Abstract:
Methods and devices for preventing temperature and pressure extrusion failure in o-ring seal assemblies. One embodiment employs a bore in the plug so that the thin wall of the plug flexes outward at high pressures to partially fill the gap between the chamber member and the plug where the o-ring is located, thereby preventing the o-ring from extruding through the narrowed gap. A second embodiment utilizes a plug of a higher coefficient of thermal expansion than the chamber member that expands outward slightly at high temperatures, thus partially filling the gap. A third embodiment secures the o-ring in the gap between a backup ring and a retaining ring, and the backup ring has a higher coefficient of thermal expansion than the plug and chamber member. At high temperatures the backup ring expands to partially fill the gap. Additional embodiments are created by combining these three embodiments.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to methods and devices that can be used alone or in combination to prevent extrusion failure of o-ring seal assemblies that are employed in high temperature and high pressure environments, such as the type of environment found down hole in a gas or oil well. Each of these methods and devices functions to reduce the gap between the plug and its associated channel member where the o-ring is located so that the when the o-ring becomes more pliable under high pressure and high temperature conditions, the gap is sufficiently narrowed to prevent the o-ring from extruding through the gap and thus preventing the failure of the o-ring. 
   2. Description of the Related Art 
   Extrusion failure of O-rings in o-ring assemblies occurs when the contained pressurized fluid forces the o-ring to extrude through the gap that exists between the adjoining parts of the seal assemblies, specifically between the plug and the chamber member. Common o-ring materials extrude more readily at very high temperatures because the rubber based material becomes weaker when very hot. Under high pressure and high temperature, an o-ring becomes more pliable and tends to flow or extrude via the gap. When this happens, the o-ring fails and the seal is lost. 
   Because the types of O-rings employed at high temperature and high pressure are very expensive, by reducing the failure of o-ring assemblies, the present invention reduces the costs associated with replacing the o-ring. These costs including the actual cost of the replacement o-ring and all of the other costs associated with replacing the o-ring. The other cost associated with replacing the o-ring can amount to much more that the cost of the o-ring itself. Depending on the application where the o-ring seal assembly is employed, these other replacement costs can include lost production time, cost of equipment needed to pull the failed assembly out of the production well, cost of manpower required to pull the failed assembly, etc. 
   Very high pressures increase the probability of extrusion failure of the o-ring for two reasons: the driving force or pressure to extrude the material is greater, and the gap between the adjoining parts increases at very high pressures in commonly used o-ring seal assemblies. In commonly used o-ring seal assemblies, as pressure in the vessel increases, the inside diameter of the vessel or chamber member increases. However, as pressure in the vessel increases, the outside diameter of the plug remains nearly constant. This results in an increasing gap between the plug and chamber member which can lead to o-ring extrusion failure. To reduce the probability of extrusion failure, it is desirable to maintain gap dimensions between the plug and chamber member near zero at very high temperatures and pressures. 
   Current methods of maintaining gap dimensions at near zero have generally focused on filling the gap with a non-metallic backup ring, such as Teflon, in order to try to place a barrier between the o-ring and the gap for the purpose of preventing the o-ring from extruding around the backup ring and then through the gap. None of the current methods have addressed the problem by utilizing the increasing temperature and pressure to assist in reducing the gap. 
   The present invention addresses this problem by employing three different methods and devices, each of which can be used alone or in combination, to reduce the gap between the plug and chamber member at high temperature and pressure and thereby prevent o-ring failure in o-ring seal assemblies. 
   SUMMARY OF THE INVENTION 
   The present invention employs three methods and devices for preventing extrusion failure in o-ring seal assemblies that are used in high temperature and high pressure environments, such as the type of environment experienced down hole in oil and gas wells. These methods and devices can be used alone or in combination. The preferred embodiment of the invention creates a bore in the plug as large as possible so that the wall of the plug is sufficiently thin to allow the wall to expand outward slightly when the bore of the plug experiences high pressure. Although not part of the invention, the chamber member is normally provided with an opening there through to allow pressurized fluid to enter the chamber member and reach the plug. As the pressure inside the o-ring assembly increases, the wall of the plug expands outward so that the outside diameter (OD) of the plug partially fills the gap created between the chamber member and the plug. This narrowing of the gap helps to prevent the o-ring from extruding through the gap as the pressure inside the o-ring assembly increases. 
   A second embodiment of the present invention utilizes a plug and chamber member constructed of different types of materials. The material from which the plug is created has a higher coefficient of thermal expansion than the material from which the chamber member is constructed. Use of these two different types of materials allows the differential thermal expansion of the plug relative to the chamber member to cause the plug to increase in diameter very rapidly with an increase in temperature as the chamber expands less under the influence of both pressure and temperature. In this embodiment, as the temperature of the seal assembly increases, the plug expands outward to a larger degree than the outward expansion of the chamber member, thus narrowing the gap that is created between the chamber member and the plug. Similar to the preferred embodiment, this narrowing of the gap helps to prevent the o-ring from extruding through the gap as the temperature and pressure of the o-ring assembly increases. 
   A third embodiment of the present invention utilizes a backup ring for the o-ring. That backup ring is constructed of material that has a higher coefficient of expansion than the materials employed in the construction of the plug and chamber member. A retaining disc is provided attached to the plug via one or more bolts or other suitable fastening means so that the o-ring is held between the backup ring and the retaining disc. As the temperature of the o-ring assembly increases, the backup ring expands more rapidly than the plug and the chamber member, thereby causing the backup ring to expand and thereby effectively narrowing a gap that is created between the backup ring and the chamber member and narrowing a second gap that is created between the backup ring and the plug. As with the second embodiment, this narrowing of the gaps helps to prevent the o-ring from extruding through the gaps as the temperature of the o-ring assembly increases. 
   A fourth embodiment is created by combining the preferred and second embodiments. A fifth embodiment is created by combining the preferred and third embodiments. A sixth embodiment is created by combining the second and third embodiments. And a seventh embodiment is created by combining the preferred, second and third embodiments. Embodiments 5 and 7 require that at least one hole be provided in the retaining disc to allow pressurization of the bore of the plug, as taught in the preferred embodiment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view of an o-ring seal assembly employing a preferred embodiment of the present invention for preventing extrusion failure of o-ring seal assemblies. 
       FIG. 2  is a cross sectional view of an o-ring seal assembly employing a second embodiment of the present invention. 
       FIG. 3  is a cross sectional view of an o-ring seal assembly employing a third embodiment of the present invention. 
       FIG. 4  is a cross sectional view of an o-ring seal assembly employing a combination of the preferred and second embodiments of the present invention. 
       FIG. 5  is a cross sectional view of an o-ring seal assembly employing a combination of the preferred and third embodiments of the present invention. 
       FIG. 6  is a cross sectional view of an o-ring seal assembly employing a combination of the second and third embodiments of the present invention. 
       FIG. 7  is a cross sectional view of an o-ring seal assembly employing a combination of the preferred, second and third embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The Invention 
   Referring now to the drawings and initially to  FIG. 1 , there is illustrated a preferred embodiment  10  of the present invention employing in an o-ring seal assembly  12  for preventing extrusion failure of the o-ring seal assembly under increased pressure and temperature conditions, such as for example the conditions that would be experienced by a tubing string located at the bottom of an oil or gas well. 
   As shown in all of the drawings, a typical o-ring seal assembly  12  consists of a chamber member  14  held in sealing arrangement with a plug  16  and its associated collar  18  via an o-ring  20  that is located in a gap  22  that exists between an inside surface  24  of the chamber member  14  and an outside surface  26  of the plug  16 . As typical with o-ring seal assemblies  12 , the collar  18  is provided with female threads  28  that engage male threads  30  provided on the chamber member  14  as a means of holding the plug  16  within the chamber member  14 , and the chamber member  14  is provided with an opening  32  extending through a wall  34  of the chamber member  14  to allow pressure to enter the chamber member  14  and reach the plug  16 . 
   Referring again to  FIG. 1 , the preferred embodiment  10  creates a bore  36  in the plug  16  as large as possible so that a wall  38  of the plug  16  surrounding the bore  36  is sufficiently thin to allow the wall  38  to expand outward slightly when the bore  36  of the plug  16  experiences high pressure. As the pressure inside the o-ring assembly  12  increases, the wall  38  of the plug  16  expands outward so that the outside surface  26  or outside diameter (OD) of the plug  16  partially fills the gap  22  that is created between the chamber member  14  and the plug  16 . This narrowing of the gap  22  helps to prevent the o-ring  20  from extruding through the gap  22  as the pressure inside the o-ring assembly  12  increases. 
   Referring now to  FIG. 2 , there is illustrated an o-ring seal assembly  12 A employing a second embodiment  10 A of the present invention for preventing extrusion failure of the o-ring seal assembly  12 A under increased pressure and temperature conditions. The second embodiment  10 A utilizes a plug  16 A and chamber member  14 A constructed of different types of materials with the material from which the plug  16 A is created having a higher coefficient of thermal expansion than the material from which the chamber member  14 A is constructed. The materials used for constructing the chamber member  14 A and the plug  16 A preferably are metals. Use of these different types of materials allows the differential thermal expansion of the plug  16 A relative to the chamber member  14 A to cause the plug  16 A to increase in diameter very rapidly with an increase in temperature as the chamber member  14 A increases less under the influence of both pressure and temperature. This creates a situation where the plug  16 A expands outward slightly relative to the chamber member  14 A when the o-ring assembly  12 A experiences high temperature. Because with increasing temperature the plug  16 A expands outward to a larger degree than the outward expansion of the chamber member  14 A, this narrows the gap  22 A that is created between the chamber member  14 A and the plug  16 A. Similar to the preferred embodiment  10 , this narrowing of the gap  22 A helps to prevent o-ring  20 A from extruding through the gap  22 A as the temperature and pressure of the o-ring seal assembly  12 A increases. 
   Referring now to  FIG. 3 , there is illustrated an o-ring seal assembly  12 B employing a third embodiment  10 B of the present invention for preventing extrusion failure of the o-ring seal assembly  12 B under increased pressure and temperature conditions. The third embodiment  10 B utilizes a backup ring  40  for an o-ring  20 B, and that backup ring  40  is constructed of material that has a higher coefficient of expansion than the materials employed in the construction of its associated plug  16 B and chamber member  14 B. As previously described for chamber member  14 A and plug  16 A, the material used for constructing the backup ring  40  will preferably be metal. A retaining disc  42  is provided attached to the plug  16 B via one or more bolts  44  so that the o-ring  20 B is held between the backup ring  40  and the retaining disc  42 . As the temperature of the o-ring assembly  12 B increases and the backup ring  40  expands more rapidly than the plug  16 B and the chamber member  14 B, this causes the backup ring  40  to narrow a first gap  22 B′ that is created between the backup ring  40  and the chamber member  14 B and a second gap  22 B″ that is created between the backup ring  40  and the plug  16 B. As with the second embodiment  10 A, this narrowing of the gaps  22 B′ and  22 B″ helps to prevent the o-ring  20 B from extruding through the gaps  22 B′ and  22 B″ as the temperature of the o-ring assembly  12 B increases. 
   Referring to  FIG. 4 , there is illustrated an o-ring seal assembly  12 C employing a fourth embodiment  10 C of the present invention for preventing extrusion failure of the o-ring seal assembly  12 C under increased pressure and temperature conditions. The fourth embodiment  10 C is a combination of the previously described preferred embodiment  10  and the previously described second embodiment  10 A. Specifically, the fourth embodiment  10 C employs a bore  36 C of plug  16 C as large as possible so that a wall  38 C of the plug  16 C expands outward slightly when the bore  36 C of the plug  16 C experiences high pressure. Also, the fourth embodiment  10 C has the plug  16 C and its associated chamber member  14 C constructed of different types of materials so the material from which the plug  16 C is created has a higher coefficient of thermal expansion than the material from which the chamber member  14 C is constructed. The combination of features of this fourth embodiment  10 C result in a narrowing of the gap  22 C between the chamber member  14 C and the plug  16 C, thereby helping to prevent o-ring  20 C from extruding through the gap  22 C as the temperature and pressure of the o-ring seal assembly  12 C increases. 
   Referring to  FIG. 5 , there is illustrated an o-ring seal assembly  12 D employing a fifth embodiment  10 D of the present invention for preventing extrusion failure of the o-ring seal assembly  12 D under increased pressure and temperature conditions. The fifth embodiment  10 D is a combination of the previously described preferred embodiment  10  and the previously described third embodiment  10 B. Specifically, the fifth embodiment  10 D employs a bore  36 D in its plug  16 D as large as possible so that a wall  38 D of the plug  16 D expands outward slightly when the bore  36 D of the plug  16 D experiences high pressure. Also, the fifth embodiment  10 D employs a backup ring  40 D for its o-ring  20 D and that backup ring  40 D is constructed of material that has a higher coefficient of expansion than the materials employed in the construction of the plug  16 D and chamber member  14 D. A modified retaining disc  42 D is also provided attached to the plug  16 D via one or more bolts  44  so that the o-ring  20 D is held between the backup ring  40 D and the modified retaining disc  42 D. This modified retaining disc  42 D is provided with at least one opening  46  extending through the disc  42 D in order to allow pressurization of the bore  36 D of the plug  16 D. The combination of features of this fifth embodiment  10 D result in a narrowing of the first and second gaps  22 D′ and  22 D″ located respectively between the backup ring  40 D and the chamber member  14 D and between the backup ring  40 D and the plug  16 D, thereby helping to prevent o-ring  20 D from extruding through the gaps  22 D′ and  22 D″ as the temperature and pressure of the o-ring seal assembly  12 D increases. 
   Referring to  FIG. 6 , there is illustrated an o-ring seal assembly  12 E employing a sixth embodiment  10 E of the present invention for preventing extrusion failure of the o-ring seal assembly  12 E under increased pressure and temperature conditions. The sixth embodiment  10 E is a combination of the previously described second embodiment  10 A and the previously described third embodiment  10 B. Specifically, the sixth embodiment  10 E employs a plug  16 E and chamber member  14 E constructed of different types of materials so the material from which the plug  16 E is created has a higher coefficient of thermal expansion than the material from which the chamber member  14 E is constructed Also, the sixth embodiment  10 E employs a backup ring  40 E for its associated o-ring  20 E and that backup ring  40 E is constructed of material that has a higher coefficient of expansion than the materials employed in the construction of the plug  16 E and chamber member  14 E. A retaining disc  42 E is also provided attached to the plug  16 E via one or more bolts  44  so that the o-ring  20 E is held between the backup ring  40 E and the retaining disc  42 E. The combination of features of this sixth embodiment  10 E result in a narrowing of the first and second gaps  22 E′ and  22 E″ located respectively between the backup ring  40 E and chamber member  14 E and between the backup ring  40 E and the plug  16 E, thereby helping to prevent o-ring  20 E from extruding through the gaps  22 E′ and  22 E″ as the temperature and pressure of the o-ring seal assembly  12 E increases. 
   Referring to  FIG. 7 , there is illustrated an o-ring seal assembly  12 F employing a seventh embodiment  10 F of the present invention for preventing extrusion failure of the o-ring seal assembly  12 F under increased pressure and temperature conditions. The seventh embodiment  10 F is a combination of the previously described preferred embodiment  10 , the previously described second embodiment  10 A, and the previously described third embodiment  10 B. Specifically, the seventh embodiment  10 F employs a bore  36 F in its plug  16 F as large as possible so that a wall  38 F of the plug  16 F expands outward slightly when the bore  36 F of the plug  16 F experiences high pressure. The seventh embodiment  10 F also has its plug  16 F and chamber member  14 F constructed of different types of materials so the material from which the plug  16 F is created has a higher coefficient of thermal expansion than the material from which the chamber member  14 F is constructed Additionally, the seventh embodiment  10 F employs a backup ring  40 F for its o-ring  20 F, and that backup ring  40 F is constructed of material that has a higher coefficient of expansion than the materials employed in the construction of the plug  16 F and chamber member  14 F. A modified retaining disc  42 F is also provided attached to the plug  16 F via one or more bolts  44  so that the o-ring  20 F is held between the backup ring  40 F and the modified retaining disc  42 F. As with the modified retaining disc  42 D, this modified retaining disc  42 F is provided with at least one opening  46  extending through the disc  42 F in order to allow pressurization of the bore  36 F of the plug  16 F. The combination of features of this seventh embodiment  10 F result in a narrowing of the first and second gaps  22 F′ and  22 F″ located respectively between the backup ring  40 F and chamber member  14 F and between the backup ring  40 F and the plug  16 F, thereby helping to prevent o-ring  20 F from extruding through the gaps  22 F′ and  22 F″ as the temperature and pressure of the o-ring seal assembly  12 F increases. 
   Although the present invention has been described for use in association with a gas or oil well, the invention is not so limited and can be used in other types of high pressure and high temperature environments where o-ring seal assemblies  12  are needed. 
   Also, it is preferable that the chamber members  12 ,  12 A,  12 B,  12 C,  12 D,  12 E, and  12 F; the plugs  16 ,  16 A,  16 B,  16 C,  16 D,  16 E, and  16 F; and the backup rings  40 ,  40 D,  40 E and  40 F are each constructed of material that is metal so that the resulting o-ring seal assemblies  12 ,  12 A,  12 B,  12 C,  12 D,  12 E, and  12 F are sufficiently strong to withstand the high temperature and high pressure environments for which the embodiments of the present invention  10 ,  10 A,  10 B,  10 C,  10 D,  10 E, and  10 F were designed. 
   While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for the purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.