Abstract:
A method for fluidly sealing two conduits having mating surfaces is described. The method includes positioning a gasket between the surfaces, securing the two conduits together with the gasket interposed between the mating surfaces wherein the gasket includes an outer seal with a first thickness and an inner seal with a thickness greater than that of the outer seal. The step of positioning and/or the step of securing includes compressing the thickness of the inner seal. Methods of making the gaskets are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. application Ser. No. 12/976,097, now allowed, which claims the benefit of Great Britain Patent Application No. 0922625.9 filed on Dec. 24, 2009, the contents of all which are incorporated herein by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to gaskets, in particular, but not exclusively, flange joint sealing gaskets with an especially advantageous application as a replacement flange joint sealing gasket. 
       BACKGROUND OF THE INVENTION 
       [0003]    The use of gaskets in sealing applications is commonplace in many industries. A well-known application for gaskets is to provide fluid sealing between two mating surfaces such as between two ends of adjoining pipes or conduits where they are commonly in the form of a flange joint for ease of assembly and disassembly and for better sealing. A flange joint sealing gasket usually comprises a compressible ring defining an aperture of a size that matches the conduit being sealed and a body that matches the dimensions of the flange mating surfaces. In many applications however the flange joint mating surfaces which are typically metal eventually become damaged either by internal chemical corrosion, erosion or external weathering. This attrition of the surface can cause pitting, crevices and other imperfections to form on the surface. In such cases, replacement of an ordinary sealing gasket will not be sufficient to effect adequate sealing under operational pressures because the surface imperfections may provide fluid escape pathways and weak points in the surface sealing. As a consequence, it may become necessary to replace or repair the flanges or even the whole flanged pipe to reestablish or improve sealing performance. 
         [0004]    In high pressure sealing applications, one preferred gasket has what is known as a Kammprofile core. This is effectively a gasket with a series of concentric serrations or a concertina-like profile on one or both facing surfaces. The profile is superimposed onto a solid core, usually metal, by the series of concentric serrations. During the sealing process the overlying softer sealing material is forced into the gaps between serrations to improve sealing by inducing stress concentrations on the sealing surfaces. The serrations also minimize lateral movement of the facing material, while the metal core provides rigidity and blowout resistance. Such a profile gives the gasket added strength for high pressure applications. As mentioned, such a gasket also includes a suitable compressible sealing material that is coated over the Kammprofile core. However, in cases of mating surfaces which have become pitted or corroded even such high pressure gaskets cannot always provide adequate sealing. It is an object of the present invention to provide an improved gasket suitable for such applications but also having wider applications for corroded or otherwise damaged mating surfaces. 
         [0005]    U.S. Pat. No. 6,092,811 relates to a corrugated gasket core that uses inner and outer laminate materials. The inner material is designed to be chemically resistant to protect the outer material from chemical attack. The use of these gaskets to seal parallel mating surfaces including scratched or pitted surfaces is discussed but no mention of including a chemical treatment agent into the material or the possibility of simultaneously chemically protecting the damaged surfaces of the gaskets is mentioned. 
         [0006]    Methods of coating the inner edge of a gasket with another sealing material usually a polymer or inorganic sealant are described in U.S. Pat. No. 6,093,467; US 2004/0007828; and US 2003/0230856. The possibility of the polymeric coating being of a greater depth to enhance sealing is disclosed as is the possibility of use with a damaged surface. However, no mention of chemically protecting the mating surfaces is mentioned. 
       SUMMARY 
       [0007]    According to a first aspect of the present invention there is provided a gasket for sealing two mating surfaces having: 
         [0000]    a) an outer portion comprising a core interposed between sealing layers, the outer portion defining a first aperture therein, the core and/or the sealing layers defining an inner edge of the outer portion, the said inner edge immediately surrounding the first aperture;
 
b) an inner portion comprising deformable material defining a second aperture therein, the inner portion having an inner edge defining the second aperture and an outer region designed to be secured to the outer portion so that the inner portion is held securely by the outer portion, the thickness of the inner portion being greater than the thickness of the outer portion so that in use the inner portion deforms to a greater extent than the outer portion, and wherein the deformable inner portion includes a chemical treatment agent operable to provide chemical protection on the surfaces of mating surfaces to be sealed.
 
         [0008]    The chemical treatment agent may thus be applied to the component mating surfaces to simultaneously treat the surface during sealing. 
         [0009]    Preferably, the outer region of the inner portion is defined by the outer edge of the inner portion which is designed to be continuously close fitting with the inner edge of the outer portion. 
         [0010]    However, alternatively, the outer region of the inner portion may overlap the inner edge of the outer portion and be secured to the upper and lower surfaces thereof. In such cases, the inner portion may be in the form of a laminate which is applied and secured to both surfaces of the outer portion at the overlapping outer region of the inner portion and is then merged together at least at the inner edges of the inner portion to define the second aperture. In such cases, at least a portion of the outer portion is not so overlapped. In any case, it will be apparent that the second aperture is smaller than and located within the first aperture. 
         [0011]    Additionally or alternatively it is possible to secure the inner portion to the outer portion by suitable fixing means. The fixing means may extend from the core to secure the two portions together. For this purpose the fixing means is preferably arranged so that it does not come into contact with the two mating surfaces in use. One possible embodiment for this purpose is to embed the fixing means in the outer and/or inner portion in such a manner that it extends in the plane of the gasket. Typically, the fixing means may be embedded in the outer portion in the sealing layer, between the sealing layer and the core or even in the core and/or it may be embedded in the inner portion. At least the outer region of the inner portion may be designed to accommodate such a fixing means. Preferably, for secure fixation, the fixing means may extend inwardly from the core, preferably, the inner edge thereof, in the plane of the gasket and into the inner portion. The fixing means may be integral with the core and may be co-planar therewith at the axial ends thereof. Preferably, the fixing means is a radially inwardly extending projection from the inner edge of the core. Typically, the radially innermost end of the projection extends part way through the inner ring in the plane of the gasket to thereby secure the inner ring to the outer ring. The accommodating socket for the projection in the inner ring may be formed by the projection or formed separately. Typically, there are at least two such projections, more preferably, at least three, most preferably, at least four. Conveniently, in this embodiment the core and projections may be pressed from the same sheet material for instance by using a punch press and/or by laser cutting. 
         [0012]    Preferably, however, the outer portion is in the form of a Kammprofile gasket which provides a solid inner edge defining the first aperture and against which the outer edge of the inner portion can engage to provide a strong abutment in use. Thus the outer portion core may comprise a solid metal core having a series of serrations formed on the facing surfaces thereof. A suitable groove profiler machine may be used to form the serrations on the core. 
         [0013]    Preferably, the chemical treatment agent is a corrosion treatment agent, more preferably a rust inhibitor. Typically, the chemical treatment agent is present in the deformable inner portion in a range of 0.01% to 50% w/w, more preferably, 0.1% to 20% w/w, most preferably, 0.5% to 5% w/w. 
         [0014]    By chemical protection is meant the provision of chemical agents to prevent chemical attack and this does not include providing physical protection against chemical attack such as by sealing of the mating surface to prevent ingress of fluid. 
         [0015]    It will be clear from the foregoing that the chemical treatment agent will be in contact with at least one and preferably both mating surfaces in use. Accordingly, the chemical treatment agent is included in such a manner that it is available on the surfaces of the inner portion material that will be in contact with the mating surfaces in use. Preferably, it is available on the majority, more preferably, substantially all of the surface of the inner portion that will be in contact with the mating surfaces in use. 
         [0016]    Preferably, the material of the inner portion is more compressible than the sealing layer of the outer portion. Suitable sealing materials for the outer portion include PTFE, graphite, Thermiculite® (or suitable vermiculite based sealing material), non-asbestos sheet, or a soft metallic face such as silver or tin, preferably, PTFE is used. The PTFE is preferably biaxially orientated. In particular, the biaxially orientated PTFE is preferably filled with hollow glass microspheres. Such a material is available from Flexitallic under trade name Sigma 500. 
         [0017]    Biaxially orientated PTFE containing hollow glass microspheres has advantages over pure or filled PTFE and envelope gaskets by reducing cold flow. 
         [0018]    Biaxially orientated PTFE is generally produced by producing a slurry of PTFE particles in a volatile solvent, optionally with fillers, dyes and/or other suitable gasket additives such as the glass microspheres mentioned above. After draining, a sheet of pliable mass is formed which is rolled in two different mutually perpendicular directions to cause the PTFE particles to fibrillate and create a network of biaxially orientated fibres in two different directions, generally at right angles to each other. The technique is well known to the skilled person and was originally developed by Du Pont and is disclosed in GB 1,049,328. 
         [0019]    Suitable non asbestos sheets are generally made by compressing and calendaring synthetic fibre, natural rubber, a suitable gasket filler and optionally, a dye. Suitable fillers will be known to the skilled person and may be selected from:—talc, clay, calcium carbonate, silica etc. 
         [0020]    Suitable synthetic fibres will be known to the skilled person and may be selected from aramid, glass fibres, mineral fibres and carbon fibres. 
         [0021]    By “soft” metallic face is meant a metal having a hardness less than 3.0 or less than copper on the Mohr hardness scale. 
         [0022]    Suitable sealing materials for the inner portion include PTFE, wherein this PTFE is preferably softer than the PTFE of the outer part, when used, more preferably a highly compressible biaxially orientated microcellular PTFE based material. 
         [0023]    As mentioned above the inner portion is preferably more compressible than the outer portion so that in use the inner material is only compressed as far as the less compressible outer portion will allow. 
         [0024]    The compression of the respective sealing materials may be measured by ASTM F36. Preferably, the compression of the outer portion falls within the range 5-50% compression, more preferably, 10-40%, most preferably, 20-30% compression, in use. In any case, the outer portion will typically have less than 50% compression, more preferably &lt;40% compression, most preferably, &lt;30% compression with reference to the original thickness. 
         [0025]    Typically, the compression of the inner portion is within the range 30-90% compression in use, more typically, 40-80%, most typically, between 50-70% compression. In any case, the inner portion will typically have more than 30% compression, more typically, more than 40% compression and most typically more than 50% compression in use. In any case, the inner portion compression is preferably greater than the outer portion. 
         [0026]    Suitable sealing materials for the inner portion include those having the above compression characteristics, particularly those which are relatively chemically inert. A suitable material is a microcellular biaxially oriented PTFE which has been produced with a water soluble filler that can be washed out after sintering of the PTFE material to produce a hollow microcellular structure. Such a production technique is known to the skilled person. Such a material can then be washed with a solution of the chemical treatment agent followed by drying to thereby impregnate the microcellular structure of the PTFE material. Repeated washing and drying steps or variation in the solution concentration can be used to effect the required concentration in the final gasket effective to produce an improvement to the flange joints in the final application. A material suitable for such impregnation is available from Flexitallic under trade name Sigma 600. 
         [0027]    Preferably, the inner portion deformable material is inherently more compressible than the sealing layer material, typically, at least 10% more compressible, more typically, at least 20% more compressible, most typically, at least 50% more compressible in the axial direction under normal operating pressures. 
         [0028]    Advantageously, the material of the inner portion allows it to be compressed into any imperfections in the mating surface thus at least partially filling any scratches, crevices or pits in the surface. By this means, a very efficient delivery mechanism to the surface imperfections for the chemical treatment agent is achieved at the same time as the surface imperfections are sealed from further attack by the inner portion deformable material. Thus a separate chemical treatment coating step for the mating surface is not required. By impregnating the material of the inner portion with a chemical treatment agent such as a rust inhibitor, further corrosion of the damaged areas is reduced by specifically applying rust inhibitor into scratches, crevices and pits using the compressibility of the inner portion as the delivery agent. Still further, the inner material has the effect of micro-sealing the imperfections in the mating surfaces by forming a seal around the edge of the surface imperfection with the rest of the mating surface thus sealing the imperfection in with the impregnated surface of the inner portion material. 
         [0029]    According to a further aspect of the present invention there is provided a method of sealing two substantially parallel surfaces, comprising: 
         [0000]    interposing between the said surfaces a gasket according to the first aspect of the present invention;
 
positioning said gasket between the two substantially parallel surfaces; and
 
securing said parallel surfaces together to thereby deform the inner portion of the gasket against the said parallel surfaces.
 
         [0030]    According to a further aspect of the present invention there is provided a method of sealing and simultaneously coating/treating mating surfaces with a gasket comprising the steps of locating a gasket according to the first aspect of the present invention on the mating surface to be sealed and securing the gasket in position so that the inner ring is compressed and the chemical treatment agent is delivered to the mating surfaces. 
         [0031]    Preferably, the mating surfaces have been damaged by corrosion. 
         [0032]    A method of producing a gasket according to the first aspect of the present invention comprising: 
         [0000]    providing a core according to the first aspect of the present invention,
 
coating the core on upper and lower faces with a core sealing layer to provide an outer portion according to the first aspect of the present invention and
 
locating a close fitting inner portion according to the first aspect of the present invention around the inner edge of the outer portion.
 
         [0033]    Preferably, the inner portion material can be compressed to between 10-90% of its original thickness under normal operating pressures, more preferably, it may be compressed to 20-85% of its original thickness under such pressures, most preferably, it may be compressed to between 50-75% of its original thickness. 
         [0034]    Generally, the inner portion material is a core free material and typically, the deformable material including the treatment agent forms the entire inner portion. However, in an alternative embodiment it may overlap with the core of the outer portion as mentioned above. 
         [0035]    By normal operating pressures is meant between 100 Kpa-43000 Kpa, more typically, 1000 Kpa-20000 Kpa. As mentioned above, the inner portion outer edge is preferably designed for close fitting engagement with the inner edge of the outer portion, typically, this is provided by a push fit arrangement which is usually satisfactory because of the resiliently deformable nature of the inner portion which allows it to be compressed sufficiently to provide a sufficiently strong seal at the junction of the inner and outer portion. 
         [0036]    For most flange gasket applications with ring shaped flanges both the inner portion and the outer portion are also in the form of rings. Typically, the outer edge of the outer portion is designed to be coextensive with the flange outer edge. However, in some embodiments, the outer edge may be defined by the mating surfaces and the outer portion of the flange may extend further to accommodate fixing components such as bolts etc. In a still further embodiment, however, the gasket may be designed to accommodate such fixings through the body of the gasket too. 
         [0037]    In a still further embodiment, the gasket may include an outwardly extending extension to the gasket to allow the gasket to be held by the fitter whilst being secured in position in a joint. Generally, the extension does not form part of the gasket unlike lugs found on some gaskets having apertures for joint fixation devices such as bolts to pass there through and thereby secure both the gasket and the faces of the joint. In fact, in a preferred embodiment, the extension is secured to such a fixation lug which itself extends integrally from the outer core of the gasket. Once the gasket is secured in position the extension which is located outside the joint may be removed. Accordingly, the extension is preferably frangible for this purpose. However, any suitable attachment means for the extension may be utilized as long as it can be removed after the gasket is secured in position in the joint. A suitable embodiment includes a generally co-planar T-shaped extension secured at its base to the outer edge of the outer portion or, optionally, a fixation lug by one or more frangible thin sections. The thin sections are strong enough to keep the extension attached to the main gasket during normal storage, transport and fitting conditions but weak enough to allow easy removal under a suitable force applied by the user after joint fixation. The handle extension also provides a convenient means to locate the gasket in the correct position in the joint. This can be particularly advantageous in subsea locations where the maintenance diver needs to avoid entrapment in the event of unexpected joint closures. For storage and transport reasons, the extension is generally co-planar with the main gasket body but it may also be advantageous for the extension to extend from the outer portion at a small angle to the plane of the gasket of about 1 to 60°, more preferably, 1 to 30°. 
         [0038]    In one embodiment, the extension is secured to the core, optionally via a fixation lug, and preferably consists of the same material. This allows the core and extension to be cut or punched therefrom as a single piece. 
         [0039]    Preferably, the core of the present invention is designed to be suitable for the operating pressures under which the gasket will be used. A particularly advantageous core design is one having serrated ridges or a concertina-like profile on the facing surfaces of a solid metal core. Such gaskets cores are well known in the art of gaskets and are described as Kammprofile gaskets. 
         [0040]    Suitable materials for the core are stainless steel, alloy 400, other suitable Monel alloys, carbon steel or other suitable metal to match the parallel surfaces to be sealed. 
         [0041]    It will be appreciated that although one particularly useful application of the present invention is in the field of flange gaskets which have become corroded due to exposure to sea water, the invention has other applications generally in the field of gaskets where two metal surfaces are mated together and one or both of the surfaces has become corroded or otherwise pitted or damaged by chemical attack. Clearly, the chemical treatment agent is selected to fill and simultaneously treat the damaged areas. For instance, a flange that was subject to acid attack may require a neutralizing agent or buffer that might resist the acid attack. Similarly, caustic attack can be treated with a corresponding neutralizing agent or an alkali buffer. Further applications may include surfaces exposed to oxidizing or reducing agents and the corresponding chemical agents can be selected accordingly. 
         [0042]    Advantageously, even if the gasket of the invention is not impregnated with a chemical treatment agent but the mating surfaces have become corroded to the extent that normal gaskets allow unacceptable leakage, a gasket according to the invention can improve the leakage characteristics of the joint. This is brought about by the greater thickness and hence deformation of the inner portion assisting the sealing of the corroded surface. Thus by use of the device of the present invention extended joint life can be achieved, particularly in corroding environments. 
         [0043]    Thus according to a further aspect of the present invention there is provided a gasket for sealing two mating surfaces having: 
         [0000]    a) an outer portion comprising a core interposed between sealing layers, the outer portion defining a first aperture therein, the core and/or the sealing layers defining an inner edge of the outer portion, the said inner edge immediately surrounding the first aperture;
 
b) an inner portion comprising deformable material defining a second aperture therein, the inner portion having an inner edge defining the second aperture and an outer region designed to be secured to the outer portion so that the inner portion is held securely by the outer portion, the thickness of the inner portion being greater than the thickness of the outer portion so that in use the inner portion deforms to a greater extent than the outer portion.
 
         [0044]    Preferably, the deformable inner portion includes a chemical treatment agent operable to provide chemical protection on the surfaces of mating surfaces to be sealed. In addition, the gasket of this aspect may include any one or more of the optional, preferred or typical features of the gaskets of other aspects. 
         [0045]    Therefore, the invention also extends to a method of sealing two substantially parallel surfaces, comprising: 
         [0000]    interposing between the said surfaces a gasket according to this further aspect;
 
positioning said gasket between the two substantially parallel surfaces; and
 
securing said parallel surfaces together to thereby deform the inner portion of the gasket against the said parallel surfaces. Preferably, at least one of the parallel surfaces has been corroded to such an extent that significant leakage occurs if a normal gasket, for example, one consisting of only an outer portion according to part (a) of this aspect of the invention but defining the second aperture therein rather than the first aperture, is secured between the said parallel surfaces.
 
         [0046]    Additionally, the invention extends to a method of producing a gasket according to this aspect of the present invention comprising: 
         [0000]    providing a core according to this aspect of the present invention,
 
coating the core on upper and lower faces with a core sealing layer to provide an outer portion according to this aspect of the present invention and
 
locating a close fitting inner portion according to this aspect of the present invention around the inner edge of the outer portion.
 
         [0047]    Furthermore, the invention extends to the use of a gasket according to this aspect as a sealing gasket for corroded parallel surfaces, typically joints, especially, flange joints, 
         [0048]    In accordance with any aspect of the invention a preferred material for the sealing coating on the core material and the inner deformable material is biaxially structured PTFE. Typically, the inner material has a microcellular structure and is impregnated with the selected chemical agent such as corrosion inhibitor. 
         [0049]    Impregnation of the inner portion material may be carried out by dipping, spraying, brush coating or any suitable technique known in the coating art. The inner portion material may be coated prior to being cut into the required gasket shape. 
         [0050]    A suitable rust inhibitor for the present invention may be selected from the list consisting of:—suitable salts of phosphates, molybdates, nitrites, borates, phosphonates or other iron chelating or sequestering agents. Typical chelating agents include EDTA (ethylenediamine tetraacetic acid), HEDTA (hydroxyethylenediamine triacetic acid), NTA (nitrilotriacetic acid) and citric acid. Preferably, a metal salt of EDTA is selected such as an alkali, alkaline earth metal salt, most preferably a sodium EDTA salt. An aqueous solution of an EDTA salt may be used to apply the EDTA salt. A suitable concentration thereof will depend on the application but a typical range will be 1-10000 g/m 3 , more typically, 10-5000 g/m 3 , most typically, 200-2000 g/m 3 . 
         [0051]    Preferably, the inner portion material compressibility is selected so as to cause it to make intimate contact in the crevices and other corrosion based defects in a flange surface, the benefit of this is firstly that it will make a good seal which is important for a gasket, but secondly where there is a corrosion cell it can passivate the cell by allowing the EDTA (or other) anion to react with iron (in the crevice on the flange surface), thus cutting off the corrosion reaction. Also, in the presence of water (and the potential beginning of a corrosion cell) the anion can be released and react with any iron available on the flange surface, passivating it, and thus making it more difficult for a corrosion cell to initiate. 
         [0052]    The invention will now be described by way of illustration only with reference to the accompanying drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0053]      FIG. 1  is an exploded perspective view of a gasket of the present invention showing the separate components. 
           [0054]      FIG. 2  is a side view of the assembled form of the gasket shown in  FIG. 1 . 
           [0055]      FIG. 3  is a top view of a core portion of a gasket of the present invention having two projections. 
           [0056]      FIG. 4  is a cross-sectional view of a gasket of the present invention having two projections. 
           [0057]      FIG. 1  is An exploded perspective view of a gasket of the present invention showing the separate components. 
       
    
    
     DETAILED DESCRIPTION 
       [0058]    Referring to  FIGS. 1 and 2 , a corrugated gasket core  2  is shown having a corrugated area  8  extending outwardly from an inner edge  10  defining a first aperture  14  to a plane surfaced outer area  12 .  FIG. 1  shows the core  2  prior to complete covering of the upper and lower surface of the corrugated area  8  with respective PTFE sealing rings  4 ,  6  having inner edges  16   a ,  16   b  which also define the first aperture  14  and outer edges  18 ( a ),  18 ( b ) which terminate at the outer edge of the corrugated area  8  when affixed to the surface of the core.  FIG. 2  shows a side view of the assembled gasket. The core  2  includes handling lugs  20 ,  22  extending outwardly from the plane surface area  12  on opposite sides of the gasket core. Each lug  20 ,  22  is integral with the core and has a centrally disposed hole  32 ,  34  to accommodate a fixing bolt (not shown) when locating the gasket in the flange joint. 
         [0059]    Referring to  FIG. 3 , a corrugated gasket core  202  is shown having a corrugated area  208  extending outwardly from an inner edge  210  defining an aperture  214  to a plane surfaced outer area  220 .  FIG. 3  shows the core without any sealing material covering the corrugated area and without a deformable inner portion.  FIG. 3  shows two projections  236   a ,  236   b  extending radially inwardly from the inner edge  210  of the core  202 . The projections are used to secure the core  202  to a deformable inner portion (not shown). 
         [0060]    Referring to  FIG. 4 , a cross-section of a gasket is shown. The gasket has a corrugated core  202  similar to that shown in  FIG. 3 , and a corrugated area  208  extending outwardly from an inner edge  210  to a plane surfaced outer area  220 . The core  202  is shown completely covered on the upper and lower surfaces of the corrugated area  208  with sealing material  204 ,  206  having inner edges  216   a ,  216   b  and outer edges  218   a ,  218   b  which may terminate at the outer edge of the corrugated area  208 . The gasket includes an inner ring  224  defined by an inner edge  226 , which itself defines an aperture  230  and an outer edge  228  adjacent to inner edges  216   a ,  216   b , and  210 .  FIG. 4  shows two projections  236   a ,  236   b  extending radially inwardly from the inner edge  210  of the core  202 . The projections  236   a ,  236   b  are used to secure the core  202  to a deformable inner portion  224 . 
         [0061]    The gasket includes an inner ring  24  defined by an inner edge  26  which itself defines a 2nd aperture  30  and an outer edge  28  which is shaped for close fitting engagement with the inner edges of the gasket core  10  and outer sealing rings  16 ( a ) and  16 ( b ). The axial depth of the inner ring  24  is roughly twice that of the assembled outer ring and it is located in such a manner that it extends beyond the surface of the outer ring equally in both axial directions. 
         [0062]    In one embodiment, the inner ring  24  is made of expanded PTFE polymer which is microcellular in structure and which has been fully immersed in a rust inhibiting aqueous solution of sodium EDTA having a concentration of 200 g/m 3 . 
         [0063]    In a further embodiment (not shown), the core includes four equally circumferentially spaced, radially inwardly extending projections, integral with the core and co-planar therewith at the axial ends thereof. The radially innermost end of the projection extends part way through the inner ring in the plane of the gasket to thereby secure the inner ring to the outer ring. The inner rings includes four matching circumferentially spaced sockets to accommodate each of the four projections in the inner ring. 
         [0064]    In a still further embodiment (not shown), one of the lugs  20 , 22  includes a generally co-planar T-shaped extension secured at its base to the radially outermost edge of the lug by one or more frangible thin sections. The thin sections are strong enough to keep the extension attached to the main gasket during normal storage, transport and fitting conditions but weak enough to allow easy removal under a suitable generally axial force applied by the user after joint fixation. 
         [0065]    In use, in one embodiment, the gasket is located between two mating parallel surfaces of a flange connection on a pipe connection wherein the surfaces of the flange have been corroded by prolonged exposure to sea water. As the mating surfaces are pressed together the deformable PTFE polymer of the inner is compressed and pushes into the crevices, scratches and pits in the surface of the flange providing sealing thereof and also delivering the sodium EDTA to the corroded areas. At the same time, the PTFE inner ring is also sealed against the undamaged areas on the surface and simultaneously treats those surfaces with rust inhibitor providing future resistance to rusting. 
         [0066]    In one embodiment, the gasket is produced by cutting the appropriate gasket shape of the solid stainless steel core and machining a series of concentric serrations of increasing radii from the inner edge thereof which defines a first central aperture. The serrations are terminated before reaching the outer edge of the solid steel core so that an outer border of non-serrated profile is provided on the gasket. An annular ring of PTFE biaxially orientated compressible sealing material sized so as to fit over the serrated ring portion of the gasket is then cut and a suitable adhesive is applied to the inner face thereof. An annular ring of Sigma 500 PTFE is applied to both serrated areas on opposite faces of the core to thereby provide the outer gasket. An inner ring of highly compressible biaxially orientated PTFE, produced by impregnating a suitable sample of Sigma 600 available from Flexitallic with a rust inhibiting aqueous solution of sodium EDTA having a concentration of 200 g/m 3  followed by drying is then cut having an outer edge of the same radius as the inner edge of the core and an inner edge which defines the 2nd aperture. Typically, the depth of the inner ring material is approximately twice that of the outer ring. In one embodiment, the depth of the inner ring is 6.5 mm and the depth of the outer ring is 3.5 mm made up of a 2 mm thick core and two facing layers each of 0.75 mm thickness. The depth of the serrations on the core is typically about 300 to 400 microns. For larger nominal pipe size flanges, or where out of flatness issues exist, the usage of thicker inner rings may be beneficial up to and including 10 mm. For certain flanges, the usage of a thicker core may also be advantageous. 
         [0067]    In one embodiment, the metallic core is serrated in the area of application of the Sigma 500 material; in all other external areas outside the sealing contact areas the metallic core is protected and covered by a layer of Fluoro Polymer (FP) based coating this can optionally include the inner and outer edges of the metallic core. The sealing faces should be masked during coating to avoid contamination thereof. Generally, the FP coating is applied before the sealing layer. This FP offers additional environmental protections and, by use of a distinctive color, clear visibility on gasket installation when in usage. Advantageously, the covering of the outer edges by the FP polymer allows the user to see which flanges contain this gasket, and which flanges do not without opening the flange. 
         [0068]    In one embodiment, the FP applied is IP9286 Red available from, for example, Indestructible Paint Ltd. 
         [0069]    Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. 
         [0070]    All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
         [0071]    Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
         [0072]    The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.