Patent Publication Number: US-2022221057-A1

Title: Gasket assembly and seal carrier

Description:
The present invention relates particularly but not exclusively to a gasket assembly and a seal carrier for a conduit, particularly a gasket assembly comprising a primary seal and one or more secondary seals. Examples of the invention can typically be useful for sealing between sections of conduit carrying high-pressure and/or high-temperature liquids or gases, particularly in oil and gas applications. 
     BACKGROUND TO THE INVENTION 
     Gaskets allow a reliable compression seal to be made between two surfaces. Most commonly, a gasket is a shaped sheet of non-metallic, often slightly pliable, material that is placed between two surfaces which are then brought together and secured to one another in order to form a compression seal. The purpose of the gasket is to fill any slight irregularities in one of, or both, of the two sealing surfaces that form the seal, thereby preventing any leaks through the seal that might otherwise occur. 
     In addition to the seal between two surfaces provided by a gasket, some apparatus also employs a secondary seal adjacent to the primary gasket seal. A secondary seal can be used in conjunction with a primary gasket seal for several different purposes, including for providing a redundant backup to the primary gasket seal, should the primary gasket seal leak or otherwise fail. 
     An RTJ (ring-type joint, alternatively known as a ring gasket) is a particular type of gasket that is commonly used to seal between sections of pipe, and which is well-suited to high-pressure and/or high-temperature applications. Typically, an RTJ is fitted between the flanged ends of two sections of pipe, and then compressed between the two pipe sections in order to complete the seal between the two pipe sections. In contrast to common gaskets, RTJs are often metallic, and the seal thus formed is therefore a metal-to-metal seal. 
     The compression required to seal two surfaces, such as the flanged ends of two pipe sections, with a gasket is often provided by fixed, non-releasable connectors, commonly by bolts fitted through the flanged ends of the pipes. However, in some applications, particularly in oil and gas applications, it may be desirable to allow the pipe sections sealed by a ring-type gasket to be separated on demand, and then subsequently re-connected, without the difficulty of removing, and then replacing, fixed connectors such as bolts. For example, a marine riser pipe carrying high-pressure fluid between a floating surface vessel and a wellhead on the seabed must allow for emergency disconnection from the wellhead if the surface vessel drifts significantly out of position above the wellhead, and then allow for subsequent re-connection of the riser to the wellhead. Such emergency disconnection systems are known. 
     The metal-to-metal seal formed by an RTJ is created by means of a high compressive load during make-up of the connection which causes localised plastic deformation of the gasket against the mating seat surfaces. An alternative to this design is a lip-type gasket in which the combination of the gasket material together with the interface geometry of the gasket and its mating seat surfaces creates sufficient metal-to-metal contact pressure to create a seal while remaining largely within the limits of elastic deformation of the gasket material. Such gaskets are therefore suitable for multiple connection make-ups. 
     The present invention seeks to provide a lip-type gasket assembly for sealing between pipes or conduits that is less expensive and easier to manufacture, and which also allows a reliable seal to be formed during each one of several separation/re-connection cycles, while retaining the advantages provided by the inclusion of a secondary seal in addition to the primary gasket seal. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a gasket assembly for sealing between conduits passing through two respective bodies, the gasket assembly comprising: a primary seal, wherein the primary seal comprises a first sealing surface adapted to form a seal with the first body of said respective bodies, and a second sealing surface adapted to form a seal with the second body of said respective bodies; and
         a primary seal carrier, wherein the primary seal is coupled to the primary seal carrier, and wherein the primary seal carrier comprises one or more secondary seals, the one or more secondary seals being adapted to form a seal with one or more of the first and second bodies.       

     The present invention therefore provides the advantages of a gasket assembly having one or more secondary seals, without the disadvantages such as material costs and associated machining requirements of producing a primary seal which incorporates an integrated secondary seal. 
     Optionally the conduits passing through the two bodies each have a central axis, and optionally the axes of the conduits passing through the two bodies are coaxial when the conduits are sealed. Optionally the first and second sealing surfaces of the primary seal are angled with respect to the axes of the conduits. Optionally the first and second bodies form a seal with the primary seal by moving in opposing axial directions with respect to the primary seal, optionally by approaching the primary seal from opposing axial directions. Optionally the first and second sealing surfaces of the primary seal form a seal by compression with the sealing surfaces of the first and second bodies as the first and second bodies are compressed, optionally axially compressed, against the primary seal. 
     Optionally the primary seal is annular, and optionally the primary seal carrier is annular. Optionally a radially outer surface of the primary seal engages with a radially inner surface of the primary seal carrier, such that the primary seal carrier optionally restricts, but does not prevent, movement of the primary seal with respect to the primary seal carrier in a radial direction. 
     Optionally a portion of the radially outer surface of the primary seal radially overlaps with a portion of the radially inner surface of the primary seal carrier, such that the primary seal carrier optionally restricts, but does not prevent, movement of the primary seal with respect to the primary seal carrier in an axial direction. Optionally the primary seal carrier is formed from a different material from the material of the primary seal, which is optionally a lower value material than the material of the primary seal. Optionally the material which forms the primary seal carrier has different physical properties from those of the material which forms the primary seal. Optionally the material which forms the primary seal has improved temperature- and/or pressure-tolerance over the material which forms the primary seal carrier. Optionally the material which forms the primary seal has greater corrosion resistance over the material which forms the primary seal carrier. 
     The position of the primary seal carrier is optionally fixed with respect to one of the first and second bodies. Optionally the radial and/or axial movement of the primary seal with respect to the primary seal carrier allows for optimum alignment of the first and second sealing surfaces of the primary seal with the respective sealing surfaces of the first and second bodies, which optionally improves the integrity of the seal between the primary seal and the sealing surfaces of the first and second bodies. Optionally, the movable coupling of the primary seal with respect to the primary seal carrier allows multi-directional alignment of at least one of the first and second sealing surfaces of the primary seal with at least one of the first and second bodies. 
     Optionally the primary seal is formed from a metal, optionally from a metal alloy, optionally from a corrosion-resistant metal alloy such as Inconel. Optionally the first and second bodies are formed from a steel alloy. Optionally the sealing surfaces of the first and second bodies are formed from an inlay of a different material from the first and second bodies, which is optionally a corrosion-resistant metal alloy such as Inconel. 
     Optionally a surface, optionally a radially outer surface, of the primary seal and a surface, optionally a radially inner surface, of the primary seal carrier form a channel, which optionally allows fluid communication between a surface portion of the first body isolated intermediate the primary seal and the first secondary seal, and a surface portion of the second body isolated intermediate the primary seal and the second secondary seal. Optionally the channel between the primary seal and the primary seal carrier is contiguous around a radially outer surface of the primary seal. 
     Optionally one of the upper or lower bodies comprises a port to allow fluid communication between the channel intermediate the primary seal and the primary seal carrier, and the external environment. 
     Optionally the radially overlapping portions of the primary seal and the primary seal carrier prevent movement of the primary seal in one axial direction, but not in an opposing axial direction. Optionally movement of the primary seal with respect to the primary seal carrier in the opposing axial direction is restricted, but not prevented, by a retaining device, which is optionally annular, and is optionally a circlip or C-clip. Optionally the retaining device is fitted to the primary seal carrier after the primary seal has been coupled to the primary seal carrier. 
     Optionally the primary seal carrier comprises at least two secondary seals. Optionally the one or more secondary seals are annular, and optionally the secondary seals are disposed on opposing axial surfaces of the primary seal carrier. Optionally the secondary seals are formed from a non-metallic material, optionally an elastomeric material, optionally a thermoplastic such as PEEK. Optionally the secondary seals have a circular profile, and are optionally recessed into one or more surfaces of the primary seal carrier, optionally within dovetail-shaped recesses. Optionally the secondary seals provide a secondary full-pressure seal, in addition to the seal provided by the primary seal, optionally indefinitely in the event of failure of the primary seal. Optionally the secondary seals seal the low-pressure side of the primary seal from the external environment, which optionally maintains an optimum pressure differential across the primary seal. 
     Optionally the primary seal carrier comprises at least one resilient portion which is optionally resiliently biased in a radial direction away from the primary seal toward a radially extended configuration, and which optionally engages with at least one portion of one of the first or second bodies when in the radially extended configuration. Optionally the at least one resilient portion of the primary seal carrier is movable radially relative to the primary seal from the radially extended configuration into a radially compressed configuration in which the at least one resilient portion is closer to the primary seal than in the radially extended configuration. Optionally when the at least one resilient portion of the primary seal carrier is engaged with at least one portion of one of the first or second bodies, the axial position of the primary seal carrier is fixed with respect to the first or second body. Optionally the primary seal carrier comprises more than one resilient portion. Optionally the resilient portions are spaced around a circumference of the primary seal carrier, optionally regularly spaced, optionally symmetrically spaced, optionally equidistantly spaced. 
     Optionally one of the first and second bodies can be detached from the other of the first and second bodies after the first and second bodies have formed a seal with the primary seal. Optionally the first body can be detached from the second body. Optionally when the first body detaches from the second body, the primary seal carrier, and the primary seal which is optionally engaged with the primary seal carrier, remains engaged with the second body. Optionally the second body comprises a guide ring, which can optionally be integrated with the second body, or can optionally be joined to the second body with one or more fixings, optionally with screws or bolts. Optionally the guide ring extends or protrudes in an axial direction from a surface of the second body, optionally in a direction substantially parallel to the direction of travel of the first body when it detaches from the second body. Optionally the guide ring is annular, and optionally has a greater diameter than both the primary seal and the primary seal carrier. Optionally the guide ring restricts the movement of the first body after it detaches from the second body to be substantially parallel to the axis of the conduit of the second body, optionally until the first body is removed from the second body by a distance approximately equal to the axial dimension of the guide ring. 
     According to another aspect of the present invention, there is provided a seal carrier for holding a seal in sealing relation between conduits passing through first and second body assemblies; the seal carrier having a latch element for latching the seal carrier to the second body assembly; the latch element having a follower on one face for following a guide profile of said first body assembly and a latch component on an opposing face for latching with said second body assembly, wherein on disengagement of said body assemblies, the interaction of the follower with the guide profile ensures the latch element is maintained at a position such that the latch component is engaged with the second body assembly until the first body assembly is at least partially axially separated from the second body assembly. 
     Optionally, the second body assembly comprises a main body and a ring member coupled thereto, the latch component engaging with a recess formed in said ring member. 
     Optionally, the latch element comprises an annular flange member. 
     Optionally the seal comprises a first sealing surface, and optionally the first body assembly comprises a second sealing surface. Optionally a seal is formed between the first sealing surface and the second sealing surface, and optionally the first sealing surface adheres to the second sealing surface when the seal is formed between the first sealing surface and the second sealing surface. Optionally when the second body assembly is latched with the seal carrier, the first body assembly can move axially between first and second axial positions while the axial position of the seal carrier is fixed. Optionally the adhesion between the first and second sealing surfaces is overcome when the first body assembly moves axially between the first and second axial positions while the axial position of the seal carrier is fixed. 
     The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification to form a novel combination. 
     Various aspects of the invention will now be described in detail with reference to the accompanying Figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the Figures, which illustrates a number of exemplary aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, each example herein should be understood to have broad application, and is meant to illustrate one possible way of carrying out the invention, without intending to suggest that the scope of this disclosure, including the claims, is limited to that example. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. In particular, unless otherwise stated, dimensions and numerical values included herein are presented as examples illustrating one possible aspect of the claimed subject matter, without limiting the disclosure to the particular dimensions or values recited. All numerical values in this disclosure are understood as being modified by “about”. All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa. 
     Language such as “including”, “comprising”, “having”, “containing”, or “involving” and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term “comprising” is considered synonymous with the terms “including” or “containing” for applicable legal purposes. Thus, throughout the specification and claims unless the context requires otherwise, the word “comprise” or variations thereof such as “comprises” or “comprising” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 
     Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention. 
     In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase “comprising”, it is understood that we also contemplate the same composition, element or group of elements with transitional phrases “consisting essentially of”, “consisting”, “selected from the group of consisting of”, “including”, or “is” preceding the recitation of the composition, element or group of elements and vice versa. In this disclosure, the words “typically” or “optionally” are to be understood as being intended to indicate optional or non-essential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention. 
     References to directional and positional descriptions such as upper and lower and directions e.g. “up”, “down” etc. are to be interpreted by a skilled reader in the context of the examples described to refer to the orientation of features shown in the drawings, and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIGS. 1 a  and 1 b    are respectively perspective section and side elevation views of an example of a gasket assembly, showing a primary seal coupled to a primary seal carrier in  FIG. 1 a   , and a complete gasket assembly in  FIG. 1 b    with a sealed conduit passing through upper and lower bodies; 
         FIG. 2 a    is a side elevation view of the primary seal, and  FIG. 2 b    is a detailed view of the sealing surfaces of the primary seal; 
         FIG. 3 a    is a side elevation view of the primary seal carrier, and  FIG. 3 b    is a detailed view of the secondary seals of the primary seal carrier; 
         FIG. 4 a    is a side elevation view of the primary seal coupled to the primary seal carrier, and  FIG. 4 b    is a detailed view of the coupling and channel between the primary seal and the primary seal carrier; and 
         FIG. 5 a    is a side elevation view of the primary seal and primary seal carrier in position between the upper and lower bodies, and  FIG. 5 b    is a detailed view of the lugs of the primary seal carrier engaged with the recess of the guide ring. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings, a gasket assembly  1  in accordance with one example of the invention is shown in  FIGS. 1 a  and 1 b   . The gasket assembly  1  comprises a primary seal  10  and primary seal carrier  30 , and is shown in  FIG. 1 b    sealing between conduits  62  and  72  (shown in  FIG. 5 a   ) passing through upper body  60  and lower body  70  respectively. 
     The primary seal  10  is shown in detail in  FIGS. 2 a  and 2 b   , and is generally cylindrically shaped and has a bore with an axis X. In this example the diameter of the radially inner surface  12  (shown in  FIG. 1 a   ) of the primary seal  10  is constant, but in other examples the inner diameter of the primary seal may vary along its axial length. The radially outer surface of the primary seal  10  comprises a central rib  16  disposed axially intermediate first and second sealing faces  14 ,  15 . In this example the first and second sealing faces  14 ,  15  on the radially outer surface of the primary seal  10  are symmetrical, and taper radially inwardly with respect to the axis X of the bore of the primary seal, toward the axial ends of the primary seal. Also in this example the radially inward taper of the first and second sealing faces  14 ,  15  has a constant gradient, and more particularly, in this example, the first and second sealing faces  14 ,  15  are frustoconical. In other examples, the first and second sealing faces  14 ,  15  may instead have a non-linear profile, in contrast to the linear profile of the first and second sealing surfaces in this example best seen in  FIG. 2 b   . In other words, in this example, the outer diameter, and therefore radial thickness, of the primary seal  10  is greatest in the region of the central rib  16 , and decreases in an axial direction toward the axial ends of the first and second sealing faces  14 ,  15 . 
     The rib  16  of the primary seal  10  extends radially outwardly from the outer surface of the primary seal. In this example, the rib  16  is disposed equidistantly intermediate the axial ends of the primary seal, and has a constant outer diameter OD(R). The rib  16  further comprises a lip  17  which protrudes radially from the outer surface of the rib  16 . In this example the lip  17  is disposed generally equidistantly intermediate the axial ends of the rib  16 , and also has a constant outer diameter OD(L), where OD(L) is greater than OD(R). Therefore, in this example the lip  17  approximately bisects the outer surface of the rib  16  into two axially-orientated faces  18   a ,  18   b , each having a diameter OD(R). The lip  17  also has a axially-orientated face  20  of diameter OD(L), and two radially-orientated faces  21   a ,  21   b . In this example the axially-orientated faces  18   a ,  18   b  and  20  of the rib  16  and lip  17  respectively are parallel to the axis X of the primary seal  10 , and the radially-orientated faces of  21   a ,  21   b  of the lip  17  are perpendicular to the axially-orientated faces  18   a ,  18   b  and  20  of the rib  16  and lip  17 , and are also perpendicular to the axis X of the primary seal. 
     The primary seal carrier  30  is shown in detail in  FIGS. 3 a  and 3 b    and is also generally cylindrically shaped and has a bore with an axis coaxial to the axis X of the primary seal  10 . The primary seal carrier  30  generally comprises a radially inner portion  32  and a radially outer wall  33 , as best seen in  FIG. 1   a.    
     The inner portion  32  of the primary seal carrier  30  has a radially inner face  34 , which in this example is also parallel to the axes of both the primary seal  10  and the primary seal carrier, and has a constant inner diameter ID(IF). Also in this example a recess  36  is disposed toward, but not adjacent to, an axial edge of the inner face  34 , and a lip  37  is disposed adjacent to the opposing axial edge of the inner face. The recess  36  has a greater inner diameter ID(R) than the inner diameter ID(IF) of the inner face  34 , while the lip  37  has a lesser inner diameter ID(L) than the inner diameter ID(IF) of the inner face. 
     The inner portion  32  also has first and second surfaces  40 ,  41  which in this example are generally parallel to each other, and which are perpendicular to the axes of both the primary seal  10  and the primary seal carrier  30 . The first and second surfaces  40 ,  41  each comprise a secondary seal recess  42   a  and  42   b . In this example there are two secondary seal recesses  42   a ,  42   b , which are generally similar to each other, with one secondary seal recess disposed in each of first and second surfaces  40 ,  41 . 
     In other examples, there may be more than one secondary seal recess in either or both of the first and second surfaces  40 ,  41 . Also in this example, both secondary seal recesses  42   a ,  42   b  have a greater radial dimension at the base of each recess than at the opening of each recess, or in other words the secondary seal recesses  42   a ,  42   b  have a trapezoidal or dovetail profile, but in other examples the secondary seal recesses  42   a ,  42   b  could have any suitable profile, for example a square profile. 
     Secondary seals  43   a ,  43   b  are disposed within each of the secondary seal recesses  42   a ,  42   b . In this example the secondary seals  43   a ,  43   b  are annular and have a circular profile, and are formed from an elastomeric material, but in other examples the secondary seals may have any suitable geometry, and may be formed from a non-elastomeric material. 
     In this example the outer wall  33  of the primary seal carrier  30  extends axially, and slightly radially outwardly, away from the inner portion  32 . Therefore, in this example, the radially outer surface  46  of the outer wall  33  is generally frustoconical, and also in this example the radial thickness of the outer wall between the radially inner and outer surfaces  46 ,  47  of the outer wall tapers toward the axial edge of the outer wall. The outer wall  33  also comprises a radially inward profile or rim  48 , disposed toward the axial edge of the primary seal carrier  30 , which is contiguous around an inner circumference of the outer wall  33 . 
     Also in this example, the primary seal carrier  30  comprises four resilient tongues  50  disposed in the outer wall  33 . Each resilient tongue  50  is formed from first and second axial slots (or notches)  51   a ,  51   b  through the outer wall  33  (and rim  48  of the outer wall), and which extend from the axial edge of the outer wall toward the inner portion  32 , but which do not extend into or through the inner portion  32 . Furthermore, in this example, the resilient tongues  50  formed by the slots  51   a ,  51   b  are disposed equidistantly around the circumference of the primary seal carrier  30 , but in other examples there may be more or fewer than four resilient tongues  50 , and the resilient tongues need not be disposed either equidistantly or symmetrically, around the circumference of the primary seal carrier. 
     In this example each resilient tongue  50  is resiliently biased such that the outer and inner surfaces of each resilient tongue are radially aligned with the outer and inner surfaces  46 ,  47  of the outer wall  33 . Also in this example a lug  52  is disposed on the outer surface of each resilient tongue  50 , toward but not adjacent to the axial edge of the outer wall  33 . Each lug  52  is an outward radial protrusion from the outer surface of each resilient tongue  50 , which extends radially beyond the outer surface  46  of the outer wall  33 . In this example, the outer wall  33  itself does not have any corresponding radial protrusions, and therefore the lugs  52  of each resilient tongue  50  form the greatest outer diameter of the primary seal carrier  30 . 
     The upper and lower bodies  60 ,  70  are shown in  FIGS. 5 a  and 5 b   . In this example the upper and lower bodies  60 ,  70  are generally cylindrical and each has an axis coaxial to the axis X of the primary seal  10 . Also in this example each of the upper and lower bodies  60 ,  70  are formed from a material such as steel alloy and have an axial conduit  62 ,  72  that passes through each upper and lower body respectively between a first axial end surface  64 ,  74  and an opposing second axial end surface  65 ,  75 . In this example the conduits  62 ,  72  comprise a single cylindrical axial bore disposed through the centre of each upper and lower body  60 ,  70  from the first axial end surfaces  64 ,  74  of the upper and lower bodies respectively. 
     In this example the first axial surface  74  of the lower body  70  has a circular recess  76  which is adjacent to, and extends radially from, the axial conduit  72 . Also in this example a portion of the inner surface  73  of the axial conduit  72  adjacent to the recess  76  is not perpendicular to the first end surface  74  of the lower body  70 , but is tapered slightly radially outwardly, such that the opening of the axial conduit  72  has a slightly greater inner diameter than an inner portion of the axial conduit. Furthermore, in this example, the boundary region between the axial conduit  72  and the recess  76  comprising the tapered portion  73  of the axial conduit  72  and the radially innermost portion of the recess  76  is formed from an inlay  78  of material that is distinct from the material of the lower body  70 , as best seen in  FIG. 5 b   . In this example the inlay  78  is formed from a corrosion-resistant metal alloy such as Inconel, but in other examples the inlay  78  may be formed from another material suitable for forming a sealing surface with the primary seal  10 , or alternatively, the sealing surface of the lower body  70  may be formed from the same material as the lower body itself. 
     Also in this example an annular guide ring  77  is disposed within the recess  76  and is fixed to the lower body  70 . The guide ring  77  has a generally trapezoidal profile and extends axially beyond the first surface  74  of the lower body  70 . In this example the outer diameter of the guide ring  77  within the recess  76  is approximately equal to the inner diameter of the recess  76 , such that the radially outer surface of the guide ring  77  abuts the radially inner surface of the recess  76 . Also in this example the guide ring  77  is formed from a steel alloy material, but in other examples the guide ring  77  may be formed from other materials, or alternatively, may be formed as an integral part of the lower body  70 . 
     The guide ring  77  in this example further comprises a recess or notch  79  disposed around an inner circumference of the guide ring, toward the axial end of the guide ring opposing the axial end of the guide ring within the recess  76 . In this example the recess  79  is contiguous around the inner circumference of the guide ring  77 , but in other examples the recess  79  may not be contiguous, or may not be present. 
     In this example the first axial surface  64  of the upper body  60  also has a circular recess  66 , which in contrast to the recess  76  of the lower body  70 , does not extend radially from the axial conduit  62 , but is radially offset from the axial conduit  62 . The recess  66  has a generally trapezoidal profile, and is shaped to admit the guide ring  77  of the lower body  70  and the outer wall  33  of the primary seal carrier  30  when the gasket assembly  1  is assembled, as will be explained below. Also in this example a portion of the inner surface  63  of the axial conduit  62  adjacent to the first end surface  64  of the upper body  60  is not perpendicular to the first end surface  64 , but is tapered slightly radially outwardly, such that the opening of the axial conduit  62  has a slightly greater inner diameter than an inner portion of the axial conduit. Furthermore, in this example, the boundary region between the axial conduit  62  and the first end surface  64  comprising the tapered portion  63  of the axial conduit  62  and the radially innermost portion of the first end surface  64  is formed from an inlay  68  of material that is distinct from the material of the upper body  60 , as also best seen in  FIG. 5 b   . In this example the inlay  68  is formed from a corrosion-resistant metal alloy such as Inconel, but in other examples the inlay  68  may be formed from another material suitable for forming a sealing surface with the primary seal  10 , or alternatively, the sealing surface of the upper body  60  may be formed from the same material as the upper body itself. 
     The upper body  60  in this example also comprises back seat ports  69  which are openings in the first end surface  64  of the upper body joined to conduits which initially pass axially through the upper body  60 , as best seen in  FIG. 5 a   . The conduits are joined to second openings on an external surface of the upper body  60 . The opening of the back seat port  69  in the first end surface  64  is disposed radially intermediate the axial conduit  62  and the recess  66 . In this example, there are two back seat ports  69 , but in other examples there may be more or fewer back seat ports, or the back seat ports may not be present. 
     The gasket assembly  1  in this example is assembled according to the following sequence of steps. The axis X of the primary seal  10  is first aligned with the axis of the primary seal carrier  30 , and the primary seal  10  moved or pushed axially toward the primary seal carrier  30 , until the radially-orientated face  21   b  of the lip  17  of the primary seal come into contact with the radially-orientated face  39  of the inner portion lip  37  of the primary seal carrier. Since the outer diameter OD(L) of the lip  17  of the primary seal  10  is greater than the inner diameter ID(L) of the lip  37  of the primary seal carrier  30 , the primary seal is prevented from further axial movement with respect to the primary seal carrier once the lip  17  comes into contact with the radially-orientated face  39 . In this example, the axial dimension of the lip  17  is less than the axial distance between the recess  36  and the lip  37  of the inner portion  32  of the primary seal carrier  30 . 
     A retaining ring  58  is then fitted into the recess  36  in the inner face  34  of the primary seal carrier  30 . In this example the retaining ring  58  is a circlip or C-clip in the form of a resilient split ring which may be fitted by reducing the outer diameter of the retaining ring  58  by means of an external radially inward force, and then axially aligning the retaining ring with the recess  36  of the inner face  34 , and then releasing the retaining ring. The retaining ring  58  resiliently expands into the recess  36 , and further axial movement of the retaining ring  58  is therefore prevented. 
     After the retaining ring  58  is fitted into the recess  36  of the primary seal carrier  30 , and the primary seal  10  is therefore coupled to the primary seal carrier  30 , the primary seal remains free to move slightly with respect to the primary seal carrier in both axial and radial directions, or in other words, there remains a degree of play between the primary seal and the primary seal carrier. As is best seen in  FIG. 4 b   , the outer diameter OD(R) of the rib  16  of the primary seal  10  is slightly less than the inner diameter ID(L) of the lip  37  of the primary seal carrier  30 , and the outer diameter OD(L) of the lip  17  of the primary seal is also slightly less than the inner diameter ID(IF) of the inner face  34  of the primary seal carrier. Therefore, radial movement of the primary seal is permitted until either the axially-orientated faces  18   a ,  18   b  of the rib  16  abut either the axially-orientated face  38  of the lip  37 , or the retaining ring  58 , or alternatively until the axially-orientated face  20  of the lip  17  abuts the inner face  34  of the primary seal carrier. Similarly, axial movement of the primary seal is permitted until either of the radially-orientated faces  21   a ,  21   b  of the lip  17  of the primary seal  10  abut either the radially-orientated face  39  of the lip  37  of the primary seal carrier  30 , or the retaining ring  58 . 
     Once the primary seal  10  has been coupled to the primary seal carrier  30 , the axis of the primary seal carrier is aligned with the axis of the conduit  72  of the lower body  70 , and the primary seal carrier is moved or pushed axially toward the lower body and into the recess  76  in the first end surface  74  of the lower body. As the outer wall  33  of the primary seal carrier  30  moves axially past the radially inner surface of the guide ring  77 , the lugs  52  of the resilient tongues  50  contact the radially inner surface of the guide ring  77 , which urges the resilient tongues  50  radially inwardly. As the primary seal carrier continues to move axially past the guide ring  77 , the lugs  52  of the resilient tongues  50  then axially align with the recess  79  of the guide ring  77 , allowing the resilient tongues  50  to expand radially outwards and return to their resiliently biased resting position. Once the lugs  52  of the resilient tongues  50  are engaged within the recess  79  of the guide ring  77 , axial movement of the primary seal carrier  30  in the opposite axial direction, away from the lower body  70 , is substantially prevented. 
     As the primary seal carrier  30  is moved or pushed axially toward the lower body  70  and into the recess  76  in the first end surface  74  of the lower body, the first sealing face  14  of the primary seal  10  also contacts the tapered portion  73  of the axial conduit  72 . As the primary seal carrier  30  is moved or pushed into its final position in the recess  76  of the lower body  70 , the freedom of movement, or play, of the primary seal  10  with respect to the primary seal carrier allows the first sealing face  14  of the primary seal to precisely align with the inlaid sealing surface  78  of the lower body, which allows the formation of a reliable seal between the first sealing face and the tapered portion of the lower body. Simultaneously, the secondary seal  43   b  of the primary seal carrier  30  also contacts and forms a seal with the inlaid sealing surface  78  of the lower body. 
     Once the primary seal carrier  30  has been positioned within the recess  76  in the first end surface  74  of the lower body  70 , and the lugs  52  of the resilient tongues  50  are engaged within the recess  79  of the guide ring  77 , the axis of the conduit  62  of the upper body  60  is then aligned with the axis of the conduit  72  of the lower body  70 , and the upper body  60  is moved or pushed axially toward the lower body  70 . As the upper body  60  approaches the lower body  70 , the radially inner and outer surfaces of the recess  66  of the upper body engage with the radially inner and outer surfaces of the guide ring  77  of the lower body, orientating the upper body with respect to the lower body so that the second sealing surface  15  of the primary seal  10  contacts the inlaid sealing surface  68  of the upper body. Simultaneously, the secondary seal  43   a  of the primary seal carrier  30  also contacts and forms a seal with the inlaid sealing surface  68  of the upper body  60 . 
     After the upper and lower bodies  60 ,  70  have been fully moved or pushed axially toward each other, an axial compression force is then applied to the upper and lower bodies. The axial compression form squeezes the first and second sealing surfaces  14 ,  15  of the primary seal  10 , and the first and second secondary seals  43   a ,  43   b  of the primary seal carrier  30 , against the inlaid sealing surfaces  68 ,  78  of the upper and lower bodies  60 ,  70  respectively. The compression of the sealing surfaces of the primary seal carrier  10  and the upper and lower bodies  60 ,  70  completes the formation of the primary and secondary seals. 
     In this example, the freedom of movement of the primary seal  10  with respect to the primary seal carrier  30  prior to the joining of the upper and lower bodies  60 ,  70  causes a cavity or channel  80  to remain between the rib  16  and lip  17  of the primary seal carrier, and the inner face  34  of the primary seal carrier. The channel  80  is a closed cavity and is sealed from both the axial conduits  62 ,  72  of the upper and lower bodies  60 ,  70  and the external environment, by the seals formed between the first and second sealing surfaces  14 ,  15  of the primary seal carrier  10 , the secondary seals  43   a ,  43   b  of the primary seal carrier  30 , and the inlaid sealing surfaces  68 ,  78  of the upper and lower bodies. 
     During operation of the gasket assembly  1 , the back seat ports  69  are in fluid communication with the channel  80 . Before the sealed axial conduit  62 ,  72  passing through the upper and lower bodies  60 ,  70  is typically pressurised prior to conveying high-pressure and/or high-temperature fluids or gases, the back seat ports  69  can optionally be used to apply a relatively low pressure fluid to the channel  80  between the first and second sealing surfaces  14 ,  15  of the primary seal carrier  10 , the secondary seals  43   a ,  43   b  of the primary seal carrier  30 , and the inlaid sealing surfaces  68 ,  78  of the upper and lower bodies. This can be used as an indication of the integrity of the primary and secondary seals  10 ,  43   a ,  43   b , since if subsequent pressure monitoring indicates that the primary seal in particular is able to maintain a seal against low-pressure fluid, where the pressure differential across the primary seal is applied in the opposite direction (i.e. pressure in channel  80  is greater than bore pressure in conduit  62 ,  72 ), it is likely that the primary seal  10  will also be reliable when exposed to a high pressure differential in the direction expected during normal operations (i.e. bore pressure in conduit  62 ,  72  greater than pressure in channel  80 ). 
     After the completion of any optional low-pressure testing, the sealed axial conduit  62 ,  72  can be pressurised, and the conduit  62 ,  72  can then be used to convey high-pressure and/or high-temperature liquids or gases. During normal operations, the back seat ports  69  can also be used to measure or monitor physical parameters such as absolute pressure, or relative pressure change over time, of the channel  80  between the first and second sealing surfaces  14 ,  15  of the primary seal carrier  10 , the secondary seals  43   a ,  43   b  of the primary seal carrier  30 , and the inlaid sealing surfaces  68 ,  78  of the upper and lower bodies. Any unexpected change in monitored parameters can indicate a failure of the primary seal  10 , allowing appropriate action or intervention to be taken. In the event of a failure of the primary seal  10 , the secondary seals  43   a ,  43   b  can provide an alternative seal to maintain the overall seal between the conduit  62 ,  72  and the external environment. For example, if the primary seal  10  fails, pressure monitoring of the back seat ports  69  can indicate the failure of the primary seal to an operator, while the second seals  43   a ,  43   b  maintain the overall seal, thus providing time for remedial action to be taken. 
     The gasket assembly  1  in this example also allows for the upper and lower bodies  60 ,  70  to be removed from each other, after being sealed as described previously. Once a seal has been formed between the first and second sealing surfaces  14 ,  15  of the primary seal carrier  10  and the inlaid sealing surfaces  68 ,  78  of the upper and lower bodies, the sealing surfaces may adhere to each other even after the axial compression across the sealing surfaces that maintains the seal is released. In this example, when removing the upper body  60  from the lower body  70 , any adhesion between the second sealing surface  15  and the inlaid sealing surface  68  may cause the primary seal  10 , and therefore also the primary seal carrier  30 , to be removed with the upper body  60 . In this example, the recess  66  of the upper body also comprises a guide profile including a radial protrusion  67 , as shown in  FIG. 5 b   , which engages with a follower in the form of rim  48  of the tongues  50  of the primary seal carrier  30 . As the upper body  60  is initially released from the lower body  70 , the radial protrusion  67  of the upper body  60  exerts a radially outwardly directed force on the rim  48  of the resilient tongues  50  of the primary seal carrier  30 , which prevents the resilient tongues from deflecting radially inwardly, thereby urging the lugs  52  of the resilient tongues to remain engaged in the recess  79  of the guide ring  77 . The primary seal carrier  30 , and therefore also the primary seal  10 , will remain stationary as long as the lugs  52  of the resilient tongues  50  remain engaged in the recess  79 , the element  46  acting as a latch ensuring the carrier  30  is held in place on the lower body. Therefore, any adhesion between the second sealing surface  15  and the inlaid sealing surface  68  as the upper body  60  moves away from the lower body  60  can be overcome, and the sealing surfaces separated. 
     After the upper body  60  has moved axially a short distance away from the lower body  70 , the radial protrusion  67  of the upper body has also moved axially past the rim  48  of the resilient tongues  50  of the primary seal carrier  30 . Therefore, the resilient tongues  50  can again be deflected radially inwardly, for example by an external tool, in order to allow the primary seal carrier  30 , and therefore also the primary seal  10 , to be removed from the lower body  70 .