Abstract:
A marine drilling riser system for securing drilling riser joints in a drilling riser string is presented. The drilling riser string is assembled by connecting a pin end of one drilling riser joint to a box end of an adjoining drilling riser joint by using a moveable ring to drive a fastener of one drilling riser joint against the adjoining drilling riser joint. A spider is used to drive the movable ring axially from a position where the fastener is not engaged against the adjoining drilling riser joint to a position where the fastener is engaged against the adjoining drilling riser joint, and vice versa. A latch is used to prevent the moveable ring from moving inadvertently from the second position. The spider may also be used to support the marine drilling riser string during assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of Ser. No. 12/139,793, which is now U.S. Pat. No. 7,913,767, filed Jun. 16, 2008. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a system for providing a secondary means of securing tubular members held together by a friction-lock system. In particular, the present invention relates to a mechanical latch that prevents drilling risers that are held together by friction from separating inadvertently. 
     BACKGROUND 
     In offshore drilling operations in deep water, the operator will perform drilling operations through a drilling riser string. The drilling riser string extends from a floating platform, such as a drilling ship, to a subsea wellhead or subsea tree assembly on the seafloor. The drilling riser string is made up of a number of individual riser joints or sections that are secured together to form the drilling riser string. The drilling riser string forms a central tube for passing a drill pipe from the floating platform to the wellhead on the sea floor. The drilling riser string normally has a number of auxiliary conduits that extend around the central tube. The auxiliary conduits may serve several purposes, such as supplying hydraulic fluid pressure to the subsea blowout preventer and lower marine riser package. 
     Typically, the central tube of a drilling riser joint has a pin member on one end and a box member on the other end. The pin end of one riser joint stabs into the box end of the adjoining riser joint. In one type of riser joint, flanges extend outward from the pin and box. The operator connects the flanges together with bolts spaced around the circumference of the coupling. In another type of riser, individual segments or locking segments are spaced around the circumference of the box. A screw is connected to each locking segment. Rotating the screw causes the locking segment to advance into engagement with a profile formed on the end of a pin. 
     In these systems, a riser spider or support on a riser deploying floor moves between a retracted position into an engaged position to support previously made-up riser joints while the new riser joint is being stabbed into engagement with the string. Wave movement can cause the vessel to be moving upward and downward relative to the riser when the riser is in operation. 
     In both types of risers, workers use wrenches to make up the bolts or screws. Personnel employed to secure the screws or the bolts are exposed to a risk of injury. Also, the process of making up the individual bolts is time consuming. Often when moving the drilling rig from one location to another, the riser has to be pulled and stored. In very deep water, pulling and rerunning the riser is very expensive. 
     A technique has been developed that uses a cam ring and dogs to secure drilling riser joints together. Each riser joint has a box end and a pin end. The pin end of one drilling riser joint is disposed within the box end of an adjoining drilling riser joint. The box ends of each drilling riser joint have dogs that are driven into engagement with the pin ends of the adjoining drilling riser joints by moving the cam ring axially. Friction between the dogs and the cam ring maintains the cam ring positioned to drive the dogs against the pin end of the adjoining drilling riser joint. No bolts or screws are used to connect drilling riser joints using this technique. 
     However, it is conceivable that friction may not be sufficient to maintain the cam rings at their desired axial positions so that the cam rings drive the dogs against the pin ends of the adjoining drilling riser joints. Were a cam ring to move from its desired axial position, its dogs could back out from the pin end of the adjoining drilling riser joint. If that were to occur, the drilling riser joints may disconnect from each other. 
     Therefore, a more effective technique is needed to secure drilling riser joints together. In particular, a technique is desired that would enable adjoining drilling riser joints to be connected quickly and remain connected during operation. 
     BRIEF DESCRIPTION 
     A technique for securing drilling riser joints in a drilling riser string is presented. The drilling riser joints have a tubular housing that has a box configuration on one end and a pin configuration on the other end. The drilling riser string is assembled by connecting the pin end of one drilling riser joint to the box end of an adjoining drilling riser joint. A moveable ring is used to connect adjoining drilling riser joints. The moveable ring is used to drive a fastener, such as a dog, of one drilling riser joint against the adjoining drilling riser joint. The moveable ring is driven axially from a first position, where the fastener is not engaged against the adjoining drilling riser joint, to a second position, where the fastener is engaged against the adjoining drilling riser joint. 
     The technique also comprises the use of a latch to prevent the moveable ring from moving inadvertently from the second position. This prevents the drilling riser joints from disconnecting inadvertently. In the embodiment described below, the latch has a cantilevered arm having a toothed profile. The moveable ring also has a toothed profile that corresponds with the toothed profile on the latch. When the moveable ring is in the second position, the toothed profile on the latch engages the toothed profile on the moveable ring. The engagement of the toothed profile on the latch with the toothed profile on the moveable ring obstructs axial movement of the moveable ring. To disconnect the drilling riser joints, a tool is used to provide sufficient force to overcome the engagement of the toothed profiles on the latch and the moveable ring. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a schematic view of a drilling riser system, in accordance with an exemplary embodiment of the present technique; 
         FIG. 2  is an elevation view of a portion of the drilling riser system of  FIG. 1 , in accordance with an exemplary embodiment of the present technique; 
         FIG. 3  is a cross-sectional view of the portion of the drilling riser system of  FIG. 2 , in accordance with an exemplary embodiment of the present technique; 
         FIGS. 4-6  are a side elevation view, a front elevation view, and a perspective view of the secondary latch for a riser joint connection, in accordance with an exemplary embodiment of the present technique; 
         FIG. 7  is an elevation view of the first drilling riser joint and second drilling riser joint with a cam ring used to secure the first drilling joint to the second drilling riser joint in a first axial position, in accordance with an exemplary embodiment of the present technique; 
         FIG. 8  is an elevation view of the first drilling riser joint and second drilling riser joint with a cam ring used to secure the first drilling joint to the second drilling riser joint in a second axial position, in accordance with an exemplary embodiment of the present technique 
         FIG. 9  is a partial cross-sectional view of a drilling riser joint and a system for connecting drilling riser joints together, in accordance with an exemplary embodiment of the present technique; 
         FIG. 10  is a partial cross-sectional view of a pair of drilling riser joints joined together by the system for connecting drilling riser joints together, in accordance with an exemplary embodiment of the present technique; and 
         FIGS. 11-13  are a sequence of elevation views illustrating the use of retractable jaws to connect a first drilling riser joint to a second drilling riser joint, in accordance with an exemplary embodiment of the present technique. 
         FIG. 14  is a top cross-sectional view of a riser joint connection, in accordance with an exemplary embodiment of the present technique; 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , the present invention will be described as it might be applied in conjunction with an exemplary technique, in this case, a drilling riser string  20  to enable a subsea well to be drilled from a floating platform  22 . The drilling riser string  20  is secured to a lower marine riser package and Blowout Preventer (BOP) stack  24 , which is, in turn, secured to a subsea wellhead or subsea tree  26  of the well. The drilling riser string  20  is supported in tension by riser tensioners  28  suspended from the floating platform  22 . 
     The drilling riser string  20  is comprised of a series of riser joints  30  that are connected together to form several tubes that extend from the floating platform  22  to the lower marine riser package  24 . The drilling riser string  20  enables drill pipe  32  to be deployed from the floating platform  22  to the lower marine riser package  24  and on through the wellhead  26  into the seabed through a central tube  34  formed by the riser joints  30 . Drilling mud may be provided from the floating platform  22  through the drill pipe  32  and back to the floating platform  22  in the annulus between the drill pipe  32  and the inner walls of the central tube  34 . Auxiliary tubes  36  formed by the riser string  20  may be used for other purposes, such as serving as choke-and-kill lines for re-circulating drilling mud below a blowout preventer (BOP) in the event that the BOP secures flow through the central tube  34 . 
     Referring generally to  FIGS. 2 and 3 , each riser joint  30  has a box end  38  and a pin end  40  that are used to connect each riser joint  30  to another riser joint  30 . As shown here, the box end  38  of a first riser joint  42  is connected to the pin end  40  of a second riser joint  44 . In this embodiment, the first riser joint  42  is oriented in a box-up orientation and the second riser joint  44  is oriented in a pin-down orientation. However, the first and second riser joints  42 ,  44  may be oriented in the opposite orientation: pin-up/box-down. Here, the pin end  40  of the second riser joint  44  is stabbed into the box end  38  of the first riser joint  42 . As will be discussed in more detail below, a tool is used to drive a cam ring  46  of the box end  38  of the first riser joint  42  downward from a first axial position to a second axial position to connect the second riser joint  44  to the first riser joint  42 . The downward axial movement of the cam ring  46  urges a series of dogs (not shown in this view) disposed on the box end  38  of the first riser joint  42  inward against the pin end  40  of the second riser joint  44 . The engagement of the dogs secures the second riser joint  44  to the first riser joint  42 . To disconnect the first riser joint  42  and second riser joint  44 , the cam ring  46  is lifted to release the dogs from engagement with the pin end  40  of the second riser joint  44 . 
     In the illustrated embodiment, a latch  48  is provided to lock the cam ring  46  in the second axial position to maintain the second riser joint  44  connection to the first riser joint  42 . The cam ring  46  is held in the second axial position by friction between the cam ring  46  and the dogs. However, the latch  48  provides an additional mechanism by which the cam ring  46  is prevented from being moved inadvertently from the second axial position to the first axial position. As will be discussed in more detail below, the latch  48  is mounted on the box end  38  of each riser joint  30  and engages the cam ring  46  when the cam ring  46  is driven downward to the second position. The engagement between the latch  48  and the cam ring  46  resists upward movement of the cam ring  46 . Thus, the latch  48  maintains the second riser joint  44  connected to the first riser joint  42 . 
     Referring generally to  FIGS. 4-6 , the latch  48  is adapted to cooperate with the cam ring  46  to prevent inadvertent axial movement of the cam ring  46 . The illustrated embodiment of the latch  48  has a toothed profile  50  that is located on one end of a cantilever arm  52 . The toothed profile  50  is configured to engage a corresponding grooved portion of the cam ring  46  when the cam ring  46  is positioned in the second axial position. Upward movement of the cam ring  46  from the second axial position to the first axial position is opposed by the engagement between the toothed profile  50  of the latch  48  and the corresponding grooved portion of the cam ring  46 . The cantilever arm  52  biases the latch  48  outward so that the toothed profile  50  will engage the corresponding grooved profile of the cam ring  46 . However, as will be discussed in more detail below, the cantilever arm  52  also enables the toothed profile  50  to be flexed inward during intentional axial movement of the cam ring  46  so that the toothed profile  50  of the latch  48  ratchets along the corresponding grooved portion of the cam ring  46 . In addition, the illustrated embodiment of the latch  48  has a pair of mounting holes  54  for securing the latch  48  to the box end  38  of each riser joint  30 . However, other arrangements and methods for securing the latch  48  to the riser joint  30  may be used. 
     Referring generally to  FIG. 7 , the cam ring  46  is presented in the first axial position on the box end  38  of the first riser joint  42 . The cam ring  46  has a toothed profile  56  that is adapted to engage the toothed profile  50  of the latch  48 . In this embodiment, the toothed profile  56  extends around the inner circumference of the cam ring  46 . The toothed profile  50  of the latch  48  does not engage the toothed profile  56  of the cam ring  46  when the cam ring  46  is in the first axial position. Instead, the toothed profiles  50 ,  56  are configured so that they are engaged only when the cam ring  46  is at or near the second axial position. The box end  38  has a cavity  58  that is provided to receive the latch  48  as the latch  48  ratchets when the cam ring  46  is moved axially. 
     Referring generally to  FIG. 8 , the cam ring  46  is presented in the second axial position on the box end  38  of the first riser joint  42 . When the cam ring  46  is driven downward, as represented by arrow  60 , dogs (not shown) of the box end  38  of the first riser joint  42  are driven into an outer profile  62  of the pin end  40  of the second riser joint  44 . The cantilever arm  52  of the latch  48  is biased outward from the cavity  58  to engage the toothed profile  50  of the latch  48  with the toothed profile  56  of the cam ring  46 . 
     Referring generally to  FIGS. 9 and 10 , a tool  64  is used to connect the riser joints  30  to form the riser string  20 . In the illustrated embodiment, the tool  64  has a plurality of retractable braces  66  that are extended outward to support a flange  68  of the first riser joint  42 . The braces  66  also align the first riser joint  42  for connection with the second riser joint  44 . The braces  66  are retracted to enable the first and second riser joints  42 ,  44  to pass through the tool  64  during assembly and disassembly of the riser string  20 . 
     The tool  64  is adapted to connect the riser joints  30  in a box-up/pin-down configuration. The first riser joint  42  is supported in the tool  64  with the box end  38  upward in this embodiment. Consequently, the pin end  40  of the second riser joint  44  is inserted into the box end  38  of the first riser joint  42 . The box end  38  of the first riser joint  42  has a plurality of dogs  70  that are used to connect the box end  38  of the first riser joint  42  to the pin end  40  of the second riser joint  44  are presented. The dogs  70  extend through windows  72  in the box end  38 . As the cam ring  46  is driven downward to the second axial position, as represented by arrow  76 , the dogs  70  are driven by the cam ring  46  inward, as represented by arrow  78 , into engagement with the outer profile  62  of the pin end  40  of the second riser joint  44 . The tool  64  has a plurality of retractable jaws  74  that are extended outward to engage the cam ring  46  and drive it axially downward or upward. 
     Referring generally to  FIGS. 11-13 , the jaws  74  are adapted to drive the cam ring  46  downward, as represented by arrow  76 , to drive the dogs  70  of the first riser joint  42  inward, as represented by arrow  78 , against the outer profile  62  of the pin end  40  of the second riser joint  44 . In addition to the latches  48 , friction between the inner surface  80  of the cam ring  46  and the outer surface  82  of the dogs  70  maintain the cam ring  46  in the second position. 
     Referring generally to  FIG. 14 , the illustrated embodiment of the box end  38  of a riser joint  30  utilizes three latches  48  that are disposed equidistant around the central tube  34  to maintain the cam ring  46  in the second axial position. However, a greater or lesser number of latches  48  may be used. As noted above, when the cam ring  46  is in the second axial position, the cam ring  46  drives dogs  70  against the pin end  40  of the upper riser  44  through windows  72  in the box end  38  of the lower riser  42 , connecting the second riser joint  44  to the first riser joint  42 . 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.