Coupling for rods
A cold worked and spinodally-hardened copper alloy comprising from about 8 to about 20 wt % nickel, and from about 5 to about 11 wt % tin, the remaining balance being copper, and having a 0.2% offset yield strength of at least 75 ksi, is used to form a sucker rod coupling or subcoupling. Each coupling is formed from a core having two ends, each end having an internal thread. These box ends engage the pin of a sucker rod or other rod. The exterior surface of the core includes grooves running between the two ends.
1. A coupling for a sucker rod, comprising a spinodally-hardened copper-nickel-tin alloy comprising from about 8 to about 20 wt % nickel, and from about 5 to about 11 wt % tin, the remaining balance being copper, wherein the alloy has a 0.2% offset yield strength of at least 95 ksi and a Charpy V-notch impact energy of at least 22 ft-lbs at room temperature.
2. The coupling of claim 1 , wherein the spinodally-hardened copper-nickel-tin alloy comprises about 14.5 wt % to about 15.5 wt % nickel, and about 7.5 wt % to about 8.5% tin, the remaining balance being copper.
3. The coupling of claim 1 , wherein the coupling is formed from a core having a first end and a second end, each end containing an internal thread.
4. The coupling of claim 3 , wherein the internal threads on the first end and the second end have the same box thread size.
5. The coupling of claim 3 , wherein the internal threads on the first end and the second end have different box thread sizes.
6. The coupling of claim 1 , wherein a bore runs through the core from the first end to the second end, the internal threads of each end being located within the bore.
7. The coupling of claim 1 , where each end also includes a counterbore at a surface of the end.
8. The coupling of claim 1 , wherein the internal threads have a Rockwell C hardness (HRC) of about 20 to about 40.
9. The coupling of claim 1 , wherein an exterior surface of the core includes at least one groove running from the first end to the second end.
10. The coupling of claim 9 , wherein the at least one groove runs parallel to a longitudinal axis extending from the first end to the second end.
11. The coupling of claim 9 , wherein the at least one groove runs spirally from the first end to the second end.
12. The coupling of claim 9 , wherein the at least one groove has an arcuate cross-section or a quadrilateral cross-section.
13. The coupling of claim 9 , wherein the first end and the second end of the coupling are tapered downwards, linearly, or parabolically.
14. A rod string, comprising:
a first rod and a second rod, each rod including an end having a pin with an external thread; and
a coupling including a core having a first end and a second end, each end containing an internal thread;
wherein the internal thread of the first end of the coupling is complementary with the external thread of the first rod, and the internal thread of the second end of the coupling is complementary with the external thread of the second rod; and
wherein the coupling comprises a spinodally-hardened copper-nickel-tin alloy comprising from about 8 to about 20 wt % nickel, and from about 5 to about 11 wt % tin, the remaining balance being copper, wherein the alloy has a 0.2% offset yield strength of at least 95 ksi and a Charpy V-notch impact energy of at least 22 ft-lbs at room temperature.
15. A pump system comprising:
a downhole pump;
a power source for powering the downhole pump; and
a rod string located between the downhole pump and the power source; wherein the rod string comprises:
a first rod and a second rod, each rod including an end having a pin with an external thread;
a coupling including a core having a first end and a second end, each end containing an internal thread;
wherein the internal thread of the first end of the coupling is complementary with the external thread of the first rod, and the internal thread of the second end of the coupling is complementary with the external thread of the second rod; and
wherein the coupling comprises a spinodally-hardened copper-nickel-tin alloy comprising from about 8 to about 20 wt % nickel, and from about 5 to about 11 wt % tin, the remaining balance being copper, wherein the alloy has a 0.2% offset yield strength of at least 95 ksi and a Charpy V-notch impact energy of at least 22 ft-lbs at room temperature.