FIELD OF THE INVENTION

The invention relates to gaskets for preventing the leakage of fluid between joined faces. In particular, the invention relates to a new gasket that provides sufficient electrical isolation between joined faces of a fluid conduit, excellent sealing between the bore and the exterior of the fluid conduit, and that also maintains sealing integrity in the case of fire.

BACKGROUND OF THE INVENTION

Gaskets are a frequently used device for preventing the leakage of fluid between joined faces. A common example of this is within the flanged end connections between sections of pipe or flow line. These flanged connections, or bolted joint assemblies, are used in many instances including interrupting a pipeline to install process (in-line) equipment such as valves, flow meters and pumps and also to extend the pipe line by joining flanged ends of pipe line together.

The choice of gasket type and material to be used in these flanged connections is made based on the assessment of application parameters such as temperature, pressure, media type, size and available bolting force.

There is a significant emphasis from many industry and customer specifications to reduce the leakage (fugitive emissions) of a bolted joint assembly. Many materials that can achieve the required fugitive emissions levels have a limited temperature or pressure capability. An example of this would be a rubber gasket that has an excellent fugitive emissions performance but has a limited pressure capability depending on the bolted joint arrangement. Many standard flanges and pipe lines also require a capability to seal significantly higher pressures and aggressive media ruling out many material selections.

In certain instances it is desirable to electrically isolate one flange face from the adjoining flange face. As an example this is a requirement when corrosion of pipelines is to be mitigated by cathodic protection. If the flanges are manufactured from dissimilar materials then electrically isolating the two dissimilar flanges prevents a potential difference between the two metals creating galvanic corrosion. This electrical isolation is typically carried out by the use of an isolating gasket to isolate the flange faces and a washer and sleeve system that isolates the bolts used to create load on the flange.

There are also instances where there is a requirement for the gasket to maintain sealing integrity in the event of a fire. Gaskets are qualified as 'fire safe' when tested against specifications such as API 607 and API 6FB.

The combination of high performance fugitive emissions performance, electrical isolation and fire safe capability is difficult to achieve in a gasket. Achieving this would be a major advancement in gasket sealing technology. Materials and gaskets developed to provide high fugitive emissions performance often do not have sufficient electrical isolation and/or fire safety properties.

WO2016/003444 discloses isolation gaskets for use between facing flanges of two conduit sections for fluid passage therethrough. The isolation gaskets a metal ring with serrations on the upper and lower surfaces of a portion of the ring. These serrated metal surfaces are known as kammprofiles. The serrated metal surfaces are coated with a fire resistant material at one part and with an electrically isolating material at another.

US2009/0243290 discloses gaskets for use between joined pieces in a flow line that is operative for fluid passage therethrough. The gaskets comprise an inner seal nearest to the fluid passage and an outer seal. The inner seal may comprise a polytetrafluoroethylene (PTFE) spring energised lip seal.

Gaskets comprising single kammprofile seals have been found to provide sufficient electrical isolation between opposing flanged faces and sufficient fire resistance if coated with an appropriate fire resistant material. However, single kammprofile seals have been found by the inventors of the present invention not to provide the requisite high performance fugitive emission properties required in many commercial uses of gaskets.

Gaskets comprising sealing rings such as PTFE spring energised seals have been found to provide excellent high performance fugitive emission properties. However, the inventors of the present invention have found that such gaskets often do not have the requisite fire resistance properties required in many commercial applications of gaskets.

Accordingly, the inventors of the present invention have identified that there is a need in the art for gaskets that provide the excellent high performance fugitive emission properties usually associated with gaskets comprising seals such as PTFE spring energised seals whilst also providing the excellent electrical isolation and fire resistance properties associated with gaskets comprising a kammprofile.

SUMMARY OF THE INVENTION

It has been found that the problems mentioned above have been solved by an isolation gasket of the present invention.

According to an aspect of the invention, there is provided an isolation gasket for use between facing flanges of two flow conduit sections for fluid passage therethrough, the isolation gasket comprising: a metal core ring having an upper face opposing a lower face and a central opening formed therein to allow fluid passage therethrough; the metal core ring comprising: a first section comprising a kammprofile along its upper face and lower face, wherein the upper and lower faces have one or more coatings thereon; a second section wherein the upper and lower faces of the second section do not comprise a kammprofile; and a third section wherein the third section comprises a kammprofile along its upper face and lower face wherein the upper and lower faces have one or more coatings thereon; wherein the kammprofiles of the first section are differently modified relative to the kammprofiles of the third section.

According to another aspect of the invention, there is provided a method of making an isolation gasket according to the invention, wherein the method comprises the following steps:

(i) providing a metal core ring having an upper face opposing a lower face and a central opening formed therein to allow fluid passage therethrough; the metal core ring comprising: a first section comprising a kammprofile along its upper face and lower face, wherein the upper and lower faces have one or more coatings thereon; a second section wherein the upper and lower faces of the second section do not comprise a kammprofile; and a third section wherein the third section comprises a kammprofile along its upper face and lower face wherein the upper and lower faces have one or more coatings thereon; wherein the kammprofiles of the first section are differently modified relative to the kammprofiles of the third section;

(ii) applying one or more coatings to the faces of the metal core ring so as to form an isolation gasket.

The present invention is based, in part, on the discovery that if kammprofiles are incorporated onto different sections of a metal core ring of an isolation gasket and are separated by a section that does not have a kammprofile upon its upper and lower faces, an improvement in the performance of the gasket may be provided if the kammprofiles on one section of the metal core ring are differently modified relative to the kammprofiles on the other section of the metal core ring. Specifically, the kammprofiles of one section may be differently modified relative to the kammprofiles of the second section according to the coating contained thereon. It has been found that the performance properties of a particular material that is coated onto the metal kammprofile surface is affected by the specific nature of the kammprofile surface. Thus, one particular material may have its performance properties optimised if coated onto one specific type of kammprofile, whereas a different type of material may have its performance properties optimised if coated onto a different type of kammprofile surface. Accordingly, by employing a metal core ring with two separated kammprofile surfaces that are differently modified, the performance properties of different coatings may be optimised if a different material is coated onto the different kammprofile sections.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a diagram of a gasket according to the present invention.

Figure 2 is an example of the specification for a spring energised sealing element comprising modified PTFE that may be used in isolation gaskets of the present invention. Figure 3 is a drawing of an isolation gasket of the present invention. Example dimensions of the gasket are shown along with groove A for a seal in between two kammprofile sections.

Figure 4 is a drawing of a kammprofile surface that may be present on the upper and lower face of the first or third sections of the metal core ring in isolation gaskets of the present invention.

Figure 5 is a graph showing sealing performance over the duration of a test cycle for a gasket of the prior art comprising a single kammprofile section coated with PTFE and mica.

Figure 6 is a graph showing sealing performance over the duration of a test cycle for a gasket of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The isolation gaskets of the present invention are suitable for use between facing flanges of two flow conduit sections for fluid passage therethrough. Industrial applications and uses of isolation gaskets are known in the art. For example, isolation gaskets may be used to seal conduit sections used to transport oil, petroleum, natural gas, and many other types of fluid. The isolation gaskets of the present invention can be used in any of these applications. The particular adaptations necessary to adapt a gasket for a given industrial use or application is also within the knowledge of the person skilled in the art.

The gaskets of the invention comprise a metal core ring comprising: a first section comprising a kammprofile along its upper face and lower face, wherein the upper and lower faces have one or more coatings thereon; a second section wherein the upper and lower faces of the second section do not comprise a kammprofile; and a third section wherein the third section comprises a kammprofile along its upper face and lower face wherein the upper and lower faces have one or more coatings thereon.

The terms "upper" and "lower" as used herein with reference to the faces of the metal core ring are only used in the sense that the faces are upper and lower relative to one another in one possible orientation of the gasket. The terms are not used to indicate the position of the gasket in any particular use or application. For example, if the gasket was used to seal opposing flange sections of a horizontal fluid conduit, then the upper and lower faces of the metal core ring would not be properly described as upper and lower relative to each other but could be more correctly described as the right face and left face.

Preferably, the first section is an innermost section directly adjacent to the central opening. Preferably, the second section is in between the first and third section. More preferably, the second section is directly between the first and third sections such that the second section is directly adjacent to the first section and directly adjacent to the section.

The metal core ring may be fabricated from any suitable metallic material known in the art suitable for being the internal core of an isolation gasket. An example of such a material is stainless steel. The metal core ring may comprise metal alloys such as the commercially available Inconel® and Hastaloys®.

The isolation gasket may further comprise a groove for a sealing element in the upper face or lower face of the metal core ring. Preferably, the isolation gasket comprises a groove for a sealing element in both the upper and lower faces of the metal core ring. Preferably, the upper and/or lower faces of the second section of the metal core ring form the bottom of the groove. In this instance, the groove for the seal may be in between the first and third sections of the metal core ring and directly adjacent to both the first and third sections of the metal core ring.

Preferably, the isolation gasket comprises a sealing element. Preferably the sealing element comprises a polymeric material such as PTFE, modified PTFE, or a combination thereof. The sealing element may comprise a spring energised seal. Preferably, the sealing element comprises a modified PTFE spring energised seal. More preferably, the sealing element comprises a TFM PTFE profile and a Phynox® helicoil spring. Examples of suitable sealing elements for inclusion in the isolation gasket of the invention are known to the person skilled in the art. An example of the specification for such a seal is shown in Figure 2.

Preferably, the sealing element is present in grooves formed in the upper and lower faces of the second section of the metal core ring. Preferably, the grooves in the upper and/or lower faces of the metal core ring defined by the varying diameters of the first, second and third sections are adapted so as to retain the seal within the grooves. The groove may be machined within the metal core ring such there is a taper on the outside diameter of the groove to retain the seal. The seal may be sized such that there is radial compression on the seal in the fitted position. An example of a seal groove A is shown in figure 3. The purpose of the spring energised seal is to provide the principal sealing function of the isolation gasket. The seal seals the gasket such that media flowing through the bore of the fluid conduit does not leak out of the fluid bore at intersection of the two opposing flanged faces that the isolation gasket is sealing. Spring seals such as those discussed above have been found to have an excellent fugitive emissions performance. That is, the seals have been found to be very good at stopping media from the bore of the fluid conduit leaking from the conduit at the intersection between opposing flanged faces of the conduit.

The first and third sections of the metal core ring have one or more coatings thereon. The term "coating" as used herein is used to refer to any layer of material applied to the upper or lower faces of the metal core ring of the isolation gasket. For example, the term is used herein to encompass both an electrically insulating coating that may be applied to the kammprofiled faces of the first and third section, and also the layers of fire resistant material and modified PTFE that may be applied to the faces of the third and first section of the metal core ring respectively on top of the layer of electrically insulating material (as discussed in more detail below). In the art, such layers of fire resistant material or modified PTFE are commonly known as facings as opposed to coatings. However, for the purposes of the present disclosure, such layers are also encompassed by the term coating.

The coatings are on the upper and lower faces of the first and third sections of the metal core ring. The upper and lower faces of the first and/or third section may be coated with a layer of electrically insulating material. Preferably, the upper and lower faces of both the first and third sections of the metal core ring are coated with a layer of electrically insulating material.

The electrically insulating material may be any suitable material that provides sufficient electrical isolation of the metal core ring from the opposing flanged faces of the fluid conduit. The electrically insulating material may be what is known in the art as an organic solvent based coating. Preferably, the organic solvent based coating comprises one or more fluoropolymers. Examples of specific coatings that may be used include XYLAN 1514, 1010 and 1052 grades, which are known to the person skilled in the art.

Ideally, the coating comprising electrically insulating material should have sufficient wear resistance, resistance to UV light and temperature resistance. Wear resistance is important so that the coating does not chip off or become scratched during handling and installation of the gasket which would compromise the electrical isolation properties of the gasket. Resistance to UV light is important since during prolonged storage of the gasket prior to use the gasket may be subjected to prolonged exposure to UV light. A breakdown of the coating on exposure to UV light would compromise the electrical isolation properties of the gasket. It is also important that the coating does not degrade or breakdown over the entire temperature range at which the gasket is designed to encounter in operation. This is -40°C to 200°C.

The thickness of the coating of electrically insulating material is preferably from 10 μιη to 80 μπι, and most preferably from 15 μιη to 30 μιη. This thickness is optimal since when the gasket is installed, significant pressure is applied to the faces of the metal core ring in order to achieve a seal. If the coating is too thin then the "teeth" of the kammprofile on the upper and lower faces of the first and third section may "bite" through the coating causing loss of electrical isolation. This is prevented by using a coating thickness in the range described above. A thickness in this range is also useful for when the electrically insulating material breaks down in the event of fire. A layer of the above thickness means that if the electrically isolating coating is coated with a further layer of fire resistant material (as discussed in more detail below), any thickness lost in the gasket due to breakdown of the electrically insulating material will not influence the sealing performance of the kammprofile section of the metal core ring coated with a fire resistant material. Post fire sealing capability is thus provided in this instance. Accordingly, the above thickness for the layer is an optimisation achieving minimal breakdown of the layer upon installation of the gasket, whilst also ensuring sealing integrity is not lost in the event of a fire.

The layer of electrically isolating material may also coat the inner face of the metal core ring directly adjacent to the central opening.

The one or more coatings on the upper and lower faces of the first and/or third sections of the metal core ring may comprise a layer of polymeric material. Preferably, the first section is coated with a layer of polymeric material. More preferably, the first section is the innermost section of the metal core ring and is directly adjacent to the fluid conduit. In this instance the upper and lower faces of the first section are preferably coated with a layer of polymeric material. In this instance, preferably the third section is not coated with a layer of the polymeric material but is coated with a layer of fire resistant material as discussed in more detail below.

The polymeric material preferably comprises polytetrafluoroethylene (PTFE), such as virgin PTFE; filled PTFE; PTFE modified so as to comprise one or more of barium sulphate, silica, glass microspheres, graphite, a lubricious additive; or any combination thereof. When the layer of polymeric material is on the upper and lower faces of the first section of the metal core ring, the layer is preferably of a thickness of from 0.3 mm to 1.0 mm, more preferably of a thickness of from 0.4 mm to 0.6 mm, and most preferably of a thickness of about 0.5 mm.

The one or more coatings on the upper and lower surfaces of the first and/or third sections of the metal core ring may comprise a layer of fire resistant material. Preferably the upper and lower faces of the third section are coated with a layer of fire resistant material and the upper and lower faces of the first section are not where the first section is the innermost section. In this instance, the first section is preferably coated with a layer of polymeric material as discussed above.

The fire resistant material may be any suitable material that does not fail in the event of fire and thus maintains sealing integrity of the kammprofile seal on which the material is coated in the event of a fire. Examples of suitable fire resistant materials include high temperature resin bonded phyllosilicate such as high temperature resin bonded mica. These materials are generally based on phlogopite or muscovite as the raw materials. Ideally, the materials should have a dielectric strength of greater than 25 KV/mm when measured using the test IEC 60371-2 ,an insulation resistance at 23°C of 10 ¹⁷ Ω/cm and 10 ¹² Ω/cm at 550°C measured using test IEC 60093, and a maximum operating temperature of from 800°C to 1000°C.

Preferably, the upper and lower faces of the first section and third section of the metal core ring are coated with a layer of electrically insulating material as discussed above; the upper and lower faces of the first section are coated with a layer of polymeric material as discussed above exterior to the layer of electrically insulating material; and the upper and lower faces of the third section are coated with a fire resistant material as discussed above exterior to the layer of electrically insulating material.

The kammprofiles of the first section are differently modified relative to the kammprofiles of the third section.

The term kammprofile as used herein is used to refer to a serrated face of a metal core ring of an isolation gasket. The term is known in the art. Examples of kammprofile surfaces for use in gaskets are described in the British Standard BS EN 12560-6:2003. Kammprofile faces of the first and third section of the metal core ring of the isolation gasket of the invention may be as described in this document. An example of the dimensions of a kammprofile face used in isolation gaskets of the invention is shown in figure 4.

Kammprofile faces of a metal core ring coated with one or more coatings are known to be used in isolation gaskets. Unlike gaskets known in the art, isolation gaskets of the invention comprise at least two separate kammprofile sections, wherein the two sections are differently modified.

The term "differently modified" as used herein means that the nature of the kammprofile of the faces of the first section is different to the nature of the kammprofile of the faces of the third section. For example, the specific dimensions of the kammprofile of the faces of the first section may be different to the specific dimensions of the faces of the kammprofile of the third section.

Preferably, the kammprofiles of the first section are differently modified relative to the kammprofiles of the third section according to the coating contained thereon. That is, the nature of the kammprofiles of the first and third sections are selected so that the performance properties of the material that is to be applied as a coating are optimised. The inventors of the present invention have discovered that the performance properties of a material coated onto a kammprofile surface are affected by the specific dimensions of the serrations and kammprofile, and that different materials have their properties optimised by different kammprofiles. Since it is preferable to have different materials coating the first and third sections of the metal core ring, the kammprofiles are differently modified so as to optimise the performance properties (for example, ability to maintain sealing integrity under compression) of the different materials coating them.

Preferably, the kammprofiles of the first section are differently modified relative to the kammprofiles of the third section in that the kammprofiles differ in one or more of the following characteristics: height, depth or pitch. Most preferably, the kammprofiles of the first section are differently modified relative to the kammprofiles of the third section in that the kammprofiles differ in height.

In the context of kammprofiles, the term height is used to refer to the difference in vertical height from the uppermost part of a serration (i.e. the tip of a serration) on the upper face of a section of the metal core ring to the lowermost part of a serration (i.e. the tip of a serration) on the lower face of the same section of the metal core ring. The term depth is used to refer to the difference in vertical height between the tip (i.e. "peak") of a serration and the bottom of the serration (i.e. "trough") of the serration. The term pitch is used herein to refer to the angle between adjacent serrations of a kammprofile surface. In figure 4, the pitch is shown as being 90°.

Figure 4 shows examples of a kammprofiled surface for use in insolation gaskets of the invention. The kammprofiled surface comprises serrations that have flat tips. The pitch (angle between the serrations) can be seen as 90°. The flat tips of each serration have a width of 0.1 mm. The distance between the centre of the tip of one serration from the centre of the tip of an adjacent serration is 1.00 mm. The radius of the grooves can also been seen in figure 4. In the first section of the metal core ring, the radius at the bottom of the groove is 0.2 mm. On the third section of the metal core ring, the radius at the bottom of the grooves is 0.3 mm. In his respect, the kammprofiles faces of the first and third sections of the metal core ring are differently modified. In this instance, the kammprofiles of the first and third sections are differently modified in that they have a different depth.

The metal core ring may also further comprise a fourth section. Preferably, the fourth section is exterior to the other sections of the metal core ring. More preferably, the fourth section is exterior and directly adjacent to the third section of the metal core ring. The fourth section preferably does not comprise a kammprofile on its upper and lower faces. The fourth section may be coated with a layer of electrically insulating material such as glass reinforced epoxy resin (GRE). This layer of material coating the fourth section isolates the fourth section of metal core ring from the adjoining flange or housing that the gasket is sealing.

An embodiment of the isolation gasket of the invention is shown in figure 1. Figure 1 shows a cross section of an isolation gasket of the invention. Parts of the gasket can be seen at the top and bottom of the figure either side of fluid conduit 5. Directly adjacent to fluid conduit 5 is the innermost section of the gasket. This comprises the first section 1 of the metal core ring. The first section 1 is coated on its innermost surface with a layer of electrically insulating material. The first section 1 of the metal core ring has a kammprofile surface in the form of serrations on its upper and lower faces. The upper and lower faces appear as right and left faces in the diagram of figure 1. The kammprofile surfaces of the upper and lower faces of the first section 1 of the metal core ring are coated with a layer of electrically insulating material which is coated with a layer of modified PTFE exterior to the electrically insulating material. Adjacent to the first section 1 of the metal core ring is the second section 2 of the metal core ring. The second section 2 of the metal core ring does not have a kammprofile surface. Adjacent to the second section 2 of the metal core ring is the third section 3 of the metal core ring. The third section 3 of the metal core ring has a kammprofile on both of its upper and lower faces. The kammprofiles of the third section 3 are differently modified to the kammprofiles of the first section 1, although this is not shown in the figure. The upper and lower faces of the third section 3 of the metal core ring are coated with a layer of electrically insulating material and a layer of fire resistant material exterior to the layer of electrically insulating material. The upper and lower faces of second section 2 of the metal core ring form the bottom of a groove in which is located a modified PTFE spring energised seal. Adjacent to third section 3 of the metal core ring is fourth section 4 of the metal core ring. In this embodiment, the upper and lower faces of the fourth section 4 of the metal core ring do not comprise kammprofiles. The fourth section 4 of the metal core ring is coated with a layer of electrically insulating material 6 which is GRE.

As discussed above, the gaskets of the present invention have associated with them the excellent fugitive emissions performance normally associated with gaskets comprising spring energised PTFE seals and also the excellent fire resistance and electrical isolation normally associated with kammprofile seals. In the gaskets of the invention, the principal sealing function is provided by the spring energised PTFE seal. This is the component believed to be responsible for the excellent fugitive emissions performance associated with gaskets of the invention. The principal function of the kammprofile element of the third section of metal core ring coated with fire resistant material is to provide a sealing in the event of a fire. In the event of a fire the PTFE spring energised sealing element may degrade as will the modified PTFE coating the first section of the metal core ring. The fire resistant material will not degrade and in conjunction with the kammprofile surfaces of the third section of the metal core ring, maintain sealing integrity in the event of a fire. The electrically insulating material coating the third section of metal core ring will also provide excellent electrical isolation to this segment of the isolation gasket. The first section of the metal core ring with the polymeric material coating provides an additional seal for the gasket. This segment of the gasket does not provide as good a sealing benefit as the spring energised seal component. However, the segment consisting of the first section of metal core ring and polymeric material coating may firstly act as an additional seal, and secondly, act to stop media from the bore of the fluid conduit entering into the gasket and coming into contact with the spring energised sealing element. If media from the gasket comes into contact with the spring energised sealing element, the spring energised sealing element may be corroded, and the media present in the gasket may stagnate. This would lead to a loss in sealing performance of the spring energised sealing element.

The first and third sections of the metal core ring and the materials coating their upper and lower faces serve the additional but important purpose of providing the optimum amount of compression to the spring energised sealing element between them in order to optimise the performance properties such as sealing integrity of the spring energised sealing element. In this respect, the performance properties of the spring energised sealing element are affected directly, inter alia, by the compression applied to either side of it by the coating of the first and third sections of the metal core ring. As discussed above, since the compression applied to and by the respective coatings of the first and third sections of the metal core ring is directly affected by the nature of the kammprofile surface on which the coatings are coated, the nature of the kammprofile surface thus affects the compression applied to the spring energised sealing element, and hence its performance properties. The kammprofile surfaces of the upper and lower faces of the first and third sections are thus differently modified so as to optimise the properties of the different materials coated onto them when compressed. In turn, when compressed, these coatings apply optimum compression to the spring energised sealing element so as to optimise its performance properties.

Different materials that coat the first and third sections of the metal core ring may have different load/compression characteristic curves. For example, a fire resistant material coating the third section may have a different load/compression curve to a PTFE coating the first section of the metal core ring. A different load/compression curve means that if a given load is applied to two coatings made from different materials but of the same starting thickness, the extent to which the coatings are compressed may be different such that the two different coatings have a different compressed thickness. This means that the optimum performance of the two materials may occur at different compressed thicknesses.

Having the kammprofile sections of the first and third sections differently modified as in the isolation gasket of the present invention means that optimal performance of the different materials coating the first and third sections of the metal core ring occur at the same compressed height. The compressed height is the thickness the two materials are reduced to in use in the isolation gasket of the invention. This optimal compressed height can also coincide with the optimal compressed height of the sealing element such as the spring energised PTFE seal. Ensuring that the optimal

compressed height of the spring energised PTFE seal coincides with that of the optimal compressed height of the PTFE and fire resistant material coatings may provide the excellent fugitive emissions performance of the isolation gasket of the invention.

Having the kammprofiles of the first and third section differently modified (for example of a different height, depth or pitch) in the gasket of the invention enables optimum compression to be applied by the gasket providing excellent fugitive emissions performance, whilst accommodating variations in the following parameters: the thicknesses of the PTFE and fire resistant coatings coating the first and third sections of the metal core ring; the thickness of the layer of electrically isolating material which may vary at different points of the layer; and different material compression characteristics. If the kammprofiles of the first and third section of the metal core ring were not appropriately different modified, it is believed that the sealing integrity of the gasket may be negatively affected by variations in these parameters from the ideal.

In gaskets of the present invention, the kammprofiles of the first section and third section of the metal core ring are preferably differently modified such that the depth of the kammprofile of the first section is different to the depth of the kammprofile of the third section.

The total thickness of the one or more coatings of the first section may be different to the total thickness of the one or more coatings of the third section. Alternatively, and preferably, the total thickness of the one or more coatings of the first section may be the same as the total thickness of the one or more coatings of the third section. As used herein, the term total thickness is used to refer to the total thickness of the one or more coatings when applied to the gasket as it is manufactured, and not the compressed thickness of the coating which would be the thickness of the coating in use.

The total thickness of the first section and the one or more coatings thereon may be equal to the total thickness of the third section and the one or more coatings thereon. Alternatively, the total thickness of the first section and the one or more coatings thereon is different to the total thickness of the third section and the one or more coatings thereon.

In an embodiment, the upper and lower faces of the first section and third section of the metal core ring are coated with a layer of electrically insulating material; and (i) the upper and lower faces of the first section are coated with a layer of polymeric material exterior to the layer of electrically insulating material;

(ii) the upper and lower faces of the third section are coated with a fire resistant material exterior to the layer of electrically insulating material; and

(iii) the layer of polymeric material exterior to the layer of electrically insulating material coating the upper and lower faces of the first section is the same thickness as the layer of fire resistant material exterior to the layer of electrically insulating material coated on the upper and lower faces of the third section.

As discussed above, in gaskets according to the invention, the layer of polymeric material on the upper and lower faces of the first section is preferably of a thickness of from 0.3 mm to 1.0 mm, more preferably of a thickness of from 0.4 mm to 0.6 mm, and most preferably of a thickness of about 0.5 mm.

The layer of fire resistant material on the upper and lower faces of the third section is preferably from 0.4 mm to 0.6 mm in thickness, and most preferably of a thickness of about 0.5 mm. When manufactured, it is typically desired to produce a PTFE layer of a thickness of around 0.5 mm. However, the manufacturing process can mean that the thickness of the layer can vary and it is common to produce layers of up to 0.75 mm in thickness despite the intention to produce those of a thickness of around 0.5 mm.

Most preferably, the thicknesses of the layer of fire resistant material and the layer of polymeric material are the same, or at least, very similar.

In a particularly preferred embodiment, gaskets of the invention comprise the following features.

(i) the upper and lower faces of the first section and third section are coated with a layer of electrically insulating material;

(ii) the upper and lower faces of the first section are coated with a layer of polymeric material exterior to the layer of electrically insulating material;

(iii) the upper and lower faces of the third section are coated with a fire resistant material exterior to the layer of electrically insulating material; (iv) the kammprofiles of the first section and third section are differently modified such that the depth of the kammprofile of the first section is different to the depth of the kammprofile of the second section; and

(v) the thickness of the polymeric material coating the upper and lower faces of the first section is equal to the thickness of the fire resistant material coating the upper and lower faces of the third section.

In this embodiment, the overall thickness of the first section and both the electrically isolating material and polymeric material coated thereon is may be different to the overall thickness of the third section and both the electrically isolating material and fire resistant material coated thereon. However, this is not essential.

The specific dimensions of the isolation gaskets of the invention and their components will of course vary depending upon the specific application of the gasket. Suitable dimensions for a specific application will be known to the person skilled in the art.

An example gasket of the invention and its dimensions are shown in figure 3. The total compressed thickness of the gasket is 6.4 mm. The thickness of the metal core ring at the first and third section (the two kammprofiled sections) is 6.2 mm. The thickness of the metal core ring at the fourth section (the outermost section of the gasket relative to the central opening) is 3.80 mm.

According to another aspect of the invention, there is provided a method of making an isolation gasket according to the invention, wherein the method comprises the following steps:

(i) providing a metal core ring having an upper face opposing a lower face and a central opening formed therein to allow fluid passage therethrough; the metal core ring comprising: a first section comprising a kammprofile along its upper face and lower face, wherein the upper and lower faces have one or more coatings thereon; a second section wherein the upper and lower faces of the second section do not comprise a kammprofile; and a third section wherein the third section comprises a kammprofile along its upper face and lower face wherein the upper and lower faces have one or more coatings thereon; wherein the kammprofiles of the first section are differently modified relative to the kammprofiles of the third section;

(ii) applying one or more coatings to the faces of the metal core ring so as to form an isolation gasket.

Methods for forming the metal core ring and applying the one or more coatings thereto will be apparent to the person skilled in the art on reading the present disclosure. The present invention also includes methods for forming isolation gaskets of the invention including all specific features as described herein.

Example

Figures 5 and 6 contrast the sealing performance of an isolation gasket according to the invention comprising two kammprofile sections and a spring energised PTFE seal with an isolation gasket of the prior art comprising a single kammprofile section coated with PTFE and a fire resistant coating comprising mica.

In the gasket of the invention, the kammprofiles are either side of the spring energised PTFE seal. The kammprofile section closer to the fluid conduit comprises a PTFE coating, and the kammprofile further away comprises a fire resistant mica coating.

Figure 5 shows the sealing performance of a prior art gasket comprising a single kammprofile section, whereas figure 6 shows the sealing performance of the gasket of the present invention.

It can be seen that the gasket of the invention retains performance throughout the 24 hour test duration, whereas the prior art kammprofile gasket loses performance gradually for the first 16 hours of the test before levelling out. Specifically, it can be seen that the leak rate of the prior art kammprofile gasket increases gradually throughout the first 16 hours of the test cycle before levelling off, whereas the leak rate of the gasket of the invention remains constant. Additionally, it can be seen that at the start of the test cycle, the leak rate for both gaskets was similar. After a short amount of time, the leak rate of the prior art gasket increased to a value above the leak rate of the gasket of the invention and remained at a higher value for the duration of the test cycle. It can also be seen that the pressure applied to both gaskets during the test was the same and remained constant for the duration of the test. Despite this equal and constant pressure, it can be seen that this caused the prior art gasket to be under a higher total amount of stress than the gasket of the invention for the duration of the test.