WO2015044536A1

WO2015044536A1 - Leak detection device and coating comprising said detection device

Info

Publication number: WO2015044536A1
Application number: PCT/FR2014/000214
Authority: WO
Inventors: Serge Albaladejo
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2013-09-24
Filing date: 2014-09-24
Publication date: 2015-04-02
Also published as: FR3011075A1

Abstract

The invention relates especially to a method for coating a conduit for transporting or storing a liquid by a device for detecting leakage of the liquid, comprising a layer of a fibrous insulating material (13) arranged so as to surround the conduit, and a layer of conductive felt (16) which extends flush with the layer of insulating material, the conductive felt (16) consisting of stainless steel fibres, wherein the layer of insulating material is secured to the wall of the conduit (10) by banding said layer with ties.

Description

Leak detection and coating device comprising this detection device

TECHNICAL AREA

The present invention relates to a device for leak detection and to a coating of a liquid transport or storage member comprising this detection device.

The invention also relates to a liquid transport or storage member equipped with such a coating, and to a method of coating a liquid transport or storage member.

The invention applies in particular to the coating of liquid sodium transport pipes and sodium storage containers forming part of a cooling circuit of a nuclear reactor.

In the remainder of the present application, unless expressly or implicitly stated otherwise, the term "conduit" is used to designate both a liquid transport conduit and a liquid storage container or an accessory - such as a valve - equipping such a conduit or container.

STATE OF THE ART

Especially in the case of sodium transport pipes, it is important to be able to control automatically and remotely, the appearance of a leak.

For this purpose, it has been proposed in patents FR2964456B 1 and WO2012032233 "Leak detection device and coating of a transport member or liquid storage device comprising this detection device" a device for detecting a leak of liquid at through the outer wall of a conduit which is electrically conductive, by detecting an electrical contact between the wall of the conduit and an electrically conductive member separated from this wall by an insulating member, the liquid being conductive as well.

The detection device described in these patents comprises a layer of a fibrous insulating material intended to extend against and surround the conduit, a layer of a fibrous conductive material which extends against and may surround the layer of fibrous insulating material, the fibrous conductive material consisting essentially of a carbon or graphite felt.

A disadvantage of this device is that when the carbon or graphite felt is brought to a high temperature in an oxidizing atmosphere, especially when the felt is heated to a temperature above 350 ° C (degree Celcius) in the air, the carbon or graphite fibers of the felt may oxidize, which may lead to carbon dioxide evolution and ash production.

This oxidation may result from the high temperature of the liquid transported or stored in the conduit, especially when this temperature reaches or exceeds 400 ° C or 500 ° C.

In this case, the thickness of the layer of insulating material could be increased in order to decrease the temperature of the carbon or graphite felt; however, this increase in thickness of the layer of insulating material would increase the time of impregnation of this layer with sodium, and could thus prevent or delay the detection of a leak.

In the case of a liquid such as sodium, this oxidation of the carbon or graphite felt may also result from an increase in temperature within the detection device when a sodium leak occurs, due to the strongly reaction. exothermic sodium in contact with air.

It is also known from patents FR2155534 and US3721970 a sodium leak detector formed by an insulating layer sandwiched between two layers of conductive material, and a device for detecting the closure of an electrical circuit between the two conductive layers.

One of the conductive layers may be formed by a metal conduit carrying the sodium. The insulating layer is formed of sodium wettable refractory fibers, in particular aluminum silicate in the form of a felt sheet, a mat, or a woven sheet. The conductive layers may be formed of a metal grid, in particular a grid or fabric formed of woven metal wires.

STATEMENT OF THE INVENTION

An object of the invention is to provide a leak detection device for a liquid flowing in a conduit or stored in a container, a conduit coating device or container incorporating this detection device, a transport or storage member of liquid equipped with such a coating, and a method of coating a liquid transport or storage member, which are improved and / or which remedy, at least in part, the shortcomings or disadvantages of the methods and devices known.

An object of the invention is to provide such devices that can quickly and reliably detect a liquid leak whose temperature can be in a range from 100 ° C (degree Celsius) to about 600 ° C, and prevent the release of combustion products in the case of a sodium leak, while maintaining or even improving the detection time of a leak.

According to one aspect of the invention, there is provided a leak detection device of a liquid stored or transported in an electrically conductive conduit, which is arranged to surround - or wrap - the conduit. The detection device comprises at least one layer of a fibrous (or filamentous) insulating material and at least one layer of a fibrous (or filamentous) conductive material which extends over / against the layer of fibrous insulating material, the fibers fibrous conductive material being made of stainless steel, the fibrous conductive material being in the form of a felt (nonwoven).

The steel alloy constituting the fibers of the fibrous conductive material generally contains at least 10.5% chromium, in particular in the order of 16% to 18% chromium, so that a passive film of chromium oxide covers the surface of the fibers.

This steel alloy may also contain nickel as well as molybdenum, to exhibit increased resistance to oxidation.

Such fibrous conductive material retains its mechanical integrity when heated to a temperature above 350 ° C, particularly when heated to a temperature of the order of 550 to 650 ° C.

In addition, when brought to such temperatures, in air, this fibrous conductive material does not produce gassing or ash.

This conductive material in the form of felt is more compact than a canvas or a grid, and has gaps smaller than the mesh of a canvas or grid. When this conductive felt is pressed against a layer of insulating material, a greater number of contact points is formed with the insulating layer, which improves the detection sensitivity of a leak.

The stainless steel felt is more flexible than a stainless steel mesh or grid, making it possible to improve the overlap of an area with a layer of fibrous insulation and thus further improve the detection sensitivity .

Thanks to the mechanical properties of the stainless steel felt which generally has a greater flexibility than a stainless steel cloth, while maintaining a rigidity / mechanical strength equivalent to that of a stainless steel cloth, a better contact between the layer of insulating material and the conduit carrying the sodium can be obtained by the mechanical action of the stainless steel felt which contributes to press the insulating layer against the sodium transport pipe, by a pressure exerted homogeneously over a large area of the insulating layer. This has the effect of improving the diffusion of sodium in the insulating layer during a leak, and thus improve the detection of this leak. The stainless steel felt, compared to the carbon felt, has a higher rigidity / mechanical strength, while maintaining an equivalent flexibility, which allows a better contact between the layer of insulating material and the conduit carrying the sodium. This also has the effect of improving the diffusion of sodium in the insulating layer during a leak, and thus improve the detection of this leak.

In case of intense liquid leakage, the layer of fibrous conductive material forms a mechanical protection limiting or preventing jets of liquid outside the detection device and the coating of the conduit including this detection device. This is particularly important for liquid sodium, because of the reactivity of sodium in contact with air.

In addition, in the case of a low intensity leak propagating by gravity in the layers of insulating material and conductive material, the structure of the stainless steel felt forming the fibrous conductive material can temporarily retain the liquid within felt.

Due to the high temperature mechanical and thermal stability of the layer of fibrous conductive material, the thickness of the layer of the fibrous insulating material of the detection device can be reduced, which makes it possible to detect a leak more quickly, more effectively even when the leak is weak.

Owing to its cohesion in particular, the fibrous conductive material makes it possible to avoid inadvertent short circuits between this material and the electrically conductive conduit, while facilitating intentional short circuits which can be carried out as described hereinafter for the control of the correct operation of the device leak detection.

According to one embodiment, the insulating material is a wool of mineral fibers, in particular a wool of woven or twisted fibers consisting essentially of silica and magnesium or calcium oxide. The fibrous conductive material may comprise one or more layers of flexible felt made of agglomerated stainless steel fibers.

Impedance monitoring, measured between the layer of the fibrous conductive material and the wall of the conduit, makes it possible to detect the presence of a conductive liquid passing through the layer of fibrous insulating material, during a leakage of this liquid through the wall of the duct.

The flexibility of the fibrous materials of the detection device allows it to adapt to the deformations of the apparatus / organs it surrounds, in particular the deformations caused by the thermal expansion of the devices.

The flexibility of the fibrous conductive material facilitates its placement around a duct previously coated with the insulating material, and avoids, when it is placed in intimate contact with and pressed against the layer of insulating material, the setting in accidental contact of the fibrous conductive material with the wall of the conduit.

The detection device may comprise first links, in particular thread-like or cord-shaped links, for securing the layer of insulating material to a conduit, for example by strapping.

The detection device may comprise second links, in particular thread-like or rope-shaped links, for securing the layer of fibrous conductive material to the conduit coated with the insulating material, for example by strapping.

The first and second links may consist essentially of fibers of an electrically insulating material, which may be the same as or similar to that constituting the insulating coating layer.

Such links make it possible to simply coat the outer wall of a conduit of complex shape, by cutting a link of suitable length, surrounding the layer considered by this link shaped in loop or ring, and closing this loop by a node made with the two free ends of the link, or using a suitable device - such as a cable clamp.

The detection device generally comprises an electronic apparatus for detecting short-circuit or impedance measurement, and electrical connection members of this apparatus with the wall of the duct, on the one hand, and with the layer of fibrous conductive material , on the other hand.

According to another aspect of the invention, there is provided a conduit coating device which comprises:

a first electrically insulating layer consisting essentially of fibers, which extends against the outer surface of the conduit;

a second electrically conductive layer consisting essentially of agglomerated stainless steel fibers which extends against the outer surface of the first layer; and

a third thermally insulating layer consisting essentially of fibers, which extends against the outer surface of the second layer.

The coating device may further comprise a rigid wall arranged to surround or envelop the third thermally insulating layer.

This rigid wall may comprise two portions - or half-shells - and connecting means for assembling these two portions.

This rigid wall may be pierced with at least one orifice for the passage of a piece for controlling the proper operation of the leak detection device, through this wall and the layers of the duct coating.

According to another aspect of the invention, there is provided a transport conduit or a storage container for a heat transfer liquid forming part of a reactor, which is equipped with such a device for detecting heat transfer fluid leakage, or which is coated with such a coating device. The invention can be applied in particular to various conductive liquids, in particular to a conductive liquid solution.

Conductive liquid is understood to mean a liquid or a solution whose electrical resistivity is at least equal to 10 ³ Siemens per meter (Snr, in particular an electrical conductivity of at least 10 ² Snr ¹ , for example an electrical conductivity of the order of January ^{^10-July} 10 Snr ^1.

If the transported liquid has a conductivity too low to be detected (example of demineralized water), it is possible to put in solution in this liquid a conductive product and / or ions.

Other aspects, features, and advantages of the invention appear in the following description which refers to the appended figures and illustrates, without any limiting character, preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic longitudinal sectional view of a conduit equipped with a detection device.

Figure 2 is a schematic longitudinal sectional view illustrating the leak detection through the wall of a conduit equipped with a detection device and covered with a layer of insulating material surrounded by a rigid wall.

FIG. 3 is a schematic longitudinal sectional view of a duct equipped with a detection device, and illustrates an alternative embodiment of the control of the proper operation of the leak detection device.

Figure 4 schematically illustrates a short circuit detection apparatus according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise explicitly or implicitly stated, elements or members - structurally or functionally - identical or similar are designated by identical reference numerals in the different figures. With reference to FIGS. 1 and 2, a conduit 10 for transporting liquid under pressure has a cylindrical wall 11 extending along a longitudinal axis 12. The wall 11 may be made of stainless steel.

With reference to FIG. 1 in particular, a layer of a fibrous insulating material 13 has been wound - or otherwise deposited - around the wall 11 and is kept in contact with the outer face of this wall, by means of cords 14 encircling the layer of material 13 and knotted (markings 15) to form closed loops enclosing the layer 13.

The fibrous insulating material 13 may have an electrical conductivity less than 10 ⁵ Siemens per meter (Snr ^1), in particular an electrical conductivity less than 10 ^"10 Snr ^1, for example an electric conductivity of the order of 10 ^{~ 15} Snr ¹ .

The material 13 may for example be a mineral fiber wool sold under the name "Superwool 607 Blanket" by the company Thermal Ceramics (USA) or "Thermipan" from the company Saint Gobain Isover.

This layer of mineral wool may have a thickness of the order of 5 to 20 millimeters approximately.

It is generally desirable for the thickness of this layer of material 13 to be as small as possible, in order to limit the time taken by the liquid escaping from the conduit to impregnate and / or pass through this layer of material and reach the layer of material in order to limit the time before the detection of the leak can take place.

Other fibrous insulating materials may be used to produce the layer 13, in particular wools comprising silica and magnesium oxide or calcium oxide fibers.

A layer of a conductive material 16 has been wound - or otherwise deposited - around the layer of fibrous insulating material 13 and is kept in contact with the outer face of this layer of material 13, by cords 17 encircling the layer of material 16 and knotted (pins 18) to form closed loops.

The conductive material 16 may for example be a 316L stainless steel felt.

The thickness of this layer of felt may be of the order of 2 to 5 millimeters approximately.

It is indeed generally desirable that the thickness of this layer of material 16 is less than or equal to 5 millimeters, in order to maintain flexibility and minimize the weight of the assembly.

The conductive material 16 may have an electrical conductivity of at least 10 ⁴ or 10 ⁵ Siemens per meter (Srrr ¹ ), in particular an electrical conductivity of the order of 10 ⁶ Srrr ¹ .

The links 14 and 17 may for example consist essentially of silica filaments.

The thickness and the flexibility of each of the two layers of fibrous material 13 and 16, as well as the flexibility of the bonds holding these materials in place, make it possible to intimately cover conduits or containers of various shapes and geometries, thus ensuring total coverage of areas of a cooling system containing a liquid leakage of which must be detected quickly and reliably.

With reference to FIG. 2 in particular, a layer of a thermally insulating material 19 has been deposited around the fibrous conductive material layer 16 and is kept in contact with the outer face of this layer of material 16 by a tubular wall 20. extending along the longitudinal axis 12 and encircling the layer of material 19.

The thermally insulating material 19 may for example consist essentially of a glass wool or rock. The thickness of the material layer 19 is generally greater than that of the material layers 13 and 16. This thickness may for example be of the order of 20 to 50 (or 100) millimeters approximately. The shell or rigid wall 20 provides in particular the mechanical protection of the layers of fibrous material 13, 16, and 19 which it surrounds.

The wall 20 is pierced with an orifice 21 allowing the passage of a piece 22 for controlling the proper operation of the leak detection device, through this wall and the layers 13, 16, and 19 of the coating of the conduit 10. .

The impedance monitoring, measured between the layer of the fibrous conductive material 16 and the wall 11 of the conduit 10, makes it possible to detect the presence of a conductive liquid which passes through and / or impregnates the layer of fibrous insulating material 13, leakage of this liquid through the wall 1 1 of the conduit.

For this purpose, the leak detection device comprises:

an apparatus 23 for detecting a short circuit by measuring impedance;

a member 24 for electrically connecting the electrically conductive layer 16 to the apparatus 23;

a member 25 for the electrical connection of the wall 1 1 of the conduit to the apparatus 23; and

two sections of conducting wire 26 respectively connecting the contact / connection members 24, 25 to the measurement terminals of the apparatus 23.

The apparatus 23 generally comprises i) an impedance measuring circuit arranged to deliver a measurement signal; ii) a comparator circuit connected to the measurement circuit for receiving the measurement signal and arranged to compare the received signal with a given signal or datum, and to output a comparison signal; and iii) an alarm control circuit connected to the comparator circuit for receiving the comparison signal and arranged to control the operation of an alarm based on the received comparison signal.

The connecting member 24 is in the form of a rod or bar and is inserted into the thickness of the filamentary conductive layer 16. Alternatively, this connection member 24 may comprise a pin-shaped contact element whose jaws can grip a portion of the fibrous conductive layer.

The second connecting member 25, which is in electrical contact with the wall of the duct, may be a metal piece welded to the duct.

For the control of the proper functioning of the leak detection device fitted to the duct 10, a short circuit is caused between the wall 11 of the duct and the layer of fibrous conductive material 16.

For this, we introduce a connector 22 such as a metal needle through the orifice 21 provided in the wall 20, and through the superimposed layers of thermally insulating material 19, conductive material 16, and insulating material 13, until contacting the longitudinal end (lower) of the connector 22 with the wall 1 1 of the conduit.

The length of the needle being greater than the cumulative thickness of the layers of insulating material 13 and conductor 16, the needle remains in electrical contact with the layer of conductive material 16 through which it extends.

The connector 22 thus makes a short circuit between the wall 11 and the material layer 16, which makes it possible to control, by the impedance measurement made by the apparatus 23, the proper functioning of the leak detection system: 23 measuring device must indicate the presence of a short circuit as the connector 22 is kept in contact with the wall 1 1 and the layer of material 16.

It should be noted that this control operation operation does not cause any damage to the coating of the conduit, especially because of the fibrous structure of the layers comprising the coating.

In the variant illustrated in FIG. 3, the apparatus 23 and the wall 11 of the duct 10 are permanently connected to a common ground, while the connector 22 which is in contact with the conductive layer 16 without being in contact with the wall January 1, is connected to this mass via a switch 27 which is normally open.

Closing the switch 27, manual or remotely controlled, then establishes the short circuit to control the proper operation of the leak detection system.

With reference to FIG. 4, the impedance measuring circuit of the apparatus 23 comprises a source 230 of voltage across which two resistors 231 and 232 are connected in series.

The members 24, 25 respectively connecting the material layer 16 and the wall January 1 to the apparatus 23, are respectively connected across the resistor 231.

A voltage measuring device (not shown) is incorporated in the apparatus 23, and connected across the resistor 232 so as to measure the voltage across it.

In the absence of leakage, this voltage is proportional to that of the source 230, in the ratio of the resistors 231 and 232.

When a leak occurs and causes a short circuit between the terminals of the resistor 231, the voltage measured across the resistor 232 becomes substantially equal to that delivered by the source.

This modification of the measured voltage makes it possible to trigger the emission of a leak indicator signal.

Claims

claims

1 - Leak detection device for a liquid stored or transported in a conduit (10) having an electrically conductive outer wall (1 1), which comprises a layer of fibrous insulating material (13) arranged to surround the conduit and a layer of a conductive felt (16) which extends against the layer of fibrous insulating material (13), characterized in that the fibers of the conductive felt are made of stainless steel.

2 - Device according to claim 1 wherein the steel alloy constituting the fibers of the conductive felt contains nickel.

3 - Device according to claim 2 wherein the steel alloy constituting the fibers of the conductive felt contains molybdenum.

4 - Device according to any one of claims 1 to 3 wherein the fibrous insulating material (13) comprises mineral fibers.

5 - Device according to any one of claims 1 to 4 wherein the thickness of the layer of felt (16) conductor is less than or equal to about 5 millimeters.

6 - Device according to any one of claims 1 to 5 wherein the thickness of the layer of fibrous insulating material (13) is less than about 20 millimeters.

7 - Apparatus for coating a sodium transport conduit or a sodium storage container, which comprises a detection device according to any one of claims 1 to 6 and a layer of a material (19) thermally insulation essentially consisting of fibers, which extends against the layer of felt (16) conductor.

8 - Device according to claim 7 which further comprises a wall (20) rigid arranged to surround or wrap the (third) thermally insulating layer, and wherein the rigid wall is pierced with at least one orifice (21) allowing the passage a piece (22) for controlling the correct operation of the detection device of leakage through this wall and the layers of the conduit liner.

9 - duct (10) for transporting or storing a heat-transfer fluid, which is equipped with a heat-transfer liquid leak detection device which is in accordance with any one of claims 1 to 6, and which comprises first links (14) for securing the layer of insulating material (13) to the wall (1 1) of the conduit, for example by strapping, and second links (17) for securing the layer of fibrous conductive material (16) to conduit coated with the material (13) insulation, for example by strapping.

10 - Method for coating a conduit (10) for transporting or storing a heat-transfer liquid by a heat-transfer liquid leak detection device which is in accordance with any one of claims 1 to 6, in which one solidarizes the layer of material (13) insulating at the wall (1 1) of the conduit, by strapping this layer by first links (14), and in which the conductive layer of felt (16) is secured to the conduit coated with the material ( 13) by strapping the layer of felt (16) conductor by second links (17).