You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     Maintaining control of fluid pressures experienced within a wellhead equipment requires proper sealing around the tubular elements in the wellhead equipment. Thus, various types of annular seals which seal around tubular elements have been developed over the years. These seals typically fall under one of three categories: elastomer, elastomer combined with metal, or metal seals. 
     Permanently-installed wellhead equipment requires seals that retain high sealing integrity when exposed to extreme pressures, or pressure fluctuations, extreme temperatures or temperature fluctuations, corrosive fluids, and dirt. Elastomer materials may break down when exposed to extreme temperature or corrosive fluids. As a result, metal seals are typically the preferred type of seal since they do not share the temperature sensitivity problems of elastomeric materials. The metal seals can be made from high-strength, corrosion-resistant materials which resist physical damage and corrosion. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, a seal system for sealing between a pair of members comprises a pair of substantially aligned peripheral walls on inner faces of the members, each peripheral wall having an internal frustoconical portion. A metal ring includes a pair of lips with external frustoconical portions sealingly engaging the internal frustoconical portions. The metal ring includes a pressure responsive surface configured to axially extend the metal ring upon application of external pressure. 
     In accordance with another aspect of the invention, a seal system for sealing between a pair of members comprises a pair of substantially aligned peripheral walls on inner faces of the members, each peripheral wall having an internal frustoconical portion. A metal ring includes a pair of lips with external frustoconical portions sealingly engaging the internal frustoconical portions. The lips are spaced apart by a groove which permits axial extension of the metal ring upon application of external pressure. 
     In accordance with yet another aspect of the invention, a seal system for sealing between a pair of members comprises a pair of substantially aligned peripheral walls on inner faces of the members, each peripheral wall having an internal frustoconical portion. A metal ring includes a pair of lips with external frustoconical portions for sealingly engaging the internal frustoconical portions. The metal ring includes at least one convolution between the lips. The convolution is configured to move the lips outwardly with respect to each other upon application of external pressure. A spacer is disposed in a groove defined by the convolution. The spacer controls the clearance between adjacent surfaces of the convolution. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a cross-sectional view of an embodiment of the invention. 
     FIG. 2 is a cross-sectional view of an embodiment of the invention during the initial stages of installing an embodiment of a seal assembly of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings wherein like characters are used for like parts throughout the several views, FIG. 1 illustrates a seal assembly 10 situated between an upper tubular member 12 and a lower tubular member 14. The seal assembly 10 includes a seal ring 16, a spacer 18, and an o-ring 20. 
     The seal ring 16 includes an upper sealing lip 22 with frustoconical sealing flank 30 and a lower sealing lip 26 with frustoconical sealing flank 34. The sealing flank 30 mates with a frustoconical sealing surface 24 on an inner peripheral wall 32 of the member 12. The sealing flank 34 mates with a frustoconical sealing surface 28 on an inner peripheral wall 36 of the member 14. The interference fit between the flanks 24 and 28 and the surfaces 30 and 34, respectively, provide a tight seal between the members 12 and 14. 
     The sealing lips 22 and 26 are spaced apart by a central convolution 38, which permits the sealing lips 22 and 26 to extend axially upon application of external pressure to the seal ring 16. The outer ends 40 and 42 of the sealing lips 22 and 26, respectively, may be made thicker to provide better resistance to axial deformation near the sealing contact region 44 and 46 and to minimize twisting of the lips. 
     The spacer 18 is disposed in a groove 48 defined by the convolution 38. The spacer 18 is a metal ring which is split to facilitate installation in the groove 48. The spacer 18 includes a groove 50 which is shaped to receive the o-ring 20. The o-ring 20 is stretched around the spacer 18 to secure the spacer 18 to the seal ring 16. 
     The clearances between the convolution 38 and the upper and lower surfaces 52 and 54 of the spacer 18 are controlled to a gap size that will prevent collapse of the convolution 38 to the extent that the convolution 38 is overstressed. The o-ring 20 cooperates with a groove 56 in the inner peripheral wall 32 of the member 12 to retain the seal assembly 10 in the member 12 when the member 12 is detached from the member 14. 
     The seal ring 16 is made from metal, preferably a high-strength, corrosion-resistant metal (e.g. Nickel Alloy N07718) A soft metal plating may be provided on the seal ring 16 to enhance the sealing capability of the seal ring. 
     A seal 58 is provided between the members 12 and 14 to provide a temporary seal between the members 12 and 14 for the purpose of testing the installation of the seal assembly 10. Pressure may be applied to the seal assembly 10 through the test port 60. 
     In operation, the seal assembly 10 is initially attached to the member 12 by fitting the o-ring 20 into the groove 56 in the inner peripheral wall 32 of the member 12. Then the face 62 of the member 12 is advanced toward the face 64 of the member 14 until the sealing flanks 24 and 28 contact the sealing surfaces 30 and 34, respectively, as shown in FIG. 2. 
     When the sealing flanks 24 and 28 make this initial contact with the sealing surfaces 30 and 34, there is a gap between the faces 62 and 64 of the members 12 and 14. As the face 62 is further advanced toward face 64, the sealing surfaces 30 and 34 move toward one another, thereby compressing the seal ring 16. The compression of the seal ring 16 causes some axial movement of the sealing lips 22 and 26 toward each other, which in turn slightly compresses the convolution 38. The spacer 18 prevents excessive compression of the convolution 38. 
     As the seal ring 16 is compressed, the sealing lips 22 and 26 also move radially inward such that the lips are placed in circumferential compression. Thus, by the time the faces 62 and 64 contact, the seal ring 16 has stored elastic force, both from the radial compression of the sealing lips 22 and 26 and the axial compression of the convolution 38. This force is directed toward achieving a tight sealing contact between the sealing flanks 30 and 34 of the seal ring 16 and the sealing surfaces 24 and 28 of the members 12 and 14, respectively. 
     When the two vessels are completely latched together as shown in FIG. 1, pressure is applied through the test port 60 to the seal assembly 10. The outer surface 68 of the seal assembly 10, together with the interior of the convolution 38 (or the groove 48), is pressurized. The pressure acting on the outer surface 68 tends to move the sealing lips 22 and 26 radially inward and to lessen the sealing force on the sealing flanks 30 and 34 of the seal assembly 10. However, the pressure in the groove 48 moves the sealing lips 22 and 26 axially apart, thus maintaining the sealing force and counterbalancing the radial movement of the lips. 
     The amount of pressure energization of the seal ring 16 can be controlled by adjusting the flexibility of the convolution 38, the rigidity of the sealing lips 22 and 26, and the angle of the frustoconical flanks and surfaces. The ratio of the radial inward movement of the sealing lips 22 and 26 to the axial extension of the convolution 38 in each direction must be no more than the tangent of the angle of the frustoconical surface to ensure that the sealing force is not diminished. 
     When the seal assembly 10 has been tested, the members 12 and 14 can be put into service. Internal pressure acting in the seal ring 16 will cause the seal ring 16 to be energized radially outward against the sealing surfaces 24 and 28 while also causing the convolution 38 to move back to its normal position. The convolution 38 is again protected from being crushed by the spacer 18. This configuration will also adjust to compensate for any axial relative movement of the members 12 and 14 due to the resilience of the sealing lips 22 and 26 and the convolution 38. 
     While the invention has been described with respect to a limited number of preferred embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. The appended claims are intended to cover all such modifications and variations which occur to one of ordinary skill in the art.

Summary:
A seal system for sealing between a pair of members is provided wherein a pair of substantially aligned walls on inner faces of the members have internal frustoconical portions. A metal ring includes a pair of lips with external frustoconical portions which sealingly engage the internal frustoconical portions. The metal ring includes at least one convolution between the lips. The convolution permits axial extension of the metal ring upon application of external pressure to the ring.