Patent Publication Number: US-6669449-B2

Title: Pad plunger assembly with one-piece locking end members

Description:
This patent application claims the benefit of U.S. provisional application No. 60/315,305, filed Aug. 27, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a gas lift plunger assembly for use in a gas-producing well and, more particularly, is concerned with pad plunger assembly with one-piece locking end members. 
     2. Description of the Prior Art 
     Gas-producing wells typically employ a plunger disposed within tubing of the well and capable of traveling vertically in the tubing as the well is cycled between shut-in and opened conditions in a manner well-known to one of ordinary skill in the art. The plunger is freely movable vertically in the well tubing and is adapted to rise vertically under the force of sufficient gas pressure to drive or lift the plunger and a slug of liquid, such as oil, above it to the surface while isolating the base of the liquid slug from the gas which lifts the plunger. The plunger falls by gravity back down the tubing of the well after the slug of liquid has been delivered to the surface and the gas pressure in the well tubing has decreased due to the transmission of gas from the well tubing to a suitable storage location. 
     One prior art plunger assembly, called a pad plunger, includes an elongated rigid non-flexible central rod or mandrel and a pair of end members attached to the opposite ends of the mandrel. The end members of the plunger have larger diameters than the mandrel and are internally threaded to permit their removable attachment to the externally threaded opposite ends of the mandrel. 
     From the foregoing description, it is readily apparent that the pad plunger is made up of an assembly of various parts. It is very important to lock the end members on the plunger so that the pad plunger does not come apart while in the well. The cost of retrieving the plunger parts from the well can range from $1000 to $5000 not including lost production. 
     Drawbacks exist, however, with the above-described prior art plunger in the manner used to lock the end member on the mandrel. Locking subassemblies  10 , such as the one shown in FIG. 1, that have been used are very labor intensive and have required numerous parts, namely, a locking ball  12  and one or more, usually three, locking rings  14  per plunger. The plunger mandrel  16  and end member  18  have to be drilled to provide a hole  20  extending through the side of the end member  18  and into the mandrel  16  so that the locking ball  12 , such as ⅜ inch in diameter, can be dropped in the hole  20  and then the locking ring  14  applied about an annular recess  22  in the end member  18  so as to overlie the hole  20  and retain the ball  12  in the hole. The presence of the ball  12  in the hole  20  prevents the end member  18  from turning and unthreading from the threaded end of the mandrel  16 . However, corrosion problems typically occur behind the rings. Over a short period of time the rings become loose causing premature plunger wear. Therefore, the locking rings are being welded in addition to being crimped, adding more time for labor. 
     Consequently, a need still exists for an innovation which will provide a solution to the aforementioned problems in the prior art without introducing any new problems in place thereof. 
     SUMMARY OF THE INVENTION 
     The present invention provides a pad plunger assembly with one-piece locking end members designed to satisfy the aforementioned need. The solution of the present invention to the aforementioned problems is to provide one-piece locking end members with features which require less labor usage and eliminate multiple parts. 
     Accordingly, the present invention is directed to a pad plunger assembly which comprises: (a) an elongated central mandrel having a pair of opposite ends with fastening elements thereon; (b) a pair of annular collars each attached to and extending about the mandrel inwardly adjacent to one of the opposite ends thereof, each of the collars having formed therein a plurality of recesses circumferentially spaced from one another about the collar; (c) a pair of end members each having an inner end with an interior bore and fastening elements therein and being removably fastened to one of the opposite ends of the mandrel; and (d) a pair of inner annular flanges each attached to and extending axially from the inner end of one of the end members and adapted to be received over one of the collars such that, for locking the end members onto the mandrel, the end members are fastened onto the opposite ends of the mandrel and then the annular flanges are crimped so as to force circumferentially displaced portions thereof into the recesses of the collars thereby locking the end members in place on the opposite ends of the mandrel such that the end members cannot then be unfastened from the mandrel nor become loosened over time. 
     More particularly, the mandrel is an elongated rigid non-flexible solid rod. The collars are integrally connected to the mandrel. Each of the inner annular flanges is integrally attached to the inner end of one of the end members. The fastening elements on the ends of the mandrel are external threads. The fastening elements in the interior bores of the end members are internal threads which threadably receive the external threads on the ends of the mandrel when the end members are fastened thereon. The mandrel, collars, end members and flanges are made of a metal. 
     Also, the assembly includes at least one subassembly of spring-loaded interlocking pad sections disposed about the mandrel and extending over the mandrel between the collars. 
     These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following detailed description, reference will be made to the attached drawings in which: 
     FIG. 1 is a fragmentary partially sectional view of a subassembly used to lock an end member on a mandrel of a prior art pad plunger assembly. 
     FIG. 2 is a longitudinal sectional view of a pad plunger assembly with one-piece locking end members in accordance with the present invention. 
     FIG. 3 is a cross-sectional view of the pad plunger assembly taken along line  3 — 3  of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings and particularly to FIGS. 2 and 3, there is illustrated a pad plunger assembly  30 , generally designated  30 , which incorporates the locking features of the present invention. Basically, the pad plunger assembly  30  includes an elongated central mandrel  32  and a pair of separate end members  34 ,  36  attached to opposite ends  32 A,  32 B of the mandrel  32 . 
     The mandrel  32  of the plunger assembly  30  is in the form of an elongated rigid non-flexible solid rod. The mandrel  32  has the pair of opposite ends  32 A,  32 B with fastening elements in the form of external threads  32 C,  32 D formed thereabout. A pair of outer annular collars  38 ,  40  are provided on the mandrel  32 , each being integrally attached to and extending about the mandrel  32  inwardly adjacent to one of the opposite ends  32 A,  32 B thereof. 
     The end members  34 ,  36  of the plunger assembly  30  have opposite outer and inner ends  34 A,  34 B and  36 A,  36 B. At least their inner ends  34 A,  36 A have larger diameters than the mandrel  32  and also have interior bores  42 ,  44  with respective fastening elements in the form of internal threads  34 C,  36 C formed therein to permit fastening, by threadable removable attachment, of the end members  32 ,  34  respectively to the externally threaded opposite ends  32 A,  32 B of the mandrel  32 . 
     Between the opposite ends  32 A,  32 B of the mandrel  32 , the plunger assembly  30  also includes at least one subassembly  46  of three spring-loaded interlocking pad sections  46 A thereon which also overlie an annular spacer  48  being integrally formed on and extending around the mandrel  32  at an intermediate location between the opposite ends  32 A,  32 B thereof. In a manner well-known to one of ordinary skill in the art, the spring-loaded pad subassembly  46  can expand outwardly from and contract inwardly toward the mandrel  32  to compensate for any irregularities in the tubing thus creating a moving frictional seal with the interior surface of the well tubing. By providing a mandrel  32  having increased length, more than one subassembly  46  can be provided over and along the mandrel  32 . 
     In accordance with the locking features of the present invention, the end members  34 ,  36  are one-piece components. In addition to having internally-threaded interior bores  42 ,  44  defined in the respective inner ends  34 A,  36 A thereof, the end members  34 ,  36  have annular inner flanges  50 ,  52  integrally attached to and extending axially from the respective inner ends  34 A,  36 A of the end members  34 ,  36  which are located outwardly of the bores  42 ,  44  and have diameter sizes adapted to be received over the annular collars  38 ,  40  about the mandrel  32  inwardly adjacent to the opposite ends  32 A,  32 B thereof. Each of the collars  38 ,  40  has a plurality of depressions or recesses  38 A,  40 A circumferentially spaced apart from one another and formed in an external surface  38 C,  40 C thereof. 
     For locking the end members  34 ,  36  onto the mandrel  32 , each end member  34 ,  36  is threadably screwed onto one of the opposite externally threaded ends  32 A,  32 B of the mandrel  32  and then the annular inner flanges  50 ,  52  of the respective end members  34 ,  36  are crimped inwardly so as to force circumferentially displaced portions  50 A,  52 A of the flanges  50 ,  52  into the recesses  38 A,  40 A of the collars  38 ,  40 . In such manner, the end members  32 ,  34  are locked in place on the opposite ends  32 A,  32 B of the mandrel  32  and cannot unthread from the mandrel  32  and become loosened over time. This arrangement also now solves the problems of corrosion and premature plunger wear. 
     All of the parts of the assembly  30 , namely, the mandrel  32 , the collars  38 ,  40 , the end members  34 ,  36 , the flanges  50 ,  52  and the pad sections  46 A are made of a suitable metal, such as steel. 
     It is thought that the present invention and its advantages will be understood from the foregoing description and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely preferred or exemplary embodiment thereof.