US3049382A

US3049382A - Anti-friction sucker rod coupling

Info

Publication number: US3049382A
Application number: US77226A
Authority: US
Inventors: George E Ell
Original assignee: Liberty Manufacturing Co of Texas
Current assignee: Liberty Manufacturing Co of Texas
Priority date: 1960-12-20
Filing date: 1960-12-20
Publication date: 1962-08-14
Anticipated expiration: 1979-08-14

Description

Aug. 14, 1962 G. E. ELL

ANTI-FRICTION SUCKER ROD COUPLING 2 Sheets-Sheet 1 Filed Dec. 20, 1960 INVENTOR. GEORGE E. ELL

ATTORNEYS I Aug. 14, 1962 e. E. ELL

ANTI-FRICTION SUCKER ROD COUPLING 2 Sheets-Sheet 2 Filed Dec. 20, 1960 INVENTOR. GEORGE E. ELL

ATTORNEYS United States Patent a corporation of Texas Filed Dec. 20, 196i), Ser. No. 77,226 2 Claims. (Cl. 3084) This invention relates to a sucker rod coupling. More particularly the invention relates to a new and novel type of anti-friction sucker rod coupling.

The method of producing oil from subterranean formations most commonly used today is the reciprocation of a bottom hole pump by a long string of sucker rods actuated in a tubing. A pumping unit, powered by a prime mover such as an electric motor or a gas engine, is positioned at the surface of the well and transmits reciprocal motion to the sucker rods.

The sucker rods actuate up and down in a length of tubing. The tubing provides means whereby the produced oil is lifted to the surface of the earth. The length of each string of sucker rods must be sufficient to reach from the surface down to an area below the level of fluid in the well to be produced. The length of the rods may therefore vary from a few hundred feet to more than fifteen thousand feet.

In the drilling of oil wells the differences in drilling rates of various geological formations which are encountered, and other factors, makes the accomplishment of a perfectly straight hole virtually impossible. Many oil wells are therefore crooked holes so that both on the up and down strokes of the sucker rod the sucker rod couplings are caused to rub against the well tubing. Even in wells which are straight a pumping rate sometimes is used such that on the down stroke of the sucker rods a portion of the sucker rods are forced under compression causing them to buckle slightly, forcing the couplings of the rods against the tubing. Due to any one of these factors, or other factors existing due to the peculiar characteristics of each well, a serious problem in the petroleum industry is the effect of the rubbing of the sucker rod couplings against the inten'or wall of the well tubing.

Many wells are pumped for long periods, such as ten to eighteen hours a day, and in fact a great many wells are pumped on a twenty-four hour a day basis. If, due to any of the factors enumerated above, the sucker rod couplings are caused to rub against the inside of the tubing in which the sucker rods are actuated, three serious difficulties are encountered. First, the effect of the rubbing of the sucker rod couplings against the interior of the tubing causes a great deal of energy loss in pumping wells. The drag which takes place on the up stroke of the pumping unit requires additional power to actuate the sucker rod string. The drag of sucker rods on the down stroke means that they do not fall as rapidly with the result of shortening of the stroke length of the pump at the bottom of the well. The high degree of friction which exists between typical sucker rod couplings in common use, which are manufactured of solid steel, against the interior of the tubing in which the sucker rods operate, results in the consumption of additional pumping energy.

Second, the wearing of the sucker rod couplings against the wall of the tubing in which they are actuated will soon wear away the coupling, causing the sucker rod string to break or separate. When this occurs, oil production ceases and an expensive process of lowering tools into the well to retrieve and repair the broken rod is required. Even though the wear on the sucker rod couplings is not suflicient in some instances to cause the rod to completely part, it is a customary procedure in working over wells when the rod string is pulled from the well, to replace the worn couplings to insure the probability of continued pumping Patented Aug. 14, 1962 of the wells without further interruption. The replacement of worn sucker rod couplings therefore becomes an expensive part of the operation of oil wells.

Third, the attrition resulting from the rubbing of the sucker rod coupling against the wall of the tubing in which the sucker rods actuate will gradually wear away the tubing itself until eventually a hole appears in the tubing when this occurs, oil can no longer be raised to the surface since the produced oil will rise to the point where the hole is encountered and will flow out of thehole back into the well. When a hole occurs in the tub-ing the complete string must be pulled to locate the hole and the tubing containing the hole replaced. Tubing, of course, being manufactured of a relatively heavy walled pipe, is expensive and the process of pulling the tubing of the well to replace the length of tubing having a hole worn in it results in loss of production, the expense of pulling the tubing from the well, and the expense of replacing worn tubing.

For these reasons it is highly desirable to provide a coupling which will have a reduced friction drag against the tubing, which will not wear holes in the tubing, and which will not wear away the coupling itself. In the past attempts have been made to provide sucker rod couplings having improved resistance against wear. One method of attempting to counteract the wear of the coupling includes case hardening the coupling itself to provide an exterior surface of an extremely hard steel calculated to resist wear. This is a satisfactory procedure to lessen wear of the coupling itself but does not assist at all in eliminating the wearing away of the tubing in which the sucker rods operate, nor in reducing the over-all frictional load of the re. ciprocal movement of the sucker rods. Others attempting to overcome the problem of the frictional wearing away of the couplings have provided couplings with bands of extremely hard metal formed around the couplings. Such a procedure likewise serves to protect the couplings but does not result in any elimination of the energy loss involved in sucker rod pumping and does not alleviate the problem of holes being worn in the tubing.

Broadly stated, and not by way of limitation, this invention may be defined as a friction reducing sucker rod coupling comprising, a hollow cylindrical metallic body portion having threads formed internally at each end thereof; at least one bonding ring integrally formed on the external cylindrical surface of said metallic body portion, said bonding rings having a greater diameter than the diameter of the cylindrical surface of said metallic body portion; and .a jacket of plastic material molded to the exterior :of said metallic body portion, said jacket terminating adjacent each of said ends of said metallic body portion, said jacket having integrally formed flutes extending the length thereof adaptable to permit the passage of fluid therethrough.

It is therefore an object of this invention to overcome the disadvantages in present sucker rod couplings and to provide an improved sucker rod coupling having friction reducing means.

Another object of the invention is to provide a sucker rod coupling having a characteristic whereby the frictional drag of the sucker rod coupling sliding against the interior of the tubing will be substantially reduced and wherein the tendency of .wearing away of the sucker rod coupling itself and the tubing which it frictionally engages will be substantially eliminated.

Another object of this invention is to provide a jacket adaptable for application to a sucker rod coupling having improved means of fluid flow of produced fluid past the sucker rod coupling.

Another object of this invention is to provide asucker rod coupling jacketof a tough, lubricative material, wherein the construction of the complete sucker rod coupling is such to prevent the possibility of the jacket becoming dislodged from the sucker rod coupling.

Another object of this invention is to provide a sucker rod coupling having an anti-friction jacket formed thereto wherein the jacket is composed of a material having a high resistance to friction and wherein the material in addition has an inherent lubricative quality.

Another object of this invention is to provide a sucker rod coupling having an anti-friction jacket bonded thereto wherein the wrench flats required by many oil well operators are providable on the jacketed coupling.

Another object of this invention is to provide a sucker rod coupling having a fluted anti-friction jacket wherein the flutes are formed at an angle to the plane of the axis of the coupling whereby the area of contact between the coupling and the tubing in which it operates will be materially increased.

These and other objects and a better understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the attached drawings, in which:

FIGURE 1 is an isometric view of a sucker rod coupling of this invention having a fluted anti-friction jacket.

FIGURE 2 is an isometric view of an anti-friction coupling of this invention showing means whereby wrench flats are provided on the coupling.

FIGURE 3 is a plan view of a coupling of this invention showing the appearance of the metallic body portion of the coupling preparatory to the steps of molding the jacket to the exterior of the coupling.

FIGURE 4 is a plan view of a coupling of this invention with the anti-friction jacket, and wherein the coupling is shown partly in cross-section.

FIGURE 5 is a cross-sectional view taken along the line 55 of FIGURE 2 showing the cross-sectional configuration of the anti-friction coupling of FIGURE 2 having wrench flats.

FIGURE 6 is a plan view of an alternate embodiment of this invention showing a configuration wherein the fluted surface of the anti-friction jacket is spiraled to ma terially increase the area of contact between the antifriction jacket and the tubing in which the sucker rod coupling actuates.

Referring now to the drawings, and first to FIGURE 1, the anti-friction sucker rod coupling of this invention is indicated generally by the numeral 10, having a metallic body portion 12. Metallic body portion 12 is a hollow, cylindrical, metallic element having ends 14A and 14B. According to the usual sucker rod construction principles, ends 14A and 14B are formed exactly perpendicular to the cylindrical axis of metallic body portion 12 so as to perfectly align the abutting sucker rods (not shown).

Formed on the exterior of metallic body portion 12 is an anti-friction jacket 16. Grooves or flutes 18 are formed in the anti-friction jacket 16 to provide improved means of permitting fluid to flow past the coupling as it reciprocates within the tubing. The construction of the coupling of this invention can best be seen in FIGURE 4. Threads 20 are formed in the interior of each end of the hollow metallic body portion 12. Threads 20 extend from each end to intersect each other in the center of metallic body portion 12. Threads 20 are adaptable to threadably receive similar threads on the pins of adjoining sucker rods (not shown) whereby the coupling supports adjacent sucker rods together. Ordinarily, sucker rods are manufactured in either 25 or 30 foot lengths so that one coupling 10 is required for each 25 or 30 feet of the sucker rod string.

One of the diflicult problems which has been overcome according to the novel principles of this invention in the formation of an anti-friction sucker rod coupling is that of providing a means whereby the anti-friction jacket 16 may be securely bonded to the external surface 22 of metallic body portion 12. It has been discovered that by providing at least one, but preferably two, or three, or more, integrally formed bonding rings 24 a bond may be achieved between metallic body portion 12 and anti-fric- 4 tion jacket 16 of suflicient strength that it can never be dislodged in normal use of the coupling 10.

FIGURE 3 discloses the external appearance of the metallic body portion 12 of the coupling preparatory to the application of the anti-friction jacket 16. The preferred embodiment wherein three bonding rings 24 are formed on the external circumference 22 of the metallic body portion 12 is shown. It has also been discovered that an important additional method of preventing the anti-friction jacket 16 from being dislodged from the metallic body portion 12 includes the provision of knurled surfaces 26 on the circumferences of the bonding rings 24.

Coupling 10 may be formed as shown wherein the diameter of bonding rings 24 is slightly larger than the diameter of the metallic body portion 12, or preferable, each bonding ring 24 may be formed by knurling the exterior surface of body portion 12 in the areas where the bond ring 24 is required. Knurling raises the surface of the metallic body portion 12 approximately fifteen-thousandths of an inch.

By providing knurled bonding rings 24 it has been possible to produce a coupling having an anti-friction jacket wherein the bonding tenacity between the jacket and the coupling is such that the jacket will not be dislodged as the sucker rods are used in the application of producing fluid from a well.

After the metallic body portion 12 is formed with knurled bonding rings 24, as it is shown in FIGURE 3, the coupling is ready to receive the application of the anti-friction jacket 16. According to the principles of this invention the anti-friction jacket 16 is applied through a process of molding a thermoplastic material to the metallic body portion 12. The thermoplastic material is injected into a mold containing the metallic body portion 12 at a temperature of from 600 to 660 Fahrenheit with a pressure of from 20,000 pounds per square inch to 30,000 pounds per square inch. The temperature and pressure with which the thermoplastic material is applied varies with the thickness of the material being applied to the coupling.

The selection of the type of thermoplastic material from which the anti-friction jacket 16 is to be composed is extremely important. It has been discovered that a glass fiber reinforced thermoplastic material provides the required strength to achieve an anti-friction jacket 16 having the high physical properties required.

An important feature of this invention is the provision of a sucker rod coupling which has greatly reduced frictional drag as the sucker rod coupling rubs against the interior of the tubing in which it operates as the sucker rod string is reciprocated up and down. It has been discovered that if the thermoplastic material of which the anti-friction jacket 16 is formed is saturated with a lubricant, then the total frictional drag of the sucker rod coupling is greatly reduced. It has further been determined that a lubricant which offers a highly superior friction reduction characteristic is molybdenum disulphide. Thus, according to the preferred embodiment of this invention the anti-friction jacket 16 is composed of a glass fiber reinforced thermoplastic with a saturate of molybdenum disulphide.

Although glass fiber reinforced thermoplastic with molybdenum disulphide saturate is considered the preferred embodiment of the invention, the invention is not to be interpreted as limited to this particular plastic material or this particular lubricative saturate as other types of plastics and other types of lubricative saturates are likewise acceptable.

Some operators of oil wells prefer sucker rod couplings having wrench flats so that the couplings may be removed from the sucker rods. If Wrench flats are required they may be provided as shown in FIGURE 2. A wrench fiat, generally indicated by the numeral 28, is formed on diametrically opposed sides of the sucker rod coupling 10,

preferrably midway between ends 14A and 14B. The cross-sectional view of FIGURE 5 discloses that the sucker rod wrench flats 28 are cut to a depth to have a distance between the opposed sucker rod wrench flats 28 which is less than the diameter of the exterior surface 22 of the metallic body portion 12. A flat metallic surface 30 is formed in the metallic body portion 12 which may be gripped by a parallel jaw wrench. The wrench flats 28 are an optional arrangement of the sucker rod coupling of this invention.

As previously stated, flutes 18 are formed in the antifriction jacket 16. Flutes 18 have two functions. First, they provide channels through which fluid may flow past the sucker rod coupling as the fluid is pumped from the bottom of the well to the surface by the actuation of the sucker rods. The sucker rod actions within some wells repeatedly force or slap the sucker rod couplings rapidly against the side of the tubing. When slapping of the sucker rod couplings against the interior wall of the tubing occurs, fluid trapped within flutes 18 acts as a cushion to soften the shock on the coupling. This softening of the contact between the coupling and the tubing is the second functional advantage of the provision of flutes 18.

Flutes 18 are disclosed in this invention as having a primarily square or rectangular configuration. Flutes having elliptical or circular configurations would provide the same function as the disclosed square configuration.

FIGURES 1, 2 and 4 disclose flutes formed so that their length substantially parallels a plane drawn through the cylindrical axis of the metallic body portion 12. In this manner, as the rods reciprocate up and down there may be a tendency for the elevated portions or lands 32 of plastic material between flutes 18 to wear in one place against the wall of the tubing in which the sucker rods are reciprocated. This would have a tendency to concentrate the wear, although materially reduced by the material of which the anti-friction jacket 16 is made, to a restricted area of the interior wall of the tubing. To overcome this an alternate embodiment of the invention is disclosed in FIGURE 6. The arrangement of FIGURE 6 is the same as that of FIGURE 1 except that flutes 18, and thus the land portions 32, of anti-friction jacket 16, are spiraled. The spiraling of flutes 18 means that the flutes would intersect a plane drawn through the cylindrical axis of the metallic body portion 12 at an angle. The angle of flutes 18 are preferably designed so that a substantially cylindrical area will engage any interior portion of the tubing contacted by sucker rod coupling 10, but wherein the angle of flutes 18 is small enough so that very little restriction of flow of fluid through the flutes 18 is occasioned by their angular configuration. As an example, if the coupling 10 of FIGURE 6 is designed so that there are twelve flutes 18 and twelve land portions 32, then flutes 18 will be formed at an angle of at least fifteen degrees (15). This minimum angle will mean that, as the coupling 10 is reciprocated, no area between two land portions 32 engaging the tubing will be untouched as the coupling 10 passes. If more than twelve flutes 18 are provided the angle of the flutes 18 may be correspondingly reduced.

The flutes 18 of FIGURE 6 are shown at an angle form ing a right hand spiral. This direction of spiral is preferred. The industry standard requires the use of right 6 hand threaded sucker rods. Right handed spiraled or angled flutes 18 will therefore tend to rotate the coupling 10 as it rubs against the side of tubing on the upward stroke of the sucker rods, in a direction to tighten rather than loosen the coupling against the upper adjacent rod.

The number of flutes, the angle of spiral and the direction of spiral may vary according to requirements of different pumping conditions and any such variations are within the scope of the invention.

By the processes of this invention sucker rod couplings can be manufactured which have greatly improved resistance to the effects of friction within well tubing and a cost comparable to that of presently used hardened sucker rod couplings.

The principles of this invention make possible a sucker rod coupling which will materially reduce the horsepower consumption of the pumping of many wells, particularly, those wells having crooked holes. The wear reducing and lubricating characteristics of the coupling will make possible the actuation of sucker rods in crooked holes wherein the service life of the rods and tubing is materially increased.

The principles of this invention may be equally applied to the application of friction reducing means to hollow sucker rod couplings and to pipe and tubing couplings.

Although this invention has been described in a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure.

I claim:

1. A friction reducing sucker rod coupling, comprising, in combination:

a hollow cylindrical metallic body member having threads formed the full length interiorly thereof, said body member having at least two knurled bonding rings spaced from each other on the exterior cylindrical surface thereof;

and a jacket of fiber reinforced lubricative saturate thermoplastic material molded to the exterior of said body member, said jacket terminating adjacent each end of said body member, said jacket tapered at each termination toward said body member, said jacket having an external configuration defined by longitudinal flutes extending the full length thereof, each of said aligned flutes to intersect a plane of the cylindrical axis of said body portion at an angle thereto.

2. A coupling according to claim 1 including wrench flats formed thereon, said wrench flats comprising diametrically opposed flat surfaces positioned substantially midway between the ends of the coupling, said flat surfaces substantially parallel to the cylindrical axis of said body member.

References Cited in the file of this patent UNITED STATES PATENTS 1,605,316 Wilson Nov. 2, 1926 1,863,823 Barclay June 21, 1932 2,247,564 Turner July 1, 1941 2,725,264 Bodine NOV. 29, 1955 2,815,253 Spriggs Dec. 3, .1957 2,946,094 Kawasaki July 26, 1960