Abstract:
The invention relates in particular to a method of covering a duct for transporting or storing a fluid in a device for detecting a leak of the fluid, the device comprising a layer of insulating fibrous material arranged to surround the duct and a layer of conductive material that extends against the layer of insulating material, the conductive material being essentially constituted by fibers of carbon or graphite, wherein the layer of insulating material is secured to the wall of the duct by strapping ties around said layer.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a device for detecting leaks and to a covering for a member for transporting or storing fluid, the covering including the detector device. 
         [0002]    The invention also relates to a member for transporting or storing fluid and fitted with such a covering, to a method of covering a member for transporting or storing fluid, and to a method of checking that such a leak detector device is operating properly. 
         [0003]    The invention applies in particular to covering ducts for transporting liquid sodium and to containers for storing sodium and forming part of a cooling circuit of a nuclear reactor. 
         [0004]    Below in the present application, and unless indicated explicitly or implicitly to the contrary, the term “duct” is used to designate equally well a duct for transporting fluid or a container for storing fluid and also an accessory, such as a valve, fitted to such a duct or container. 
       STATE OF THE ART 
       [0005]    In particular for sodium transport ducts, it is important to be able to monitor for the appearance of a leak, both automatically and remotely. 
         [0006]    For this purpose, patents FR-A-2 155 534 and FR-A-2 455 707 propose devices for detecting a leak of sodium through the wall of a duct by detecting electrical contact between the wall of the duct and an electrically conductive element spaced apart from the wall by an insulating element. 
         [0007]    The device described in FR-A-2 455 707 comprises a rigid and insulating shell made of a material comprising fibers embedded in a binder. The shell has grooves receiving metal tapes or wires and holding the tapes or wires spaced apart from the wall of the duct. 
         [0008]    A drawback of that device stems from the difficulty of making a shell, or a half-shell, that is a good fit to the outside surface of the duct for which it is intended, in particular when said outside surface is complex in shape. 
         [0009]    The device described in FR-A-2 155 534 comprises an insulating sheet made of refractory fibers suitable for winding around a metal duct, and a metal fabric or grid wound around the insulating sheet and in tight contact with the insulating sheet. 
         [0010]    A drawback of that device results from the difficulty in shaping the fabric or grid so that it fits closely to the insulating sheet without some portion of the fabric or grid penetrating into the insulating sheet and thereby involuntarily establishing contact between the fabric or grid and the wall of the duct, which is generally made of metal. 
         [0011]    Furthermore, fabrics, grids, tapes, or wires made of metal run the risk of oxidizing. Under such circumstances, the formation of a film of oxide on the surface of such a metal conductive element can impede or slow down the detection of a short circuit between said element and the wall of the duct, and can consequently impede or slow down the detection of a leak. 
         [0012]    Furthermore, such conductive metal elements may deform by thermal expansion during variations in the temperature of the duct, and that also can lead to a malfunction of the leak detector system. 
       SUMMARY OF THE INVENTION 
       [0013]    An object of the invention is to provide a device for detecting a leak of a fluid flowing in a duct or stored in a container, a device for covering the duct or container and incorporating the detector device, a member for transporting or storing fluid and fitted with such a covering, a method of covering a member for transporting or storing fluid, and a method of checking proper operation of such a leak detector device, which are improved and/or which remedy, at least in part, the shortcomings or drawbacks of prior methods and devices. 
         [0014]    An object of the invention is to propose a device for detecting a leak of liquid sodium under pressure at a temperature that may lie in a range going from about 100° C. (degree Celsius) to about 600° C., a device for covering a duct and including the detector device, a member for transporting or storing said fluid and fitted with such a covering, a method of covering a member for transporting or storing said fluid, and also a method of checking proper operation of such a leak detector device. 
         [0015]    In an aspect of the invention, there is provided a device for detecting a leak of a fluid stored or transported in an electrically conductive duct, which device is arranged to surround, or envelop, the duct. The detector device comprises a layer of an insulating fibrous material and a layer of a conductive fibrous (or filamentary) material that extends over/against the layer of insulating fibrous material, the conductive fibrous material being constituted essentially by a carbon or graphite felt. 
         [0016]    In particular because of its cohesion, the conductive material serves to avoid untimely short circuits between said material and the electrically conductive duct, while also facilitating making short circuits deliberately as described below for the purpose of checking proper operation of the leak detector device. In an embodiment, the insulating material is a mineral fiber wool, in particular a wool of woven or twisted fibers constituted essentially of silica and magnesium or calcium oxide. 
         [0017]    The conductive fibrous material may comprise one or more layers of flexible felt, essentially constituted by agglomerated carbon or graphite fibers. 
         [0018]    By monitoring the impedance as measured between the layer of conductive fibrous material and the wall of the duct, it is possible to detect the presence of a conductive fluid that has passed through the layer of insulating fibrous material in the event of the fluid leaking through the wall of the duct. 
         [0019]    Such a conductive fibrous material is relatively insensitive to oxidation and its ability to conduct electricity is little affected by potential oxidation thereof. 
         [0020]    Furthermore, the flexibility of this material enables it to adapt to deformations of the equipment/members that it surrounds, in particular the deformations resulting from thermal expansion of the equipment. 
         [0021]    The flexibility of this conductive material makes it easier to install on a duct that has already been covered in the insulating material, and makes it possible to avoid contact being made accidentally between the conductive fibrous material and the wall of the duct while the conductive material is being put into intimate contact with and pressed against the layer of insulating material. 
         [0022]    Furthermore, the conductive fibrous material contributes to providing the duct with thermal insulation, thereby serving to limit losses of heat from the fluid flowing in or stored in the duct, and serving to protect operators against the risk of being burnt. 
         [0023]    The detector device may comprise first ties, in particular filamentary ties or ties in the form of cords, that are used for securing the layer of insulating material to a duct, e.g. by being strapped around it. 
         [0024]    The detector device may include second ties, in particular filamentary ties or ties in the form of cords, that are used for securing the layer of conductive fibrous material to the duct covered in the insulating material, e.g. by being strapped around it. 
         [0025]    The first and second ties may be constituted essentially by fibers of an electrically insulating material, which may be identical or similar to the material constituting the insulating covering layer. 
         [0026]    Such ties enable the outside wall of a duct of complex shape to be covered in simple manner by cutting a tie to a suitable length and surrounding the layer in question by the tie shaped to form a loop or ring, and then closing the loop by knotting the two free ends of the tie together, or by using an appropriate device for connecting the ends together, such as a cable clamp. 
         [0027]    The detector device generally includes a first connection member, or terminal, that is arranged to facilitate making an electrical connection between the electrically conductive layer and an electrical or electronic detector device such as an impedance meter. 
         [0028]    The connection member may comprise a contact element in the form of a rod or a bar that may be inserted or buried at least in part in the conductive fibrous layer. Under such circumstances, in particular, the contact element may be made at least in part of graphite or of carbon, and it may present a shape and dimensions that are adapted to the thickness of the agglomerated filamentary structure of the conductive layer. 
         [0029]    Alternatively, the connection member may comprise a contact element in the form of a clamp having jaws suitable for clamping against a portion of the conductive fibrous layer. 
         [0030]    In addition to the appliance for detecting a short circuit or measuring impedance, a detector device generally also includes a second connection member, or terminal, that is in contact with the wall of the duct. 
         [0031]    According to another aspect of the invention, there is provided a device for covering a duct, which device comprises:
       an electrically insulating first layer essentially made up of fibers and extending against the outside surface of the duct;   an electrically conductive second layer essentially constituted by agglomerated carbon or graphite fibers and extending against the outside surface of the first layer; and   a thermally insulating third layer essentially constituted by fibers that extend against the outside surface of the second layer.       
 
         [0035]    The covering device may also include a rigid wall arranged to surround or envelop the thermally insulating third layer. 
         [0036]    The rigid wall may comprise two portions, or half-shells, and connection means for assembling the two portions together. 
         [0037]    The rigid wall may be pierced by at least one orifice suitable for passing a tool for checking proper operation of the leak detector device through said wall and the layers of the covering of the duct. 
         [0038]    According to another aspect of the invention, there is provided a duct for transporting or a container for storing a heat-transfer fluid forming part of a reactor, which duct or container is fitted with such a device for detecting a leak of the heat-transfer fluid, or is covered in such a covering device. 
         [0039]    According to another aspect of the invention, there is provided a method of checking proper operation of a leak detector device fitted to a duct and including a layer of insulating fibrous material covered in a layer of conductive fibrous material, wherein a short circuit is established between the wall of the duct and the layer of conductive fibrous material. 
         [0040]    In a preferred implementation of the method, an electrically conductive tool is inserted for this purpose through the layer of conductive material and through the layer of insulating material, and the tool is put into contact with the (conductive) wall of the duct while keeping said tool in contact with the layer of conductive material through which the tool extends, in order to establish the short circuit and check that the leak detector system is operating properly by making use of impedance measurement to measure the impedance between the wall of the duct and the layer of conductive material. 
         [0041]    The electrically conductive tool may be made of metal, and in particular it may be in the form of a rod or a needle. 
         [0042]    Other aspects, characteristics, and advantages of the invention appear from the following description that refers to the accompanying figures showing preferred embodiments of the invention without any limiting character. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0043]      FIG. 1  is a diagrammatic longitudinal section view of a duct covered in a layer of insulating fibrous material. 
           [0044]      FIG. 2  is a diagrammatic longitudinal section view of the duct covered in the  FIG. 1  insulating layer and covered in a layer of conductive fibrous material. 
           [0045]      FIG. 3  is a diagrammatic longitudinal section view of the duct fitted with a  FIG. 2  detector device, and also covered in a layer of insulating material surrounded by a rigid wall. 
           [0046]      FIG. 4  is a diagrammatic longitudinal section view showing how a leak through the wall of the duct shown in  FIG. 3  is detected. 
           [0047]      FIG. 5  is a diagrammatic longitudinal section view showing the leak detector system of  FIG. 4  being checked for proper operation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    Unless stated explicitly or implicitly to the contrary, elements or members that are structurally or functionally identical or similar are given identical references in the various figures. 
         [0049]    With reference to  FIGS. 1 to 5 , a duct  10  for transporting liquid sodium under pressure has a cylindrical wall  11  extending along a longitudinal axis  12 . The wall  11  may be made of stainless steel. 
         [0050]    With reference to  FIG. 1  in particular, a layer of insulating fibrous material  13  has been wound, or laid in some other way, around the wall  11  and is held in contact with the outside face of that wall by cords  14  surrounding the layer of material  13  and knotted (references  15 ) in order to form closed loops surrounding the layer  13 . 
         [0051]    By way of example, the material  13  may be a mineral fiber wall sold under the name “Superwool 607 Blanket” by the supplier Thermal Ceramics (USA). 
         [0052]    This layer of mineral wool may present thickness of about 2 millimeters, and up to about 5, 10, or millimeters, for example. 
         [0053]    It is generally desirable for the thickness of this layer of material  13  to be less than 20 millimeters so as to limit the time taken by fluid escaping from the duct to impregnate and/or pass through this layer of material and reach the layer of conductive material, and thus limit the time that elapses before it is possible to detect a leak. 
         [0054]    Other insulating fibrous materials may be used for making the layer  13 , and in particular wools having fibers of silica and magnesium or calcium oxide. 
         [0055]    With reference to  FIG. 2  in particular, a layer of conductive material  16  has been wound, or otherwise laid, around the layer of insulating fibrous material  13  and is held in contact with the outside face of the layer of material  13  by cords  17  surrounding the layer of material  16  and knotted (references  18 ) in order to form closed loops. 
         [0056]    The conductive material  16  may for example be a graphite felt sold under the name “Sigratherm® GFA” by the supplier SGL Carbon GmbH (Germany). Such a graphite felt may be obtained by graphitizing a carbon felt. 
         [0057]    The thickness of this layer of felt may be of the order of about 5 millimeters, and may lie in the range about 5 millimeters to at least about 10 millimeters, e.g. up to about 20 millimeters, about 30 millimeters, or about 50 millimeters. 
         [0058]    It is generally desirable for the thickness of this layer of material  16  to be greater than or equal to 5 millimeters in order to increase the thermal insulation it provides, to facilitate its electrical connection with an impedance measurement appliance, and to facilitate checking the detector device is operating properly, as described below. 
         [0059]    Other conductive fibrous materials may be used for making the layer  16 , in particular carbon fiber felts. 
         [0060]    The ties  14  and  17  may for example be essentially constituted by filaments of silica. 
         [0061]    The thickness and the flexibility of each of the two layers of fibrous materials  13  and  16 , and also the flexibility of the ties holding these materials in place, enable ducts or containers of a wide variety of shapes to be covered closely, thereby ensuring that it is possible to cover all of the zones of a cooling circuit that contains a fluid for which a leak needs to be detected quickly and reliably. 
         [0062]    With reference to  FIG. 3  in particular, a layer  19  of thermally insulating material has been laid around the layer of conductive fibrous material  16  and is held in contact with the outside face of the layer of material  16  by a tubular wall  20  extending around the longitudinal axis  12  and surrounding the layer of material  19 . 
         [0063]    By way of example, the thermally insulating material  19  may be constituted essentially by glass or rock wool. The thickness of the layer of material  19  is generally greater than that of the layers of material  13  and  16 . By way of example, this thickness may be of the order of about 20 to 50 (or 100) millimeters. 
         [0064]    The rigid wall or shell  20  serves in particular to provide mechanical protection to the layers of fibrous material  13 ,  16 , and  19  that it surrounds. 
         [0065]    The wall  20  is pierced by an orifice  21  for passing a tool (reference  22  in  FIGS. 4 and 5 ) for checking proper operation of the leak detector device through said wall and the layers  13 ,  16 , and  19  of the covering of the duct  10 . 
         [0066]    With reference to  FIG. 4  in particular, monitoring impedance as measured between the layer of conductive fibrous material  16  and the wall  11  of the duct  10  serves to detect the presence of a conductive fluid that has passed through, and impregnated, the layer of insulating fibrous material  13 , in the event of the fluid leaking through the wall  11  of the duct. 
         [0067]    For this purpose, the leak detector device comprises:
       an appliance  23  for detecting a short circuit by measuring impedance;   a member  24  for electrically connecting the electrical conductive layer  16  to the appliance  23 ;   a member  25  for electrically connecting the wall  11  of the duct to the appliance  23 ; and   two segments of conductor wire  26  respectively connecting the contact/connection members  24  and  25  to the measurement terminals of the appliance  23 .       
 
         [0072]    In general, the appliance  23  comprises: i) an impedance measuring circuit arranged to deliver a measurement signal; ii) a comparator circuit connected to the impedance measuring circuit for receiving the measurement signal and arranged to compare the received signal with a determined signal or data, and to deliver a comparison signal; and iii) an alarm control circuit connected to the comparator circuit to receive the comparison signal therefrom and arranged to cause an alarm to operate as a function of the received comparison signal. 
         [0073]    The connection member  24  shown in  FIGS. 4 and 5  is in the form of a rod or bar of graphite or carbon and it is inserted in the thickness of the conductive filamentary layer  16 . 
         [0074]    The second connection member  25 , which is in electrical contact with the wall of the duct, may be a metal part welded to the duct. 
         [0075]    In order to check that the leak detector device fitted to the duct  10  is operating properly, a short circuit is established between the wall  11  of the duct and the layer  16  of conductive fibrous material. 
         [0076]    With reference to  FIGS. 4 and 5 , a metal needle  22  is inserted (along arrow  27  in  FIG. 5 ) for this purpose through the orifice  21  provided in the wall  20  and through the superposed layers of thermally insulating material  19 , of conductive material  16 , and of insulating material  13 , so as to put the longitudinal (bottom) end of the conductive needle  22  into contact with the wall  11  of the duct. 
         [0077]    Since the length of the needle is greater than the total thickness of the layers of insulating and conductive material  13  and  16 , the needle remains held in electrical contact with the layer of conductive material  16  through which it passes. 
         [0078]    The needle  22  thus establishes a short circuit between the wall  11  and the layer of material  16 , thus making it possible, by using the appliance  23  to measure impedance, to check whether the leak detector system is operating properly: the impedance measuring appliance  23  must indicate the presence of a short circuit so long as the needle  22  is kept in contact with the wall  11  and with the layer of material  16 . 
         [0079]    It should be observed that this operation of checking proper operation can be performed at any moment that is felt to be appropriate throughout the lifetime of the installation, and that this operation does not lead to any damage of the covering of the duct, in particular because of the fibrous structure of the layers making up the covering.