GB2072853A

GB2072853A - Electrode probe assemblies

Info

Publication number: GB2072853A
Application number: GB8107132A
Authority: GB
Original assignee: Sybron Corp
Current assignee: Sybron Transition Corp
Priority date: 1980-03-31
Filing date: 1981-03-06
Publication date: 1981-10-07
Also published as: MX151475A; GB2072853B; BR8101728A; JPH0145574B2; JPS56160651A

Abstract

An electrical fault finder for monitoring the insulated lining of steel or other metal vessels, pipes or containers has an electrode 1 with a threaded stud inserted in a hole (18, 19) in a member 10, with an insulating gasket 7 between the electrode and the member, and an insulating member 6, covering the portion of the stud adjacent the electrode. Resilient means interacting with a securing nut threaded on the stud bias the electrode toward the gasket 7 so as to prevent leakage due to shrinkage of the gasket. Electrical connection to an external circuit is made via the stud. <IMAGE>

Description

SPECIFICATION Electrode probe assemblies This invention relates to the electrical testing of protective linings provided in steel or other metal pipes, vessels and other containers for liquids and is more particularly concerned with the structure of an electrode probe assembly for performing such tests.

Steel containers such as vessels and pipes are widely used in the food and chemical industries for the processing of liquids. A protective lining of a material such as glass, a plastics material or rubber is often required in order to separate the steel shell of the container from the liquid, which can have a corrosive effect on the container. It is important for the lining to be free from defects or faults, because contact between the liquid and the shell could cause the steel to corrode and could possibly result in failure of the container. Also, corroded steel particles would contaminate the liquid product.

For these reasons, electrical fault finders have been used for the detection of defective linings, eliminating unexpected and possibly catastrophic vessel failures and allowing transfer of the liquid product to another vessel before contamination of the product with iron has become critical.

Because of the early warning of the presence of defects in the linings given by these fault finders, repairs to the linings can be made, before the damage becomes permanent and irreparable.

An intact lining functions as an electrical insulator between the conductive liquid product and the steel or other metal of the container. This insulating property can be utilized in testing for defects.

One way'to detect faults in the lining is to apply a voltage between an electrode immersed in the conductive liquid product in the container and the steel shell or other metal component of the container holding the liquid. If current flow occurs, then clearly this indicates the presence of one or more defects in the lining.

In an alternative technique, passive galvanic fault finders may be used. These operate on the principle that dissimilar metals electrically connected together and immersed in an electrolyte, namely, the conductive liquid product, will generate a voltage between the metals. Such a voltage will be produced if there is electrical contact through the lining, so that galvanic fault finders indicate the presence of such a fault by detecting this voltage or the current consequently produced. U.S. Patent Specifications 3,831,058 and 3,858,114 describe an arrangement in which a platinum electrode is immersed in the electrolyte, namely the liquid contents of a lined steel vessel. The platinum electrode must be mounted in such a way that it is electrically insulated from the steel shell.If the liquid contents of the vessel make contact with the steel shell, a voltage arises between the shell and the electrode.

Since such a contact can only occur by way of a fault in the lining, monitoring to detect the existence of this voltage or the resultant current provides an indication of the presence of a fault.

Both the impressed voltage and the galvanic action arrangements can use similar probe assemblies in order to locate an electrode in the liquid contents of a vessel or other container. One known kind of probe assembly, for use in a vessel, includes an electrode mounted on the outlet flush valve of the vessel. Probes may also be mounted on other components, such as spacer rings, blind flanges and baffles.

Prior to the present invention, it has been necessary for the component or, in general terms, the member on which the electrode is mounted to be electrically insluated both from the container and from any grounded metal. This is because the metal member is used as part of the electrical circuit of the probe assembly. An example of a prior art arrangement is shown in Figure 3 of the accomapnying drawings, described in detail below, which represents an electrode screwed into the head of a flush valve. The electrode, the valve head and the valve stem, as well as a handwheel and a valve frame, form the various components of an electrical circuit leading from the electrode and are electrically insulated from the valve body and the vessel shell by virtue of the glass or other lining provided.The various parts maintain their electrical isolation by the provision of insulating spacers or by actual physical separation from any grounded metal.

Environmental factors and maintenance routines tend to degrade the electrical isolation of probe assemblies. Humidity, rain, corrosive vapours, smog and dust build up deposits on the exposed parts of probes. These deposits can electrically bridge across insulating spacers or can otherwise affect the electrical continuity between parts of the electrical circuit. It is common practice for vessels to be hosed down to keep them clean.

This ruins the electrical isolation of the probe assemblies, until they dry out. Sometimes, evidence of these problems is not easily seen. As an example, corrosion of the handwheel threads on a flush valve probe can create an open circuit.

Metal-to-metal contact between the mating parts of the threaded handwheel is necessary in order to complete the electrical fault-detection circuit.

Corrosion of other parts of the electrical circuit can also occur, possibly resulting in an open electrical circuit.

Another problem arises from tampering with the exposed parts of probe assemblies. An example is the common practice of field mounting an air actuator on the probe of a flush valve, so that the valve can be remotely opened and closed.

Improper installation of the actuator grounds the valve probe, rendering it ineffective.

Another difficulty with this design of probe assembly is caused by leakage and/or breakage of the electrode, which is made of a tantalum alloy.

This material is very brittle and over-tightening of the electrode can easily cause it to break. The acceptable tightening torque is very low. Also, when the electrode is installed, a polytetrafluorethylene (PTFE) gasket is used to make a liquid-tight seal. However, if the electrode has sharp edges, the electrode may cut through the gasket as it is screwed into place. Another problem is caused by relaxation of the PTFE gasket caused by the passage of time or by temperature changes. Both cutting and relaxation of PTFE gaskets can result in leakage of the probe installation.

If leakage from the electrode installation does occur, the associated instrumentation system may or may not indicate this, depending upon its principle of operation. With a galvanic fault detection system, a negative reading is usually indicative of a leakage at the electrode, if no open circuit exists in other parts of the electrical arrangement. With an impressed low-voltage direct current system, there is no indication at all if the electrode leaks. In either case, leakage at the electrode can result in corrosive attack on the member, leading to component damage.

There is thus a need for an electrical testing arrangement applicable to lined containers for liquids which avoids the problems of existing arrangements. The present invention provides an electrode probe assembly which meets this need.

According to this invention, an electrode probe assembly for locating faults in the lining of a lined metal vessel, pipe or other container for liquids is provided, which comprises a member associated with the container and having a bore extending from outside the container and ending inside the container, an electrode positioned on the member at the inside end of the bore, an insulating gasket located between the electrode and the member, a threaded stud fixed to the electrode and extending through the gasket and the bore, an insulating member covering the part of the stud nearer the electrode, a securing nut threaded on the other part of the stud so as to secure a resilient member mounted on the stud, whereby the electrode is biased toward the gasket and the member, and an electrical conductor extending from the stud out of the vessel.

Preferably, the bore comprises a first bore portion extending from outside the container to a junction located inside the member and a second bore portion extending from the junction to the end of the bore, the part of the stud covered by the insulating member being disposed in the second bore portion and the securing nut and the resilient member being located in the first bore portion. In an especially preferred form of construction, the bore junction is bevelled and a hub bevelled on one side to conform to the bevelled part of the junction surrounds the stud and is located between the bore junction and the resilient member. The detailed construction preferably includes an insulating washer, which is located on the stud between the hub and the resilient member.

According to a preferred feature of the invention, the resilient member comprises a plurality of disc springs insulated from the member supporting the electrode.

According to a further preferred feature, the electrode comprises platinum, the stud is a steel set screw having one end threaded into the electrode and the electrical conductor comprises an insulated wire attached to the other end of the stud. Preferably, the electrode comprises a platinized tantalum nut.

Examples of members include valve heads, pipe spacers, baffles and blind flanges. In a particuiaily preferred form of the invention, the member is a one-piece valve head and stem having the bore extending along its axis.

In order that the invention may be fully understood, various embodiments of probe assemblies are illustrated in the accompanying drawings, by way of example, wherein: Figure 1 shows an electrode, subassembly for use as a component of a probe in accordance with the present invention; Figure 2 shows a complete probe assembly mounted in a valve head, as an example of a member on which the probe assembly of the invention may be mounted; Figure 3 shows a probe assembly of the prior art mounted in a valve head, for comparison with the probe assembly of Figure 2; Figure 4 shows a part-sectional, partelevational view of a drain valve which includes the valve head of Figure 2; Figure 5 shows an exploded view of the probe assembly shown in assembled form in Figure 2; Figure 6 shows a wrench suitable for assembling the probe assembly; and Figure 7 shows an elevational view of a pipe spacer, as an example of another member upon which the probe may be assembled.

In contrast to the closest prior art, the electrode probe of the present invention is completely electrically isolated from the member on which it is mounted and also from the wall or shell of the vessel, pipe of other metal container for liquid in which it is used. Furthermore, the probe has an insulated electrical circuit leading from the electrode to the outside of the container. This circuit is immune to corrosion, humidity and water. The electrode probe includes a sealing gasket arranged so as to make a liquid-tight seal, which is maintained even if the sealing gasket relaxes somewhat after installation.

Figure 1 shows the electrode subassembly of the probe. The electrode 1 has an active portion which is preferably made of platinum. Becauseof the high cost of platinum the electrode 1 preferably comprises only a thin layer of platinum applied to an electrode substrate, which preferably is an inert alloy of tantalum. For the purposes of this description, including the claims, the term "electrode" refers to the entire component of platinized tantalum, constituting the preferred form of the electrode 1.

The present invention provides an improvement in the mechanical function of the electrode. In the closest prior art construction, the electrode takes the form of a screw located by being screwed into a steel member, which thus needs to be electrically isolated from the vessel or other container equipped with the probe. In contrast, it is a preferred feature of the invention that the electrode 1 may be in the form of a nut, which is intrinsically much stronger than a screw.

As shown in Figure 1, the underside of the electrode nut 1 is drilled and tapped. The drilling and tapping of tantalum are difficult, but, for the purposes of this invention, a good quality internal thread is not necessary. The thread quality in the drilling need only be adequate to receive and hold fully a socket head set screw 3. The design allows for reasonably coarse tolerances and the use of a coarse thread on the set screw 3. This coarse thread eliminates the chance of cross-threading.

Furthermore, the socket head set screw 3 forms the threaded portion of the electrode subassembly and is preferably made of hardened steel.

Therefore, in contrast to the prior art, the threaded portion is no longerformed of a tantalum alloy, which could easily break off because of the brittleness of tantalum and its alloys.

It is also difficult to solder or weld components to tantalum, becuase of its high temperature properties. In the preferred embodiment, a PTFE coated wire 4 is soldered in the socket 5 at the end of the steel screw 3 or is otherwise affixed to the set screw 3, thus making a reliable electrical connection to the electrode 1. Thus, the set screw 3 serves both as a mounting stud and as an electrical connection to the electrode 1.

The set screw 3 is electrically insulated over most of its iength by means of heat-shrinkable tubing 6, so that only the end part of the set screw 3 where it is joined to the wire 4 is exposed. A PTFE gasket 7 is slipped over the screw 3 and the tubing 6 and pushed up against the underside of the nut forming the electrode 1, which is preferably provided with a dependent peripheral sealing lip 2. In practice, the probe is mounted in an aperture in the metal member with which the probe is to be assembled, the aperture receiving the probe so that it contacts the tubing 6 and the gasket 7. The tubing 6 and the gasket 7 thus provide electrical insulation from the steel or other metal member in which the probe is mounted.

The electrode subassembly is also shown in Figure 2, in conjunction with the member with which it is assembled, namely a valve head 10.

The electrode probe thus comprises the insulated ,electrode sub-assembly described above, a bevelled hub 8 and a probe subassembly 9 which is shown in detail exploded view in Figure 5 and described further below. The arrangement and function of these latter items are best explained in relation to a probe assembled in a vessel, pipe or other container. A probe assembly in a valve head is shown in Figure 2, for comparison with the prior art probe assembly of Figure 3, and an example of a vessel or container is the drain valve shown in Figure 4.

The valve heads of Figures 2 and 3 are identical except for the modifications necessary in the former to allow it to accept the improved electrode arrangement of the invention. The valve head 10 and its valve stem 11 are fabricated in one piece from steel and a layer of insulating material, for example glass, is provided over the surface of the valve head 10 and valve stem 11.

As shown in Figure 4, the valve head 10, when closed, mates with a matching valve seat 12, preferably made of PTFE. The valve stem 11 extends through the housing of the drain valve of Figure 4 and is connected by means of a junction member or bearing 13 to a screw 14 and handwheel 1 5. The screw 14 is threaded through a tapped valve frame 16. Bars 17 extend from the junction member 13 to slots in the frame 1 6.

Rotation of the handwheel 1 5 turns the screw 14, which axially moves the valve head 10 with respect to the valve seat 12. The bars 17 prevent angular movement of the valve stem 11 and the valve head 10. The same arrangement would be used in a drain valve equipped with the prior art electrode of Figure 3, such an electrode having the deficiencies discussed above, however.

Referring to the improved arrangement of Figure 2, the valve stem 11 has a passageway along its axis comprising a first bore 1 8 which is drilled through the valve stem 11 and terminates in the valve head 10. The passageway also includes a second and smaller diameter bore 19, drilled in the opposite direction along the axis of the valve head 10 and meeting the first bore 18 at a junction 20. A diamond tip bit may be required in carrying out the drilling operation, e.g. through glass layers to produce the second bore 19. The junction 20 of the two bores 1 8, 1 9 is bevelled and this is conveniently achieved by making it to the same angle as the bit used for drilling the first bore 18.

The electrode subassembly of Figure 1 is fitted on the valve head 10, the set screw 3 being inserted in the smaller diameter second bore 1 9 and extending into the larger diameter first bore 18.

A hub 8, bevelled on one side to conform to the bevel formed at the junction 20, is mounted over the set screw 3 where the electrode subassembly protrudes into the first bore 18. The other side of the hub 8 provides a flat surface against which the probe subassembly 9 presses. The heat-shrinkable tubing 1 6 on the set screw 3 and the PTFE gasket 1 7 provide electrical insulation between the screw 3 and the steel of the valve head 10, as well as between the former and the bevelled hub 8. The gasket 1 7 and the sealing lip 2 on the electrode 1 prevent liquid from reaching the steel of the member 10 on which the probe is mounted.

The probe subassembly, Figure 5, includes, in order, from the flat surface of the hub 8, a ceramic insulating washer 21, a first flat metal washer 22, a plurality of disc springs 23, a second flat metal washer 22 and a securing nut 24 having a thread matching that of the set screw 3. The components of the probe subassembly are held together by a piece of PTFE heat-shrinkable tubing 26. The tubing 26 electrically insulates the subassembly 9 from the steel of the member 10, 11.

During assembly of the probe, the nut 24 is tightened by an extending hollow wrench 25, such as that shown in Figure 6. The probe subassembly 9 is placed on the wrench 25, slipped over the electrode wire 4 and inserted up the first bore 1 8.

The electrode 1 is held to prevent rotation and the nut 24 of the probe subassembly 9 is screwed on to the set screw 3, by means of the wrench 25, thereby clamping the sealing gasket 7 between the lip 2 on the nut 1 and the surface of the valve head 10.

If the gasket 7 relaxes, due to cold-flowing, the disc springs 23 compensate for the amount of relaxation, thus maintaining a liquid-tight seal.

Because the electrode 1 is held stationary during installation, the gasket 7 is not cut by the lip 2 on being tightened. The ceramic insulating washer 21 electrically insulated the first metal washer 22 from the hub 8.

The electrode wire 4 continues down the first bore 18 and may be fed through a hole provided in one of the bars 17 to a terminal box 27 provided at the end of the bar 1 7. Armoured cable is preferably used for connection of the probe assembly to instrumentation.

The electrode probe is not limited to use with valves, but may be mounted on a variety of members for use both in vessels and in pipes.

Because the probe is self-insulating, there is no need to insulate the member from the rest of the structure or from ground.

In Figure 7 of the drawings, the probe is shown mounted in a pipe spacer 28. A rod 29 is radially attached to the side of the spacer 28 and bores (not shown) are provided in the spacer 28 and the tube or pipe associated with the spacer 28, in order to receive the probe. Otherwise, the arrangement is the same as that used in the valve stem shown in Figures 2 and 4 and need not be described further. Other possible members include baffles and blind flanges.

The invention markedly improves upon the performance and reliability of earlier faultdetection probe assemblies used for many years.

Parts other than the electrode are located inside the member and are protected from environmental factors and subsequent degradation. The probe assembly is therefore unaffected by moisture, dirt and breakage. It maintains a leak-tight seal up to the limits of the gasket material. The function of the fault detection system is not hindered or degraded in any way by the improved structure, but is more reliable and trustworthy than the closest prior art.

Claims

1. An electrode probe assembly for locating faults in the lining of a lined metal vessel, pipe or other container for liquids, which comprises a member associated with the container and having a bore extending from outside the container and ending inside the container, an electrode positioned on the member at the inside end of the bore, an insulating gasket located between the electrode and the member, a threaded stud fixed to the electrode and extending through the gasket and the bore, an insulating member covering the part of the stud nearer the electrode, a securing nut threaded on the other part of the stud so as to secure a resilient member mounted on the stud, whereby the electrode is biased toward the gasket and the member, and an electrical conductor extending from the stud out of the vessel.

2. An electrode probe assembly according to claim 1, wherein the bore comprises a first bore portion extending from outside the container to a junction located inside the member and a second bore portion extending from the junction to the end of the bore, and part of the stud covered by the insulating member being disposed in the second bore portion and the securing nut and the resilient member being located in the first bore portion.

3. An electrode probe assembly according to claim 2, wherein the bore junction is bevelled and a hub bevelled on one side to conform to the bevelled part of the junction surrounds the stud and is located between the bore junction and the resilient member.

4. An electrode probe assembly according to claim 3, wherein an insulating washer is located on the stud between the hub and the resilient member.

5. An electrode probe assembly according to any preceding claim, wherein the resilient member comprises a plurality of disc springs insulated from the member supporting the electrode.

6. An electrode probe assembly according to any preceding claim, wherein the electrode comprises platinum, the stud is a steel set screw having one end threaded into the electrode and the electrical conductor comprises an insulated wire attached to the other end of the stud.

7. An electrode probe assembly according to claim 6, wherein the electrode comprises a platinized tantalum nut.

8. An electrode probe assembly according to any preceding claim, wherein the member is a one-piece valve head and stem having the bore extending along its axis.

9. An electrode probe assembly according to any of claims 1 to 7, wherein the member is a pipe spacer having a rod radially attached thereto and the bore extends through the rod into the interior wall of the pipe spacer.

10. An electrode probe assembly according to any of claims 1 to 7, wherein the member is a baffle.

11. An electrode probe assembly according to any of claims 1 to 7, wherein the member is a blind flange.

12. An electrode probe assembly substantially as hereinbefore described with reference to Figures 1,2 and 4 to 7 of the accompanying drawings.