Abstract:
This invention relates to a rotary and a method for facilitating the connection of pipes, and more particularly, but not exclusively, to a rotary for a powered drill pipe tong for facilitating the connection of sections or strands of drill pipe to a string of drill pipe.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a rotary and a method for facilitating the connection of pipes, and more particularly, but not exclusively, to a rotary for a powered drill pipe tong for facilitating the connection of sections or stands of drill pipe to a string of drill pipe. 
     Drill pipe tongs are commonly used for facilitating the connection of sections or stands of drill pipe to a pipe string. Typically, the pipe string hangs in a wellbore from a spider in a floor of an oil or gas rig. 
     A section or stand of drill pipe to be connected to the pipe string is swung in from a drill pipe rack to the well centre above the pipe string. A pipe handling arm may be used to guide the drill pipe to a position above the pipe string. A stabbing guide may then be used to align a threaded pin of the drill pipe with a threaded box of the pipe string. A drill pipe tong is then used to tighten the connection to a torque of typically 68,000 Nm (50,000 lb.ft) 
     The drill pipe tong is also used for disconnecting drill pipe. This operation involves breaking the connection which requires a torque typically greater than the tightening torque which may typically be in the order of 110,000 Nm (80,000 lb.ft). 
     A drill pipe tong generally comprises jaws mounted in a rotary which is rotatably arranged in a housing. The jaws are moveable relative to the rotary in a generally radial direction towards and away from an upset part of the pipe to be gripped. The upset parts of the pipe are generally located above the pin and below the box of the pipe and have an enlarged outer diameter and/or a reduced inner diameter. 
     In use, the rotary is rotated forcing the jaws along cam surfaces towards the upset part of the section of pipe. Once the jaws fully engage the upset part, the rotary carries on rotating applying torque to the threads and hence tightens the connection between the section of pipe and the pipe string. 
     Several problems have been observed with such prior art drill pipe tongs. 
     In particular, such drill pipe tongs can badly scar the upset part of the pipe, particularly if the jaws start rotating relative to the drill pipe. 
     Once scarred, the pipe is then lowered into the wellbore. Friction between the wellbore (or casing lining the wellbore) and the scarred upset grinds the upset, reducing the diameter. 
     Scarring of the upset may also be caused by having to reapply the jaws. This is especially common when connecting pipe with “wedge threads” which requires approximately 80° of turn in order to toque the connection. Many prior art wrenching tongs need to be reapplied to the pipe every 25°. 
     A reduction in diameter of the upset requires the use of a new drill pipe tong or for the old drill pipe tong to be modified therefor. 
     An attempt at solving this problem is disclosed in PCT Publication Number WO 92/18744, which discloses a rotary comprising hydraulically operated active jaws and stationary passive jaws. The hydraulically activated jaws are engaged fully with the pipe prior to rotation of the rotary, thereby substantially reducing scarring. A hydraulic circuit is provided on the rotary for actuating the jaws. A plunger is used to activate the hydraulic system by depressing a hydraulic piston of the hydraulic circuit repeatedly. This operation takes time. If several seconds can be saved per connection, the overall cost of the construction of an oil or gas well can be drastically reduced, as long as reliability is not sacrificed. 
     Another problem associated with the rotary disclosed in PCT Publication Number WO 92/18744 is that repeated depressing of the plunger for engaging the jaws fully with the pipe may itself cause some scaring. 
     SUMMARY OF THE PRESENT INVENTION 
     According to a first aspect of the invention, there is provided a rotary comprising at least one jaw and means for displacing said at least one jaw, characterised in that said means is actuable by or connectable to pneumatic fluid. 
     Preferably, said pneumatic fluid is supplied from a supply external to said rotary. 
     Advantageously, said supply is connectable to said rotor by a coupling. 
     Preferably, said at least one jaw is displaceable on a piston. 
     Advantageously, said means for displacing said at least one jaw comprises a hydraulic circuit. 
     Preferably, said hydraulic circuit comprises a hydraulic pump driven by said pneumatic fluid. 
     Advantageously, said hydraulic circuit comprises a bellows which, in use may be used to pressurise said hydraulic circuit. 
     Preferably, said hydraulic circuit comprises an accumulator, which in use, is used to displace said at least one jaw. 
     Advantageously, said rotary comprises three jaws, all of which are displaceable by said means. 
     There is also provided a method for facilitating the connection of pipes using the rotary of the first aspect of the invention, the method comprising the step of applying pneumatic fluid to said means to displace said at least one jaw. 
     According to a second aspect of the invention, there is provided a rotary comprising at least one jaw and hydraulic fluid in a hydraulic circuit for displacing said at least one jaw, characterised in that said rotary comprises a pump for pumping said hydraulic fluid through said hydraulic circuit. 
     Preferably, said at least one jaw is displaceable on a piston. 
     Advantageously, said pump is drivable by a pneumatic fluid. 
     Preferably, said rotary further comprises an accumulator, which in use is charged by said hydraulic pump for displacing said at least one jaw. The accumulator may be used for disengaging the at least one jaw from a pipe and/or for engaging the at least one jaw with a pipe. 
     There is also provided a method for facilitating the connection of pipes using the rotary of the second aspect of the invention, the method comprising the step of pumping hydraulic fluid through said hydraulic circuit to displace said at least one jaw. 
     The rotary disclosed in PCT Publication Number WO 92/18744 comprises an accumulator for maintaining full engagement of said jaws with a pipe in case of any leaks or movement of the jaws. A similar device is used in the specific embodiment of the present invention, but is referred to as a bellows. 
     According to a third aspect of the invention, there is provided a rotary comprising at least one jaw and means for displacing said jaw characterised in that said rotary comprises an accumulator for storing a charge for displacing said jaw. The accumulator may be used to displace said at least one jaw for disengaging a pipe or engaging a pipe. The accumulator may comprise a hydraulic accumulator or any other form of energy storage device, for example a spring or an electrical accumulator (not recommended). 
     Preferably, said at least one jaw is displaceable on a piston. 
     Advantageously, said means for displacing said jaws comprises a hydraulic circuit. 
     Preferably, said hydraulic circuit comprises a pump for charging said accumulator. 
     Advantageously, said pump is drivable by said pneumatic fluid. 
     Preferably, said accumulator is provided with a check valve arranged in series, such that said accumulator may be charged therethrough inhibiting said is accumulator discharging. 
     Advantageously, said accumulator is provided with a release valve arranged in series therewith, such that upon actuation of said release valve said charge discharges from said accumulator to displace said at least one jaw. 
     Preferably, said release valve is provided with at least a second release valve arranged in parallel therewith. 
     There is also provided a method for facilitating the connection of pipes using the rotary of the third aspect of the invention, the method comprising the step of charging said accumulator and using said charge to displace said at least one jaw. 
     Another problem associated with the rotary disclosed in PCT Publication Number WO 92/18744 is that disengagement of the jaws is carried out by relieving the pressure of the hydraulic fluid in the hydraulic circuit and moving the jaws from engagement with a pipe manually. 
     According to a forth aspect of the invention there is provided a rotary comprising at least one jaw and means for moving said jaw into engagement with a pipe, characterised in that there is also provided power operable retracting means for retracting said at least one jaw. 
     Preferably, said at least one jaw is displaceable on a piston. 
     Advantageously, said retracting means comprises an accumulator. 
     Preferably, said means for displacing said at least one jaw comprises a hydraulic circuit. 
     Advantageously, said hydraulic circuit comprises a pump for charging said accumulator. 
     Preferably, the accumulator is located in said rotary. 
     There is also provided a method for facilitating the connection of pipes using the rotary of the forth aspect of the invention, the method comprising the step of operating said disengagement means for disengaging said at least one jaw from a pipe. 
     Another problem associated with the rotary disclosed in PCT Publication Number WO 92/18744 is that the hydraulic circuit arranged on the rotary comprises a reservoir which is open to the ambient air and may allow hydraulic fluid to leak therefrom. 
     According to a fifth aspect of the invention there is provided a rotary comprising at least one jaw and hydraulic fluid in a hydraulic circuit for displacing said jaw characterised in that said hydraulic circuit is sealed. No hydraulic fluid is open to air. 
     Preferably, said hydraulic circuit comprises a bellows for containing hydraulic fluid. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawings, in which: 
     FIG. 1 is a top plan view of a rotary of a drill pipe tong in accordance with the invention with parts shown in cross-section; and 
     FIG. 2 is a schematic of a part hydraulic, part pneumatic circuit used in the rotary of FIG.  1 ; 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1 there is shown a rotary which is generally identified by reference numeral  1 . 
     The rotary  1  comprises a rigid housing  2  which is provided with a toothed perimeter  3  for engagement with toothed drive wheels in a stator of the drill pipe tong (not shown). The housing  2  is also provided with an opening  4  for receiving a drill pipe. 
     Three piston and cylinders  5 ,  6  and  7  are arranged about the rotary  1  spaced at 120° to each other and are directed to the centre of the rotary  1 . The piston and cylinders  5 ,  6  and  7  comprise pistons  8 ,  9  and  10  each provided with a piston head  11 ,  12  and  13 . Cylinders  14 ,  15  and  16  are slidable along said piston heads  11 ,  12  and  13  towards and away from the centre of the rotary  1 . Sealing rings  17 ,  18  and  19  are provided in the piston heads  11 ,  12  and  13  between the piston heads  11 , 12  and  13  and the cylinders  14 ,  15  and  16 . 
     Cylinders  14 ,  15  and  16  are provided with jaws  20 ,  21  and  22  for engaging with the upset of a drill pipe. The jaws  20  and  21  are located in corresponding dovetail slots  23  and  24 . The cylinder  16  is shown provided with an extension member  25  between the cylinder  16  and the jaws  22 . The extension member  25  is located in dovetail slots  26  and the gripping elements  22  are located in corresponding dovetail slots  27  in the extension member  25 . In use, either all of the cylinders  14 ,  15  and  16  are provided with extension members  25  or none of the cylinders  14 ,  15  and  16  are provided with extension members  25 . 
     Hydraulic lines  28 ,  29  and  30  and hydraulic lines  31 ,  32  and  33  are arranged in each piston  8 ,  9  and  10  for the provision of hydraulic fluid in front of and behind the piston heads  11 ,  12  and  13 . 
     A quick release pneumatic fluid supply connection  38 , an accumulator switch  39  and two release switches  40  and  41  are arranged on the housing  2 . 
     The quick release pneumatic fluid supply connection  38  is slidably arranged in a slot  42  in the housing  2 . The slot  42  is shaped to be concentric with the perimeter of the rotary  1 . This allows the rotary  1  to rotate a few degrees with a pneumatic fluid supply line attached. 
     The release switches  40  and  41  are arranged on opposite sides of the rotary so that, when release of the gripping elements  20 ,  21  and  22  from the drill pipe is required, at least one will be within easy reach of an operator. In particular, in use, part of the stator of the drill pipe tong (not shown) may obscure use of one of the release switches. 
     Referring now to FIG. 2 there is shown a circuit which is generally identified by reference numeral  100  arranged in and on the housing  2  of the rotary  1 . 
     The circuit  100  is provided with a quick release pneumatic fluid connection  38  slidably arranged in slot  42  of the housing  2  of the rotary  1 . The pneumatic fluid is supplied from a source  101  via hose  102 , through a valve  103  and through hose  104  to the connection  38 . The source supplies pneumatic fluid at approximately  10  bar. A pneumatic line  105  in the housing  2  divides into two branch lines  106  and  107  supplying a pneumatic pump  108  and a bellows  109  respectively. Pneumatic line  107  comprises an valve  110  which is biased by spring  111  to an open position to allow pneumatic fluid to flow to bellows  109 . 
     The circuit  100  is charged while the drill pipe tong is situated away from the drill pipe. This step is carried out by moving the valve  103  to an open position to allow pneumatic fluid to flow from source  101  through pneumatic line  105  and by depressing accumulator switch  39 . With the accumulator switch  39  depressed, branch line  107  is blocked. Pneumatic fluid actuates pneumatic pump  108 , which pumps hydraulic fluid around a sealed circuit  112 . 
     Hydraulic fluid drawn through line  116  and  117  from the bellows  109  is pumped through line  118 , through a check valve  120  into an accumulator  121 . A line  119  leads from the rear of check valve  120  to a rear side of spring loaded check valve  122 . The spring loaded check valve  122  is biased towards a closed position by a spring  123 . A control line  124  leads from a rear side of the spring loaded check valve  122 , in parallel with spring  123 . 
     Since accumulator switch  39  is depressed hydraulic fluid is prevented from being pumped through line  113  by the valve  114  being in a closed position. 
     Hydraulic fluid is prevented from being pumped through a control line  124  by release valves  40 ,  41  which are closed and by a check valve  125 . Hydraulic fluid is also prevented from being pumped through control line  126  by the check valve  125 . 
     The check valves  120  and  125  inhibit high pressure hydraulic fluid escaping from the accumulator  121 . 
     Control line  126  leads from a front side of the check valve  125  to the rear side of a spring loaded check valve  127  in parallel with a spring  128  which bias the spring loaded check valve  127  to a closed position. 
     Pneumatic fluid  129  in the accumulator  121  is compressed by the pneumatic pump  108  to approximately 280 bar. The pump  108  is prevented from overloading the accumulator by being designed to stall at 280 bar or by use of a pressure relief valve (not shown). The supply of pneumatic fluid is stopped by closing the valve  103 The accumulator switch  39  is now released. 
     The drill pipe tong can now be offered up to the drill pipe (not shown). The drill pipe is located between the jaws  20 ,  21  and  22  of the rotary  1  through the opening  4 . 
     The jaws  20 ,  21  and  22  are activated to engage the upset of the drill pipe by opening the valve  103 . Pneumatic fluid flows through the valve  103 , through line  105  into line  106  and drives the pump  108  and also through line  107  to one side of a membrane  130  in bellows  109 , squeezing hydraulic fluid to the cylinders  14 ,  15  and  16  at a high flow rate. Hydraulic fluid pressure acting against spring  128  of the spring loaded check valve  127  opens the spring loaded check valve  127 . A small amount of hydraulic fluid is allowed to seep from line  126  past the ball of the spring loaded check valve  122  as it opens. 
     The pump  108  pumps hydraulic fluid into line  113  through valve  114  into line  131 , through a check valve  132  and into the cylinders  14 ,  15  and  16  via branch lines  133 ,  134  and  135 . The pump  108  draws hydraulic fluid from the bellows  109  and from behind the piston heads  11 ,  12  and  13  through lines  136 ,  137  and  138 , through device  139 , through lines  141 ,  142  into line  140  and through line  143  into line  144  via a flow diverter  145 , into line  116  into pump  108 . The jaws  20 ,  21  and  22  engage the pipe. The pump  108  will stall or is stopped by removing the pneumatic fluid once the desired engaging force has been reached. This is typically when the pressure in the circuit  100  has built up to 280 bar. 
     It should be noted that, during this procedure, the accumulator  121  is simultaneously brought up to the same pressure as the engaging pressure if it does not already retain a pressure equal to or higher than the engaging pressure. 
     The flow diverter  145  is biased to allow fluid communication between lines  143  and  144 . The device  140  comprises three rotors  146 ,  147  and  148  arranged on a common shaft  149 . When hydraulic fluid flows through the rotors  146 ,  147  and  148 , the rotors allow equal volumes of fluid to pass, thereby ensuring even movement of the jaws  20 ,  21  and  22  arranged on the cylinders  14 ,  15  and  16 . 
     The hose  104  may now be disconnected from the connection  38 . 
     The rotary  1  may now be rotated to rotate the drill pipe to connect drill pipe. 
     Once rotation has ceased, the jaws  20 ,  21  and  22  are disengaged and retracted from the drill pipe. This is carried out by pressing one or both of the release valves  40 ,  41 . This allows hydraulic fluid to flow from the accumulator  121  through control line  124 , through spring loaded check valve  122  and through release valves  40  and/or  41  into line  115 , line  116  and line  117  to bellows  109 . A small amount of hydraulic fluid is allowed to seep past the ball of the spring loaded check valve  122 . Hydraulic fluid under pressure also flows from control line  126 , allowing pressurised hydraulic fluid to flow from infront of the piston heads  11 ,  12  and  13  to bellows  109 . High pressure hydraulic fluid shifts the flow diverter  145 , allowing high pressure hydraulic fluid to flow into line  143 . The flow through line  143  rotates the rotor  147 , which rotatably drives rotors  146  and  148  via shaft  149  and sucks hydraulic fluid out of bellows  109  into the cylinders behind the piston heads  11 ,  12  and  13  and retracts the jaws  20 ,  21  and  22  in unison. A valve  150  is arranged in parallel with line  143  and bypasses the device  139 . The valve  150  is biased by a spring  151  to a closed position, however upon the pressure increasing on the rear side of the piston head  12 , the valve  150  opens equalling the flow rate between the driving rotor  147  and the driven rotors  146  and  148 . 
     The hydraulic fluid in front of the piston heads  11 ,  12  and  13  is expelled through branch lines  133 ,  134  and  135  into line  131   a  and passes through spring loaded check valve  128  into line  117  and into bellows  109 . The residual hydraulic fluid due to the difference in volumes of the cylinders  14 ,  15  and  16  when engaged and retracted, flows is stored in the bellows  109 . 
     Restrictors  152  and  153  inhibit sudden changes in pressure upon depression of the release valve  40 ,  41  and the opening of spring loaded check valve  122 . A safety release valve  155  is provided such that if pressure in the accumulator  121  needs to be released the safety valve can be operated to vent the hydraulic fluid to atmosphere or into a safety release accumulator  156 . The safety release valve may be operated by a control or be a removable cap  157  in a block  200 . 
     The valves  120 ,  122 ,  125 ,  127 ,  132 ,  145 ,  155  and the respective lines and control lines are arranged in a single block  200 . The block  200  may be any suitable material such as aluminium, aluminium alloys or steel. It should be noted that the entire circuit  100  is arranged in or/and an the rotary  1 . The pneumatic fluid source  101  is of the type provided on most drilling rigs and is typically at a pressure of 10 bar. 
     Various modifications are envisaged to the above apparatus. In particular, it is envisaged that a further accumulator could be provided for providing a charge for moving the jaws into engagement with a pipe. This has the advantage that the pneumatic fluid line may be removed from the drill pipe tong before the drill pipe tong is moved about the pipe thus saving vital seconds disconnecting the hose from the rotary. 
     It is also envisaged that the apparatus could be used with thin walled pipe, as it is relatively simple to alter the force applied to the pipe by the jaws. 
     It is also envisaged that the accumulator could take the form of a spring or a battery.