Abstract:
Sealing systems for high pressure applications that provide electrical isolation between joined elements as well as enhanced resistance to leakage of media during a fire. High pressure sealing is accomplished using a metallic core to which an electrically isolating material is bonded on either or both sides. Sealing is achieved through a dielectric sealing element, such as a spring-loaded polytetrafluoroethylene (PTFE) ring. Flanges of the joint may be bolted together with the seal interposed therebetween, and the flanges bolted together. In the event of a fire, heat may be generated that is at a high enough temperature to burn away the isolating material and PTFE ring. Systems of various embodiments provide a metal core backup seal and a compression limiter, which, respectively, prevent the media from leaking from the joint and maintain bolt load at the flanges.

Description:
FIELD 
     The present invention relates generally to an isolation gasket which is adapted to be interposed and compressed between joined pieces of pipe in a flow line that is operative for fluid flow therethrough without leakage. More particularly, the present invention is directed to an electrical isolation gasket that is part of a seal system which is particularly useful in high pressure, high temperature and/or highly corrosive environments. The seal device of the present disclosure is specifically adapted to provide enhanced fire resistance and electrical isolation between joined pipe sections. 
     BACKGROUND 
     Seal systems using gasket devices are well known and have been used in a variety of applications to prevent fluid from leaking between joined pieces. For example, a seal device is interposed and compressed between flanged end connections of a flow line. In some cases, in-line process control equipment is to be installed at various points in a flow line, and may be associated with flanged end connections of a flow line. Inline process control equipment may include such things as valves, pumps, flow meters, temperature controllers, pressure controllers and the like. In addition, ends of pipe sections are provided with flanges so that the sections may be connected, end-to-end, to form the flow line. It is known to provide gasket devices at the interfaces of the joined sections to prevent leakage of the fluid at the joint. 
     Regardless of the nature of the joint, that is, whether it is between the joined sections of pipe or whether the joint is used to connect in-line process control equipment, it is desirable for a gasket device and seal system to be selected based on various factors that are associated with a particular joint and the particular media that is conveyed through the joint. These factors include the corrosive nature of the media flowing through the pipe line as well as the physical characteristics of that flowing media. Such physical characteristics include the pressure, temperature and velocity of the media. Additionally, in many cases it is also necessary not only to provide a reliable seal for the joint but also electrically isolate one side of the joint from the other. For example, a well known method of corrosion resistance for pipelines is cathodic protection. This method of corrosion protection requires sealing joints that provide electrical isolation. Another example is when two sides of the joint are of dissimilar metals. In this case the electrical potential difference between the two metals can create a galvanic corrosion cell if the two sides are not electrically isolated. Finally, it is also desirable for a sealing joint to provide an effective seal during the event of a fire. Fires pose a very serious threat to the safety of the pipeline workers and become even more dangerous if the sealing elements between joints are not capable of containing the media during a fire. 
     Therefore, flow line sealing systems face numerous challenges. For example, many materials which resist corrosive gases are not suitable for high pressure applications since the materials deform. Materials which are less prone to deformation, such as a graphite filled spiral wound metal seal, conduct electricity. Many materials that are used to create seal systems may melt at high temperatures, such as those that would result in a fire, so that the seal between flanges is compromised. This is an extremely dangerous situation since compromise of the seal system allows the media, such as a petroleum or gas product, to rapidly leak from the flow line which can increase the available combustion products for such a fire. Therefore, a sealing system that can contain high pressures, electrically isolate and provide safety during a fire would be a significant improvement in the field of effective flow line sealing. 
     SUMMARY 
     The present disclosure recognizes that a sealing system that can contain high pressures, electrically isolate and provide safety during a fire would be a significant improvement in the field of effective flow line sealing. Embodiments disclosed herein provide sealing systems for high pressure applications that provide electrical isolation between joined elements as well as enhanced resistance to leakage of media during a fire. High pressure sealing is accomplished using a metallic core to which an electrically isolating material is bonded on either or both sides. Sealing is achieved through a dielectric sealing element, such as a spring-loaded polytetrafluoroethylene (PTFE) ring. Flanges of the joint may be bolted together with the seal interposed therebetween, and the flanges bolted together. In the event of a fire, heat may be generated that is at a high enough temperature to burn away the isolating material and PTFE ring. Systems of various embodiments provide a metal core backup seal and a compression limiter, which, respectively, prevent the media from leaking from the joint. 
     One aspect of the present disclosure provides an isolation device for use between joined pieces in a flow line that is operative for fluid passage therethrough without leakage. The isolation device of this aspect comprises, for example, a flat metal plate, such as a flat annular metal plate, having opposing side surfaces and an opening formed in the metal plate to allow passage of fluid therethrough. In addition, a sheet of dielectric material is disposed on at least one side surface of the metal plate. Further, an inner groove and an outer groove are formed on the side surface or surfaces on which the sheet of dielectric material is disposed, which penetrate through the dielectric material and into the metal plate and which extend completely around the opening formed in the metal plate. A primary seal element is disposed in the inner groove, and a secondary seal element is disposed in the outer groove and there is a compression limiter acting on this seal in some manner, for example, it could be disposed in the outer groove or it could be the gasket retainer itself. 
     According to embodiments of the invention, grooves formed on the side surface or surfaces on which the sheet of dielectric material is disposed can have a cross section that is, for example, a rectangular shape, an isosceles trapezoid shape, a trapezoid shape, or a parallelogram shape. According to other embodiments of the invention, the primary seal element disposed in the inner groove can be, for example, a spring energized PTFE lip seal or an O-ring seal element. According to further embodiments, the secondary seal element disposed in the outer groove can be, for example, an annular metal body seal element having an E-shaped or C-shaped cross section, and the annular metal body seal element can additionally be provided with a coating of isolating material. In further embodiments, the compression limiter that could be disposed in the outer groove is disposed adjacent to the secondary seal element and could be an annular metal ring having a substantially rectangular cross section, and the compression limiter can additionally be provided with a coating of isolating material. According to further embodiments, the compression limiting action can also be provided by the gasket&#39;s dielectric facing material if the groove depth and seal cross section are properly sized. 
     Other aspects of the present disclosure provide an electrical isolation system between joined flange pieces, each of which has an inner and an outer face, in a flow line that is operative for fluid passage therethrough without leakage which utilizing, for example, a flat metal gasket with an opening formed therein to allow fluid passage therethrough, which flat metal gasket has opposing side surfaces on which are laminated sheets of dielectric material, each of which side surfaces has portions defining inner and outer grooves that penetrate through the layer of dielectric material and into the metal plate and extends completely around the opening, the inner groove having a primary seal element disposed therein and the outer groove having a secondary seal element and a compression limiter acting on said secondary seal. 
     In further aspects, the present disclosure provides use of gaskets in combination, for example, with at least one isolating sleeve receivable in an aligned bore formed in each of the joined flange pieces, which sleeve has a length that is substantially equal to a distance between the outer faces of the joined flange pieces with the gasket interposed therebetween. The isolating sleeve can be made, for example, of glass reinforced polymer material, epoxy material, phenolic material, or meta-aramid material. Further, such other embodiments include, for example, at least one elongate metal fastener with opposing ends, such as a headed metal bolt with threads for receiving a nut, which fastener is receivable in the isolating sleeve for connecting the joined flange pieces to one another with the flat metal gasket interposed therebetween. 
     Such aspects further comprise, for example, at least one washer made wholly or partly of materials having electrical isolation properties, such as a sheet of dielectric material laminated to one side of an annular washer substrate or a metal washer coated with a dielectric material, which washer is receivable on the elongated metal fastener with the electrical isolation material abutting one of the flange piece outer faces. 
     Still further aspects of the present disclosure provide an electrical isolation device that comprises a flat metal plate having opposing side surfaces and an opening formed therein to allow fluid passage therethrough, a layer of dielectric material disposed on one or both of the opposing side surfaces, at least an inner groove and an outer groove formed on the side surface or surfaces on which the sheet of dielectric material is disposed which penetrates through the dielectric material and into the metal plate and which extends completely around the opening formed in the metal plate. An annular primary seal element is disposed in the inner groove, and an annular secondary seal and a compression limiter acting on said secondary seal is disposed in the outer groove. 
     These and other advantages and novel features of the disclosure will be set forth in part in the description which follows, which discloses various embodiments, including the currently preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view in elevation and partial cross-section showing the isolation gasket and sealing system according to a first exemplary embodiment of the present disclosure; 
         FIG. 2  is an enlarged side view in partial cross-section showing a representative nut and bolt set used with various isolating components for electrically isolating a flange joint for various exemplary embodiments; 
         FIG. 3  is a perspective view of an isolation gasket according to an exemplary embodiment; 
         FIG. 4  is an exploded cross-sectional view of the isolation gasket of  FIG. 3  for an exemplary embodiment; 
         FIG. 5  is an enlarged cross-sectional view of an inner seal groove of the isolation gasket of various exemplary embodiments; 
         FIG. 6  is an enlarged cross-sectional view of an outer seal groove of the isolation gasket of various exemplary embodiments; 
         FIG. 7  is a cross-sectional view of a portion of an isolation gasket according to another exemplary embodiment; 
         FIG. 8(   a )- 8 ( d ) are cross-sectional views diagramming various groove cross-sections that may be used with the isolation gaskets of various different embodiments; and 
         FIG. 9  is a cross-sectional view partially broken away of an isolation gasket according to a further exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     For a more complete understanding of this invention, reference is now made to the following detailed description of several embodiments as illustrated in the drawing figures, in which like numbers represent the same or similar elements. Various embodiments are described herein, with specific examples provided in many instances to serve to illustrate and discuss various concepts included in the present disclosure. The specific embodiments and examples provided are not necessarily to be construed as preferred or advantageous over other embodiments and/or examples. 
     The present invention is generally directed to an isolation gasket adapted to be used between two flanges in a flow line application. Such flanges may be the flange connection between two sections of pipeline which are connected in end-to-end relation. Alternatively, such flanges may be those used to connect monitoring equipment to the flow line. Accordingly, such a flange connection will be introduced in reference to the end-to-end connection of a pair of pipeline sections, but it should be clearly understood that the present invention is not limited to such applications. Thus, for example, as is illustrated in  FIG. 1 , an isolation gasket  10  is located in a flange connection  12  between two pipe sections  14  in a flow line application. Each of the pipe sections  14  includes flanges  16  which may be placed in confronting relationship with gasket  10  therebetween. Flanges  16  are provided with bores  20  which align with one another so that flanges  16  may be connected by nut and bolt sets  18 , as is known in the art. 
     With continued reference to  FIG. 1 , and with reference to  FIG. 2 , it may be seen that electrical isolation between flanges  16  is accomplished by a plurality of different components associated with each aligned pair of bores  20 . Here, a pair of aligned bores  20  is provided with a sleeve  22  constructed, for example, of a glass reinforced polymer although other materials, such as epoxy, phenolic and nomex materials may be suitably employed. Sleeve  22  is dimensioned to have a length that is about the same as the distance between outer surfaces  24  of flanges  16  with gasket  10  interposed therebetween. Once sleeve  22  has been inserted into a pair of aligned bores  20 , isolating washers  26  are placed on either side of bores  20  on outer surfaces  24  of flanges  16 . In this embodiment, optional metal washers  28  are then positioned against washer  26  and bolt  18  is passed through the washers and sleeve  22  after which it is secured by nuts  32 . This assembly is undertaken for each of the aligned bores  20  after which nuts  32  may be tightened to compress gasket  10  at a desired pressure. 
     Various embodiments described herein contemplate an isolation gasket  10 , isolating washers  26 , and sleeves  22  to provide electrical isolation of separate pipe sections  14 . Isolating washers  26 , as illustrated in  FIGS. 1-2 , is positioned against outer surfaces  24  of flanges  16  and, in combination with sleeve  22 , provide electrical isolation between the nut and bolt sets  18  and the flanges  16 . The isolating washers  26  may be metal core washers that are coated with a dielectric material. 
     Illustrated in  FIGS. 3-6 , the construction of isolation gasket  10  is described, for an exemplary embodiment. In this embodiment, isolation gasket  10  includes the gasket body  38  formed by a flat annular metal plate  40  having an opening  44  therethrough to allow fluid passage in a flow line application. In one embodiment, the metal plate  40  is formed from 11 gauge stainless steel. Dielectric linings  42  are laminated on each outer surface of metal plate  40 . As illustrated in  FIG. 4 , a pair of grooves  46  and  48 , in this embodiment, are formed on a surface of gasket body  38  with each of these grooves penetrating through the dielectric linings  42  and into metal plate  40 . Groove  48 , as illustrated, has a larger diameter than groove  46  so that grooves  46  and  48  are radially offset from one another relative to opening  44 . Groove  46  may be referred to as inner groove  46 , and groove  48  may be referred to as outer groove  48 . In the embodiment illustrated in  FIGS. 4-6 , the gasket body  38  has various dimensions illustrated. As will be understood, these dimensions are illustrative of but one embodiment, and are provided for purposes of illustration and discussion only. One skilled in the art will readily recognize that numerous variations may exist for various different applications and different sizes of flow lines. In this embodiment a 6 inch (15.24 cm) gasket has an opening  44  with a diameter A of 6.000 inches (15.24 cm), an inner groove  46  diameter B of 6.565 inches (16.68 cm), an outer groove  48  diameter C of 7.838 inches (19.91 cm), and a total diameter D of 9.813 inches (24.93 cm). The total thickness E of gasket body  38  is 0.308 inches (7.82 mm), which comprises a core thickness of 0.120 inches (3.05 mm), and a dielectric coating thickness of 0.093 inches (2.36 mm) on each surface. Inner groove  46 , illustrated in the detail view of  FIG. 5 , has a width F of 0.150 inches (3.81 mm), and a depth G of 0.111 inches (2.82 mm). In this embodiment, the radially outward side of groove  46  is beveled at an angle of 75 degrees. Such a beveled surface provides enhanced retention of a seal that is disposed in the inner groove  46 , and as will be discussed in more detail below. The outer groove  48  of this embodiment is illustrated in the detail view of  FIG. 6 , and has a width H of 0.111 inches-0.252 inches (2.82 mm-6.40 mm), and a depth I of 0.093-0.123 inches (2.36-3.12 mm). As will be understood, the dimensions of the embodiment of  FIGS. 3-6  are exemplary, and other suitable dimensions may be used in various different applications as will be readily apparent to one skilled in the art. 
     As illustrated in  FIG. 7 , suitable seals  50  and  52  are sized and adapted to be nested in respective grooves  46  and  48 . Seal  50  is disposed in the inner groove  46 , and may be referred to as primary seal  50 , because in this embodiment seal  50  provides the primary sealing for the gasket when installed in a joint. Primary seal  50 , in an embodiment, is a lip seal comprised of a PTFE material having a spring  51  located therein to provide structural support to the seal  50 . The primary seal  50 , as illustrated, is a lip seal that prevents media from passing and is fitted to be seated into groove  46 . Groove  46  has a half-dovetail configuration such that, when media applies pressure to seal  50 , the seal  50  is pressured against the inside surface of the half-dovetail groove  46  and thus forced into the groove  46 . The seal  50 , in this embodiment, includes a beveled edge  53  that helps seat seal  50  in groove  46 . Seal  52  is disposed in the outer groove  48 , and may be referred to as a backup or secondary seal  52 , because in this embodiment seal  52  is not exposed to media unless there is a failure in the primary seal  50 . The secondary seal  52 , in this embodiment, is comprised of a metal seal having an E-shape, also referred to as an E-ring seal. The secondary seal  52 , in various embodiments, has a coating of PTFE thereon to provide electrical isolation. Such a PTFE coating may be, for example, three to five mils (0.076-0.127 mm) on an E-ring made of 0.0095 inch (2.41 mm) thick Inconel material. A compression limiter  54  could also be disposed in the outer groove  48 . The compression limiter  54 , as illustrated in the embodiment of  FIG. 7 , may be located in the outer groove  48  adjacent to the secondary seal  52 . A compression limiter may also be integrated such that it is the gasket retainer itself. In an exemplary embodiment, the compression limiter  54  is formed of carbon steel and is coated with a dielectric material such as ECTFE (Ethylene-ChloroTriFluoro-Ethylene). The compression limiter  54  has a thickness that corresponds with the depth of outer groove  48 . 
     In normal operation, a gasket body  38  is installed in a flow line joint, with primary seal  50  containing the media within the joint. In the event of a failure of the primary seal  50 , secondary seal  52  contains the media within the joint. As discussed above, a common application for such gaskets is in high pressure hydrocarbon pipelines, such as oil and gas pipelines. Also as discussed above, a significant concern for such pipelines is fire, and it is desirable to have a gasket that will maintain a seal even in the event of a significant fire. The gasket of the embodiments of  FIGS. 3-7  provides enhanced performance in the event of a fire. In such an event, high temperatures of the fire may melt or burn away the primary seal  50  as well as the dielectric coating  42  on the gasket body  38 . Thus the primary seal  50  fails, but secondary seal  52 , being formed of a metal, maintains the media within the joint. As mentioned, the loss of the dielectric coating  42  also may occur, which results in the gasket thickness E being reduced. Compression limiter  54  acts to maintain a virtual gasket thickness E in such an event, which acts to help maintain the appropriate loads on the bolts  18  that hold the flanges  16  of the joint together and not allow the secondary seal to be over compressed due to the gasket thickness E being reduced. In the absence of a compression limiter  50 , when dielectric coating  42  is reduced, the bolt load on bolts  18  is also reduced, thereby resulting in a loose joint which may result in media leaking from the joint. Thus in such a situation, a compression limiter, such as compression limiter  50 , acts to help maintain bolt load and not allow the seal to be over compressed. In the event of a fire and the loss of the isolating dielectric coating  42 , the sides of the joint are no longer electrically isolated, however, such an event will require repair of the flow line and replacement of the gasket in any event. 
     With reference now to  FIGS. 8(   a )- 8 ( d ), it should be appreciated that various configurations of grooves, such as grooves  46  and  48  may be employed with the present invention. For example, in  FIG. 8(   a ) groove  80  is a rectangular cross-section groove formed through dielectric material  42  and into metal core  40 .  FIG. 8(   b ) provides a groove  82  that is a trapezoidal dovetail configuration. Groove  82  is again cut through dielectric layer  42  and into metal core  40 . In  FIG. 8(   c ), groove  84  has the cross-section of a parallelogram and is again formed through isolating layer  42  and into metal core  40 . Finally,  FIG. 8(   d ) illustrates a trapezoidal groove  86  having one side thereof oriented at a right angle to the base. Groove  86  is cut through dielectric layer  42  and into metal core  40 . One skilled in the art will readily recognize that such groove configurations are exemplary only, and that other groove configurations may be used. 
     With reference now to  FIG. 9 , another exemplary embodiment is described.  FIG. 9  is a cross-sectional illustration of one half of a gasket  100 . Illustrated in  FIG. 9 , is a gasket  100  comprising a metal core  104  and dielectric layers  108  on each side of the metal core. Inner groove  112  and outer groove  116  are formed in the gasket  100 , each of which extending through the dielectric layer  108  and into metal core  104 . In some embodiments, inner groove  112  may not penetrate entirely through dielectric layer  108 , and outer groove  116  may penetrate through the dielectric layer  108  and into the metal core  104 . As illustrated in  FIG. 9 , suitable seals  120  and  124  are sized and adapted to be nested in respective grooves  112  and  116 . Seal  120  is disposed in the inner groove  112 , and may be referred to as primary seal because in this embodiment seal  120  provides the primary sealing for the gasket when installed in a joint. Primary seal  120 , in an embodiment, is comprised of a PTFE material having a spring located therein to provide structural support to the seal  120 . The primary seal  120  may, in operation, be a lip seal that prevents media from passing. Seal  124  is disposed in the outer groove  116 , and may be referred to as a backup or secondary seal  124 , because in this embodiment seal  124  is not exposed to media unless there is a failure in the primary seal  120 . The secondary seal  124 , in this embodiment, is comprised of a metal seal having an E-shape, also referred to as an E-ring seal. The secondary seal  124 , in various embodiments, has a dielectric coating thereon to provide electrical isolation. Such a coating may be, for example, a PTFE coating that is three to five mils (0.076-0.127 mm) in thickness on an B-ring made of metal. The gasket  100  of this embodiment has varying depths of the inner groove  112  and outer groove  116 , thereby providing a compression limiter for the secondary seal  124 . In such a manner, if dielectric layers  108  are reduced, the metal core  104  will remain, with secondary seal  124  disposed in the outer groove  116 . The depth of the outer groove  116  into the metal core  104  is such that the secondary seal  124  is less likely to be over compressed, and thus will continue to provide a seal. 
     In another embodiment, the gasket may include a single groove rather than dual grooves. In such an embodiment, the gasket, similarly as described above, may include a metal core and dielectric layers on each side of the metal core. The single groove may be formed in the gasket, extending through the dielectric layer and into metal core. A single seal is adapted to be nested in the single groove. In such an embodiment, the single seal is comprised of a metal seal having an B-shape, also referred to as an E-ring seal, although other configurations may be used. The single seal of such an embodiment may have a dielectric coating thereon to provide electrical isolation. Such a coating may be, for example, a PTFE coating that is three to five mils (0.076-0.127 mm) in thickness on an E-ring made of metal. The gasket of such an embodiment may also provide a compression limiter for the single seal. Such a compression limiter may include any compression limiter such as described above, such as carbon steel coated with a dielectric material, or the configuration of the depth of the groove relative to the metal core such that the single seal  124  is less likely to be over compressed in the even that the dielectric layer is reduced. 
     As will be appreciated by those skilled in the art, industries such as the oil and gas industry utilize many, many miles of connected metal pipelines that are subjected, for example, to a natural flow of current through the pipeline and across the metal-to-metal flange connections in the pipeline which causes the flange connections to corrode and build up corrosion similar to battery terminals. The isolation gasket for embodiments of the invention interrupts that current flow through a pipeline and prevents the flanges from corroding and building up corrosion in the way in which they would with a metal-to-metal seal. 
     It is to be understood that embodiments of the invention cover a wide range of applications, including without limitation, not only isolation but also potential fire safety, such as fire sealing applications. In that regard, combinations including washers for embodiments of the invention are significant aspects of the invention because, for example, if the washer material deforms or begins to flow because of heat, bolt load will be lost. If the bolt load is lost, there is no longer any compression in the joint between the two flanges in the flow line, which means the gasket no longer seals the joint. Further to this point, having a dielectric coating on the face of the gasket body that eventually loses thickness due to fire can result in over compression of metal formed seals. Thus a compression limiter of some type is provided to help both bolt load loss and seal over compression. 
     It is to be further understood that a method of making the gasket material for embodiments of the invention involves bonding the dielectric lining material to both sides of the metal substrate in large sheets to assure uniformity of the lamination. According to such a method, a water jet is thereafter utilized to cut appropriately dimensioned I.D and O.D. circles for gaskets out of the large sheets, and the grooves are formed on opposite sides of the cut-out circular gasket material, for example, with the circular gasket material mounted on a lathe. The resulting isolation gasket for embodiments of the invention has the stability and/or rigidity of a metal gasket with a stainless steel core having excellent corrosion resistance properties, while the glass reinforced epoxy laminated to the opposing surfaces of the gasket provides excellent isolating properties. 
     As likewise previously noted, another important aspect of embodiments of the invention is the seating of a suitable type of seal in the grooves of the gasket body. Representative examples of seal options include spring energized PTFE seals, as well as other types of O-ring or soft material as a back-up seal, or metal seals coated, for example, with a softer isolating material, such as PTFE. As similarly previously noted, a further important aspect of embodiments of the invention is the shape of the grooves formed in the gasket body. A factor in selecting one or more of the groove shapes previously described is the particular type of seal that is intended to be used. As internal pressure acts on the seal, the shape of the groove provides support for the seal and helps prevent the seal from blowing out. Thus, as will be readily recognized by one of skill in the art, a groove with a particular cross section may provide better support and enable better sealing characteristics for a particular type of seal element than a groove with a different cross section. 
     The previous description of the disclosed embodiments is provided to enable a person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.