1. Technical Field
The present invention relates in general to terminating choke, kill, and auxiliary lines for riser strings on an offshore drilling rig and, in particular, to an improved system, method, and apparatus for a line termination system that is radially-movable relative to the riser string.
2. Description of the Related Art
Offshore drilling rigs must compensate for many environmental hazards including tidal conditions, ocean swells, and weather conditions such as wind and severe weather. The forces generated by these hazards cause significant motion of the rig that must be compensated to maintain the continuity of the riser string that extends down from the rig and is fixed to the ocean floor. A slip joint is typically used near an upper end of the riser string to compensate for vertical motion of the rig. The slip joint compensates for motion with inner and outer barrels that move axially relative to each other. The various choke, kill, and auxiliary lines associated with riser strings also must be configured to compensate for motion. These lines are typically terminated adjacent the slip joint with a device such as a Karrot Top or KT ring assembly.
A conventional KT ring assembly 11 is shown in FIG. 1 and comprises a ring adapter 13 that is mounted to the outer barrel 15 of the slip joint 17. The ring adapter 13 lands on a shoulder 19 inside a large, solid ring body 21, which completely circumscribes the ring adapter 13 and slip joint 17. The ring body 21 includes numerous terminal blocks 23 for terminating the choke, kill, and auxiliary lines. The ring body 21 also typically incorporates a fluid bearing 25 and a tension ring 27 for supporting the overall assembly.
Although conventional KT rings provide numerous advantages they also have a few limitations. For example, because the ring body is solid, the entire riser string must be run through the KT ring assembly during construction of the riser string. The large size of the ring body makes it somewhat cumbersome to manipulate, and it consumes significant space between the floors of drilling rig. In addition, the ring body must first be secured to the bottom of the diverter housing. Thus, although conventional KT rings are workable, an improved design would be desirable.