Patent Document

FIELD OF THE INVENTION 
     This invention relates to a method of repairing drill pipes, and to a new lathe, particularly for use in repairing drill pipes. 
     BACKGROUND OF THE INVENTION 
     Drill pipes are threaded together in use in drill strings during drilling, for example of oil or gas wells. One end of a drill pipe has an internally threaded box or female connection, while the other end has an externally threaded pin or male connection so that the drill pipes may be threaded together. The drill pipe adjacent the box or pin is enlarged to form an upset and provide strength for the joint, but to reduce the cost of making the drill pipe, the upset typically does not extend very far down the pipe length, typically not much more than about twice the pipe diameter. The internal bores and threads of the box and pin are machined precisely to allow the box and pin to seal together on sealing surfaces at either end of the threads, and also perhaps at intermediate points between threaded portions. 
     During drilling, stresses on the drill pipe and especially on the boxes and pins cause the interior surface of the box and the exterior surface of the pin to become worn, such that they do not seal together, and fluid within the drill pipe can leak. Since drill pipe is expensive, rather than throw out the drill pipe when it is worn, drilling contractors will repair or have the drill pipe repaired by refinishing the boxes and pins. The refinishing is carried out by machining a new set of threads and sealing surfaces deeper into the box and pin respectively. This eliminates a part of the enlarged portion of the box and pin. After several repairs, the enlarged portion of the box or pin is gradually eliminated until no further repairs can be carried out and the drill pipe is discarded. 
     The machining of the drill pipe is typically carried out using a lathe having a chuck with jaws mounted in a plane at one end of the lathe. The chucks hold and rotate one end of a drill pipe against a working tool. The other end of the drill pipe is held in a steady rest. Often, the drill pipe will be bent at the end, with the consequence that when cradled in the lathe, the portion of the end being worked on does not rotate precisely in a circle. In this instance, a large amount of metal on the end of the drill pipe may need to be taken off in order to obtain a precisely configured box or pin. This limits the number of times the drill pipe can be repaired, and consequently increases the operating costs of the drilling contractor. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a method of allowing multiple repairs of bent drill pipes without losing too much of the box or pin material. According to a further aspect of the invention, a novel chuck and lathe is provided for carrying out the method of the invention. 
     There is thus provided in accordance with one aspect of the invention, a method of repairing a drill pipe having first and second connector ends, each of the first and second connectors ends including a threaded portion and sealing portions, with a lathe having a chuck with longitudinally spaced first and second sets of jaws, the method comprising the steps of mounting the drill pipe in a lathe, gripping the first connector end of the drill pipe with each of the first and second sets of jaws, orienting the first connector end by manipulation of the first and second sets of jaws into a working position; and rotating the drilling pipe against a working tool to machine the threaded portion and sealing portion of the first connector end and produce a new threaded portion and sealing portion of the first connector end. 
     There is also provided in accordance with a further aspect of the invention, a lathe for machining a drill pipe, the lathe comprising a chuck, first and second sets of jaws adjustably mounted on the chuck, the first set of jaws being mounted radially in the chuck at a first longitudinal position and the second set of jaws being mounted radially in the chuck in a second longitudinal position spaced from the first first longitudinal position, each of the first and second sets of jaws including x and y positioning jaws, a motor for rotating the chuck; and means to machine a drill pipe gripped by the jaws. 
     In a further aspect of the invention, each set of jaws includes first and second pairs of jaws mounted orthogonally to each other. 
     In a further aspect of the invention, the first set of jaws is mounted further away from the lathe than the second set of jaws, and the jaws of the first set of jaws are longer in a direction perpendicular to the orientation of the first set of jaws than the jaws of the second set of jaws. 
     In a further aspect of the invention, a workpiece positioning device is provided so that repeated cuts of pipes may be made without re-positioning the pipes. In this aspect of the invention, there may only be one set of jaws. 
     These and further aspects of the invention will now be described. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There will now be described preferred embodiments of the invention, with reference to the drawings, by way of illustration, in which like numerals denote like elements and in which: 
     FIG. 1 is a schematic showing a drill pipe in position on a lathe for machining the box or pin at one end of the drill pipe; 
     FIG. 2 is a side view, partly in section, of a typical drill pipe showing where the chuck of the invention grips the drill pipe; 
     FIG. 3 is a top view, partly in section, showing a chuck for a lather according to the invention; 
     FIG. 4 is an end view of a chuck for a lathe according to the invention; 
     FIG. 5 is a side view of a chuck and jaws according to the invention showing a workpiece positioning device in working position on the chuck; 
     FIG. 5A is a blow up of a portion of FIG. 5; 
     FIG. 6 is an end view of the chuck, jaws and workpiece positioning device; 
     FIG. 7 is a section, partially exploded, through the device shown in FIGS. 5 and 6 along the line A—A shown in FIG. 6; 
     FIG. 7A is a blow up of a portion of FIG. 7; 
     FIG. 8 is a perspective view of a chuck, jaws and workpiece positioning device according to the invention; and 
     FIG. 9 shows an alignment system for initial alignment of a workpiece before cutting. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a lathe  10  with a chuck  12  mounted on one side of a lathe motor  14 . The chuck  12  is driven rotationally under power by the lathe motor  14  in conventional fashion. A drill pipe  16  being worked has one connector end  18  resting in a steady rest or cradle  20 , and the other connector end  22  is held by the chuck  12  in working position against a tool  24 . As the drill pipe  16  rotates, the tool  24  may be moved by machine assembly  26  in accordance with a desired pattern that is input by an operator. The tool  24  and machine assembly  26  form a means to machine work pieces mounted on the lathe. Any of various conventional tools and associated machine assemblies may be used, such as boring, facing, turning, threading and bevelling tools made by such well known manufacturers as Kennametal Limited, Raleigh, S.C., U.S.A., Sandvik Coromant Co., Fairlawn, N.J., U.S.A., and Valenite Inc. of Madison Hts., Mich., U.S.A. 
     Referring to FIG. 2, a joint between two drill pipes  16   a  and  16   b  is shown. The joint is formed between the box connection  28  of drill pipe  16   a  and pin connection  30  of drill pipe  16   b . In this patent document, the box and pin connection both may be referred to as connector ends, which are enlarged in relation to the rest of the drill pipe. Each connector end includes mating threaded portions  32  and sealing portions  34  and  36 . 
     Referring to FIGS. 3 and 4, there is shown a chuck  12  with longitudinally spaced radially oriented first and second sets of jaws  40 ,  42  mounted on the chuck  12 . The first set of jaws  40  is mounted in a first longitudinal position A and the second set of jaws  42  is mounted in a second longitudinal position B spaced from the first longitudinal position. Each position A and B is shown roughly bisecting the jaws. Each of the first and second sets of jaws  40 ,  42  include jaws mounted on x and y axes for positioning the jaws along the respective axes. In FIG. 4, both x and y axes are in the plane of the figure, while in FIG. 3, one of the axes is perpendicular to the plane of the figure. Each jaw  40 ,  42  has slots  44  formed in the side of the jaw  40 ,  42 , and the jaws  40 ,  42  are mounted in the chuck  12  with ridges  46  received by the slots  44 . The slots  44  and ridges  46  form tracks for the jaws to slide on and retain the jaws  44  within the chuck  12 . The jaws  40 ,  42  may be adjusted in the chuck  12  by screws  48 . The screws  48  are received by threaded semi-cylindrical slots  50  in the chuck  12 . Corresponding threaded semi-cylindrical slots  52  in the jaws  42  complete threaded holes for receiving the screws  48 . The tops of the screws  48  have hexagonal slots  54  for receiving hex wrenches. Rotation of the screws  48  causes the jaws  40 ,  42  to move radially in the chuck  12 . The screws  48 , together with the slots  44 ,  50  and  52  and ridges  46 , form means to adjust the position of each of the jaws in the chuck. Each jaw of each set of jaws is independently adjustable. 
     A pipe  38 , without upset, is shown gripped by the chuck  12  in FIG. 3, with its pin connection  39  extending forward from the chuck  12  in working position. In this instance, the chuck  12  may be located as close as is feasible to the pin connection  39 . In the case of machining connector ends of drill pipe  16   a  or  16   b , the front set of jaws  40  may be centered at the position marked A in FIG. 2, and the rear set of jaws  42  may be centered at the position marked B in FIG.  2 . The exact location of the jaws will depend to some extent on the length of upset as indicated by the notation C in FIG.  2 . If the upset is large enough, as with box connection  28 , both sets of jaws  40 ,  42  may fit on the upset as shown in FIG.  2 . With a short upset it may be possible only to fit one of the sets of jaws on the upset. 
     As shown in FIGS. 3 and 4, it is preferable that there be two mutually orthogonal pairs of jaws in each set of jaws, for a total of eight jaws. It is possible to use only six jaws, with three jaws mounted at 120° to each other in each set, but this makes it difficult for the operator to adjust the drill pipe. While such a design does allow manipulation of the connector end of the drill pipe in both the x and y directions, it is hard to adjust because rotation of any two jaws necessarily changes the position of the drill pipe in both x and y directions. With the design shown in FIGS. 3 and 4, two jaws can be operated independently for each of the x and y directions. 
     The jaws  40  of the front set of jaws are elongated by addition of jaw pieces  56  screwed by screws  58  onto the sides of the jaws. The jaw pieces  56  make the total jaw length, in a direction along the chuck (perpendicular to the plane defined of the first set of jaws), greater than the length of the jaws  42  of the second set of jaws. Both sets of jaws may be elongated in this manner if possible, but there is not enough room for the second set of jaws  42  to be extended in the chuck shown. In the case of jaws  42 , the body of the chuck gets in the way on one side of the jaws and on the other side the lathe motor itself must be connected by a drive (conventional and not shown) to the chuck and this leaves no room for additional jaw length. The additional length of jaws permits the jaws to grip the pipe firmly. 
     In the method of operating the lathe with the chuck of FIGS. 3 and 4, the first step is to mount the drill pipe in a lathe with one end of the drill pipe  16  resting in steady rest  20 . Next, one connector end  22  (either end  16   a  or  16   b ) of the drill pipe is gripped with each of the first and second sets of jaws  40 ,  42 , by insertion of the drill pipe into the chuck and tightening the jaws  40 ,  42  onto the drill pipe. The operator may then rotate the drill pipe to determine if the connector end  22  is rotating in a circle. Conventional means may be used to determine the deviation of the rotation from a circle. If the connector end  22  is not rotating in a circle, within measurable tolerances, then the connector end may be oriented by manipulation of the first and second sets of jaws into a working position. The connector end may be moved in either or both of the x and y directions by screwing of the x and y jaws respectively. Once orientation of the jaws is complete, the drilling pipe may be rotated against the working tool. Both the threaded portion and sealing portions of the connector end may be machined to produce a new threaded portion and sealing portion of the connector end. The method of the invention is believed applicable to any cylindrical work piece with an end requiring work, but has particular utility for machining a box or pin connection of a drill pipe. While the connector end is being worked, the other end of the relatively flexible drill pipe rests on the steady rest  20 . The drill pipe, once repaired, may be returned to the drilling contractor and used again for drilling. As the drill pipe is used and the connector ends become worn again, the drill pipe can continue to be repaired by repetition of the method of the invention until insufficient upset remains to permit further machining of the connector ends. 
     A workpiece positioning device will now be described in relation to FIGS. 5-8. A chuck  12  with jaws  40  and  42  are used as described in relation to FIG.  3 . The workpiece positioning device uses a frame or spider assembly  71  for repeated exact positioning of a tool joint pipe  38  within chuck  12 . The pipe  38  has a shoulder  89 . The spider assembly  71  has four arms  80  extending from a hub  82 , which when the spider assembly  71  is fixed to the chuck is aligned with the opening in the chuck which receives the pipe to be worked on. Each arm  80  terminates outwardly at a pedestal  84  from which a cam pin  70  extends parallel to the axis of the hub  82 . A spider mounting frame  65  formed of four arms disposed between the jaws  40  is secured to the chuck  12  using T-slot blocks  62  and capscrews  64 . Each arm of the spider mounting frame  65  has a cam pin receiving hole  86  and cam  63  for receiving and securing the cam pins  70  of the spider assembly  71 . At the hub  82  is a tool joint jig  69  with a shoulder  88 , the bore  90  of the tool joint jig  69  being sized to snugly receive a connector end of a pipe  38 . The spider assembly  71  is supplied with a locking nut  72  threaded onto a ring  85  screwed onto the hub  82  over a collet  73 , a bushing  74  within hub  82  and a jam wing nut  75  that threads onto exterior threads  83  of the tool joint jig  69 . See FIG. 7A in particular for these features. The tool joint jig  69 , hub  82 , locking nut  72 , collet  73 , bushing  74  and wing nut  75  permit a tool joint pipe to be secured within the spider assembly  71  in a fixable, and repeatable position. Bushing  74  inside diameter is about the same size as the central portion of the tool joint jig  69  for it fits snugly within the tool joint jig  69 . A keyway  99  on the tool joint jig receives a key  97  in the bushing  74  (See FIG.  5 A). 
     Operation of the spider assembly for cutting workpieces is according to the following face and chase procedure. 
     1 Install spider mounting frame  65  into machine chuck  12  with t-slot blocks  62  and capscrews  64 . 
     2 Install top jaws  40  with top jaws capscrews  76 . 
     3 Install tool joint pipe  38  into chuck  12  a predetermined distance conventionally determined according to the work order, secure with top jaws  40  by turning operating screw  48 A and align pipe I.D. with alignment jaws  42 , by turning operating screws  48 B. 
     4 Cut tool joint as per work order. 
     5 Move tool post  92  with alignment dials  94 ,  96  and  98  until they engage shoulders of the pipe  38  as illustrated in FIG. 9, and set dials to “0” reading. 
     6 Back off tool post  92  and remove alignment dials  94 ,  96  and  98 . 
     7 Install tool joint jig  69  onto tool joint pipe  38  until shoulder  88  makes-up tight to shoulder  89 . 
     8 Install spider assembly  71  into spider mounting frame  65  and lock in cam pins  70  in position with cams  63 . with the tool joint jig  69  in the hub  82 . 
     9 Install jam wing nut  75  onto tool joint jig  69  to align bushing  74  such that shoulders  87  and  91  abut and tighten up. 
     10 Tighten up locking nut  72  to lock in position collet  73 . 
     11 Unlock and remove jam wing nut  75 . 
     12 Unlock cams  63  and remove spider assembly  71 . 
     13 Unscrew and remove tool joint jig  69 . 
     14 Loosen-up operating screws  48 B to back-up alignment jaws  42  to clear tool joint o.d. 
     15 Loosen-up operating screws  48 A to back-up top jaws  40  and remove tool joint pipe  38 . 
     16 Install damaged tool joint pipe through chuck  12  to predetermined distance (do not tighten jaws  40 ). 
     17 Install tool joint jig  69  onto damaged tool joint pipe until shoulder  88  makes-up tight to shoulder of damaged tool joint pipe. 
     18 Install spider assembly  71  onto tool joint jig  69 . 
     19 Install jam wing nut  75  and tighten-up to spider assembly  71 . 
     20 Line-up one cam pin  70 , which may be marked for this purpose, in relation to a correspondingly marked socket  86  on spider mounting frame  65  and install spider assembly  71  with tool joint pipe  38  as one unit and lock-in cams  63 . 
     21 Tighten-up top jaws  40  by turning operating screws  48 A onto tool joint pipe  38  and align tool joint pipe  38  with alignment jaws  42  by turning operating screws  48 B. 
     22 Unlock and remove jam wing nut  75 . 
     23 Unlock cams  63  and remove spider assembly  71 . 
     24 Unscrew and remove tool joint jig  69 . 
     25 Check alignment of pin seal faces by seal alignment jig  92  with alignment dials  94 ,  96  and  98 . Move seal alignment jig  92  until dials read “0” (do not re-adjust dials). 
     26 Recut tool joint  38  (face &amp; chase operation or as step  4 ). 
     27 Repeat steps  14  to  26  for another damaged tool joint pipe. 
     A person skilled in the art could make immaterial modifications to the invention described in this patent document without departing from the essence of the invention that is intended to be covered by the scope of the claims that follow.

Technology Category: 4