Abstract:
An insert slot for a slip segment of a rotary hand slip is described. The insert slot includes a milled recess cut into a metal slip segment so as to form a rectangular-shaped insert slot designed to receive an insert therein used in the hand slip, and circular corners drilled into the slip segment at a lower corner locations of the insert slot so as to relieve two bottom end corners of the slot.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/719,993 to the inventor, filed Oct. 30, 2012, the entire contents of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    Example embodiments generally relate to an insert slot for inserts of a rotary hand slip and to a method of forming the insert slot in the slip. 
         [0004]    2. Related Art 
         [0005]    Conventionally at an oil rig site, drill collar slips, power slips, and rotary hand slips may be used to hold tool inserts or grip inserts against drill pipe.  FIG. 1  is a front view of conventional extra long rotary hand slip, and  FIG. 2  is cross-sectional cut taken of the rotary hand slip attached to a portion of drill pipe. Referring to  FIGS. 1 and 2 , there is shown a conventional extra long rotary hand slip  100 . Slip  100  includes three slip segments  110 , handles  120 , with each slip segment  110  having an insert slot holding a set of inserts  115  which are designed to interface and grip a pipe  150  under actuating tension of a pin drive master bushing  130  and bowl  140  on the slip  100  (slip segments  110 ). Typically, stresses imparted in this operation may be uneven on the insert  115 , sometimes causing bowing at the toe  125  of the segment  110 , to where the toe  125  may break off and fall into the drill hole. 
         [0006]      FIG. 3  is a top view of a portion of a slip segment showing the toe of conventional insert slot design for inserts; and  FIG. 4  is a side view of  FIG. 3  on a slip segment. The conventional insert slot  116  for an insert  115  employs a design using a half-moon shaped button  117  to finish out the bottom of the dove tail insert groove  119 . The half moon-shaped button  117  is a cast part and is put in place and welded, as shown by weld  118 . The problem with this conventional insert slot design is that under stress of the weight on the inserts  115  (not shown) down on it, the cast part of the half moon  117  wants to shear the groove  119  due to the weight load. Also if the bottom of the insert  115  is tapered and does not sit on the insert slot  116  flat, the insert  115  often will pop out of the slot  116 . Further, the insert  115  must be installed tight in the cutout for slot  116  or the weld  118  will break. 
         [0007]    Another way for conventional insert slot design is to simply cut a slot straight across the bottom of the dove tail in the slip segment  110 . This creates a gap and a flat bottom. The problem with this design is the cut weakens the toe  125  of the slip segment  110 . This can cause the toe  125  to bend, permitting the insert  115  to come out. 
         [0008]      FIG. 5  is a photograph of a top view of a portion of a slip segment showing the conventional insert slot design at the segment toe without inserts therein; and  FIG. 6  is a photograph of a top view of a portion of a slip segment showing the conventional insert slot design with inserts installed in the slot channel.  FIGS. 5 and 6  show the issues discussed above with the conventional half-moon insert slot design. Referring to  FIG. 5  it can be seen in the picture without insert  115  installed that a half-moon button  117  welded piece is in place. 
         [0009]    Three issues at least pose problems with this design. First, the slot  116  has to be machined into the toe  125  area. This area can flex or move during use, causing the button  117  to come out or loosen up. Secondly, the button  117  may not fully seat against the bottom dovetail cutout  119  formed in the slip segment  110  as the insert slot  116 ; thus the weight of the insert  115  would be resting on the weld  118  and not supported by slot  116 . Third, and as shown in  FIG. 6 , when the insert  115  is installed, an interface between the bottom of the insert slot  116  and the top of the button  117  becomes very critical. If the insert  115  rests on the back edge of the half moon button  117 , it will cause the half moon button  117  to pop out. 
         [0010]    In  FIG. 6  with the insert  115  installed in the slot  116 , a crack can be seen around the half moon button  117 . The crack (small chips in weld  118  that follows arc of button  117 ) has formed because the insert  115  was not fully resting on the milled insert slot  116  when the half moon button  117  was welded in place; thus the insert  115  could break out.  FIG. 6  also shows how much closer the slot  116  had to be milled to the end of the slip segment that is represented by the toe  125  area. 
         [0011]    Accordingly, with the conventional insert slot designs, the weight of the insert can sit on the weld  118 , the half-moon button  117  can crack or break, and stresses on these parts can force the toe  125  of the slip segment  110  to break off into the drill hole. If the bottom angle of the inset groove is greater than 1 degree from back to front, it will not create a stable level bottom groove for the insert, acting as a cam surface to create a shear weight interface between the top of the half moon button  117  and where the bottom of the softer metal insert sits on it. As this interface is critical, the weld  118  of the half moon  117  will crack or the half moon  117  will simply pop out of its weld  118 . 
         [0012]    In fabrication, the half-moon is imprecisely saw cut, and the insert slot is milled cut. So, due to the angle on the bottom of the back surface of the insert slot  116  within the slip segment  110  being less than 90 degrees, this causes shear stress to pop the half-moon  117  out of the insert slot  116 . Accordingly, an insert slot design which evenly distributes the stress of an insert  115  down onto the flat bottom within the insert slot  116  so it rests stably in a flat-bottom groove is needed. 
       SUMMARY 
       [0013]    An example embodiment is directed to an insert slot for a slip segment. The inset slot includes a milled recess and corners drilled in to relieve the bottom ends of the slot. 
         [0014]    Another example embodiment is direction to a method of fabricating an insert slot for a slip segment. In the method, a billet of metal is straight end milled to a first depth, square end milled to square corners of the insert slot, dovetail cut to create a groove along lengthwise sides of the billet, and end milled to create corner holes at bottom end corners. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Example embodiments will become more fully understood from the detailed description given herein below and the accompanying drawings, wherein like elements are represented by like reference numerals, which are given by way of illustration only and thus are not limitative of the example embodiments herein. 
           [0016]      FIG. 1  is a front view of conventional extra long rotary hand slip. 
           [0017]      FIG. 2  is cross-sectional cut taken of the rotary hand slip attached to a portion of drill pipe. 
           [0018]      FIG. 3  is a top view of a portion of a slip segment showing the toe of conventional insert slot design for inserts. 
           [0019]      FIG. 4  is a side view of  FIG. 3  on a slip segment. 
           [0020]      FIG. 5  is a photograph of a top view of a portion of a slip segment showing the conventional insert slot design at the segment toe without inserts therein. 
           [0021]      FIG. 6  is a photograph of a top view of a portion of a slip segment showing the conventional insert slot design with inserts installed in the slot channel. 
           [0022]      FIG. 7  is a top view of a portion of a slip segment showing the toe of an insert slot design for inserts according to an example embodiment. 
           [0023]      FIG. 8  is a side view of  FIG. 7  on a slip segment. 
           [0024]      FIGS. 9A to 9E  illustrates a process for fabricating an insert slot in a slip segment according to an example embodiment. 
           [0025]      FIG. 10  is a photograph of a top view of a portion of a slip segment showing the insert slot design of the example embodiment at the slip segment toe without inserts therein. 
           [0026]      FIG. 11  is a photograph of a top view of a portion of a slip segment showing the insert slot design of the example embodiment with inserts installed in the slot channel. 
           [0027]      FIG. 12  is a photograph of a test apparatus used to test the strength of a segment toe with the insert slot design of the example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    As to be described hereafter, an example embodiment is directed to an insert slot for inserts of a rotary or hand slip and to a method of forming the insert slot in the slip. 
         [0029]    As to be shown hereafter, a novel design for an insert slot to hold tool inserts or grip inserts in slips such as drill collar slips, hand slips, power slips, and the like, may provide a slip segment with an insert slot and toe that based on testing is 20% stronger than the conventional insert slot design described above. The example insert slot to be described hereafter is not subject to the limitations of the conventional insert slot. Namely, by having a flat bottom on the groove at the bottom of the insert slot, unlike the half-moon style of the conventional design, downward forces may be evenly distributed. 
         [0030]      FIG. 7  is a top view of a portion of a slip segment showing the toe of an insert slot design for inserts according to an example embodiment, and  FIG. 8  is a side view of  FIG. 7  on a slip segment. Referring to  FIGS. 7 and 8 , the insert slot  216  of the example embodiments employs milled corner holes  218 . As such, these holes  218  are above the toe  125  area so as not to be in the flex zone where there could be a radial stress causing toe  125  breakage into the pipe hole. This was not possible with the half-moon design because the half moon design must be machined into the toe area due to its size. In the conventional design, the toe area is filled back in by the half moon but it is not solid. It is only a weld attachment in one spot. 
         [0031]    The design described herein, on the other hand, is a solid design in this area, so any flex or movement will not cause failure of the toe  125 . The new design is much stronger due to the fact that it remains above and hence out of the toe  125  area. 
         [0032]    Also, no weldments are required. There is no extra half-moon welded piece, so the issue of potential gaps or mismatch between a welded closeout and cast material (i.e., half-moon and slip segment) has been eliminated. Thus, all the material for the insert slot  216  is made of casting; this means that the tensile properties and yield of the material can be definitively known and tested, i.e., what it takes to break it. Designers can therefore have a constant and can rate the slip  100 , e.g., how much weight the slip  100  will hold before it breaks. 
         [0033]      FIGS. 9A to 9E  illustrates a process for fabricating an insert slot in a slip segment according to an example embodiment. Initially in  FIG. 9A , a piece of cast steel billet that will form the insert slot  216  of the slip segment  110  is milled using precision computer numerically controlled (CNC) machining centers, such as in a straight end mill with a straight mill ¾″ cut. Next, at  FIG. 9B , a 5/16″ square end mill cut is applied to make the radiuses of the eventual corner holes  218  a bit smaller and square the corners so the insert  115  will sit flat on the bottom of the cutout (bottom of insert slot  116 ). In  FIG. 9C , a dovetail cutter is employed to groove a 15° angled groove (½″ deep cut) down both vertical sides of the billet, top to bottom (see dotted lines). This is done down the length of the slip segment  110 . To create the corners  218 , a flat (trig) end mill creates a ⅜″ deep hole with a ⅛″ radius ( FIG. 9D ) so as to relieve the corners at the bottom of the slip segment  110  and thus form the bottom of the insert slot  216 .  FIG. 9E  shows what an insert  115  would look like in the completed slot  216 , flush against the bottom groove with the corners  218  providing ample space for the ends of the insert  115 . 
         [0034]      FIG. 10  is a photograph of a top view of a portion of a slip segment showing the insert slot design of the example embodiment at the segment toe without inserts therein, and  FIG. 11  is a photograph of a top view of a portion of a slip segment showing the insert slot design of the example embodiment with inserts installed in the slot channel. In  FIG. 10 , the insert slot  216  design has no separate parts welded in, and machining stops above the toe  125  area. Additionally, it does not matter how the insert  115  (not shown) rests on the bottom of the slot  216 .  FIG. 11  shows the example slot  216  design with the insert  115  installed. The machining stops ¾″ above where the conventional design does, and does not extend into the toe  125  area like the conventional half-moon design of  FIGS. 5 and 6 . As can be seen, there is no welded-in part, the interface between the bottom of the insert  115  and the slot  216  does not matter, and this design is repeatable and can be controlled for testing. 
         [0035]      FIG. 12  is a photograph of a test apparatus used to test the strength of a segment toe with the insert slot design of the example embodiment. The apparatus of  FIG. 12  is a hydraulic ram pushing an insert down into an insert slot. This apparatus was set to test and measure the force needed to break an insert slot of a slip segment (at the toe area of the slip segment) for any type of slip (power slip, hand slip, etc.). Both the conventional half-moon insert slot design and the example insert slot design described herein were tested. 
         [0036]    A sampling was done every hundredth of a second. Two (2) strain gauges were used to measure force at two (2) separate locations: (a) strain at the toe  125  (flex in the toe); (b) strain at where the bottom of the insert  115  sits in the insert slot  116 / 216 . The following TABLE summarizes the results from this comparative test. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 
               
               
                   
                   
               
               
                   
                 Generic 
                 Generic  
                   
               
               
                   
                 350 Ohm 
                 350 Ohm 
                 400 Ton jack 
               
               
                   
                 Uniaxial 
                 Uniaxial 
                 on Channel 1 
               
               
                   
                 Strain Gage 
                 Strain Gage 
                 calibrated 
               
               
                   
                 on channel 1 
                 on channel 2 
                 values 121 (lb) 
               
               
                   
                 [001] MAX Strain 
                 [002] MAX Strain 
                 Maximum 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Half-Moon 
                 4906 
                   
                 88887 
               
               
                 Design 
               
               
                 Half-Moon 
                   
                 8879 
                 96446 
               
               
                 Design 
               
               
                 Example 
                 8192 
                   
                 104004 
               
               
                 Embodiment 
               
               
                 Example 
                   
                 9638 
                 104004 
               
               
                 Embodiment 
               
               
                   
               
             
          
         
       
     
         [0037]    Referring to the Table, for the channel  1  strain in the toe area, the example embodiment showed about a 17% improvement in strength before failure (failing at 104004 lb versus 88887 for the half-moon design). For the insert slot/insert strain point, the example embodiment showed about an 8% improvement. Over a series of test runs, the new design showed an approximate 20% strength improvement as compared to the conventional insert slot design. 
         [0038]    The example insert slot and method of making thereof may be applicable to Pipe slips, drill collar slips, hand slips, etc. The slip formed with this insert slot technology provides a slip which is made repeatable and allows the manufacturer to provide a constant to rate slips, something heretofore which has not been contemplated in the industry. 
         [0039]    The example embodiments being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as departure from the example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included in the following claims.