Abstract:
A drive system for a catwalk skate that uses a hydraulic skate-cable drive system. The system includes two counteracting hydraulic cylinders, each with a sheave connected to the cylinder rods, and a cable that winds around each of the sheaves and connects to both ends of the skate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application No. 61/782,040, filed Mar. 14, 2013, the contents of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention generally relate to catwalks for conveying pipe to a drill floor from a lower section of a drilling rig or drill site. Specifically, embodiments of the invention relate to a hydraulic skate-cable drive system that is used instead of the chain and motor drive or winch system that are used by prior art catwalks. 
     2. Description of the Related Art 
     In a drilling operation or rig work-over operation, whether on a water-based or land-based drilling rig, pipe for the drilling operation, casing, or other tubulars are often stored at or supplied from a level that is lower than the drill floor. Operators typically use a “catwalk” to convey the pipe from the lower level to the drill floor. The pipe is typically mechanically transported (e.g. pushed with a skate and/or pulled in a v-shaped trough) from a level below the rig floor to the rig floor. 
     Prior art catwalks use a skate that is pulled from the lower end of the catwalk by a chain on a loop that is powered by a motor, or by a cable that is pulled toward the top of the catwalk trough using a winch. Such systems also require the use of a brake to stop the skate at a position where the skate causes the opposite end of the pipe or other tubular to be positioned near the drill floor where the rig workers can attach the end of the pipe to another hoist and move the pipe to the rotary or a setback area on the drill floor. The use of a motor and chain or a cable and winch along with a brake can lead to many mechanical breakdowns and to several potentially dangerous situations. If the chain breaks, the pipe and skate could move uncontrollably toward the bottom of the catwalk. If the brake fails, the pipe could be moved too far into the drill center, putting the drill floor workers at risk. 
     Accordingly, it would be useful to have a skate drive system that would prevent the skate and pipe from falling toward the bottom of the catwalk in the event of a system failure. It would also be useful to have a system that does not require the use of a brake to prevent the skate from moving too far up the trough so that the pipe does not put the rig workers at risk. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention provide a drive system for a catwalk skate that uses a hydraulic skate-cable drive system. The system has two counteracting hydraulic cylinders, each with a sheave connected to the rod. A cable winds around each of the sheaves as well as a number of other sheaves and is connected to both ends of the skate that move the pipe in the trough. The cable and the skate are moved by retraction of the rod of one cylinder which causes the second cylinder to extend as the second cylinder is connected to the one cylinder through the cable and the skate. As the counteracting cylinders are physically connected only through the cable and skate, it is possible to automatically tension the cable during operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited aspects of the invention can be understood in detail, a more particular description of embodiments of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1A  shows an embodiment of the invention in the position in which pipe is loaded onto the catwalk and into the trough or unloaded from the trough. 
         FIG. 1B  shows an embodiment of the invention in the position in which the trough is in the process of being raised to the drill floor level. 
         FIG. 1C  shows the trough in an elevated position in which pipe is being conveyed to or from the drill floor. 
         FIG. 2  shows the trough and the skate for advancing tubulars to a drill floor. 
         FIG. 3A  is a cross section of the trough that shows the two hydraulic cylinders, the sheave connected to the ends of the rods for each of the cylinders, the sheaves attached to the inner walls of the catwalk, the skate, and the cable used with the cylinders to move the skate. 
         FIGS. 3B, 3C, and 3D  are inset view of the sheaves, hydraulic cylinders, and cables according to one embodiment of the invention. 
         FIG. 4  is a detailed view of the sheaves, brackets, cable and skate shown in  FIG. 3B . 
         FIG. 5A  is a detailed view of the sheave, the rod for the upper hydraulic cylinder and the lower hydraulic cylinder shown in  FIG. 3C . 
         FIG. 5B  is another view of the components shown in  FIG. 3C , which shows the rollers on each side of the lower hydraulic cylinder which support the rod for the upper hydraulic cylinder rod as it is advanced and retracted. 
         FIG. 6  is a detailed view of the upper hydraulic cylinder, the lower hydraulic cylinder rod, the sheaves, brackets, and cable shown in  FIG. 3D . 
         FIG. 7  is a detailed view of the sheave and bracket at the drill floor end of the trough. 
         FIGS. 8A and 8B  illustrate a schematic diagram of the valve system for the hydraulic system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows trough  2  in its lowered position in catwalk  1 . One or more sections of pipe are loaded into trough  2  for transfer to a higher level drill floor. Skate  3  may move and advance pipe toward the drill floor. 
       FIG. 1B  shows trough  2  in the process of being raised toward a drill floor. A leg  40  of the catwalk  1  is raised by hydraulic cylinders  50 A and  50 B to raise trough  2 . Skate  3  would be moving pipe along trough  2  toward the drill floor. 
       FIG. 1C  shows trough  2  fully raised where the upper end of trough  2  would be adjacent to a drill floor. Skate  3  advances pipe to the drill floor end of trough  2  so that the pipe can be removed from the trough by the crew on the drill floor and moved toward the rotary or into a setback area on the drill floor. Generally, catwalks use a skate that is pulled from the lower end of the catwalk by a chain on a loop that is powered by a motor or by a cable that is pulled toward the top of the catwalk trough using a winch. 
       FIG. 2  shows a side view of the trough  2  and the skate  3 . The trough  2  may include one or more sections coupled together. The skate  3  begins at trough end  2 A and advances pipe toward trough end  2 B, which is adjacent to a drill floor when the trough  2  is fully raised. 
       FIG. 3A  is a cut away view of trough  2  showing a drive system according to one embodiment of the invention. The drive system comprises hydraulic cylinder  4 , shown in  FIGS. 3C and 5  with its rod  7  retracted inside the cylinder  4 , and hydraulic cylinder  5 , shown with its rod  6  extended. As shown in  FIG. 3C , rod  7  of cylinder  4  is connected to bracket  10  and sheave set  8 . Sheave set  9  and bracket  11  are connected to rod  6 , as shown in  FIG. 3D . Bracket  10  is positioned around cylinder  5 . Rollers  22 A and  22 B (shown in  FIG. 5B ) on the inside of bracket  10  roll on opposite side of cylinder  5  as sheave set  8  and bracket  10  move down the length of cylinder  5  when rod  7  is extended from cylinder  4  or retracted into cylinder  4 . Bracket  11  has rollers  22 C and  22 D (shown in  FIG. 6 ) that are positioned around and roll on opposite sides of cylinder  4  as rod  6  is retracted into or extended from cylinder  5 . 
     Sheaves  12 ,  13 ,  14 ,  15 , and  17  (as shown in  FIGS. 3A, 3B, and 3D ) are fixed to the interior of trough  2  via brackets. 
     As illustrated in  FIG. 3B , cables  16 A and  16 B are attached to ends  3 A and  3 B, respectively, of skate  3 . As shown in further detail in  FIG. 4 , from end  3 A, cable  16 A loops around sheave  12 . From there, cable  16 A wraps around sheave  8 B, as shown in  FIG. 5A , and then around sheave  13  as shown in  FIG. 4 . From there, cable  16 A wraps around sheave  8 A, as shown in  FIG. 5A , and then connects to connector  20  as shown in  FIG. 4 . 
     From end  3 B of skate  3 , cable  16 B travels and goes around sheave  17  at end  2 B of the trough  2 , as shown in detail in  FIG. 7 . From sheave  17 , cable  16 B goes under sheave  15 , as shown in  FIG. 3D  and  FIG. 6 , around sheave  9 A, around sheave  14 , around sheave  9 B and then to connector  21 , which is affixed to the same bracket as sheave  14 . 
     To advance the pipe to the drill floor, skate  3  is moved from end  2 A of the trough  2  toward end  2 B by advancing hydraulic cylinder  4  and retracting hydraulic cylinder  5 . Hydraulic fluid is used to retract rod  6  into cylinder  5 , causing sheave set  9  to move toward cylinder  5 . At the same time, rod  7  is extended from cylinder  4  and sheave set  8  moves away from cylinder  4 . Because multiple lengths of cable are wrapped around sheath set  8  and sheath set  9 , for each foot that the hydraulic cylinders rods  6 ,  7  advance or retract, the skate  3  moves about four feet. Sequence valves in the hydraulic system maintain and hold tension on cables  16 A and  16 B while skate  3  is advanced. 
     When rod  7  is fully extended from cylinder  5  and rod  6  is fully retracted into cylinder  5 , skate  3  will stop moving and workers at the drill floor will remove the pipe from the skate  3 . Skate  3  is returned to end  2 A of trough  2  by retracting rod  7  into cylinder  4  and extending rod  6  from cylinder  5 . 
       FIGS. 8A and 8B  show a schematic for the hydraulic system for hydraulic cylinders  4  and  5 . Sequence valves  30 A and  30 B hold tension between the cable drive system. The sequence valves  30 A,  30 B retain positive pressure on whichever of hydraulic cylinder  4  and hydraulic cylinder  5  are in the process of advancing. In the event that a pipe is dropped from the drill floor down the trough  2  and onto the skate  3 , relief valves  31 A and  31 B allow oil to be routed from the rod end of hydraulic cylinder  5  to the rod end of hydraulic cylinder  6  so that the skate  3  and the hydraulic cylinders  4 ,  5  absorb the impact of the pipe and the system is not damaged. 
     While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.