Abstract:
A tubular connector secures two coaxial tubulars using a box and pin connection. A pin end tubular member having an axis and a pin end inserts into a box end tubular member having a box end. A pin end flange formed on an outer diameter of the pin end tubular member receives an end of the box end of the box end tubular member. An inwardly depending flange is disposed on the inner diameter of the box end portion. The inwardly depending flange is spaced apart from the box end planar surface and has a box end shoulder formed at an angle to the axis facing a same direction as the box end planar surface of the box end tubular member. An end of the pin end of the pin end tubular member engages with the inwardly depending flange for compressive load transfer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to drilling and production of oil and gas wells and, in particular, to a tubular connector having a secondary load transfer shoulder. 
     2. Brief Description of Related Art 
     Offshore hydrocarbon wells often contain one or more casing strings of large diameter pipe, such as 16 inches or greater in diameter. Production risers extending from subsea well equipment to the surface are also made up of fairly large diameter pipes. The joints of pipe, whether in a casing string or production riser string, are connected together by threaded connections. A typical threaded connection has internal threads on a conical portion of a box that engage external threads on a pin. Normally, the pin has an external shoulder at the base of the threads that is engaged by the rim of the box when made up. A compressive load on the string of casing acts against the external shoulder. Typically, the compressive load capacity of the connector is less than the compressive load capacity of the pipe. 
     Connectors having both external and internal load shoulders are known in the prior art. The nose of the pin engages the internal load shoulder and the rim of the box engages the external load shoulder. However, tolerance stack ups and high stiffness make it difficult to achieve proper engagement of both the internal and external shoulders. Under compressive loading, the outer diameter shoulder also creates an internal bending moment that is offset from the compressive load path transmitting through the pipe to the connector and back into the pipe. The bending moment contributes to the connectors having a compressive load strength that is less than the compressive load strength of the tubular members individually. Internal shoulders alone create very eccentric paths for tension loads and very high stresses under combined compression and internal pressure. As a result, the connectors are often formed of stronger materials or have larger diameters to accommodate the additional compressive load. This can make it difficult to manufacture the tubulars, add to their weight, and make manipulating the tubulars more difficult. In addition, where the joined tubulars are run concentrically through another set of tubulars, the outer tubulars must be increased in size to accommodate the larger diameter of the joints. 
     Attempts have been made to place dual load transfer shoulders on both the internal and external diameters of the connectors to increase the load transfer area and counteract the bending moment. However, this resulted in little control of where the load transfers due to tolerance stack up issues and high stiffness of the internal shoulder. 
     SUMMARY OF THE INVENTION 
     These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention that provide a tubular connector having a secondary load transfer shoulder. In accordance with an embodiment of the present invention, a tubular connector has a pin having a nose, an external shoulder, and a conical portion between the external shoulder and the nose containing a set of external threads. A box has a bore, a rim that engages the external shoulder and a set of internal threads in the bore that engage the external threads. An internal shoulder in the bore is engaged by an end of the nose when the rim of the box engages the external shoulder. An annular recess is formed in the bore of the box on a side of the internal shoulder opposite the nose. The annular recess is sized to provide flexibility to the internal shoulder so as to allow the internal shoulder to deflect when engaged by the end of the nose. 
     When the pin end of the pin end tubular member is inserted into the box end of the box end tubular member, the pin end of the pin end tubular member and the box end of the box end tubular member secure the pin end tubular member to the box end tubular member. The pin end shoulder of the pin end flange is adjacent to the planar surface of the end of the box end of the box end tubular member, and the box end shoulder of the inwardly depending flange is adjacent to the planar surface of the end of the pin end portion of the pin end tubular member. Compressive load transfer occurs through at least one of the planar surface of the end of the box end portion and the pin end shoulder and the planar surface of the end of the pin end portion and the box end shoulder. When an increased compressive load is applied to the pin end tubular member and the box end tubular member, a portion of the compressive load transfers across the box end shoulder of the inwardly depending flange of the box end portion of the box end tubular member and the end of the pin end portion of the pin end tubular member. 
     An advantage of a preferred embodiment is that it provides a tubular connector that has an increased compressive load capacity over prior art tubular connectors. In some disclosed embodiments, the compressive strength of the tubular connector is equal to the compressive strength of the pipe joined by the tubular connector. Still further, the disclosed embodiments provide an internal shoulder that is not subject to the tolerance stack up and high stiffness complications of prior art internal shoulders. The internal shoulder is a designed spring that deflects and gets stiffer as load is applied. As the load increases, it does not all go to the outer shoulder, and since the internal shoulder is in line with the pipe, the load path is straight. The straight load path results in less moment generated as with a traditional external shoulder. The disclosed embodiments also provide a tubular connector that has a greater bending capacity than prior art tubular connectors. Still further, the disclosed embodiments do not interfere with the flow profile through the central passage of the joined tubulars. The disclosed embodiments also provide a joint connector for tubular members that does not require a substantial increase in diameter of the joint to have increased capabilities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained, and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings that form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic representation of a riser extending between a subsea wellhead assembly and a surface platform in accordance with an embodiment. 
         FIG. 2  is a side sectional view of a portion of a joint for connecting two tubulars of the riser of  FIG. 1  in accordance with an embodiment. 
         FIG. 3  is a sectional detail view of a secondary shoulder of the joint of  FIG. 2  in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. Additionally, for the most part, details concerning rig operation, subsea assembly connections, riser use, and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the skills of persons skilled in the relevant art. 
     Described herein are example embodiments of connecting tubulars to form a string of tubulars. Shown in a side view in  FIG. 1  is one example of an offshore platform  11  having a production riser  13  depending subsea for connection with a subsea wellhead assembly  15  shown on the sea floor. Riser  13  may be formed of a plurality of tubulars, for example a lower tubular  17  and an upper tubular  19 , extending several thousand feet between platform  11  and subsea wellhead assembly  15 . In the embodiment of  FIG. 1 , riser  13  is assembled by connecting tubulars  17 ,  19  at a joint  21  in the manner described in more detail below. 
     Referring to  FIG. 2 , a sectional view of joint  21  in a made-up position is shown. Lower tubular  17  has a pin end  23  having an upward facing shoulder  25  on an outer diameter portion of lower tubular  17 . As shown in  FIG. 2 , pin end  23  includes an outer diameter flange  27  having an outer diameter larger than the diameter of lower tubular  17 . Outer flange  27  may be axially spaced from an end  29  of pin end  23  along an axis  31  of lower tubular  17 . Upward facing shoulder  25  extends from an outer diameter of pin end  23  radially outward to the outer diameter of flange  27 . Pin end  23  includes an upwardly extending pin  33 . Pin  33  includes a cylindrical proximal pin end portion  35  proximate to flange  27 . Proximal pin end portion  35  may join flange  27  proximate to upward facing shoulder  25 . Pin  33  includes a conical medial pin end portion  37  extending toward end  29  from proximal pin end portion  35 . In the illustrated embodiment, medial pin end portion  37  tapers from proximal pin end portion  35  to a nose or distal pin end portion  39  of pin  33  at end  29  of pin  33 . In the illustrated embodiment, medial pin end portion  37  is wider at proximal pin end portion  35  than at distal pin end portion  39 . Threads or grooves  41  may be formed on an outer diameter surface of medial pin end portion  37 . Distal pin end portion  39  may be generally cylindrical as shown in  FIG. 2  and have an axial length such that end  29  may be spaced apart from medial pin end portion  37 . Distal pin end portion  39  also includes an upwardly facing end or shoulder  43  at end  29 . In the illustrated embodiment, upwardly facing shoulder  43  may be conical and face slightly toward axis  31 . In this example, A person skilled in the art will recognize that in other embodiments upwardly facing shoulder  43  may be cylindrical. 
     Continuing to refer to  FIG. 2 , upper tubular  19  includes a box end  45  having an outer diameter substantially equivalent to the outer diameter of flange  27  of pin end  23 . Box end  45  depends downwardly from upper tubular  19  and has a lower end that defines a downward facing shoulder  47 . A tubular wall at box end  45  has a thickness at downward facing shoulder  27  that is substantially equivalent to the width of upward facing shoulder  25  of flange  27 . Box end  45  has a length substantially equivalent to the length of pin  33  and includes a distal box end portion  49 , a medial box end portion  51 , and a proximal box end portion  53 . Proximal box end portion  53  joins upper tubular  19 . Proximal box end portion  53  has an inner diameter that is substantially equivalent to the inner diameter of upper tubular  19 . Distal box end portion  49  may be located at an end of box end portion  45  opposite proximate box end portion  53 . Distal box end portion  49  may be substantially cylindrical and have an outer diameter equivalent to the outer diameter of flange  27  of lower tubular  17  and an inner diameter greater than the inner diameter of upper tubular  19 . In the illustrated embodiment, the inner diameter of distal box end portion  49  is substantially equivalent to the outer diameter of proximal pin end portion  35  so that distal box end portion  49  may surround proximal pin end portion  35  of lower tubular  17 . Medial box end portion  51  has a general conical inner diameter extending between distal box end portion  49  and proximal box end portion  53 . Medial box end portion  51  may have threads  55  formed on an inner diameter surface that mate with threads  41  on the outer diameter surface of pin end medial portion  37 . A person skilled in the art will recognize that the angle of the conical surfaces of pin end medial portion  37  and medial box end portion  51  may be the same so that threads  41 ,  55  may thread together to join upper tubular  19  to lower tubular  17 . A person skilled in the art will understand that upper tubular  19  and lower tubular  17  may be joined by any suitable means. For example, upper tubular  19  and lower tubular  17  may be secured by threaded couplers as shown herein, cammed couplers, collet couplers, or the like, provided joint  21  accommodates compressive load transfer as described in more detail below. 
     Proximal box end portion  53  may be generally cylindrical and extends form upper tubular  19  to medial box end portion  51 . Proximal box end portion has a first diameter  57  at medial box end portion  51 , and a second inner diameter  59  at upper tubular  19 . Proximal box end portion  53  has an inwardly depending flange  61  positioned intermediate of upper tubular  19  and medial box end portion  51 . In an embodiment, inwardly depending flange  61  is spaced apart from the end of distal box end portion  49  so that when pin  33  is inserted into box end  45 , upwardly facing shoulder  43  of pin  33  is adjacent to or abuts inwardly depending flange  61 . Referring to  FIG. 3 , inwardly depending flange  61  has a generally cylindrical inner diameter surface  63  that may be substantially equivalent to the inner diameter of upper tubular  19  and the inner diameter of pin end  23 . An annular recess  65  is formed on the inner diameter surface of proximal box end portion  53  to define an upwardly facing surface  67  of inwardly depending flange  61  formed at a first angle to axis  31 . In the illustrated embodiment, upwardly facing surface  67  is a conical surface. Annular recess  65  is an annular feature having a conical surface  69  formed at a second angle to axis  31  and depending generally toward the outer diameter of box end  45  so that axial surface  69  joins upwardly facing surface  67  spaced outwardly from the inner diameter of upper tubular  19 . 
     Inwardly depending flange  61  includes an internal conical downwardly facing shoulder  71  formed at an angle to axis  31  so that downwardly facing shoulder  71  generally faces outwardly. The angle of downwardly facing shoulder  71  gives more contact pressure to a metal to metal seal that may be placed between upper tubular  19  and lower tubular  17 . Where downwardly facing shoulder  71  joins first diameter  57 , a generally circular annular groove  73  may be formed. When viewed in the transverse cross section of  FIG. 3 , groove  73  appears as a partial circle, extending about 250 to about 270 degrees about a centerline of groove  73 . Groove  73  may have a diameter sufficient to accommodate a corner of distal pin end portion  39  as described in more detail below. In an exemplary embodiment, inwardly depending flange  61  is flexible based in part on the cut of annular recess  65 , the angles of upwardly facing surface  67  and conical surface  69 , and the material properties of inwardly depending flange  61 . For example, as the angle formed by upwardly facing surface  67  with axis  31  varies from perpendicular to axis  31 , the flexibility of inwardly depending flange  61  may increase. Flange  61  has a minimum thickness T that is greater than 40% of the width W of flange  61 . Minimum thickness T of flange  61  extends from upwardly facing surface  67  to a lower surface of the internal shoulder measured generally perpendicular to upwardly facing surface  67 . Width W is measured from base B of flange  61  to the inner diameter surface  63 . Width W is measured along a line that is parallel with the inclination of upwardly facing surface  67  of annular recess  65 , Base B of flange  61  extends from the outer most diameter of annular recess  65  to the outermost diameter of groove  73 . Because of groove  73 , the axial dimension of inner flange  61  is less at its base where it joins the box of box  19  than at inner diameter  63 . In the embodiment shown, the axial extent of inner flange  61  at inner diameter  63  is less than the axial extent of annular recess  65  measured at the inner diameter of annular recess  65 . In one embodiment, the radial depth of annular recess  65  is the same or greater than the radial thickness of nose  29  of pin  17 . The inner diameter  59  of the bore is the same as inner flange inner diameter  63  and immediately above annular recess  65 . 
     When joint  21  is made up, described in more detail below, flange  27  and distal box end portion  49  act as the primary compressive load shoulder. However, as compressive loading is increased, pin end distal portion  29  will push against downwardly facing shoulder  71  of inwardly depending flange  61 . As this occurs, and the contact between downwardly facing shoulder  71  and upwardly facing shoulder  43  increases, a portion of the compressive loading of upper tubular  19  and lower tubular  17  is picked up between this interface. In this manner, a portion of any compressive loading will be transferred through inwardly depending flange  61  and pin end distal end portion  29 . Due to annular recess  65  and groove  73 , inwardly depending flange  61  is flexible, having a decreasing stiffness as compressive loading increases. A person skilled in the art will recognize that the compressive loading between flange  27  and distal box end portion  49  and pin end distal portion  29  and inwardly depending flange  61  may be proportionally allocated based on the sizing of the relative flanges  27 ,  61 , and may vary according the amount of compressive loading and initial amount of contact between upwardly facing shoulder  43  and downwardly facing shoulder  71 . Preferably the stiffness to axial deflection of inner flange  63  is much less than the stiffness to axial deflection of pin external flange  27 , such as less than 25%. The deflection of inner flange  63  may be elastic or it may be permanent. 
     In an exemplary non-illustrated embodiment, inwardly depending shoulder  61  is formed such that downwardly facing shoulder  71  is perpendicular to axis  31 . In these embodiments, the flexibility of inwardly depending shoulder  61  is increased. 
     Referring again to  FIG. 2 , joint  21  may be assembled in the following manner. Box end  45  of upper tubular  19  may be brought proximate to pin end  23  of lower tubular  17 . Upper tubular  19  may be manipulated to place box end  45  around pin end  23 , bringing threads  41 ,  55  axially adjacent to each other. In an exemplary embodiment, box end  45  will be brought proximate to and may land on shoulder  25 . Threads  51 ,  55  may be in contact, but not engaged, with one another. Upper tubular  19  may then be rotated relative to lower tubular  17 , causing threads  41 ,  55  to engage and securing upper tubular  19  to lower tubular  17 . A person skilled in the art will understand that the relative positions of upper tubular  19  and lower tubular  17  may be reversed so that lower tubular  17  and pin end  23  may be stabbed into upper tubular  19  and box end  45 . A person skilled in the art will also understand that different methods to secure upper tubular  19  to lower tubular  17  may be used. Additionally, it is possible that pin nose end  43  may contact internal shoulder  71  before the rim of box end portion  49  lands on external shoulder  25 . 
     In an exemplary embodiment, when distal box end portion  49  lands on flange  27 , downward facing shoulder  47  may abut upward facing shoulder  25  and downwardly facing shoulder  71  may land on upwardly facing shoulder  43 . In another exemplary embodiment, downwardly facing shoulder  71  may be adjacent to, but not in contact with, upwardly facing shoulder  43 . When upper tubular  19  and lower tubular  17  are compressed along axis  31 , compressive load transfer between upper tubular  19  and lower tubular  17  occurs primarily through box end  45  and flange  27  through downward facing shoulder  47  and upward facing shoulder  25 . However, a portion of the compressive loading may transfer through downwardly facing shoulder  71  and upwardly facing shoulder  43 . The proportion of this load transfer will increase as the compressive loading of upper tubular  19  and lower tubular  17  increases. In this manner, inwardly depending flange  61  acts as a secondary load shoulder for joint  21 . 
     A person skilled in the art will understand that while the tubular members are referred to as a lower tubular member and an upper tubular member, it is not necessary that the members be assembled or positioned relative to one another as shown. For example, a first tubular member  17  having upwardly facing shoulder  43  may be axially above a second tubular member  19  having box end  45  and the components described above. Joint  21  may then operate generally as described above. A person skilled in the art will recognize that such positioning is contemplated and included in the disclosed embodiments. 
     Accordingly, the disclosed embodiments provide numerous advantages. For example, the disclosed embodiments provide a tubular connector that has an increased compressive load capacity over prior art tubular connectors. In some disclosed embodiments, the compressive strength of the tubular connector is equal to the compressive strength of the pipe joined by the tubular connector. Still further, the disclosed embodiments provide an internal shoulder that is not subject to the tolerance stack up and high stiffness complications of prior art internal shoulders. The disclosed embodiments also provide a tubular connector that has a greater bending capacity than prior art tubular connectors. Still further, the disclosed embodiments do not interfere with the flow profile through the central passage of the joined tubulars. The disclosed embodiments also provide a joint connector for tubular members that does not require a substantial increase in diameter of the joint. 
     It is understood that the present invention may take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or scope of the invention. Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.