Turning – Lathe – Work rest
Reexamination Certificate
1998-07-28
2001-03-13
Tsai, Henry (Department: 3722)
Turning
Lathe
Work rest
C082S165000, C082S113000, C082S167000, C082S164000
Reexamination Certificate
active
06199462
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of repairing drill pipes, and to a new lathe, particularly for use in repairing drill pipes.
BACKGROUND OF THE INVENTION
Drill pipes are threaded together in use in drill strings during drilling, for example of oil or gas wells. One end of a drill pipe has an internally threaded box or female connection, while the other end has an externally threaded pin or male connection so that the drill pipes may be threaded together. The drill pipe adjacent the box or pin is enlarged to form an upset and provide strength for the joint, but to reduce the cost of making the drill pipe, the upset typically does not extend very far down the pipe length, typically not much more than about twice the pipe diameter. The internal bores and threads of the box and pin are machined precisely to allow the box and pin to seal together on sealing surfaces at either end of the threads, and also perhaps at intermediate points between threaded portions.
During drilling, stresses on the drill pipe and especially on the boxes and pins cause the interior surface of the box and the exterior surface of the pin to become worn, such that they do not seal together, and fluid within the drill pipe can leak. Since drill pipe is expensive, rather than throw out the drill pipe when it is worn, drilling contractors will repair or have the drill pipe repaired by refinishing the boxes and pins. The refinishing is carried out by machining a new set of threads and sealing surfaces deeper into the box and pin respectively. This eliminates a part of the enlarged portion of the box and pin. After several repairs, the enlarged portion of the box or pin is gradually eliminated until no further repairs can be carried out and the drill pipe is discarded.
The machining of the drill pipe is typically carried out using a lathe having a chuck with jaws mounted in a plane at one end of the lathe. The chucks hold and rotate one end of a drill pipe against a working tool. The other end of the drill pipe is held in a steady rest. Often, the drill pipe will be bent at the end, with the consequence that when cradled in the lathe, the portion of the end being worked on does not rotate precisely in a circle. In this instance, a large amount of metal on the end of the drill pipe may need to be taken off in order to obtain a precisely configured box or pin. This limits the number of times the drill pipe can be repaired, and consequently increases the operating costs of the drilling contractor.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a method of allowing multiple repairs of bent drill pipes without losing too much of the box or pin material. According to a further aspect of the invention, a novel chuck and lathe is provided for carrying out the method of the invention.
There is thus provided in accordance with one aspect of the invention, a method of repairing a drill pipe having first and second connector ends, each of the first and second connectors ends including a threaded portion and sealing portions, with a lathe having a chuck with longitudinally spaced first and second sets of jaws, the method comprising the steps of mounting the drill pipe in a lathe, gripping the first connector end of the drill pipe with each of the first and second sets of jaws, orienting the first connector end by manipulation of the first and second sets of jaws into a working position; and rotating the drilling pipe against a working tool to machine the threaded portion and sealing portion of the first connector end and produce a new threaded portion and sealing portion of the first connector end.
There is also provided in accordance with a further aspect of the invention, a lathe for machining a drill pipe, the lathe comprising a chuck, first and second sets of jaws adjustably mounted on the chuck, the first set of jaws being mounted radially in the chuck at a first longitudinal position and the second set of jaws being mounted radially in the chuck in a second longitudinal position spaced from the first first longitudinal position, each of the first and second sets of jaws including x and y positioning jaws, a motor for rotating the chuck; and means to machine a drill pipe gripped by the jaws.
In a further aspect of the invention, each set of jaws includes first and second pairs of jaws mounted orthogonally to each other.
In a further aspect of the invention, the first set of jaws is mounted further away from the lathe than the second set of jaws, and the jaws of the first set of jaws are longer in a direction perpendicular to the orientation of the first set of jaws than the jaws of the second set of jaws.
In a further aspect of the invention, a workpiece positioning device is provided so that repeated cuts of pipes may be made without re-positioning the pipes. In this aspect of the invention, there may only be one set of jaws.
These and further aspects of the invention will now be described.
REFERENCES:
patent: 286333 (1883-10-01), Sanders
patent: 630998 (1899-08-01), Smith
patent: 771997 (1904-10-01), Palm
patent: 2816301 (1957-12-01), Hopkins
patent: 4819527 (1989-04-01), Redman
patent: 5615590 (1997-04-01), Speckhahn
patent: 5680801 (1997-10-01), Keller
Christensen O'Connor Johnson & Kindness PLLC
Tsai Henry
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