Patent Publication Number: US-2003221472-A1

Title: Well casing and method for threading

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates in general to well casing, particularly a method for threading thin wall well casing that includes a preliminary step of swaging.  
       DESCRIPTION OF THE PRIOR ART  
       [0002] Well casing of the type concerned herein is made up of sections of pipe each typically about 38 to 43 feet in length. Each section of pipe has external threads on both ends. The pipe sections are joined by collars that have internal threads.  
       [0003] The threads are normally a standard API thread that is formed with a taper. That is, the crests of the threads will taper from a larger diameter to a reduced diameter at the end of the pipe. The threads are form-ed in a conventional manner using equipment that cuts them on the cylindrical end of the pipe.  
       [0004] This method works well enough if the pipe wall thickness relative to the taper angle and the depth of the threads is sufficient. The threads at the end will still have adequate supporting metal and the depth of each thread remains constant throughout the threaded section.  
       [0005] However, there are occasions where thinner wall pipe is desired, such as in shallow gas wells. With very thin wall pipe, the supporting metal under the threads decreases near the end of the pipe because of the conical taper of the thread crests. At the extreme end of the pipe, the threaded section may not have adequate gripping strength because of the thinness of the supporting metal. As a result, when attached to a threaded collar and pulled in a tensile test, the threaded sections may pull apart from each other.  
       [0006] A procedure has been used in the past on some tubular members that increases the wall thickness of the pipe near the pipe rim so that the threads will have adequate supporting metal throughout the threaded section. In that procedure, first, the outer diameter of the tubular member is swaged to provide a conical taper. Then, the threads are cut on the conical taper. To applicant&#39;s knowledge, this has been performed only with heavier wall pipe for use in high pressure installations, such as proprietary type connections that form metal to metal seals. The wall thickness of such pipe before swaging is typically in excess of 0.275″. Also, the swaging operation is a slow process because of the equipment utilized.  
       SUMMARY OF THE INVENTION  
       [0007] The swaging apparatus of this invention has a head with an axis of rotation and a plurality of holes spaced in a circular array, concentric and parallel with the axis of rotation. Shafts are located in each of the holes, each of the shafts having a supporting portion on a forward side of the head. A roller is rotatably mounted to a supporting portion of each of the shafts. Each of the rollers has a tapered exterior. A chucking member is located on the rearward side of the head for engagement by a rotary member to rotate the head.  
       [0008] This apparatus is used to swage thin walled pipe for use as well casing. The pipe is held stationary while the swaging head is rotated. The head and pipe are brought together, with the rollers forming a conical taper on an end section of the pipe. The swaged taper is preferably equal to or less than the thread taper. Conventional threads are formed on the tapered exterior.  
       [0009] Preferably the pipe has an outer diameter in the range from 4½″ to 5½″ and a wall thickness from about 0.125″ to 0.219″. The swaged taper is preferably in the range from about 0.035 to 0.0625 inch per inch, and the thread taper is preferably 0.0625 inch per inch. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010]FIG. 1 is a front view of a swaging apparatus constructed in accordance with this invention.  
     [0011]FIG. 2 is a sectional view of one of the rollers of the apparatus of FIG. 1, taken along the line  2 - 2  of FIG. 1.  
     [0012]FIG. 3 is a sectional view of the swaging apparatus of FIG. 1, taken the along the line  3 - 3  of FIG. 1 and shown with only one of the rollers.  
     [0013]FIG. 4 is a sectional view of a pipe after swaging and prior to being threaded.  
     [0014]FIG. 5 is a sectional view of the pipe of FIG. 4 after being threaded and coupled to a collar.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0015] Referring to FIG. 1, swaging apparatus  11  has a head  13 , which is a large circular plate of steel. It may have a hole  15  in its center, hole  15  being concentric with an axis of rotation  17 . A plurality of holes  19  (FIG. 3) are spaced in a circular array around hole  15 . Holes  19  are parallel and concentric with axis  17 .  
     [0016] As shown in FIG. 2, a shaft  21  extends into each of the holes  19 . A roller  23  is rotatably mounted to a supporting portion of shaft  21  located on the forward side of head  13 . Each roller  23  has a conical tapered exterior  25  that has a taper is in the range from 0.035 to 0.0625 inch per inch. A set of bearings  27  supports each roller  23  on each shaft  21 .  
     [0017] While holes  19  could be threaded for receiving shafts  21 , preferably each shaft  21  extends completely through one of the holes  19  as shown in FIG. 2. Each shaft  21  has a threaded end  29  on the rearward side of head  13  that receives a nut  31 .  
     [0018] A chucking plate  33  is mounted to the rearward side of head  13 . In the preferred embodiment, chucking plate  33  is a circular steel plate having approximately the same outer diameter as head  13 . Chucking plate  33  has a perimeter wall  35  on its forward side that engages an annular recess  37  formed on the rearward side of head  13 . Once abutted, as shown in FIG. 3, a cavity  39  will be defined between the rearward side of head  13  and a forward side of chucking plate  33 . The threaded ends  29  and nuts  31  of each shaft  21  locate within cavity  39 . Chucking plate  33  may optionally have a central hole  41  that is coaxial with axis  17  (FIG. 1).  
     [0019] A plurality of mounting holes  43  are spaced around the perimeter of chucking plate  33 . Mounting holes  43  align with mounting holes  45  in head  13 . Fasteners (not shown) are employed to extend through holes  43  and  45  and secure chucking plate  33  to head  13 . A circular hub  47  is formed on the rearward side of chucking plate  33 . Hub  47  is of a considerably smaller diameter than perimeter wall  35  and protrudes rearwardly a short distance from the rearward side of chucking plate  33 . Hub  47  is concentric with hole  41  and axis  17  (FIG. 1). A rotary machine such as a large lathe will clamp about hub  47  to rotate chucking plate  33  and head  13 . Although shown with a separate chucking plate  33 , head  13  could be formed so that it is engaged by a rotary member directly.  
     [0020] Referring to FIG. 4, a section of pipe  49  is shown after it has been swaged with swaging apparatus  11 . Pipe  49  is of steel for forming thin wall casing. Typically it will be manufactured by rolling a flat plate into a cylinder, then welding the seam. However, pipe  49  could be formed in other manners. Pipe  49  has an outer diameter  51  preferably in the range from 4½″ to 5½″. Its wall thickness between its outer diameter  51  and inner diameter  53  is in the range from 0.125″ to 0.219″, and preferably about 0.156″.  
     [0021] Swaged section  55  has been swaged by swaging apparatus  11 , resulting in both a tapered exterior  57  and tapered interior  59 , which are at approximately the same taper angle. In the preferred embodiment, tapered exterior  57  is in the range from 0.035 to 0.0625 inch per inch, and preferably 0.035 inch per inch. The engagement of rollers  23  on exterior  57  results simultaneously in the formation of tapered interior  59 .  
     [0022] Threads  61  are then formed on swaged section  55 . Threads  61  are preferably conventional API threads, such as eight threads per inch having a triangular shape. Threads  61  are also cut on a taper that is equal to or greater than the taper of swaged section  55 . Preferably the crests of the threads  61  will have a taper that is 0.0625 inch per inch. In the preferred embodiment, which has a taper of 0.035 inch per inch on swaged section exterior  57 , the remaining wall thickness through swaged section  55  will thus decrease from end  62  to rim  60  after threading. The depth of threads  61  is uniform at about 0.07125 inch throughout swaged section  55  except at the thread run out at end  62 . The difference in the taper of threads  61  and the taper of swaged section exterior  57  is selected so as to avoid unduly reducing the wall thickness of the supporting metal under threads  61  near pipe rim  60 . A conventional collar  63  having mating threads is shown secured to threads  61  in FIG. 5.  
     [0023] In operation, pipe  49  is held against rotation while swaging apparatus  11  rotates about axis  17 . Swaging apparatus  11  and pipe  49  are then brought together, normally by advancing swaging apparatus  11  linearly toward pipe  49 . Alternately, pipe  49  could be moved toward swaging apparatus  11 , or both moved toward each other. Rollers  23  will begin to engage the cylindrical exterior of the end of pipe  49  as pipe  49  is continually advanced toward swaging head  13 . Rollers  23  will form tapered exterior  57  on swaging section  55  as illustrated. After swaging, threads  61  are cut on swaging section  55  in a conventional manner beginning at pipe rim  60 . The length of threaded section  61  is the same as the length of swaging section  55 .  
     [0024] The invention has significant advantages. The swaged ends allow tapered threads to be cut on thin wall pipe without unduly reducing the supporting metal wall thickness near the pipe rim. This pipe is able to meet tensile tests. The swaging machine is fast and efficient. The rollers can be readily removed for replacement.  
     [0025] While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.