Patent Publication Number: US-8984734-B2

Title: Step-to-step wedge thread connections and related methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional application and claims benefit under 35 U.S.C. §120 to U.S. patent application Ser. No. 13/310,241, filed Dec. 2, 2011, which is a continuation application, and thus claims benefit pursuant to 35 U.S.C. §120, of U.S. patent application Ser. No. 12/890,290 filed Sep. 24, 2010. The contents of those applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     Embodiments disclosed herein relate generally to threaded connections. More particularly, embodiments disclosed herein relate to two-step wedge thread connections and related methods of makeup. 
     2. Background Art 
     Casing joints, liners, drill pipe, and drill collars (collectively referred to as “tubulars”) are often used in drilling, completing, and producing a well. Casing joints, for example, may be emplaced in a wellbore to stabilize a formation, to protect a formation against elevated wellbore pressures (e.g., wellbore pressures that exceed a formation pressure), and the like. Casing joints may be coupled in an end-to-end manner by threaded connections, welded connections, and other connections known in the art. The connections may be designed so as to form a seal between an interior of the coupled casing joints and an annular space formed between exterior walls of the casing joints and walls of the wellbore. The seal may be, for example, an elastomeric seal (e.g., an o-ring seal), a metal-to-metal seal formed proximate the connection, or similar seals known in the art. In some connections, seals are formed between the internal and external threads. Connections with this characteristic are said to have a “thread seal.” As used herein, a “thread seal” means that a seal is formed between at least a portion of the internal thread on the box member and the external thread on the pin member. 
     It will be understood that certain terms are used herein as they would be conventionally understood where tubular joints are being connected in a vertical position along a central axis of the tubular members such as when making up a pipe string for lowering into a well bore. Thus, the term “load flank” designates the side wall surface of a thread that faces away from the outer end of the respective pin or box member on which the thread is formed and supports the weight (i.e., tensile load) of the lower tubular member hanging in the well bore. The term “stab flank” designates the side wall surface of the thread that faces toward the outer end of the respective pin or box member and supports forces compressing the joints toward each other such as the weight of the upper tubular member during the initial makeup of the joint or such as a force applied to push a lower tubular member against the bottom of a bore hole (i.e., compressive force). The term “face” of the box is the end of the box member facing outward from the box threads and the term “nose” of the pin is the end of the pin member facing outward from the threads of the connection. Upon makeup of a connection the nose of the pin is stabbed into and past the face of the box. 
     One type of thread commonly used to form a thread seal is a wedge thread. In  FIGS. 1A and 1B , a connection  100  having a wedge thread is shown. “Wedge threads” are characterized by threads that increase in width (i.e., axial distance between load flanks  125  and  126  and stab flanks  132  and  131 ) in opposite directions on the pin member  101  and box member  102 . Wedge threads are extensively disclosed in U.S. Pat. No. RE 30,647 issued to Blose, U.S. Pat. No. RE 34,467 issued to Reeves, U.S. Pat. No. 4,703,954 issued to Ortloff, and U.S. Pat. No. 5,454,605 issued to Mott, all assigned to the assignee of the present invention and incorporated herein by reference. 
     On the pin member  101 , the pin thread crest  122  is narrow towards the distal end of the pin member  101  while the box thread crest  191  is wide. Moving along the axis  105  (from right to left), the pin thread crest  122  widens while the box thread crest  191  narrows. The rate at which the threads change in width along the connection is defined by a variable known as the “wedge ratio.” As used herein, “wedge ratio,” although technically not a ratio, refers to the difference between the stab flank lead and the load flank lead, which causes the width of the threads to vary along the connection. Furthermore, as used herein, a thread “lead” refers to the differential distance between a component of a thread on consecutive threads. As such, the “stab lead” is the distance between stab flanks of consecutive thread pitches along the axial length of the connection. In  FIGS. 1A and 1B , the thread surfaces are tapered, meaning that the pin thread  106  increases in diameter from beginning to end while the box thread  107  decreases in diameter in a complimentary manner Having a thread taper improves the ability to stab the pin member  101  into the box member  102  and distributes stress in the connection. 
     For wedge threads, a thread seal is accomplished by the contact pressure caused by interference over at least a portion of the connection between the pin load flank  126  and the box load flank  125  and between the pin stab flank  132  and the box stab flank  131 , which occurs when the connection is made-up. Close proximity or interference between the roots  192  and  121  and crests  122  and  191  completes the thread seal when it occurs over at least a portion of where the flank interference occurs. Higher pressure may be contained with increased interference between the roots and crests (“root/crest interference”) on the pin member  101  and the box member  102  and by increasing flank interference. This particular connection also includes a metal-to-metal seal that is accomplished by contact between corresponding sealing surfaces  103  and  104  located on the pin member  101  and box member  102 , respectively. 
     A property of wedge threads, which typically do not have a positive stop torque shoulder on the connection, is that the make-up is “indeterminate,” and, as a result, the relative position of the pin member and box member varies more for a given torque range to be applied than connections having a positive stop torque shoulder. As used herein, “make-up” refers to threading a pin member and a box member together. A final make-up refers to threading the pin member and the box member together up to a desired amount of torque, or based on a relative position (axial or circumferential) of the pin member with the box member. 
     For wedge threads that are designed to have both flank interference and root/crest interference at a selected make-up, both the flank interference and root/crest interference increase as the connection is made-up (i.e. increase in torque increases flank interference and root/crest interference). For wedge threads that are designed to have root/crest clearance, the clearance decreases as the connection is made-up. Regardless of the design of the wedge thread, corresponding flanks and corresponding roots and crests come closer to each other (i.e. clearance decreases or interference decreases) during make-up. 
     Indeterminate make-up allows for the flank interference and root/crest interference to be increased by increasing the torque on the connection. Thus, a wedge thread may be able to thread seal higher pressures of gas and/or liquid by designing the connection to have more flank interference and/or root/crest interference or by increasing the torque on the connection; however, this also increases stress on the connection during make-up, which could lead to failure during use. 
     Prior to make-up a flowing joint compound commonly referred to as “pipe dope” is typically applied to surfaces of a threaded connection to improve the thread seals and provide lubrication during make-up of the connection. For example, the base (e.g., a grease) of the pipe dope may assist a wedge-threaded connection in achieving a thread seal between load and stab flanks thereof, e.g., as disclosed in U.S. Pat. No. RE 34,467 issued to Reeves. Further, pipe dope may contain metallic particle additives, such as copper to protect the threads of the pin and box members from friction galling during make-up and break-out. 
     When a wedge thread connection is made-up, excess pipe dope may become trapped (rather than being squeezed out) between engaging pin and box threads, which may either cause false elevated torque readings (leading to insufficient make-up or “stand-off”) or, in certain circumstances, damage the connection. Pipe stand-off due to inadequate evacuation of the pipe dope is detrimental to the structural integrity of wedge thread connections. As the pressure build-up may bleed off during use, the connection is at risk of accidentally backing off during use. Therefore, stand-off in wedge thread connections is of particular concern as it may lead to loss of seal integrity or even mechanical separation of the two connected members. 
       FIG. 2  shows a prior art two-step connection  150 . The threads that form the connection are separated on two different “steps,” a large step indicated by the bracket  31  and a small step indicated by the bracket  32 . The portion between the large step  31  and the small step  32  is commonly referred to as a mid-step  901 . In some connections, the mid-step  901  may be used as a metal-to-metal seal. The pin thread crest  222  on the small step  32  of the pin member  101 , at its full design height, does not interfere with the box thread crest  221  on the large step  31  of the box member  102  when the pin member  101  is stabbed into the box member  102 . The diameter of the small step  32  of the pin member  101  is smaller than the smallest crest-to-crest thread diameter on the large step  31  of the box member  102 . The pin thread  106  on the small step  32  can be stabbed past the box thread  107  on the large step  31 . The threads on both the small step  32  and the large step  31 , which have substantially the same nominal lead, engage with each revolution to make-up the connection. Thus, the number of revolutions during which the threads slide or rub against each other is reduced for the same number of engaged threads. A two-step connection allows for each of the steps to have threads with different characteristics as long there is little or no variance in the nominal lead of the threads on the steps. 
     A two-step wedge thread connection is disclosed in U.S. Pat. No. 6,206,436 issued to Mallis and assigned to the assignee of the present invention. That patent is incorporated herein by reference. Mallis discloses a two-step wedge thread connection having different wedge ratios, one of which is considered to be an “aggressive” wedge ratio and the other a “conservative” wedge ratio. “Aggressive” refers to the larger wedge ratio, and “conservative” refers to the smaller wedge ratio. Everything else the same, the greater the wedge ratio, the more determinate the make-up. Too large of a wedge ratio may have an inadequate wedging effect, which can allow the connection to back-off during use. Smaller wedge ratios are better able to resist backing-off of the connection. Too small of a wedge ratio may have such an indeterminate make-up that galling may occur over the lengthened make-up distance. Mallis discloses that one of the steps can have a wedge ratio that is optimized for a more determinate make-up (aggressive), while the other step can have a wedge ratio that is optimized for preventing back-off of the connection (conservative). 
       FIGS. 3A and 3B  show cross-section views of a conventional two-step wedge thread connection  200  prior to a final makeup. The connection  200  includes a pin member  201  having pin wedge threads  106  thereon and a box member  202  having corresponding box wedge threads  107  thereon. Further, the connection  200  has first step  31  and second step  32 , with a mid-step region  901  located therebetween. As shown, an axial separation of the two wedge thread steps  31 ,  32  of the pin member  201 , indicated by distance ‘B,’ is substantially equal to an axial separation of the two wedge thread steps  31 ,  32  of the box member  202 , indicated by distance ‘A.’ Thus, the pin wedge threads  106  on the first step  31  of the pin member  201  may be characterized as “in-phase” with the box wedge threads  107  on the first step  31  of the box member  202 . Likewise, the pin wedge threads  106  on the second step  32  of the pin member  201  may be characterized as “in-phase” with the box wedge threads  107  on the second step  32  of the box member  202 . 
     The corresponding pin and box threads on the two steps  31 ,  32  are in-phase such that during makeup, gaps  137  between approaching load flanks  125 ,  126  are equal to gaps  138  between approaching stab flanks  131 ,  132  on the first step  31 . Similarly, gaps  137  between approaching load flanks  127 ,  128  are equal to gaps  138  between approaching stab flanks  133 ,  134  on the second step  32 . Thus, corresponding load flanks  125 ,  126  and stab flanks  131 ,  132  on first step and corresponding load flanks  127 ,  128  and stab flanks  133 ,  134  on second step  32  will contact at substantially the same time (i.e., at final makeup).  FIGS. 3C and 3D  illustrate the conventional two-step wedge thread connection  200  at a final makeup. Because the corresponding load flanks  125 ,  126  and stab flanks  131 ,  132  on first step  31 , and corresponding load flanks  127 ,  128  and stab flanks  133 ,  134  contact at substantially the same time, the interference generated between the surfaces is substantially equal. 
     A threaded connection having improved make-up and break-out torque characteristics would be appreciated by those skilled in the art. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect, embodiments disclosed herein relate to a threaded connection including a pin member comprising a first pin step and a second pin step, and pin wedge threads disposed on each of the first and second pin steps and a box member comprising a first box step and a second box step, and box wedge threads disposed on each of the first and second box steps, wherein an axial separation of the first and second pin steps differs from an axial separation of the first and second box steps. 
     In other aspects, embodiments disclosed herein relate to a threaded connection including a pin member comprising a first pin step and a second pin step, and pin wedge threads disposed on each of the first and second pin steps and a box member comprising a first box step and a second box step, and box wedge threads disposed on each of the first and second box steps, wherein the pin wedge threads on at least one of the first and second pin steps and the corresponding box wedge threads on at least one of the first and second box steps are axially misaligned. 
     In other aspects, embodiments disclosed herein relate to a method of making up a threaded connection, the method including rotationally engaging a pin member having pin wedge threads with a box member having corresponding box wedge threads, wherein the pin and box wedge threads are formed on corresponding first and second pin and box steps of the pin and box members and engaging opposing pin and box stab and load flanks at different times during makeup of the threaded connection. 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A and 1B  show a cross-section view of a prior art connection having a wedge thread. 
         FIG. 2  shows a cross-section view of a prior art two-step threaded connection. 
         FIGS. 3A and 3B  show cross-section and top views, respectively, of a prior art two-step wedge thread connection during makeup. 
         FIGS. 3C and 3D  show cross-section and top views, respectively, of the prior art two-step wedge thread connection in  FIGS. 3A and 3B  at a final makeup. 
         FIGS. 4A and 4B  show cross-section and top views, respectively, of a reduced box step-to-step wedge thread connection during makeup in accordance with one or more embodiments of the present disclosure. 
         FIGS. 4C and 4D  show cross-section and top views, respectively, of the reduced box step-to-step wedge thread connection of  FIGS. 4A and 4B  at a final makeup in accordance with one or more embodiments of the present disclosure. 
         FIGS. 5A and 5B  show cross-section and top views, respectively, of a reduced pin step-to-step wedge thread connection during makeup in accordance with one or more embodiments of the present disclosure. 
         FIGS. 5C and 5D  show cross-section and top views, respectively, of the reduced pin step-to-step wedge thread connection of  FIGS. 5A and 5B  at a final makeup in accordance with one or more embodiments of the present disclosure. 
         FIG. 6  shows a cross-section view of a two-step wedge thread connection having a vanishing box thread in accordance with one or more embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In one aspect, embodiments disclosed herein relate to threads for tubular connections. More particularly, embodiments disclosed herein relate to two-step connections having a step-to-step wedge by which increased interference is generated between opposing thread flanks at a final makeup of the connection. 
       FIG. 4A  shows a cross section of a two-step wedge thread connection  300  having a step-to-step wedge in accordance with one or more embodiments of the present disclosure. The connection  300  includes a pin member  301  having pin wedge threads  306  and a box member  302  having corresponding box wedge threads  307 . The pin and box wedge threads  306 ,  307  may be configured having a dove-tailed profile. Further, the pin and box members  301 ,  302  each have corresponding first steps  31  and second steps  32  formed thereon and a mid-step region  901  located between corresponding steps  31 ,  32 . 
     The connection  300  is configured such that an axial separation of the two wedge thread steps  31 ,  32  of the pin member  301 , indicated by distance ‘B,’ differs from an axial separation of the two wedge thread steps  31 ,  32  of the box member  302 , indicated by distance ‘A.’ Stated otherwise, an axial length of a mid-step region  901  located between steps  31 ,  32  of the pin member  301  may differ from an axial length of a mid-step region  901  located between steps  31 ,  32  of the box member  302 . As such, the pin wedge threads  306  on the first step  31  of the pin member  301  may be characterized as “out-of-phase” with the corresponding box wedge threads  307  on the first step  31  of the box member  302 . Likewise, the pin wedge threads  306  on the second step  31  of the pin member  301  may be characterized as “out-of-phase” with the corresponding box wedge threads  307  on the second step  32  of the box member  302 . 
     As used herein, a connection having axial length differences between steps may be referred to as the step-to-step wedge. Distances A and B may be measured from any fixed coaxial locations on pin and box members from a first step  31  to a second step  32 . As shown here, the coaxial locations on the pin and box members are corresponding pin and box thread flanks but those skilled in the art will understand other locations from which the distances may be measured. 
     In certain embodiments, distance A (i.e., axial separation of the two wedge thread steps  31 ,  32  of the box member  302 ) may be slightly less than distance B (i.e., axial separation of the two wedge thread segments  31 ,  32  of the pin member  301 ). In this instance, the two-step wedge thread connection  300  may be termed a “reduced box step-to-step wedge thread connection” because the axial separation, distance A, between steps  31 ,  32  of the box member  302  is reduced. As shown, distance A of the box member  302  is reduced by a specified amount (i.e., x.xxx inches−.xxx inches) from an amount of distance B (i.e., x.xxx inches) of the pin member  301 . In certain embodiments, the difference in axial separation (i.e., .xxx inches) may be greater than zero or within a range of between about 0.0005 inches to about 0.015 inches. In other embodiments, the difference in axial separation may be about 0.003 inches. 
     Referring now to  FIG. 4B , a top view of engaging wedge threads on steps  31 ,  32  of connection  300  during makeup in accordance with one or more embodiments of the present disclosure is shown. Because of the reduced axial separation between steps  31 ,  32  of the box member  302 , corresponding flanks on the two steps  31 ,  32  may engage at different times during makeup. In this case, on step  31 , corresponding load flanks  125 ,  126  may engage prior to corresponding stab flanks  131 ,  132 , while on step  32 , corresponding stab flanks  133 ,  134  may engage prior to corresponding load flanks  127 ,  128 . 
       FIGS. 4C and 4D  show the reduced box step-to-step wedge thread connection  300  of  FIGS. 4A and 4B  at a final makeup in accordance with one or more embodiments of the present disclosure. At final makeup, load flanks  125 ,  126  and stab flanks  131 ,  132  on the first step  31  and load flanks  127 ,  128  and stab flanks  133 ,  134  on the second step  32  are engaged. However, an amount of interference between engaged stab and load flanks differs. As such, on first step  31 , a higher interference  135  (illustrated as overlap) is generated between load flanks  125 ,  126  than stab flanks  131 ,  132 , while on the second step  32 , a higher interference  137  (illustrated as overlap) is generated between stab flanks  133 ,  134  than load flanks  127 ,  128  due to the difference in axial separation between steps  31 ,  32  of the pin member  301  and box member  302 . In certain embodiments, on step  31 , load flanks  125 ,  126  may engage while stab flanks  131 ,  132  may not completely engage or engage at all, while on step  32 , stab flanks  133 ,  134  may engage while load flanks  127 ,  128  may not completely engage or engage at all. 
     In certain embodiments with the reduced box step-to-step connection, a mid-seal may be formed in mid-step region  901  as corresponding metal surfaces of the pin and box members in the mid-step region  901  between steps  31 ,  32  may engage to form a metal-to-metal mid-seal. As shown in  FIGS. 4C and 4D , the forces applied to the mid-step region  901  due to increased interference on outwardly facing flanks (or stated otherwise, flanks facing away from the mid-step region  901 ), i.e., load flanks  125 ,  126  on step  31  and stab flanks  133 ,  134  on step  32 , further forces metal surfaces of the mid-seal to remain in contact due to a Poisson effect in the mid-seal region. In essence, due to the reduced box step-to-step wedge, tension is created in the box member causing a central portion (mid-step region  901 ) to “neck” inward (i.e., move radially inward). At the same time, due to the reduced box step-to-step wedge, compression is created in the pin member causing a central portion (mid-step region)  901  to “bow” outward (i.e., move radially outward). Thus, the corresponding inwardly necked central portion of the box member and the outwardly bowed central portion of the pin member cause a radial increased interference (due to the Poisson effect) between metal surfaces in the mid-step region  901  of the pin and box members. 
     The axial increased interference created in load flanks  125 ,  126  on the first step  31  and stab flanks  133 ,  134  on the second step  32  in the reduced box step-to-step wedge thread connection may cause a mid-step region  901  of the box member  302  to stretch at final makeup, effectively pre-tensioning the box member  302 . In addition, a mid-step region  901  of the pin member  301  may be pre-compressed. By having pre-loaded members, i.e. a pre-tensioned box member  302  and a pre-compressed pin member  301  after makeup, the threaded connection  300  may be able to delay the reduction of the mid-seal increased interference that external compressive or tensile forces acting on the string may cause on the mid-seal. For example external tension forces acting on the connection may produce, in the mid-seal sealing surface of the pin member, a reduction of the interference contact stresses. However, the pre compression of the pin mid step region delays the effect of such external tensile forces, because the pre-compression needs to be first overcome by the external tensile force before the mid step region is affected. Similarly, external compression forces acting on the connection may produce, in the mid-seal sealing surface of the box member, a reduction of the interference contact stresses. However, the pre tension of the box mid step region delays the effect of such external compressive forces, because the pre-tension needs to be first overcome by the external compressive force before the mid step region is affected. 
     Wedge threads in combination with dovetail thread profiles may provide a radial interlocking effect, which locks the pin member and box member together radially and provides resistance against separation caused by internal or external pressure. In addition, the step-to-step wedge introduces a backup interlocking mechanism. If the standard wedge fails to provide such interlocking, the step-to-step wedge may provide additional resistance to the internal or external pressure and prevent radial separation of the pin and box members. In sum, embodiments disclosed herein provide a connection that obtains the trapping effect for the metal to metal seal in the central portion  901 , from the step-to-step wedge, in combination with the interlocking effect of the dovetail thread profile in the individual steps. Moreover, even if the wedge thread of the individual steps would happen to fail, (due to, for example, standoff caused either by dope entrapment or by insufficient make up torque), the trapping or interlocking effect may still be provided by the step-to-step wedge. In certain embodiments, internal pressure support in the connection may be distributed approximately two-thirds to the box thickness at the mid-seal and one-third to the locking effect of the step-to-step wedge. 
     Referring now to  FIG. 6 , a cross-section view of a two-step wedge thread connection  600  having the step-to-step wedge and also having a mid-seal in accordance with one or more embodiments of the present disclosure is shown. The pin member  601  and box member  602  having corresponding steps  31 ,  32  are engaged such that sealing surfaces  603  (of pin member  601 ) and  604  (of box member  602 ) engage. The sealing surfaces  603 ,  604  are established at assembly by metal-to-metal interference. Upon full make-up of the connection  600 , engagement of the step-to-step wedge may induce additional radial positional interference into the contacting sealing surfaces  603 ,  604  (i.e., an “increased interference” effect). In addition to this, the pre-loading of pin and box members due to the step-to-step wedge may delay the reduction of the Poisson effect (i.e., the neck inward and bow outward mechanism) that compressive or tensile loads acting on the connection (i.e. forces transmitted by the pipe string) may produce. The seal pressure retention characteristic of the threaded connection  600  is related to the ability of the sealing surfaces  603 ,  604  to remain in contact with one another as radial deflection of the joint occurs from either internal pressure of external pressure. Seal retention of embodiments having a locked-in or trapped mid-seal result from a locking effect of the step-to-step wedge thereby preventing loss of surface contact between surfaces  603  and  604 . The locking in effect causes the two surfaces  603  and  604  to deflect as one. 
     Methods of making up a reduced box step-to-step connection include engaging pin wedge threads  306  of pin member  301  with corresponding box wedge threads  307  of box member  302 . During makeup, on step  31 , corresponding load flanks  125 ,  126  may engage prior to corresponding stab flanks  131 ,  132 , while on step  32 , corresponding stab flanks  133 ,  134  may engage prior to corresponding load flanks  127 ,  128 . As makeup of the connection continues, interference between load flanks  125 ,  126  on the first step  31  and stab flanks  133 ,  134  increases up to a final makeup. At final makeup, stab flanks  131 ,  132  on the first step  31  and load flanks  127 ,  128  on the second step  32  also engage. Thus, at final makeup, a higher interference  135  is generated between load flanks  125 ,  126  than stab flanks  131 ,  132 , while on the second step  32 , a higher interference  137  is generated between stab flanks  133 ,  134  than load flanks  127 ,  128 . 
     Referring now to  FIG. 5A , a cross section of a two-step wedge thread connection  400  having a step-to-step wedge in accordance with one or more embodiments of the present disclosure is shown. The connection  400  includes a pin member  401  having pin wedge threads  406  thereon and a box member  402  have box wedge threads  407  thereon. Further, the pin member  401  and box member  402  each have corresponding first steps  31  and second steps  32  formed thereon. A mid-step region  901  is located between corresponding steps  31 ,  32 . 
     The connection  400  is configured such that a distance B (i.e., axial separation of the two wedge thread steps  31 ,  32  of the pin member  401 ) may be slightly less than distance A (i.e., axial separation of the two wedge thread segments  31 ,  32  of the box member  402 ). In this instance, the two-step wedge thread connection may be termed a “reduced pin step-to-step wedge thread connection” because the axial separation, distance B, between steps  31 ,  32  of the pin member  401  is reduced. As shown, distance B of the pin member  401  is reduced by a specified amount (i.e., x.xxx inches−.xxx inches) from a specified amount of distance A (i.e., x.xxx inches) of the box member  402 . In certain embodiments, the difference in axial separation (i.e., .xxx inches) may be within a range of between about 0.0005 inches to about 0.015 inches. In other embodiments, the difference in axial separation may be about 0.003 inches. 
     Referring now to  FIG. 5B , a top view of engaging threads on steps  31 ,  32  of connection  400  during makeup in accordance with one or more embodiments of the present disclosure is shown. Because of the reduced axial separation between steps  31 ,  32  of the pin member  401 , corresponding flanks on the two steps  31 ,  32  may engage at different times during makeup. In this case, on step  31 , corresponding stab flanks  131 ,  132  may engage prior to corresponding load flanks  125 ,  126 , while on step  32 , corresponding load flanks  127 ,  128  may engage prior to corresponding stab flanks  133 ,  134 . 
       FIGS. 5C and 5D  show the reduced pin step-to-step wedge thread connection  400  at a final makeup in accordance with one or more embodiments of the present disclosure. At final makeup, load flanks  125 ,  126  and stab flanks  131 ,  132  on the first step  31  and load flanks  127 ,  128  and stab flanks  133 ,  134  on the second step  32  are engaged. However, an amount of interference between engaged stab and load flanks differs. On the first step  31 , a higher interference  135  (illustrated as overlap) is generated between stab flanks  131 ,  132  than load flanks  125 ,  126 , while on the second step  32 , a higher interference  137  (illustrated as overlap) is generated between load flanks  127 ,  128  than stab flanks  133 ,  134 , due to the difference in axial separation between steps  31 ,  32  of the pin member  401  and box member  402 . In certain embodiments, on step  31 , stab flanks  131 ,  132  may engage while load flanks  125 ,  126  may not completely engage or engage at all, while on step  32 , load flanks  127 ,  128  may engage while stab flanks  133 ,  134  may not completely engage or engage at all. 
     Methods of making up a reduced pin step-to-step connection include engaging pin wedge threads  406  of pin member  401  with corresponding box wedge threads  407  of box member  402 . During makeup, on step  31 , corresponding stab flanks  131 ,  132  may engage prior to corresponding load flanks  125 ,  126 , while on step  32 , corresponding load flanks  127 ,  128  may engage prior to corresponding stab flanks  133 ,  134 . As makeup of the connection continues, interference between stab flanks  131 ,  132  on the first step  31  and load flanks  127 ,  128  on second step  32  increases up to a final makeup. At final makeup, load flanks  125 ,  126  on the first step  31  and stab flanks  133 ,  134  on the second step  32  also engage. Thus, at final makeup, on the first step  31 , a higher interference  135  is generated between stab flanks  131 ,  132  than load flanks  125 ,  126 , while on the second step  32 , a higher interference  137  is generated between load flanks  127 ,  128  than stab flanks  133 ,  134 . 
     In one or more embodiments disclosed herein, the threaded connection may be a two-step wedge thread connection having a standard wedge on both steps, i.e., the thread lead on both steps  31 ,  32  have wedge ratios that are substantially the same. In other embodiments, the threaded connection may have a thread lead on the first step  31  having a first wedge ratio and a thread lead on the second step  32  having a second wedge ratio (i.e., different wedge ratios on each step). As previously described, one of the wedge ratios may be considered to be an “aggressive” wedge ratio and the other a “conservative” wedge ratio (“aggressive” refers to the larger wedge ratio, and “conservative” refers to the smaller wedge ratio). In one or more embodiments disclosed herein, thread leads on one step may have an aggressive wedge ratio of between about 0.035 and 0.045 inches per revolution while the thread leads on the other step may have a conservative wedge ratio of between about 0.003 and 0.010 inches per revolution. In other embodiments, the thread leads on one step may have an aggressive wedge ratio of about 0.019 inches per revolution and the thread leads on the other step may have a conservative wedge ratio of about 0.011 inches per revolution. 
     Further, the wedge threads on steps  31 ,  32  of the threaded connection may have a number of different clearance/interference combinations between corresponding roots and crests. For example, in certain embodiments, the threads on one or both steps  31 ,  32  may have a root/crest clearance at a final makeup. In other embodiments, the threads on one or both steps  31 ,  32  may have root/crest interference at a final makeup. Still further, in certain embodiments, the threads on the first step  31  may have a root/crest clearance while the threads on the second step  32  have a root/crest interference, or vice versa. Still further, in certain embodiments, the threads on the first step  31  and second step  32  may have alternating root/crest clearance and interference in adjacent threads. 
     In certain embodiments, the threaded connection may include a vanishing thread form as shown in  FIG. 6 .  FIG. 6  shows a cross-section view of a two-step wedge thread connection  600  having a step-to-step wedge. As shown, the pin member  601  and box member  602  have corresponding steps  31  and  32  with pin and box threads  606 ,  607  thereon, and a mid-step region  901  therebetween. Further, the box thread  607  has a thread height that diminishes along an axial length of the threads moving away from a distal end of the box member  602 . The box thread  607  may be characterized as a vanishing thread form because of the diminishing thread height. 
     As used herein, “vanishing” threads may be defined as box threads which rather than being “perfect” full form threads, vanish when the thread taper intersects the pipe body surface. Therefore, “vanishing” threads have their crests truncated, thus leaving a radial gap between the thread crests and the thread root of the mating member. The “vanishing” thread concept may enhance both tension and compression capabilities of integral connections when applied to sections of full pipe body wall thickness. It matters not whether the full pipe body wall thickness section occurs in a plain end pipe section or in a swaged pipe body section as long as the outer diameter (“OD”) of the section is comprised of pipe body surface (non-machined) and the inner diameter (“ID”) of the section is comprised of pipe body surface (non-machined). 
     In a threaded connection, the tension critical section works off of the thread load flank at the thread root. When a “perfect” full form thread intersects the pipe body surface, the critical section is a function of the pipe body inner and outer surfaces minus the depth of the “perfect” full form thread. When the thread is allowed to “vanish” into the pipe body surface, a thread with less than full thread height is intersecting the pipe body surface. A load flank that is less than fully engaged with the mating member can carry the full tension load applied to the connection. In certain embodiments, approximately 30%-70% thread load flank engagement may carry the full tension load. Therefore, the connection critical section area may be significantly increased by taking advantage of a “vanishing” thread. For wedge threads, compression capacity works off of the thread stab flank at the thread crest. So if the thread form intersects the pipe body surface in a section of the full pipe body wall thickness, whether at a “perfect” thread form height or just partially as in a “vanishing” thread, the compression capacity of the connection is equal to that of the pipe body. 
     Embodiments disclosed herein for the step-to-step wedge thread connection provide a number of advantages. First, embodiments disclosed herein address dope compound entrapment within the wedge threads, which is an inherent problem in larger diameter wedge products, and subsequent low break-out torques experienced as the thread compound pressure relieves with time, loading, or temperature. Even if individual wedges trap the dope compound, the substantial wedging effect that is created between the two steps of the connection is still sufficient to provide required break-out torque resistance. Thus, dope entrapment is tolerated by the step-to-step wedge such that it is no longer deleterious to the structural integrity of the threaded connection. 
     Next, embodiments disclosed herein address manufacturing limitations involved with thread machining. Generally, a thread is cut on a tubular using a substantially constant thread lead (including the load lead and the stab lead), however, some variance in the thread lead occurs during the manufacturing process, which is typically includes machining with a mill or lathe. During machining, the variance in the thread lead manifests as a slight periodic variation in the thread lead above and below the intended value for the thread lead. This phenomenon is commonly referred to as “thread drunkenness.” The sensitivity of thread drunkenness may be determined as a ratio of the magnitude of the variations or “bumps” in the thread flanks and a width of the wedge thread itself. Previously, the width of the wedge thread was just the distance between opposing thread flanks themselves (i.e., distance between opposing stab and load flanks) Instead, embodiments disclosed herein re-establish a width of the wedge as the distance across the steps of opposing stab and load flanks, thereby increasing the width of the wedge. This effectively reduces the sensitivity of thread drunkenness and thereby reduces or eliminates manufacturing limitations previously caused by thread machining operations. 
     Still further, embodiments disclosed herein allow the threaded connection to withstand multiple make-ups and break-outs without losing energy retention in the wedge thread. Because of the wedging effect that is created across the two steps, a higher spring effect may be created over a larger distance. This allows the connection to retain energy better and allow for increased energy retention in the wedge over multiple uses. The spring effect also reduces the chances of galling the thread surfaces during make-up of the connection. 
     While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.