Abstract:
A tubular cutting tool includes two or more sets of electrically actuated retractable anchoring legs mounted at longitudinally spaced apart locations and an electrically driven rotary cutting head with a retractable cutting blade. The anchoring legs can be arranged such that they are capable of compensating for variations in the internal radii of the tubular to be cut, thereby ensuring that the cutting tool is clamped rigidly in position.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a tubular cutting tool, namely a device for remotely cutting tubulars, such as well casings, drill pipes and underwater or buried pipes, from the inside, using an electrically driven cutting head. 
   During certain phases of well drilling and development it is necessary to recover metal tubulars, or sections thereof, from the borehole. In order to achieve this, a device must be lowered inside the tubular, then operated remotely to perform a cut. The devices commonly employed in the art for this purpose can be largely divided into two categories. 
   The first category encompasses explosive or “chemical cutting” devices which are deployed on a cable, wireline or electric line. Examples of such devices are described in U.S. Pat. Nos. 5,129,322 and 4,125,161. These devices suffer from logistical and operational difficulties and impediments arising from the additional safety precautions required when utilising explosives and corrosive chemicals. 
   The second category consists of mechanical or hydraulic cutting devices which are deployed on the end of drill pipe, coiled tubing or other tubular; examples of such cutting devices are to be found in European Patent Application No. 0 266 864 and U.S. Pat. No. 3,859,877. Such devices suffer from the disadvantage of being cumbersome, as well as expensive to purchase, deploy and operate; the operation and deployment of the devices commonly requires a complete drill rig. Furthermore, in situations where the tubular to be cut is narrow employment of devices in this category may be precluded. Typically, devices in this category incorporate a number of large blades which gouge their way through the tubular. Gouging a cut through the tubular, rather than performing a precision cut, suffers from the disadvantage of requiring a large amount of energy as well as producing long “apple peel” spirals of metal which can fall into the tubular and hinder the cutting operation as well as future operations on the cut tubular. 
   In general, even tubular cutting tools incorporating more than one blade to perform a precision cut, rather than gouging a cut, suffer from the disadvantage that multiple blades have a tendency to “skip” in and out of the individual cuts they produce, resulting in an increased propensity for the blades to snap; in a single bladed tool, the single cutting blade runs around the wall of the tubular in its own cut, even in a slight eccentric or angled deployment. 
   In addition to the disadvantages already discussed, devices in both categories typically leave the cut end of the tubular in a ragged condition, which can occlude subsequent operations involving the tubular. Furthermore, those devices in both categories which include a mechanism for anchoring the device within a tubular, typically utilise some form of hydraulic or pneumatic means for part of the deployment of that mechanism. The use of hydraulic and/or pneumatic means results in the devices requiring multiple cables/hoses which can lead to additional deployment problems when the device is to be used in a tubular, for example, a live oil well, having a seal and airlock mechanism and/or when a cut is to be made at great depth. 
   SUMMARY OF THE INVENTION 
   According to the present invention there is provided a tubular cutting tool for remotely cutting tubulars from the inside, comprising: a housing; two or more sets of retractable anchoring means mounted in the housing at longitudinally spaced apart locations, adapted to be advanced from an initial retracted position out of contact with the internal wall of a tubular to be cut to an anchoring position in contact with the internal wall of the tubular, such as to anchor the tubular cutting tool rigidly in position within the tubular, and to be subsequently retracted from the anchoring position back to the retracted position; first electrically powered or controlled actuating means mounted in the housing and coupled to the retractable anchoring means for moving the retractable anchoring means from the retracted position to the anchoring position prior to performing a cut and then for moving the retractable anchoring means from the anchoring position back to the retracted position once a cut has been performed; a rotary cutting head mounted on the housing, the rotary cutting head having a retractable cutting blade adapted to be progressively advanced from an initial retracted position out of contact with the internal wall of the tubular to a cutting position in contact with the internal wall of the tubular, and to be subsequently retracted from the cutting position back to the retracted position out of contact with the internal wall of the tubular once a cut has been performed; second electrically powered or controlled actuating means mounted in the housing coupled to the retractable cutting blade for progressively advancing the cutting blade from the initial retracted position out of contact with the internal wall of the tubular towards the internal wall of the tubular and for subsequently progressively retracting the cutting blade back to the retracted position out of contact with the internal wall of the tubular once a cut has been performed; and third electrically powered or controlled actuating means mounted in the housing and coupled to the rotary cutting head for rotating the rotary cutting head. Advantageous features of the invention are set forth in the dependent claims to which reference should now be made. 
   A preferred embodiment of the invention for use in remotely cutting tubulars from the inside is described below in more detail with reference to the drawings. 
   According to the preferred embodiment of the invention, there is provided a tubular cutting tool with a cylindrical housing having an upper housing portion or section and a lower housing portion or section. The upper housing section contains support circuitry, a first electric motor, a first gearbox and a ball screw. An interface electronics cartridge and a deployment cable, for lowering or pushing the tool into a tubular, are attached to the end of the upper housing section distant to the lower housing section. The lower housing section contains support circuitry, a central shaft, a mechanical anchoring arrangement mounted around the central shaft, actuating means coupled to the mechanical anchoring arrangement and the central shaft, a second electric motor and a second gearbox. The mechanical anchoring arrangement comprises a set of retractable upper and lower achoring legs and a resilient material. The first electric motor, first gearbox, ball screw, central shaft and actuating means are operable to radially advance the retractable upper and lower anchoring legs from an initial retracted position out of contact with the internal wall of a tubular to an anchoring position in contact with the internal wall of the tubular. As the anchoring legs are radially advanced from the retracted position to the anchoring position the resilient material is compressed, so that the upper and lower anchoring legs are advanced to different radii while maintaining a similar force on the internal wall of the tubular. 
   An electrically driven rotary cutting head having a retractable cutting blade is mounted on the end of the lower housing section distant from the upper housing section. The second electric motor and the second gearbox contained in the lower housing section are coupled to the electrically driven rotary cutting head and are operable to rotate the cutting head and thereby radially advance the cutting blade from an initial retracted position out of contact with the internal wall of the tubular to a cutting position in contact with the internal wall of the tubular. The electrically driven rotary cutting head is designed so that the cutting blade is radially advanced in predetermined increments for each rotation of the cutting head. 
   The upper housing section is locked to the lower housing section, and the lower housing section is locked to the electrically driven rotary cutting head, by weakened linking pins. The weakened linking pins are designed to break under a shearing or tensional force, enabling the majority of the preferred embodiment of the tubular cutting tool according to the invention to be recovered from the inside of the tubular, in the event that either the anchoring mechanism and/or the rotary cutting mechanism should fail or jam, by pulling or winching on the deployment cable. 
   The present invention overcomes the difficulties encountered in the prior art by providing a tubular cutting tool which can be deployed on a single cable with a small crane and winch unit to produce a clean cut end, reminiscent of a machined edge, by incorporating both an electrically actuated anchoring mechanism capable of compensating for variations in the internal radii of the tubular to be cut, thereby ensuring that the cutting tool device is clamped rigidly in position, and an electrically driven rotary cutting head having a single, small sharp cutting blade. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example, with reference to the accompanying drawings in which: 
       FIG. 1  is a longitudinal sectional view through a tubular cutting tool, according to a preferred embodiment of the invention, with the upper and lower anchoring legs and the cutting blade fully retracted; 
       FIG. 2  shows a transverse sectional view of the tubular cutting tool of  FIG. 1  with the upper and lower anchoring legs fully retracted; 
       FIG. 3  shows the upper anchoring leg arrangement of the tubular cutting tool of  FIG. 1  with the legs fully retracted; 
       FIG. 4A  shows the upper and lower anchoring leg arrangement of the tubular cutting tool of  FIG. 1  with the legs fully retracted; 
       FIG. 4B  shows the upper and lower anchoring leg arrangement of the tubular cutting tool of  FIG. 1  with the legs radially extended; 
       FIG. 5  shows a longitudinal sectional view through the rotary cutting head of the tubular cutting tool of  FIG. 1 ; and 
       FIG. 6  shows the rotary electric cutting head of the tubular cutting tool of FIG.  1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The preferred tubular cutting tool  2  illustrated in  FIG. 1 , has a cylindrical housing  4 , having an upper housing section  6  to the top of the Figure and a lower housing section  8  to the bottom of the Figure. The upper and lower housing sections are locked together by weakened linking pins  10 . An electrically driven rotary cutting head  12  having a retractable cutting blade  14  is mounted on the end of the lower housing section  8  distant from the upper housing section  6 . The electrically driven rotary cutting head  12  is locked to the lower housing section  8  by weakened linking pins  16 . The end of the electrically driven rotary cutting head  12  distant to the lower housing section  8  has a tapered nose cone  18 . 
   A deployment cable and an interface electronics cartridge, are attached to the upper end of the upper housing section  6 , distant to the lower housing section  8 ; for simplicity the electronics cartridge and deployment cable have been omitted from the FIGS.. The upper end portion  20  of the upper housing section  6  contains a set of electrical connectors/pressure barriers  22  and a floating piston  24 , which are separated from one another by a space  26 . The lower end portion  28  of the upper housing section  6  contains a first electric motor  30 , having an integral gearbox not shown in the FIGS., which is coupled via a first torque limiter  32  to a ball screw  34 , which is in turn coupled via a carriage  36  to a hollow central shaft  38 . The ball screw  34  is surrounded by a compression spring  40 . 
   The hollow central shaft  38  extends from the lower portion  28  of the upper housing section  6  of the tubular cutting tool  2  into the lower housing section  8  of the tubular cutting tool  2 . A stationary protective cylinder  42 , accommodating electrical wiring, runs through the hollow central shaft  38  from the upper housing section  6  to a connector  44  in the lower housing section  8 . The connector  44  is coupled to a second electric motor  46 . The second electric motor  46  is connected to a three stage planetary gearbox  48  which is coupled to a shaft  50 . The shaft  50  is joined by a splined connection  51  to the electrically driven rotary cutting head  12  mounted on the lower end of the lower housing section  8 . 
   The lower housing section  8  also contains a set of upper mechanical anchoring legs  52 , mounted around the central shaft  38  in the upper portion of the lower housing section  8 , and a set of lower mechanical anchoring legs  54 , mounted around the shaft  50  in the lower portion of the lower housing section  8 . The legs are shown in greater detail in  FIGS. 3 ,  4 A,  4 B and  5 . As shown in  FIG. 2 , each of the sets of anchoring legs is comprised of three individual anchoring legs which are disposed circumferentially around the cylindrical housing  4  at 120° degree intervals. For clarity,  FIGS. 1 ,  3 ,  4 A and  4 B show two of the individual anchoring legs of the upper set of mechanical anchoring legs as though they were diametrically opposed. Throughout the following discussion, reference will only be made to the components and mode of operation of an upper leg  56  and a lower leg  58 , but it is to be understood that the components of all upper and all lower legs are identical, and that references to the mode of operation of the upper leg  56  and the lower leg  58  apply equally to the other upper and lower legs, respectively. 
   Upper leg  56  comprises a leg section  60  and a leg section  62 , both of which are pivoted about a parallel axis directed tangentially. The leg sections  60  and  62  are connected at a hinge joint  64  between the leg sections, to form a jointed leg-pair assembly. The end of the leg section  60  distant to the hinge joint  64  with the leg section  62  is mounted by a pivot pin  66  to a mounting block  68 , which is fixed relative to the cylindrical housing  4 . The end of the leg section  62  distant to the hinge joint  64  with the leg section  60 , is mounted by a pivot pin  70  to a mounting block  72  which is longitudinally moveable relative to the cylindrical housing  4 . Adjacent to the side of the mounting block  72  distant to the mounting block  68 , a first or upper spring stack  74 , having a spring  76 , is mounted on the central shaft  38 . A deployment block  78 , which is connected to the central shaft  38 , is mounted adjacent to the side of the upper spring stack  74  distant to the mounting block  72 . A ring  79 , which is connected to the central shaft  38 , is mounted adjacent to the side of the mounting block  72  distant to the upper spring stack  74 . 
   Lower leg  58  comprises a leg section  80  and a leg section  82 , both of which are pivoted about a parallel axis directed tangentially. The leg sections  80  and  82  are connected at a hinge joint  84  between the leg sections, to form a jointed leg-pair assembly. The end of the leg section  80  distant to the hinge joint  84  with the leg section  82  is mounted by a pivot pin  86  to a mounting block  88 , which is fixed relative to the cylindrical housing  4 . The end of the leg section  82  distant to the hinge joint  84  with the leg section  80 , is mounted by a pivot pin  90  to a mounting block  92  which is longitudinally moveable relative to the cylindrical housing  4 . The mounting block  92  contains a linkage  94  which is attached to one end of an outer sleeve  96  of the cylindrical housing  4 . The other end of the outer sleeve  96  is attached to a linkage  98  which is contained in a block  99  mounted, in the upper portion of the lower housing section  8 , on the central shaft  38  adjacent to the side of the deployment block  78  distant to the upper spring stack  74 . Adjacent to the side of the linkage  98  distant to the deployment block  78 , a second or lower spring stack  100 , having a spring  102 , is mounted on the central shaft  38 . A deployment block  104 , which is connected to the central shaft  38 , is mounted adjacent to the side of the lower spring stack  100  distant to the linkage  98 . 
   The electrically driven rotary cutting head  12  of the tubular cutting tool  2  is shown in greater detail in  FIG. 6  in which, for clarity, all the parts are shown in the same plane. The electrically driven rotary cutting  12  head comprises a head shaft  106  coupled via a second torque limiter  108  to a primary gear ring  110  which rides on the head shaft  106 . The primary gear ring  110  engages a first pinion  112  on a pair of compound idler gears  114  which are located in an extension  116  to the cylindrical housing  4 ; in  FIG. 6  for simplicity only one of the compound idler gears is shown. A second pinion  118  on the compound idler gears  114  engages an external ring gear on a transfer ring  120  which is located on the head shaft  106 . An internal ring gear  122  on the transfer ring  120  engages a pinion  124  mounted on a drive shaft  126  in the electrically driven rotary cutting head  12 . The drive shaft  126  is connected to a worm which is mounted on a wheel  128 . The wheel  128  is mounted on a drive thread  130  which is connected to a blade holder  132  which holds the cutting blade  14 ; the worm lies out of the plane of FIG.  6 . The cutting blade  14  is held in the blade holder  132  by three bolts  134 . The blade holder  132  is locked to the remainder of the electrically driven cutting head  12  by three weakened linking pins; the three pins are not shown in the Figures. 
   The mode of operation of the preferred embodiment of the invention will now be described. 
   The preferred tubular cutting tool  2  illustrated in  FIG. 1  is lowered or pushed into the borehole, pipeline or other tubular to be cut on an deployment cable. Once the apparatus is in position, power is applied down the cable, together with telemetry signals, to the interface electronics cartridge attached to the upper end of the upper housing section  6  of the tool, farthest from the electrically driven rotary cutting head  12 ; for simplicity the electronics cartridge and deployment cable have been omitted from the Figures. 
   The initial or starting configuration of the tool having been lowered or pushed into the tubular is shown in FIG.  1 . As power is supplied, the first electric motor  30  drives the ball screw  34 , by way of the internal gearbox, winding the carriage  36  up the thread of the ball screw  34 , towards the first electric motor  30 . The movement of the carriage  36  results in the longitudinal movement of the central shaft  38  in the same direction. The movement of the central shaft  38  results in the longitudinal movement of the ring  79  and the deployment block  78 , which are attached thereto, towards the first electric motor  30  and the upper leg  56 . As the deployment block  78  moves towards the upper leg  56 , it pushes upon the adjacent upper spring stack  74  which is mounted on the central shaft  38 . The pushing force exerted by the deployment block  78  on the upper spring stack  74  causes the stack to slide longitudinally along the central shaft  38  and thereby to push upon the adjacent mounting block  72 . The pushing force exerted on the mounting block  72  causes the block to slide longitudinally along the central shaft  38  towards the mounting block  68 , which is fixed relative to the cylindrical housing  4 . As the mounting block  72  slides towards the mounting block  68 , the upper leg section  62  is forced to pivot in a clockwise direction about the pivot pin  70 , and the upper leg section  60  is forced to pivot in an anti-clockwise direction about the pivot pin  66 , thereby slowly forcing the hinge joint  64  radially outwards towards the internal wall of the tubular to be cut. 
   Simultaneously, the longitudinal movement of the central shaft  38  results in the longitudinal movement of the deployment block  104 , which is attached thereto, towards the upper leg  56 . As the deployment block  104  moves towards the upper leg  56 , it pushes upon the adjacent lower spring stack  100  which is mounted on the central shaft  38 . The pushing force exerted by the deployment block  104  on the lower spring stack  100  causes the stack to slide longitudinally along the central shaft  38  and thereby to push upon the adjacent block  99  containing the linkage  98 , to which the outer pull sleeve  96  of the cylindrical housing  4  is attached. The pushing force exerted on the linkage  98  causes the linkage to slide longitudinally along the central shaft  38  towards the upper leg  56 . As the linkage  98  slides towards the upper leg  56 , the outer pull sleeve  96  of the cylindrical housing  4 , and the deployment block  92  which is attached thereto by way of linkage  94 , are pulled in the direction of movement of the central shaft  38 . The pulling force exerted on the deployment block  92  causes the block to slide longitudinally along the lower housing section  8  in the direction of movement of the central shaft  38 . As the deployment block  92  slides, the lower leg section  82  is forced to pivot in a clockwise direction about the pivot pin  90 , and the lower leg section  80  is forced to pivot in an anti-clockwise direction about the pivot pin  86 , thereby slowly forcing the hinge joint  84  radially outwards towards the internal wall of the tubular to be cut. In the preferred embodiment of the invention, the surfaces of the upper and lower jointed leg-pair assemblies which, when the legs are in the anchoring position, contact the internal wall of the tubular are sharpened or knurled such as to provide grip on the internal wall of the tubular. 
   As the upper anchoring leg  56  contacts the internal wall of the tubular, the longitudinal movement of the mounting block  72  along the central shaft  38  is restricted and the force exerted by the deployment block  78  on the upper spring stack  74  increases, causing the upper spring  76  to compress slightly. 
   As the lower anchoring leg  58  contacts the internal wall of the tubular, the longitudinal movement of the mounting block  92 , and consequently of the linkage  94  and outer pull sleeve  96 , is restricted. As a result, the force exerted by the deployment block  104  on the lower spring stack  100  increases, causing the lower spring  102  to compress slightly. 
   Compression of the springs occurs independently for the upper and lower anchoring leg sets, allowing the upper and lower legs to deploy to a slightly different radii while maintaining a similar level of force on the internal wall of the tubular. Compression of the springs thereby provides compensation for any small variation in the internal radii of the tubular between the sets of upper and lower legs, ensuring the tubular cutting tool  2  is clamped rigidly, and nominally centrally, in position within the tubular.  FIG. 4B  shows the upper and lower mechanical anchoring leg arrangement of the tubular cutting tool  2  of  FIG. 4A  with the legs radially extended; for simplicity, the upper and lower spring stacks have been omitted from  FIGS. 4A and 4B . In the preferred embodiment of the invention, the springs employed in the upper and lower spring stacks are belleville washers, it will be appreciated, however, that any resilient material could be used. 
   As the force exerted by the anchoring legs on the internal wall of the tubular increases, so does the torque associated with the first electric motor  30 . At a certain torque, the first torque limiter  32 , which may simply be a clutch or spline, operates preventing the first electric motor  30  from stalling; an electronic current limiter could be employed instead of the torque limiter  32 . The electronics then cut power to the first electric motor  30 . 
   A telemetry signal then instructs the electronics to divert power to the second electric motor  46 . The second electric motor  46  drives the shaft  50 , which in turn drives the rotary cutting head  12 , shown in greater detail in  FIGS. 5 and 6 , by way of the three stage planetary gearbox  48 . As the rotary cutting head  12  rotates, the gear train  110 ,  112 ,  114 ,  118 ,  120 ,  122 ,  124 ,  126 ,  128  and  130  advances the blade holder  132  radially outwards, towards the internal wall of the tubular; at this point the blade holder  132  is rotating and advancing. The rotary cutting head  12  of the preferred embodiment of the tubular cutting tool  2  further comprises a spring loaded window which in the initial or starting configuration of the tubular cutting tool  2  covers an aperture  136 , thereby protecting the cutting blade  14  as the tubular cutting tool  2  is lowered into the tubular to be cut. The window is designed such that on the first revolution of the electrically driven rotary cutting head  12  the window opens to expose the cutting blade  14 , allowing the blade holder  132  to be advanced through the aperture  136  on subsequent revolutions of the electrically driven rotary cutting head  12 . The window is driven by the rotation of the electrically driven rotary cutting head  12  by way of a torque limiter  137 . In the preferred embodiment of the invention, the torque limiter  137  is a canted-coil spring, but may alternatively be a sealing element. 
   The gear train  110 ,  112 ,  114 ,  118 ,  120 ,  122 ,  124 ,  126 ,  128  and  130  is designed such that, through a mismatch of gears, the blade holder  132  is advanced slowly, by a fixed amount per revolution of the electrically driven rotary cutting head  12 , and is adjusted such that an optimum advance rate is achieved. If the blade holder  132  advances too slowly, the cutting blade  14  will grind on the internal wall of the tubular, and if it advances too quickly heavy loads will be experienced. 
   The blade holder  132  moves transversely in a dovetailed groove in the rotary cutting head  12  such that rotation of the head shaft  106  advances the blade holder  132 . As the head shaft  106  rotates, the gear train  110 ,  112 ,  114 ,  118 ,  120 ,  122 ,  124 ,  126 ,  128  and  130  simultaneously converts the rotation to a continuous geared feed of the blade holder  132 . As the head shaft  106  rotates, the primary gear ring  110 , coupled thereto, drives the first pinion  112  on the compound idler gears  114 . The second pinion  118  on the compound idlers then drives the external ring gear on the transfer ring  120 . As a result, the internal ring gear  122  on the transfer ring  120  drives the pinion  124  mounted on the drive shaft  126 . The drive shaft  126  turns the worm which rotates the wheel  128  on the drive thread  130  which in turn advances the blade holder  132 . The overall arrangement is such that rapid rotation of the head shaft  106 , typically of the order of 75 revolutions per minute (rpm), causes the worm to slowly advance the cutting blade  14 , typically by about a few thousandths of an inch per revolution of the head shaft  106 ; the slowness of the advance is achieved by the small difference in gear ratios as the rotary motion of the head shaft  106  is picked up by the compound idler gears  114  and then transferred back to the wheel  128 . The advance rate of the cutting blade  14  per revolution of the head shaft  106  is independent of the speed of rotation of the head shaft  106  and is altered by adjustment of the worm. In the preferred embodiment of the tubular cutting tool  2  the head is filled with oil as far as possible. 
   The blade holder  132  advances until the cutting blade  14  contacts the internal wall of the tubular and commences cutting. In the event that the mechanical anchoring legs slip while the cutting blade  14  is in the cutting position, in contact with the internal wall of the tubular, rotation of the cutting head  12  will have the undesirable tendency to cause the entire tubular cutting tool  2  to rotate and the deployment cable to, therefore, twist. In the preferred embodiment of the invention, in order to prevent rotation of the entire tubular cutting tool  2  and twisting of the cable, the deployment cable is attached to the tubular cutting tool  2  by a swivel joint and a centrifugal switch, which cuts power to the electrically driven rotary cutting head  12  if rotation of the tubular cutting tool  2  is detected, is incorporated into either the interface electronics cartridge or the top of the tubular cutting tool  2 . Additionally, in the preferred embodiment of the invention, cylinders  138 , as shown in  FIGS. 1 and 3 , may be included in the upper and/or lower spring stacks in order to limit the longitudinal movement of the spring stacks once the anchoring legs are deployed and thereby prevent the upper and/or lower anchoring legs collapsing under heavy dynamic side loads generated by the rotation of the cutting head  12 . 
   During the cutting process, the electric current consumption and rpm of the rotary cutting head  12  are monitored remotely, via telemetry, by the operator of the tubular cutting tool  2 . Once the cutting blade  14  has advanced a sufficient amount, and the tubular is fully cut, the operator observes a drop in power consumption and instructs the tubular cutting tool  2  to stop. Power is then applied in reverse to the second electric motor  46 . The shaft  50  drives the rotary cutting head  12  in the opposite direction, by way of the three stage planetary gearbox  48 . Since the cutting system is positively geared, reversing the rotation of the cutting head  12  causes the blade holder  132 , and therefore the cutting blade  14 , to slowly retract radially inwards, away from the internal wall of the cut tubular. Once the blade holder  132  is returned to its home starting position, shown in  FIG. 1 , the second torque limiter  108  operates to prevent the second electric motor  46  from stalling. The electronics then cut power to the second electric motor  46 . The resulting cut edge of the tubular is clean and reminiscent of a machined edge; the use of the sets of upper legs  52  and lower legs  54  provides a rigid stable platform with which to apply the rotary cutting blade to the wall of the tubular without danger of the blade breaking or gouging. 
   A telemetry signal then instructs the electronics to apply reverse power to the first electric motor  30 . The first electric motor  30  drives the ball screw  34  in the opposite direction, winding the carriage  36  down the thread of the ball screw  34 , away from the first electric motor  30 . The longitudinal movement of the central shaft  38  pushes the ring  79  and the deployment block  78  towards the rotary cutting head  12 , back to the initial position shown in  FIGS. 1 and 3 . As the ring  79  moves towards the rotary cutting head  12 , it pushes upon the adjacent mounting block  72  causing both the mounting block  72  and the adjacent upper spring stack  74  to slide longitudinally along the shaft away from the mounting block  68 ; the pushing force exerted by the deployment block  78  on the upper spring stack  74  having been removed by the movement of the deployment block  78  towards the rotary cutting head  12 . As the mounting block  72  slides away from the mounting block  68 , the upper leg section  60  pivots in a clockwise direction about the pivot pin  66 , and the upper leg section  62  pivots in an anti-clockwise direction about the pivot pin  70 , thereby slowly drawing the hinge joint  64  radially inwards away from the internal wall of the cut tubular, ultimately to the fully retracted starting position shown in  FIGS. 1 ,  3  and  4 A. 
   Simultaneously, the longitudinal movement of the central shaft  38  pushes the deployment block  104  towards the rotary cutting head  12 , back to the initial position shown in  FIGS. 1 and 3 , thereby removing the pushing force exerted by the deployment block  104  on the lower spring stack  100 . As the deployment block  78  moves towards the rotary cutting head  12 , it pushes upon the block  99  causing the block  99 , the linkage  98 , contained therein, and the adjacent lower spring stack  100  to slide longitudinally along the central shaft  38  away from the upper leg  56 , towards the rotary cutting head  12 . As the linkage  98  moves towards the rotary cutting head  12 , the outer pull sleeve  96  of the cylindrical housing  4 , and the mounting block  92  which is attached thereto by way of the linkage  94 , are pushed towards the rotary cutting head  12 . The pushing force exerted on the mounting block  92  causes the block to slide longitudinally towards the electrically driven rotary cutting head  12 . As the mounting block  92  slides, the lower leg section  80  pivots in a clockwise direction about the pivot pin  86 , and the lower leg section  82  pivots in an anti-clockwise direction about the pivot pin  90 , thereby slowly drawing the hinge joint  84  radially inwards away from the internal wall of the cut tubular, ultimately to the fully retracted starting position shown in  FIGS. 1 ,  4 A and  5 . 
   Once the upper and lower anchoring legs are fully retracted, the tubular cutting tool  2  may be moved to an alternative position inside the tubular in order to perform another cut, or the apparatus may be pulled out of the tubular and recovered. In the preferred embodiment described, the upper and lower legs are orientated such that, when in the deployed position shown in  FIG. 4B , the weight of the tubular cutting tool  2  tends to force the anchoring legs radially further outwards, but so that pulling on the tubular cutting tool  2  from above, on the deployment cable, tends to force the anchoring legs radially inwards to the retracted position shown in FIG.  4 A. Additionally, in the preferred embodiment of the invention the surfaces of the upper and lower jointed leg-pair assemblies which, when the legs are in the deployed position, contact the internal wall of the tubular are slightly cam shaped in the direction tangential to the central shaft  38  such that the reaction torque generated by rotation of the electrically driven rotary cutting head  12  tends to increase the radial force exerted by the legs on the internal wall of the tubular. Although the preferred embodiment described has three upper anchoring legs and three lower anchoring legs, it will be appreciated that two or more upper and/or lower legs could be used to provide sufficient anchoring force to hold the tubular cutting tool  2  in position within the tubular. It will also be appreciated that while the retractable anchoring means of the preferred embodiment of the tubular cutting tool described consists of upper and lower sets of jointed leg-pairs disposed circumferentially around the housing, other, similarly disposed, anchoring means could be employed, such as wedges disposed in wedge-shaped slots around the housing; such means are commonly termed “slips” in the art. 
   In the preferred embodiment of the invention described, the second electrically powered actuating means, for advancing and retracting the cutting blade  14 , and the third electrically powered actuating means, for rotating the rotary cutting head  12 , are powered by a common electric motor, the second electric motor  46 . It will be appreciated that the second and third electrically powered or controlled actuating means could alternatively be powered or controlled by two separate electric motors. In addition, in the preferred embodiment of the invention described, the first electrically powered actuating means, for moving the retractable anchoring means  52  and  54 , and the second and third electrically powered actuating means are powered by two separate electric motors, the first electric motor  30  and the second electric motor  46 . It will be appreciated that, with the inclusion of additional gearboxes and torque limiters, the first, second and third electrically powered or controlled actuating means could alternatively be powered or controlled by a single, common electric motor. In the preferred embodiment of the invention the first, second and third actuating means, for moving the retractable anchoring means, rotating the rotary cutting head and advancing and retracting the cutting blade respectively, are powered directly by one or more electric motors. It will be appreciated, however, that the actuating means could alternatively comprise an electrohydraulic system, wherein one or more electric motors are used to control a number of pressure compensated hydraulic pumps and/or motors which then power the retractable anchoring means, rotary cutting head and cutting blade. 
   In addition to the features already discussed, the preferred embodiment of the tubular cutting tool  2  also comprises features which enable the tubular cutting tool  2  to be recovered from a tubular in the event that the mechanism for retracting the upper and lower anchoring legs should fail, as a result of loss of electrical power, for example. Pulling upon or winching the deployment cable produces tension at the top end of the tubular cutting tool  2  furthest from the rotary cutting head  12 , and exerts a shearing force on the weakened linking pins  10  which lock the upper housing section  6  of the cylindrical housing  4  to the lower housing section  8 . A narrow section  140  of the weakened linking pins  10  are designed to shear under such force, and once this occurs, further pulling upon the deployment cable, and hence the upper housing section  6 , causes the upper housing section  6  to pull away from the lower housing section  8 , until a wider section  142  of the weakened linking pins  10  engages a flange  144  of the lower housing section  8 . The longitudinal movement of the upper housing section  6  relative to the lower housing section  8 , pulls the first torque limiter  32 , connected to the first electric motor  30 , apart causing it to disengage, as a result of which the ball screw  34  is able to “free wheel”. In the absence of motor power, the compression spring  40  drives the ball screw  34 , winding the carriage  36  down the thread of the ball screw  34 , away from the first electric motor  30 . The resultant movement of the central shaft  38  in the same direction, causes the radially extended upper and lower sets of anchoring legs to collapse, away from the internal wall of the tubular, against the tool weight and deployment cable tension in the manner previously described. Once the upper and lower anchoring legs have collapsed, the tubular cutting tool  2  may be recovered intact from the tubular by further pulling on the deployment cable. 
   In the event that the electrically driven rotary cutting head mechanism jams whilst the cutting blade  14  is advanced and in contact with the internal wall of the tubular being cut, there are three possible ways in which the preferred embodiment of the tubular cutting tool  2  may be recovered by the operator from within the tubular. Firstly, pulling on the deployment cable may cause the cutting blade  14  to snap thereby freeing the remainder of the tubular cutting tool  2 , which can then be recovered from the tubular by further pulling on the cable. In the preferred embodiment of the invention the cutting blade  14  is intentionally weakened near to the tip to facilitate breakage. 
   Secondly, if pulling on the deployment cable does not cause the cutting blade  14  to snap, it will exert a shearing force on the three weakened linking pins which lock the blade holder  132  to the remainder of the rotary cutting head  12 ; it will be appreciated that different numbers of linking pins could be employed. The weakened linking pins  134  are designed to shear under such force, thereby separating the deployed cutting blade  14  and blade holder  132  from the remainder of the tubular cutting tool  2  which can then be recovered from the tubular by further pulling on the deployment cable. 
   Finally, if pulling on the deployment cable fails either to snap the blade or to cause the three weakened linking pins  134  to shear, it will exert a shearing force on the weakened linking pins  16  which lock the lower housing section  8  of the cylindrical housing to the non-rotating extension  116  of the rotary cutting head  12 . The weakened linking pins  16  are designed to shear under such force, thereby enabling the splined connection  51  between the rotary cutting head  12  and the shaft  50  to be uncoupled by further pulling on the deployment cable. The upper and lower housing sections of the tubular cutting tool  2  can then be recovered by pulling on the deployment cable, leaving the cutting head  12  behind in the tubular. In the preferred embodiment of the invention, the profile of the neck  146  of the rotary cutting head  12  which forms the splined connection  51  with the shaft  50  is such that it can be easily latched onto using conventional recovery equipment, thereby allowing the rotary cutting head  12  of the tubular cutting tool  2  to be subsequently recovered from the tubular. 
   In the preferred embodiment of the invention, the entire internal workings of the tubular cutting tool  2  are filled with an oil, or another suitable fluid, which is then pressurized. The oil, or other fluid, is introduced into the tubular cutting tool  2  through filling/drainage parts  148  in the upper housing section  6  of the cylindrical housing  4  and then pressurized by means of the floating piston  24 ; the unoccupied space  26  in the upper housing section  6  acts as a reservoir for the oil or other fluid. Production of a tubular cutting tool with thin outer walls is desirable as a method of reducing the overall diameter of the tool, thereby enabling the tool to be employed to cut tubulars of narrow internal diameter. However, decreasing the outer wall thickness of the tool reduces its ability to withstand the external over-pressure experienced in the tubular borehole liner or pipeline to be cut, which may exceed 15,000 psi (1000 atm.). Filling the internal workings of the tool with an oil, or another fluid, which is then pressurized by means of the floating piston  24 , compensates for the reduced external pressure resistance of a thin outer wall by equalizing the internal pressure within the tool to match the external pressure experienced by it when inside a typical tubular or borehole. In addition, filling the tool with a pressurized fluid means that the mechanical anchoring mechanism is compensated for the external hydrostatic pressure within the tubular and does not, therefore, have to overcome it in order to move from the retracted position to the anchoring position. The tubular cutting tool  2  according to the preferred embodiment of the invention has an overall external diameter of between about 2 inches (50 mm) and about 4 inches (100 mm), more preferably between about 2.5 inches (64 mm) and about 3 inches (76 mm), making it suitable for use in cutting tubulars with internal diameters of between about 3.5 inches (89 nun) and about 10 inches (254 mm)