Patent Publication Number: US-4653953-A

Title: Sucker rod construction

Description:
This is a continuation of co-pending application Ser. No. 532,920 filed on Sept. 16, 1983, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to sucker rod constructions and more particularly to fiberglass sucker rods. Sucker rods are joined together to form a sucker rod string which connects a sub-surface well pump to a surface pumping unit. This string imparts a reciprocating pumping motion to the sub-surface well pump. Although the sucker rods were generally for decades constructed from steel, it is now known to construct them with a fiberglass rod portion. An example of such a fiberglass sucker rod construction is found in U.S. Pat. No. 4,360,288, the contents of which are hereby incorporated in their entirety by reference. 
     In the early 1970s, a solution was sought for the chemical and stress corrosion problems related to the use of steel sucker rods. It was found that, in addition to significantly reducing corrosion problems of steel sucker rods, the use of fiberglass rods resulted, in many cases, in increased production. The lighter weight of the rods cuts the pumping unit loads significantly and the reduced pumping unit load allows the pumping unit to operate faster. Also, the elasticity of the prestressed fiberglass rods string generates significant production increases due to the &#34;overtravel.&#34; A weight is attached on the bottom of the fiberglass sucker rods, such as steel sucker rods or sinker bars, and this weight causes a higher upstroke relative to the surface stroke and a lower downstroke, that is, overtravel. This provides for a maximum overtravel whereby the pump stroke generates a greater production. The lighter fiberglass rods also allows for a longer string to be used and thus deeper wells to be dug. 
     Although the fiberglass sucker rods have resulted in greatly increased production and associated reduced pumping costs, premature fatigue failures has been a problem. These premature fatigue failures have occurred both in field applications and in cyclic duty tests of sample rods. It has also been experienced that the ends of the connector members would cut into the fiberglass rods thereby cutting the fibers and weakening the rod. 
     OBJECTS OF THE INVENTION 
     Accordingly, it is the principal object of the present invention to provide an improved fiberglass sucker rod construction. 
     Another object of the present invention is to provide an improved fiberglass sucker rod construction which is not subject to premature fatigue failures. 
     A further object of the present invention is to provide a novel fiberglass sucker rod construction design. 
     A still further object of the present invention is to provide an improved fiberglass sucker rod construction for the one-inch and the one and a quarter inch diameter fittings. 
     Another object of the present invention is to provide a novel construction for preventing the connector member from digging into and thereby weakening the fiberglass rods. 
     Other objects and advantages of the present invention will become more apparent to those persons having ordinary skill in the art to which the present invention pertains from the foregoing description taken in conjunction with the accompanying drawings. 
    
    
     THE DRAWINGS 
     FIG. 1 is a perspective view of a sucker rod construction embodying the present invention. 
     FIG. 2 is an enlarged cross-sectional view taken along line 2--2 of FIG. 1. 
     FIG. 3 is an enlarged fragmentary view of the portion of FIG. 2 illustrated by line 3. 
     FIG. 4 is a fragmentary view similar to the lower left corner of FIG. 3 illustrating a second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a sucker rod shown generally at 10 embodying the present invention is illustrated. Sucker rod 10 generally comprises four basic members: a connector member shown generally at 12 formed of a single, continuous piece of steel and having a rod receptacle 14 therein; a cylindrical fiberglass rod 16 which fits in rod receptacle 14; a body of adhesive material 18 positioned within rod receptacle 14 and between fiberglass rod 16 and connector member 12; and a plastic, cylindrical sleeve 20 positioned at the outer end 22 of connector member 12 and at least partially positioned between connector member 12 and fiberglass rod 16. 
     Connector member 12 at its inner end 24 has a coupling member shown generally at 26. Although shown as a male coupling, this coupling will screw into a generally identical connector member differing only in coupling member 26 being a female coupling. The fiberglass rods will then have a connector member at one end with a male coupling and one with a female coupling at the other end and will measure 37 feet 6 inches, including threaded end fittings. Generally adjacent coupling member 26 are a plurality of wrench flats 28 to which a standard sucker rod wrench is attached for coupling and uncoupling adjacent sucker rods from one another. A long cylindrical portion 30 having outside surface 32 extends from wrench flats 28 toward outer end 22. A cylindrical collet 34 having a diameter smaller than the diameter of cylindrical portion 30 forms the outer end portion of connector member 12. A joining means shown generally at 36 joins cylindrical portion 30 and collet 34 and more particularly forms an annular surface 38 joining outside surface 32 and collet outside surface 40. 
     Referring to FIGS. 3 and 4, joining means 36 and annular surface 38 are illustrated in greater detail. As shown, joining means 36 is a portion of connector member 12, in other words, cylindrical portion 30, collet 34 and joining means 36 are formed from one continuous solid piece of metal. It is further, and perhaps more importantly noted, that annular surface 38 defines a smooth curve defined by a first curve 41 with radius R1 tangent at one end to outside surface 32. At its other end it is generally tangent to oppositely curving second curve 42, and second curve 42 with radius R2 is tangent at its other end to collet outside surface 40. While the embodiment of FIG. 3 illustrates R1 being smaller than R2, it is also within the scope of the present invention, as shown in FIG. 4, for R1 to be larger than R2. The prior art &#34;joining means&#34; had sharp beveled edges which were subject to cracking and breaking when stressed. By contrast, the present invention eliminates this problem by providing for a novel configuration of annular surface 38 employing a smooth curve and more specifically a pair of joined and oppositely facing curves. 
     Rod receptacle 14 defines a unique configuration. At its outer end, as best shown in FIG. 2, collet 34 has an inner recessed, annular surface 44 which extends a short distance from the end. Annular surface 44 is provided to hold sleeve 20 between collet 34 and fiberglass rod 16. Although collet 34 is adapted to snuggly hold rod 16 in rod receptacle 14, non-axial relative movement of collet 34 and fiberglass rod 16 has in the past caused collet outer edge 46 to bite into the fiberglass and damage and weaken the rod. Sleeve 20 provides a protective material between collet outer edge 46 and the rod thereby preventing damage to the rod. 
     At the end of rod receptacle 14 opposite collet 34 is a bore 48, best shown in FIG. 2, fitting closely with the surface of the end of the rod and together with the collet supporting the rod in rod receptacle 14. Wrench flats 28 ideally should be even with the outer diameter of bore 48. Positioned between bore 48 and collet 34 in rod receptacle 14 are a plurality of integrally-formed, axially-spaced-apart, outwardly-converging, tapered frusto-conical annular surfaces. Although three such annular surfaces 50, 52 and 54 are illustrated in FIG. 2, it is within the scope of the present invention to provide up to seven annular surfaces. These annular surfaces, which are recessed from rod 16, provide a series of wedge shaped cavities or chambers into which adhesive material 18 is positioned. Adhesive material 18 is initially liquid when placed in the cavities and cures to bond to the outer surface of rod 14 and hardens to form a plurality of shear and compression resistant frusto-conical wedges which cooperate with the annular surfaces 50, 52 and 54 and prevent the movement of rod 16 axially out of rod receptacle 14. 
     Each of the wedge shapes is defined by (1) annular surfaces 50, 52 or 54, (2) rod surfaces 58, 60 or 62, respectively, each of which intersects at its outer end with its annular surface 50, 52 or 54, respectively, and (3) slanted ends 66, 68, and 70. Each slanted end terminates at the inner end of its rod surface and the inner end of its annular surface. The intersection of annular surface 50 and rod surface 58 defines taper angle A, annular surface 52 and rod surface 60 defines taper angle B, and annular surface 54 and rod surface 62 defines taper angle C. In the prior art it is known to make taper angles A, B and C equal. However, as previously discussed, these prior art sucker rods have experienced premature fatigue failures. 
     The present invention, therefore, provides for sucker rods having different taper angles within each rod receptacle. More particularly, the angles progressively increase from the outer to the inner end of the receptacle by at least one and one half degrees between adjacent angles and preferably two degrees. For instance, it has been found, as shown below, that surprisingly increased fatigue failure resistance is experienced when angles within the above guidelines are as follows: angle A=6°±30&#39;, angle B=4°±30&#39; and angle C=2°±30&#39;. Most significantly, the present invention is most evident when the angles are 6°, 4° and 2°, each ± about 5 minutes also as shown below. These angles have been found to &#34;even&#34; the stresses at each of the three rod/connector interfaces and thereby reduce the maximum equivalent stresses experienced. Thus, it is possible with the present invention to have vastly greater number of cycles before stress fatigue results. 
     In fact, in a test conducted by the Inventors, the following results were obtained: 
     
         ______________________________________                                    
                        *AVG. CYCLES                                      
FITTING TEST            TO FAILURE                                        
______________________________________                                    
Controls - Fitting with 41/2° tapers                               
                         42,364                                           
(All cracked)                                                             
TM-648 Fitting (21/2°-4°-51/2° tapers)               
                         87,750                                           
(All cracked)                                                             
TM-648 Fitting with longer sleeve                                         
                        136,105                                           
(All cracked)                                                             
TM-648 Fitting with Tuff Tubing in sleeve                                 
                        189,488                                           
(All cracked)                                                             
TM-650 Fitting (2°-4°-6° tapers)                     
                        1,025,935                                         
(5 of 12 cracked)                                                         
______________________________________                                    
 *Average cycles is to first crack except for TM650 fitting, contains data
 from 7 good rods.                                                        
 
    
     It is thus seen from these test results that by having the tapers progressively increased by 11/2° degrees the cycle life of the sucker rod (before all of the test rods crack) increases by over 100%. Further, the use of the Inventors longer smooth curving sleeve increases the cycle life an additional 50% plus, and with the tuff tubing an additional 40%--making for a total cycle improvement of about 350% over the prior art. An example of the preferred embodiment, wherein the tapers increase progressively by 2°, was also tested. The 2°-4°-6° embodiment was chosen and after over a million cycles the test was concluded even though less than half of the test rods had cracked. 
     To further improve the stress fatigue life of the sucker rod, the outer end of annular surface 54 shown at 64 is positioned directly radially inward of the tangent point of second curve 42 which collet outside surface 40 shown at 65. The tolerance of the placement of outer end 64 and tangent point 65 should be within 1/8 inch. 
     From the foregoing detailed description, it will be evident that there are a number of changes, adaptations, and modifications of the present invention which come within the province of those persons having ordinary skill in the art to which the aforementioned invention pertains. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the appended claims.