Abstract:
A high pressure metal-to-metal seal utilizes an expandable metal seal element able to withstand caustic fluids, high pressure, and high temperature. The metal-to-metal seal assembly is resilient for repeatable sealing and comprises an energizing metal ring and a metal sealing ring. Engagement of these two rings expands surfaces of the metal sealing ring to create inner and/or outer metal-to-metal seals.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to metal-to-metal seals and, more particularly, to a resilient metal-to-metal seal that in one embodiment may be mounted in a wellhead or BOP to control very high pressures, high temperature, and caustic fluids. 
     2. Description of the Prior Art 
     Metal-to-metal seals have advantages over non-metallic seals in that they operate over a wider range of temperatures, fluids, and pressures. Non-metallic seals of various materials are best matched to a particular range of temperatures, fluids, and pressures. Neither the operator nor the manufacturer will always know the conditions under which wellhead devices may be utilized, which increases the risk of failure. 
     In the past, metal-to-metal seals have often been made of soft metals that deform to create a one-time-use seal. One of the problems of soft metal seals is that all seals must be replaced whenever the wellhead device is opened. The deformed material is unlikely to seal again when used more than once. Another problem is that these types of seals do not always make an initial seal, thereby necessitating opening up the wellhead device and replacing that seal as well as all other metal seals. 
     To the extent that hard metal-to-metal seals are utilized in the prior art, fine tolerances are often required that essentially limit the pressure that can be sealed. Moreover, small variations in the tolerances can render the seal ineffective. 
     To the extent resilient metal seals have been utilized, they are subject to problems in obtaining an initial seal and/or maintaining a seal with over wide pressure variations. 
     The following U.S. patents describe various prior art efforts related to making metal-to-metal seals: 
     U.S. Pat. No. 4,911,245, issued Mar. 27, 1990, to Adamek et al, discloses a metal seal for sealing against casing in a well with a plurality of circumferentially axially spaced metal bands. An inlay material partially fills the cavities located between the metal bands. The metal bands are soft enough to deform when the seal is pressed into contact with the casing. The bands deform to a point flush with the inlay material. If the casing later moves axially relative to the seal because of temperature change or tension loading, then the inlay material will wipe across the band faces to maintain the seal. 
     U.S. Pat. No. 5,257,792, issued Nov. 2, 1993, to Putch et al, discloses a metal well head seal for sealing between inner and outer concentric well head components which includes a circular metal seal having a flat end and a tapered end and positioned between the inner and outer components. A forcing cone on one of the components engages the tapered end for sealing, a backup shoulder engages the flat end as the inner and outer components are longitudinally moved together for setting the metal seal. An adjusting nut adjusts the tolerances between the tapered end and the forcing cone. 
     U.S. Pat. No. 4,771,832, issued Sep. 20, 1988, to Bridges, discloses a wellhead assembly with a metal seal that accommodates misalignment between casing and the bore of the wellhead housing. The metal seal assembly includes a metal seal ring and a wedge ring. The seal ring has a cylindrical inner wall and a conical outer wall. The centerlines of the inner and outer walls are offset with respect to each other, making the ring eccentric. Similarly, the wedge ring has a conical inner wall and an outer wall. Its inner and outer walls are offset with respect to each other. The rings can be rotated relative to each other and to the casing to coincide the axis of the outer wall of the wedge ring with the axis of the wellhead housing bore. The inner wall of the seal ring has protruding bands which deform as a result of the softness of the metal to enhance sealing. 
     U.S. Pat. No. 3,166,345, issued Jan. 19, 1965, to Pinkard, discloses an improved sealing means including a seal ring, sealing between the cylindrical, upwardly extending neck of a tubing hanger element positioned in a tubing head, and a recess or socket of a bonnet flange, which is positioned over the upwardly extending cylindrical neck of the tubing hanger. 
     U.S. Pat. No. 4,455,040, issued Jun. 19, 1984, to Shinn, discloses a tubing head, tubing head adapter and tubing hanger sealed against annulus fluid or downhole pressure by an upper and a lower, pressure-energizing sealing assembly. The sealing assemblies are bi-directional, pressure-energizing and operate under working pressures of up to 30,000 psi. Each assembly consists of a metal seal ring made of highly elastic and ductile 316 stainless steel with a yield strength of approximately 30,000 psi, having a frustoconical shape, with the upper and lower tips of the cone enclosing an angle of approximately 28.degree. in the prestressed state. In the axial direction, the seal ring engages a support ring on one end and a tubing hanger shoulder at the other end, both of which form inclines of 30 degrees with the vertical (radial) plane. The support ring and the tubing hanger shoulders are made of materials having yield strengths of 50,000 psi and 75,000 psi, respectively. The preload applied to the seal assemblies is such that the seal ring plastically conforms to the harder surrounding surfaces and assumes a cone taper angle of 30 degree, in conformity with the mating support ring and tubing hanger shoulder. Thereafter, working pressure applied from either axial direction will be resolved along the incline of interacting surfaces into radial components which further enhance the sealing pressure along the inner and outer sealing surfaces. Because of this bidirectional pressure-enhancement, both seal assemblies may be tested through the application of test pressure from one common test port located between the two assemblies. 
     U.S. Pat. No. 4,056,272, issued Nov. 1, 1977, to Morrill, discloses an oil well pipe suspension apparatus including a wellhead having a pipe hanger supported therein and a Christmas tree supported thereon, a frusto-conical metal gasket providing a metal-to-metal seal between the hanger and the wellhead, and an “X” cross section resilient metal gasket providing a metal-to-metal seal between the hanger and the Christmas tree. 
     U.S. Patent Application No. 20050082829, published Apr. 21, 2005, to Dallas, discloses a metal ring gasket for a threaded union with a high-pressure, fluid-tight, metal-to-metal seal between subcomponents of a fluid conduit. The metal ring gasket is made of carbon steel or stainless steel depending on a composition of the fluid to be conveyed through the conduit. The metal ring gasket has beveled corners and is received in a beveled annular groove on mating surfaces of the subcomponents of the threaded union. When compressed in the annular groove between the subcomponents, the metal ring gasket creates an energized, high-pressure, fluid-tight seal that is highly resistant to pressure and is capable of maintaining a seal even at elevated temperatures resulting from direct exposure of the fluid conduit to fire. 
     U.S. Pat. No. 4,190,270, issued Feb. 26, 1980, to Vanderford, discloses a hanger for supporting tubing in a well head including a tubular body adapted for connection to a casing head and having a tapered and upwardly facing seat, a tubular hanger positioned within the body and supported on the seat, a downwardly converging annular space between facing portions on the exterior of the hanger and on the interior of the body, a metal seal ring positioned within the converging space, a seal actuator sleeve positioned between the hanger and the body and being movable axially to engage the seal ring, and a wedging screw extending through the body. The wedging screw engages the seal actuator sleeve and wedges the seal actuator sleeve onto the seal whereby the seal is forced into sealing engagement in the converging space between the hanger and the body. 
     U.S. Pat. No. 3,104,121, issued Sep. 17, 1963, to Nordin et al, discloses a seal assembly designed to withstand pressures such as those encountered at high pressure well heads which may be in the order of 20,000 p.s.i. A high pressure seal assembly for a flow control device, wherein the assembly includes co-acting surfaces between the flow control device and the main body for accommodating a seal structure to provide an improved seal equally effective against pressure applied from either direction. 
     U.S. Pat. No. 3,494,638, issued Feb. 10, 1970, to Todd et al, discloses a tubing hanger assembly including an adapter and seal assembly, mounted between the tubing head and the valve fitting at the top of a well, with the seal assembly being mounted in the bore of the adapter body, and held therein by a removable retaining nut and with the addition of a liquid seal injection valve communicating with the seal therein and a test port through the wall of the adapter for receiving a gauge for testing the seal prior to installing the adapter on the tubing head. 
     The solutions to the above described and/or related problems have been long sought without success. Consequently, those of skill in the art will appreciate the present invention, which addresses the above problems and other significant problems uncovered by the inventor that are discussed hereinafter. 
     SUMMARY OF THE INVENTION 
     It is a general purpose of the present invention to provide an improved metal seal assembly and method. 
     An object of the present invention is to provide an improved high pressure sealing assembly and method that may be utilized in pressure control equipment such as wellheads and BOPs. 
     Accordingly, the present invention provides a resilient and/or flexible metal seal that may be utilized without deformation. In one embodiment, a seal ring comprises seal members that are pliable, and which may be bent repeatedly within their range of operation without injury or damage. The metal seal comprises a metal seal ring that is capable of returning to an original shape or position after having been compressed. Unlike many metal seals, the metal seal assembly components of an embodiment of the present invention may be taken apart and when put back together will seal. 
     The apparatus in accord with one possible embodiment of the invention may comprise an energizing metal ring comprising metal energizing surface(s). The metal energizing surface(s) engage a groove in the metal sealing ring. When the metal energizing surfaces are urged into engagement with the metal groove of the metal sealing ring, one or both of an inner metal surface and an outer metal surface expand outwardly to increase the seal pressure applied by sealing surfaces. In this way, the present invention may be utilized to produce metal-to-metal seals, such as inner metal-to-metal seal and/or an outer metal-to-metal seal. 
     The apparatus may comprise forming an undercut portion which may be positioned at a mid-section of the metal sealing ring. The undercut portion decreases the thickness of at least one metal wall on which the sealing surfaces are formed to thereby increase flexibility of the inner metal member and/or the outer metal member. 
     The apparatus may comprise an initial seal mechanism positioned to engage the energizing metal ring and/or the metal sealing ring to form an initial metal-to-metal seal. 
     The apparatus may further comprise the initial seal mechanism comprising at least one threaded member and/or a third metal ring. The third metal ring may be a spacer ring sized to produce the initial metal-to-metal seal when engaging the energizing metal ring and/or the metal sealing ring. An inner and/or outer seal ring may be mounted on the third metal ring. 
     In one embodiment, the one or more metal energizing surfaces on the energizing metal ring or elsewhere can comprise one or more wedging surfaces such as a conical wedging surface and/or a flat wedging surface when viewed in a cross-section. 
     In another embodiment, the apparatus may comprise one or more protrusions mounted on the inner metal surface and/or the outer metal surface of the metal sealing ring wherein the line-of-contact metal-to-metal seals are produced by engagement with the protrusions. A protrusion may comprise rounded surfaces which engage surfaces such as inner and/or outer metal tubular surfaces. In one embodiment, the inner and/or outer metal tubular surfaces may comprise an annulus or pocket within pressure control equipment such as a BOP or wellhead. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements may be given the same or analogous reference numbers and wherein: 
         FIG. 1  is an elevational view of a wellhead device that shows metal-to-metal seals utilized within a wellhead device in accord with one possible embodiment of the present invention. 
         FIG. 2  is an elevational view, partially in cross-section, that shows a metal-to-metal seal assembly in accord with one possible embodiment of the present invention. 
         FIG. 3  is an elevational view, partially in cross-section, that shows a resilient expandable metal-to-metal sealing ring in accord with one possible embodiment of the present invention. 
         FIG. 4  is an elevational view, in cross-section, that shows an enlargement of region  4  of  FIG. 1  wherein a metal-to-metal sealing ring is mounted in a wellhead device in accord with a possible embodiment of the present invention. 
         FIG. 5  is an elevational view, in cross-section, that shows an enlargement of region  5  of  FIG. 1  wherein a metal-to-metal sealing ring is mounted in a wellhead device in accord with a possible embodiment of the present invention. 
         FIG. 6  is an elevational view, in cross-section, that shows an enlargement of region  6  of  FIG. 1  wherein a metal-to-metal sealing ring is mounted in a wellhead device in accord with a possible embodiment of the present invention. 
     
    
    
     While the present invention will be described in connection with presently preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents included within the spirit of the invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and more particularly to  FIG. 1 , there is shown pressure control equipment  100  that is intended to be representative of various types of wellhead equipment, which may comprise wellheads, tubing assemblies, BOP&#39;s, spool assemblies, hanger assemblies, and the like. The present invention is not limited to use in pressure control equipment or to any particular pressure control equipment. Moreover, pressure control equipment  100  may comprise various additional components that are not shown. 
     Pressure control equipment  100  can be utilized to seal off a well to control fluids such as liquids and gasses. The fluids may be at high pressures or low pressures, may comprise a wide range of different fluids including acidic and caustic fluids, and may operate under a wide range of temperatures. In one embodiment of the present invention, a metal-to-metal sealing mechanism in accord with the present invention may be utilized to control pressures up to 30,000 psi for a wide range of fluids and temperatures. 
     Sealing assemblies in accord with embodiments of the present invention are shown at  10 A,  10 B,  10 C, and  10 D. In this embodiment, sealing assemblies  10 B and  10 D are actually the same assembly but are shown in different views that include different components. However, conceivably the components of  10 B and  10 D might be utilized in separate seal ring assemblies and are therefore referred to separately to show multiple possibilities. Various components applicable to sealing assemblies  10 A,  10 B,  10 C, and  10 D are also shown in greater detail in  FIG. 2  and  FIG. 3 . The embodiments of  10 A,  10 C and  10 D with surrounding features of pressure equipment  100  are shown enlarged in  FIG. 4 ,  FIG. 5 , and  FIG. 6  respectively. These components are discussed in greater detail hereinafter. 
     Pressure control equipment  100  may be utilized to control pressure in tubing  102  and casing  104 , which may be at different pressures, contain different fluids, and be at different temperatures. For example, tubing  102  may be under very high pressure, perhaps 30,000 psi while casing  104  might be under a relatively much lower pressure, such as 500 psi, atmospheric pressure, or even a vacuum. Different fluids and temperatures may also be present. The present invention is operable to control the fluids of different pressures, types of fluids, and temperatures. 
     As general background for pressure control equipment  100 , tubing head spool assembly  106  may be secured to tubing head adapter assembly  108  at flanges  110  and  112  by connectors such as stud/nut assemblies  114 . Tubing hanger  109  is secured within tubing head adapter assembly  108 . Tubing string  102  is supported by tubing hanger  109 . An end of tubing  102  may be threadably secured to tubing hanger  109  which is supported by internal shoulders within tubing head spool assembly  106 . 
     Casing hanger assembly  116  is secured to tubing head spool assembly  106  at flanges  118  and  120  by stud/nut assemblies  122 . Casing slip hanger assembly  124  secures casing  104  within casing hanger assembly  116 . Lockdown screw assembly  142  may be utilized for securing into position internal components of tubing head spool assembly  106 . Lockdown screw assembly  142  may also be utilized to provide energizing force for sealing assembly  10 D (and  10 C). 
     Various ports may be utilized for monitoring/testing seals in pressure control equipment  100 , for instance, to verify that the seals are not leaking. Seal monitor ports  126  and  132  may be utilized, for example, to monitor pressure at seal assembly  10 A and  10 C, respectively. Flange test ports  128  and  134  may be utilized for example, to monitor or perhaps inject test pressure at flange joints  130  and  136 , respectively. Pressures and other seals may be tested utilizing ports such as port  133 . Terminating sleeve assembly  140  may also be utilized for control lines and/or monitoring and/or testing pressures. Other pressure/control lines and/or test ports such as port  144  and control lines  146  and/or other related components may also be utilized, as desired. Outlet wing valves  168  and  170  may be utilized to control flow through outlets  172  and  174 , respectively. 
     Referring now to  FIG. 2 , there is shown one embodiment of enlarged metal-to-metal sealing assembly  10 A. In this embodiment, metal-to-metal sealing assembly  10 A may comprise energizing ring  12 , seal ring  14 , and spacer ring  16 . In  FIG. 3 , another embodiment of a seal ring, namely seal ring  14 A is shown, which is inverted as compared to seal ring  14  shown in  FIG. 2 . In practice, seal ring assemblies  10 A,  10 B,  10 C, and  10 D may be mounted inverted or not, as is considered most suitable to the particular application. The seal ring assemblies seal in both directions. 
     In general operation, metal-to-metal sealing assembly  10 A produces an initial seal but is also responsive to a differential pressure applied across the assembly. If necessary and/or desired, the sealing force created may increase with increasing pressure and decreases with decreasing pressure. Due to the flexibility and relative movement of the sealing assembly components of the present invention, high tolerances are not required to provide a reliable hard metal-to-metal seal at high pressures. Pressure may be two-way and may be applied on either side of sealing ring  14 . 
     Spacer ring  16  is relatively movable with respect to sealing ring  14 . If pressure is applied to spacer ring  16 , then spacer ring  16  is urged against sealing ring  14  whereupon metal-to-metal sealing assembly  10 A responds to thereby increase the sealing force. If pressure against spacer ring  16  is relaxed, then spring pressure of inner and outer wings  20  and  22  may urge spacer ring  16  away from sealing ring  14 . 
     However, in the embodiment shown in  FIG. 2 , spacer ring  16  may act as an initial seal mechanism by being mounted on a shoulder to provide an initial position for spacer ring  16 . Accordingly, spacer ring  16  may be sized to urge metal seal ring  14  against energizing ring  12  to provide an initial seal without pressure being present as discussed in more detail hereinafter. Thus, the present invention provides for a seal that is always effective low pressure as well as high pressures. 
     In one embodiment as best shown in  FIG. 3 , seal ring  14  defines metal groove  18  which separates inner wing  20  and outer wing  22 , which are resiliently flexible. Many components of metal seal ring  14  and  14 A may be substantially the same, and therefore are numbered the same in either  FIG. 2  or  FIG. 3 . However, due to enlargement, some features metal seal ring  14  are more easily shown in  FIG. 3 . Inner wing  20  and outer wing  22  may expand and contract with respect to each other. Unlike other metal seals which comprise deformable metal, inner wing  20  and outer win  22  are comprised of a hard metal alloy which does not deform during the operational range of movement, but instead may be arranged to allow inner wing  20  and outer wing  22  to elastically or resiliently flex with changing pressure requirements. 
     Energizing ring  12  may comprise inner and outer energizing surfaces  24  and  26  (See  FIG. 2 ) which engage the interior surfaces  28  and  30  (See  FIG. 3 ) of metal seal ring  14  and metal seal ring  14 A. In this embodiment, inner and outer energizing surfaces  24  and  26  comprise, at least in cross-section, a flat wedging surface that when urged against mating interior surfaces  28  and  30  act to expand inner wing  20  and/or outer wing  22  and/or allow contraction. While flat mating wedging surfaces are shown in cross-section, other surfaces may be utilized such as rounded or otherwise engagable surfaces that may allow expanding and/or contraction of inner wing  20  and outer wing  22 . In this embodiment, the angle of the wedging surfaces with respect to the horizontal are about 75 degrees. However, this amount may vary in one embodiment by five to ten degrees or in another embodiment by twenty or thirty degrees, and/or may be varied as desired. Energizing ring  12  engages sealing ring  14  to produce an initial seal. A force is applied by energizing surfaces  24  and/or  26  to expand inner wing  20  and outer wing  22  with respect to each other, which then engage corresponding metal surfaces to create a seal. 
     The force may vary due to differential pressure acting on surfaces  28  and  30  to provide a corresponding expansion of inner wing  20  and outer wing  22 . If the differential pressure decreases, the force will decrease and inner wing  20  and outer wing  22  may thereby reduce the force acting to expand inner wing  20  and outer wing  22 . Thus, depending on the desired configuration, it may not be necessary that a high sealing force be maintained at all times when a high force is not necessary to control the differential pressure. Instead, the sealing force may be adjusted to the differential pressures. This provides a long-lasting, reliable seal assembly that tightly seals even very high pressures, but which avoids the need for extremely tight tolerances for a high pressure metal-to-metal seal. 
     In one embodiment, the seal is made with line-of-contact metal-to-metal sealing. Thus, in metal seal ring  14 A, multiple round protrusions  32  and  34  are formed on outer surface  36  of metal seal ring  14 . In a cross-sectional view, the outermost tips of the protrusions will then engage an inner surface at what is effectively a point, because a circle makes contact with a line at a point. Because the point extends around metal seal ring  14 , this creates a circular line-of-contact. Metal seal ring  14 A comprises two inner seal contact points  44  and  46 , on inner surface  37 , and two outer seal contact points  32  and  34 . Contact points  34  and  46  may be configured to engage first and points  32  and  44  may subsequently engage. The contact pressure on the different sets of round protrusions may be different or may be approximately the same depending on the design. 
     The point of contact is shown in cross-section in  FIG. 4  at line-of-contact point  38  for protrusion  40 . Thus, a line-of-contact seal is made at point  38 , as shown in cross-section, between metal seal ring  14  and inner tubular wall  148 . Likewise, a line-of-contact seal is made between metal seal ring  14  (or protrusion  42 ) and outer tubular wall  150 . Inner and outer tubular walls  148  and  150  are formed within pressure control equipment  100 , and essentially create a ring-shaped pocket which is utilized to hold seal assembly  10 A in position. 
     While the geometrical concepts of points and lines are an abstraction due to an assumption that the point and lines are infinitely small, the present invention provides a practical example of real world use of these concepts to provide a sealing mechanism. Therefore these contacts are described herein as points and lines even though they are not infinitely small. 
     As discussed above, it will be noted that metal seal ring  14 A has two outer protrusions  32  and  34  whereas metal seal ring  14  has only one outer protrusion  42 . Likewise metal seal ring  14  has only one inner protrusion  40 , whereas metal seal ring  14 A has two inner protrusions  44  and  46 . In one embodiment, for a radius of the protrusions might be in the approximate range of about 0.062 inches for a ring in the general range of 8 inches OD. However, this may vary. 
     The protrusions and/or other seal ring surfaces may comprise a contact surface that is overlaid with non-corrosive high strength hard alloy so that dents are not formed during operation. Thus, deformation of metal seal ring  14  and  14 A is avoided. 
     Another possible feature of metal seal ring  14  and  14 A is an undercut  48  which may be utilized to increase the flexibility of inner and outer wings  20  and  22 . In one possible embodiment, undercut  48  may comprise ends with radius of 0.06 inches. However, this may be adjusted as desired. Undercut  48  is positioned about midway at the bottom of the sloping portion of groove  18 . As well, inner and outer wings  20  and  22  may be made thinner or thicker depending on the desired flexibility. 
     Lower embodiment  50  may comprise a threaded socket to permit adjustment and/or mounting into an assembly and/or provide for easier removal. However, if desired, additional opening of groove  18  may be provided at lower portion  50  to provide even more flexibility of operation, if desired. 
     To provide back-up sealing, non-metallic seal rings may be utilized that may be likely to encounter lower pressures. For example, inner secondary seal ring  54  and outer secondary seal ring  52  may be utilized on spacer ring  16  as shown in  FIG. 2  and  FIG. 4 . As another possible example, as shown in  FIG. 5 , inner secondary seal ring  74  and outer secondary seal ring  72  can also be utilized on an embodiment of a metal seal ring in accord with the invention, such as metal seal ring  14 A. Secondary seal rings may be comprised of non-metal materials and be of different types. 
     As discussed above, various means may be utilized for providing an initial seal for sealing mechanisms  10 A,  10 B,  10 C, and  10 D. In one embodiment, a spacer ring, such as spacer ring  16  may be sized so as to provide sufficient force to create an initial seal once the assembly is in position within pressure control equipment  100 . For example, as best shown in  FIG. 4 , lower surface  58  of spacer ring  16  engages shoulder  152  formed within pressure control equipment  100 . Upper surface  56  of spacer ring  16  engages lower surface  62  of seal ring  14 . Moreover, upper surface  60  of energizing ring  12  has limited upper movement, which results in some spreading of protrusions  40  and  42  for making an initial metal-to-metal seal. Therefore, spacer ring  16  may comprise a sufficient vertical size, as shown in  FIG. 4 , to urge metal seal ring  14  into sufficient engagement with energizing ring  12  to provide an initial metal-to-metal seal. Retaining ring  160  may be utilized to hold seal assembly  10 A in position during assembly. As discussed above, spacer ring  16  may also be slightly moveable and may act as a piston to increase pressure against sealing ring  14 . 
     A large differential pressure from above sealing assembly  10 A, as indicated by arrow  158 , will act on the interior surface of wings  20  and  22 , as discussed above, providing addition force for spreading protrusions  40  and  42 , and thereby increasing the sealing force applied at the line-of-contact seal. The large differential pressure may pass by energizing ring sidewalls  162  and  164  to engage surfaces  28  and  30  (see  FIG. 3 ) of sealing ring  14 . Energizing ring sidewalls  162  and  164  may have a tolerance in the range of about five thousandths of an inch for sliding engagement with inner tubular wall  148  and outer tubular wall  150 . Likewise, as discussed above, pressure from below sealing ring assembly  10 A, as indicated by arrow  166  might be sufficient to urge spacer ring  16  upwardly and increase the sealing force. 
     In  FIG. 5 , an enlarged view of sealing assembly  10 C is shown. In this embodiment, a different initial seal mechanism is utilized. In this embodiment, seal protector ring  64 , locking ring  66 , compression ring  68 , and/or screw  70  may be utilized to create an initial seal. In this embodiment, the assembly may be held in position during assembly by locking ring  66  and screw  70 . If the vertical height of compression ring  68  is not sufficient to produce an initial metal-to-metal seal, as discussed above in connection with spacer ring  16  operation, then screw  70  may be utilized to provide an additional initial metal-to-metal seal adjustment. Moreover, an additional lockdown screw assembly may be utilized, as discussed subsequently in conjunction with seal ring  10 D. 
     In operation, sealing assembly  10 C as shown in  FIG. 5 , may function similarly to that of seal assembly  10 A. A high pressure above seal assembly  10 C, will create a differential pressure across seal assembly  10 C that will urge additional expansion or spreading force acting on an interior of inner and outer wings  20  and  22  and thereby increase the seal force produced by metal seal ring  14 C. Line-of-contact metal-to-metal seals are made at  78  and  76 . As noted above in this embodiment, inner secondary seal  74  and outer secondary seal  72  are provided on metal seal ring  14 C. 
     Sealing assembly  10 D may utilize wedging surfaces  82  and  84  to engage spacing ring  80  which urges sealing ring  14 D into engagement with energizing ring  12 . Wedging surfaces  82  and  84  may be activated by lockdown screw assembly  142  to force sealing ring  14 D into engagement with energizing ring  12  with a desired force for sealing. Thus, the sealing force can be adjusted if necessary. For instance, if pressure is detected across the seal, such at a test port, then addition sealing force may be applied. 
     In summary of general operation of a seal ring assembly, energizing ring  12  is urged against the sealing ring to spread the wings of the sealing ring whereby a metal-to-metal seal created. A spacer ring may be utilized to urge energizing ring into engagement with the sealing ring. The spacer ring may be sized to produce a desired force. The spacer ring may act as a piston that increases force with increasing differential pressure. Other means for urging energizing ring against seal ring may comprise bolts, locking mechanisms, and the like, some possible specific examples of which are illustrated herein. 
     In general, it will be understood that such terms as “up,” “down,” “vertical,” “upper,” “lower,” “above”, “below”, and the like, are made with reference to the drawings and/or the earth and that the devices may not be arranged in such positions at all times depending on variations in operation, transportation, mounting, and the like. As well, the drawings are intended to describe the concepts of the invention so that the presently preferred embodiments of the invention will be plainly disclosed to one of skill in the art but are not intended to be manufacturing level drawings or renditions of final products and may include simplified conceptual views as desired for easier and quicker understanding or explanation of the invention. One of skill in the art upon reviewing this specification will understand that the relative size and shape of the components may be greatly different from that shown and the invention can still operate in accord with the novel principals taught herein. While inner and outer seals are created as shown above, only an inner or outer seal might be created in accord with the present invention. 
     Accordingly, because many varying and different embodiments may be made within the scope of the inventive concept(s) herein taught, and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative of a presently preferred embodiment and not in a limiting sense.