Abstract:
A method of accurately measuring applied torque in a hydraulic breakout machine involves using at least one sensor to measure reactive torque, and using the reactive torque measurement as an accurate indication of applied torque.

Description:
FIELD 
       [0001]    A hydraulic breakout machine used to apply torque to couple and uncouple threaded tubular components. There is described a method of accurately measuring applied torque in a hydraulic breakout machine and a hydraulic breakout machine that measures applied torque in accordance with the teachings of the method. 
       BACKGROUND 
       [0002]    Operation of a typical breakout machine involves positioning the work piece in the headstock and closing the clamp cylinder onto the work piece, which anchors the work piece to the bed, then positioning the tailstock at the appropriate position and closing the clamping cylinders. The generated force is applied through the fixed moment arm, which applies that generated torque to the work piece. The magnitude of the torque is variable, by adjusting the pressure that is applied to the torque cylinders. 
         [0003]    Breakout machines currently use hydraulic pressure supplied to the torque cylinders to determine the magnitude of the torque being applied to the work piece. The hydraulic pressure supplied to the torque cylinders is varied to adjust the torque output. The torque cylinder piston area (break side) and the piston area minus the rod area (make side) are set, as well as the moment arm length or the torque cylinders. At a given pressure, the force generated multiplied by the torque arm length is used to determine the magnitude of the torque applied by one of the torque cylinders and then multiplied by two. Two torque cylinders applying torque in unison is the preferred method, as it reduces the amount of error. There are errors caused by the hydraulic system, mechanical system, as well as the geometry of the machine that limit its accuracy and performance. 
         [0004]    Hydraulic system errors are the total sum of all the small losses due to flow through the hydraulic components and force lost to friction operating components. Pressure and flow moves pistons or valve spools and have spring forces to work against. Each hydraulic component has a number of seals or wear rings that cause pressure losses. The clamp cylinders along with the torque cylinders are relatively large cylinders that all have large stiff seals and large wear rings. These components can be designed to minimize these losses, but the combination of these components can cause significant total loss. The system pressure applied to the torque cylinders must be accurate when varied from 0 through 3,000 psi. An error of 100 psi is not significant at the maximum system pressure of 3,000 psi, but such an error is significant to the accuracy of the lower range of torque application. The hydraulic error outlined is one of the errors that limits the accuracy of the torque that can be applied at the low end of its range. Generally, existing machines offer a minimum torque application of 4,000 lb-ft to 5,000 lb-ft is specified for the “make up” range. Current drilling industry practice is to use smaller diameter tools with smaller diameter threaded connections, which call for lower make up torques being applied. This limits the applications of current breakout machines. 
         [0005]    Mechanical errors are caused by the bearings, hinges, pivot points, and hoses all causing friction during operation. Good design practice reduces the friction these items cause. A good maintenance/lubrication program will minimize the friction and wear caused, but will not eliminate it. As the machine is operated friction and wear will occur. 
         [0006]    The arrangement of the torque cylinders causes an error due to the arc the cylinders travel through a make/break cycle. The moment arm length changing through the torque cylinder travel causes this error, the moment arm length is used to determine the magnitude of the torque being applied. Breakout machines that use the system pressure to determine the torque being applied must have a set moment arm length. Using a moment arm length in one position or an average moment arm length all add an error due to the geometry. Again, good design practice can be used to minimize this error. One method is to limit the arc length the torque cylinders travel. Smaller arc travel results in less moment arm length change, but require more arc travel cycles to complete one full revolution of the work piece. 
         [0007]    The errors combine to create a total amount of error affecting the accuracy of the torque being applied. The effects of wear and tear on a machine and its systems results in a breakout machine that requires re-certification on a annual or bi-annual basis to maintain accurate torque application. The re-certification process is at the end users expense and can be very expensive. The result of the re-certification process, is a chart that indicates the actual torque being applied for a given torque setting read on the breakout machine. This can be very confusing to the operator who has go back and forth between the chart and the machine to determine the torque output, increasing the possibility of operator error. 
       SUMMARY 
       [0008]    According to one aspect, there is provided a method of accurately measuring applied torque in a hydraulic breakout machine. The method involves using at least one sensor to measure reactive torque and using the reactive torque measurement as an accurate indication of applied torque. 
         [0009]    According to another aspect, there is provided a hydraulic breakout machine that includes a bed with a headstock fixed to the bed. The headstock has clamping cylinders for clamping a work piece to the headstock. A tailstock is movable along the bed. The tailstock has clamping cylinders for clamping a work piece to the tailstock. The tailstock or the headstock has torque cylinders for applying rotational torque to the work piece. At least one sensor is provided for measuring reactive torque. 
         [0010]    Measuring reactive torque avoids inaccuracies caused by the hydraulic, mechanical and geometry errors described above. There will hereinafter be described how to measure reactive torque using one or more sensors on the headstock. There is more than one way that this can be done. The preferred way is to provided a reactive torque bracket which is mounted for limited rotational movement within to the headstock. The reactive torque bracket is anchored to the headstock by load sensors, which limit rotational movement and measure reactive torque. 
         [0011]    Although beneficial results may be obtained from the apparatus described above, in order to increase the lower operating range of the breakout machines, it is preferred that there be provided two torque cylinders on the tailstock and means for deactivating one of the torque cylinders for operation in lower torque ranges. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
           [0013]      FIG. 1  is a side elevation view of a hydraulic breakout machine. 
           [0014]      FIG. 2  is a headstock end elevation view of the hydraulic breakout machine of  FIG. 1 . 
           [0015]      FIG. 3  is a tailstock end elevation view of the hydraulic breakout machine of  FIG. 1 . 
           [0016]      FIG. 4  is partially cutaway end elevation view of a reactive torque bracket. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    A hydraulic breakout machine, generally identified by reference numeral  10 , will now be described with reference to  FIGS. 1 through 4 . 
       Structure and Relationship of Parts: 
       [0018]    Referring to  FIG. 1 , breakout machine  10  is used for breaking and making threaded connections used on tools and equipment, for example, tools and equipment that may be used for drilling wells. Breakout machine  10  includes a bed  12  and a hydraulic power console  14 . Bed  12  extends from zero to approximately sixteen feet or more and has a fixed head stock  16 . Bed  12  also includes a movable tailstock  18 , which can traverse the length of bed  12 . Referring to  FIGS. 2 and 3 , headstock  16  and tailstock  18  both have hydraulic clamping cylinders  20  mounted in them. Clamping cylinders  20  are mounted in a radial configuration about a work piece centerline  21 . In this configuration, clamping cylinders  20  can be stroked open and closed in unison to clamp on work pieces of various diameters. Clamping cylinders  20  on headstock  16  are closed on the work piece holding it in a fixed position. Tailstock  18  is then positioned along the work piece by traversing the length of bed  12 . Clamping cylinders  20  of tailstock  18  are then closed at the appropriate position. In this position, tailstock  18  or headstock  16  is capable of applying a torque in a make or break rotation to the work piece. Referring to  FIG. 3 , tailstock  18  has its radial mounted clamping cylinders  20  held in a large bearing  22  that is free to rotate about the center of the clamping cylinders  20 . In turn, a rotating bracket  24  (also referred to as a torque application head) that holds clamping cylinders  20  has two moment arms  26  to which torque cylinders  28  are mounted which can be activated to apply a force through the moment arms  26  resulting in torque being applied to the work piece. In operation, clamping cylinders  20  of headstock  16  and tailstock  18  can be operated individually. Torque cylinders  28  mounted to rotating bracket  24  of tailstock  18  can also be operated independently from clamping cylinders  20 . Referring to  FIG. 1 , hydraulic power console  14  includes a pump  30 , a hydraulic reservoir  32 , and controls  34  to allow operation and the ability to vary supplied pressure to radial clamping cylinders  20  and torque cylinders  28 . 
         [0019]    Referring to  FIG. 4 , a reactive torque bracket  36  is positioned in headstock  16  supported by bearing  38 . Reactive torque bracket  36  is similar to rotating bracket  24  of tailstock  18 . Reactive torque bracket  36  has stop members  39  that engage load cells  40 , which are attached to a mounting plate  41  on headstock  16 . Load cells  40  prevent reactive torque bracket  36  from rotating, and measure the amount of torque experienced by bearing  38 . While two load cells  40  are shown, the actual number may vary, and there may only be a single push/pull load cell  40 . In the depicted embodiment, it is preferred that reactive torque bracket  36  be free to rotate a minimal amount to prevent erroneous readings from any loads on load cells caused by forces other than reactive torque. Each load cell  40  is mounted between both headstock  16 , via mounting plate  41 , and reactive torque bracket  36 , via stop member  39 . Referring to  FIG. 1 , load cells  40  are coupled to a gauge  42  on hydraulic power console  14  and function as sensors to provide an accurate measurement of reactive torque upon headstock  16 . As will hereafter be described, reactive torque gives an accurate indication of the actual torque applied as it is not distorted by the inherent hydraulic, mechanical and geometry errors previously described. 
         [0020]    Referring to  FIG. 1 , breakout machine  10  has a switch  44  that changes from operating on two torque cylinders to one torque cylinder. This can be an automatic pressure sensing switch or a manually selected switch. 
         [0021]    The description above and the drawings show rotating bracket  24  with tailstock  18  and reactive torque bracket  36  positioned in headstock  16 . In an alternative embodiment, the position of these elements may be reversed, such that torque cylinders  28  and rotating bracket  24  are at headstock  16 , and reactive torque bracket  36  is positioned in tailstock  18 , with suitable adjustments made to the rest of breakout machine  10  to accommodate for this change, as well as to the operation steps described below. 
       Operation: 
       [0022]    Referring to  FIG. 1 , in operation, clamping cylinders  20  on headstock  16  are closed on the work piece. Tailstock  18  is then positioned along the work piece by traversing the length of bed  12  and then closing clamping cylinders  20  of tailstock  18  at the appropriate position. Referring to  FIG. 3 , torque cylinders  28  are then activated to apply a force through the moment arms  26  resulting in torque being applied to the work piece. Instead of using hydraulic pressure delivered to torque cylinders  28  to determine torque output, breakout apparatus  10  determines the torque output utilizing load cells  40 . Referring to  FIG. 4 , as pressure is applied by torque cylinders  28 , a reactive torque is applied to reactive torque bracket  36 . However, the rotational movement of reactive torque bracket  36  relative to headstock  16  is limited by load cells  40  positioned about the periphery of reactive torque bracket  36  that anchor reactive torque bracket  36  to headstock  16 . Referring to  FIG. 1 , the reactive torque, as measured by load cells  40 , is shown as a torque reading by gauge  42  on hydraulic power console  14 . The errors outlined previously are still present, but by using reactive torque all of those errors are taken into account, resulting in an accurate torque reading. This results in a direct torque reading by the operator that is more accurate and not sensitive to the position of moment arms  26 . The likelihood of operator error is therefore reduced. The wear and tear of operation, which results in changes in the hydraulic and mechanical error, does not affect the resultant reactive torque reading; therefore the requirement for re-calibration of torque output can be greatly reduced, which significantly reduces operating costs. Once reactive torque is utilized for the torque output, the entire layout of the breakout machine may be refined to optimize efficiency. It is no longer necessary to minimize the amount of arc travel to minimize the moment arm error. A simple increase in the arc travel from 30 to 40 degrees rotation changes one full work piece rotation from 12 arc cycles to 9 arc cycles, increasing operator efficiency. 
         [0023]    A further feature that significantly increases the ability of breakout machine  10  is its ability to apply low make up torque. Prior art breakout machines are limited in their ability to apply a torque below approximately 5,000 lb-ft. Breakout machine  10  can apply an accurate torque well below that of any other breakout machine. Below a given pressure supplied to the torque cylinders one of the torque cylinders has both sides vented, eliminating that cylinder from providing any force. As previously described, this is made possible through switch  44 , which is preferably pressure or manually activated. 
         [0024]    In summary, breakout machine  10  advances breakout machine performance in two ways: 
         [0025]    1. The use of load sensors measures reactive torque, thereby eliminating hydraulic and mechanical system errors, as well errors due to the geometry. 
         [0026]    2. The hydraulic control circuitry has provisions to selectively allow the elimination of one torque cylinder from the load calculation, resulting in a significant reduction in the applied torque. 
         [0027]    These differences result in less error, an increase in the lower torque range and a significant reduction of maintenance and operating costs. 
         [0028]    In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
         [0029]    The following claims are to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the described embodiments can be configured without departing from the scope of the claims. The illustrated embodiments have been set forth only as examples and should not be taken as limiting the invention. It is to be understood that, within the scope of the following claims, the invention may be practiced other than as specifically illustrated and described.