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BACKGROUND 
       [0001]    Embodiments of the present disclosure relate generally to the field of drilling and processing of wells. More particularly, present embodiments relate to a system and method for measuring a tubular internal stress or force introduced by a tubular grappling system. 
         [0002]    In conventional oil and gas operations, a well is typically drilled to a desired depth with a drill string, which includes drill pipe and a drilling bottom hole assembly (BHA). Once the desired depth is reached, the drill string is removed from the hole and casing is run into the vacant hole. In some conventional operations, the casing may be installed as part of the drilling process. A technique that involves running casing at the same time the well is being drilled may be referred to as “casing-while-drilling.” 
         [0003]    Casing may be defined as pipe or tubular that is placed in a well to prevent the well from caving in, to contain fluids, and to assist with efficient extraction of product. When the casing is run into the well, the casing may be internally gripped by a grappling system of a top drive. Specifically, the grappling system may exert an internal pressure or force on the casing to prevent the casing from sliding off the grappling system. With the grappling system engaged with the casing, the weight of the casing is transferred to the top drive that hoists and supports the casing for positioning down hole in the well. 
         [0004]    When the casing is properly positioned within a hole or well, the casing is typically cemented in place by pumping cement through the casing and into an annulus formed between the casing and the hole (e.g., a wellbore or parent casing). Once a casing string has been positioned and cemented in place or installed, the process may be repeated via the now installed casing string. For example, the well may be drilled further by passing a drilling BHA through the installed casing string and drilling. Further, additional casing strings may be subsequently passed through the installed casing string (during or after drilling) for installation. Indeed, numerous levels of casing may be employed in a well. For example, once a first string of casing is in place, the well may be drilled further and another string of casing (an inner string of casing) with an outside diameter that is accommodated by the inside diameter of the previously installed casing may be run through the existing casing. Additional strings of casing may be added in this manner such that numerous concentric strings of casing are positioned in the well, and such that each inner string of casing extends deeper than the previously installed casing or parent casing string. 
       BRIEF DESCRIPTION 
       [0005]    In accordance with one aspect of the disclosure, a system includes a tubular grappling system having a mandrel, an actuator disposed about and coupled to the mandrel, and a plurality of grapples coupled to the actuator, wherein the actuator is configured to translate the plurality of grapples along angled surfaces of the mandrel, and the plurality of grapples is configured to engage with an inner diameter of a tubular. The system also includes a tubular stress measurement system having a first sensor configured to detect a parameter indicative of an axial or circumferential position of the plurality of grapples and a calculation system configured to calculate an internal stress on the tubular based on the parameter. 
         [0006]    Another embodiment includes a method including detecting a first parameter indicative of an axial or circumferential position of a plurality of grapples configured to engage with an inner diameter of a tubular, calculating a radial travel distance of the plurality of grapples based on the parameter indicative of the axial or circumferential position of the plurality of grapples using one or more processors of a calculation system, and calculating an internal stress on the tubular based on the radial travel distance of the plurality of grapples using the one or more processors of the calculation system. 
         [0007]    In accordance with another aspect of the disclosure, a system includes a data collection system having a magnet coupled to a plurality of grapples configured to engage with an inner diameter of a tubular, a magnetometer coupled to an actuator housing of an actuator, wherein the actuator is configured to axially actuate the plurality of grapples, wherein the magnetometer is axially aligned with the magnet, and a signal transmitter coupled to the actuator and configured to transmit a measurement detected by the magnetometer to a calculation system. 
     
    
     
       DRAWINGS 
         [0008]    These and other features, aspects, and advantages of present embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0009]      FIG. 1  is a schematic of a well being drilled, in accordance with present techniques; 
           [0010]      FIG. 2  is a cross-sectional schematic of a tubular grappling system and tubular stress measurement system, in accordance with present techniques; 
           [0011]      FIG. 3  is a graph illustrating pressure measurements of an actuator of the tubular grappling system and a radial travel distance of grapples of the tubular grappling system with respect to time, in accordance with present techniques; 
           [0012]      FIG. 4  is schematic of a data collection system of the tubular stress measurement system, in accordance with present techniques; and 
           [0013]      FIG. 5  is a schematic of a calculation system of the tubular stress measurement system, in accordance with present techniques. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Present embodiments provide a tubular (e.g., casing) stress measurement system for a top drive system. Specifically, the tubular stress measurement system is configured to measure a stress or force acting on a string of tubular when a grappling system of the top drive system is engaged with the tubular. The grappling system includes grapples and a mandrel that are positioned within the tubular prior to hoisting. As described in detail below, the grapples are translated downward along angled surfaces of the mandrel to force the grapples radially outward such that the grapples engage with the internal diameter of the tubular. With the grapples engaged with the tubular, the grapples may apply a force or pressure on the tubular and thereby block the tubular from sliding off the grappling system when the tubular is hoisted and run into a well or hole by the top drive system. As the grapples are translated downward along the mandrel, the tubular stress measurement system measures an axial travel distance of the grapples. In the manner described in detail below, the measured axial travel distance of the grapples may be used to calculate a radial travel distance of the grapples. The radial travel distance of the grapples may then be used to calculate a stress (e.g. internal stress) on the tubular caused by the grapples. 
         [0015]    Turning now to the drawings,  FIG. 1  is a schematic of a drilling rig  10  in the process of drilling a well in accordance with present techniques. The drilling rig  10  features an elevated rig floor  12  and a derrick  14  extending above the rig floor  12 . A supply reel  16  supplies drilling line  18  to a crown block  20  and traveling block  22  configured to hoist various types of drilling equipment above the rig floor  12 . The drilling line  18  is secured to a deadline tiedown anchor  24 , and a drawworks  26  regulates the amount of drilling line  18  in use and, consequently, the height of the traveling block  22  at a given moment. Below the rig floor  12 , a casing string  28  extends downward into a wellbore  30  and is held stationary with respect to the rig floor  12  by a rotary table  32  and slips  34 . A portion of the casing string  28  extends above the rig floor  12 , forming a stump  36  to which another length of tubular  38  (e.g., casing) may be added. In certain embodiments, the tubular  38  may include 30 foot segments of oilfield pipe having a suitable diameter (e.g., 13⅜ inches) that are joined as the casing string  28  is lowered into the wellbore  30 . As will be appreciated, in other embodiments, the length and/or diameter of segments of the casing  16  (e.g., tubular  38 ) may be other lengths and/or diameters. The casing string  28  is configured to isolate and/or protect the wellbore  30  from the surrounding subterranean environment. For example, the casing string  28  may isolate the interior of the wellbore  30  from fresh water, salt water, or other minerals surrounding the wellbore  30 . 
         [0016]    When a new length of tubular  38  is added to the casing string  28 , a top drive  40 , hoisted by the traveling block  22 , positions the tubular  38  above the wellbore  30  before coupling with the casing string  28 . The top drive  40  includes a grappling system  42  that couples the tubular  38  to the top drive  40 . In operation, the grappling system  42  is inserted into the tubular  38  and then exerts a force on an internal diameter of the tubular  38  to block the tubular  38  from sliding off the grappling system  42  when the top drive  40  hoists and supports the tubular  38 . 
         [0017]    As described in detail below, the grappling system  42  further includes a tubular stress measurement system  44 . The tubular stress measurement system  44  is configured to measure a stress (e.g., internal stress) in the tubular  38  caused by the force exerted on the tubular  38  by the grappling system  42 . As shown, the tubular stress measurement system  44  includes a data collection system  46  and a calculation system  48 . The data collection system  46  is coupled to the grappling system  42  and collects data for use in calculating the stress in the tubular  38 . The data collected by the data collection system  46  is described in further detail below. The calculation system  48  of the tubular stress measurement system  44  receives (e.g., by wired or wireless transmission) the collected data from the data collection system  46  and calculates the stress in the tubular  38  using the collected data. In the illustrated embodiment, the calculation system  48  is separate from the data collection system  46 . However, in other embodiments, both systems  46  and  48  may be combined and resident on the top drive  40 . 
         [0018]    It should be noted that the illustration of  FIG. 1  is intentionally simplified to focus on the top drive  40  and grappling system  42  with the tubular stress measurement system  44  described in detail below. Many other components and tools may be employed during the various periods of formation and preparation of the well. Similarly, as will be appreciated by those skilled in the art, the orientation and environment of the well may vary widely depending upon the location and situation of the formations of interest. For example, rather than a generally vertical bore, the well, in practice, may include one or more deviations, including angled and horizontal runs. Similarly, while shown as a surface (land-based) operation, the well may be formed in water of various depths, in which case the topside equipment may include an anchored or floating platform. 
         [0019]      FIG. 2  is a cross-sectional side view of the grappling system  42  and the tubular stress measurement system  44  of the top drive  40 . In the illustrated embodiment, the grappling system  42  includes an actuator  50 , a mandrel  52 , and grapples  54  (e.g., dies, gripping surfaces, friction surfaces, etc.). To grip the tubular  38 , the mandrel  52  and the grapples  54 , which are disposed about the mandrel  52 , are inserted or “stabbed” into the tubular  38 . After the mandrel  52  and grapples  54  are disposed within the tubular  38 , the grapples  54  may be translated downward, in a direction  56 , by hydraulic actuation of the actuator  50 . However, in other embodiments, the grapples  54  may be translated rotationally by mechanical actuation of the actuator  50 . In the manner described below, the grapples  54  are forced radially outward, as indicated by arrows  58 , and engaged with an inner diameter  60  of the tubular  38  when the grapples  54  are pushed downward by the actuator  50 . Similarly, in embodiments where the actuator  50  rotates the grapples  54 , the grapples  54  may similarly be forced radially outward to engage with the inner diameter  60  of the tubular  38 . 
         [0020]    In the illustrated embodiment, the actuator  50  is a hydraulic actuator. However, in other embodiments, the actuator  50  may be a mechanical actuator, electromechanical actuator, pneumatic actuator, or other type of actuator. The illustrated actuator  50  includes a hydraulic cylinder  62  coupled to the mandrel  52  and a piston  64  disposed within the hydraulic cylinder  62  and about the mandrel  52 . The piston  64  is coupled to a piston sleeve  66  that extends around an outer diameter  68  of the mandrel  52 . Additionally, the piston sleeve  66  extends out of the hydraulic cylinder  62  at a base  70  of the hydraulic cylinder  62  and couples to the grapples  54  disposed about the mandrel  52 , as indicated by juncture  72 . 
         [0021]    To actuate the actuator  50  (e.g., the piston  64 ) in the illustrated embodiment, a hydraulic fluid (e.g., oil) is pumped into a piston chamber  74  of the actuator  50  from a hydraulic fluid source  76 . For example, after the mandrel  52  and the grapples  54  are inserted into the tubular  38 , hydraulic fluid may be pumped into the piston chamber  74  on a first side  78  of the piston  64  through a first port  80 . As the hydraulic fluid is pumped into the piston chamber  74  on the first side  78  of the piston  64 , pressure on the first side  78  builds, thereby forcing the piston  64  and the piston sleeve  66  downward (i.e., in the direction  56 ). As the grapples  54  are rigidly coupled to the piston sleeve  66  at the juncture  72 , the grapples  54  also translate downward in the direction  56  when the hydraulic fluid is pumped into the piston chamber  74  on the first side  78  of the piston  64 . 
         [0022]    As mentioned above, when the grapples  54  are translated downward, the grapples  54  are forced radially outward by the mandrel  52 , which remains stationary. Specifically, each of the grapples  54  includes one or more angled surfaces  82  that engage with one or more corresponding angled surfaces  84  of the mandrel  52 . In the illustrated embodiment, each grapple  54  includes three angled surfaces  82 . However, other embodiments of the grapples  54  may include a fewer or greater number of angled surfaces  82 , where each angled surface  82  corresponds with one of the angled surfaces  84  of the mandrel  52 . Each of the angled surfaces  84  of the mandrel  52  has a profile disposed at an outward angle  86  relative to a central axis  88  of the mandrel  52 . In certain embodiments, the outward angle  86  may be approximately 1 to 10, 2 to 8, or 3 to 6 degrees. As will be appreciated by those skilled in the art, the magnitude of outward angle  86  (e.g., an angle of approximately 1 to 10, 2 to 8, or 3 to 6 degrees) may enable gradual radially outward movement of the grapples  54 , thereby enabling improved control and/or operation of the grappling system  42 . Furthermore, each angled surface  82  of the grapples  54  has a profile disposed at an inward angle  90  relative to the central axis  88  of the mandrel  52 , where the inward angle  90  has a magnitude equal or similar to the outward angle  86  of the angled surfaces  84  of the mandrel  52 . As the grapples  52  are forced downward by the actuator  50 , the angled surfaces  82  of the grapples  54  will engage with the corresponding angled surfaces  84  of the mandrel  52  to force the grapples  54  radially outward (e.g., in the direction  58 ). 
         [0023]    Each of the grapples  54  has a radially outward surface  92  that engages with the inner diameter  60  of the tubular  38  when the grapples  54  are forced radially outward by a sufficient amount using the actuator  50 . When the radially outward surfaces  92  of the grapples  54  engage with the inner diameter  60  of the tubular  38 , friction between the grapples  54  and the tubular  38  is increased, thereby blocking the tubular  38  from moving or slipping relative to the grapples  54  when the top drive  40  hoists and supports the tubular  38  during a well forming operation. In certain embodiments, the radially outward surfaces  92  may have coarse surfaces or may include surface treatments to increase friction between the grapples  54  and the inner diameter  60  of the tubular  38 . 
         [0024]    As mentioned above, the embodiments disclosed herein describe the actuator  50  having a hydraulic actuation mechanism. However, it will be appreciated that the actuator  50  may have other actuation mechanisms in other embodiments. For example, the actuator  50  may be mechanically actuated to rotate the grapples  54 . In such an embodiment, the angled surfaces  82  of the grapples  54  and the angled surfaces  84  of the mandrel  52  may have horizontal orientations, as compared to the vertical orientations of the angled surfaces  82  and  84  shown in  FIG. 2 . In other words, the outward and inward angles  86  and  90  of the angled surfaces  82  and  84 , respectively, may have a horizontal orientation. Additionally, in such an embodiment, the angled surfaces  82  and  84  may be curved to extend (e.g., partially extend) around a circumference of the mandrel  52 . When the actuator  50  mechanical actuates (e.g., rotates) the grapples  54 , the angled surfaces  82  of the grapples  54  will engage with the angled surfaces  84  of the mandrel  52  to radially expand the grapples  54  such that the grapples  54  engage with the inner diameter  60  of the tubular  38 , as similarly described above. 
         [0025]    After the tubular  38  is positioned above and coupled to the casing string  28 , the grappling system  42  may release the tubular  38 . Specifically, in the illustrated embodiment, hydraulic fluid may be pumped from the hydraulic fluid source  76  into the piston chamber  74  on a second side  94  of the piston  64  through a second port  96 . The actuator  50  may include seals  97  disposed between the piston  64  and the cylinder  62  to block hydraulic fluid from flowing from the second side  94  to the first side  78 . Similarly, the actuator  50  may include additional seals  99  disposed between the piston sleeve  66  and the cylinder  62  to block hydraulic fluid from exiting the piston chamber  74 . As hydraulic fluid is pumped into the piston chamber  74  on the second side  94  of the piston  64 , pressure may build on the second side  94  of the piston  64  to force the piston  64  upwards in a direction  98 . As the piston  74  is forced upwards, the hydraulic fluid previously pumped into the piston chamber  74  on the first side  78  of the piston  64  (i.e., to engage the grapples  54  with the tubular  38 ) may exit the piston chamber  74  through the first port  80  and return to the hydraulic fluid source  76 . As the piston  64  is actuated upwards, the piston sleeve  66  and the grapples  54  are also translated upwards (i.e., in the direction  98 ). As a result, the angled surfaces  82  of the grapples  54  may slide inwards and upwards along the angled surfaces  84  of the mandrel  52 , and the radially outward surfaces  92  of the grapples  54  may disengage with the inner diameter  60  of the tubular  38 . Thereafter, the grapples  54  and the mandrel  52  may be removed from the tubular  38 , and the grappling process described above may be repeated to grab and hoist another length of tubular  38 . 
         [0026]    As will be appreciated, it may be desirable to monitor the stress (e.g., internal stress) on the tubular  38  that is caused by the grappling system  42  (e.g., the grapples  54 ). For example, if the force applied by the grapples  54  to the tubular  38  during the grappling process exceeds a threshold (e.g., a yield pressure of the tubular  38 ), the tubular  38  may deform and/or degrade. Accordingly, the top drive  40  and the grappling system  42  include the tubular stress measurement system  44  mentioned above. The tubular stress measurement system  44  includes the data collection system  46 , which collects measurements associated with the operation of the grappling system  42 . For example, the data collection system  46  includes a distance sensor system  100  and a pressure sensor system  102 . The distance sensor system  100  may be configured to measure an axial travel distance of the piston sleeve  66  while the grapples  54  are engaged with the tubular  38 . In other embodiments, such as embodiments where the actuator  50  mechanically rotates the grapples  54 , the distance sensor system  100  may be configured to measure a rotational travel distance of the piston sleeve  66  and/or grapples  54 . The axial or rotational travel distance of the piston sleeve  66  (or grapples  54 ) measured by the distance sensor system  100  may then be used to calculate an internal stress of the tubular  38 . The components of the distance sensor system  100  are described in further detail below with reference to  FIG. 4 . 
         [0027]    The pressure sensor system  102  includes two pressure sensors (e.g., a first pressure sensor  104  and a second pressure sensor  106 ) to measure pressures inside the piston chamber  74 . Specifically, the first pressure sensor  104  is exposed to the piston chamber  74  on the first side  78  of the piston  64 . Similarly, the second pressure sensor  106  is exposed to the piston chamber  74  on the second side  94  of the piston  64 . The pressure measurements collected by the first and second pressure sensors  104  and  106  may be used to help determine when the grapples  54  are engaged with the inner diameter of the tubular  38 . For example, in the illustrated embodiment, the grapples  54  are not yet engaged with the inner diameter  60  of the tubular  38 . Accordingly, during initial actuation of the actuator  50  (e.g., when hydraulic fluid is first pumped into the piston chamber  74  on the first side  78  of the piston  64 ), the pressure of the piston chamber  74  measured by the first pressure sensor  104  may be relatively low. After the hydraulic fluid forces the piston  64  downward to the point where the grapples  54  are engaged with the inner diameter  60  of the tubular  38 , the pressure measured by the first pressure sensor  104  will increase more sharply as the tubular  38  provides resistance. 
         [0028]      FIG. 3  is a graph  120  that illustrates the measurements of the first pressure sensor  104  and the radial travel distance of the grapples  54  when the grappling system  42  is actuated by the actuator  50 . Specifically, the graph  120  includes an X-axis  122  representing time, a first Y-axis  124  representing the radial travel distance of the grapples  54 , and a second Y-axis  126  representing pressure measured by the first pressure sensor  104 . A first line  128  represents the radial travel distance of the grapples  54  during actuation of the grappling system  42  as a function of time. A second line  130  represents the pressure measured by the first pressure sensor  104  during actuation of the grappling system  42  as a function of time. 
         [0029]    As mentioned above, after the mandrel  52  and grapples  54  are initially inserted into the tubular  38 , the grapples  54  may not be in contact with the inner diameter  60  of the tubular  38 . As a result, when the actuator  50  is first actuated by pumping hydraulic fluid into the piston chamber  74  on the first side  78  of the piston  64 , the pressure measured by the first pressure sensor  104  may be relatively low. For example, at a time  132 , hydraulic fluid may begin pumping into the piston chamber  74  on the first side  78  of the piston  64 . During a first time period  134  when the hydraulic fluid is pumping into the piston chamber  74 , the piston  64  and the piston sleeve  66  may translate downwards, and the grapples  54  may begin moving radially outwards toward the inner diameter  60  of the tubular  38 , as indicated by segment  136  of the first line  128 . During the first time period  134 , the pressure measured by the first pressure sensor  104  is relatively low and increases marginally, as indicated by segment  138  of the second line  130 , because the piston  64  moves with little resistance as the grapples  54  have not yet contacted the inner diameter  60  of the tubular  38 . 
         [0030]    At a time  140 , the grapples  54  contact the inner diameter  60  of the tubular  38 . When the grapples  54  contact the inner diameter  60  of the tubular  38 , movement of the grapples  54 , and therefore the piston  64 , is resisted by the tubular  38 . Accordingly, the pressure inside the piston chamber  74  on the first side  78  of the piston  64  will increase more rapidly, as indicated by segment  140  of the second line  130 . Additionally, as radially outward movement of the grapples  54  is resisted by the tubular  38  when the grapples  54  contact the tubular  38 , the travel distance of the grapples  54  will increase more slowly, as indicated by segment  142  of the first line  128 . Indeed, the radially outward travel distance of the grapples  54  when the grapples  54  are in contact with the inner diameter  60  of the tubular  38  may equal or approximately equal a radially outward travel distance (e.g., expansion) of the tubular  38 . Accordingly, as described in detail below, the data collection system  46  of the tubular stress measurement system  44  is configured to measure the axial travel distance of the piston sleeve  66 , which may then be used to calculate the radially outward travel distance of the grapples  54  after the grapples  54  have contacted the inner diameter  60  of the tubular  38 . As will be appreciated, once the radially outward travel distance (e.g., expansion) of the tubular  38  is determined, a stress (e.g., internal stress) on the tubular  38  may be calculated. 
         [0031]      FIG. 4  is a schematic representation of the data collection system  46  of the tubular stress measurement system  44 . As mentioned above, the data collection system  46  may be configured to measure an axial travel distance (or a rotational travel distance) of the piston sleeve  66  during actuation of the actuator  50  with the distance sensor system  100 . To this end, the data collection system  46  or distance sensor system  100  includes a variety of sensors that enable measurement of the axial travel distance of the piston sleeve  66 . For example, in the illustrated embodiment, the data collection system  46  includes a magnetometer  160  (e.g., Hall effect sensor) disposed above a magnet  162  (e.g., a cylindrical or rectangular rare earth magnet) that is positioned on an axial end  164  of the piston sleeve  66 . As will be appreciated by those skilled in the art, the magnetometer  160  (e.g., Hall effect sensor) may be configured to precisely and accurately measure a magnetic field strength of the magnet  162 . The magnetometer  160  and the magnet  162  may also be resistant to extreme temperatures, debris, or other environmental conditions to which the data collection system  46  may be exposed. However, in other embodiments, the distance sensor system and/or data collection system  46  may include other sensors and components, such as lasers, optical sensors, ultrasonic sensors, acoustic sensors, radio-frequency identification (RFID) chips or tags, etc. For example, in such embodiments, an emitter (e.g., laser, ultrasonic device, etc.) may be positioned in the location of the magnetometer  160 , and the emitter may emit a wave (e.g., light wave or sound wave) that reflects off of the axial end  164  of the piston sleeve  66 . The wave reflecting off of the piston sleeve  66  may then be detected by a detector, which may be integrated with the emitter or positioned next to the emitter (e.g., at or near the position of the magnetometer  160 ). 
         [0032]    In the illustrated embodiment, the magnetometer  160  is mounted to a sensor mount  166  (e.g., an aluminum bracket) coupled to the cylinder  62  of the actuator  50 . The magnetometer  160  is a transducer that varies its output voltage in response to a magnetic field measurement, and the magnet  162  is a permanent magnet that emits a strong magnetic field. For example, the magnet  162  may be a neodymium magnet or a samarium-cobalt magnet. The centers of the magnetometer  160  and the magnet  162  are axially aligned or positioned relative to one another to enable the magnetometer  160  to reliably measure the magnetic field strength of the magnet  162 . For example, the magnetometer  160  may measure the magnetic field strength of the magnet  162  at a frequency of approximately 100 Hertz. 
         [0033]    When the piston sleeve  66  (and thus the grapples  54 ) move axially, the magnetic field of the magnet  162  measured by the magnetometer  160  will change, as the magnetometer  160  remains fixed to the cylinder  62  of the actuator  50 , while the magnet  162  moves with the piston sleeve  66 . For example, when the piston sleeve  66  and the grapples  54  move downward during actuation of the actuator  50 , the magnetic field of the magnet  162  measured by the magnetometer  160  may decrease as the magnet  162  moves away from the magnetometer  160 . Conversely, when the piston sleeve  66  and the grapples  54  move upward during release of the grapples  54  from the tubular  38 , the magnetic field of the magnet  162  measured by the magnetometer  160  may increase as the magnet  162  moves closer to the magnetometer  160 . As mentioned above, the magnetometer  160  outputs a voltage indicative of the measured magnetic field strength of the magnet  162 . Thus, a change in the voltage output of the magnetometer  160  is indicative of a change in axial position of the magnet  162 . 
         [0034]    In embodiments where the actuator  50  mechanically rotates the grapples  54 , the magnet  162  may be disposed on a side (e.g., outer circumference) of the piston sleeve  66  and the magnetometer  160  may be radially offset from the piston sleeve  66  and mounted to the sensor mount  166 . In such an embodiment, the magnetometer  160  may similarly measure a change in the measured magnetic field of the magnet  162  as the grapples  54 , the piston sleeve  66 , and the magnet  162  rotate. For example, as similarly described above, when the grapples  54 , piston sleeve  66 , and magnet  162  rotate, the magnet  162  may rotate away from the magnetometer  160 , and the voltage output of the magnetometer  160  may decrease. Conversely, when the grapples  54 , piston sleeve  66 , and magnet  162 , the magnet  162  may rotate toward from the magnetometer  160 , and the voltage output of the magnetometer  160  may increase. As similarly described above, a change in the measured magnetic field of the magnet  162  is indicative of a change in rotational position of the magnet  162 , and thus the grapples  54 . 
         [0035]    The data measurements obtained by the magnetometer  160  may be transmitted to the calculation system  48  of the tubular stress measurement system  44 . In the illustrated embodiment, the magnetometer  160  is coupled to electrical components disposed inside a junction box  168  that is mounted to an exterior  170  of the cylinder  62  of the actuator  50 . The electrical components include a printed circuit board  172 , a battery  174 , and a signal transmitter  176 . The printed circuit board  172  receives the measured data from the magnetometer  160 , and the signal transmitter  176  transmits the measured data to the calculation system  48  of the tubular stress measurement system  44 . For example, the signal transmitter  176  may include an antenna that transmits the data as a radio signal to a signal receiver of the calculation system  48 . The signal transmitter  176  may also transmit measurements obtained by the first and second pressure sensors  104  and  106  to the calculation system  48 . In other embodiments, the data collection system  46  and the calculation system  48  may be hard wired to one another. For example, the data collection system  46  and the calculation system  48  may be integrated or combined with one another and may both be positioned on the top drive  40 . 
         [0036]    The data collection system  46  further includes additional magnetometers (e.g., magnetic latching switches)  178  coupled to the sensor mount  166 . More particularly, the additional magnetometers  178  are positioned approximately 90 degrees from the magnetometer  160 . Accordingly, the additional magnetometers  178  are positioned on a lateral side of the magnet  162 . In certain embodiments, the additional magnetometers  178  may be positioned a distance of approximately one-third the total stroke of the piston sleeve  66  from the magnetometer  160  (e.g., approximately 1 to 2 inches). In other words, the additional magnetometers  178  may be positioned one above the other, where the average distance of the additional magnetometers  178  is approximately one-third the total stroke of the piston sleeve  66  from the magnetometer  160 . 
         [0037]    The additional magnetometers  178  enable calibration of the magnetometer  160 . While the illustrated embodiment includes two additional magnetometers  178  for redundancy, other embodiments may include fewer or more additional magnetometers  178 , including no additional magnetometers  178 . In  FIG. 4 , the piston sleeve  66  is shown in a baseline or “zeroed out” position when the actuator  50  is not actuated. In this baseline position, axial distances  180  between the magnet  162  and each of the additional magnetometers  178  may be known. When the piston sleeve  66  moves downward during actuation of the actuator  50 , the magnet  162  may pass the one or both of the additional magnetometers  178 . As each of the additional magnetometers  178  have an orientation perpendicular to the orientation of the magnet  162 , the magnetic field of the magnet  162  measured by the additional magnetometers  178  will switch (e.g., from north to south) when the magnet  162  passes each of the additional magnetometers  178 . Thus, when the measured magnetic field switches for one of the additional magnetometers  178 , an operator or user will know the precise axial position of the magnet  162  and the piston sleeve  66  at that time. Therefore, each stroke of the piston  64  may be used to calibrate the measurements of the magnetometer  160 . 
         [0038]      FIG. 5  is a schematic representation of the calculation system  48  of the tubular stress measurement system  44 . The calculation system  48  includes one or more microprocessors  200 , a memory  202 , a signal receiver  204 , and a display  206 . The memory  202  is a non-transitory (not merely a signal), computer-readable media, which may include executable instructions that may be executed by the microprocessor  200 . Additionally, the memory  202  may be configured to store data collected by the calculation system  48 . For example, the signal receiver  204  may receive data measurements from the data collection system  46 . These data measurements may include voltage output data from the magnetometer  160  and/or additional magnetometers  178 , pressure measurements from the first and second pressure sensors  104  and  106 , or other data. Using the collected data, the microprocessor  200  may calculate an axial position (or rotational position) of the magnet  162 , the piston sleeve  66 , and the grapples  54 . In certain embodiments, one or more of the components described above (e.g., microprocessors  200 , memory  202 , signal receiver  204 , and/or display  206 ) may be additionally and/or alternatively located within the junction box  168  coupled to the actuator  50 . Similarly, the components of the junction box  168  may additionally and/or alternatively be included with the calculation system  48 . 
         [0039]    Based on the measured axial (or rotational) position of the magnet  162 , the radially outward travel distance of the grapples  54  can be calculated. Specifically, as described above, when the piston sleeve  66  and the grapples  54  are actuated axially downward (or rotationally around), the angled surfaces  84  of the mandrel  52  force the grapples  54  radially outward toward the inner diameter  60  of the tubular  38 . As the angle  86  of the angled surfaces  84  of the mandrel  52  is known, the radial travel distance of the grapples  54  can be calculated based on the axial travel distance (or rotational travel distance) of the piston sleeve  66  and grapples  54  measured by the magnetometer  160 . In particular, the radial travel distance of the grapples  54  once the grapples  54  have contacted the inner diameter  60  of the tubular  38  (i.e., once the pressure measured by the first pressure sensor  104  begins to increase rapidly) may be calculated. Thereafter, the internal stress of the tubular  38  may be calculated based on the radial travel distance of the grapples  54  after the grapples  54  have contacted the inner diameter  60  of the tubular  38 . In certain embodiments, a threshold internal stress valve may be stored in the memory  202 . If the calculated internal stress meets or exceeds the threshold internal stress value, an alarm  208 , such as an auditory and/or visual alarm, of the tubular stress measurement system  44  may be activated to alert a user or operator that the calculated internal stress of the tubular  38  has exceeded the threshold. 
         [0040]    As discussed in detail above, the present embodiments provide the tubular stress measurement system  44 . Specifically, the tubular stress measurement system  44  is configured to measure a stress or force acting on a length of tubular  38  when the grappling system  42  of the top drive  40  is engaged with the tubular  38 . The grappling system  42  includes the grapples  54  and mandrel  52  that are positioned within the tubular  38  prior to hoisting. Within the tubular  38 , the grapples  54  are translated downward or rotationally (e.g., by actuator  50 ) along angled surfaces  84  of the mandrel  52  to force the grapples  54  radially outward such that the grapples  54  engage with the internal diameter  60  of the tubular  38 . With the grapples  54  engaged with the tubular  38 , the grapples  54  may apply a force or pressure on the tubular  38  and thereby block the tubular  38  from sliding off the grappling system  42  when the tubular  38  is hoisted and run into the wellbore  30  by the top drive  40 . As the grapples  54  are translated downward or rotationally along the mandrel  52 , the tubular stress measurement system  44  measures an axial or rotational travel distance of the grapples  54 . Specifically, the tubular stress measurement system  44  includes magnetometers  160  and  178  that measure the magnetic field strength of the magnet  162  coupled to the piston sleeve  66  actuating the grapples  54 . The measured magnetic field strength is then used to calculate the axial or rotational travel distance of the grapples  54 . Thereafter, the axial or rotational travel distance of the grapples  54  may be used to calculate a radial travel distance of the grapples  54 . More specifically, the radial travel distance of the grapples  54  after the grapples  54  have contacted the inner diameter  60  of the tubular  38  is calculated using the method described above. Once the radial travel distance of the grapples  54  is determined, a stress (e.g. internal stress) in the tubular  38  caused by the grapples  54  may be calculated. 
         [0041]    While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Summary:
Present embodiments are directed to a tubular stress measurement system including a first sensor configured to detect a parameter indicative of an axial or circumferential position of the plurality of grapples and a calculation system configured to calculate an internal stress on the tubular based on the parameter.