FR2510711A1 - DEVICE FOR ENSURING SEALING BETWEEN THE WALLS OF A MOBILE VALVE AXIS AXIALLY AND A BOX WITH FITTINGS - Google Patents

Abstract

THE INVENTION RELATES TO A DEVICE INTENDED TO ENSURE THE SEALING BETWEEN THE ROD AND THE GASKET BOX OF A VALVE TO OPERATE UNDER HIGH PRESSURES AND AT TEMPERATURES VARIING CYCLICALLY. THE SEALING DEVICE MAY INCLUDE TWO ASSEMBLIES 119, 121 PLACES BETWEEN THE ROD 51 AND THE GASKET BOX 65 OF A VALVE. EACH SET INCLUDES TWO METAL ANNULAR TRIMS 131 PROVIDED ON EACH OTHER WITH TWO SUPPORT RINGS 133 IN FLEXIBLE AND HARD MATERIAL, A SUPPORT RING 137, WHICH CAN BE MADE IN THE SAME MATERIAL AND WITH AN ANNULAR CORE 135 WHOSE EXPANSION COEFFICIENT IS NOTABLY LOWER THAN THAT OF THE RINGS 133. FIELD OF APPLICATION: DIRECT PASS VALVES FOR OIL AND GAS WELLS.

Description

The invention relates to a sealing device for the stem of a

  a high-pressure, high-temperature, direct-flow, balanced outer-stem type valve similar to the valves described in United States Patent Application Nos. 833,684 filed September 15, 1977, by David P Herd and No 697,084

  filed on 16 June 1976 by C Harles D Morrill.

  In the oil and gas industry, tempera-

  erations and pressures at the bottom of drilled wells are continually growing, and these wells are sometimes drilled in "corrosive" gas fields where well fluids contain relatively high percentages of H 2 S Valve seals have recently been developed

  oilfields and wellheads that are relatively

  are resistant to deterioration due to the combined effects of high pressures and temperatures and fluids

  caustics contained in the wells, such as H 25.

  U.S. Patent No. 4,056,272 discloses a gasket between a wellhead and a column hanger mounted therein, the gasket comprising two frustoconical ring gaskets of resilient metal, of substantially rectangular cross-section, which are flattened by a locking screw and a compression ring and placed under stress until the edges of the metal ring gaskets flow plastically or make a metal-to-metal tight contact by "stamping", with the cylindrical walls

  parallel of the wellhead and the suspension device

  In this static seal, a deformable ring, initially having a substantially trapezoidal cross-section and made, for example, of polyurethane or rubber "Teflon", is arranged between the metal annular fittings and is compressed during the flattening of the

  ring fittings to take a trans-

  rectangular diaphragm and come into contact with the walls of the wellhead and the column suspension device The deformable ring of this gasket assumes the function of secondary seal for metal ring gaskets in the case where the latter do not do not perfectly seal, for example,

  because of the presence of scratches or marks of

  swimming on the wellhead o on the suspension device

  The deformable ring flue in these stripes or marks

  machining and sealing.

  A seal used to ensure the impermeability

  and the static seal between the valve stem and the valve body or cap includes rectangular frustoconical metal ring gaskets of rectangular cross-section, disposed in a boot with gaskets around the stem, with intermediate rings in softer material disposed between annular resilient metal gaskets The reasons why annular metal gaskets are resilient and similar to Belleville springs, although not made of spring steel, but of softer material, are that: (1) the gaskets have a larger inside diameter and a smaller outside diameter when not loaded, so that the entire seal can be easily set up and removed from the stuffing box without undesirable friction against the stem

  of the valve or against the stuffing box; (2) the boys

  Niters retain their contact under stress with the stem and the stuffing box during the use of the valve, despite slight variations in the dimensions of this valve under the effect, for example, of temperature and pressure variations, these variations being risky to slightly modify the deformation or stress exerted on the linings and initially resulting from the tightening of the lining retainer. In other words, the linings must be elastic to retain

their preload.

  The aforementioned valve stem seal is described in the aforementioned application No. 697,084 and in an ASME article entitled "Seals for Valve Stems and Wellheads in High Pressure High Temperature Service" by CD Yororill and CW Meyer, prepared to be presented at a conference given in Mexico City, Mexico, from 19 to 24

  September 1976 The described seal is compressed by a

  threaded retainer of the liners so that the metal annular linings are flattened and their inner and outer peripheral edges are deformed or applied in metal-to-metal sealing, by "stamping" against both the outer surface of the

  the valve stem and the sides of the stuffing box.

  The intermediate rings placed between the metal ring gaskets are also deformed during the compression of the seal to fit the shapes of the metal ring gaskets and to come into contact with the stem and the stuffing box. The intermediate rings must therefore have a certain degree of elasticity The

  initial deformity usually causes deformity

  initial initialization of the intermediate rings, but

  the latter retain a certain degree of elasticity.

  Materials used for the intermediate rings of such seals include fluoroplastic materials, for example a tetrafluoroethylene polymer and graphite materials. Such materials also include a tetrafluoroethylene polymer loaded to about

% of molybdenum disulfide.

  The intermediate rings of the stem seal

  described above constitute dynamic seals which act mainly during the movements of the

  rod to seal between the packings

  metallic lugs and the rod when said lining

  metal rings are affected by the force of

  These intermediate rings also tend to lubricate the areas of contact between the rod and the metal ring linings by rubbing on the rod to a certain degree in order to reduce the friction between the latter and the rods.

  metal ring fittings The intermediate rings

  Also, the intermediate rings behave like secondary seals reinforcing the metal ring gaskets, in the same manner as the seals also produce a lubricating effect reducing the friction between the shank and the same intermediate rings, and between the latter and the metal ring seals. that the deformable annular secondary seals indicated above for the wellhead gasket and the column suspension device described in the aforementioned patent No. 4,056,272, these secondary seals fluent in any scratches or machine marks present on the rod and ensuring therein sealing. The invention described herein is an improvement to the stem seal of the present invention.

valve described above.

  An embodiment of the stem seal described above includes three metal ring gaskets

  and two intermediate rings arranged between these

  tures, and this seal is known as being of the "SMT" type.

  The seal of the SMT type proved to be satisfactorily

  health of the valve stem working at

  pressures of up to about 175 M Pa at temperatures below

  between -30 and 1500 ° C. In the case of valves subject to working pressures of 210 M Pa or more, the seal of the type

  However, SMT does not always provide excellent

  The graphite materials used alone, for example, are not desirable for SMT-type rod joints intended for valves to be operated under conditions that are expected to be encountered during service. pressures of 210 M Pa, as these materials tend to extrude beyond the metal ring gaskets as they flatten to solicit the seal, as the graphite begins to extrude before the gaskets are sufficiently flattened to form a seal with the valve stem and the stuffing box In addition, the movement of the valve stem tends to remove by wear or erosion the graphite-based materials deposited on the rod and driven by the rod to This extrusion and wear removal of the graphite-based material under service conditions 210 M Pa can lead to the appearance of leakage of fluids from the well by the seal and the need to replace the graphite ring. Similarly, tetrafluoroethylene polymer ("TFE") materials, or such materials containing Mo 52 as an additive, are not suitable for SMT-type seals for pressure valves of the type. order of 210 M Pa, because these materials are not always able to maintain tightness under such pressures after the valve has been subjected to cyclically varying temperatures A valve in service in an oil field in which well fluids under high pressure flows from deep wells can be heated, by these fluids, to a temperature of about 1500 C When fluids from the well stop flowing through the valve, for example if the well is closed, the valve can cool down to room temperature, for example 210 ° C, and if the well is opened again and the fluids start flowing again, the valve can again be heated to a temperature of 1500 ° C. The temperature of the valve varies cyclically between approximately 210 ° C and 1500 ° C. A valve stem seal must be able to remain sealed at all temperatures and during all the temperature cycles to which the valve is subjected in service. A seal of the type MS using tetrafluoroethylene polymer rings or Mo S-filled tetrafluorethylene polymer rings, seals well fluids at pressures of about 210 M Pa at ambient temperatures, for example 210 C, and again at high temperatures, for example 150 ° C. However, when the valve is subjected to a thermal cycle from room temperature to 150 C and bringing it back to room temperature, the SMT type seal does not always remain sealed; sometimes, the seal has small leaks, either during the movement of the valve stem, or while the valve stem is stationary, both during movement and periods of immobility Although the leak may be stopped by retightening the packing retainer, the leak reappears after further temperature cycles. The object of the invention is to solve the problems described above by means of a reliable rod seal of

  valve, suitable for valves with working pressures

  The invention has for another object such a seal which remains leakproof and shows no leakage when it is submitted to a temperature range of -300 ° C. to 1500 ° C. well fluids having pressures of 210 M Pa or more and when the valve temperature changes from ambient temperature to about 150 ° C and returns to ambient temperature without the need to tighten the The invention also relates to such a seal which is simple, inexpensive and economical, and easy to manufacture, install and put into service. The invention also relates to such a seal which has a low friction, which is durable and relatively resistant to deterioration due to extreme fluctuations and temperatures, high pressures and chemical activity

  well fluids to which it seals.

  In accordance with the invention, a high-pressure, balanced outer shaft, direct-pass valve has a rod sealant associating a metal-to-metal contact and a flexible material between the valve body cap and the valve stem. control of the valve and between the chamber formed in the body of the valve and the balanced rod Each sealing device comprises at least one group of joints comprising two frustoconical annular fittings of elastic metal between which are arranged two auxiliary rings or flexible but hard connection, with power

  high lubricant, for example a tetrafluoropolymer

  ethylene, a booster ring being adjacent to one of the annular metal fittings and the other booster ring being adjacent to the other one of these seals An annular core is disposed between the booster rings and consists of a material whose volumetric expansion is appreciably less, under the effect of heat, than that of the auxiliary rings, for example compressed graphite. The annular core has an inside diameter larger than the inside diameter of the rings. A backing ring, which may be made of the same type of material as that used for the booster rings, for example a tetrafluoroethylene polymer, is disposed on the periphery of the inner periphery of the annular core, between the latter and the stem of

  valve control or balancing rod Each

  The joints are arranged in a ring-shaped box, in the adjacent part of the valve body running around the stem. Each packing box

  is closed by an annular packing retainer

  sufficiently screwed into the stuffing box to flatten the frustoconical metal annular fittings so that the inner and outer edges of each annular metal seal are against the shank and against the stuffing box, respectively, under a

  sufficient pressure to cause plastic deformation

  tick of the inner peripheral edge of these fillings

  on their concave side and their outer peripheral edge.

  The stack, consisting of the annular core and the support ring disposed between the booster rings, is deformed to conform to the shape of the flattened metal ring gaskets and to fill

  practically the entire space between these

  The volume of the annular core is approximately equal to one third of the total volume of the stack. When the valve is in service and is subjected to a thermal cycle, the seal remains tight and preserves its preload it is necessary to tighten the retaining element

  The stem joint assembly according to the invention

  It can also be used for the sealing of locking screws and in other cases where it is necessary to seal between moving parts which are mutually movable and subjected to a thermal cycle, both during and after

  after relative movements of these pieces.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which: FIG. 1 is a vertical section of a valve according to the invention; and FIGS. 2A and 2B are partial vertical sections in the same plane as that of FIG. 1, but on an enlarged scale, showing an embodiment of the control rod sealing device according to FIG.

  the invention, an embodiment in which the gar-

  The truncated metal annular nitrides are oriented in a direction away from the pressure towards which the seal is to be sealed inside the valve, FIG. 2B showing the rod sealing device according to the invention, such as mounted in the valve, but before being urged by clamping the seal retainer and Figure 2A showing the device

  stem sealing in the stressed state.

  FIG. 1 shows a valve comprising a hollow body which has a chamber 21 and to which a

  cap 23 is fixed by studs 25 and nuts 27.

  A suitable lining 29, urged by pressure,

  ensures the seal between the cap 23 and the chamber 21.

  Seats 31 and 33, located at the inner ends of channels 35 and 37, cooperate with two pierced shutters 39 and 41 which control the flow of a fluid, through

  example of water, oil or gas, through the valve.

  A sealing material is stored in reservoirs

  see 43 and 45 and it is directed automatically, by channels 47 and 49 distribution, to 'Interfaces between the shutters and the seats and between the collars

  seats and the body of the valve to ensure the

at these interfaces.

  The shutters 39 and 41 are equipped with a movement

  alternatively by a substantially cylindrical control rod 51 to move between a closed position, shown in FIG. 1 and in which the fluids can not flow through the channels 35 and 37, and an open position permitting this flow and in which the orifices 53 and 55 of the shutters are

  aligned with holes 57 and 59 of seats 31 and 33.

  The upper end of the control rod 51 projects outwardly from the chamber 21 of the valve and passes into a hole 61 of the cap 23. A sealing device 63 according to the invention ensures the seal between

  the rod 51 and a substantially cylindrical packing box

  The sealing device 63 is compressed in the packing box 65 by a packing retainer 67 which is screwed into a threaded collar 69 located at the top of the cap 23 A purge port 71 is used for leak detection of fluids between rod 51 and

  the orifice 61 after replacing the rod.

  The outer surface of the collar 69 of the cap is also threaded and screwably receives a bearing cap 73 A control nut 75 is screwed onto the threaded upper portion 77 of the control rod 51 and has a flange 79 disposed between stops axial

  upper and lower 81 and 83 The axial abutment

  83 against the upper surface of a washer disposed on the top of the trim retainer 67. The lower axial abutment 81 bears against

  the upper inner end of the support cap 73.

  A hand wheel 87 has a non-circular opening 89 fitted to a section 91 of corresponding shape of

  the control nut 75 The flywheel 87 is kept in position

  by a retaining nut 96 which is screwed onto the end

  The purge port 75 allows the fluids to escape from between the threaded portion 77 of the rod 51 and the control nut 75.

  A balancing rod 97, substantially cylindrical,

  drique, is connected to the lower ends of the shutters and protrudes outside the chamber of the valve through a hole 99 A sealing device 101 according to the invention ensures the seal between this rod 97 balancing and a substantially cylindrical packing box 103 located in the body of the valve The sealing device 101 is compressed in the packing box 103 by a lower element 105

  retainer which is screwed into a threaded hole

  coaxial with hole 99 and with stuffing box 103.

  A purge port 109 is used to detect, as the case may be, leakage of fluids from between the balancing rod 97 and the hole 99 when the widened section at the upper end of the balancing rod is fully seated. in the ring seat located in the body of the valve, around the hole 99 A lower cap 111 is screwed onto the body of the valve, above the lower element 105 and the lower end restraint

  of the balancing rod 97, by means of screws 113.

  When the flywheel 87 is rotated, the control nut 75 rotates and causes, via the

  51 control rod, the rise or fall of the shutters

  39 and 41 to which the rod is connected by a hub This in turn causes a rise or fall movement.

  downward movement of the balancing rod 97 connected to the shutters

  Thus, there is a relative axial movement between each of the rods 51 and 97 and the respective sealing devices 63 and 101 of these rods. These sealing devices 63 and 101 must therefore remain tight before, during and after. such movements

relative axes.

  The sealing devices 63 and 101 are

  identical, so that the detailed description of a

  Only one of these devices suffices. As shown in FIGS. 2A and 2B, the sealing device 63 comprises

  an upper seal assembly 119 and a lower one

  121 A basic adapter ring 123 is disposed in the bottom of the annular box 65 to

  gaskets, below the lower seal assembly 121.

  The lower surface of the adapter ring 123 tightly and complementarily bears against the bottom of the stuffing box. A movable ring 125 for adaptation is disposed between the lower face 127 of the packing retainer element 67 and the upper assembly 119 sealing The upper end of the movable adapter ring is applied closely and correspondingly against the lower face 127 of the retaining element 67 An intermediate ring 129 of adaptation

  is disposed between the sealing assemblies 119 and 121.

  The upper face of the base adapter ring 123, the lower face of the adapter ring 125

  and the upper and lower faces of the inner ring

  mediator 129 are of frustoconical shape

  sensing the desired cone angles for the shapes of the sealing assemblies 119 and 121 in their final assembly positions In this regard, it should be noted that FIG. 2B shows the sealing device according to the invention as mounted in the valve, but before being urged by clamping the retaining element of the

  fittings, and that Figure 2A illustrates the same arrangement

  sealing device in the stressed state, the retaining element

  naked gaskets being screwed further into its threaded housing and the sealing assemblies and adapter rings being in their assembly positions

  As described in more detail below,

  metallic annular faces of the seal assemblies have a more pronounced conical shape, i.e., smaller crown angles, in their relaxed state

  as shown in Figure 2 B only in their requested state.

  As is shown in FIG. 2A, if desired, either or both of the rings 123 and adapter may be omitted, in which case the bottom of the stuffing box and / or the lower end of the retaining element 67 then have a surface

  frustoconical having the desired cone angle and area.

  When used, the adapter rings 123, 125 and 129 may be made of a relatively hard material, for example 4140 steel It is sufficient that the body and the cap of the valve are made of any steel conventionally used for valves to

high pressure.

  The sealing assemblies 119 and 121 are identical, so that it suffices to describe in detail only one of these assemblies.

  includes two truncated metal ring fittings

  131 between which are arranged two rings 133 identical auxiliary These rings 133 are made

  in a soft and hard solid material, having a certain

  It has a lubricating ring with a modulus of elasticity that is lower than that of the metal annular fittings. A booster ring is arranged in close proximity to one of the metal annular fittings and the other booster ring is arranged in the immediate vicinity of

the other garnish.

  An annular core 135 is disposed between the auxiliary rings 133 This annular core 135 presents

  a volumetric thermal expansion coefficient in-

  The inner diameter of the annular core 135 is larger than that of the inner diameter of the auxiliary rings 133. A support ring 137 made of a solid material is

  flexible, with a certain lubricating power and

  be of the same type as used for rings

  133, is disposed on the periphery of the edge

  the annular core 135 between the latter and the rod 51 for controlling the valve.

  support makes a sliding fit in the opening

ture of the annular core 135.

  The metal annular lining 131 in the relaxed state has a substantially rectangular section which forms an angle of approximately 300 with the horizontal. Thus, the angle of the cone formed by the lining 131 in the relaxed state is approximately 1200 mm. in this relaxed state, the linings 131 have a radial clearance with both the rod 51 and the stuffing box 65, so that neither the rod nor the stuffing box are damaged during the fitting of the linings 131 in the valve Le. assembly of the lining 131 is simply to make them fall into position When the sealing device is urged by a tightening of the lining retaining element, the latter are flattened so that the inside diameter of each lining decreases and the diameter outside of each trim

  increases sufficiently so that the peripheral edge

  on the concave face and the outer peripheral edge on the convex face of each lining are applied in leaktight contact, metal to metal,

  by deformation or "stamping", that is to say, creep

  tick, with the upper and the boot with trims, respectively

  In order not to damage by friction or to damage the rods, the metal ring fittings must

  be made of a softer metal than the -

  valve stems Valve stems can be

  for example, although a comparable steel may be suitable. It is preferable that the rod has a hard coating, for example a coating of tungsten carbide with a thickness of

  0.075 to 0125 mm, intended to increase the hardness and

  Such a coating raises the hardness of the rod by passing it from a Rockwell value of about 30 to about 60. The metal ring gaskets must be sufficiently plastic to

  enable forging the peripheral edges under the application of a high stress in order to achieve the metal seal on

  metal, and they must be sufficiently strong to withstand the high precharge and fluid pressures encountered in the wells in service. These gaskets may be made, for example, of annealed (austenitic) stainless steel, for example of the 316 type, or of other metals such as mild steel or alloy steel To further reduce

  the greater the risk of damage by friction or

  damage to the stems, the inner peripheral edge of the concave face of each trim is rounded

  preferably at a radius equal to about half the thickness

  For example, a 0.5 mm radius for a 1 mm thick gasket. When in a flattened state, the annular metal gaskets 131 are at an angle of about 150 to the horizontal, corresponds to a

  cone angle of about 1500, conforming to the truncated faces

  of the adapter rings 123, 125 and 129 which are

  also arranged in such a way as to form an angle of

  It is evident that, although the metal annular fittings are preferably frustoconical, it is possible to use trimmings.

  metal rings having shapes other than truncated

  conical. The material used for the booster rings

  133 and the support ring 137 must have a low coefficient of

  friction, that is to say a high lubricity The material used for the auxiliary rings 133

  and the support ring 137 must also have a resistance

  sufficient strength and hardness to maintain its

  grit under high pressures, and must withstand the chemical activity of the fluid controlled by the valve and must be able to withstand temperatures within the range expected to be encountered during service, for example from 150 to -300 Such a material must also be sufficiently flexible or elastic to creep into all small spaces

  which may exist between metal ring gaskets

  and rod and lining box due to scratches or machining marks on the

  stem or the stuffing box, or between

  metal annular tines and the surface of the newly adjacent stem, during and after the movements of this rod Spaces of the latter type may appear, for example, due to the fact that, during and after the movements of the stem, the peripheral edges The interior of the metal ring gaskets do not instantly, and perhaps never, plastically flush to conform to the newly adjacent surface of the stem. The materials of the fillers and the backing ring creep into all these small spaces. The fillers and the back-up ring can also be considered as sealing rings. The materials suitable for the back-up rings 133 and the backing ring 137 comprise , for example, a tetrafluoroethylene polymer such as that marketed under the trademark "Teflon", and that marketed under the trademark "Moly-Teflon", which is similar to "Tef Ion", but contains up to about 15% molybdenum disulfide Mo 52 A particular suitable material contains 5% by weight of Mo 52 and 95% by weight of TFE and is marketed by the company Allied Chemical

  Company under the designation "No. 2021".

  The material used for the annular core 135 must, like the material used for the rings 133 and 137, have sufficient strength to withstand the high stress required for the preload of the joint,

  and it must also be resistant to chemical activity

  that fluids from the well to which we must ensure

  watertightness and must be able to withstand

  erations within the expected range of

  counter during service, for example from 150 to -60 ° C.

  The Applicant's discovery of what appears to be the cause of leakage of the SMT type seal

  at high pressures and under the effect of temperature cycles

  However, it is obvious that the gasket disclosed herein solves the problem of leaks regardless of the theory of its operation. The leaks presented by the SMT-type rod seal, using TFE or TFE rings loaded with Mo 52, at pressures of the order of 210 M Pa, after cyclical temperature variations, apparently result in a partial loss. Preload exerted on the seal It is possible to consult, by way of comparison, the loss of preload occurring in fully elastomeric linings, described in the aforementioned ASME article. When the seal of the SMT type is put in place or requested for the first time, time, it is subjected to mechanical compression resulting from the tightening of the lining retainer, so that it is placed under

  a constraint of a degree higher than that of the con-

  which would be exerted by the high-pressure well fluids When a valve with the SMT-type rod seal warms up to ambient temperature up to 150 ° C, the TFE rings tend to expand, but they can not expand so significantly because they are virtually retained on all sides by metals that expand less rapidly than these rings of TFE The seal is then placed under a constraint of

  preload greater than that applied to it initially

  tialement, that is to say before heating up When the valve cools down and returns to room temperature, the precharge stress not only decreases from its high level reached at the time the valve was heated, but also goes down at a lower value than it originally had. This seems to be due to one or other of the following effects, or maybe both effects. When the valve is heated to about 1500 C, the high stress, which exceeds the already high preload stress exerted on the joint and the surrounding metal structure maintaining it, as a result

  thermal expansion of the TFE rings, can provoke

  cause a slight permanent or permanent deformation,

  that is to say a slump, of this metallic structure

  and maintain, so as to increase the volume occupied by the seal when the latter returns cooling at room temperature, which reduces the stress exerted on the seal and makes it lower below its prehàrge Alternatively, or perhaps in moreover, when the TFE rings are placed under the high level stress due to the thermal expansion resulting from the heating of the valve to 150 ° C, the TFE rings can undergo a permanent deformation beyond that caused by the preload stress, that is to say that they may take another compressive deformation, which remains after the cooling of the valve at room temperature and which results in a relief of the stress exerted in the rings of TFE, this relief somewhat neutralizing the effect

  of compression exerted by the retained Cd element and the

  Therefore, after a cyclic temperature variation, to restore the proper preload, it is necessary to tighten the lining retainer. In the absence of such a retightening, the valve is unable to provide the seal. sealing against

  pressures of the order of 210 M Pa without light leaks.

  According to the invention, a certain part of the preferred material, consisting of TFE or TFE loaded with Mo 52, located between the metal annular fittings of the SMT-type rod seal, is replaced by a material

  which has a relatively small dilatation,

  It is heated, compared to that of the TFE loaded or not Mo 52 In the preferred embodiment of the invention, this low thermal expansion material

  constitutes the annular core 135, the three faces of which

  metal rings and the stem are covered by the auxiliary rings 133 and the support ring 137. Thus, the annular core 135 must have

  a coefficient of volumetric thermal expansion

  This material suitable for the annular core 135 is a compressed graphite sold under the trademark "Grafoil" (see US Pat. No. 3,404,061). volumetric thermal expansion of the TFE, for example, is substantially greater than that of the "Grafoil", actually several times higher, although accurate values are not known However, published data indicate that the "Grafoil", which is produced in the form of thin flexible laminate sheets or strips, has a linear coefficient of expansion of about -0.036 10-5 cm / cm 2 C in directions parallel to the graphite layers, i.e. along their length

  and their width, in the range of 21 to 1100 ° C, and of

  2.72 10-5 cm / cm 2 C in directions perpendicular to the layers, i.e. transverse to their thickness, in the range of 21 to 2200 WC. The TFE has a linear expansion coefficient of about 12.72-18, 18 10-5 cm / cm OC over the range of 25-260 ° C For solid bodies, the volumetric coefficient of thermal expansion is equal

  about three times the coefficient of thermal expansion

  than linear (see for this purpose the book "The Handbook of Chemistry and Physics", 48th edition, page F-90 (Chemical Rubber Co 1967) If we assume then that the "Grafoil" has a volumetric expansion, in being heated, having values three times higher than the values given above for the linear expansion, we obtain

  values which remain less than a quarter of the

  volumetric thermal temperature for the TFE when the valve is heated to temperatures between

about 25 and 150 WC.

  The stacking of rings or spacer rings, comprised between the metal annular fittings and hereinafter referred to as the "intermediate stack", consisting of the annular core 135, the support ring 137 arranged around the edge inner peripheral of this core and 133 auxiliary rings arranged near the upper and lower faces of the rings 135 and 137,

  is deformed to match the shape of the annular

  131 and to fill approximately

  The spacing between these liners 131 when flattened in the biased state. The rings and rings of the intermediate extrusion generally have a rectangular cross-section, but they can be deformed with the press before they are pressed. installation in the valve to take the frustoconical shapes shown in Figure 2 B and which correspond to frustoconical surfaces 1 9 of the adapter rings 123, 125 and 129 against which the metal annular fittings are flattened Alternatively, the rings of the interlayer stacking can be set up in their configuration, in section, rectangular of origin, and brought to the frustoconical shape

  when the seal is pressurized or pressurized.

  The dobby constituting the stress relieving ring 135 may be in the form of a "Grafoil" tape wound tightly and compressed into a closed ring or closed ring. This tape may be of the type marketed by Union Carbide Corporation under the designation "Grafoil Ribbon-Pack" and described in

  technical newsletter of the same company, no. 524-

  204 A ring made of such a tightly wound ribbon

  and has been compressed presents its largest expan-

  in the radial direction when it is installed in the stuffing box around the rod, that is to say in the direction of the rod and the stuffing box Alternatively, the ring 135 can be cut in a "Grafoil" sheet or in several stacked "Grafoil" sheets The commercially available "Grafoil" may only be compressed or compacted to about%, but it may be compressed or compacted completely,

  that is to say 100%, either in a press before the

  as previously described either once in place in the valve, during the solicitation or

under pressure of the joint.

  The auxiliary rings 133 are thinner in the axial direction than the ring or the ring 135 and the ring 137 which have substantially the same axial thickness when the ring 135 is fully compressed, but they are wider in the radial direction, that these two rings 135 and 137 The total radial widths

  of the two rings 135 and 137 is substantially equal to the

  The rings 133 and 137 must make a tight fit on the rod during the installation of the intermediate stack in the valve. When the intermediate stack is compressed at the time of the solicitation of the seal, the inner peripheral edges of the rings 133 and 137 are applied more closely against the shank 51, and the outer peripheral edges of the rings 133 and 135 are applied tightly against the walls of the box

with fittings 65.

  Although two sealing assemblies 119 and 121 are shown in the figures, it has been found that only one sealing assembly is sufficient to obtain a

  satisfactory seal The second sealing assembly, that is,

  that is the furthest away from the fluids which must be sealed, is intended to be used as a backup or reinforcement in the case where the first sealing assembly has a failure A channel 139,

  in the hat 23 and in alignment and communication

  cation with a channel 141 through the intermediate ring

  129 when the joint is stressed,

  Another feature of relief or reinforcement sealing is channel 139 also communicates with an injector 140 disposed in a tapped hole.

  in the outer surface of the cap 23 An annular groove

The channel 143, which communicates with the channel 139, is made around the walls of the stuffing box 65, and an annular groove 145, which communicates with the channel 141, is formed around the inner peripheral surface of the intermediate ring 129. In the event of failure of the sealing assemblies 119 and 121, sealing material may therefore be injected by means of the injector 140 and channels 139 and 141 into the grooves 143 and 145 to form a seal. emergency or reinforcement around the stuffing box and stem respectively. The sealing device according to the invention is preloaded by clamping the lining retaining element to a stress substantially greater than that which is expected that the pressure of the fluid exerts

  when the valve is in service A constraint of

  Typical load for rod seals for a valve such as that shown in FIG. 1, whose nominal working pressure is 210 MPa, is

262.5 M Pa.

  When a valve incorporating the

  According to the invention, the pH of the rod is raised from ambient temperature, for example 210.degree. C. to about 150.degree. C., for example by the fluids passing therethrough, and is then cooled to room temperature.

  additional tightening of the retaining element is not

  Therefore, the original preload exerted

  the valve is maintained during the cyclical variations

  This seems apparently due to the fact that the stress exceeds the initial precharge stress and due to the thermal expansion attempted by the

  material between metal ring fittings 131-

  is not big enough to cause a deformation

  of the metal structure of

  This is formed by the parts of the valve adjacent to the gasket due to the smaller thermal expansion of the annular core 135 than the booster rings 133 and the support ring 137. For the same reason, the additional constraint due to the heating seems apparently low enough to avoid permanent deformation or additional deformation by compression of the rings 133 and 137, which, consequently, avoids any loss of the precharge stress when the rings 133 and 137

relax while cooling.

  It appeared that the sealing device

  according to the invention suitably ensures the

  fluidity under a pressure of 210 M Pa and on

  temperature cycles from -30 to 1500 C, without additional tightening

  of the liner retainer, when the booster rings 133 and the backup ring 137 are made of TFE loaded at 5% Mo 52, when the annular core 135 is made of "Grafoil" and when the volume of the stress relieving ring 135 is equal to about one-third of the total volume of the interposing stack. In other words, in the preferred embodiment, the combined volume of the booster rings 133 and the support ring 137 is about double the volume

  of the annular core 135 The material used for the

  fillers 133 has no extrusion beyond the annular metal fittings 131 when pressurizing the seal, and it maintains the annular core 135 in "Grafoil" between these rings 133 when pressurizing the seal , so as to prevent the extrusion of this core beyond the lining 131 before the latter make the metal-on-metal sealed contacts with the rod and the stuffing box In addition, the support ring 137 made of TFE loaded with 5 % of MB 52, placed on the periphery of the inner peripheral edge of the soul

  ring 135 in "Grafoil", reduces friction

  between the rod and the sealing device of the latter and prevents any unwanted wear of the core

  Thus, an annular core in "Grafoil", pre-

  having a low thermal expansion, coated on its

  three sides adjacent to the rod and metal fittings

  TFE rings loaded at 5% Mo.sub.22, and occupying about half of the total volume of TFE rings loaded at 5% Mo.sub.22, are preferred for interleaving the device according to the invention. than other volume relationships for the rings

  and interstage stacking rings can also provide

  satisfaction, as well as the use of other

  materials for making rings and rings

storing the interleaving stack.

  Although Figures 1, 2 A and 2 B show that the cones of the metal annular fittings and the rings of the intermediate stack are oriented towards the opposite side to that against which is applied the pressure to which it must be sealed, when the seal is to be made between parallel surfaces, the inner and outer peripheral edges of the seal make analogous contacts and the seal

  is therefore reversible Therefore, the cones of

  metal rings and the rings of the intermediate stack may, in a variant, be arranged so as to be directed towards the pressure against which it is necessary to seal. Moreover, it is obvious that it is not necessary that the rings and rings 133 and 137 are separated They may alternatively be in the form of, for example, a cylindrical ring in one piece having a groove formed in the middle of its outer peripheral surface, that is to say a ring with a U-shaped section The ring of "Grafoil" can then be snapped elastically into position in the throat

before installation in the valve.

  It goes without saying that many modifications can be made to the device described and shown

  without departing from the scope of the invention.

Claims (11)

  1 Device for sealing   in high pressure applications and temperature cycles   grooves, between the walls of a valve rod (51) movable axially, and a box (65) with gaskets surrounding the rod and whose bottom has an orifice through which   the valve stem passes and leaves this box, the arrangement   characterized in that it comprises first and second resilient metal annular liners (131) disposed in the stuffing box around the valve stem, and a flexible annular seal assembly disposed in said packing box. around the valve stem and placed between said packings, the seal assembly comprising first and second annular portions (133) of flexible and hard material, respectively adjacent to the first and second packings, and a core (135) disposed between the first and second parts   and made of a material having a coefficient of   less than that of the material of the first   first and second annular parts.   2 Device according to claim 1, characterized   rised in that the material of the first and second parts   rings has a low coefficient of friction.   3 Device according to claim 2, characterized   in that the material of the first and second annular parts comprises a tetrafluoroethylene polymer and   the material of the core comprises compressed graphite.   4 Device according to claim 3, characterized   in that the material of the first and second annular parts further comprises up to about 15% of molybdenum disulfide.   Device according to claim 4, characterized in that the first and second annular portions comprise reinforcing rings (133) in sealing contact with the stem and the stuffing box and that the core   comprises an annular core (135) whose integral diameter   The device further comprises a support ring (137) of flexible and hard material, disposed around the periphery of the inner peripheral edge of the annular core, between the outer diameter of the rod, the device further comprising the latter and the stem.   Device according to claim 5, characterized   rised in that the material of the support ring is the same than that of the extra rings.   Device according to claim 6, characterized   in that the annular core and the support ring occu-   together almost all the space between the booster rings, in the axial direction, and between   the stem and the stuffing box in the radial direction.   8 Device according to claim 7, characterized   in that the volume of the annular core is equal to about half of the total volume of the rings and the support ring.   Apparatus according to claim 1, characterized   in that the coefficient of thermal expansion of the material of the core is less than a quarter of that   of the material of the first and second annular parts.   Device according to claim 1, characterized in that it comprises means (67, 123, 125,   129) for compressing the first and second   so that the latter are partially flattened and that their inner and outer peripheral edges are applied in metal-on-metal, stamped contact against said rod and the stuffing box, said means also being intended to push the first and second annular parts. of the sealing assembly in sealed contact with the stem and the box with fittings.   11 Device according to claim 10, characterized in that the core has an annular shape whose outer radial peripheral edge is adjacent to the boot lining and whose inner diameter is   greater than the outer diameter of the stem, the   seems to contain a third part   laire (137) in flexible and hard material, arranged between the soul and the stem.   12 Apparatus according to claim 11, characterized in that the first, second and third annular portions are made of a tetrafluoroethylene polymer and in that the core is made of compressed graphite. Apparatus according to claim 11, characterized in that the first, second and third   annular parts consist of a material comprising   95% of a tetrafluoroethylene polymer and 5% of molybdenum disulfide, the core consisting of compressed graphite, the first, second and third annular parts and the core occupying substantially all of   of the space between the annular metal fittings   the rod and the stuffing box when said linings are compressed, the core having an equal volume   about a third of the total volume of this space.