Patent Publication Number: US-2010127461-A1

Title: Seal ring and method

Description:
FIELD OF THE INVENTION 
     This invention relates to seal rings of a type for sealing between first and second members each having a throughbore, such as flanges, clamps, and hub type connectors. More particularly, this invention relates to a seal ring which is pressure energized within the groove receiving the sealing ring, thereby maintaining sealing integrity even if the securing bolts between the first and second members elongate to permit flange separation. 
     BACKGROUND OF THE INVENTION 
     Pressure vessels are conventionally composed of structural sections having flanges or other connectors at their extreme ends. The flanges are secured to the assembly by securing bolts that extend through the mating flanges. The opposed flanges may be drawn together about a metal sealing ring with sufficient force to cause metal-to-metal sealing between surfaces on the seal ring and tapered surfaces on the opposing seal grooves in the first and second members. 
     An API seal ring may leak under circumstances where the bolts are properly tightened to secure the flanges in sealed engagement, but thereafter excessive heat causes bolt extension such that the flanges are allowed to be moved apart a slight amount. When this occurs, there may be insufficient mechanical force between the seal ring and the mating wall surfaces of the seal groove to maintain a fluid tight seal. Also, when the flange bolts are made up very tightly, metal coining between the seal ring and the mating wall surfaces may occur, in which case only a slight movement of the flanges may cause seal leakage. Coining of the seal ring typically occurs, because the seal ring metal is less hard than the metal defining the receiving grooves in the flange. Overstressing the studs to shut off a leak may also cause coining of the seal ring groove. It is frequently recommended to employ periodic tightening of flange bolts to prevent leaking in high temperature applications. 
     U.S. Pat. No. 4,410,186 discloses a seal ring for flanged joints, and was part of a seal concept for nuclear reactor applications. Due to wide tolerances, an API seal ring groove would be coined by this type of seal ring. To eliminate coining, one would have to make several sizes of a seal ring for a specific ring groove. This type of seal ring also would not seem suitable for holding pressures at high temperatures when the studs elongate because of its limited flexibility. 
     U.S. Pat. No. 5,058,906 discloses a seal ring formed from a high strength material. For the seal ring to function, the ring flexes against the ring groove wall to burnish and form a seal. The seal ring is intended to flex within its elastic limits, and again would require numerous different seal rings to work satisfactorily within a single API ring groove. 
     U.S. Pat. No. 5,240,263 discloses a seal ring with a substantial uniform cross sectional thickness. The patent teaches substantially planar contact between surfaces of the seal ring and the tapered surfaces defining the seal groove. This type of seal may leak because there is no pressure energization. Because the seal areas are large, pressure can migrate into the seal area thus equalizing pressure, resulting in leakage. 
     The disadvantages of the prior art are overcome by the present invention, and an improved seal ring and method are hereinafter disclosed for reliable sealing between two members. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a seal ring for sealing between first and second members each having an outer groove surface and an inner groove surface includes a metal seal body for engagement with each of the radially outward surfaces on the first and second members when the securing members secure the first member to the second member. A metal flexible flange radially inward of the seal body has a cantilevered end which provides substantially line contact sealing engagement with a respective inner groove surface, while a spacing or gap between the flexible flange and the seal body provides for fluid pressure energization of the flexible flange. The flexible flange is deformed beyond its elastic range when the securing members secure the first member to the second member. 
     In another embodiment, the seal ring includes a metal flexible flange supported on the seal body and extending radially inward such that a cantilevered end of a flexible flange provides substantially line contact engagement with one of a groove base surface and an inner groove surface on the respective first or second member. The flexible flange is deformed beyond its elastic limit when the securing members secure the first member to the second member, and a spacing or gap between the flexible flange and the seal body provides for fluid pressure energization of the flexible flange. 
     The seal ring as disclosed herein is able to maintain dynamic sealing integrity even in the event of a fire. Due to plastic yielding and/or telescoping, the shape of the seal is able to change while maintaining high sealing reliability. 
     These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a side view of a seal ring according to the present invention for sealing between first and second members. 
         FIG. 2  illustrates in greater detail a cross section of the seal ring shown in  FIG. 1 . 
         FIG. 3A  discloses an alternate embodiment of a seal ring, and  FIG. 3B  discloses a seal ring as shown in  FIG. 3A  when the securing members have secured the first member to the second member. 
         FIG. 4  discloses yet another embodiment of a seal ring wherein the flexible flanges are slidably movable relative to the seal body. 
         FIG. 5  discloses yet another embodiment of a seal ring. 
         FIGS. 6 and 7  disclose additional embodiments of a seal ring. 
         FIG. 8  discloses an embodiment of a seal ring with a radially extending flexible flange. 
         FIG. 9  discloses a flexible flange slidably movable relative to a seal body. 
         FIGS. 10A and 10B  illustrate yet another embodiment of a seal ring wherein a pair of flexible flanges are shown in  FIG. 10A  supported on a seal ring before the securing members are tightened, and  FIG. 10B  illustrates the same sealing ring with the securing members tightened. 
         FIG. 11A  depicts yet another embodiment of a seal ring prior to the member being secured to the second member, and  FIG. 11B  shows the same seal ring with the first and second members secured. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a seal ring  10  for sealing between first and second members  12 ,  14  each having a respective throughbore  13 ,  15 . Each member  12 ,  14  has an outer tapered groove surface  16  directed radially inward in a direction away from an interface between the members  12 ,  14 , and an inner tapered groove surface  18  directed radially outward in a direction away from the interface between members  12  and  14 . A groove base  20  is shown spaced between the surfaces  16 ,  18 , and is substantially perpendicular to a common axis  22  of the throughbores. A plurality of securing members  24 , such as bolt and nut assemblies, are arranged circumferentially about the members  12 ,  14  and secure the first member to the second member. In some applications, clamping devices or other types of flange connecting members may be used to rigidly secure the first member to a flange end of a second member. An annular groove formed by the surfaces  16 ,  18 ,  20  is thus provided for receiving the sealing ring  10  therein. 
     Referring to  FIG. 2 , the sealing ring  10  comprises a metal seal body  26  for engagement with the radially outer surface  16  on the first and second members when the securing members  24  secure the first member to the second member. An annular flange  28  may be pressed on or otherwise secured to the seal body  26 , and is compressed between the surface  25  on the body  12  and surface  27  on the body  14  when the bolts  24  are tightened. The sealing ring  10  further includes a pair of metal flexible flanges  30 ,  32  each radially inward of the seal body  26 , such that a cantilevered end  31 ,  33  of each flexible flange provides substantially line contact sealing engagement with the inner tapered surface  18  on a respective first and second member  12 ,  14 . A spacing  34 ,  36  between each flexible flange and the seal body  26  provides for fluid pressure energization of the flexible flange. The cantilevered or tip end  31 ,  33  of each flange is thus forced radially inward into tighter sealing engagement with a respective surface  18  in response to high pressure fluid in the bore of the members  12 ,  14 . 
     For the embodiment as shown in  FIG. 2 , the seal body  26  and the flexible flanges  30 ,  32  are formed from a unitary homogeneous material. In other applications discussed below, the annular flange  28  and the seal body  26  may be formed from a unitary homogeneous material. The seal body  26  and the pair of flanges  30 ,  32  as shown in  FIG. 2  form a substantially C-shaped cross-sectional configuration, as shown in  FIGS. 1 and 2 . 
       FIG. 2  depicts in dashed lines the “as manufactured” configuration of the seal body and flexible flanges, and illustrates in solid lines the final position of the seal body and flexible flanges after the bolts have been tightened and before high pressure is applied to the seal ring  10 . There is a small angular mismatch between the radially outer tapered surface  29  on the seal body  26  and the corresponding outer tapered surface  16  on each of the members  12  and  14 , with this mismatch resulting in a substantially line contact seal  38  between the seal body and the surfaces  16 . Those skilled in the art appreciate that, in response to high fluid pressure within the bore, the mismatched surfaces on the seal body may be pressed outward into substantially planar engagement with the groove surfaces  26  on the first and second members, since the seal body deforms slightly in response to this high fluid pressure. Whether under high pressure or low pressure, the seal between these components is effectively provided by line contact engagement, since even under high pressure, substantially higher sealing forces are exerted at point  38  than at other points along the radially outer surface  27  of the seal body. Thus even if high pressure results in substantially planar contact between surfaces  27  and  16 , substantially line contact metal-to-metal sealing is achieved at point  38 . 
     Sealing effectiveness of the seal ring is not solely dependent upon bolt loading, since the flexible flange of the seal ring is also pressure energized. Also, the surface on the first and second member which is sealingly engaged by a metal flexible flange preferably is not coined. The seal ring changes its shape to maintain seal integrity when opposing seal grooves move apart due to temperature changes or changes in the seal ring due to flexure or yielding, or by telescoping of the seal ring, as explained further below. During substantial separation of the first and second members, the flanges may move axially apart 0.025 inches or greater, yet seal integrity may be maintained at a high pressure. The seal maintains an effectiveness during flange separation, and is interchangeable with standard API and/or ANSI seal rings. 
     By including a flexible flange on the seal ring ID and an interference fit on the seal ring OD, the installed flexible flange tip makes sealing contact with a wall of the groove, while a corner of the OD of the seal ring and/or an annular sealing bump on the OD of the seal ring contacts the outside groove wall. When the flange bolts are tightened, the flexible flange is flexed outwardly while the OD of the seal ring is flexed inward, resulting in strengthened self-energization of the seal ring. When internal pressure is applied to the seal ring, an additional fluid pressure generated force is created on the flexible flange, while simultaneously an outward force is created on the seal body. These fluid pressure induced forces further strengthen the seal and establish a pressure-energized seal. The seal ring maintains sealing integrity during flange face separation since the inward flexure of the seal body and the outward flexure of the flexible flange stores energy in the seal ring, acting in the manner of a spring. This stored energy is released when being supplemented by the internal fluid pressure within the first and second members to maintain contact between the seal ring and the groove walls during separation. 
       FIG. 3A  depicts an alternate seal body  42  and a pair of metal flexible flanges  44  and  46  with a spacing  48 ,  50  provided between each flexible flange and the seal body  42 . The seal body as shown in  FIG. 3A  does not include a annular flange, and accordingly the surface  25  on the member  12  directly engages the surface  27  on the member  14  when the bolts are tightened, as shown in  FIG. 3B . 
       FIG. 3B  also depicts each flexible flange  44 ,  46  in substantially line contact sealing engagement with the base surface  20  at point  45  on the cantilevered end of flanges  44  and  46 . Again, the configuration of the seal body and flexible flanges in its “as manufactured” condition is shown in dashed lines in  FIG. 3B , and is shown in solid lines in its position when the bolts are tightened. Other seal configurations discussed below also show the “as manufactured” and “final” position, although only the final position is shown in some figures. All seal configurations are, however, deflected before obtaining the final configuration. The end surface  45  forming a substantially line contact seal is thus similar to the end surface  31  shown in  FIG. 2 , except that sealing engagement in the  FIG. 3B  embodiment is with the base surface  20  rather than the inner groove surface  18 . A mismatch between the angle of the surface  16  and the radially outward angled surfaces  43  on the seal body  42  are depicted, with the body thus being configured for substantially line contact sealing engagement with each of the annular flanges. Referring to  FIG. 4 , the seal body  52  is provided with an annular flange  28 . A mismatch between the outer surface  53  on body  52  and the tapered outer groove surface  16  results in line contact sealing engagement with the members  12 ,  14  at sealing point  38 . A pair of metal flexible flanges  54  and  56  provide a line contact seal with the surfaces  18  on the first and second members at point  31 , while spacing  55 ,  57  between the metal flexible flanges  54 ,  56  and the seal body  52 , and in this case between the flexible flanges  54 ,  56  and the flange supporting component  58  of each flexible flange, provides fluid pressure energization of the flexible flange. The flange component  58  is slidable in a generally axial direction relative to the seal body  52 , and the surfaces  59  on the flanges  54 ,  56  engage the base surface  20  of the groove in response to high fluid pressure, as shown. Again, the flexible flange is deformed beyond its elastic range when the securing member secure the first member to the second member. Sealing between  58  and  52  is accomplished by tapering one of the surfaces on  58  or  52  which engage the other component, and/or by providing an annular bump or protrusion on one of these surfaces. 
       FIG. 5  depicts yet another embodiment of a seal ring, wherein the seal body  60  is unitary and homogeneous with the annular flange  28 . In this case, the seal body supports flexible end flanges  62  and  64  each open to fluid pressure energization by a respective gap  66  provided between the surface  18  and the body  60 . Spacings  63 ,  65  provide for fluid pressure energization of the flexible flanges  62  and  64 . Additional slots  67 ,  68  and  69  are provided for increasing the flexibility of the end flanges  62 ,  64 , with slots  67  and  69  being directed substantially radially inward, and the slot  68  being directed substantially radially outward. The seal ring  60  seals at point  38  with the surface  16  as previously explained, and the cantilevered end  31  of each flange member  62 ,  64  thereby obtains substantially line contact sealing engagement with the surface  18 . 
       FIG. 6  depicts another embodiment on a metal seal body  70  having a radially outward flange  28  secured thereto. The seal body is intended for substantially line contact sealing engagement with the radially outward surface of each member  12 ,  14 , and accordingly annular bump  72  is provided on the member  12  for substantially line contact sealing engagement with the seal body  70 , while the mismatch of the angles between the outer surface of the seal body and the radially outward groove wall  16  also may or may not provide line contact sealing at point  73 . As an alternative to providing the raised bump  72  on the member, a sealing bump  74  may be provided on the seal body, as shown in  FIG. 6 . A pair of metal flexible flanges  76  and  78  are each configured for substantially line contact sealing engagement with the radially inward tapered surface of the members  12 ,  14  at point  31 . A spacing  77 ,  79  is provided between each flexible flange and the seal body for fluid pressure energization of the flexible flanges. Each of the flexible flanges  76 ,  78  is deformed beyond its elastic limit when the securing members secure the first member to the second member. 
     The embodiment in  FIG. 7  illustrates an alternative seal body  80  which is integral with the radially outward flange  28 . Line contact sealing engagement with the member  12  is provided by the annular bump  82  on the seal body, and by the mismatch surfaces which may result in line contact sealing at point  84 .  FIG. 7  also depicts a bump  86  provided on the lower member  14  for line contact sealing engagement with the seal body. The pair of flexible flanges  88  and  90  include respective spacings  89  and  91  for fluid pressure energization of the flexible flanges. Each flange  88 ,  90  is thus pressure energized, and provides a substantially line contact seal with the groove surface  18  at point  31 . If desired, one of the bumps on the seal body or on the member  12 ,  14 , or one of the line contact seals  84  created by angular mismatch, may be eliminated, since both a primary and a backup seal with each member  12 ,  14  is shown in  FIGS. 6 and 7 . 
       FIG. 8  depicts yet another seal body  92  having a flange  28  secured thereto, with the seal body  92  supporting a pair of flexible flanges  94  and  96  each configured for substantially line contact sealing engagement at  31  with the radially inner wall  18  of each body  12 ,  14 . A substantially radially extending gap  95  and  97  is provided between and flexible flange and the seal body for fluid pressure energization of each flexible flange. 
       FIG. 9  depicts an alternative seal body  110  having a radially outward flange  28  secured thereto. In this case, flange  114  is provided on the seal body for substantially line contact sealing engagement at  31  with the tapered surface  18  on the lower member  14 , with a groove  115  provided between the flexible flange  114  and the body  110 . A flange  112  is provided on flange support  116 , which is slidable in a substantially radial direction relative to the body  110 . A bump  118  on the flange support  116  provides substantially line contact sealing engagement with the body  110 , while the mismatch between the outer surface of the support  116  and the inner surface of the body  110  provides for substantially line contact sealing engagement at  120 . Spacing  113  provides for fluid energization of the flexible flange  112 . The body  110  also seals with the members  12 ,  14  by line contact sealing of mismatched angular surfaces, as previously discussed. Increased flexibility is provided since flange  112  is axially movable relative to body  110 . 
       FIG. 10A  depicts yet another embodiment of a seal ring including a metal seal body  122  having a flange  28  integral therewith. An annular bump  124  on the seal body is provided for sealing engagement with the radially outward surface  126  of each member  12 ,  14 . A pair of metal flexible flanges  128  each include a support member  130  for slidable engagement with the inner wall  132  of the body  122 , and an annular bead or raised section  134  is provided for substantially line contact sealing engagement with the metal seal body. Each flange  128  includes an annular bead  136  for substantially line contact sealing engagement with the inner wall  138  of the groove. Shown in  FIG. 10B , the seal ring seals with each member  12 ,  14  by substantially line contact sealing engagement with radially inward groove surface  138  at point  136  between the metal flexible flange and a respective member, by the seal  134  provided between each flange support member  130  and the metal seal body  122 , and by annular bead  124  provided between the metal seal body and the radially outward groove wall  126  of the members  12 ,  14 . The spacing  127  between each flexible flange  128  and a respective support member  130  provides for fluid pressure energization of the flexible flange. Each flexible flange is axially movable relative to the body  122 , so that axial variations between the base surfaces  20  of the ring groove do not have a significant adverse effect on sealing effectiveness. 
       FIG. 11A  discloses another embodiment, wherein the seal body  140  has a flange  28  integral and homogeneous therewith. A mismatch between the outer surfaces on the flange body and the outer tapered groove surfaces  16  on the members  12 ,  14  provides for substantially line contact sealing engagement between the seal body and the members at point  142 , as shown in  FIG. 11B . Surfaces  141  on body  140  may be tapered to facilitate sliding the base piece  143  on the seal body  140 . Each seal body also includes a pair of flexible flanges  144  and  146  each in contact with an insert body  148 . When assembled, line contact sealing engagement at point  31  is formed between each flange  144 ,  166  and the respective body  12 ,  14 . Protrusion  145  on each base piece  143  forms a line contact seal with surface  141  on seal body  140 . The spacing  147  between flexible flanges  144  and  146  and the sliding base piece  143  is preferably filled with a compressible material, as shown in  FIG. 11A , such as an elastomer, a high temperature graphite, Teflon™, or a plastic. Base piece  145  may be formed from metal, but alternatively may be a plastic material component. When the bolts are tightened, the insert  148  is compressed, resulting in the seal body shown in  FIG. 11B . 
     According to the present invention, comparatively low preloading may be used to form an effective seal between the groove surfaces of the ANSI or API flange and the seal ring. An API or ANSI flange joint may have mismatched members, and the seal ring groove surface diameters may vary by ±0.032 or more. The seal ring may be pressure energized by the internal pressure within the first and second members to maintain an effective seal. 
     An API or ANSI seal ring material may have a yield strength of 30,000 pounds or less. The seal ring will thus only stretch 0.001 inches or less per inch of diameter. If the yield strength of the seal ring gasket is increased to 60,000 psi or greater, the seal ring as well as the groove walls may be permanently deformed. The seal ring is sufficiently flexible that the internal pressure will flex the seal ring and make it yield under applications of use, such as flange separation at high temperature. One seal ring may be made to fit one size groove without a problem because of a flexure, yielding, and telescoping capabilities of the seal ring, without the sealing surface being coined and preferably only burnished at the point of sealing contact. 
     The seal ring is highly interchangeable since the seal ring fits into a standard API and/or ANSI seal ring groove. The features of the seal ring are realized when the flange joint is assembled according to recommended practices. 
     In a room temperature test on a 2 1/16th inch, 5,000 psi API flange connection with a seal ring according to the present invention, the flange joint was made up finger tight on the bolts, yet the connection held sealing integrity at 100 psi at 70° F. Pressure was subsequently increased to 10,000 psi, and was maintained for 24 hours without leakage. 
     In a fire test, flanges made from A105 carbon steel, 2 inch size, Class 300 with B7 studs were torqued to 125 pounds. The API classification for this flange is Class F, meaning that the flange should leak under the requirements of the test. During the test, the upper flange reached a temperature of 1225° F., and the lower flange temperature was 1265° F., and the stud temperature reached 1250° F. Sealing integrity was maintained with no leakage, and the flange was subjected to a connection test of 555 psi. As the test equipment cooled down to 72° F., measurements of the stud showed that they averaged 0.010 inch permanent elongation due to high stud torque applied to the studs. The fluid internal pressure does not exert enough separation load on the flange to make the studs yield at this temperature. 
     It should be understood that the terms “line contact seal” or “substantially line contact sealing” mean that sealing engagement between the metal components is provided by substantially aligned contact engagement, e.g., of a metal flexible flange with one of the first and second members. Such line contact sealing engagement is significantly more effective at sealing than substantial planar-to-planar engagement of metal surfaces. Substantially line contact engagement may nevertheless result from sealing engagement of surfaces over a short length, so that the forces resulting in sealing are concentrated along a small surface area. 
     Each of the embodiments disclosed herein provides for a relatively thin flexible flange which is responsive to high fluid pressure within the interior of the members  12 ,  14  to increase sealing effectiveness. Each flexible flange is thus forced into tighter sealing engagement with the respective member when fluid pressure increases. Each flexible flange is also deformed from its original as manufactured condition to a sealing position in which at least part of the seal ring is deformed beyond its elastic limit when securing members secure the first member to the second member. 
     The seal disclosed herein may be used in API or ANSI flange ring grooves and other special ring grooves, and will maintain seal integrity with very low restraining load, such as stud load, even if the flanges separate a small amount in a fire and the studs elongate in response to a temperature of up to about 1200° F. The seals are especially sensitive to leakage with flange separation. For example, for every 0.001″ of flange separation, a prior art seal may lose 0.001″ squeeze in each ring groove, and if the seal shifts, the seal may lose 0.002″ squeeze and leak. Any movement on standard seals will leak. For the seal as disclosed herein to work in these types of grooves, it forms a dynamic seal that changes its shape as the gland formed by the two ring grooves changes shape, and the seal is pressure energized. The seal design is thus based on flexure, instead of rigidity and high compression loading common for standard seals. 
     The metal seal body disclosed herein is designed so that it changes shape by flexing, yielding and/or telescoping. Because the seal body can change shape these three ways, shape changes such as thermal expansion and contraction can practically be ignored. 
     The pressure energized metal seal achieves high sealing with a pressure multiplier designed into the seal. This feature creates a substantially greater force per square inch between the seal ring and the ring groove than the internal pressure on the seal body causing this force. If the internal pressure of 1000 psi acts on 10 square inches and the seal engages the groove at only 0.5 square inches, the force acting on the seal to force sealing engagement is 20,000 pounds. 
     Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.