Abstract:
A locking assembly for seals within inner and outer members. The locking assembly includes a segmented tube with an inner surface that is segmented into a plurality of pieces cut in radial or reversed angles to allow assembling segments in a circumferential groove machined in the internal diameter of a housing. The housing has an internal diameter that is smaller than the outside diameter of the segmented tube. The segments that make up the segmented tubing are locked into place within the housing via a bushing or locking ring that match a profile on the inner surface of the segmented tube to lockingly engage. The bushing and segmented tube retain a lower inner seal in place and support an upper inner seal. The segmented design of the segmented tube allows for smaller diameter members to be used and minimizes leak paths.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to valves and wellhead equipment, and in particular, to an internal locking device for retaining a sealing device within a valve or wellhead equipment. 
     BACKGROUND OF THE INVENTION 
     Typically, equipment designed for normal operation and for high pressures and high temperatures that is used in the oil and gas industry, requires sealing. As new seals are developed in the oil and gas industry to handle higher pressures and higher temperatures, the application of these seals can lead to issues on the overall design of the equipment. Usually internal grooves are machined allowing the assembly of soft seal materials, such as o-rings. However, when installing a tougher more robust seal, more space is typically required to lock the parts together. The size and assembly of the equipment that may result can present challenges in the design of the seal. 
     On certain types of equipment, such as valves, wellheads, subsea christmas trees, tubing spools, or production adapter bases, there may be issues related to the assembly condition of radial seals due to size constraints and load capacities. In a valve bonnet or in a wellhead, for example, a first seal may be installed within a packing gland or wellhead housing. A second seal or backup seal may also typically be installed that is separate from the first seal below. To keep the seal separate, a locking device is installed within the valve bonnet to hold the first seal in place while providing a shoulder or rim for the second seal or backup seal to land. A progressive drilled system is typically used to machine the internal portion of the bonnet or wellhead as this typically works well with soft materials. The locking device thus maintains the first seal in place and provides the second seal a shoulder on which to land. 
     However, in the design described above, separate parts are typically threaded together to form a seal groove and to allow for installation of the locking device. This can lead to secondary leak paths in the sealing system. To attempt avoidance of the secondary leak path, sealing systems are usually designed with larger bores and sizes. Maintaining the same size for lower and upper seals however is difficult without introducing additional leak paths that allow for installation. In certain oil and gas applications, this secondary leak path can be an issue, especially when sealing production fluids and gases. The larger bores lead to larger and heavier equipment which is also costlier. 
     A need exists for a technique to minimize the bore size of equipment via an improved locking device. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the invention, a seal locking assembly includes a segmented tube or ring and a locking ring or bushing that allows for a design of seal grooves that accommodate seals required for certain sizes of the equipment or when mechanical properties of the seals are an issue. 
     In an embodiment of the invention, the segmented tubular, circular ring or tube, has a threaded internal diameter and is segmented with radial or reversed angle cuts that may alternate between adjacent segments to allow assembling each of the segments in a circular or circumferential groove machined in an internal diameter of a housing or adapter. The housing inner diameter is smaller than the outside diameter of the outer L-shaped portion that protrudes radially outward from the segmented tube. The protrusion of the segmented tube corresponds to the groove machined in the housing. After each of the segments are placed inside the internal circumferential groove of the housing, they are locked in place by means of the locking ring with external threads that match the internal threads of the segmented tube. Alternatively, locking may be achieved by a sliding interface. To prevent backing out of the locking ring, a set screw may be installed that traverses through locking ring, segmented tube, and into housing. 
     The assembled locking ring in conjunction with the segmented tube may retain a lower inner seal in place and also create an internal step or shoulder to an upper radial or circular seal. The shoulder provides sufficient support for assembling the seal in a groove located at inner diameter of housing. The shoulder also provides for sealing against devices, such as a stem, that may slidingly engage inner diameter of housing and of the locking ring. 
     This invention can be used in several types of equipment where a circular housing is present and there is a need to lock a seal in place or provide a locking feature. For example, the locking assembly can be used on shafts or stems that have axial movement relative to a housing and/or has a size constraint on seal designs. This invention may be applied for subsea and surface valves and actuators, radial seals of subsea wellhead tools, or any kind of equipment that requires a groove to assemble a radial seal or similar device and a secondary leak path is not allowable or is not desired. 
     Another technical advantage of the invention is that it allows the design of an internal locking mechanism for applications with size constraints, which may lead to reduced size and weight of equipment. For example, the invention allows for the use of radial seals with smaller cross sections or radial seals with hard material designs where the radial size of the equipment is a concern. Smaller and lighter equipment can potentially lead to a reduction in the overall cost of the equipment. Further, the invention can improve the design of other systems, such as subsea X-trees, tubing spools, or production adapter bases, where sizes and weights are limited by the installation and operating condition of the equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 , illustrates a partial sectional view of an embodiment of the seal assembly locating within an outer and inner member, in accordance with the invention; 
         FIG. 2 , illustrates a partial sectional view of the seal locking assembly of  FIG. 1 , in accordance with the invention; 
         FIG. 3 , illustrates a partial sectional view of an embodiment of a seal locking assembly, in accordance with the invention; 
         FIG. 4 , illustrates partially exploded perspective view of the locking assembly of  FIG. 3 , in accordance with the invention; 
         FIG. 5 , illustrates a top view of a segmented tube shown in the embodiment of  FIG. 4 , in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a partial sectional view of an embodiment of a seal assembly  10  of the invention installed between an outer member  12  and an inner member  14 . In this embodiment outer member  12  may be a valve bonnet. Alternatively, outer member may also be a wellhead housing or other type of housing where a seal assembly  10  could be used. In this embodiment, inner member  14  may be a valve stem. Alternatively, inner member  14  may also be a hanger, such as a casing hanger. 
     Referring to  FIG. 2 , an enlarged sectional view of the seal assembly  10  of  FIG. 1  is shown. In this embodiment, outer member or bonnet  12  has a bore  13  that may slidingly engage an outer surface  15  of the inner member or valve stem  14 . O-ring type seal  20  is located at an interface between outer member  12  and an outer surface of seal assembly  10 . Further, O-ring type seal  22  is located at an interface between upper member  16  and an outer surface of seal assembly  10 . An additional seal  24  is located at a top portion of the outer member  12 . Seals  20 ,  22 ,  24  provide sealing at leak paths created by interfaces between parts. A locking device  30  is located at an interface between bore  13  of outer member and outer surface  15  of inner member. Internal locking device  30  may be installed within a groove or recess  32  formed in a housing or packing gland adapter  34 . Locking device  30  may include a cylindrical ring or tube  33  that has an L-shaped outer profile  36  that corresponds to a circumferential groove  32  of housing  34  and an L-shaped inner profile  38  that radially extends over a lower inner seal  40  to retain lower inner seal in place. Cylindrical tube  33  may be segmented and will be described below in further detail. 
     Continuing to refer to  FIG. 2 , a lower inner seal  40  is located between housing and inner member  34 ,  14  and provides a first seal between housing and inner member  34 ,  14 . The locking device  30  also includes a bushing or locking ring  42  for lockingly engaging with the cylindrical tube  33  to maintain it within the housing  34 . Bushing  42  has an inner diameter  44  facing inner member  14  and an outer surface  46  that engages an inner surface  48  of the cylindrical tube  33 . Outer and inner surfaces  46  and  48  may be threaded to allow engagement. The components of the locking device  30  will be described further below in a discussion of  FIGS. 3-5 . A pin or dowel  50  may be used as a stop or for orienting the cylindrical tube  33 , however it could also be omitted as shown in later Figures. To prevent the locking device from backing out of position once installed, a set screw  52  may be installed that traverses corresponding passages in the bushing  42  and cylindrical tube  33 . Set screw  52  may be sheared during disassembly of seal assembly  10 . An upper surface  54  of locking device  30  may then serve to support an upper inner seal  56  that can function as a secondary or backup seal to lower inner seal  40 . The separation created between the lower and upper inner seals  40 ,  56  by the locking device  30  allows decoupling of forces placed on lower and upper inner seals, preventing upper seal from being crushed. 
     Referring to  FIGS. 3-5 , the locking device  30  and its components are described further.  FIG. 3  shows an enlarged view of an embodiment of the locking device  30 . As previously explained L-shaped outer profile  36  of cylindrical tube  33  fits within groove  32  formed in housing  34 . When mated in this fashion, axial movement between the cylindrical tube  33  and housing  34  is restricted. Further, the L-shaped outer profile  36  partially rests on upward facing shoulder  60  of groove  32 , which also acts as a stop. To allow for installation of the cylindrical tube  33  within housing  34  via engagement of the L-shaped outer profile  36  with the groove  32 , without requiring a larger bore size for the housing, the cylindrical tube  33  is segmented as shown in  FIG. 5 . Once tube segments  62  are installed within groove  32 , the bushing  42  can be threaded into locking engagement with the segments  62  making up the cylindrical tube  33 . Other types of locking devices or mechanism may also be used. For example a sliding mechanism having a latch-type lock or a helical mechanism with a spring-type lock may be used. Further, a roller-type with positive lock may also be used to achieve locking engagement. As previously explained threaded engagement is achieved by the threaded outer surface of bushing  42  and threaded inner surface  48  of each of the segments  62  that make up the cylindrical tube  33  as shown in the perspective illustration of  FIG. 4 . As previously mentioned, other types of locking mechanisms, such as a sliding interface, may be used. Machining precision is thus required to ensure alignment of threads of each segment  62 . of in housing. Although the embodiment shown in  FIG. 5  utilizes eight segments  62 , it is understood that more or less segments may be utilized depending on the application and size of the cylindrical tube  33 . 
     Referring to  FIG. 5 , a top view of the cylindrical tube  33  shows how the tube segments  62  are arranged to allow for their installation within housing  34  ( FIG. 3 ), tube segments are cut in a novel way to allow for such installation. In this embodiment, a first tube segment  63  is cut in a novel fashion, with a first cut surface  64  extending radially outward towards inner diameter  66  of cylindrical tube  33 . A second cut surface  68  is a mirror image of the first cut surface  66  about an axis Ax. First and second cuts on first tube segment  63  give segment a wedge shape, with a wider width at inner diameter  66  than at outer diameter. The opposite is true of an adjacent second tube segment  70 , which has a first cut surface  72  that corresponds to second cut surface  68  on the first tube segment  63 . Thus, first cut surface  72  on second tube segment  70  extends radially inward towards inner diameter  66  of cylindrical tube  33 . On second tube segment  70 , second cut surface  74  is a mirror image of first cut surface  72  about an axis Ay. As opposed to first tube segment  63 , second and adjacent tube segment has a wider width at outer diameter than at inner diameter  66 . Each cut surface for each tube segment is cut at an angle ⊖ which may vary from between about 10 to 70 degrees. In the embodiment shown, an angle ⊖ of 30 degrees is utilized. It is this novel segmented cylindrical tube  33  that allows locking device  30  to be advantageously installed within housing  34 . This advantageously avoids creating an additional leak path which would result from needing to use an additional removable part above a one-piece-type tube to allow for installation. 
     During installation, referring to  FIG. 2 , the housing or packing gland adapter  34  is landed in outer member  12 , such as a wellhead housing or valve bonnet. The lower inner seal  40 , which may be elastomeric or metal-to-metal, may then be mounted in a recess in housing  34 . Tube segments  62  ( FIG. 4 ) making up the cylindrical tube  33  are then installed within housing  34  such that mating occurs with L-shaped outer profile  36  of each segment with groove  32  formed in the housing  34 . Once installed, the tube segments  62  keep the inner lower seal  40  in place. The tube segments  62  are installed such that alternating angled cut surfaces correspond with each other. Bushing or locking ring  42  ( FIG. 3 ) may then be threaded onto threads formed on tube segments  62  to lock segmented rings in place. Alternatively, a latch-type lock may slidingly lock the segments  62  in place or a helical mechanism with a spring-type lock may be used to lock the segments in place. Further, a roller-type with positive lock may also be used to achieve locking engagement of the segments  62 . Set screws  52  ( FIG. 2 ) can be installed to prevent backing out of bushing  42 . Once busing  42  is installed, upper surface of bushing and tube segments  62  form an upward facing shoulder  54  ( FIG. 3 ) for landing upper inner seal  56  as well. 
     Applications for this segmented tube feature of the invention can include installation in a bonnet of actuator valves, in a wellhead, or any application where one would want to minimize leak paths to the outside. Further, the invention allows for limitation of casing or bonnet sizes and eliminates drilling from outer to inner diameters. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. These embodiments are not intended to limit the scope of the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.