Abstract:
A sealing ring assembly for sealing a joint between two members ( 20, 22 ). An annular sealing ring  28  abuts an annular backup ring ( 38, 44 ) of substantially the same diameter. The annular backup ring is split to permit radial expansion and has a greater thickness on its outer periphery than on its inner periphery. When the joint being sealed ( 24 ) is under high pressure, the sealing ring urges the backup ring to expand radially to cover any gap ( 32 ) between the members being sealed, maintaining the seal, even under high temperature conditions, and preventing the sealing ring from extruding into the gap.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under contract number DAAH01-93-C-R243 awarded by the United States Army. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention pertains to a sealing ring assembly. More particularly, the present invention pertains to a sealing ring assembly including an annular sealing ring and an annular backup ring positioned adjacent the annular sealing ring. The annular backup ring is split to permit radial expansion and has a greater thickness on its outer periphery than on its inner periphery. As a consequence, when the sealing ring assembly is used to seal a joint between two members, such as pipes, in a high pressure application, the annular sealing ring presses against the annular backup ring, causing the annular backup ring to expand radially to cover any gap that might exist between the two members, and so inhibiting extrusion of the sealing ring into such gap. 
     BACKGROUND OF THE INVENTION 
     Annular sealing rings, often referred to o-rings, are frequently utilized to provide a fluid seal between two members, such as two pipes, threaded or otherwise joined together. In the absence of a sealing ring, fluid within the pipes might leak through gaps at the joint at which the two members are connected. 
     Sealing rings are commercially available and are often made of a resilient, rubber-like material, for example rubber, ethylene, or propylene. Such materials are commercially available under the trademarks VITON and KALREZ. These scaling rings provide satisfactory sealing at comparatively low pressures and temperatures. However, at higher pressures and temperatures, for example pressures in excess of 3400 psia and temperatures in excess of 300° F., these sealing rings do not always work satisfactorily. The high temperature might cause expansion of the members being joined, with resultant expansion of any gaps at the joint. The high temperature also might soften the material of the sealing ring. The high pressure then might result in extrusion of the sealing ring into the enlarged gaps. This can result in damage to the sealing ring. When the high pressure and high temperature condition ends, the members being joined contract, but any extruded portion of the scaling ring might not withdraw from the previously enlarged gap. In that event, the sealing ring may be damaged, and when the high pressure and high temperature condition is next experienced, the damaged sealing ring may not provide an adequate seal. This problem is exacerbated with each cycle of high pressure and high temperature. 
     SUMMARY OF THE INVENTION 
     The present invention is a sealing ring assembly for sealing a joint between two members. An annular backup ring is positioned downstream of an annular sealing ring of substantially the same diameter. The annular backup ring is split to permit radial expansion and has a greater thickness on its outer periphery than on its inner periphery. When the joint being sealed is under high pressure, the sealing ring urges the backup ring to expand radially to cover any gap between the members being sealed, maintaining the seal even under high temperature conditions, and preventing the sealing ring from extruding into the gap. The sealing ring is made of a resilient rubber-like material such as rubber, ethylene or propylene, for example a VITON™ or KALREZ™ material, while the backup ring is preferably made of a strong, rigid material, such as a metal, for example aluminum, titanium or steel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and advantages of the present invention are more apparent from the following detailed description of the claims, particularly when considered in conjunction with the accompanying drawings. In the drawings: 
     FIG. 1 is a fragmentary elevational view of two pipe members coupled together in a joint incorporating a sealing ring, assembly in accordance with the present invention; 
     FIGS. 2A,  2 B, and  2 C are fragmentary sectional views, taken along line  2 — 2  of FIG. 1, illustrating one form of a conventional sealing ring assembly under different conditions; 
     FIGS. 3A,  3 B and  3 C are fragmentary sectional views, taken along, line  2 — 2  of FIG. 1, illustrating, another form of a conventional sealing ring, assembly under different conditions; 
     FIGS. 4A and 4B are fragmentary sectional views, taken along, line  2 — 2  of FIG. 1, illustrating a first embodiment of a sealing ring assembly in accordance with the present invention under different conditions; 
     FIGS. 5A and 5B are fragmentary plan views of an annular backup ring in accordance with the present invention under different conditions and are taken, respectively, in the direction of arrow  5 A in FIG.  4 A and in the direction of arrow  5 B in FIG. 4B; 
     FIGS. 6A and 6B are fragmentary elevational views of the annular backup ring under different conditions and are taken, respectively, in the direction of arrow  6 A in FIG.  4 A and in the direction of arrow  6 B in FIG. 4B; and 
     FIGS. 7A and 7B are fragmentary sectional views, taken along line  2 — 2  of FIG. 1, illustrating a second embodiment of a sealing ring assembly in accordance with the present invention under different conditions. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a first pipe member  20  having one end inserted within one end of a second pipe member  22 . The area adjacent junction  24  of pipes  20  and  22  thus constitutes a pipe joint. FIG. 2A depicts a first form of a conventional sealing ring assembly which might be utilized to seal joint  24 . Within outer pipe  22 , inner pipe  20  terminates in a gland or cavity  26  within which a sealing ring  28  is provided. In the illustrative example of FIG. 2A, inner pipe  20  and outer pipe  22  include threaded sections  30  which threadingly mate to join the inner pipe and outer pipe together; however, the sealing ring assembly of the present invention is usable at junctions or joints of members, including pipe members, that are not threaded. 
     Although the outer diameter of inner pipe  20  and the inner diameter of outer pipe  22  are selected such that the two pipes fit together snugly at joint  24 , nevertheless, a slight gap or crevice  32  may exist at joint  24 , permitting fluid flow through threaded sections  30  to the outside of the pipes. Sealing ring  28  is provided within cavity  26  to inhibit fluid flow from the interior of pipes  20  and  22  through gap  32  to the outside of the pipes, as well as fluid flow through the gap in the opposite direction. 
     If the fluid within pipes  20  and  22  is at a high pressure, for example a pressure in excess of 3400 psia, that high pressure can deform sealing ring  28  by compressing it. A portion  34  of sealing ring  28  may then extrude into gap  32 , damaging sealing ring  28 , as illustrated in FIG.  2 B. When the high pressure condition ends, nothing withdraws extruded portion  34  from gap  32 . When the high pressure condition returns, further damage may occur to sealing ring  28 . 
     If the fluid within pipes  20  and  22  is at a high temperature, for example a temperature in excess of 300° F., then pipes  20  and  22  are likely to expand. If pipes  20  and  22  do not have substantially the same coefficient of thermal expansion, then gap  32  may change size. If the gap narrows, sealing ring  28  is likely to be further damaged. If the gap enlarges, the high pressure may force more of sealing ring  28  to extrude into gap  32 . In addition, the high temperature might soften sealing ring  28 , increasing the likelihood and amount of extrusion of the sealing ring into gap  32 . Consequently, the combination of the high temperature and high pressure can result in significant damage to sealing ring  28 , as depicted in FIG.  2 C. 
     The damage is exacerbated if the high pressure, high temperature condition at joint  24  cycles on and off. When the pressure decreases, there is nothing to cause extruded portion  34  to withdraw from crevice  32 . When the temperature decreases, pipes  20  and  22  contract, compressing the extruded portion  34 . Repeated cycling of the high pressure, high temperature condition may result in further damage to sealing ring  28 . 
     FIG. 3A illustrates a conventional manner of overcoming this problem by positioning a backup ring  36  in cavity  26 , between scaling ring  28  and downstream wall  37  of cavity  26 . In the low pressure, low temperature condition depicted in FIG. 3A, sealing ring  36  prevents sealing ring  28  from entering crevice  32 . FIG. 3B illustrates such a sealing ring assembly subjected to high pressure within pipes  20  and  22 . The high pressure may force some extrusion of sealing ring  28  into the gap between backup ring  36  and the wall of pipe  22 , and possibly into gap  32 . If a high temperature causes gap  32  to enlarge, a portion of sealing ring  28  may extrude past backup ring  36  into gap  32 , as depicted in FIG.  3 C. Thus, a conventional backup ring, such as backup ring  36 , does not adequately overcome the problem. 
     FIGS. 4A and 4B depict a first embodiment of a sealing ring assembly in accordance with the present invention which overcomes this problem in conventional sealing ring assemblies. As depicted in FIG. 4A, a backup ring  38  is positioned in cavity  26 , between sealing ring  28  and downstream wall  37  of cavity  26 . Whereas backup ring  36 , depicted in FIGS. 3A,  3 B and  3 C, has a substantially rectangular cross-section, the cross-section of backup ring  38  depicted in FIGS. 4A and 4B, is substantially straight on its downstream surface facing wall  37  of cavity  26  and arcuate on its upstream surface facing sealing ring  28 . Preferably, the curvature of the arcuate surface of backup ring  38  substantially matches the curvature of the cross section of sealing ring  28 . 
     Rather than being an unbroken ring, backup ring  38  has a split in it. Consequently, as illustrated in FIG. 4B, when the sealing ring assembly including split backup ring  38  is subjected to a high pressure and high temperature, scaling ring  28  compresses and pushes against backup ring  38 , forcing backup ring  38  to enlarge circumferentially. Consequently, backup ring  38  moves radially outward to cover crevice  32 , preventing sealing ring  28  from entering the crevice. The split permits backup ring  38  to enlarge as it is forced radially outwardly by sealing ring  28 . 
     FIG. 5A depicts the circumferentially outer surface of backup ring  38  under the low pressure and low temperature conditions of FIG. 4A, when backup ring  38  is not enlarged, and is taken in the direction of arrow  5 A in FIG.  4 A. FIG. 6A is an elevational view illustrating the surface of backup ring  38  that faces downstream wall  37  in this condition and is taken in the direction of arrow  6 A in FIG.  4 A. Portions  38   a  and  38   b , adjacent split  40 , abut at the split, as illustrated in FIGS. 5A and 6A. 
     FIG. 5B illustrates the outer circumferential surface of backup ring  38  under the high pressure and high temperature conditions of FIG. 4B when the backup ring is enlarged, and is taken in the direction of arrow  5 B in FIG.  4 B. FIG. 6B is an elevational view illustrating the surface of backup ring  38  that faces downstream wall  37  under the high pressure and high temperature condition and is taken in the direction of arrow  6 B in FIG.  4 B. The pressure exerted on the arcuate surface of backup ring  38  forces the backup ring to expand radially, and so portions  38   a  and  38   b  of backup ring  38  move apart at split  40  as illustrated in FIGS. 5B and 6B. As a consequence, as depicted in FIG. 4B, backup ring  38  moves radially outwardly to abut the inner surface of outer pipe  22 , positioning the backup ring to cover gap  32 , thereby sealing the crevice and preventing extrusion of sealing ring  28  into the crevice. 
     Preferably, split  40  is angled with respect to the two faces of backup ring  38 , as depicted in FIGS. 5A and 6A. The split preferably forms an acute angle α with the downstream annular surface of backup ring  38  as depicted in FIG. 5A, more preferably an angle of less than 10°, and most preferably an angle in the order of about 5°. As a result, even when backup ring  38  is expanded, resulting in an area  42  between portions  38   a  and  38   b , as illustrated in FIGS. 5B and 6B, still there is no gap through the backup ring, and so no path for ready extrusion of a portion of sealing ring  28 . 
     FIGS. 7A and 7B illustrate an alternative embodiment of a backup ring  44  differing from annular backup ring  38  by having a substantially triangular cross section. In a preferred embodiment the substantially triangular cross section has angles of 30°, 60°, and 90°. 
     Following are test data regarding tests on sealing ring assemblies of the prior art and in accordance with the present invention. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 Sealing 
                   
                 Gap 
                   
                   
                   
               
               
                 Ring 
                 Backup Ring 
                 Width 
                 Temper- 
                 Pressure 
               
             
          
           
               
                 Material 
                 Material 
                 Design 
                 (inches) 
                 ature (° F.) 
                 (psia) 
                 Failure 
               
               
                   
               
               
                 Viton 
                 None 
                 — 
                 0.008 
                 300 
                 3250 
                 Yes 
               
               
                 884-75 
               
               
                 Viton 
                 None 
                 — 
                 0.010 
                 300 
                 3250 
                 Yes 
               
               
                 884-75 
               
               
                 Viton 
                 Teflon 
                 Rectangular; 
                 0.010 
                 300 
                 3600 
                 No 
               
               
                 884-75 
                   
                 no split 
               
               
                 Viton 
                 Teflon 
                 Rectangular; 
                 0.008 
                 314 
                 4000 
                 No 
               
               
                 884-75 
                   
                 no split 
               
               
                 Viton 
                 Teflon 
                 Rectangular; 
                 0.010 
                 400 
                 3250 
                 No 
               
               
                 884-75 
                   
                 no split 
               
               
                 Viton 
                 Teflon 
                 Rectangular; 
                 0.010 
                 500 
                 3250 
                 Yes 
               
               
                 884-75 
                   
                 no split 
               
               
                 Kalrez 
                 Teflon 
                 Rectangular; 
                 0.008 
                 275 
                 3200 
                 Yes 
               
               
                 1045 
                   
                 no split 
               
               
                 Kalrez 
                 Alumi- 
                 Rectangular; 
                 0.010 
                 510 
                 3400 
                 Yes 
               
               
                 1045 
                 num 
                 split 
               
               
                 Kalrez 
                 Alumi- 
                 Arcuate 
                 0.010 
                 505 
                 2800 
                 Yes 
               
               
                 1045 
                 num 
                 10° split 
               
               
                 Viton 
                 Alumi- 
                 Arcuate 
                 0.010 
                 520 
                 3400 
                 No 
               
               
                 747-75 
                 num 
                 5° split 
               
               
                 Kalrez 
                 Alumi- 
                 Arcuate 
                 0.010 
                 520 
                 3200 
                 After 
               
               
                 1045 
                 num 
                 5° split 
                   
                   
                   
                 test 
               
               
                   
                   
                   
                   
                   
                   
                 over 
               
               
                   
                   
                   
                   
                   
                   
                 and ring 
               
               
                   
                   
                   
                   
                   
                   
                 cool 
               
               
                 Viton 
                 Alumi- 
                 Arcuate 
                 0.010 
                 520 
                 3200 
                 No 
               
               
                 747-75 
                 num 
                 5° split 
               
               
                   
               
             
          
         
       
     
     The Teflon backup rings had no split, but because of the plastic nature of Teflon, under the heat and pressure of the test conditions the Teflon flowed or extruded into the gap, thus damaging the backup rings. Consequently, even when there was no failure, the Teflon backup rings were not satisfactory. 
     Although the present invention has been described with reference to preferred embodiments, rearrangements, alterations and substitutions can be made, and still the result will be within the scope of the invention.