Abstract:
A method of connecting a first threaded tubular to a second threaded tubular includes: engaging threads of the tubulars; and rotating the first tubular relative to the second tubular, thereby making up the threaded connection. The method further includes, during makeup of the threaded connection: detecting a shoulder position; and after detection of the shoulder position, monitoring for potential yielding of the threaded connection. The method further includes terminating the makeup according to: a first criterion in response to detection of the potential yielding; or a second criterion in response to absence of the potential yielding.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional Pat. App. No. 61/499,984, filed Jun. 22, 2011, which is herein incorporated by reference in its entirety. 
    
    
     Applicant&#39;s paper OTC 21874 titled “Shoulder Yielding Detection During Pipe Makeup” and presented at the Offshore Technology Conference held in Houston, Tex. from May 2 to May 5, 2011 is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to a method for detecting yielding of a shoulder during tubular makeup. 
     2. Description of the Related Art 
     In wellbore construction and completion operations, a wellbore is formed to access hydrocarbon-bearing formations (e.g., crude oil and/or natural gas) by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill support member, commonly known as a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. An annulus is thus formed between the string of casing and the formation. The casing string is temporarily hung from the surface of the well. A cementing operation is then conducted in order to fill the annulus with cement. The casing string is cemented into the wellbore by circulating cement into the annulus defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons. 
     A drilling rig is constructed on the earth&#39;s surface or floated on water to facilitate the insertion and removal of tubular strings (e.g., drill pipe, casing, sucker rod, riser, or production tubing) into a wellbore. The drilling rig includes a platform and power tools, such as an elevator and slips, to engage, assemble, and lower the tubulars into the wellbore. The elevator is suspended above the platform by a draw works that can raise or lower the elevator in relation to the floor of the rig. The slips are mounted in the platform floor. The elevator and slips are each capable of engaging and releasing a tubular and are designed to work in tandem. Generally, the slips hold a tubular or tubular string that extends into the wellbore from the platform. The elevator engages a tubular joint and aligns it over the tubular string being held by the slips. One or more power drives, e.g. a power tong and a spinner, are then used to thread the joint and the string together. Once the tubulars are joined, the slips disengage the tubular string and the elevator lowers the tubular string through the slips until the elevator and slips are at a predetermined distance from each other. The slips then reengage the tubular string and the elevator disengages the string and repeats the process. This sequence applies to assembling tubulars for the purpose of drilling, deploying casing or deploying other components into the wellbore. The sequence is reversed to disassemble the tubular string. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention generally relate to a method for detecting yielding of a shoulder during tubular makeup. In one embodiment, a method of connecting a first threaded tubular to a second threaded tubular includes: engaging threads of the tubulars; and rotating the first tubular relative to the second tubular, thereby making up the threaded connection. The method further includes, during makeup of the threaded connection: detecting a shoulder position; and after detection of the shoulder position, monitoring for potential yielding of the threaded connection. The method further includes terminating the makeup according to: a first criterion in response to detection of the potential yielding; or a second criterion in response to absence of the potential yielding. 
     In another embodiment, a tubular makeup system includes: a power drive operable rotate a first threaded tubular relative to a second threaded tubular; a torque cell; a turns counter; and a programmable logic controller (PLC) operably connected to the power drive and in communication with the torque cell and turns counter. The PLC is configured to control an operation including: engaging threads of the tubulars; and rotating the first tubular relative to the second tubular, thereby making up the threaded connection. The operation further includes, during makeup of the threaded connection: detecting a shoulder position; and after detection of the shoulder position, monitoring for potential yielding of the threaded connection. The operation further includes terminating the makeup according to: a first criterion in response to detection of the potential yielding; or a second criterion in response to absence of the potential yielding. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1A  is a partial cross section view of a connection between threaded premium grade tubulars.  FIG. 1B  is a partial cross section view of a connection between threaded premium grade tubulars in which a seal condition is formed by engagement between sealing surfaces.  FIG. 1C  is a partial cross section view of a connection between threaded premium grade tubulars in which a shoulder condition is formed by engagement between shoulder surfaces. 
         FIG. 2A  illustrate a plot of torque with respect to turns for the premium connection.  FIG. 2B  illustrates plots of the rate of change in torque with respect to turns for the premium connection. 
         FIG. 3A  is a perspective view of a tong assembly in an upper position.  FIG. 3B  is a block diagram illustrating a tubular makeup system, according to one embodiment of the present invention. 
         FIG. 4A  illustrates yielding of a threaded premium connection.  FIG. 4B  illustrates an acceptable makeup shoulder connection for a connection similar to  FIG. 4A .  FIG. 4C  illustrates yielding of another threaded premium connection similar to  FIG. 4A .  FIG. 4D  illustrates yielding of another threaded premium connection different from  FIG. 4A . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  illustrates a connection  1  between premium grade tubulars  2 ,  4 . The tubulars  2 ,  4  may be any oil country tubular good, such as production tubing, casing, liner, or drill pipe. The connection  1  may include a first tubular  2  joined to a second tubular  4  through a tubular coupling or box  6 . The end of each tubular  2 ,  4  may have a tapered externally-threaded surface  8  (aka a pin) which co-operates with a correspondingly tapered internally-threaded surface  10  on the coupling  6 . Each tubular  2 ,  4  may be provided with a torque shoulder  12  which co-operates with a corresponding torque shoulder  14  on the coupling  6 . At a terminal end of each tubular  2 ,  4 , there may be defined an annular sealing area  16  which is engageable with a co-operating annular sealing area  18  defined between the tapered portions  10 ,  14  of the coupling  6 . Alternatively, the sealing area  16  may be located at other positions in the connection than adjacent the shoulder  12 . 
     During makeup, the pin  8  is engaged with the box  6  and then screwed into the box by relative rotation therewith. During continued rotation, the annular sealing areas  16 ,  18  contact one another, as shown in  FIG. 1B . This initial contact is referred to as the “seal condition”. As the tubulars  2 ,  4  are further rotated, the co-operating tapered torque shoulders  12 ,  14  contact and bear against one another at a machine detectable stage referred to as a “shoulder position”, as shown in  FIG. 1C . The increasing pressure interface between the tapered torque shoulders  12 ,  14  cause the seals  16 ,  18  to be forced into a tighter metal-to-metal sealing engagement with each other causing deformation of the seals  16  and eventually forming a fluid-tight seal. 
     During makeup of the tubulars  2 ,  4 , torque may be plotted with respect to turns.  FIG. 2A  shows a typical x-y plot (curve  50 ) illustrating the acceptable behavior of the premium connection  1  shown in  FIGS. 1A-1C .  FIG. 2B  shows a corresponding chart plotting the rate of change in torque (y-axis) with respect to turns (x-axis). Shortly after the tubulars engage one another and torque is applied, the measured torque increases substantially linearly as illustrated by curve portion  52 . As a result, corresponding curve portion  52   a  of the differential curve  50   a  is flat at some positive value. 
     During continued rotation, the annular sealing areas  16 ,  18  contact one another causing a slight change (specifically, an increase) in the torque rate, as illustrated by point  54 . Thus, point  54  corresponds to the seal condition shown in  FIG. 1B  and is plotted as the first step  54   a  of the differential curve  50   a . The torque rate then again stabilizes resulting in the linear curve portion  56  and the plateau  56   a . In practice, the seal condition (point  54 ) may be too slight to be detectable. However, in a properly behaved makeup, a discernable/detectable change in the torque rate occurs when the shoulder position is achieved (corresponding to  FIG. 1C ), as represented by point  58  and step  58   a.    
       FIG. 3A  is a perspective view of a power drive, such as tong assembly  1 , in an upper position. A group  140   g  of clamps has been removed for illustrative purposes. The tong assembly  100  may include a power tong  102  and a back-up tong  104  located on a drilling rig  106  coaxially with a drilling center  108  of the drilling rig  106 . The assembly  100  may be coupled in a vertically displaceable manner to one or more guide columns  110  (two shown) arranged diametrically opposite each other relative to the drilling centre  108 . The guide columns  110  may be connected to a chassis  112  which by wheels  114  and hydraulic motors (not shown) may be displaced horizontally on rails  116  connected to the drilling rig  106 . In the operative position, the assembly  100  may be located immediately above the slips  118  of the drilling rig  106 . 
     The power tong  102  may include a power tong housing provided with a through aperture that corresponds to the guide columns  110 , and an undivided drive ring connected via a bearing ring (not shown). The bearing ring may have a toothed ring (not shown) in mesh with cogwheels (not shown) on one or more hydraulic motors (not shown), such as two. One of the motors may be a spinner motor (high speed, low torque) and the other motor may be one or more torque motors (high torque, low speed). The toothed ring may be coupled to the drive ring by screw-bolt-joints (not shown). The hydraulic motors may be arranged to rotate the drive ring about the drilling centre  108 . The two hydraulic motors may be disposed on diametrically opposite sides of the drive ring. A cover may be provided to cover the power tong housing. 
     In the drive ring and co-rotating with this may be two crescent-shaped groups  140   g  (only one shown) of clamps. Each group  140   g  of clamps may be provided with one or more, such as three, clamps distributed around the drilling center  108 . Each clamp may include a cylinder block provided with one or more, such as three, cylinder bores arranged in a vertical row. In each cylinder bore may be a corresponding longitudinally displaceable piston that seals against the cylinder bore by a piston gasket. A rear gasket may prevent pressurized fluid from flowing out between the piston and the cylinder bore at the rear end of the piston. 
     The pistons may be fastened to the housing of the group  140   g  of clamps by respective screw-bolt-joints. On the part of the cylinder block facing the drilling center  108  there may be provided a gripper. The gripper may be connected to the cylinder block by fastening, such as with dovetail grooves or screw-bolt-joints (not shown). Surrounding the drive ring there may be provided a swivel ring that seals by swivel gaskets, the swivel ring may be stationary relative to the power tong housing. The swivel ring may have a first passage that communicates with the plus side of the pistons via a first fluid connection, a second passage that communicates with the minus side of the pistons via a second fluid connection, and a further passage. The cylinder and the piston may thereby be double acting. The swivel ring, swivel gaskets and drive ring may together form a swivel coupling. 
     The backup tong  104  may also include the clamp groups. The back-up tong  104  may further include a back-up tong housing with guides  176  that correspond with the guide columns  110 , and a retainer ring for two groups of clamps. At the guides  176  there may be cogwheels that mesh with respective pitch racks of the guide columns  110 . Separate hydraulic motors may drive the cogwheels via gears. A pair of hydraulic cylinders may be arranged to adjust the vertical distance between the power tong  102  and the back-up tong  104 . 
     In operation, when a tubular joint  2  is to be added to tubular string  20  (already including tubular joint  4 ), the assembly  100  may be displaced vertically along the guide columns  110  by the hydraulic motors, the gears, the cogwheels and the pitch racks until the back-up tong  104  corresponds with the pin  8  of the tubular string  20 . The box  6  may have been made up to the pin  8  of the joint  2  offsite (aka bucking operation) before the tubulars  2 ,  4  are transported to the rig. Alternatively the box  6  may be bucked on the joint  4  instead of the joint  2 . Alternatively, the box  6  may be welded to one of the tubulars  2 ,  4  instead of being bucked on. 
     The vertical distance between the back-up tong  104  and the power tong  102  may be adjusted so as to make the grippers correspond with the box  6 . The clamps may be moved up to the box  6  by pressurized fluid flowing to the first passage in the swivel ring and on through the first fluid connection to the plus side of the pistons. The excess fluid on the minus side of the pistons may flow via the second fluid connection and the second passage back to a hydraulic power unit (not shown). 
     The grippers may then grip their respective pin or box while the hydraulic motors rotate the drive ring and the groups  140   g  of clamps about the drilling center  108 , while at the same time constant pressure may be applied through the swivel ring to the plus side of the pistons. The power tong  102  may be displaced down towards the back-up tong  104  while the screwing takes place. After the desired torque has been achieved, the rotation of the drive ring may be stopped. The clamps may be retracted from the tubular string  20  by pressurized fluid being delivered to the minus side of the pistons via the swivel ring. The assembly  100  may be released from the tubular string  20  and moved to its lower position. 
     When a joint  2  is to be removed from the tubular string  20 , the operation is performed in a similar manner to that described above. When tools or other objects of a larger outer diameter than the tubular string  20  are to be displaced through the assembly  100 , the grippers may easily be removed from their respective clamps, or alternatively the groups  140   g  of clamps can be lifted out of the drive ring. 
     Alternatively, other types of tong assemblies may be used instead of the tong assembly  100 . 
       FIG. 3B  is a block diagram illustrating a tubular makeup system  200 , according to one embodiment of the present invention. The tubular makeup system  200  may include the tong assembly  100 , a tong remote unit (TRU)  204 , a turns counter  208 , a torque cell  212 , and the control system  206 . The control system  206  may communicate with the TRU  204  via an interface. Depending on sophistication of the TRU  204 , the interface may be analog or digital. Alternatively, the control system  206  may also serve as the TRU. 
     A programmable logic controller (PLC)  216  of the control system  206  may monitor the turns count signals  210  and torque signals  214  from the respective sensors  208 ,  212  and compare the measured values of these signals with predetermined values  224 - 230 . The predetermined values  224 - 230  may be input by an operator for a particular connection. The predetermined values  224 - 230  may be input to the PLC  216  via an input device  218 , such as a keypad. 
     Illustrative predetermined values  224 - 230  which may be input, by an operator or otherwise, include a shoulder threshold gradient  224 , a dump torque value  226 , minimum and maximum delta turns values  228 , minimum and maximum torque values  230 . The minimum and maximum torque values  230  may include a set for the shoulder position and a set for the final position. The torque values  230  may be derived theoretically, such as by finite element analysis, or empirically, such as by laboratory testing and/or analysis of historical data for a particular connection. The dump torque value  226  may simply be an average of the final minimum and maximum torque values  230 . During makeup of the connection  1 , various output may be observed by an operator on output device, such as a display screen, which may be one of a plurality of output devices  220 . By way of example, an operator may observe the various predefined values which have been input for a particular connection. Further, the operator may observe graphical information such as the torque rate curve  50  and the torque rate differential curve  50   a . The plurality of output devices  220  may also include a printer such as a strip chart recorder or a digital printer, or a plotter, such as an x-y plotter, to provide a hard copy output. The plurality of output devices  220  may further include a horn or other audio equipment to alert the operator of significant events occurring during makeup, such as the shoulder condition, the terminal connection position and/or a bad connection. 
     Upon the occurrence of a predefined event(s), the PLC  216  may output a dump signal  222  to the TRU  204  to automatically shut down or reduce the torque exerted by the tong assembly  100 . For example, dump signal  222  may be issued upon detecting the final connection position and/or a bad connection. 
     The comparison of measured turn count values and torque values with respect to predetermined values is performed by one or more functional units of the PLC  216 . The functional units may generally be implemented as hardware, software or a combination thereof. The functional units may include one or more of a torque-turns plotter algorithm  232 , a process monitor  234 , a torque gradient calculator  236 , a smoothing algorithm  238 , a sampler  240 , a comparator  242 , a connection evaluator  252 , and a target detector  254 . The process monitor  234  may include one or more of a thread engagement detection algorithm  244 , a seal detection algorithm  246  a shoulder detection algorithm  248 , and a yield detection algorithm  250 . Alternatively, the functional units may be performed by a single unit. As such, the functional units may be considered logical representations, rather than well-defined and individually distinguishable components of software or hardware. 
     In operation one of the threaded members (e.g., tubular  2  and box  6 ) is rotated by the power tong  102  while the other tubular  4  is held by the backup tong  104 . The applied torque and rotation are measured at regular intervals throughout the makeup. In one embodiment, the box  6  may be secured against rotation so that the turns count signals accurately reflect the rotation of the tubular  2 . Additionally, a second turns counter (not shown) may be provided to sense the rotation of the box  6 . The turns count signal issued by the second turns counter may then be used to correct (for any rotation of the box  6 ) the turns count signal  210 . 
     The frequency with which torque and rotation are measured may be specified by the sampler  240 . The sampler  240  may be configurable, so that an operator may input a desired sampling frequency. The torque and rotation values may be stored as a paired set in a buffer area of memory. Further, the rate of change of torque with respect to rotation (hereinafter “torque gradient”) may be calculated for each paired set of measurements by the torque gradient calculator  236 . At least two measurements are needed before a rate of change calculation can be made. The smoothing algorithm  238  may operate to smooth the torque gradient (e.g., by way of a running average). These values (torque, rotation, and torque gradient) may then be plotted by the plotter  232  for display on the output device  220 . 
     The values (torque, rotation, and torque gradient) may then be compared by the comparator  242 , either continuously or at selected events, with predetermined values, such as the values  224 - 230 . Based on the comparison of the measured and/or calculated values with the predefined values  224 - 230 , the process monitor  234  may determine the occurrence of various events and whether to continue rotation or abort the makeup. The thread engagement detection algorithm  244  may monitor for thread engagement of the pin  8  and box  6 . Upon detection of thread engagement a first marker is stored. The marker may be quantified, for example, by time, rotation, torque, a derivative of torque with respect to rotation, or a combination of any such quantifications. During continued rotation, the seal detection algorithm  246  monitors for the seal condition. This may be accomplished by comparing the calculated torque gradient with a predetermined threshold seal condition value. A second marker indicating the seal condition may be stored if/when the seal condition is detected. At this point, the torque value at the seal condition may be evaluated by the connection evaluator  252 . 
     For example, a determination may be made as to whether the turns value and/or torque value are within specified limits. The specified limits may be predetermined, or based off of a value measured during makeup. If the connection evaluator  252  determines a bad connection, rotation may be terminated. Otherwise rotation continues and the shoulder detection algorithm  248  monitors for the shoulder position. This may be accomplished by comparing the calculated torque gradient with the shoulder threshold gradient  224 . When the shoulder position is detected, a third marker indicating the shoulder position is stored. The connection evaluator  252  may then determine whether the torque value at the shoulder position is acceptable by comparing to the respective input torque values  230 . 
     Upon continuing rotation, the target detector  254  monitors for the dump torque value  226 . Once the dump torque value  226  is reached, rotation may be terminated by sending the dump signal  222 . Alternatively, the dump signal  222  may be issued slightly before the dump torque  226  is reached to account for system inertia. Once the connection is complete, the connection evaluator  252  may calculate a delta turns value based on the difference between the final turns value and the turns value at the shoulder condition. The connection evaluator  252  may compare the delta turns value with the input delta turns values  228 . Similarly, the connection evaluator may compare the final torque value to the respective input torque values  230 . If either criteria is not met, then the connection evaluator  252  may indicate a bad connection. 
     Alternatively, a delta turns value may be entered instead of the dump torque  226 . The target detector  254  may then calculate a target turns value using the shoulder turns and the delta turns value (target turns equals shoulder turns plus delta turns). 
       FIG. 4A  illustrates yielding of a threaded premium connection  1  (see also FIG. 5 of the OTC 21874 paper). Before makeup, thread lubricant (aka dope) may be applied to pin  8  and the box  6 . Contamination of the thread dope may lead to overturning the connection. Overturning the connection may plastically deform (aka yield) the connection, resulting in a reduction of an inner diameter of the connection and possible leaking of the connection during service. Contamination of the thread dope may occur due to rain water. Other factors that may cause yielding include incorrect makeup parameters, other environmental effects, malfunction of the measurement system, and malfunction of firmware/software. Other environmental parameters may include rain water on the connection and temperature sensitivity of the thread dope. 
     The shoulder position  335  is reached in shoulder region  305  evinced by rapid increase in the torque and corresponding increase in the gradient. Once the shoulder position  335  is reached, makeup of the connection  1  may continue until the dump torque  226  is reached. As rotation continues to the dump torque value  226 , the connection may enter a linear elastic region  310 . In this region  310 , the torque may increase with an almost constant gradient as the connection experiences reversible elastic deformation. The gradient may have a nearly constant maximum value  325  in the linear region  310 . As rotation continues, the connection  1  may enter a non-linear elastic range  315 . In this region  315 , the torque may increase non-linearly as the connection experiences partially elastic and partially plastic deformation. The gradient may decrease from the maximum in a stepwise fashion. 
     As rotation continues, the connection may enter a plastic region  320 . In this region  320 , the torque may continue to increase but at a nearly constant gradient as the connection experiences plastic deformation. The gradient may be substantially less than the maximum gradient  325  achieved in the linear region  310  and may also be less than the shoulder threshold gradient  224 . The delta turns (final turns minus shoulder turns) is about 0.15 turn. The connection  1  experiences a maximum torque gradient  325  in the first half of the delta region (divided by median  340 ). 
       FIG. 4B  illustrates an acceptable makeup shoulder connection for a connection similar to  FIG. 4A . In contrast to  FIG. 4A , the delta region (between shoulder and final) is less than 0.1 turns and the connection  1  experiences the maximum gradient  325  in a second half of the delta region. A substantial portion of the linear elastic region  310  is also located in the second half of the delta region. The non-linear region  315  is substantially reduced and the plastic region  320  is non-existent. 
       FIG. 4C  illustrates yielding of another threaded premium connection similar to  FIG. 4A . The delta turns value is substantially greater than 0.1 turns. The maximum gradient  325  and linear elastic region  310  are each located in the first half of the delta turns region. The plastic region  320  appears at the end of the delta region. The average gradient in the plastic region  320  is substantially less than in the linear elastic region  310 . 
       FIG. 4D  illustrates yielding of another threaded premium connection different from  FIG. 4A . The delta turns value equals 0.1 turns. The maximum gradient  325  and linear elastic region are each located in the first half of the delta region. The plastic region  320  appears at the end of the delta region. The average gradient in the plastic region  320  is substantially less than in the linear elastic region  310 . 
     The torque gradient calculator  236  may also calculate a rate of change of the torque gradient with respect to rotation (hereinafter “yield gradient”) for each paired set of torque gradient calculations. At least two calculations are needed before yield gradient calculation can be made. The smoothing algorithm  238  may operate to smooth the yield gradient (e.g., by way of a running average). The torque gradient calculator  236  may not begin the yield gradient calculation until the shoulder position  335  is detected and may iteratively calculate the yield gradient (at a frequency set by the sampler  240 ). 
     The yield detector  250  may calculate a target turns value  330  using the turns value of the shoulder position  335  and the maximum delta turns value  228 . The yield detector  250  may also calculate the median  340  of the delta region using the maximum delta turns value  228 . The median turns  340  may equal the shoulder turns plus one-half the maximum delta turns  228 . The target turns value  330  may equal the shoulder turns plus the maximum delta turns  228 . The target turns value  330  may be slightly reduced by a safety factor to account for system inertia. 
     As rotation of the connection continues past the shoulder position  335 , the yield detector  250  may iteratively (at a frequency set by the sampler  240 ) monitor the yield gradient for a potential maximum of the torque gradient. The yield detector may also monitor turns. Once a potential maximum for the torque gradient is detected, the yield detector may store a first marker. The first marker may include the torque gradient and turns values corresponding to the detection of the potential maximum value. The yield detector  250  may then compare the turns value to the median turns value  340  to determine whether the potential maximum occurred in the first half or second half of the delta region. If the potential maximum is in the second half of the delta region, the yield detector  250  may shift into a passive mode (allow connection to be completed by the target detector  254 ). As discussed above, comparison of the turns value at the maximum torque gradient to the median turns value may provide a predictive indicator of whether the connection is susceptible to yielding. 
     If the potential maximum is in the first half of the delta region, the yield detector  250  may continue to monitor the yield gradient for a subsequent maximum torque gradient value indicating that the potential maximum torque gradient may not be the actual maximum torque gradient. The yield detector  250  may continue to monitor the yield gradient and the turns until the target turns value  330  is reached. If the target turns value is reached before the yield detector  250  detects a subsequent maximum torque gradient, then the yield detector may abort the connection by issuing the dump signal  222  to prevent yielding of the connection. 
     If a subsequent potential maximum value is detected, the yield detector  250  may store a second marker including the torque gradient and turns values corresponding to the detection of the subsequent maximum value. The yield detector  250  may then compare the subsequent torque gradient to the initial torque gradient to determine which of the gradients is the potential maximum. If the subsequent torque gradient is the potential maximum, then the yield detector  250  may then compare the turns value to the median turns value to determine whether the potential maximum occurred in the first half or second half of the delta region. If the potential maximum is in the second half of the delta region, the yield detector  250  may shift into the passive mode. If either the subsequent potential maximum is in the first half of the delta region or the initial torque gradient remains the potential maximum, then the yield detector  250  may continue to monitor for a subsequent potential maximum value. The yield detector  250  may iterate either until the target turns value  330  is reached or the yield detector shifts into the passive mode. 
     If the connection  1  is aborted by the yield detector  250 , the connection evaluator  252  may still evaluate the connection, as discussed above. Since the yield detector  250  may abort before yielding, the connection  1  may not be damaged. The connection evaluator  252  may determine if the aborted connection  1  is still acceptable. If the connection  1  is acceptable, makeup of the tubular string  20  may continue without disassembling the connection. The plotter  232  may add the markers from the yield detector  250  to one or more of the curves  50 ,  50   a . Alternatively or additionally, the plotter  232  may plot the yield gradient curve. The operator may evaluate the data and recommendation of the connection evaluator and make the final decision as whether the connection  1  is acceptable or not. 
     A target torque value may be used instead of or in addition to the target turns value  330 . Alternatively or additionally, the initial potential maximum may be compared to the subsequent torque gradient and the connection aborted if the subsequent torque gradient becomes substantially less than the potential maximum, such as less than three-quarters, two-thirds, or one-half the potential maximum. Alternatively or additionally, the initial potential maximum may be compared to the subsequent torque gradient, the corresponding subsequent yield gradient compared to zero, and the connection  1  aborted if both the subsequent torque gradient is substantially less than the initial potential maximum and the corresponding subsequent yield gradient is equal to, nearly equal to, and/or less than zero. Alternatively or additionally, the connection  1  may be aborted if the torque gradient becomes less than the shoulder threshold gradient  224 . Alternatively or additionally, the shoulder detector  248  may detect the shoulder position  335  by monitoring the torque differential (i.e., see discussion of  FIGS. 2A and 2B , above), mark the torque differential at the shoulder position (i.e.,  56   a ), and abort the connection  1  if the torque differential becomes less than the marked torque differential 
     Further, the target turns and median turns formulas may include a connection specific yield factor. The connection specific yield factor may be derived theoretically, such as by finite element analysis, or empirically, such as by laboratory testing and/or analysis of historical data for a particular connection. With the yield factor, the target turns value  330  may equal the shoulder turns plus the maximum delta turns minus the yield factor. The median turns value  340  may equal the shoulder turns plus one-half the difference of the maximum delta turns and the yield factor. 
     In operation, the yield detector  250  may be applied to  FIG. 4A  as follows. Assuming a maximum delta turns  228  of 0.13 turn and a yield factor of 0.025 turn, the shoulder  335  is detected at about 0.753 turn. The yield detector  250  may then calculate the median  340  at about 0.806 turn and the target  330  at about 0.858 turn. The yield detector  250  may detect a first potential maximum torque gradient at 0.78 turn and then detect the actual maximum  325  at about 0.799 turn. The yield detector  250  may also detect the subsequent inflections in the torque gradient curve. The yield detector  250  may then abort the connection at the target  330  before yielding occurs. The connection evaluator  250  may accept the connection since the torque at the aborted target exceeds the minimum final torque. 
     In operation, the yield detector  250  may be applied to  FIG. 4B  as follows. Assuming a maximum delta turns  228  of 0.13 turn and a yield factor of 0.025 turn, the shoulder  335  is detected at 0.958 turn. The yield detector may then calculate the median  340  at 1.011 turn and the target  330  at 1.063 turns. The yield detector  250  may detect a first potential maximum at about 0.99 turn and then detect the maximum  325  at about 1.015 turn. The yield detector  250  may also detect the subsequent inflections in the torque gradient curve. The yield detector  250  may not abort the connection both since the maximum  325  is detected in the second half of the delta region and since the makeup of the connection  1  is terminated by the target detector  254  well before the target turns value  330  is reached. 
     In operation, the yield detector  250  may be applied to  FIG. 4C  as follows. Assuming a maximum delta turns  228  of 0.13 turn and a yield factor of 0.025 turn, the shoulder  335  is detected at 0.235 turn. The yield detector  250  may then calculate the median  340  at 0.288 turn and the target  330  at 0.340 turn. The yield detector  250  may detect the maximum torque gradient  325  at about 0.273 turn. The yield detector  250  may also detect the subsequent inflections in the torque gradient curve. The yield detector  250  may then abort the connection at the target  330  before yielding occurs. The connection evaluator  252  may or may not accept the connection  1  since it is unclear whether the torque at the aborted target  330  exceeds the minimum final torque  230 . 
     In operation, the yield detector  250  may be applied to  FIG. 4D  as follows. Assuming a maximum delta turns of 0.13 turn and a yield factor of 0.055 turn, the shoulder  335  is detected at 0.946 turn. The yield detector  250  may then calculate the median  340  at 0.984 turn and the target  330  at 1.026 turns. The yield detector  250  may detect the maximum torque gradient  325  at about 0.979 turn. The yield detector  250  may then abort the connection at the target  330  before yielding occurs. The connection evaluator  252  may reject the connection since the torque at the aborted target  330  is less than the minimum final torque  230 . 
     Alternatively, the tubular makeup system power drive may be a top drive instead of the tong assembly. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.