Abstract:
A power tong for use during installation and dismantling of pipes when drilling in the ground, such as is known from e.g. petroleum production, comprising a drive ring and at least one clamping device, where the clamping device is arranged to grip a pipe string, the power tong being equipped with a driving mechanism for rotation of the clamping device about the longitudinal axis of the pipe string, and where the clamping device communicates with a fluid supply via a swivel ring that encircles the drive ring.

Description:
REFERENCE TO PENDING APPLICATIONS 
     This application claims the benefit of PCT/NO04/00355, filed Nov. 19, 2004, which claimed the benefit of Norway Application No. 20035234, filed Nov. 25, 2003. 
     BACKGROUND OF THE INVENTION 
     This invention regards a power tong. More particularly, it regards a power tong without a radial opening, the power tong being particularly well suited for use during installation of piping when drilling in the ground, such as is known from e.g. petroleum production. The tong has a swivel coupling surrounding the tong for transferring pressurized fluid from an external source of pressurized fluid to the tong when the tong rotates about the longitudinal axis of the pipe. 
     It is known, among other things from petroleum production, to use power tongs for installing and dismantling lengths of piping to or from a pipe string associated with a drilling rig. It is common to use mechanical pipe tongs that, following the screwing or unscrewing of a pipe joint, on the whole are moved horizontally away from the pipe string, the pipe string being located at the drilling centre of the drill rig. 
     This method is dependent on the power tong having a radial opening, whereby the power tong can be displaced in the horizontal plane when being removed from the pipe string. 
     Having this type of radial opening in a power tong that has to be able to rotate about the longitudinal axis of the pipe obviously complicates the design of the power tong. The opening weakens the structure surrounding the pipe considerably. As a result, the structure must be up-rated in order to accommodate the relatively large forces being transferred between the power tong and the pipe string. A relatively complicated mechanical device is required to close the radial opening when the power tong is in use, and in many cases also to transfer forces between the sides of the opening. 
     The object of the invention is to remedy or diminish at least one of the disadvantages of prior art. 
     The object is achieved in accordance with the invention, by the characteristics stated in the description below and in the following claims. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the invention the power tong is provided with an undivided drive ring enclosing the vertical central axis of the drilling centre. The drive ring has been given a relatively large inner diameter so as to allow movement of e.g. drilling tools having a considerably larger outer diameter than the pipe string, through the power tong. 
     The drive ring is rotatably supported in the power tong housing and is preferably driven in a manner that is known per se, by at least one hydraulic motor. 
     In the drive ring there is provided at least one pressurized fluid driven radially displaceable clamping device (clamp). Most preferably there is a plurality of clamps distributed around the pipe in two groups. Each group of clamps is removably attached to the drive ring, each group of clamps being arranged so as to allow it to be lifted out of the drive ring in connection with e.g. maintenance or movement of a large object through the power tong. 
     Pressurized fluid from a pressurized fluid system connected thereto is delivered to the fluid cylinders of the clamps via a swivel coupling that sealingly encircles the drive ring. The swivel ring of the swivel coupling is stationary with respect to the power tong housing. 
     It is greatly advantageous for the clamp in the inactive position to be retracted relative to the pipe string, among other things to prevent sparking between the pipe string and the clamps during drilling. Thus, in a preferred embodiment, the swivel coupling is provided with a first passage that communicates with the plus side of the fluid cylinders, a second passage that communicates with the minus side of the fluid cylinders, and also a drainage duct. 
     Preferably the parts of the clamps abutting the pipe have replaceable grippers. Gripper sets can be manufactured in different shapes and sizes, allowing them to be adapted to the pipe dimension in question and the desired geometry of engagement between the gripper and the pipe string. The invention allows the clamps to be moved relatively far back relative to the pipe string. 
     In a preferred embodiment the power tong constitutes an upper installation tong in a joint assembly with an underlying back-up tong. The joint assembly is connected to a horizontally displaceable chassis by means of vertical guides, to allow the joint assembly to be moved away from the drilling centre. 
     The heights of the power tong and the back-up tong are mutually adjustable to compensate for the relative axial displacement of the pipes during screwing and unscrewing, and in order to allow work to be carried out between the tongs. Preferably weight-compensating cylinders are provided between the power tong and the back-up tong in order to take up weight when screwing sensitive threads. 
     Most preferably there is provided between the power tong and the back-up tong a collecting device for drilling fluid. The collecting device is connected to a mud outlet. 
     Preferably the back-up tong can be provided with a traversing lifting device on the underside, to make it possible to lift e.g. the slips etc. 
     The time it takes to tie in and dismantle pipes will be reduced when compared with prior art, as the time spent moving the power tong to and from the drilling centre no longer applies. The comparatively simple construction of the power tong results in improved reliability and lower maintenance costs. 
     All spinning and force operations are performed by use of the tong, so there is no need to use a separate so-called spinner. 
     The structure is compact and does not require a lot of space in the longitudinal direction of the pipe string. It is well suited for building in cleaning and lubricating equipment for the pipe thread. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The following describes a non-limiting example of a preferred embodiment illustrated in the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a joint assembly of a power tong, in which a group of clamps has been removed for illustrative purposes, and a back-up tong on a horizontally displaceable chassis, where the assembly has been moved to its upper position; 
         FIG. 2  shows the same as  FIG. 1  but here the joint assembly is in its lower position; 
         FIG. 3  is a perspective view of the power tong with the cover removed, on a larger scale; 
         FIG. 4  shows a section III-III through  FIG. 3 ; 
         FIG. 5  is a perspective view of the back-up tong with the cover and groups of clamps removed, on a larger scale; 
         FIG. 6  shows the same as  FIG. 1  but here the back-up tong has been moved downwards slightly relative to the power tong; and 
         FIG. 7  is a schematic representation of the drilling fluid collecting device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the drawings reference number  1  denotes a joint assembly of a power tong  2  and a back-up tong  4  located on a drilling rig  6  coaxially with the drilling centre  8  of the drilling rig  6 . The assembly  1  is coupled in a vertically displaceable manner to two guide columns  10  arranged diametrically opposite each other relative to the drilling centre  8 . 
     The guide columns  10  are connected to a chassis  12  which by means of wheels  14  and hydraulic motors (not shown) can be displaced horizontally on rails  16  connected to the drilling rig  6 . 
     Thus, in the operative position the assembly  1  is located immediately above the slips  18  of the drilling rig  6 , a pipe string  20  projecting up through the slips  18  and on up through the assembly  1 . The pipe string  20  consists of screwed-together lengths  22  of piping. 
     The power tong  1 , see  FIGS. 3 and 4 , comprises a power tong housing  24  provided with a through aperture  26  that corresponds to the guide columns  10 , and an undivided drive ring  30  connected via bearing ring  28 . The bearing ring  28  has a toothed ring  32  in mesh with cogwheels (not shown) on two hydraulic motors  34 . The toothed ring  32  is coupled to the drive ring  30  by screw-bolt-joints (not shown). Thus the hydraulic motors  34  are arranged to rotate the drive ring  30  about the drilling centre  8 . Mechanically it is preferable for the two hydraulic motors  34  to be disposed on diametrically opposite sides of the drive ring  30 . 
     A cover  36  is provided to cover the power tong housing  24 . 
     In the drive ring  30  and co-rotating with this are two crescent-shaped groups  38  of clamps, of which only one is shown in the drawings, for illustrative purposes. 
     Each group  38  of clamps is typically provided with three clamps  40  distributed around the drilling centre  8 . A clamp  40  comprises a cylinder block  42  provided with three cylinder bores  44  arranged in a vertical row. In each cylinder bore  44  is a corresponding axially displaceable piston  46  that seals against the cylinder bore  44  by means of a piston gasket  48 . A rear gasket  50  prevents pressurized fluid from flowing out between the piston  46  and the cylinder bore  44  at the rear end of the piston  46 . 
     The pistons are removably attached to the housing  52  of the group  38  of clamps by means of respective screw-bolt-joints  54 . 
     On the part of the cylinder block  42  facing the drilling centre  8  there is provided a gripper  56 . The gripper  56  may be connected to the cylinder block  42  by means of dovetail grooves or screw-bolt-joints (not shown). 
     Surrounding the drive ring  30  there is provided a swivel ring  60  that seals by means of swivel gaskets  58 , the swivel ring  60  being stationary relative to the power tong housing  24 . The swivel ring  60  has a first passage  62  that communicates with the plus side of the pistons  46  via a first fluid connection  64 , a second passage  66  that communicates with the minus side of the pistons  46  via a second fluid connection  68 , and a further passage  70 . The cylinder  44  and the piston  46  are thereby double acting. 
     The swivel ring  60 , swivel gaskets  58  and drive ring  30  together form a swivel coupling. 
     The back-up tong  4  comprises a back-up tong housing  74  with guides  76  that correspond with the guide columns  10 , and a retainer ring  77  for two groups of clamps (not shown in this drawing). At the guides  76  there are cogwheels  78  that mesh with respective pitch racks  80  of the guide columns  10 , see  FIG. 5 . 
     Separate hydraulic motors  82  drive the cogwheels  78  via gears  84 . 
     A pair of hydraulic cylinders  86  are arranged to adjust the vertical distance between the power tong  2  and the back-up tong  4 . 
     A collecting device comprises a collecting bellows  90 , see  FIG. 6 . The collecting bellows  90  is arranged to seal between the power tong  2  and the back-up tong  4 . 
     The collecting device is drained via a pipe  96  to a vacuum tank  98 , see  FIG. 7 . The vacuum tank  98  is filled and drained in a manner that is known per se, by use of valves  100  and a vacuum pump  102 . 
     When a length  22  of piping is to be joined to the pipe string  20  the assembly  1  is displaced vertically along the guide columns  10  by means of the hydraulic motors  82 , the gears  84 , the cogwheels  78  and the pitch racks  80  until the back-up tong  4  corresponds with the upper socket part (not shown) of the pipe string  20  in a known manner. The vertical distance between the back-up tong  4  and the power tong  2  is adjusted so as to make the grippers  56  correspond with the lower socket part of the length  22  of piping. 
     The clamps  40  are moved up to the length of piping by pressurized fluid flowing to the first passage  62  in the swivel ring  60  and on through the first fluid connection  64  to the plus side of the pistons  46 . The excess fluid on the minus side of the pistons  46  flows via the second fluid connection  68  and the second passage  66  back to a hydraulic unit (not shown). 
     The grippers  56  then grip their respective piping sections while the hydraulic motors  34  rotate the drive ring  30  and the groups  38  of clamps about the drilling centre  8 , while at the same time constant pressure is applied through the swivel ring  60  to the plus side of the pistons  46 . 
     The power tong  2  is displaced down towards the back-up tong  4  while the screwing takes place. 
     After the desired tightening moment has been achieved, the rotation of the drive ring  30  is stopped. The clamps  40  are retracted from the pipe string  20  by pressurized fluid being delivered to the minus side of the pistons  46  via the swivel ring  60 . 
     Thus the joint assembly  1  is released from the pipe string  20  to be displaced to its lower position if desired, see  FIG. 2 . 
     When a length  22  of piping is to be detached from the pipe string  20  the operation is performed in a similar manner to that described above. The collecting bellows  90  collects drilling fluid that is present in the length  22  of piping, and which flows out when the length  22  of piping is disconnected. The collected fluid flows via pipe  96  to the vacuum tank  98 . 
     When drilling tools or other objects of a larger outer diameter than the pipe string  20  are to be displaced through the assembly  1 , the grippers  56  can easily be removed from their respective clamps  40 , or alternatively the groups  38  of clamps can be lifted out of the drive ring  30 . 
     Weight-compensating cylinders  104  may be provided between the power tong  2  and the back-up tong  10  in order to take up weight when screwing sensitive threads. A schematic representation of these weight-compensating cylinders  104  is shown in  FIG. 6 . 
     The back-up tong  10  may also be provided with a traversing lifting device  106  on the underside, to make it possible to lift. e.g., the slips. etc. A schematic representation of a traversing lifting device  106  is shown in  FIG. 6 .