Abstract:
A method of assembling pipe joints in a pipe string allows the circumferential orientation of a first pipe in the pipe string to be determined relative to a second pipe in the pipe string. Each pipe joint has a coupling member and at least one pin member, the pin member being threadingly connected to the coupling member to create the pipe joint. Threads are created for the pin member and the coupling member of each joint, and each pin member and coupling member is marked with an alignment mark. The threads for each pin member are created so that they are identical to the threads on the other pin members in the pipe string. This is done by gaging the overall rotational capacity of each pin member with a coupling marking gage and adjusting a thread depth as needed. The threads for each coupling member are created so that they are identical to the threads on other coupling members in the pipe string. This is done by gaging the overall rotational capacity of each coupling member with a pin marking gage and adjusting a shoulder stop depth as needed. After threading the pin members and the coupling members, the joints are assembled, and the alignment mark for each pin member and each coupling member is aligned with the alignment mark on each of the other pin and coupling members in the pipe string.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to pipe joints and in particular to a method for assembling pipe joints so that the down-hole circumferential orientation of a pipe in a pipe string can be determined by the orientation of any other pipe in the same pipe string. 
     2. Description of Related Art 
     In a pipe string having a series of joints, each joint having a pin member threadingly connected to a coupling member, it is often desirable to know the circumferential orientation of one pipe in the pipe string relative to another pipe in the string. One method of accomplishing this result is to control the threading process of each pin member and each coupling member so that the relative orientation of one pipe to another is known when any pin member is connected to any coupling member. The circumferential orientation of one pipe relative to another is demonstrated by an alignment mark placed on each pin member and coupling member during the threading process. 
     U.S. Pat. No. 4,962,579 teaches a method for visually determining on the rig floor if a joint is properly made up with the right amount of torque. A registry mark is placed on the exterior of the first pipe section for proper axial engagement of the pin member with the coupling or box member. The position is determined by finite element analysis. 
     U.S. Pat. No. 5,212,885 shows a method for achieving proper sealing positioning and proper make up torque of threaded pipe sections. The method is described in column 4, lines 33-44 of the specification. If the face of the box member is properly positioned relative to a triangle mark on the pipe section, make up is terminated. If the face has not reached edge of the triangle mark, torque is increased until either the face progresses into the body of the triangle mark or until maximum torque occurs. 
     U.S. Pat. No. 4,614,120 shows a method for determining proper make-up torque for pipe joints. A reference mark is set on the male element and on the female element. A grease is applied to the joint and the joint is made up using sufficient torque to cause one element to rotate with the respect to the other element. The joint is torqued until one element reaches a predetermined angle beyond the point where the reference marks are facing each other. This operation is repeated with a determination being made of the range of torques to be applied to the joint with a particular grease being utilized. 
     U.S. Pat. No. 5,661,888 shows an apparatus for positing two threaded pipes within a target range of relative axial positions. The device supposedly offers advantages over using visual “bench marks” placed on the pin and box members. The device includes a sensor and calibrating device for positioning the sensor a calibrated distance from the end of one of the pipes. A signal generator generates a signal once the sensor head indicates that the relative axial position of the pipes are within the target range desired. 
     Each of the above references primarily deal with methods for properly torqueing a threaded pipe connection. As such, they do not teach the current method for assembling a series of pipe joints so that the circumferential orientation of one pipe in the pipe string can be determined by reference to another pipe in the string. 
     A need continues to exist for a simple and economical method for indexing a string of pipe containing a plurality of joints by which the circumferential orientation of one pipe in the pipe string can be determined by reference to another pipe in the string. 
     A need also exists for such a method which does not require elaborate gaging systems or electronic sensors or sensing systems. 
     A need also exists for such a method which does not add appreciably to the costs of the pipe threading process, which is simple to implement, and which is reliable in operation. 
     BRIEF SUMMARY OF THE INVENTION 
     The method of assembling pipe joints according to the present invention allows the circumferential orientation of a pipe in a pipe string to be determined relative to that of another pipe in the same pipe string. The pipe string is made up of a series of joints, each joint having a coupling member and at least one pin member which are threadingly connected. 
     Before machining threads on the pin members or the coupling members, a pin marking gage and a coupling marking gage are prepared. The two gages are adapted to threadingly engage each other. A pin gage alignment mark is scribed on the pin marking gage, and a coupling gage alignment mark is scribed on the coupling marking gage. When the pin marking gage and the coupling marking gage are threadingly connected in a first contact position, the pin gage alignment mark and the coupling gage alignment mark are separated by a circumferential offset which represents the amount of rotation remaining to put the gages in a fully engaged position. 
     A pin alignment mark is placed on each pin member, and a coupling alignment mark is placed on each coupling member. A plurality of threads is machined on an exterior annular surface of the pin member to an initial pin depth. The coupling marking gage is threadingly connected to the pin member, and a circumferential offset between the coupling gage alignment mark and the pin alignment mark is recorded. Based on the circumferential offset, the pin member is again machined, thus altering the initial pin depth of the threads so that the pin alignment mark will align with the coupling gage alignment mark when the gage and the pin member are connected in the first contact position. 
     A plurality of threads is machined on an interior annular surface of the coupling member to an initial coupling depth. The pin marking gage is threadingly connected to the coupling member, and a circumferential offset between the pin gage alignment mark and the coupling alignment mark is recorded. Based on the circumferential offset, the coupling member is again machined, thus altering the initial coupling depth so that the coupling alignment mark will align with the pin gage alignment mark when the gage and the coupling member are connected in the first contact position. 
     After machining threads on each pin member and each coupling member according to the preceding method, the pipe string is assembled by connecting each pin member to a coupling member. As each joint is assembled, every pin alignment mark in the pipe string is aligned with all of the other pin alignment marks as well as all of the coupling alignment marks. The alignment of the marks along the pipe string allows determination of the orientation of any pipe in the string by observing the orientation (indicated by the alignment marks) of any other pipe in the string. 
     Additional objects, features, and advantages will be apparent in the written description which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional view of a pipe joint used with the method of the present invention. 
     FIG. 2 is a detailed cross-sectional view taken along lines III—III showing the threads of the coupling member of the pipe joint of FIG.  1 . 
     FIG. 3 is a perspective view of a coupling marking gage and a pin marking gage in a first contact position, both gages being used with the method according to the present invention. 
     FIG. 4 is a partial cross-sectional side view taken at IV—IV of the gages of FIG.  3 . 
     FIG. 5 is a perspective view of a coupling blank being installed in a threading machine according to the method of the present invention. 
     FIG. 6 is a cross-sectional side view taken at VI—VI of the threading machine and the coupling of FIG.  5 . 
     FIG. 7 is a perspective view of the threading machine and coupling of FIG. 5 with the pin marking gage of FIG. 3 installed in the coupling according to the method of the present invention. 
     FIG. 8 is a perspective view of a plain end pipe being installed in a threading machine according to the method of the present invention. 
     FIG. 9 is a cross-sectional side view taken at IX—IX of the threading machine and the plain end pipe of FIG.  8 . 
     FIG. 10 is a perspective view of the threading machine and plain end pipe of FIG. 8 with the coupling marking gage of FIG. 3 installed on the pin according to the method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 in the drawings, a pipe joint  11  used with the method of the present invention is illustrated. Pipe joint  11  is a typical threaded and coupled (TNC) connection having two pipes, or pin members  13  and a coupling member  15 . Each pin member  13  includes a front surface  17  and an exterior surface  19  with a plurality of threads  21  formed thereon. Plurality of threads  21  are machined onto exterior surface  19  in a typical tapered arrangement. Threads  21  have a lead distance a as shown in FIG.  2 . Coupling member  15  includes an internal shoulder stop  23 , an exterior surface  25 , and an interior surface  27  with a plurality of threads  29  formed thereon. Threads  29  are also tapered to provide a proper mating arrangement for threads  21  of pin members  13 . 
     Pipe joint  11  is formed by threadingly connecting coupling member  15  to pin members  13 . In a fully engaged position (shown in FIG.  1 ), pin member  13  has been rotated into coupling member  15  with a predetermined torque. The torque that is applied in assembling the joint varies based on the type of material used in the joint, the size of the joint, and the particular application involved. In the fully engaged position, front surface  17  of pin member  13  mates with shoulder stop  23 . Shoulder stop  23  provides a positive stopping point for pin members  13  as they are threaded into coupling member  15 . 
     The method according to the present invention is used to circumferentially time the plurality of pipes in a pipe string. The intended result of the method can be seen in FIG.  1 . Both pin members  13  have a pin alignment mark  35 ,  35 ′ scribed on exterior surface  19 . Pin alignment marks  35 ,  35 ′ are preferably scribed parallel to a longitudinal axis which runs along an axial length of pin member  13 . A coupling alignment mark  37  is scribed in a similar fashion on exterior surface  25  of coupling  15 . By manufacturing pin members  13  and coupling members  15  using the method described herein, all pin alignment marks  35 ,  35 ′ and all coupling alignment marks  37  in a given pipe string will be circumferentially aligned when each pin and coupling member is in the fully engaged position. 
     It is important to note that the method of the present invention is not limited to TNC pipe joints such as the one illustrated in FIG.  1 . The method can also be used with integral connected joints (not shown). In an integral connected joint, separate coupling members are not used. Instead, each pipe in the pipe string has at one end a pin member and at the other end a coupling member. In other words, the coupling member is integral to each pipe in the pipe string. The circumferential timing method can be used with such an integral connection provided that a positive stop is encountered when threadingly connecting the pin member to the coupling member. 
     The main portion of the method of the present invention involves machining threads onto a plain end pipe to create pin member  13  (FIG. 1) and machining threads into a coupling blank to create coupling member  15 . Therefore, a plain end pipe is a pin member without threads, and a coupling blank is a coupling member without threads. Referring to FIGS. 3-10 in the drawings, the method according to the present invention is illustrated. 
     Before preparing pin member  13  or coupling member  15 , a coupling marking gage  43  and a pin marking gage  45  are prepared (see FIGS.  3  and  4 ). Coupling marking gage  43  is similar to coupling member  15  in that coupling marking gage  43  includes a plurality of tapered threads  47  machined on an inner surface  49  of the gage  43 . Coupling marking gage  43  also includes an outer surface  51  and a positive stop shoulder  53 . Coupling marking gage  43  is adapted to be threadingly connected to pin member  13  so that positive stop shoulder  53  mates with front surface  17  of pin member  13 . 
     Pin marking gage  45  is similar to pin member  13  in that pin marking gage  45  includes a plurality of tapered threads  59  machined on an outer surface  61 . Pin marking gage  45  also includes a positive stop face  63  for mating with positive stop shoulder  53 . Pin marking gage  45  is adapted to be threadingly connected to coupling member  15  so that positive stop face  63  mates with shoulder stop  23  of coupling member  15 . 
     Unlike pin member  13 , pin marking gage  45  includes a stepped portion  65  which increases the outer diameter of the gage  45  so that outer surface  61  is flush with outer surface  51  of coupling marking gage  43 . This feature of pin marking gage  45  is not critical but allows for easier marking and reading of both gages  43 ,  45 . 
     After preparing gages  43  and  45 , pin marking gage  45  is threadingly connected to coupling marking gage  43 . The gages  43 ,  45  are rotatably threaded to each other until reaching a first contact position (shown in FIG.  3 ). In the first contact position, positive stop face  63  has come into initial contact with positive stop shoulder  53 . Although more torque could be applied and the gages  43 ,  45  subjected to additional rotation, gages  43 ,  45  are only rotated until positive stop face  63  initially contacts positive stop shoulder  53 . 
     Pin marking gage  45  and coupling marking gage  43 , now in the first contact position, are scribed with alignment marks. A pin gage alignment mark  71  is placed on pin marking gage  45 . A coupling gage alignment mark  73  is placed on coupling marking gage  43 . Marks  71 ,  73  are separated by a circumferential offset β. Circumferential offset β is determined primarily by the amount of torque required to place the pin member and the coupling member in the fully engaged position. Circumferential offset β can vary depending on the material strength, the diameter, and the thickness of the pipes to be assembled. After scribing marks  71 ,  73  on gages  45 ,  43 , the two gages  45 ,  43  are disassembled. 
     Referring more specifically now to FIGS. 5-7 in the drawings, the threading process for coupling member  15  is illustrated. A lathe member  79  having a front surface  81  and a plurality of chucks  83  is used to position and hold a coupling blank  85  during the threading operation. Coupling blank  85  includes a first end  87 , a second end  89 , an inner surface  91 , an outer surface  93 , a front face  97 , and a rear face  99 . Lathe member  79  is one component of a commercially available, computer numerical controlled (CNC) threading machine (not all components shown) used to thread coupling blank  85 . A reference alignment mark  105  is placed on any one of chucks  83 . A coupling alignment mark  107  (this mark is analogous to coupling alignment mark  37  of coupling member  15  shown in FIG. 1) is placed on outer surface  93  of coupling blank  85 . 
     Coupling blank  85  is installed in lathe member  79  between chucks  83 . Chucks  83  hold coupling blank  85  in a fixed position relative to lathe member  79  during the threading process. As coupling blank  85  is installed between chucks  83 , coupling alignment mark  107  is aligned with reference alignment mark  105 . 
     After installation of coupling blank  85 , a face-off distance γ (shown in FIG. 6) is established by removing a portion of front face  97  of coupling blank  85 . Face-off distance γ is the distance between front face  97  and front surface  81  of lathe member  79 . During the threading of the first end of the initial coupling blank, face-off distance γ could be a predetermined value that is selected, or it could be an arbitrary value. After a threading operation has been completed on the first end of the first coupling blank, face-off distance γ has been established and is used on all subsequent coupling blanks. 
     After establishing face-off distance γ, the threading machine is used to bore and profile a tapered surface  111  on inner surface  91  of coupling blank  85 . The bore and profiling steps create a shoulder stop  113  at an initial coupling depth δ (shown in FIG.  6 ). Tapered surface  111  is then threaded. In the preferred embodiment, the threading operation is computer controlled and is carried out by a single point cutting tool (not shown). The cutting tool begins each threading operation from the same radial and arcuate position relative to a given coupling blank, provided that coupling alignment mark  107  is aligned with reference alignment mark  105 . 
     After threading coupling blank  85 , pin marking gage  45  is threadingly connected to coupling blank  85 . Pin marking gage  45  is rotated into coupling blank  85  until initial contact between positive stop face  63  and shoulder stop  113  of coupling blank  85  (the first contact position). The relative circumferential position of pin gage alignment mark  71  is then compared to coupling alignment mark  107 . 
     The circumferential offset between pin gage alignment mark  71  and coupling alignment mark  107  is recorded and used to calculate how much initial depth δ should be increased in order to make the marks  71 ,  107  align. The result of this calculation yields a final coupling depth (not shown) to which shoulder stop  113  must be manufactured. The final coupling depth is recorded by the computer-controlled threading machine. The factors that determine the final coupling depth include the diameter of coupling blank  85 , thread lead α, and the circumferential distance between pin gage alignment mark  71  and coupling alignment mark  107 . 
     After calculating the final coupling depth, initial coupling depth δ of shoulder stop  113  is increased to the final coupling depth. Pin marking gage  45  is again threadingly connected to coupling blank  85  to observe the relative positions of pin gage alignment mark  71  and coupling alignment mark  107 . After increasing the depth of shoulder stop  113  to the final coupling depth, pin gage alignment mark  71  and coupling alignment mark  107  should be aligned. 
     Since coupling blank  85  needs threads on both first end  87  and second end  89 , the process described in the preceding paragraphs is repeated after turning coupling blank  85  around in the chucks  83  so that rear face  99  is where front face  97  was in the preceding operations. Since face-off distance γ and the final coupling depth are known and recorded, the threading operation for second end  89  of coupling blank  85  and for all subsequent couplings now involves fewer steps. 
     Face-off distance γ is established for second end  89  of coupling blank  85  by machining rear face  99  of blank  85 . The value of the face-off distance is the same as that recorded during the threading of first end  87 . Second end  89  is then bored and profiled to establish a tapered portion and a shoulder stop (not shown) at the final coupling depth. The tapered portion is then threaded. 
     Since the threading tool begins the threading process in the same position every time and since the final coupling depth remains the same, the threads machined into second end  89  of coupling blank  85  are timed the same as the threads on first end  87  of coupling blank  85 . After manufacturing the second set of threads, coupling blank  85  is considered a coupling member (similar to coupling member  15 ). The recorded final coupling depth and face-off distance γ can now be used to manufacture subsequent coupling blanks of the same size and material. 
     Referring specifically to FIGS. 8-10, the process for threading a plain end pipe  119  to create pin member  13  is very similar to the threading process used on coupling blank  85 . Lathe member  79  is used to position and hold plain end pipe  119  during the threading operation. Plain end pipe  119  includes a first end and a second end, an inner surface  123 , an outer surface  125 , a front surface  127 , and a rear surface (not shown). A reference alignment mark  129  is placed on any one of chucks  83 . Mark  105  used to thread coupling blank  85  can be used as reference alignment mark  129 . A pin alignment mark  131  (this mark is analogous to pin alignment mark  35  of pin member  13  shown in FIG. 1) is placed on outer surface  125  of plain end pipe  119 . 
     Plain end pipe  119  is installed in lathe member  79  between chucks  83 . Chucks  83  hold plain end pipe  119  in a fixed position relative to lathe member  79  during the threading process. As plain end pipe  119  is installed between chucks  83 , pin alignment mark  131  is aligned with reference alignment mark  129 . 
     After installation of plain end pipe  119 , a face-off distance ε (shown in FIG. 9) is established by removing a portion of front surface  127  of plain end pipe  119 . Face-off distance ε is the distance between front surface  127  and front surface  81  of lathe member  79 . For the first plain end pipe that is threaded, face-off distance ε could be a predetermined value that is selected, or it could be an arbitrary value. After a threading operation has been completed on the first end of plain end pipe  119 , face-off distance ε is used on all subsequent plain end pipes. 
     After establishing face-off distance ε, the threading machine is used to profile a tapered portion  133  onto outer surface  125  of plain end pipe  119  to an initial pin depth η. Tapered portion  133  is then threaded. In the preferred embodiment, the threading operation is computer controlled and is carried out by a single point cutting tool (not shown). The cutting tool begins each threading operation from the same radial and arcuate position relative to a given plain end pipe, provided that pin alignment mark  131  is aligned with reference alignment mark  129 . 
     Once threaded, coupling marking gage  43  is threadingly connected to plain end pipe  119 . Coupling marking gage  43  is rotated onto plain end pipe  119  until initial contact between positive stop shoulder  53  of coupling marking gage  43  and front surface  127  of plain end pipe  119  (the first contact position). The relative circumferential position of coupling gage alignment mark  73  is then compared to pin alignment mark  131 . 
     The circumferential offset between coupling gage alignment mark  73  and pin alignment mark  131  is recorded and used to calculate how much to decrease initial pin depth η in order to make the marks  73 ,  131  align. The result of this calculation gives a final pin depth (not shown) to which plain end pipe  119  must be manufactured. The final pin depth is recorded by the computer-controlled threading machine. The factors used to calculate the final pin depth include the diameter of plain end pipe  119 , thread lead α, and the circumferential distance between coupling gage alignment mark  73  and pin alignment mark  131 . 
     After calculating the final pin depth, initial pin depth η is decreased to the final pin depth by removing material from front surface  127  of plain end pipe  119 . This operation also changes the value of face-off distance ε, the new value of which is recorded. Depending on how much material is removed, the threads (which are tapered) may have to be “reshaped” to a smaller diameter. Following the completion of this operation, coupling marking gage  43  is again threadingly connected to plain end pipe  119  to observe the relative positions of coupling gage alignment mark  73  and pin alignment mark  131 . After decreasing the thread depth of plain end pipe  119  to the final pin depth, coupling gage alignment mark  73  and pin alignment mark  119  should be aligned. 
     Since both ends of plain end pipe  119  must be threaded, the process described in the preceding paragraphs is repeated for the second end of plain end pipe  119 . Since the new value of face-off distance ε and the final pin depth are known and recorded, the threading operation for the second end of plain end pipe  119  and for all subsequent pipes now involves fewer steps. 
     Face-off distance ε, which was previously recorded, is established for the second end of plain end pipe  119  by machining a portion of the rear surface of plain end pipe  119 . Plain end pipe  119  is then profiled and threaded to the final pin depth. Since the threading tool begins the threading process in the same position every time and since the final pin depth remains the same, the threads machined onto the second end of plain end pipe  119  are timed the same as the threads on the first end of plain end pipe  119 . The recorded face-off distance and final pin depth can now be used to manufacture subsequent plain end pipes of the same size and material. 
     The use of pin marking gage  45  when threading coupling members and the use of coupling marking gage  43  when threading pin members as described above ensures that the alignment marks  35 ,  37  will align when pin member  13  and coupling member  15  are threadingly connected in a fully engaged position (see FIG.  1 ). 
     The primary advantage of the present invention is that it allows pin members and coupling members to be manufactured while knowing that the pin members and coupling members will be circumferentially aligned (relative to the alignment marks) when installed in the fully engaged position. One result of this advantage is that the orientation of a down-hole pipe in a pipe string can be determined by observing the orientation of a pipe at a surface location of an oil well. This is useful in drilling operations where it is necessary to know the orientation of a down-hole tool. In offshore drilling applications, it is often necessary to know the orientation of a sub-sea valve. If the valve is connected to a pipe string assembled according to the current invention, the orientation of the sub-sea valve can be easily determined. 
     Another advantage of the method is that it allows installation of equipment to the exterior surface of the pipe string when the alignment of the equipment is critical. A typical example of this is when a fluid-carrying tubing system is attached to the pipe string. Typically, the tubing will be attached to each pipe in the pipe string prior to the assembly of the pipes. As the pipes that comprise the pipe string are assembled, it is essential that the pre-attached tubing on each section of pipe align with the tubing on the other pipes. If the method according to the current invention is used, it possible to know how each pipe in the pipe string will be oriented relative to the other pipes. This allows the tubing to be accurately attached prior to assembly of the pipe string. 
     It should be apparent from the foregoing that an invention having significant advantages has been provided. While the invention is shown in only one of its forms, it is not just limited but is susceptible to various changes and modifications without departing from the spirit thereof.