PATENT ABSTRACT
An expandable tubular pin and box connection is described having a feature of trapping the pin nose after preferably deforming the pin nose plastically in an outward direction away from the longitudinal axis of the connection. The box end is held away from the pin wall before expansion so that its tendency to curl inwardly upon expansion causes it to bend against the pin wall for sealing with it. The thread profile is also optimized to reduce flank separation as a result of expansion.

PATENT DESCRIPTION
PRIORITY INFORMATION 
   This application claims the benefit of U.S. Provisional Application No. 60/563,950, filed on Apr. 21, 2004. 

   FIELD OF THE INVENTION 
   The field of this invention relates to pipe connections to be expanded and more particularly pin and box connections and couplings for downhole tubulars to be expanded after makeup. 
   BACKGROUND OF THE INVENTION 
   Oilfield tubulars are joined at their ends with threads. Typically, the male or pin thread on a tubular to be run into a wellbore is screwed to the female or box end of the tubular previously run into the wellbore. There are many thread designs available for normal well applications that don&#39;t involve expansion. However, when tubulars are expanded problems with known thread designs have occurred. In some cases the load flanks on the thread have spread apart allowing for leakage under pressure conditions. In other cases, the pin or box have failed from stress cracks due to the expansion. In yet other cases, the pin end of the connected joint shrank longitudinally due to the expansion and curled inwardly putting itself in the way of moving other tools or equipment through the expanded connection. In yet other circumstances, the combination of flank separation from expansion and applied pressure allowed fluid leakage to the outside of the connection past the box nose. 
   Various designs for expandable threaded oilfield tubular connections have been devised. Examples of some of the more contemporary designs can be seen in U.S. Pat. Nos. 6,409,175; 6,607,220 and 6,604,763. 
   The present invention seeks to address issues of connection failure by addressing issues relating to flank separation, pin end curling and fluid leakage past the box end to the exterior of the connection. A variety of embodiments are presented both in the form of a threaded pin and box and coupling type connections. Those skilled in the art will more readily appreciate the scope of the invention from the claims that appear below and the examples relating to the below described preferred embodiments. 
   SUMMARY OF THE INVENTION 
   An expandable tubular pin and box connection is described having a feature of trapping the pin nose after preferably deforming the pin nose plastically in an outward direction away from the longitudinal axis of the connection. The box end is held away from the pin wall before expansion so that its tendency to curl inwardly upon expansion causes it to bend against the pin wall for sealing with it. The thread profile is also optimized to reduce flank separation as a result of expansion. 

   
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a made up pin and box prior to expansion and a detail of the thread profile; 
       FIG. 2  is an alternative embodiment of  FIG. 1  having a seal in the box and varying wall thickness in the box; 
       FIG. 3  shows a coupling joint before expansion featuring a soft seal between the tubular ends; 
       FIG. 4  shows a made up coupling before expansion including a metallic seal between the tubular ends. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1  the pin  10  is shown threaded to the box  12  in a two-step thread  14  and  16 . The leading portion of the pin thread  18  preferably makes an angle of about 60° plus or minus about ½° with the longitudinal axis  20  as reflected in angle B. The trailing side of the pin thread  22 , which carries the makeup load, is preferably oriented at angle A with respect to the longitudinal axis  20 , where angle A is preferably about 80° plus or minus about ½°. These orientations on the pin thread that are matched by the corresponding box thread have been determined to minimize gapping after expansion between opposed surfaces  22  on the pin and  24  on the box. The separation occurs during expansion due to differential longitudinal shrinkages between the pin  10  and the box  12 . Those skilled in the art will appreciate that while a two-step thread is shown the invention encompasses other thread types with one or more steps. The invention seeks to address the issue of thread separation resulting from expansion and the preferred embodiment is illustrative of a type of thread that works toward that goal, recognizing that other variations of known thread designs that currently exhibit this separation phenomenon can be undertaken to minimize such separation within the scope of the invention. 
   The pin  10  has a nose  26  that is captured on makeup by a reverse torque shoulder  28 . Shoulder  28  can have a variety of orientations up to a radial orientation with respect to axis  20 . The objective is to capture the nose  26  and plastically deform it in a direction away from axis  20 . Doing this has several advantages. First, despite longitudinal shrinkage due to expansion, the nose  26  remains captured by shoulder  28 . Secondly, since nose  26  is a free end of pin  10 , expansion would normally tend to not only shrink it in length but also make it curl inwardly toward the axis  20 . Plastically deforming it on makeup resists this curling effect. Additionally, the plastic deformation on makeup also provides sealing contact between the nose  26  and surface  30  on the inside of the box  12  both before and continuing after expansion. 
   The box  12  has an end  32  that is cantilevered above pin surface  34 , as shown on the left side of  FIG. 1 . A projection  36 , which can come in a variety of designs and quantities, lifts or maintains end  32  from surface  34  on makeup. Depending on the height of the projection  36  end  32  may either be pushed away from axis  20  or not, upon makeup. However, after expansion end  32  will shrink longitudinally and will also tend to curl inwardly into a sealing contact with pin surface  34  to create an external seal in the vicinity of projection  36 . 
     FIG. 2  is similar to  FIG. 1  with the addition of a groove  38  in which there is a seal ring  40  to further seal between surface  30  on the box  12  and the pin nose  26 . To make up for the reduced wall thickness caused by groove  38 , the box  12  has a thick section  42  to help retain the pressure rating of the expanded connection, which will thin as a result of expansion. For similar reasons, a thick section  44  is provided in the thread area on box  12 . 
     FIG. 3  illustrates a coupling connection featuring tubular  46  having a groove  48  at its end to hold a soft seal  50 . Tubular  52  has a projection  53  to touch the seal  50  when the two tubulars are placed in an abutting relationship. A coupling  54  joins tubulars  46  and  52 . Preferably, shoulders  60  and  62  located respectively on the tubulars  46  and  52  respectively capture both ends  56  and  58  of the coupling  54 . This capture preferably bends the ends  56  and  58  and preferably into the plastic deformation range. Tubulars  46  and  52  respectively have projections  64  and  66  for the same purpose as previously described with regard to projection  36 . The thread surface orientations can also be along the preferred angles described with regard to  FIG. 1 . Seal  48  is a soft material, preferably an elastomer, but can be another material that meets the temperature and chemical exposure requirements of the application. Coupling  54  is thicker in the threaded region to compensate for anticipated wall thinning resulting from expansion. Upon expansion, ends  56  and  58  will curl into a sealing or a further sealing relationship with tubulars  46  and  52  respectively. The capture of end or ends  56 and  58  can also create some sealing contact even before expansion. 
     FIG. 4  is an alternative to  FIG. 3 . Here ends  56  and  58  are not captured but are still cantilevered over projections  64  and  66 . Instead of the soft seal  48  there is a more rigid ring seal  68  that extends into grooves  70  and  72  respectively in tubulars  46  and  52 . What is different in  FIG. 4  is that the seal  68  is sufficiently rigid to hold the ends  74  and  76  together during and through expansion and to help hold those ends against their tendency to curl inwardly due the expansion. Optionally, ends  56  and  58  can still be captured, as described with regard to  FIG. 3 . The thread form can preferably have the configuration described in  FIG. 1 . 
   Those skilled in the art will appreciate that surfaces  22  and  24  help keep the thread together during expansion. Surface  18  provides ease of makeup. The illustrated thread can be quick started or blunt started because the thin feather or incomplete portion of the thread is removed to facilitate makeup. It should also be noted that the contact between end  32  and projection  36  in  FIG. 1  could create a metal-to-metal seal even before expansion. The same effect can be realized for the designs of  FIGS. 3 and 4 . When the coupling design is used, as shown in  FIGS. 3 and 4 , the coupling  54  can be of a different composition that the tubulars  46  and  52 . This allows the use of a more expansion friendly material for the coupling  54  that also can have higher notch tolerance so that it will be less likely to allow stress cracks to form on expansion. Single or multi-step threads are envisioned. The amount of expansion can be in the order of about 22% and the preferred material is L80 for its high strength against burst and collapse despite a lower ductility when compared to stainless steels. 
   The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: