Patent Publication Number: US-2007102926-A1

Title: Flanged connection device

Description:
FIELD OF THE INVENTION  
      The present invention relates to a flanged prestressed leaktight connection device comprising a first flange presenting a first contact surface, a second flange presenting a second contact surface situated facing said first contact surface, a sealing gasket disposed in a gasket housing formed between said first and second contact surfaces, and clamping means for clamping together the first and second flanges, the clamping means being disposed between the gasket housing and the periphery of the first and second flanges so as to put into contact at least a portion of the first and second contact surfaces between the flanges.  
      The invention relates more particularly to leaktight connection devices for use in severe environments with extreme operating conditions, in particular under high pressure, in the presence of vibration, and over temperature ranges that are very high or on the contrary very low.  
     PRIOR ART  
      To assemble members that are subjected to high internal pressure, such as, for example engines or pipework used in space, it is common practice to use flanged leaktight connections providing a face-to-face connection, as shown for example in FIGS.  1  to  3 .  
       FIG. 1  shows an example of a connection between two pipework elements  10  and  20  fitted with flanges  30  and  40  of the face-to-face type that are assembled together using connection members  50  such as bolts.  
       FIG. 2  is an axial section showing the  FIG. 1  connection in an initial state before pressure is exerted inside the pipework elements  10  and  20 . At this instant, after the bolts  50  have been tightened, the plane face  31  of the cylindrical plane flange  30  is pressed against the plane face  41  of the cylindrical plane flange  40  that is situated facing the flange  30 . The flange  40  presents a step  42  that defines an empty space  70  for receiving a sealing gasket  60 , which is thus held captive between the face  31  of the flange  30  and the step  42  of the flange  40 .  
      As can be seen in  FIG. 3 , in operation with internal pressure P created by the presence of fluid inside the pipework elements  10  and  20 , the faces  31 ′ and  41 ′,  42 ′ of the flanges  30  and  40  deform under the action of the pressure field inside the connection. This opens the housing  70  for the gasket  60 . As a result, the sealing gasket  60  expands and loses a portion of its performance.  
      In an attempt to conserve leaktightness, it is necessary to use special gaskets having a large amount of usable elastic restitution, which are more complicated to manufacture, e.g. than gaskets such as those described in patent documents EP-A-0 261 350, EP-A-0 711 938, or EP-A-0 851 258. Such special gaskets designed specifically to handle the problem of the housing  70  opening, thus present non-negligible production costs.  
      In addition, repeated opening and closing of the housing  70  in the event of operation with repeated “ON/OFF” cycles, as applies for example to rocket engines, generates wear and fatigue in the gaskets. The relative flexibility of a face-to-face type connection makes it difficult to control the lifetime of systems. Reducing excess flexibility in such a face-to-face connection requires the weight of the flange to be increased, and that is penalizing, in particular for space applications.  
      Proposals have also been made, as in the embodiment shown in  FIGS. 4 and 5 , to form a land  33  on a face  31  of a first flange  30  facing a face  41  of a second flange  40 , in a zone that is situated between the gasket housing  70  containing a sealing gasket  60 , and the connection means  50  applying prestress on the annular flanges  30 ,  40  associated with the pipework elements  10 ,  20  or with other elements defining an enclosure of axis  1 .  
      Under such circumstances, prior to tightening the connection means  50  and applying internal pressure, an empty space E ( FIG. 4 ) is defined at the periphery of the flanges  30 ,  40  between the surface  31   a  of the flange  30  outside the land  33  and the surface  41  of the flange  40 .  
      In operation, after the connection means have been tightened, and in the presence of a pressure field P inside the pipework  10 ,  20 , the empty space between the surface  31   a′  of the flange  30  and the surface  41 ′ of the flange  40  becomes smaller and enables the land  33  of the flange  30  to remain in contact with the surface  41 ′ of the flange  40 . Nevertheless, at the periphery of the flanges  30 ,  40 , the empty space between the surfaces  31   a′  and  41 ′ does not close completely. This leads to various drawbacks because there is a risk of pollution entering the empty space between the flanges, and this empty space leads to creep over time, thereby producing bending in the plates of the flanges which are not held in reliable manner by the connection elements  50  because of the clearance that exists.  
     OBJECT AND BRIEF SUMMARY OF THE INVENTION  
      The invention seeks to remedy the above-mentioned drawbacks and to provide a flanged prestressed leaktight connection device that does not make it essential to use special gaskets having a very high level of elastic restitution and that minimizes the risks of pollution or of the connection becoming modified during operation under severe conditions of temperature, pressure, vibration, and chemical attack, while being suitable for implementation without extra cost and without increasing the weight of the connection device.  
      These objects are achieved by a flanged prestressed leaktight connection device comprising a first flange presenting a first contact surface, a second flange presenting a second contact surface situated facing said first contact surface, a sealing gasket disposed in a gasket housing formed between said first and second contact surfaces, and clamping means for clamping together the first and second flanges, the clamping means being disposed between the gasket housing and the periphery of the first and second flanges so as to put into contact at least a portion of the first and second contact surfaces between the flanges, wherein the first and second contact surfaces present at least a first bearing zone situated in the vicinity of the sealing gasket and a second bearing zone situated between the clamping means and the periphery of the first and second flanges, such that after the clamping means have been tightened, the minimum force exerted on the second bearing zone is less than the minimum force exerted on the first bearing zone, but without being zero; wherein the sealing gasket presents usable restitution that is less than 0.1 millimeters (mm); and wherein the first and second contact surfaces define first and second bearing zones such that after the clamping means have been tightened, the minimum force exerted on the second bearing zone constitutes 1% to 20%, preferably 5% to 20%, and more preferably 8% to 12% of the minimum force exerted on the first bearing zone.  
      The device of the invention thus makes it possible to control the deformation of the flanges which, in prior art devices, leads to the gasket being off-loaded.  
      By minimizing the deformation of the flanges at the gasket housing, it is possible to achieve the sealing function while avoiding having recourse to special gaskets with a high level of usable restitution, which gaskets present high performance and are expensive.  
      Because, during assembly of the flanges, a bending stress field is generated in opposition to the field that is generated when the connection is put under pressure, the deformation of the flanges when put under pressure is minimized, in particular at the location of the gasket housing.  
      Furthermore, the presence of two bearing zones makes it possible to avoid the risks of pollution and of the connection deteriorating while in use, while contributing to controlling the stiffness of the flanged connection and to reducing fatigue in the connection means, thereby increasing reliability, without involving additional constraints relating to the weight of the connection device, nor implying extra machining costs.  
      In an aspect of the invention, prior to the clamping means being tightened, the distance between the first and second contact surfaces in the second bearing zone is greater than the distance between the first and second contact surfaces in the first bearing zone.  
      In a first possible embodiment, the first and second contact surfaces are continuous surfaces between the first and second bearing zones.  
      This embodiment is preferred, in particular when it is desired to encourage the removal of heat through the flanged connection.  
      In another possible embodiment, at least one of the first and second contact surfaces defines a land at least in one of the first and second bearing zones.  
      This embodiment provides a high level of control over the forces exerted on the flanges and the connection means.  
      More particularly, a connection device in this embodiment may be such that the first contact surface of the first flange has a first land formed in the first bearing zone and a second land formed in the second bearing zone, while the second contact surface of the second flange presents a continuous uniform surface.  
      In another possible embodiment, the first contact surface of the first flange includes a first land formed in the first bearing zone, while the second contact surface of the second flange presents a second land formed in the second bearing zone.  
      The first bearing zone is advantageously situated between the sealing gasket and the clamping means, thus making it possible in particular to protect the gasket thoroughly against the outside environment.  
      The connection device of the invention is particularly adapted for including a sealing gasket presenting usable restitution (Ru) lying in the range 2 mm to 0.1 mm.  
      The connection device of the invention can be applied to pipework or to an enclosure containing a fluid under pressure, in particular for use in space or indeed in industrial sectors such as the chemical, petrochemical, or nuclear industries that involve using equipments under pressure under environmental conditions that can be severe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Other characteristics and advantages of the invention appear from the following description of particular embodiments given with reference to the accompanying drawings, in which:  
       FIG. 1  is a perspective view of an example of a prior art flanged connection;  
       FIGS. 2 and 3  are axial section views of an example of a prior art flanged connection device of the face-to-face type, respectively prior to tightening and after tightening the bolts that provide prestress;  
       FIGS. 4 and 5  are axial half-section views of an example of a prior art flanged connection device of the type having a single land, shown respectively before tightening and after tightening the bolts that provide prestress;  
       FIGS. 6 and 7  are axial half-section views of a first example of a flanged prestressed leaktight connection device of the invention of the type having continuous surfaces, respectively before and after tightening the bolts that provide prestress;  
       FIGS. 8 and 9  are axial half-section views of a second example of a flanged prestress leaktight connection device of the invention of a type having two lands formed on a single flange, and shown respectively before and after tightening the bolts that provide prestress;  
       FIG. 10  is a simplified graph showing variation in the compression force on a gasket as a function of the flattening thereof;  
       FIGS. 11 and 12  are axial half-section views of a third example of a flanged prestressed leaktight connection device of the invention, of the type having two lands formed on two different flanges, and shown respectively before and after tightening the bolts that provide prestress;  
       FIG. 13  is an axial half-section view showing the application of a leaktight connection device of the invention to a tank of fluid under pressure;  
       FIGS. 14 and 15  are detail views showing the leaktight connection device for the tank of  FIG. 13 , and shown respectively before and after tightening the pins that provide prestress;  
       FIG. 16  is a graph showing the variation in the tension in a pin of the device of  FIGS. 14 and 15  while it is being put under pressure, as a function of the conicity of the surfaces of the flanges of the leaktight connection device; and  
       FIG. 17  is a graph showing the off-loading and the usable restitution of a gasket as a function of the conicity of the surfaces of the flanges of the leaktight connection device of  FIGS. 14 and 15 .  
    
    
     DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS  
      Reference is made initially to  FIG. 10  which shows in simplified manner how the compression force on a gasket varies as a function of the flattening of the gasket in a conventional flanged connection device of the kinds described with reference to FIGS.  1  to  5 .  
      Curve C in its portion between points O and A represents compression of the gasket during a stage in which the gasket is being flattened, as occurs when the flanges are assembled together and the connection elements are tightened.  
      Curve D is an off-loading straight line, and between points A and B it represents variation in the off-loading of the connection, referenced d, i.e. the relaxing of the gasket from its maximum flattening δ obtained during assembly, and as occurs under the effect of operating pressure being applied inside the pipework elements or the tank elements interconnected by the flanged connection, the force exerted on the gasket passing from a value F A  at point A to a lower value F B  at point B.  
      In order for the connection to be leaktight, the value F B  must remain greater than a sealing limit force written F seal , which corresponds to the usable restitution Ru of the gasket.  
      The connection remains leaktight if the usable restitution Ru of the gasket remains greater than the off-loading d.  
      In a prior art flanged connection of the face-to-face type, such as that shown in  FIGS. 2 and 3 , the off-loading of the gasket can reach values greater than 0.10 mm, which makes it necessary to use special gaskets possessing usable restitution greater than 0.10 mm, or else stiffening the flanged connection, thereby making it heavier, which constitutes a handicap in various applications, particularly in space.  
      There follows a description with reference to  FIGS. 6 and 7  of a first embodiment of a flanged prestress leaktight connection device in accordance with the invention.  
      In this embodiment, the pipework or tank segments  110 ,  120  in the form of bodies of revolution about an axis  101  are connected to respective annular flanges  130  and  140 . The flanges  130  and  140  have connection elements  150  such as bolts, screws, pins, or the like, passing through them and serving to exert prestress on the flanges  130 ,  140 .  
       FIG. 6  shows the connection device before the connection elements  150  are tightened.  
      It can be seen that the bottom face  131  of the top flange  130  which extends substantially transversely to the axis  101  is a continuous surface without any set-back portion (apart from the openings for passing the connection elements  150 ). The top face  141  of the bottom flange  140  is situated facing the face  131  of the flange  130  and is likewise a continuous surface extending essentially transversely to the axis  101 , with the exception of openings for passing the connection elements  150 , and a set-back portion  142  that is to form the housing  170  for the gasket  160 .  
      It should be observed that the terms “bottom” and “top” are used for convenience with reference to the position of the flanges in the drawing, and that the flanged connection could naturally take up any position relative to the vertical.  
      In the initial position shown in  FIG. 6 , the surfaces  131  and  141  are in contact over a first zone Z 1  in the vicinity of the gasket  160 , e.g. over a distance which may be of the order of several millimeters if the diameter of the flange is less than or equal to about 200 mm, or of the order of several centimeters if the diameter of the flange is greater than about 200 mm. In contrast, in a zone Z 2  situated between the connection means  150  and the periphery of the flanges  130  and  140 , the surfaces  131  and  141  are spaced apart from each other by a certain distance E which may be of the order of a few tenths of a millimeter, for example lying in the range 0.2 mm to 0.5 mm.  
      After the connection elements  150  have been tightened ( FIG. 7 ), the empty space between the surfaces  131  and  141  that were previously diverging in the zone Z 2  is closed, and the faces of the flanges  130  and  140  situated facing each other are in contact over their entire area. Even when an internal pressure P is applied inside the pipework elements  110 ,  120 , the surfaces  131  and  141  do not come apart in the zone Z 1  or in the zone Z 2 .  
      The distance E in the zone Z 2  is determined in such a manner that after the clamping means  150  have been tightened, the minimum force exerted on the bearing zone Z 2  is less than the minimum force exerted on the first bearing zone Z 1 , but without being zero, constituting 1% to 20%, advantageously, 5% to 20%, and preferably 8% to 12% of the minimum force exerted on the first bearing zone Z 1 . As a result, in operation with an internal pressure field P, the phenomenon of the connection gaping (the housing for the gasket opening) is not observed, as it would be in a face-to-face type connection, and the phenomenon of the gasket being off-loaded is reduced to values of the order of 0.06 mm, for example, thus making it possible to use standard gaskets, for example gaskets in which the usable restitution lies in the range 0.08 mm to 0.10 mm.  
      The clamping force can be distributed as follows: knowing the minimum clamping force to be exerted on the first bearing zone Z 1 , as a function of the pressure and the external loading, calculations based on finite elements are used to optimize the difference in height between the two bearing zones Z 1  and Z 2 , or else to optimize the angle between the surfaces  131  and  141  in an embodiment as shown in  FIG. 6 , where the flange is conical, with this being done by parameterization and by varying the parameters in such a manner as to obtain a force on the second bearing zone Z 2  that lies in the range 1% to 20%.  
      Under such circumstances, after clamping, the facing surfaces  131 ,  141  of the flanges  130 ,  140  are in contact, and there does not exist any space where pollution can occur between the flanges, and heat is dissipated well through the flanges. Furthermore, in operation under the influence of internal pressure, the contact pressure in the zone Z 1  moves towards the outer diameter in the zone Z 2 , but nevertheless the contact area remains large in the zone Z 1 , and no or minimal separation is observed, so the quality of the sealing provided by the gasket is not affected.  
      The profiles of the surfaces  131 ,  141  are defined, for example, by calculation using finite elements in such a manner that after tightening, the contact pressure remains low in the zone Z 2  and is high in the zone Z 1  situated closer to the gasket.  
      There follows a description of another embodiment of the invention given with reference to  FIGS. 8 and 9 .  
      In  FIGS. 8 and 9 , elements that are similar to those of the embodiment of  FIGS. 6 and 7  are given the same reference numerals and they are not described again.  
      The flanged prestress leaktight connection device of  FIGS. 8 and 9  presents a flange  140  that is identical to the flange  140  of the device of  FIGS. 6 and 7 . In contrast, the flange  130  of the device in  FIGS. 8 and 9  has a bottom surface  131  that is not continuous but that includes a set-back portion  131   a  following the zone Z 1  where the surface  131   c  of the top flange  130  (which constitutes a first land) is in contact over a length e with the surface  141  of the bottom flange  140 , with the set-back portion  131   a  being followed by an end portion  131   b  that constitutes a second land.  
      In the assembly position, prior to tightening the connection bolts  150  ( FIG. 8 ), the surface  131   c  of the flange  130  is in contact with the surface  141  of the flange  140  in the zone Z 1  over the distance e, which distance is a few millimeters, for example, if the diameter of the flange is less than or equal to about 200 mm, or is equal to one or more centimeters if the diameter of the flange is greater than about 200 mm. There is also a space E of the order of a few tenths of a millimeter, e.g. 0.3 mm to 0.8 mm in the zone Z 2  between the first land  131   b  of the flange  130  and the facing surface  141  of the flange  140 .  
      After the clamping means  150  have been tightened ( FIG. 9 ), the surfaces  131   c  and  141  remain in contact in the zone Z 1 , and the land  131   b  itself comes into contact with the surface  141  of the flange  140  so that there is no open space at the periphery of the flanges  130  and  140 .  
      As in the embodiment of  FIGS. 6 and 7 , after the bolts  150  have been tightened, the minimum force exerted on the bearing zone Z 2  is less than the minimum force exerted on the bearing zone Z 1 , but without being zero, and constituting 1% to 20%, advantageously 5% to 20%, and preferably 8% to 12% of the minimum force exerted on the bearing zone Z 1 .  
      In operation, when a pressure P is exerted inside the pipework segments  110 ,  120 , no gaping of the connection is observed, i.e. no gaping of the kind that would be observed in a similar connection, but of the face-to-face type without a land. Furthermore, an embodiment with lands  131   c  and  131   b  in the zones Z 1  and Z 2  as described above presents a function of limiting turning of the flanges because of the thrust delivered in the zone Z 2  by the outer land  131   b.    
      On assembly, contact pressure is observed to be localized close to the diameter of the gasket in the bearing zone Z 1 . In operation, the contact pressure moves towards the outer diameter, but contact continues to be remained over both lands  131   b  and  131   c.  This enables contact pressure to be conserved closer to the gasket.  
      A two-land type connection device as shown in  FIGS. 8 and 9  makes it possible to reduce the off-loading on the gasket relative to a traditional face-to-face connection even more than with the device of  FIGS. 6 and 7 , thus making it possible to use gaskets having smaller usable restitution, e.g. of the order of 0.05 mm or even presenting usable restitution that is less than that, e.g. 0.02 mm for flanges of small diameter. In general, it is possible to use gaskets presenting usable restitution that is less than 0.1 mm.  
      A two-land type flanged prestressed leaktight connection device presents very great stiffness and deformation that is quasi-constant between assembly and operation, while defining a space that is closed against external pollution.  
      The presence of two contact surfaces in two bearing zones Z 1 , Z 2  situated on the two lands  131   c,    131   b  enables contact pressure to be distributed as well as possible while avoiding any clearance and giving great flexibility in design and assembly since the machining required is easy and it is possible for the bolts to be over-tightened, since the second land  131   b  forms a safety abutment.  
      As can be seen from  FIG. 8 , the outer land  131   b  is smaller in height than the inner land  131   c,  and it is this difference in level that makes it possible to adjust the prestress and to distribute forces so that the load at the periphery of the flanges tends towards zero (zone Z 2 ) while the load is maintained at a high level in the vicinity of the gasket (zone Z 1 ).  
       FIGS. 11 and 12  show a variant embodiment for the connection device of  FIGS. 8 and 9 .  
      In the embodiment of  FIGS. 11 and 12 , the facing surfaces  131  and  141  of the flanges  130  and  140  continue to define two lands, but they are not made on the same surface.  
      In the embodiments of  FIGS. 11 and 12 , the contact surface  131  of the flange  130  has a single land  131   c  formed in the bearing zone Z 1 , making it possible on assembly and prior to the bolts  150  being tightened to have contact with the surface  141  of the flange  140  over a length e ( FIG. 11 ).  
      The other flange  140  has its own land  141   b  formed facing the surface  131   a  of the flange  130  in the bearing zone Z 2 , leaving a space E relative to this surface  131   a  before the bolts  150  are tightened ( FIG. 11 ).  
      After the bolts  150  have been tightened, the land  141   b  of the surface  141  of the flange  140  comes into abutment against the surface  131   a  of the flange  130  in the bearing zone Z 2 , thereby contributing to closing the space between the flanges  130  and  140  at their periphery ( FIG. 12 ).  
      When the pipework segments  110  and  120  are put under internal pressure P, the lands  131   c  and  141   b  perform exactly the same roles as the lands  131   c  and  131   b  in the embodiment of  FIGS. 8 and 9 .  
      In some circumstances, making only one land per flange can make it easier to fabricate the flanges  130 ,  140 , but from a functional point of view the embodiment of  FIGS. 11 and 12  is strictly equivalent to that of  FIGS. 8 and 9 .  
      In the embodiment shown in  FIGS. 11 and 12 , the length e of the bearing zone Z 1  can be of the order of a few millimeters or a few centimeters, while the empty space E between the land  141   b  and the facing surface  131   a,  prior to the bolts  150  being tightened, can typically be of the order of 0.05 mm. The height of the land  141   b,  like that of the land  131   b  in  FIGS. 8 and 9 , can also typically be of the order of 0.05 mm, such that height of the land  131   c  can typically be of the order of 0.1 mm.  
      FIGS.  13  to  15  show an application of the invention to an enclosure that is to contain a fluid, such as hydrogen, under pressure, e.g. of the order of 320 bar.  
      In this application, a flange  230  is constituted by the peripheral portion of a stopper or lid  210 . The flange  230  rests on a flange  240  constituted by the top portion of the tank  220 , the flange  240  defining an internal opening or manhole  280 . The flanges  230  and  240  are connected together by pins  250  distributed around the periphery of the annular flanges  230  and  240 .  
      In the example described, the opening  280  presents a diameter of 500 mm, and a gasket  260  placed in a gasket housing  270  in the vicinity of the opening  280  presents a diameter of 520 mm.  
      The pins  250  are distributed on a circle having a diameter of 900 mm, there being sixteen pins. The tension on each pin is 565 kilonewtons (kN).  
      The O-ring gasket used presents a torus diameter of 9.4 mm and has usable restitution of 0.09 mm. The flattening force of the gasket is 580 N/mm.  
      The configuration visible in  FIG. 14  prior to tightening the pins  250 , and in  FIG. 15  after tightening the pins  250 , is similar to that described above with reference to  FIGS. 6 and 7 .  
      Thus, the bottom surface  231  of the portion  230  of the stopper  210  is machined in such a manner that when the stopper  210  is assembled on the tank  220 , and prior to tightening the pins  250 , there is no contact between the entire bottom surface  231  of the flange  230  and the top surface  241  of the flange  240 , unlike a face-to-face type connection, but instead these surfaces  231  and  241  diverge and come into contact initially only over a distance e, e.g. of the order of 12 mm, in a bearing zone Z 1  situated in the vicinity of the gasket  260 , whereas at the periphery of the flanges  230 ,  240 , outside the pins  250 , in a zone Z 2 , there is an empty space E, e.g. lying in the range 0.3 mm to 0.6 mm between the surfaces  231  and  241  ( FIG. 14 ).  
      After the pins  250  have been tightened, there is no longer any empty space E in the bearing zone Z 2  and the connection is closed in sealed manner with prestress that increases the sealing margin and reduces the off-loading of the gasket  260 .  
       FIG. 17  shows that for a gasket  260  presenting usable restitution Ru of 0.09 mm, the off-loading of this gasket depends on the conicity of the connection, i.e. on the value of the empty space E between the surfaces  231  and  241  in the bearing zone Z 2  before the pins  250  are tightened, in the above example.  
      Curve G shows that values for E lying in the range 0.3 mm to 1 mm make it possible to obtain off-loading lying in the range 0.025 mm to 0.035 mm, i.e. much smaller than the usable restitution Ru of the gasket, thereby guaranteeing good sealing, without it being necessary to make use of a gasket that provides much greater usable restitution.  
      It can thus be seen that the greater the value E, the smaller the value of the off-loading. Nevertheless, if account is also taken of variation in the tension in a pin during pressurization and as a function of conicity (the value of the empty space E), as shown by curve F in  FIG. 16 , it can be seen that a cone having an opening (empty space E) of about 0.3 mm makes it possible, in the example described, to minimize variation in the tension in a pin to a value of about 1%, whereas this variation in tension can be as great as 15% for values of E that are of the order of 0.6 mm.  
      Thus, in the example described, selecting a value of 0.3 mm for E makes it possible to obtain off-loading of 0.036 mm ( FIG. 17 ) with very small variation in the tension in a pin (about 0.7%).  
      Off-loading of 0.036 mm represents a margin of 150% relative to the usable restitution of the gasket which is 0.09 mm. Conversely, a conventional face-to-face type connection (corresponding to the empty space E having a value equal to zero) would give rise to an increase of 52% in the tension in a pin  250  during pressurization, and to off-loading of about 0.21 mm, which is not compatible with a gasket having usable restitution of 0.09 mm. With a conventional face-to-face type connection it would therefore be necessary to design a special gasket presenting usable restitution greater than about 0.3 mm, because of the large opening created in the vicinity of the gasket in such a conventional face-to-face type connection, whereas in a connection in accordance with the invention of the kind described above there is practically no opening in the vicinity of the gasket housing  270 , with deformation of the stopper matching deformation of the bottle in the vicinity of the flanges  230 ,  240 .  
      Finally, it should be observed that in flanged prestressed leaktight connection devices, the flanges are advantageously made integrally without any fittings being added other than the clamping members  150 ,  250 , thus giving them excellent ability to withstand vibration.