 21. The cap 1 is secured to the body 2 by a push (interference) fit between the protrusion 12 and the shoulder recess 26. The protrusion 12 may alternatively be arranged to press fit into the circular recess 24, without the additional shoulder recess 26.

The assembled sensor housing thus defines an internal chamber, defined by the recess 13 of the cap I and the recess 24 of the body 2. Providing a shoulder recess 26 allows the interior of the internal chamber have smooth walls, thereby encouraging uniform flow of fluid around the elements 21 and assisting to prevent or reduce the formation of any areas of fluid stagnation within the internal chamber.

The arrangement of the sensor elements across the internal chamber, perpendicular to the axis of the body 2 (and parallel to the circular cross section of the body 2) allows the eLements to be disposed across the internal chamber 24 while at the same time allowing ease of assembly The assembly can thus be of compact form; and minimise frictional resistance in the pipeline in which the sensor is installed, thus avoiding significantly negatively impacting upon the system performance.

The sensor elements 21 conveniently comprise thin metal foil, wire or other member of an electrically conductive material, and which is corrodible in a manner similar to the types of material present in the fluid system in which the device is installed. By way of example, the material may comprise a thin iron foil. However, it will be appreciated that other materials may be used and the invention is not restricted in this regard. The sensor elements 21 are, as mentioned above, electrically connected to the conductors 25! and are mechanically secured between the cap 1 and body 2 of the housing at the shoulder recess 26 where the protrusion 12 of the cap 1 is received in the body 2. The cap 1 and body 2 in this region comprise a relatively compliant material that is not corrodible, for example a plastics material.

The cap 1 and body 2 seal around the sensor elements 21 to reduce, or ideally prevent, fluid from contacting the junctions.7 and/or the conductors 25, or restrict fluid entry into these regions. Both galvanic corrosion and crevice corrosion are thereby prevented, or at least reduced, at the junction 27 which may result from dissimilar metals at the junction, and from flow stagnation around the junction respectively.

Furthermore, sealing the integral condUctors 25 and/or junctions 27 away from the fluid mitigates the potential for a conducting path through an electrically conductive fluid that bypasses the sensor elements 21. Sealing around the sensor elements 21 may be accomplished due to the compliance of the cap 1 and body 2 around. the sensor elements 21, or with the aid of an additional gasket, or by the use of an adhesive or similar.

As the skilled person will appreciate, the conducting path through the fluid has the potential to make it difficult to detect a change in electrical conductivity as a result of a loss of continuity in the element. For sensor elements with low resistance (for example: that are relatively thick) or for working fluids that are relatively poor conductors (for example de-ionised water), conductivity through the fluid may not be a limiting factor. In some applications, for example early corrosion detection in central heating, the fluid conducts relatively well, and the need for a highly sensitive sensor element results in a relatively resistive sensor element 21.

The sensor elements 21 may therefore be arranged to tail leaving a minimal surface area in contact with the fluid at either side of the chamber: The conduction path into the working fluid may consequently be sufficiently poor that it is relatively straightforward to distinguish a loss of electrical continuity in even relatively resistive elements. One arrangement that may facilitate such a mode of failure of the element 21 is to use a sensor element of substantially uniform thickness so that it corrodes away fairly uniformly, leaving no conducting parts within the chamber. The sensor elements 21 may aLternatively be arranged to fail at the both chamber walls at substantially the same time.

The sensor eLements 21 are secured spaced away from the base and lid of the chamber; and extend across the chamber spaced well apart from the base and lid of the chamber. The sensor elements 21 preferably extend across the chamber substantially equidistant from the base and ld of the chamber.

With the arrangement of the embodiment, the sensor elements 21 extend from a waD of the internal chamber of the housing, and no regions of the sensor elements 21 are exposed to the fluid in crevices which are subject to very low flow velocity and at which fluid may not be readily exchanged by diffusion. This is intended to reduce crevice corrosion, which can lead to unrepresentative corrosion rates where corrodible elements are in contact with a corrosive fluid at crevices, for example in a crack or narrow aperture between components. The orientation of the sensor elements 21 so that they present a very low cross section perpendicular to fluid flow within the chamber further improves the uniformity of fluid velocity within the chamber.

The sensor elements 21 may comprise a thinned region in the region that extends across the chamber, and thicker more robust regions where they are connected to the electrical contacts 2. Varying numbers of sensor elements 21 may be used, as appropriate to the requirements of the application, for example one oi three elements may be used instead of two. Multip!e sensor elements may be arranged to break at the same level of corrosion to provide a degree of redundancy and/or reliability, or an array of sensor elements with different corrosion thresholds may be used to indicate an amount of corrosion.

The conductors 25 incorporate electrical connectors suitable for making connections to the electrical readout circuit.

The entry hole 22 and exit hole 23 of the body together comprise a flow restriction which limits the hydrodynamic farces imposed on the sensor elements 21 is use, while providing sufficient fluid communication with the elements 21 for the corrosion of the sensor elements 21 to be representative of corrosion within the fluid handling system.

A filter may be provided at the entry hole 22, which may be integrally formed as part of the body, or may be a separate part The filter prevents or reduces damage to the sensor element arising from particle impingement. The entry hole 22 and exit hole 23 are arranged to allow fluid to flow past the sensor elements 21 when the housing is assembled.

Although the entry hole and exit hole have been described as on the body 2, a plurality of fluid inlets and outlets may be arranged in different positions on the cap or the body.

The sensor body 2 may be of such diameter to allow it to be filled to a system of pipe-work or a heating component such as a radiator or boiler using a standard compression fitting. Alternatively, the sensor body 2 may be provided with a threaded outer body and connector to al]ow it to be attached to a system of pipe-work or heating component.

The sensor body 2 and cap 1 may comprise a plastics material; a resin or an acrylic, or may be a ceramic or formed from another material, preferably a material that is not electrically conductive. The material of the cap 1 may be selected to reduce the risk of particles adhering thereto, in use. Whilst this may be achieved by the use of a suitable material, it may also be possible to achieve this effect by the application of an appropriate coating to all or part of the cap. The body 2 and cap 1 preferably comprise an electrically insulating material which is resistant to chemicals, for example acids, has good mechanical properties, is suitable for use at elevated temperatures such as degrees C, and is able to withstand fluid pressures in excess of 6 bar. For example they may comprise an engineering plastics material and/or a fluoropolymer such as polytetrafluoroethylene. Where a coating is used, this may also be of a fluoropolymer such as polytetrafluoroethylene It will be appreciated that in the arrangements described hereinbefare the sensor element 21 is electrically conductive and that its continuity is monitored by sensing whether or not a current can flow along the length of the sensor element 21.

B

Figure 4 shows an assembly 4 comprising two valves 41, a fluid coupling element 42, a bypass tube 44 and an inhibitor injection point 43. The fluid coupling element 42 is a T connector, and is arranged with a co-axial main fluid inlet and main fluid outlet, and an aperture 45, substantially perpenthcular with the axis of the main inlet and out]et, into which the sensor housing is at least partly received in use. The valves 41 are conveniently designed so as to be of multipart form, allowing replacement of the sensor without requiring the system to be drained.

In use, the sensor housing may protrude into the main flow through the coupling element 42, and the sensor body 2 may be augned such that axis of the entry hole 22 and exit hole 23 are parallel with the main fluid flow. The flow wifl thereby impinge on the external face of the body in the region of the exft hole, resulting in pressure difference between the entry hole 22 and exit hole 23 that drives fluid flow through the chamber 24 of the sensor housing. The sensor housing and the coupling element 42 may be provided with corresponding features that assist in achieving the proper relative orientation, for example a visual indicator, or a mechanical guide.

As is understood by the skilled person, an increase in fluid velocity is accompanied by a decrease in fluid pressure and vice versa (by Bernoulli's principle). The greater velocity of the main flow relative to the fluid velocity within the sensor chamber may therefore result in a pressure difference that assists in removing air from within the chamber 24 via the purge holes 11 in the cap. Provided the sensor housing is suitably oriented, the buoyancy of the air in the fluid may alternatively or additionally assist in removing air from the chamber 24 via the purge holes 11. Purging or bleeding air from the chamber 24 in this manner is advantageous in that it assists in ensuring that the elements 21 are completely bathed in the fluid. The risk of erroneous outputs arising from the elements 21 being only partly immersed in the fluid are reduced, and so the accuracy of the device is enhanced.

The multport valves 41 may be used to divert fluid flow away from the fluid coupling element 42 into the bypass tube 44, thereby isolating the fluid coupling element 42 from the fluid handling system so that maintenance or inspection of the sensor may be undertaken without disruption. With the fluid coupling element 42 isolated, the sensor housing may be removed from the coupling element 42, for instance to replace or inspect a broken sensor element 21. The valves 41 may also be arranged so that when flow is permitted through the bypass tube 4-4 from the fluid handling system, corrosion inhibitor can be introduced into the bypass tube 44 via the injection point 43, thereby introducing the inhibitor to the fluid handling system. The bypass tube 44 may be of transparent form, or include a transparent section, to aHow visual inspection of the cleanliness of the fluid in the system.

Figure 3 is a schematic diagram of a control and readout device 3 of a corrosion monitor comprising sensor connection points 31, a reset/test button 32, an antenna 36 and indicator l[ghts 33, 34, 35. The three junctions 25 of the sensor elements 21 may be connected to the sensor connection points via the integral conductors 25 of the sensor as indicated schematically in Figure 2.

The indicator lights 33, 34, 35 comprise a red 33, amber 34 and green 35 light that illuminate to indicate respectively that action is necessary, action should be taken at the next service, and that the situation is acceptable. The amber indication may correspond to a break in continuity of a single sensor element 21, and the red indication may correspond to a break in continuity of both sensor elements 21. The green indication may correspond to all sensor elements having continuity.

The antenna 36 of the control and readout device may also enable remote monitoring via a mobile phone, building management system, PC or laptop (not shown) to provide a warning to the user. The control and readout device may comprise a micro-processor arranged to control operation of the corrosion monitor.

It will be appreciated that the invention provides a low cost, convenient method and apparatus for corrosion detection. More specifically the invention provides for an obvious, clear indication that remedial action is required to prevent fluid systems from suffering significant damage from corrosion. The lateral orientation of the sensor elements with respect to the axis of the sensor housing allows the sensor elements to be readily replaced, and the arrangement described herein mitigates crevice corrosion, which would result in unrepresentative rates of corrosion.

Prior art approaches have generally been directed towards providing a measurement of the rate of corrosion1 and therefore required constant monitoring to indicate that a threshold had been reached. Known predetermined threshold based corrosion indicators are limited in their sensitivity and are not suitable for application in central heating systems using water that has not been specially treated to remove dissolved ions, and for which a highly sensitive sensor element is required.

An arrangement has been described in which the problem of electrical conduction through the fluid has been mitigated, thereby enabling the practical application of corrosion detection devices to central heating systems It will further be appreciated that providing an assembly with a valve to control fluid communication with the sensor element allows the sensor element to be conveniently replaced without disrupting the operation of the system. Providing two valves results in the potential for flow through the assembly past the sensor element in a manner which is representative of the corrosion environment of the parts to be protected. Little or no water loss takes place on installing the assembly, and no air is introduced to the system. Replacement of the sensor is very simple, requiring only a few minutes.

Whilst the description hereinbefore is of one design of sensor which, in use, is installed part way along a length of pipework, and the various openings are described as performing different ones of the flow rate trimming or control function, particulate separation or filtration function and means by which air can be purged or otherwise removed from the sensor, it will be appreciated that depending upon the orientation in which the device is installed, different ones of the openings may perform at least some of these tasks. For example, if the sensor is installed at a bend, for example by replacing a 9Q0 elbow for a T-shaped part, and installing the sensor in the T-shaped part, the face of the cap 1 may be exposed to the fluid flow and one or more of the openings formed there may serve as the opening by which fluid enters the sensor. In these circumstances, this openingS may serve as a particulate separator and/or flow rate trimmer. It will be appreciated that, depending upon the orientation in which the sensor is installed, others of the openings may perform these functions. It will be understood, therefore, that the invention is not restricted to the specific arrangement described hereinbefore, and that a number of modifications and alteration fall within the scope of the invention. ii

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments wfthout departing from the scope of the present invention.

Claims (1)

1. <claim-text>CLAIMS: 1 Apparatus for corrosion detection within a fluid handling system containing a fluid, the apparatus comprising: an element that is sensitive to corrosion, in contact with a fluid of the fluid handling system and arranged to break in response to a predetemiined level of corrosion; an electrical readout circuit arranged to monitor the electrical continuity of the element; indication means for providing an indication that the electrical readout circuit has detected a break in continuity of the element; a sensor housing, to protect the element from particles and hydrodynamic forces while allowing sufficient fluid communication for corrosion of the element to be 1 5 representative of corrosion in the fluid handling system; wherein the sensor housing is provided with a purge hole through which, in use, air is expelled from the sensor housing to ensure that the element is fully wetted by the fluid.</claim-text> <claim-text>2. The apparatus of claim 1, wherein the purge hole is arranged so that in use, substantial communication of the fluid will not take place through the purge hole.</claim-text> <claim-text>3. Apparatus for corrosion detection within a fluid handling system containing a fluid, the apparatus comprising: an element that is sensitive to corrosion, in contact with a Ildid of the fluid handling system and arranged to break in response to a predetermined level of corrosion; an electrical readout circuit arranged to monitor the electrical continuity of the element; indication means for providing an indication that the electrical readout circuit has detected a break in continuity of the element; a sensor housing, to protect the element from particles and hydrodynamic forces while allowing sufficient fluid communication for corrosion of the element to be representative of corrosion in the fluid handling system; wherein the sensor housing is of, or provided with a coating of, a low friction and/or non-stick material.</claim-text> <claim-text>4. The apparatus of claim 3, wherein the low friction material is a fluoropolymer.</claim-text> <claim-text>5. The apparatus of claim 4, wherein the fluoropolymer is PTFE.</claim-text> <claim-text>6. The apparatus of any preceding claim: wherein the sensor element extends across the internal chamber substantially equidistant from a base and a lid that define the internal extent of the chamber.</claim-text> <claim-text>7. The apparatus of any preceding claim, wherein the sensor elements are arranged to break in response to corrosion so that no part of the sensor e[ement remains extended into the fluid.</claim-text> <claim-text>3. The apparatus of claim 7, wherein the sensor elements are of substantially uniform thickness.</claim-text> <claim-text>9. The apparatus of any preceding claim, wherein the sensor housing has a substantially circular external cross section and comprises a cap and a body that, in use, define an internal chamber, and the eLement extends across the internal chamber in a direction substantially parallel to the plane of the substantially circular cross section 10. The apparatus of claim 9, wherein the sensor housing and/cl cap is provided with an entry hole through which fluid is communicated into the chamber, and the sensor housing and/or cap is provided with an exit hole through which fluid is communicated out of the chamber.11. The apparatus of claim 10, wherein the entry hole and/or exit hole define a flow restriction arranged to protect the element from hydrodynamic forces and/or particulate impact or erosion damage.12. The apparatus of claim 10 or cLaim 11, wherein a filter is arranged at the entry hole to protect the element from particles.13. The apparatus of any of claims 10 to 12, wherein the eLement extends across the flow from the entry hole to the exit hole.14. The apparatus of any of claims 10 to 13, wherein the entry hole and exit hole are substantially parallel to a diameter of the circular cross section.15. The apparatus of any of claims 9 to 14, wherein the substantially circular cross section is defined by a feature of the housing that mates with a standard plumbing fitting.16. The apparatus of any of claims 9 to 15! wherein the element is secured to the cap.17. The apparatus of any of claims 9 to 15, wherein, in use, the element is secured between the cap and body of the housing.18. The apparatus of any preceding claim, wherein a plurality of elements is provided which break in response to different predetermined levels of corrosion.19. The apparatus of any preceding claim, further comprising a coupling element comprising a main fluid inlet and a main fluid outlet, and an aperture arranged to receive the housing; the housing and coupling element being adapted so that, in use, a fraction of a main fluid flow between the main fluid inlet and main fluid outlet is directed through the chamber.20. The apparatus of claim 19, wherein, in use, the housing protrudes at least partly into the main fluid fLow.21. The apparatus of claim 19 or 20 when ultimately dependant on claim 1, wherein the coupling element and housing are arranged so that, in use, air within the chamber is drawn out of the purge hole by the main fluid flow.22. The apparatus of any of claims 19 to 21 when ultimately dependant on claim 1, wherein the purge hole exits the cap on a face which is substantially parallel to the main fluid flow.23. The apparatus of any of claims 19 to 22, wherein the coupling element comprises a T connector, with a coaxia] main inlet and main outlet, and an aperture for receiving the housing which is perpendicuLar to the flow.24. The apparatus of any of claims 19 to 23, wherein the main inlet and the main outlet comprise standard plumbing connections.</claim-text>