Patent Publication Number: US-9850730-B2

Title: Ram blowout preventer piston rod subassembly

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional Application Ser. No. 62/025,700 filed Jul. 17, 2014, titled “Ram Blowout Preventer Operator Piston Rod Subassembly” the full disclosure of which is hereby incorporated herein by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     This disclosure relates generally to blowout preventers used in hydrocarbon drilling and production operations. In particular, the disclosure relates to systems and methods to facilitate assembly, disassembly and on-site maintenance of a piston rod subassembly of a blowout preventer. 
     2. Description of Related Art 
     In hydrocarbon drilling and production operations, blowout preventers can be used to block the flow of fluids through a wellbore by having rams that close across the wellbore. The rams can either seal an empty wellbore, or seal the wellbore around a drillpipe, polished rod, or other tools or equipment that is within the wellbore. The ram may alternately be a shear ram, which, when activated, moves to engage and physically shear any member in the wellbore. The rams can alternately be gripping rams that can engage the tubular, polished rod, or other equipment in the well to prevent axial or rotational movement of such tubular, polished rod, or other equipment in the well. 
     The piston rod subassembly of some current blowout preventers can be a single member with both a piston rod and tail rod that are fully formed of expensive alloys to achieve the desired strength of the piston rod, as the rams and piston rods can be subjected to significant forces and an extreme environment during operation of the blowout preventer. 
     In some current systems where the piston rod assembly is formed of multiple members, the connection between the members can be preloaded so that the members do not work loose during operation of the blowout preventer. However, the preload on the connection between the members of such current systems requires that the components be sent off-site in order to separate the members for repair, replacement, or salvage. 
     SUMMARY OF THE DISCLOSURE 
     Embodiments of this disclosure provide a piston rod subassembly for use in a subsea or surface blowout preventer that allows for a simplified assembly and disassembly process that can take place on site, improving the ability to make repairs and salvage parts. Systems and methods described herein also save on material costs compared to some current piston rod assemblies that have piston rod subassemblies fully formed of expensive alloys. The piston rod assembly described herein provides the piston rod as a separate member so that the piston can be formed of a less costly material. 
     Systems and methods described herein also provide for a preloaded piston rod connection that does not require a fixture for assembly or disassembly since preload is induced when the preload ring fasteners are secured with a hand tool. The preload can be broken directly during disassembly by removing preload ring fasteners with the hand tool. This allows for repairs to be made on site, such as offshore, and makes it easier to salvage parts without additional operations such as machining. 
     In an embodiment of this disclosure, a piston rod subassembly for use in a blowout preventer includes a piston rod having a rod threaded interface and having a rod shoulder on an outer diameter of the piston rod. A preload ring has a ring threaded interface for engaging the rod threaded interface to couple the piston rod to the preload ring. A protruding end surface of the piston rod protrudes past an end face of the preload ring when the piston rod is coupled to the preload ring and the rod shoulder engages a ring shoulder of the preload ring. A piston has a pocket for receiving the preload ring. Preload ring fasteners couple the preload ring to the piston to form a piston rod connection between the piston rod and the piston, such that the protruding end surface of the piston rod engages an interior surface of the pocket and a preload is induced in the piston rod connection. 
     In an alternate embodiment of this disclosure, a piston rod subassembly of a blowout preventer includes a piston rod having a rod threaded interface and a rod shoulder on an outer diameter of the piston rod at a first end. A ram connector is located at a second end that is opposite of the first end. A preload ring has a ring threaded interface for engaging the rod threaded interface to couple the piston rod to the preload ring. A protruding end surface of the piston rod protrudes past an end face of the preload ring when the piston rod is coupled to the preload ring and the rod shoulder engages a ring shoulder of the preload ring. A piston has a pocket for receiving the preload ring. The piston also has an outer diameter seal selectively engaging an inner diameter of a piston chamber of a bonnet assembly of the blowout preventer and is moveable within the piston chamber between an extended position and a retracted position. The piston further has a tail rod, the tail rod being a threaded elongated member extending in a direction opposite from the piston rod and threadingly engaging the bonnet assembly of the blowout preventer and inducing a rotation in the piston when the piston moves between the extended position and the retracted position. Preload ring fasteners couple the preload ring to the piston to form a piston rod connection between the piston rod and the piston, such that the protruding end surface of the piston rod engages an interior surface of the pocket and a preload is induced in the piston rod connection. 
     In yet another alternate embodiment of this disclosure, a method of assembling a blowout preventer with a piston rod subassembly includes providing a piston rod having a rod threaded interface and having a rod shoulder on an outer diameter of the piston rod. The piston rod is threaded into a preload ring. The preload ring has a ring threaded interface for engaging the rod threaded interface to couple the piston rod to the preload ring. A protruding end surface of the piston rod protrudes past an end face of the preload ring when the piston rod is coupled to the preload ring and the rod shoulder engages a ring shoulder of the preload ring. The preload ring can be located in a pocket of a piston. The preload ring can be coupled to the piston with preload ring fasteners to form a piston rod connection between the piston rod and the piston, such that the protruding end surface of the piston rod engages an interior surface of the pocket and a preload is induced in the piston rod connection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features, advantages and objects of this disclosure, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the disclosure briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the disclosure and is therefore not to be considered limiting of its scope as the disclosure may admit to other equally effective embodiments. 
         FIG. 1  is a partial, cross sectional view of an operator piston rod subassembly installed within an operator of a blowout preventer in accordance with an example embodiment of the present disclosure. 
         FIG. 2  is a cross-sectional view of the operator piston rod subassembly of  FIG. 1 . 
         FIG. 3  is a detail cross-sectional view of a portion of the operator piston rod subassembly of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The methods and systems of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The methods and systems of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
     Referring to  FIG. 1 , ram blowout preventer operator assembly  11  is a part of an assembly that is secured to bonnet  14  of bonnet assembly  13 . Ram blowout preventer operator assembly  11  can be used to control fluids flowing into and out of a wellbore of a subterranean well, or to control axial or rotational movement of a member passing through the wellbore, such as a tubular member, polished rod, or equipment. Piston rod subassembly  15  is located within bonnet assembly  13  and is operably responsive to the selective introduction and removal of a pressure media entering and exiting piston chamber  17  defined within bonnet assembly  13 . The pressure media can be, as an example, a hydraulic fluid, pressurized air, or other suitable fluid or gas used in pressure systems. The pressure media can be supplied by an operator or controller through one or more fluid passages that extend into piston chamber  17 . 
     As one skilled in the art will recognize, piston rod subassembly  15  is operable to connect to a ram (not shown), such as a pipe ram, which, when activated, moves to engage and surround drillpipe and well tools to seal a wellbore. The ram may alternately be a shear ram, which, when activated, moves to engage and physically shear any member in the wellbore. The rams can further alternately be gripping rams that can engage the tubular, polished rod, or other equipment in the well to prevent axial or rotational movement of such tubular, polished rod, or other equipment in the well. Operation of an exemplary piston rod subassembly  15  and an associated ram is described in greater detail in commonly owned U.S. Pat. No. 7,699,554, which is hereby incorporated by reference herein. 
     Looking at  FIG. 2 , piston rod subassembly  15  is constructed of piston rod  19  with a first end  21  having a rod threaded interface  23 . Rod threaded interface  23  includes threads on an outer diameter of piston rod  19 . First end  21  also has rod shoulder  25  on an outer diameter of piston rod  19 . Rod shoulder  25  is an annular sloped surface that flares outward and faces towards rod threaded interface  23 . The annular sloped surface defines an increase in the outer diameter of piston rod  19 . Piston rod  19  has ram connector  27  on a second end  29  of piston rod  19 . Second end  29  of piston rod  19  can extend into bonnet  14  of blowout preventer operator assembly  11  and be configured for connecting to a ram (not shown) having a T-slot defined therein. Ram connector  27  can be restrained by the ram so that ram connector  27  and second end  29  of piston rod cannot rotate about a longitudinal axis of piston rod  19 . Piston rod  19  can be formed, for example, of an alloy. 
     The first end  21  of piston rod  19  can be coupled with preload ring  31 . Preload ring  31  has ring threaded interface  33  for engaging rod threaded interface  23  to couple piston rod  19  to preload ring  31 . Ring threaded interface  33  can include internal threads on an inner diameter of a bore that extends through preload ring  31 . Preload ring  31  has a ring shoulder  35  that is positioned and shaped to engage and mate with rod shoulder  25 . Ring shoulder  35  is a sloped annular shoulder on an inner surface of the bore of preload ring  31 . Ring shoulder  35  is positioned within the bore of preload ring  31  so that when piston rod  19  is coupled to preload ring  31  and rod shoulder  25  engages ring shoulder  35 , end surface  37  of piston rod  19  protrudes past end face  39  of preload ring  31  ( FIG. 3 ). 
     Preload ring  31  can be coupled to piston  41 . Piston  41  has piston body  43  with an outer diameter seal  45  that can sealingly and slidingly engage an inner diameter of piston chamber  17 . By injecting the pressure media into piston chamber  17  on a first side of piston body  43 , piston rod subassembly  15  can be moved within piston chamber  17  from a retracted position to an extended position. By injecting the pressure media into piston chamber  17  on a second side of piston body  43 , piston rod subassembly  15  can be moved within piston chamber  17  from the extended position to the retracted position. When piston  41  and piston rod subassembly  15  are in the retracted position, second end  29  of piston rod  19  is proximate to or closer to bonnet assembly  13 . When piston  41  and piston rod subassembly  15  are in the extended position, second end  29  of piston rod  19  is extended away from, and farther from, bonnet assembly  13  so that the rams extend into the wellbore. 
     Piston  41  also has tail rod  47 . Tail rod  47  can be a threaded elongated member extending in a direction opposite from the piston rod  19 . Tail rod  47  can be an integrally formed portion of piston  41  so that tail rod  47  and piston body  43  are a single member. Piston  41  and preload ring  31  can be formed of a material that is less expensive than used to form piston rod  19 . Piston  41  and preload ring  31  can be formed, as an example, from a steel material. 
     Piston  41  further has pocket  49  for receiving preload ring  31 . Preload ring fasteners  51  can couple preload ring  31  to piston  41  to complete piston rod connection  53  between piston rod  19  and piston  41 , as can best be seen in  FIG. 3 . In the example embodiments shown, preload ring fasteners  51  can extend through preload ring  31  to engage piston  41 . Preload ring fasteners  51  can include, as an example, an annular array of cap screws. Because end surface  37  of piston rod  19  protrudes past end face  39  of preload ring  31 , end surface  37  of piston rod  19  engages interior surface  55  of pocket  49  and at least a portion of end face  39  of the preload ring  31  is spaced apart from interior surface  55  of pocket  49  forming gap  57 . This helps to ensure that operational loads travel appropriately through the piston rod  19 . 
     When preload ring fasteners  51  couple preload ring  31  to piston  41  a preload is induced in piston rod connection  53 . At least a portion of end face  39  of the preload ring  31  is spaced apart from interior surface  55  of pocket  49  so that gap  57  remains during the preloading of piston rod connection  53 . Piston rod connection  53  includes: the coupling of piston rod  19  to preload ring  31  through ring threaded interface  33  engaging rod threaded interface  23 ; preload ring fasteners  51  coupling preload ring  31  to piston  41 ; rod shoulder  25  engaging ring shoulder  35 ; and end surface  37  of piston rod  19  engaging interior surface  55  of pocket  49 . Preload ring fasteners  51  will be acting to pull preload ring  31  towards piston  41 , while end surface  37  of piston rod  19  engaging interior surface  55  of pocket  49  will be resisting such pull. The pull of preload ring  31  towards piston  41  will also apply a load on the interface between preload ring  31  and piston rod  19 , such interface being ring threaded interface  33  engaging rod threaded interface  23  and rod shoulder  25  engaging ring shoulder  35 . The preloading of piston rod connection  53  will help to ensure that the components of piston rod connection  53  will remain well secured together throughout the operation of piston rod subassembly  15  within blowout preventer operator assembly  11 . 
     Tail threads  59  of tail rod  47  threadingly engage internal threads of blowout preventer operator assembly  11 . The threads of the blowout preventer operator assembly  11  can be part of a nut and clutch assembly that can allow the threads of the blowout preventer operator assembly  11  to rotate freely when piston  41  moves between the extended position and the retracted position through injection of the pressure media into piston chamber  17 . Therefore, when piston  41  moves between the extended position and the retracted position through injection of the pressure media into piston chamber  17 , the nut can rotate around tail threads  59  without inducing a rotation on piston  41 . The nut and clutch assembly allows piston  41  to be locked at various locations along the linear path, as needed during operation. When the nut and clutch assembly is engaged, which occurs when operator pressure is vented, piston  41  is locked. When there is pressure in the wellbore, a pressure end load is applied to second end  29  of piston rod  19 . This pressure end load urges piston rod subassembly  15  towards a retracted position. Because second end  29  of piston rod  19  cannot rotate about the longitudinal axis of piston rod  19 , and the nut and clutch assembly is engaged, linear movement of piston  41  induces a torque on piston rod connection  53 . 
     Tail threads  59  of tail rod  47  can be oriented in an opposite direction than threads of rod threaded interface  23  so that rotation of piston  41  causes threaded interface  33  and rod threaded interface  23  to rotate relative to each other so that rod shoulder  25  further engages ring shoulder  35 . In this way, the connection between preload ring  31  and piston rod  19  will tend to further tighten when pressure end load urges piston rod subassembly  15  towards a retracted position. Because of the mating of rod shoulder  25  with ring shoulder  35 , piston rod  19  cannot be rotated out of preload ring  31  and piston rod connection  53  will remain secure during the operation of blowout preventer operator assembly  11 . In this way, rod shoulder  25  acts as an anti-rotation device so that piston rod  19  cannot be rotated out of preload ring  31 . 
     In order to maintain piston rod subassembly  15  or replace or salvage parts of piston rod subassembly  15 , preload ring fasteners  51  are operable to release preload ring  31  from piston  41  with a hand tool at the site of blowout preventer operator assembly  11  to relieve the preload in piston rod connection  53 . No machining, permanent removal of material of piston rod assembly  15 , or other destruction of the components of piston rod assembly  15  is required to disassemble each of the parts of piston rod assembly  15 . 
     In an example of operation, in order to assemble blowout preventer operator assembly  11  with piston rod subassembly  15 , second end  29  of piston rod  19  can be fed through the bore that extends through preload ring  31  and piston rod  19  can be rotated so that ring threaded interface  33  engages rod threaded interface  23  to couple piston rod  19  to preload ring  31 . Piston rod  19  can be rotated until ring shoulder  35  engages and mates with rod shoulder  25 . When ring shoulder  35  engages and mates with rod shoulder  25  end surface  37  of piston rod  19  protrudes past end face  39  of preload ring  31 . Preload ring  31  can then be located within pocket  49  and preload ring fasteners  51  can couple preload ring  31  to piston  41 . Protruding end surface  37  of piston rod  19  will engage interior surface  55  of pocket  49  and a preload will be induced in piston rod connection  53 . Preload ring fasteners  51  can cause a sufficient force on preload ring  31  that preload ring  31  can be deformed during the preloading of piston rod connection  53 . 
     During operation of blowout preventer operator assembly  11 , piston rod subassembly  15  moves between the retracted and extended positions by injecting pressure media into piston chamber  17  on a first side of piston body  43  or on a second side of piston body  43 , as applicable. When piston  41  moves between the retracted and extended positions, the nut and clutch assembly can allow the threads of the blowout preventer operator assembly  11  to rotate freely so that the nut can rotate around tail threads  59  without inducing a rotation on piston  41 . 
     In order to maintain piston rod subassembly  15  or replace or salvage parts of piston rod subassembly  15 , preload ring fasteners  51  are operable to release preload ring  31  from piston  41 , such as, for example, with a hand tool at the site of blowout preventer operator assembly  11  to relieve the preload in piston rod connection  53 . Therefore, if blowout preventer operator assembly  11  is used offshore, piston rod subassembly  15  can be disassembled offshore and without sending the entire piston rod subassembly  15  to an onshore location for the disassembly. Also, since no machining is required, the components of piston rod subassembly  15  can be more easily salvaged when components are replaced or maintained. 
     Therefore, as described herein, embodiments of this disclosure simplify the assembly and disassembly of piston rod assembly  15  compared to some current systems by eliminating the need for extra fixtures to induce and break the preload of piston rod connection  53 , as well as by eliminating the need for machining to separate the parts of piston rod assembly  15 . System and methods described herein also reduce material costs of piston rod subassembly  15  by providing embodiments that require that only piston rod  19  be formed of an expensive alloy, while the remainder of piston rod subassembly  15  can be formed of a simple steel. 
     The terms “vertical”, “horizontal”, “upward”, “downward”, “top”, and “bottom” are used herein only for convenience because blowout preventer operator assembly  11  may be installed in various positions. 
     System and methods described herein, therefore, are well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of this disclosure and the scope of the appended claims.