Metal working – Method of mechanical manufacture – Shaping one-piece blank by removing material
Reexamination Certificate
2000-05-23
2002-09-03
Bryant, David P. (Department: 3726)
Metal working
Method of mechanical manufacture
Shaping one-piece blank by removing material
C409S066000, C409S076000
Reexamination Certificate
active
06442826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to connections for forming pipe joints and in particular to a method for manufacturing a flush or semi-flush threaded pipe connection in which changes in the machining make more efficient use of available wall thickness in order to increase the compressive and torsional resistance of the pipe joint.
2. Description of Related Art
In a pipe string having a series of joints, each joint having a pin member threadingly connected to a box member, it is desirable to have pipe joints that are especially resistant to compressive and torsional forces, as well as tension and pressure. Compressive forces are often encountered during temperature changes in the well bore, or when running a pipe string into a highly deviated or horizontal well. If the pipe string encounters an obstruction or “bottoms-out” at the bottom of the well bore, the weight of the pipe string can be transferred to any or all of the pipe joints, also creating compressive stresses within the affected pipe joints. Torsional forces are applied to the pipe joints during assembly of the pipe string and are also encountered as a part of normal drilling operations. Horizontal drilling operations present a special case situation in which torsional and compressive forces can become significant. In order to run a pipe string into a highly deviated, or horizontal well bore, the pipe string is often rotated about its longitudinal axis during insertion. The horizontal orientation of the pipe, as well as contact with the bore hole, creates torsional stresses within each pipe joint. When a rotating string encounters the curved section, or build interval of the well bore, alternating tensile and compressive stresses are generated from the associated bending.
The resistance provided by an integral pipe joint to compressive and torsional forces is generally dictated by the surface area of contact of selective regions of the pin member and the box member. The area of contact that contributes most to the compressive and torsional strength of the pipe joint is that between an external shoulder located on the pin member and a box end terminal surface located on the box member. The effective area of the box end terminal surface is typically small due to efforts to reduce pipe wall thicknesses. This area is also reduced due to threading operations, which generally cut threads through the box end terminal surface, thereby decreasing its effective surface area.
If more efficient use were made of the available wall thickness, particularly in the box end terminal surface, improved compressive and torsional resistance would result.
U.S. Pat. No. 4,728,129 shows a connector for tubing and casing joints in which the pin member of the joint includes a tapered stop shoulder.
U.S. Pat. No. 5,505,502 shows a connector for pipe-riser sections in an offshore installation. The pin and box members both include thin-walled sealing extensions or lips.
U.S. Pat. No. 5,064,224 shows an oil field tubular connection which features a long, slightly thinner wall portion at the pin end of the connection between the threads and the metal-to-metal seal “to allow tubing pressure to increase the sealing effectiveness of the metal-to-metal seal.”
U.S. Pat. No. 5,007,665 shows a joint for well casing which includes a pin member with a conically shaped seat and a facing surface.
None of the above references teach a pipe joint having an enlarged box end terminal surface to increase the compressive and torsional strength of the pipe joint. Additionally, none of these references show a recess being used just behind the box end terminal surface to allow the threading operation to begin behind the recess.
A need continues to exist for a simple and economical method for manufacturing pipe joints with improved integrity.
A need specifically exists for such a method which adds increased torsional and compressive resistance to the pipe joint so manufactured.
A need also exists for such a method which does not add appreciably to the costs of the pipe joint manufacturing process, which is simple to implement, and which is reliable in operation.
BRIEF SUMMARY OF THE INVENTION
The method of manufacturing a pipe connection according to the present invention allows the surface area of a box end terminal surface to be increased. Upon make-up, the compressive and torsional resistance of the pipe connection are increased. A pipe string is made up of a series of connections or joints utilizing the manufacturing method of the invention with each joint having a coupling member and a pin member which are threadingly connected.
The pin member is machined onto one end of a plain end pipe by first profiling the pipe to create a tapered surface on an exterior of the pipe. An external shoulder is also created during the profiling step, the tapered surface being axially bounded by a pin end terminal surface at an outer extent of the pin member and the external shoulder at an opposite extent thereof. After creating the tapered surface, a plurality of threads are cut into the tapered surface.
The box member is machined on one end of a plain end pipe by first profiling a tapered surface on an interior of the pipe having a mouth opening. An internal shoulder is created during the profiling step, the tapered surface being axially bounded by a box end terminal surface adjacent the mouth opening of the box member at one extent and the internal shoulder at an opposite extent. After creating the tapered surface and prior to threading, a recess is circumferentially cut into the tapered surface on the pipe interior just behind the box end terminal surface.
A plurality of threads are cut into the internal surface of the box member. Instead of beginning the threading pass in front of the box end terminal surface (as does the traditional method), a cutting tool is placed in the recess, and the threading pass is started behind the recess. This process cuts threads in the internal surface between the recess and the internal shoulder. Since the threading process does not pass through the box end terminal surface, the structural integrity of the box end terminal surface is maintained, which gives the surface a greater surface or contact area.
The box member and the pin member are threadingly connected so that the internal shoulder of the box member engages the pin end terminal surface. More important, when the box member and pin member are fully connected, the box end terminal surface engages the external shoulder of the pin member. Since the box end terminal surface has an increased surface area (when compared to conventionally manufactured box members), the compressive and torsional resistance of the pipe joint are greatly increased.
Additional objects, features, and advantages will be apparent in the written description which follows.
REFERENCES:
patent: 3083043 (1963-03-01), Thornhill
patent: 4127927 (1978-12-01), Hawk et al.
patent: 4186631 (1980-02-01), Grider
patent: 4375708 (1983-03-01), Hellnick et al.
patent: 4707001 (1987-11-01), Johnson
patent: 4728129 (1988-03-01), Morris
patent: 5007665 (1991-04-01), Bovisio et al.
patent: 5064224 (1991-11-01), Tai
patent: 5454605 (1995-10-01), Mott
patent: 5505502 (1996-04-01), Smith et al.
Page from Vetco catalog.
Reeves Doyle E.
Staudt John J.
Blount Steve
Bracewell & Patterson LLP
Bryant David P.
Hunting Oilfield Services, Inc.
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