WO2000066929A1

WO2000066929A1 - Rotationally locked tool joint for connecting drill pipe sections together

Info

Publication number: WO2000066929A1
Application number: PCT/US2000/011578
Authority: WO
Inventors: Gerald E. Wilson
Original assignee: Grant Prideco, Inc.
Priority date: 1999-04-29
Filing date: 2000-04-29
Publication date: 2000-11-09
Also published as: WO2000066929A9; AU5124300A

Abstract

The ends of drill pipe sections are connected together with a connection that mechanically locks the sections against relative rotational movement. The connection includes a pin member (12) on the end of one of the tubular sections that is received within a box member (11) formed at the end of an adjoining pipe section. The two members (11, 12) have a splined structure (17, 18) that meshes to lock the adjoined connections against relative rotary movement. The two sections are held together axially by a threaded lock collar (13) threadedly engaged within the box member (11) of the connection. Threaded engagement of the collar (13) into the box (11) draws a pin shoulder (15) into a tapered metal-to-metal seal (28) within the box to seal the annular area between the mated connection components. A secondary, annular elastomeric seal member (24) may also be disposed in the overlapping pin (12) and box (11) area.

Description

ROTATIONΛLLY LOCKED TOOL JOINT FOR CONNECTING DRILL PIPE SECTIONS TOGETHER

Background of the Invention

Field of the Invention The present invention relates to connectors for assembling the ends of tubular bodies to each other. More specifically, the present invention relates to a connector for assembling the ends of drill pipe tubes together to form an elongate drill pipe siring.

Description of the Prior Art

Conventional drill pipe sections referred to as "joints" have a pin connector at one end of the joint and a box connector at the opposite end ofthe joint. The box is internallv threaded, and the pin is externally threaded. Pipe joints arc secured to each other_, or made up, by inserting the pin of one joint into the box of an adjacent joint and rotating one of the joints, usually in a clockwise direction, to engage the threads. The pin advances into the box until an annular metal shoulder at the base of the pin threads is engaged with an annular metal shoulder at the face ofthe box. The connection is referred to as a rotary shouldered connection. The engaged shoulders provide a mctal-to-metal seal in the rotary shouldered connection. The engaged threads hold the connection together and maintain a bearing pressure on the mctal-to-mctal seals.

The scaling capacity of the engaged metal-to-mctal seals in a rotary shouldered connection is determined by the bearing pressure of the seals against each other. The bearing pressure, in turn, is determined by the thread design and the amount of torque applied in securing the pin and box together. Depending upon the size and tvpe of connection being made up, it is not uncommon to require makeup torques in the range of 50,000 fl-lbs. and more. Some recent tool joint connection designs employ the thread interference to provide a pressure seal rather than shouldered metal seal surfaces. These new connections may require the application of high levels of torque for several revolutions ofthe connection, in which case heavy-duty, expensive rotary power tongs are employed to make up the connection. Most rotary drilling operations require clockwise rotation ofthe drill string and the associated bottom hole assembly carried at the bottom of the drill string. This rotation, referred to as right-hand rotation, tends to apply a clockwise torque to each of the connections in the string, which tends to increase the engagement between the connections. In so e circumstances, it may be necessary to rotate the drill string in a counterclockwise direction. Such left-hand rotation must be carefully applied and may only be performed at very low torque levels lest the right-hand threaded connections in the assembly become unthreaded, permitting the string to separate.

Modern drilling techniques require that some well bores be diverted from the vertical to angular deviations as great as 90° or greater. As the drill string bends around these curvatures, the sides of the drill string connections at the inside of the curve arc stressed in compression, and the sides ofthe connection at the outer edge ofthe curve are somewhat relieved of compressive stress. The result is that a differential in the forces acting across the drill pipe connection is produced as the drill string bends around the curve in a deviated well bore. When the drill string is rotated around the curve, the area of increased and decreased stress travels around the connection each revolution of the drill pipe. These alternating stress forces can induce fatigue failures in the drill pipe connection.

Summary of t e Invention The connection of the present invention mechanically locks one drill pipe joint to another so that rotary motion between the two joints is precluded. The rotary lock is provided by non-threaded, mechanically interfering surfaces carried at the ends o the adjoined pipe connections. In the preferred form, the rotary interfering structure is a spline connection. One ofthe connected members is a pin. and the adjoining connection member is a box. The pin is provided with an enlarged, annular shoulder that engages an annular seat in the box. A lock sleeve carried over the pin is provided with threads that engage threads formed within the box. Threading the sleeve into the box draws the enlarged pin shoulder into the box where the shoulder is seated against the annular box seat to provide a metal-to-metal shouldering seal. The torque required to fully mate the sleeve and box and to obtain the desired metal-to-mctal pressure seal is very low compared with that required for securing conventional drill pipe connections. The engaged metal seal surfaces between the pin and the box of the present invention arc tapered relative to the common axis of the joined pin and box components. The engaged surfaces form an annular, metal-to-metal, lϊustoconical scaling area that maintains a pressure seal between the inside and the outside ofthe connection during the cyclic stresses of rotation around curved bore hole section. The tapered configuration of the mctal-to-mctal seal is optimized to minimize the effect of the alternating increasing and decreasing stress force applications on the connection as it is being rotated in a deviated well bore without unduly increasing the radial size of the connection.

The mechanical spline engagement between the pin and box prevents relative rotation of the connected drill pipe joints. The drill string made up with these connections thus may be rotated either to the left or to the right without concern for unthreading the connection. The mctal-to-mctal seal is carried within the box at a protected location where it is shielded from the effects of contact with the surrounding bore hole wall. A secondary, annular, clastomeric seal is provided between the pin and box to provide additional sealing between the engaged components. In the preferred form ofthe invention, the resilient seal is carried in a groove extending annularly within the area of the tapered metal seal area ofthe pin.

The lock collar ofthe invention may be applied to the pin connector after the tool joint has been welded onto the drill tube section or after the tube is upset to form the tool joint configuration. In the latter situation, the tool joint may be formed by upsetting the tube end to eliminate the need for welding a tool joint to the tube. As a further advantage, the multiple-piece lock sleeve may be removed as required to recondition or repair the sleeve. The threads of the lock collar and box are preferably left-handed to prevent a back-off of the connection when the drill string is rotated to the right. The outside diameter of the collar is smaller than the outside diameter of the box to minimize the effects of drag on the collar as it is rotated in the well bore.

An adapter is provided for attaching a drill string made up with connections of the present invention to a conventional top drive system. The pin component of the connection of the present invention is provided at one end of the adapter, and a conventional rotary shouldered pin connection is provided at the adapter's opposite end. Thc conventional rotary shouldered pin connection mates with the box connection at the drive end of a conventional top drive. If desired, the adapter may also be equipped with the multiple-piece lock collar.

From the foregoing, it will be appreciated that a primary object of the present invention is to provide a connector for securing together the ends of drill pipe sections whereby a drill string assembled from such sections may be rotated to the left or the right without danger of disengaging the connection.

Another object of the present invention is to provide a connector for drill pipe joints that can be employed in a drill string that extends through a curved well bore section and rotated therein without causing fatigue damage to the components o the connector.

Yet another object ofthe present invention is to provide a connector that may be assembled using a relatively low power torque wrench to eliminate the need for use of a large, high torque wrenching device for securing the connectors together. It is also an object of the present invention to provide a drill pipe connector having a wrench area that is smaller in diameter than the remainder ofthe connection to reduce the drag ofthe wrench area on the well bore wall during rotation ofthe drill string. An important object of the present invention is to provide a tapered metal-to- metal seal in a pin and box connection whereby the connection can be alternately stressed at different points along said seal without causing excessive fatigue in the connection. Yet another object of the present invention is to provide a connection for drill pipe joints that is inexpensive to fabricate and repair and that can be easily made up with low torque equipment and that can be rotated within a curved well bore without excessive loading of the connection. An object of the present invention is to provide a drill string connector having a lock collar with left-hand threads whereby the right-hand rotation ofthe connector within a well bore does not tend to unthread the lock collar from the connector.

The foregoing, as well as other, objects, features, and advantages of the present invention may be more readily understood and appreciated by reference to the following figures, specification, and claims. Bricf Description of he Drawings

Fig. 1 is a vertical quarter-sectional view of a connector of the present invention; Fig. 2 is a horizontal cross-sectional view taken along the line 2-2 of Fig. 1 illustrating details in the spline engagement of the present invention; Fig. 3 is a view taken along the line 3-3 of Fig. 1 ;

Fig. 4 is an isometric view of a pin member of the present invention; Fig. 5 is an enlarged detail of the tapered mctal-to-mctal seal and spline area of the present invention;

Fig. 6 is an enlarged, partial sectional view illustrating details in the resilient sealing element of the present invention;

Fig. 7 is a modified form ofthe pin of he present invention; Fig. 8 is a modified form of the pin section of the present invention having a resilient seal in the tapered mclal-to-mctal seal area of (he pin;

Fig. 9 is a vertical, quarter-sectional view illustrating a modified form o the connection of the present invention;

Fig. 10 is a vertical elevation of an adapter subasscmbly employed in connecting the drill string and connectors of the present invention to a top drive assembly;

Fig. 1 1 is a vertical quarter-sectional view illustrating a modified form of the connector ofthe present invention with a multiple-part locking collar; Fig. 12 is a full horizontal cross-section taken along the line 12-12 of Fig. 1 1 ;

Fig. 13 is a full horizontal cross-sectional view illustrating a modified form ofthe connector of the present invention employing multiple locking collar segments;

Fig. 14 is a vertical elevation illustrating a modified top drive subasscmbly ofthe present invention; Fig. 15 is a vertical sectional view illustrating a connector of the present invention designating critical dimensions of the connector;

Fig. 16 is a horizontal cross-sectional view taken along the line 16-16 of Fig. 15; Figs. 17A, 17B, and 17C are stress analysis illustrations, in quarter-sectional views, depicting an initial preload producing 0.010-inch interference in the seals of a connector of the present invention; Figs. 18Λ, 18B, and 18C arc stress analysis illustrations, in quarter-sectional views, depicting stress distributions over the connector ofFigs. 17A, 17B, and 17C with an applied tension load of600,000 lbs.;

Figs. 19A, 19B, and 19C are stress analysis illustrations, in quarter-sectional views, depicting stress distribution over the connector depicted in Figs. 17A, 17B. and 17C with a tension load of 666,536 lbs.;

Figs. 20A, 20B, and 20C are stress analysis illustrations, in quarter-sectional views, depicting an initial preload producing 0.010-inch interference in the seals of a connection ofthe present invention; Figs. 21 A, 21B, and 21C are stress analysis illustrations, in quarter-sectional views, depicting stress distribution over the connection of Figs. 20A, 20B, and 20C having a tension loading of 733,190 lbs.;

Figs. 22A, 22B, and 22C are stress analysis illustrations, in quarter-sectional views, depicting stress distribution over a connection ofthe present invention depicting an initial preload producing 0.010-inch interference in the seals of a connection of the present invention;

Figs. 23A, 23B, and 23C are stress analysis illustrations, in quarter-sectional views, depicting the connector of Figs. 22A, 22B, and 22C with an applied tension loading of 844,244 lbs; and Fig. 24 is a chart illustrating various pipe dimensions and ratings for different pipe connectors ofthe present invention.

Description of t e Preferred Embodiments

The connection ofthe present invention is indicated generally at 10 in Fig. 1. The connection is used to connect the ends of tubular pipe sections used for a drill string in drilling wells. The connection comprises a box member 1 1 and a pin member 12. The pin member includes an externally threaded lock collar 13. An annular end shoulder surface 14 at the nose ofthe lock collar 1 engages a correspondingly configured annular torque shoulder 15 formed on the pin member. The surfaces 14 and 15 engage to form an axial bearing force surface indicated at 16. Circumfcrentially spaced, axially extending rib sections 17 project radially inwardly from the internal surface ofthe box 1 1. As may best be noted by joint reference to Figs. 1 -3, the ribs 17 arc engaged within axially extending, circun.ferentially spaced recesses 18 formed along the external circumferential surface ofthe base of pin 12. The recesses 18 and rib sections 17 cooperate to provide a rotation lock in the foπn of a spline connection that prevents relative rotary movement between the pin 12 and the surrounding box 1 1 while permitting relative axial movement of the pin and box components during the assembly and disassembly of the connection.

The nose of the pin 12 is tapered, as indicated at 19, to assist in guiding the pin recesses over the box ribs when the pin is stabbed into the box during the initial assembly of the connection. A central opening 20 extends axially through the center of the pin section and communicates with a central opening 21 extending axially through the box section 1 1. As will be understood, the openings 20 and 21 conduct drilling fluids through the drill string formed by multiple pipe sections connected end to end with connectors such as the connector 10.

In use, the connector 10 of the present invention is employed to secure together multiple, similar tubular drill pipe sections ("joints") to foπn an elongate drill string. Each drill pipe joint is provided with a pin member at one axial end and a box member at the opposite axial end. The combined string is foπncd by engaging the pin member of one joint with the box member of an adjacent joint. Engagement ofthe rotation lock permits the drill string to be rotated in a clockwise or counlcrclockwise direction without danger of unthreading the connections in the string. The lock collar design of the connection also peπnits the connection to be secured in a lcakproof connection with much smaller makeup torques than required for conventional rotary shouldered tool joint connections.

The lock collar 13 is provided with external threads 22 that mate with internally formed threads 23 in the box 1 1. An elastomeric seal ring 24 carried in an annular groove 25 formed in the box 1 1 engages the external surface of the pin section 12 to provide a resilient seal between the pin and box sections. A fπistoconical, internal shoulder scat 26 formed along the surface ofthe box 1 1 engages a frustoconical. radially extending, external shoulder 27 formed along the surface of the pin 12 to provide a shouldering, metal-to-metal seal 28.

The connection 10 is assembled by lowering the pin section 12 into the box section 1 1, causing the splincd arrangement of ribs 17 and recesses 1 S to meet and mesh. With the spline engaged, the pin connection is advanced into the box until the conical surfaces 26 and 27 engage in the metal-to-metal seal 28. During this assembly process, the pin nose taper 19 assists in directing the end of the pin past the seal surface 27 and into meshing engagement with the box. Once the pin is seated within the box, the collar 13 may be rotated to cause engagement between the threads 22 and 23. In the preferred foπn of the invention_, threads 22 and 23 arc "left-hand" threads that are engaged by rotating the collar 13 in a counterclockwise direction. The outer surface ofthe collar 13 between the threads 22 and the upper collar end provides a wrench area 29 that is cngageablc by a power wrench, or rotary power tong (not illustrated), employed to apply torque to the collar when the connection is being secured or released. The area 29 is provided with sufficient axial length to receive the tong jaws. The diameter of the wrench area 29 is preferably less than that of the box 1 1 to minimize dragging of the collar on the well bore wall during rotary drilling. The upper end of the lock collar 13 has an annular taper surface 30 employed to deflect the connection 10 from internal well bore obstructions as the drill siring is retrieved to the well surface. The connection 10 is secured to a tubular drill siring body 31 having an upset area 32. The tube 1 is welded at 33 with the pin body 12. The box 1 1 is secured to a similar tubular drill string body (not illustrated) that carries a pin connector at its opposite end. Fig. 4 is a perspective view of the pin member of the connection of the present invention. The pin member includes the collar 13 that is axially and rotatably movable over the underlying tubular body of the pin connection 12.

Fig. 5 illustrates a modified form of the invention illustrating a resilient seal assembly, indicated generally at 34, employed in combination with the metal-to-metal seal 28. Fig. 6 is an enlarged, detail illustration of the resilient seal 34. The seal assembly 34 is carried in an annular groove 35 extending circumfcrentially within the metal-to-metal seal area ofthe pin connection 12. The angle ofthe scat 26 relative to the common central axis of the connection foπncd by the engaged pin 12 and box 13 is indicated at A. In the illustrated embodiment, the angle A is approximately 30°. The metal-to-metal seal surface 28 is illustrated as being formed by the overlapping of the metal seat surface 26 and the metal surface ofthe conical shoulder 27. In the illustrated embodiment, the two conical surfaces engage to produce a compression or interference of 0.010 inches.

The assembly 34 is a two-part seal having an elastomeric. O-ring seal member 36 contained within a surrounding annular contact seal ring 37. The seal assembly 34 provides an annular, resilient seal contact surface 38 to effect a pressure seal between the conical metal seal surface ofthe pin 12 and the conical, internal metal scat 26 ofthe box connection 1 1. The illustrated resilient seal assembly 34 cooperates with the mctal-to- metal seal 28 to prevent the passage of fluids between the engaged box 1 1 and pin 12. The contact seal ring 37 may advantageously be constructed of a material such as a glass-filled Teflon composition or other suitable material. The elastomeric O-ring seal 36 may be constructed of a resilient fiuorocarbon compound having a desirable elastomeric characteristic. In operation, the seal ring 37 is forced radially outwardly by the O-ring 36 to provide a firm, resilient bearing pressure against the scat 26. The material of the seal ring 37 withstands physical contact and wear against the metal surface ofthe scat 26 while the O-ring seal member 36 provides a resilient force urging the seal ring 37 into firm scaling engagement with the scat 26.

The size of the angle A is an important factor in the operation ofthe connection ofthe present invention. If the angle A is too small, the induced radial expansion forces acting on the box 1 1 can undesirably stress the box, causing damage or even pcπnitting separation of the pin and box connection. Wliile the damaging effects of the radial expansion may be reduced by increasing the thickness of the wall of the box 1 1, it is desirable to keep the external diameter ofthe box 1 1 as small as possible to optimize the clearance between the connection and the surrounding well bore ofthe well being drilled. The angle has a preferred range of from 5° to 80°. Another critical area ofthe connection is the cross-scclional area at 39 o the box.

The area 39 occurs at the last engaged thread connection between the lock collar 1 and the box 1 1. The forces in the engaged connection of the present invention acting at the critical area 39 include the preload forces imposed by threadcdly advancing the collar shoulder 14 against the pin shoulder 15. The preload force must be sufficient to prevent the metal-to-metal seal from failing as the pin and box are being pulled apart by the forces imposed by the drilling motion, the string weight, and the rig lifting forces. These forces combine to impose a separation force at the critical box area that can force the box to fail when the maximum force loads are exceeded.

The force exerted by advancing the collar 13 against the bearing surface 15 is employed to impose a preload on the mctal-to-mctal seal 2S that maintains a pressure seal between the pin and box. The total contact surface of engagement in the metal-to-metal seal 28 is desirably held to the smallest area practical to achieve the desired sealing pressure. The various forces acting on the connection arc related in that the greater the bearing surface area of the metal-to-metal seal, the greater the preload force required to obtain a desired scaling pressure, which in turn imposes the need for a larger, stronger box to prevent failure ofthe box. Selection ofthe angle A and the preload scaling force is made with consideration for the anticipated drilling forces to ensure that the connection is sufficiently strong to withstand the expected drilling application while maintaining the desired seal between the pin and box. The effective sealing area occurring along the tapered mctal-to-mctal seal 28 is calculated by dctcπnining the effective preload force required for obtaining a seal in a hypothetical, 90° mctal-to-mctal seal surface. As the angle A decreases toward 0°, the force required to obtain a desired sealing pressure becomes greater. Accordingly, the larger the .angle A, the less preload force required to obtain the desired sealing pressure for a given metal-to-metal seal area.

Fig. 7 illustrates a modified pin member 45 in which an annular, elastomeric O- ring seal 46 is carried in a groove 47 extending annulariy about the pin 45. The modified pin 45 includes splined recesses 48 and an annular, fhistoconical metal-to-metal shoulder 49 adapted to engage and seal with the seat of an adjoining box connection (not illustrated). The seal ring 46 may be constructed in a manner similar to that illustrated in Fig. 6 or may comprise a single clement, O-ring seal assembly constructed of a suitable elastomeric material. The pin member connection 45 provides an elastomeric seal between the outer cylindrical area ofthe pin body and the internal, cylindrical wall ofthe connection box.

Fig. 8 illustrates another modified foπn of the pin member of the connection of the present invention, indicated generally at 50. The modified pin member 50 includes an annular, elastomeric O-ring seal 51 carried on the metal-to-metal seal surface 52 of the pin. As with the embodiment of Fig. 5, the annular seal ring 51 is adapted to engage and seat with the tapered frusloconical scat of the box (not illustrated) to provide an clastomcric seal that cooperates with the mclal-lo-mctal seal formed by the frustoconical. external metal-to-metal seal 52.

Fig. 9 illustrates a modified form of the connection of the present invention indicated generally at 60. The connection 60 includes an axially extending pin section 61 and an axially extending box section 62. A locking collar 63 is employed to secure the pin and box connections firmly together to prevent relative axial movement between the pin and box. Threads 64 on the collar 63 mate with threads 65 on the box 62. whereby rotation of the collar into the box advances the pin section 61 into the box to form a metal-to-metal seal at 67. An annular, elastomeric seal ring 68 carried in an annular groove 69 in the base ofthe box 62 provides a secondary, resilient seal between the pin and box connection.

A rotation lock is provided to prevent relative rotation between the engaged pin and box. The rotation lock is provided by interlocking engagement of the pin end projections 70 extending from the base ofthe pin section 61 into box recesses 71 formed in the base of the box 62.

Engagement ofthe pin 61 in the box 62 provides for a pressure seal between the pin connector section 61 into the box connection 62. The connection 60 also provides the required mechanical connection between the pin and box to retain the two components together. As with the earlier described designs, the lock collar 63 is employed to apply a preload to the metal-to-metal seal area 67 and to trap the pin within the box to prevent axial separation ofthe connection. The engagement ofthe projections 70 and recesses 71 provide a rotation lock that prevents relative rotation between the pin section 61 and the box section 62 without imposing any of the forces of rotation in the threaded components ofthe connector. The lock collar 63 is made up into the box 62 by rotary motion applied with a power tong or other suitable device. The threads 64 and 65 are preferably "left-hand threads" to prevent the collar 63 from being backed out of the box when the drill string assembly connected by the connection 16 is being rotated in a normal clockwise direction, as employed during conventional drilling procedures. The outside diameter of the lock collar 63 is also preferably smaller than the outside diameter of the box section 62 in the engaged thread area to minimize the effects of drag on the collar 63 as the drill string is rotated. Fig. 10 illustrates a top drive adapter, indicated generally at 80, employed to cross over between the connection of a conventional top drive and the connector of the present invention. As is well known in the art, a top drive is a system for powering a drill string and is used to replace the function of a rotary table in a standard drilling rig. The top drive provides rotary and lifting movement through the length ofthe drilling derrick. The drive motor in a top drive assembly is movable from the floor level to the top of the derrick along a vertical guide system. Connection ofthe top drive to a drill string ofthe present invention requires crossing a conventional pin connector to a box connector of the present invention. The adapter 80 employs a conventional rotary shouldered pin connection 81 to mate with the box at the end of a conventional top-drive output shall (not illustrated). The tool joint 81 is welded to a tubular connecting body S2 having a pin member 83 of the present invention. A locking collar 84 extending around the tubular connection section 82 is movable axially between the tool joint S 1 and the pin section S3. The collar 84 is provided with pin threads 85 that arc adapted lo mate and engage with the box threads at the top end of a drill string secured together with pipe sections having the connections of the present invention.

In use, the pin section 83 is introduced into a box such as illustrated in Fig. 1. The collar 84 is then advanced over the tube 82 until the threads 85 arc engaged with the box threads and the collar is then rotated to engage the threads S5 with the threads in the box. The form of the pin assembly 82 illustrated in Fig. 10 includes an annular, elastomeric seal ring 85 carried in a groove formed along the external, tapered metal-to- metal surface 87 of the pin section. Spline grooves 88 arc provided at the base of the adapter, which in other respects is also similar to the pin sections described with respect to the pin connections earlier described in other embodiments of the invention. Engagement of the pin section of the adapter 80 to the box at the top of a drill string provides a connection similar to those described with reference to the embodiments of Figs. 1-9, to secure the top drive to the drill string. As with the other connections in the drill string, the threads 85 arc "left-hand threads" so that the collar S4 is rotated in a counterclockwise direction lo engage and preload the pin connection S3 with the annular seat in the box within which it is connected. Where high left-hand rotation torques are anticipated, the connection to the top drive may be clamped or otherwise fixed to prevent disengagement of the tool joint pin connection 81 from the top drive shaft. The adapter imparts the vertical and rotational movement of a top drive to the drill string connected to the adapter. As with the embodiments of Figs. 1-9, rotation of the top drive connected to the upper end ofthe top drive adapter SO is transmitted through the spline components 88 of the adapter to the drill string connected to the lower end of the adapter. The mechanical engagement ofthe collar 84 with the box ofthe drill string prevents relative axial movement between the adapter and the drill string so that the vertical movement ofthe top drive is also imparted to the drill string.

Fig. 1 1 illustrates yet another embodiment of the connector of the present invention indicated generally at 90. Corresponding components in the various embodiments described herein operate in a similar fashion. The embodiment of Fig. 1 1 includes a two-piccc lock collar 91 that may be applied lo the drill pipe body 92 al er the pin section 93 has been upset lo provide an enlarged area for the spline connection 94 and the locking shoulder 95. With joint reference to Figs. 1 1 and 12, the lock collar 91 is formed from two mating half-slccvcs 96 and 97 that arc held together by clamping rings 98 and 99. Four guide pins, such as guide pins 100 and 101 arc employed to provide matching alignment of the two sleeve sections 96 and 97. Pins 101 and 100 may be permanently secured in one ofthe sleeve sections 96 or 97 and have a free end extending into a closely fitting, axially extending groove 102. Engagement ofthe pins 101 and 100 in the groove 102 places the two sleeve sections in proper alignment so that external threads 103 on the sleeve sections properly mate with each other and form a continuous pin thread configuration for mating threaded engagement with internal threads 104 formed within a box 105.

The clamp rings 98 and 99 may be formed ofany suitable material that can secure the two lock collar sleeves together and hold them on the tube body ofthe pin connection 92 when the collar is not engaged in the box. The alignment pins 100 and 102 arc not stressed structurally when the assembled sleeves arc threaded into the box 105. The alignment pins thus need only have sufficient mechanical strength to maintain the alignment and relative position ofthe two sleeves around the pin tube 92 during the time that the lock collar is not engaged with the box. Similarly, the clamps rings 9S and 99 need only be sufficiently strong to hold the two sleeve sections in position about the pin tube 92 when the lock collar is not engaged in the threaded box. The advantage of a lock collar constmcted as illustrated in Fig. 12 is that the collar may be applied to the drill pipe section after the pin end of the drill pipe section has been upset or welded onto the drill pipe tube. This eliminates the need to position a continuous single piece locking collar over the tube before cither end has been upset or before a pin or box tool joint is welded to the end of the pipe body. An additional advantage results when it is necessary to repair the lock collar 91. In the event the collar requires repair, it is only necessary to disengage the lock rings 98 and 99 to permit the collar to be removed and thereafter replaced with a repaired or new tube section locking collar. Where the locking collar is a single piece sleeve positioned on the drill pipe body before the tool joint is welded on or before the upset is formed at the end of the drill pipe tube, it is not practical to remove and replace a single piece lock collar.

Fig. 13 illustrates a modified foπn of the connector of the present invention indicated generally at 1 10. The connector 1 10 is similar to the connector illustrated in Fig. 12, except that the two mating lock collar sections 1 1 1 and 1 12 arc welded together at their junctions 1 13 and 1 14. As with the embodiment of Fig. 12. the connector 1 10 may have the collar sections 1 1 1 and 1 12 applied to a pipe body 1 15 after the end ofthe pipe body has been upset or a tool joint has been welded to the tube. The collar, comprised of sections 1 1 1 and 1 12, may be removed from the pipe body 1 15 for replacement or repair by grinding out the welds 1 13 and 1 14 or by otherwise cutting the collar assembly open.

A modified form ofthe top drive adapter employed with the present invention is indicated generally at 120 in Fig. 14. The adapter 120 is similar to the adapter illustrated in Fig. 10 except that the lock collar 121 is assembled in two pieces held together by clamp rings 122 and 123. Guide pins (not illustrated) or other alignment mechanisms may also be employed in the embodiment 120 to provide proper matching ofthe threads formed on each ofthe two sections comprising the threaded lock collar 121. As with the lock collar embodiment described with reference to Fig. 1 , the lock collar 121 may also be welded together rather than being secured by the lock rings 122 and 123. The same advantages as described with respect to drill pipe joints applies to a top drive adapter equipped with mating lock collar sections that may be applied after the ends of the adapter have been formed or secured to the tube body supporting the lock collar. Fig. 15 is a vertical cross-section illustrating a connection ofthe present invention indicated generally at 125. The connection includes a pin section 126 engaged in a box section 127. A 30° tapered mctal-to-mctal seal 128 is formed between the pin and box sections. The pin and box arc secured together by the threaded engagement of a lock collar 129 with the box 127. Threads 130 formed on the pin section 129 mate with threads 131 formed internally ofthe box 127. The threads 130 and 131 may preferably be of a PAC thread form, having a 0.75 inch per foot taper. The end of the pin section engages with the base ofthe box section to form a spline connection, indicated generally at 132. The spline may preferably be a fillet root, side fit configuration illustrated in detail in Fig. 16.

A finite clement analysis of the connection 125 illustrated in Fig. 15 was performed for evaluation ofthe connection at the indicated diameters in Fig. 15. In Fig. 15, the OD min is the minimum tool joint outside diameter; ODtj is the tool joint outside diameter; PDt is the thread pitch diameter; ODp is the outside diameter; Dsh is the shoulder diameter; IDtj is the tool joint internal diameter; Do is the major external diameter; Dre is the minor external diameter; Di is the minor internal diameter; Dri is the major internal diameter; Lsh is the minimum shoulder length; Lt is the thread length; and Ls is the actual spline length in the area of the engaged spline members of the pin and box assembly. In Fig. 16, PDs is the spline pitch diameter; p is the circular pitch; h is the depth of engagement; and t is the spline circular thickness.

Figs. 17A, 17B, and 17C are finite clement stress analyses of a connection such as the connection of Figs. 15 and 16, except that the metal-to-mctal seal 12S taper is 15° rather than 30°. The connection is a 7%-inch by 4⁷8-inch JWSC connection with an interference ofO.010 inch between the pin and box sections ofthe mctal-to-mctal seal at the optimum makeup torque for this connection.

Fig. 17A illustrates a quarter-sectional view of the made-up connection with the different colorations indicating differing degrees of stress occurring at the area of coloration. Fig. 17B is an enlarged section of Fig. 17A, and Fig. 17C is an enlarged area of the connection section of the figures. The color code associated with the figures indicates the stresses induced in the connection when the tension imposed on the metal- to-metal seal area is at initial makeup. Stresses at a tension load of 600,000 lbs. are illustrated in Figs. 18A, 18B, and 18C. Stress at a tension load of 666,536 lbs. is illustrated in Figs. 19A, 19B, and 19C. The red areas illustrated in Figs. 19A, 1 B. and 19C show an excess of stress acting across the entire wall of the connection box representative of a failure condition. Figs. 20A, 20B, and 20C are similar to Figs. 17A, 17B, and 17C, illustrating low stress distribution in a 7' -inch by 4⁷/β-inch JWSC connection with an interference of 0.010 inch in the engaged metal-to-metal seal area. The metal-to-metal seal area is also a 15 "taper; however, the connection is otherwise similar to the connection illustrated in Figs. 15 and 16. Fig. 20A is a quarter-sectional view of the stresses induced in the connection, as indicated by the different coloration located at the stressed points of the engaged components. Fig. 20B is an enlarged view of Fig. 20A, and Fig. 20C is an enlarged section of the engaged connector of the invention.

Figs. 21 A, 21 B, and 21 C illustrate the stresses induced in the connection of Fig. 20Λ when the force engaging the collar nose and pin shoulder surfaces is 733,160 lbs. As may be noted in Fig. 21 C by minimal presence of the maximum stresses (indicated in red), increasing the connection box diameter by '/, inch appreciably increases the structural strength of the box, pcnuilting additional tension to be applied to the connection without danger of failure.

Figs. 22A, 22B, and 22C illustrate stress distribution on a connector having a 7.497-inch outside diameter (OOtj), 4.764-inch inside diameter ( lOtj) with a preload interference of 0.010 inch.

Figs.23 A, 23B, and 23C illustrate the connector of Figs. 22 A, 22B, and 22C with an applied tension load of 844,224 lbs. As may be noted in Fig. 2 A, the tension load exceeds the maximum rating for the drill pipe body; the connector, however, is within permitted loading limits. The groove for an elastomeric seal ring is not illustrated in the analysis of Figs. 22 A, 22B, and 22C.

Fig. 24 is a table illustrating dimensions and ratings for different pipe connections. In a connection according to the present invention, the torque required to make up the lock collar to a pipe having a 5'/--inch outside diameter with a 1\ .-inch tool joint OD; 4.1875-inch ID, with a shoulder diameter of 6.349 inches and a minimum shoulder length of 0.739 inches; a thread length of 3 inches and a thread pitch diameter of 6.586 inches is 4,816 ft-lbs. By comparison, the make-up torque required to secure a conventional tool joint having a similar outside box diameter is 50,000 ft-lbs. Thus, it may be appreciated that the torque required to secure a connection of the present invention is much less than that required to secure a corresponding conventional tool joint connection, and accordingly, relatively small power tongs may be employed to engage the connection ofthe present invention.

It is desired that the outside diameter of the connector of the present invention be made as small as possible to enhance the drilling characteristics of the drill string. To this end, where a tool joint is welded onto the drill pipe tube, the tube may advantageously be internally upset to thereby decrease the outside diameter of the tool joint. Additionally, the steel used for the tool joint may be made of 135,000 psi material lo permit a reduction in the outside diameter of the tool joint.

While specific examples of the connector of the present invention have been described herein in detail, it will be appreciated that various modifications of the connector may be made without departing from the scope of the invention. Thus, the elastomeric seal ring described need not be included in the connector where the mctal-to- mctal seal provides adequate scaling. The connector may also be employed to join pipe sections other than drill pipe joints. The threads ofthe lock collar and box may be right- hand threads where the drilling operation docs not impose a risk of backing off the connection during right-hand drill string rotation. The connector may also be advantageously used for only one or a few connections in an otherwise conventional string of rotary shouldered pipe connections. Accordingly, it is intended that the invention be limited only by the scope and spirit of the appended claims rather than by the specific examples described in the specification and drawings.

Claims

What is claimed is:

1. A connector for securing together and sealing the ends of tubular bodies, comprising: a box connection carried at the end of an axially extending, first tubular body; a pin connection carried at the end of an axially extending, second tubular body, said pin connection being receivable within said box connection; a lock collar having the threaded area thrcadably engagcablc between said box and said pin connections for securing said box and pin connections together to prevent axial separation between said box and pin connections; a box rotation lock carried by said box connection; a pin rotation lock carried by said pin connection, said box and pin rotation locks being engagcablc when said pin connection is received in said box connection for preventing relative rotation between said pin and said box connections; and a metal pin seal and a metal box seal for foπning a pressure seal between said pin and box connection when said pin connection is received within said box connection, said metal pin and metal box seal comprising engagcablc axially tapering annular scaling surfaces formed on said pin connection and said box connection.

2. A connector as defined in Claim 1 wherein said box is internally threaded and said lock collar is externally threaded whereby said lock collar may be threadably engaged within said box for holding said pin seal engaged with said box seal.

3. A connector as defined in Claim 2 wherein said pin connection includes an enlarged annular shoulder extending radially from said second tubular body for limiting the axial movement of said lock collar relative to said second tubular body whereby rotary motion of said lock collar threadedly engaging said box advances said pin connection into said box connection.

4. A connector as defined in Claim 1 , further including an annular, elastomeric seal disposed between said pin and box connections.

5. A connector as defined in Claim 4 wherein said elastomeric seal is disposed in a tapering, annular sealing surface of said pin or said box.

6. A connector as defined in Claim 4 wherein said elastomeric seal is disposed in an annular, cylindrical space defined between said pin and box connections.

7. A connector as defined in Claim 1 wherein said box rotation lock and said pin rotation lock each comprise axially extending radial ribs and recesses foπning a spline connection in which ridges and recesses of the engaged pin and box connections register to prevent relative rotational movement between said pin connection and said box connection.

8. A connector as defined in Claim 1 wherein said lock collar includes a tool engagement surface extending axially away from said threaded area of said lock collar whereby said lock collar may be engaged and rotated by a tool to engage and disengage said lock collar and said box connection.

9. A connector as defined in Claim 8 wherein the external diameter of said tool engagement surface is smaller than the external diameter of said box connection.

10. A connector as defined in Claim 1 wherein said lock collar is provided with left-handed threads whereby said lock collar is advanced into said box connection by counterclockwise rotation.

1 1. A connector as defined in Claim 1 wherein said tapering annular sealing surfaces are inclined relative to a common central axis of said pin connection and said box connection by 5 ° to 45 ° .

12. A connector as defined in Claim 1 wherein said metal pin seal and metal box seal are respectively inclined at an angle of between 15 ° and 30° relative to a central axis of said pin connection and said box connection.

13. A connector as defined in Claim 1 wherein said lock collar is comprised of multiple components secured together with alignment and retention stnicturc whereby said lock collar may be assembled with said connection after said pin connector is connected to said second tubular body.

14. A connector as defined in Claim 1 , further comprising a threaded tool joint connection secured to an end opposite said pin connection on said second tubular body for forming a top drive subasscmbly.

15. A string of drill pipe for drilling a well bore, said string being comprised of a plurality of engaged tubular pipe sections, each pipe section having a box end connection formed at one axial end and a pin end connection foπned at its other axial end, said pin and box connections of adjoining pipe sections being engageablc with each other to form an elongate string, each of said connections of said string comprising: a box connection earned at the end of an axially extending, first tubular body; a pin connection carried at the end of an axially extending, second tubular body. said pin connection being receivable within said box connection; a lock collar having a threaded area threadably engagcablc between said box and said pin connections for securing said box and pin connections together to prevent axial separation between said box and pin connections; a box rotation lock carried by said box connection; a pin rotation lock carried by said pin connection, said box and pin rotation locks being engagcablc when said pin connection is received in said box connection for preventing relative rotation between said pin and said box connection; and a metal pin seal and a metal box seal for fomiing a pressure seal between said pin and box connection when said pin connection is received within said box connection. said metal pin and metal box seal comprising cngageable axially tapering annular sealing surfaces formed on said pin connection and said box connection.