Coupling for drilling-with-casing operations
A modified API Buttress threaded casing connection is disclosed for use in drilling oil and gas wells in lieu of using conventional drill pipe. The coupling threads only are multiple tapered yet can be mated with standard API Buttress pin threads having a single taper. The coupling is also shortened to permit abutment of the mating pins at the center of the coupling and can be further enhanced with an integral, sacrificial wear sleeve on one end of the coupling.
1. A tubular coupling for joining together two externally threaded pipe ends comprising:
a generally cylindrical body having a first end and a second end;
an axial, generally cylindrical bore extending from the first end of the body to the second end of the body with at least a portion of the bore being internally threaded with a continuous thread, the threaded portion having a first section proximate the first end wherein the internal diameter varies at a first taper angle and a second section adjacent to the first section wherein the internal diameter varies at a second taper angle which is less than the first taper angle and a third section adjacent to the second section wherein the internal diameter varies at a third taper angle which is less than the second taper angle.
2. A coupling as recited in claim 1 wherein the threaded portion of the coupling will mate with a threaded pipe end having external, buttress-type threads.
3. A coupling as recited in claim 1 wherein the coupling is for threaded pipe ends that have a single taper angle and at least one of the taper angles of the coupling has the same taper angle as the threaded pipe ends.
4. A coupling as recited in claim 1 which comprises two internally threaded portions that are mirror images of each other and each threaded portion has at least three taper sections for each threaded pipe to be joined together and each of the three sections has a different taper angle.
5. A coupling as recited in claim 4 wherein the taper angle in the first section of each threaded portion is greater than the taper angle in the second section of each threaded portion and the taper angle in the second section of each threaded portion is greater than the taper angle in the third section of each threaded portion.
6. A coupling as recited In claim 1 wherein the multiple taper angle threaded portion of the coupling will mate with buttress-type threads having a single taper angle.
7. A coupling as recited in claim 1 further comprising two pipes, each having one end in threaded engagement with the coupling such that the pipe ends connected with the coupling abut one another when the connection is fully assembled.
8. A coupling as recited in claim 1 further comprising an internal reinforcing ring at the center of the coupling, the reinforcing ring having approximately square shoulders such that the ends of two pipes joined by the coupling will each butt against an internal square shoulder when the connection is fully assembled.
9. A coupling as recited in claim 1 further comprising a generally cylindrical wear sleeve Integral with one end of the coupling body and having an inner wall surface and an outer wall surface.
10. A coupling as recited in claim 9 wherein the wear sleeve comprises a surface having additional, externally-applied wear protection alone at least a portion of its outer diameter and on its leading face.
11. A coupling as recited in claim 10 where the additional wear protection is externally applied hard banding.
12. A coupling as recited in claim 9 wherein a portion of the inner wall surface of the wear sleeve is cylindrical for a first portion of its length and tapers outwardly in a direction toward the threaded portion of the coupling body in a second portion of its length.