Background of the Invention Oilfield tubular members, such as drill-pipe, frequently have a larger ID in the tube section than the ID in the connectors in order to decrease weight and increase flexibility. Accordingly, the tube section may be upset and tool joints with a smaller ID welded to the ends of the tube section.. In other applications, it is desirable to form an entire joint from an integral bar for economic and material availability reasons, but since one end has to be a fox end for receiving the pin end of another joint, the threaded connection is not able to have a"double shoulder"which provides increased torsional strength.

Oilfield tubular connections with double shoulders are known in the art.

U. S. Patent 1,326, 643 discloses a double shoulder connection. U. S. Patents 4,548, 431 and 4,548, 432 illustrate versions of a double shoulder connections.

More recent designs for double shoulder connections are disclosed in U. S.

Patents 5,472, 375, 5, 549, 336 and 5, 908, 212.

The disadvantage of the prior art are overcome by the present invention and an improved oilfield tubular connection is hereinafter disclosed.

Summary of the Invention In a preferred embodiment, the oilfield connection includes a box on one end of a tubular and a pin on the other end of the tubular, with mated threads joining the tubular.

It is a feature of the invention that a double shoulder connection may be used to retrofit previously manufactured drill string members to provide the double shouldered connection.

A further feature of the invention is that the double shoulder connection may be provided on both the box end and the pin end of the connection, with one sleeve provided in the box and another sleeve provided on the pin.

A further feature of the invention is that the tubular member may be manufactured with two different IDs at its ends: a smaller ID for the pin and a larger ID for the remaining entire length of the joint, including the box.

Another feature of the invention is that the sleeve may be made from either a similar or a dissimilar material as the corresponding pin or box.

Another feature of the invention is that the sleeve may be retained in the box with one of an interference fit, a tapered fit, a threaded connection, or a weldment. The ID of the sleeve preferably approximates the ID of the pin.

These and further features and advantages of the invention will become

apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.

Brief Description of the Drawings Figure 1 is a conventional pin and box connection with mated threads.

Figure 2 illustrates a double shoulder pin and box connection according to one embodiment of the invention.

Figure 3 illustrates a pin provided with a sleeve.

Figure 4 illustrates a spiral upset section along a drill pipe.

Figure 5 is a cross-sectional view of the spiral upset shown in Figure 4.

Figure 6 illustrates the box end, with one-quarter cutaway, and the full sleeve in the box, as shown in Figure 2.

Detailed Description of the Preferred Embodiments Figure 1 shows a conventional box end 10 and a pin end 12 with mated threads 14. Only a single shoulder 16 is provided. According to the present invention, the same box 10 as shown in Figure 1 may be provided with an inner sleeve 18, which engages the box at shoulder 20, thereby providing the double shoulders 16, 22. Each shoulder preferably lies substantially within a plane perpendicular to a central axis of the connection.

Accordingly, the drill string member may be initially manufactured with two different IDs at its ends, a smaller ID for the pin 12, and a larger ID for the entire remaining length of the joint, including the box 10. Sleeve 18 may be made of a similar or dissimilar material, and may be retained in the box 10 by various techniques, including an interference fit, including a tapered interference fit, a threaded retention, or welding. Figure 2 illustrates the sleeve 18 secured to the box 10 by threads 19 spaced axially between thread 14 and shoulder 20. The cylindrical outer surface 21 on the sleeve 18 below the shoulder 20 may have a slight interference fit with the mating cylindrical shoulder or the box. The ID of the sleeve 18 preferably approximates the ID of the pin 12, which the OD of the sleeve 18 provides for retention and absorption of loads.

In a preferred embodiment, the box sleeve 18 may be formed from a dissimilar material from that used to fabricate the box end 10, so that the desired characteristics of the box may be met by the selected material for forming a box 10, while the desired characteristics for the sleeve 18 may be met by selecting a different material for the sleeve. In a preferred embodiment, an internal diameter of the box sleeve 18 approximates the internal diameter of the pin 12. Moreover, in a preferred embodiment, each of the first shoulder 16 and the second shoulder 22 has a substantial radial thickness compared to radial thickness of the oilfield connection, so that both shoulder 16,22 are able to carry a significant portion of

the axial load transmitted through the connection. In a preferred embodiment, the radial thickness of the shoulder 16 and the radial thickness of the shoulder 22 are each at least 25% of the radial thickness of the oilfield connection.

Accordingly, if the radial thickness between the outer cylindrical surface 52 of the connection as shown in Figure 2 and the inner cylindrical surface 54 of the pin 12 is approximately 1.6 inches, then the radial thickness of each of the shoulders 16,22 is preferable at least 0.4 inches, and in many applications, one or both of the shoulders 16,22 may be about 30% or more of the radial thickness of the connection.

The sleeve 18 as shown in Figure 2 may be applied to retrofitting drill string members previously manufactured without a double shoulder connection.

Also, this same concept may be employed on both the box and pin ends of the connection, in which case the box may be provided with the sleeve 18 as shown in Figure 2, and the pin bore provided with a similarly shaped sleeve 24, as shown in Figure 3. More particularly, sleeve 24 engages the pin 12 at shoulder 28. Sleeve 24 may be similarly secured to the pin by threads 27, with outer cylindrical surface 29 engaging the mating cylindrical surface or the pin.

Table A provides characteristic for high performance drill pipe in several sizes according to the present invention, listing dimensions for both the tube and the drill joint.

TABLE A TUBE TUBE DIMENSIONS MECHANICAL PROPERTIES Tensile Torsional ominal ominal. D. of aximum OD Yield, Yield, Drill Pipe Inside Spiral of End LB FT-LB Size, In Diameter, Upsets, Upsets, In In In 5-1/2 4-1/2 7 5-11/16 1,020, 973 112,745 5-7/8 4-1/2 7 6 1,456, 591 163,209 6-5/8 5-5/8 8-1/2 6-15/16 1,250, 718 171, 364 TOOL JOINT TOOL JOINT DIMENSIONS MECHANICAL PROPERTIES Connection Outside Box Inside Pin Inside Tensile Torsiona Size, In Diameter, In Diameter, In Diameter, Yield, Yield, In LB FT-LB HT 55 7 4-1/2 3-3/4 1,711, 745 103,645 XT 57 7 4-1/2 4 1, 658, 209 125, 509 6-5/8 FH 8-1/2 5-5/8 4-1/2 2,240, 845 116, 291 Figure 4 illustrates pictorially a spiral upset connection 42, which may be spaced along the one or both of the joints connected by the double shoulder connection discussed above. Figure 5 is a cross-section of the spiral upset connection. Figure 6 illustrates the box and sleeve generally shown in Figure 2.

While preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.