You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF INVENTION 
   The present invention relates generally to an in-line swivel for use in drilling and pipeline operations. More particularly, the invention relates to an in-line swivel permitting deflection when the tubular string below the swivel is deflected by relative motion from the longitudinal axis of the remainder of the tubular string. More particularly still, the invention relates to an in-line swivel permitting deflection of a pipe string resulting from “wave action” and wind changes experienced when used in conjunction with floating drilling rigs or tankers. 
   The use of in-line drill string swivels in drilling applications has long been known to those in the drilling industry. Often, during sea-based drilling operations on floating platforms, the drill string suspended from a drilling mast may experience movement not generally experienced by land based drilling rigs which are fixed to the ground. These floating drill rigs may have drilling masts extending hundreds of feet above the rotary table support the drill string hanging below. If the rotary table floor rotates or rocks while the in-line swivel is supporting the drill string, damage may occur to the drill string or Kelly drive. Particularly, if a drill string on a movable platform is connected to a fixed or rigid tubular string, stress and strain will build up if a provision to allow rotation and deflection therebetween is not present. Furthermore, movement of the platform or vessel from wave action or wind (or intentional movements) can overstress and even loosen a threadably connected pipe string. Finally, in addition to “drill string” applications, other applications of pipe, either threadably connected or bolted, exist where angular and rotational deflections are an issue. 
   SUMMARY OF INVENTION 
   The present invention relates to a deflection swivel providing a tubular retainer sub, a tubular swivel mandrel having an enlarged rounded head at its upper end, and a retainer nut providing an opening larger than the outer diameter of a lower end of the tubular swivel mandrel, connected to the tubular retainer sub enclosing said rounded head of the tubular swivel mandrel to permit deflection of the swivel mandrel and enclosing a bearing having an upper surface conforming to the rounded head of the tubular swivel mandrel to thereby permit rotational movement of the mandrel upon deflection of the swivel mandrel from the longitudinal axis of the retainer sub. 
   The hardened wear collar inserted in the interior surface of the retainer sub provides a profile conforming to the rounded head of the tubular swivel mandrel thereby permitting the rounded head to rest within the profile, evenly distributing the strain caused by lateral movement of the mast of the drilling structure, around the collar surface. The wear collar is retained between an upper edge of the bearing and the lower hemispherical surface of the swivel mandrel to permit deflection of the swivel mandrel. Alternatively, the wear collar could be formed as the upper edge of the bearing. Each embodiment can be slipped over the lower end of the mandrel member upon makeup and positioned between the retainer sub and the bottom hemispherical surface of the swivel mandrel. The wear collar moreover could be segmented to allow portions of the wear collar to be replaced without replacement of the whole. 
   The bearing which supports the rotation of the mandrel can be lubricated by injection of lubricant from a lower edge of retainer nut. The bearing and its lubrication are protected from the damage that can be observed from the ingress of drilling fluid into the bearing race since the present invention provides one or more seals on the upper hemispherical surface of the swivel mandrel to prevent egress of drilling fluid around the rounded head of the mandrel into the bearing supporting the mandrel in the retainer sub. 
   A hardened insert can be retained in a lower radial portion of the retainer sub providing a cooperating hemispherical surface conforming to the rounded upper surface shape of the swivel mandrel or this cooperating surface may be formed on the inner surface of the enlarged lower end of the retainer sub. Since this surface can experience wear from repeated deflections of the swivel from its principal longitudinal axis, a wear surface preventing premature wearing of the retainer sub is expected to be preferred. This hardened surface would provide seals to prevent drilling fluid from flowing around the hardened insert to reach the bearing. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a partial sectional drawing of the deflection sub in accordance with a preferred embodiment of the present invention. 
       FIG. 2  is a cross-sectional drawing side view of the deflection sub of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1 and 2  collectively, a deflection sub  10  in accordance with a preferred embodiment of the present invention is shown. Deflection sub  10  assembly preferably includes a tubular retainer sub  20 , a swivel mandrel  30 , a retainer nut  50 , and a bearing  60 . Retainer sub  20  preferably includes a rotary threaded drill connection  22  at its distal end to permit connection thereto with additional threaded pipe string components. While threaded connection  22  is shown as a female connection, it should be understood that any connection known in the art may be employed to connect retainer sub  20  to other components. Additionally, retainer sub  20  preferably includes a bore  24  therethrough to allow the flow of drilling fluids from the fluid system into the drill string. Retainer sub  20  is shown including an enlarged end  26  including threads  28  on an exterior lateral surface and a recess on its interior surface providing a seat  27  for a socket bushing  40 . 
   Socket bushing  40  preferably includes an exterior surface mating with seat  27  and a hemispherical interior surface  43 . A passage through socket bushing  40  permits drilling fluid to flow through into the throat of swivel mandrel  30  without obstruction. Socket bushing  40  can be integral to retainer sub  20 . Furthermore, socket bushing  40  preferably includes exterior circumferential seals  41  and  42  to prevent the escape of fluids or the ingress of contaminants between the outer surface of socket bushing  40  and retainer sub  20 . Seals  41 ,  42  may be designed to allow rotation of socket bushing  40  with respect to retainer sub  20 , if a dynamic-type sealing arrangement is desired. Optionally, the cavity, if any, between seals  41 ,  42  may be filled with a generally incompressible lubricant to effectuate the integrity of the seals. While seals  41 ,  42  are shown schematically as o-ring type seals, it should be understood by one of ordinary skill in the art that any sealing mechanism may be employed, including metal to metal seals. 
   Swivel mandrel  30  is preferably constructed as a tubular member having a spherically-shaped ball end  32 . Ball end  32  is preferably configured to be substantially the same contour and profile as hemispherical inner surface  43  of socket bushing  40 . A plurality of sealing elements  33  are preferably located about the leading edge of ball end  32  to prevent leakage of fluid from bore  24  around the outer profile of ball end  32 . As mentioned above, seals  33  are shown schematically as o-ring type seals, but any sealing scheme known to one skilled in the art may be employed, including a metal to metal design. Furthermore, seals  33  are preferably designed such that relative movement of ball end  32  with respect to socket bushing  40  is permitted without compromising the integrity of the seals. 
   Following the installation of socket bushing and swivel mandrel into seat  27  of retainer sub  20 , a backup ring  44  is installed. Backup ring  44  is preferably designed with a semispherical profile on its leading end and a planar surface on its trailing end. With backup ring  44  securely held in place, ball end  32  of swivel mandrel  30  will be firmly held in place within retainer sub  20 . Following installation of backup ring  44 , a bearing assembly  60  is installed. Bearing assembly  60  is preferably constructed as a thrust bearing, one whereby axial loads of swivel mandrel  30  and retainer sub  20  are resisted without damaging components of deflection sub assembly  10 . Construction of bearing assembly  60  may be of any design known by one skilled in the art but should be capable of resisting the magnitude of the axial loading expected to be experienced by deflection sub assembly  10 . Bearing assembly  60  is preferably constructed to allow the rotational movement of swivel mandrel  30  and ball end  32  with respect to retainer sub  20 . 
   Following the installation of bearing assembly  60 , retainer nut  50  is installed. Retainer nut  50  is threaded onto retainer sub  20  and provides interior threads to correspond with outer threads of retainer sub  20 . Retainer nut preferably includes an interior lip  52 , and a pair of hydraulic ports  54 . Interior lip  53  retains bearing assembly  60 , backup ring  44 , ball end  32 , and socket bushing  40  against seat  27  of retainer sub  20 . Hydraulic ports  54  may be used to either fill cavities within the space formed between retainer nut  50  and retainer sub  20  or, in the alternative, may serve to energize bearing assembly  60 . With deflection sub assembly  10  completely assembled with retainer nut  50  tightly threadably secured to retainer sub, a grub screw  56  can be tightened to prevent the loosening thereof. 
   Numerous embodiments and alternatives thereof have been disclosed. While the above disclosure includes the best mode belief in carrying out the invention as contemplated by the named inventors, not all possible alternatives have been disclosed. For that reason, the scope and limitation of the present invention is not to be restricted to the above disclosure, but is instead to be defined and construed by the appended claims.

Summary:
A deflectable in-line swivel that permits axial deflection of a tubular string is presented. The in-line swivel is preferably constructed as a ball and socket design whereby the ball of a swivel mandrel is permitted to articulate within a socket of a retainer sub. The system preferably includes a thrust bearing to allow the tensile loads to be carried across the swivel.