Description of the Prior Art Conventional drillpipe sections referred to as "joints" have a pin connector at one end of the joint and a box connector at the opposite end of the joint. The box is internally threaded, and the pin is extemally threaded. Pipe joints are 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 of the box. The connection is referred to as a rotary shouldered connection. The engaged shoulclers provide a metal-to-metal seal in the rotary shouldered connection. The engaged threads ho hold the connection together and maintain a bearing pressure on the metal-to-metal seals.

The scaling capacity of the engaged meta)-to-mc (a) seats in a rotary shouldered connection is determined by the bearing pressure of the scals 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 type of connection being made up, it is not uncommon to require makeup torques in the range of 50, 000 ft-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 of the connection, in which case heavy-duty, expensive rotary power tongs are employed to make up the connection.

Most rotary drilling operations require clockwise rotation of the 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 appty a ciockwisc torque (o each of the connections in the string, which tends to increase the engagement between the connections. In some circumstances, it may be necessary to rotate the dri ! ! 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 are stressed in compression, and the sides of the connection at the outer edge of the curve are somewhat relieved of compressive stress. The result is that a differential in the forces acting across the drill pipc connection is produced as the drill string bends arould 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 altcmating strcss forces can induce fatiguc failurcs in tile cirill pipe connection.

Summary of the Invention The connection of the present invention mechanically locks one drill pipe joint to another so that rotary motion between the two joints is prcctudcd. The rotary) ock is provided by non-threaded, mechanically interfering surfaces carried at the ends of the adjoined pipe connections. In the preferred form, the rotary interfering structure is a splinc connection. One of the connected members is a pin. and the adjoining connection member is a box. The pin is provided with an cntarged. annular shoutder 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-metal pressure seal is very low compared with that required for securing conventional drill pipe connections.

The engaged metal seat surfaces between the pin and the box of the present invention arc tapered relative to the common axis ofthc joined pin and box components.

The engaged surfaces form an annular, metal-to-metal, li-ustoconical sealin area that maintains a pressure seal between the inside and the outside of the connection during the cyclic stresses of rotation around curved bore hole section. The tapered configuration of the metal-to-metal seal is optimized to minimize the effect ofthe 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 lcfl or to the right without concern for unthreading the connection. The mctal-to-mcta) 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, elastomeric seat is provided between the pin and box to provide additional sealing between the engaged components. In the preferred form of the invention, the resilient seal is carried in a groove extending annularly within the area of the tapered metal seal area of the pin.

The lock collar of the 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 multiplc-piccc lock slccvc may be removed as required to recondition or repair the sleeve.

The threads of the lock collar and box are preferably ten-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.

The 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 of the connector.

Yet another object of the 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 (it-ill pipe connector having a wrench area that is smaller in diameter than the remainder of the connection to reduce the drag of the wrcnch area on the well bore wall ciuring rotation of thc 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 of the 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 rcadity understood and appreciated by reference to the following figures, specification, and claims.

Brief Description of the Drawings Fig. 1 is a vertical quartcr-scctional view of a connector of thc prcscnt invcntion ; Fig. 2 is a horizontal cross-sectional view taken along the line 2-2 of Fig. I illustrating details in the spline engagement of the present invention ; Fig. 3 is a view taken along the line 3-3 of Fig. I ; Fig. 4 is an isometric view of a pin member of the present invention ; Fig. 5 is an enlarged detail of the tapered metal-to-metal 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 of the pin of the present invention ; Fig. 8 is a modified form of the pin section of the present invention having a resilient seal in the tapered metal-to-metal seal area of the pin; Fig. 9 is a vertical, quartcr-scctiona) view illuslrating a modificci forn of thc connection of the present invention ; Fig. 10 is a vertical elevation of an adapter subassembly employed in connecting the drill string and connectors of the present invention to a top drive assembly ; Fig. 11 is a vertical quarter-sectional view illustrating a modified form of the connector of the present invention with a multiple-part locking collar ; Fig. 12 is a full horizontal cross-section taken along the line 12-12 otFig. 1 1 ; Fig. 13 is a full horizontal cross-sectional view illustrating a modified form of the connector of the present invention employing multiple locking collar segments ; Fig. 14 is a vertical elevation illustrating a modified top drive subassembly of the 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- ! 6 of Fig. ! 5 ; 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. 18A, 18B, anci 18C arc strcss analysis illustrations, in quarter-sectional views, depicting stress distributions over the connector of Figs. 17A, 17B, and 17C with an applied tension load of 600, 000 lbs. ; Figs. 19A, 19B, and 19C are stress analysis illustrations, in quartcr-scctional views, depicting stress distribution over the connector depicted in Figs. 17A, 17B, and 17C with a tension load or666, 536 Ibs. ; Figs. 20A, 20B, and 20C are stress analysis illustrations, in quarter-sectional views, depicting an initial prcload producing 0. 010-inch interference in the seals of a connection of the present invention ; Figs. 21A, 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 of the 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 of the present invention.

Description of the Preferred Embodiments The connection of the 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 ! ! and a pin member 12. The pin member includes an externally threaded lock collar 13. An annular end shoulder surfacc 14 at thc nose of thc lock collar 13 engages a correspondingly configured annual torque shoulder 15 formed on the pin member. the surfaces 14 and 15 engage to form an axial bearing force surface indicated at 16.

Circumferentially spaced, axially extending rib sections 17 project radially inwardly from the internal surface of the box 11. As may best be noted by joint reference

to Figs. 1-3, the ribs 17 are engaged within axially extencling, circumferentially spaced recesses 18 formed along the external circumferential surface of the base of pin 12. The recesses 18 and rib sections 17 cooperate to provide a rotation lock in the form of a spline connection that prevents relative rotary movement between the pin 12 and the surrounding box 1 I while pcrmitting relative axial movement of the pin and box components during the assembty and disasscmbty of the connection.

The nose of the pill 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 initia) assembly of the connection. A central opening 20 extends axially through the center of the pin section and communicates with a central opening 2 ! extending axiaHy through the box section 11. As will be understood, the openings 20 and 21 conduct drilling fluids through the drill string formed by multiplc 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 form an clongate 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 formed by engaging the pin member of one joint with the box member of an adjacent joint. Engagement of the rotation lock permits the drill string to be rotated in a clockwise orcountcrctockwisc direction without danger of unthreading the connections in the string. The lock collar design Of the connection a ! so permits the connection to be secured in a leakproof connection with much smaller makeup torques than required forconventiooal rotary shoaldered tool joint connections.

The lock collar 13 is provided with extcma) threads 22 that mate with imernally formed threads 23 in the box 11. An clastomcric scal 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 seat between the pin and box sections. A fmstoconical, internal shouidcrscat 26 formed atong the surface of the box)) engages a frustoconical. radially extending, external shoulder 27 formed along the surface of the pin 2 to provide a shouldering, metal-to-mctal scal 28.

The connection 10 is assembled by lowering the pin section 12 into the box section 11, causing the splincd arrangement of ribs) 7 and recesses 18 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 form of the invention. threads 22 and 23 arc"ten-hand"threads that are engaged by rotating the collar 13 in a counterclockwise direction. The outer surface of the collar 13 between the threads 22 and the upper collar end provides a wrench area 29 that is cngagcable 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 axiat length to receive the tong jaws. The diameter of the wrench area 29 is preferably less than that of the box 11 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 string is retrieved to the well surface. The connection 10 is secured to a tubular drill string body 31 having an upset area 32. The tube 31 is wetdcd at 33 with me pin body 12. The box 11 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 Die resilient seal 34. The seal assembly 34 is carried in an annular groove 35 extending circumfcrentially within the metal-to-metal seal area of the pin connection 12. The angle of the seat 26 relative to the common central axis of the connection formed by the engaged pin ! 2 and box 1 : 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 of the 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 scat having an clastomcric. 0-ring sea) member 36 contained within a surrounding annular contact scal ring 37. The scal assembly 31 provides an annular, resilient seal contact surface 38 to effect a pressure sea ! between the conical metal seal surface of the pin 12 and the conical, internal metal scat 26 of the box connection 11. The illustrated resilient scal assembly 34 cooperates evitll tilc metal-to- metal seal 28 to prevent the passage of fluids between the engaged box 11 and pin 12.

The contact seal ring 37 may advantageously be constructed of a material such as a glass-fillcd Tef) on composition or other suitablc matcrial. The clastomeric O-ring seal 36 may be constructed of a resilient duorocarbon compound having a desirable elastomeric characteristic. In operation, the seal ring 37 is forced radially outvardly 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 meta) surface of the seat 26 while the O-ring scal 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 of the connection of the present invention. If the angle A is too small, the induced radial expansion forces acting on the box 11 can undesirably stress the box, causing damage or even permitting separation of the pin and box connection. White the damaging effects of the radial expansion may be reduced by increasing the thickness of the wall of the box 11, it is desirable to keep the external diameter of the box I 1 as small as possible to optimize the clearance between the connection and the surrounding well bore of the well being drilled.

The angle has a prcfcrrcd rangc of from 5'to 80'.

Another critical area of the connection is the cross-sectional area at 39 of the box The area 39 occurs at the last engaged thread connection between the lock collar 13 and the box 11. The forces in the engaged connection of the present invention acting at the critical area 39 include the preload forces imposed by threadedly 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. Thcsc

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 prcload on the metal-to-metal seat 28 that maintains a pressure sea ! 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 are rotated in that the greater the bearing surface area of the metal-to-metal scal, 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 of the box. Selection of the anglc A and the preload seating 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 scaling area occurring along the tapered metal-to-metal seal 28 is calculated by determining the effective preload force required for obtaining a seal in a hypothetical, 90° metal-to-metal 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 Iess 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 annularly about the pin 45. The modified pin 45 includes splined recesses 48 and an annular, fmstoconical 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 element, 0-ring sea) assembly constructed of a suitable elastomeric matcrial. The pin member connection 45 provides an etastomeric seal between the outer cylindrical area of the pin body anci the intenal, cylindrical wall of the connection box.

Fig. 8 illustrates another modified form of the pin member of the connection of the present invention, indicated gcncratiy at 50. The modified pin member 50 indudcs an annular, elastomeric 0-ring seal 51 carried on the metal-to-metal seal surface 52 of the pin. As with the embodiment of Fig. 5, the annular sen ! ring 51 is adapted to engage and seat with the tapered frustoconical seat of the box (not illustrated) to provide an

clastomcric seal that cooperates with the mctal-to-mctal scat fbmicd by the frustoconicat. 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 scal ring 68 carried in an annular groove 69 in the base of the box 62 provides a secomiary, resilient scal 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 of the pin section 6I into box recesses 71 formed in the base of the box 62.

Engagement of the pin 61 in the box 62 provides for a pressure seat 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 of the connection. The engagement of the 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 of the connector. The lock collar 63 is made up into the box 62 by rotary motion appliccl wilh a power long or other suitable device. The threads 64 and 65 are preSerably"Iell-hand threads"to prevent the collar 63 from being backed out of the box when the drill string assembly connected by the connection) 6 is being rotated in a normal clockwise direction, as employed during conventional drifting 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 drifting rig. The top drive provides rotary and li fling movement through the length of the drifting derrick. The drive motor in a top drive assembly is movablc from the floor tevet to the top of the derrick along a vertical guide system. Connection of the top drive to a drill string of the 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 joinl 81 is wclded 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 to 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 are 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 seat ring 85 carried in a groove formed along the external, tapered metal-to- metal surface 87 of the pin section. Spline grooves 88 are 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 are"left-hand threads"so that the cottar 84 is rotated in a counterclockwise direction to 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 8 ! 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 of the 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 of the collar 84 with the box of the drill string prevents relative axial movement between the adapter and the drill string so that the vertical movement of the top drive is also imparted to the drill string.

Fig. 11 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. t ! includes a two-piece lock collar 91 that may be applied to the drill pipe body 92 after the pin section 93 has been upset to provide an enlarged arc :) tor the sptinc connection 94 and the locking shoulder 95. With joint reference to Figs. I I and 12. the lock cottar 9t is formed from two mating half-siccvcs 96 and 97 that are held together by clamping rings 98 and 99. Four guide pins, such as guide pins 100 and 10 ! arc employed to provide matching alignment of the two sleeve sections 96 and 97. Pins 101 and 100 may be permanently secured in one of the sleeve sections 96 or 97 and have a free end extending intoacloselyfitting, axiallyextendinggroove 102. Engagementofthopins 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 of any suitable material that can secure the two lock collar sleeves together and hold them on the tube body of the pin connection 92 when the collar is not engaged in the box. The alignment pins 100 and 10'arc not stressed structurally when the assembled sleeves are threaded into the box t05. The alignment pins thus need only have sufficient mechanical strength to maintain the alignment and relative position of the two sleeves around the pin tube 92 during the time that the lock collar is not engaged with the box. Similarly, the clamps rings 98 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 constructed 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 wcldcd onto the drill pipe tube. This eliminates the need to position a continuous single piece locking collar over the tube before either 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 ol tilc (llill pipc tube, it is not practical to remove and replace a single piece lock collar.

Fig. 13 illustrates a modified form of the connector of the present invention indicated generally at 110. The connector 110 is similar to the connector illustrated in Fig. 12, except that the two mating lock collar sections I I I and 112 are wcldcd together at their junctions 113 and 114. As with the embodiment of Fig. 12, the connector 110 may have the collar sections 111 and 112 applied to a pipe body 115 Uler the end of the pipe body has been upset or a tool joint has been welded to the tube. The collar, comprised of sections 111 and 112, may be removed from the pipe body 115 for replacement or repair by grinding out the welds 113 and 114 or by otherwise cutting the collar assembly open.

A modified form of the 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 of the threads formed on each of the two sections comprising the threaded lock cottar 121. As with the lock collar embodiment described with reference to Fig. 13, the lock cottar 121 may atso 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 of the present invention indicated generally at 125. The connection includes a pin section 126 engaged in a box section 127. A 30° tapered mctal-to-metal seal 12S is formed between the pin and box sections. The pin and box arc secured together by the threaded engagement of a) ock collar 129 with the box 127. Threads 130 formed on the pin section 129 mate with threads 131 formed internally of the 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 of the 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. 1t was performed for evaluation of the 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 intemal 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 element stress analyses of a connection such as the connection of Figs. 15 and 16, except that the metal-to-metal seal 12S taper is 1 t ° rather than 30°. The connection is a 7%-inch by 47/8-inch J'SC connection with an interference of 0.001 inch between the pin and box sections of the metal-to-metal 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 cntargcd 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, I 8B, and 18C. Stress at a tension load of 666, 536 Ibs. is illustrated in Figs. 19A, 198, nd 19C. The rcd arcas illustratcci in Figs. 19A, 19B. 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'/2-which by 47/8-inch JWSC connection with an interference of 0. 010 inch in the engaged metal-to-metal seal area. The metal-to-metal scal 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.

20A 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 structura) strength of the box, permitting additiona) 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 ( ! 0tj) with a preload interference of 0. 010 inch.

Figs. 23A, 23B, and 23C illustrate the connector of'Figs. 22A, 22B, and 22C with an applied tension load of 844, 224 lbs. As may be noted in Fig. 23A, the tension load exceeds the maximum rating for the drill pipe body ; the connector, however, is within permitted loading limits. The groove for an clastomcric seal ring is not illustrated in the analysis of Figs. 22A, 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 51/2-inch outside diameter with a 71/2-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 n-lbs. By comparison, the make-up torque required to secure

a conventional tool joint having a similar outside box diameter is 50, 000 fl-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 of the 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 urset 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 to 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 madc without dcparting from the scopc of the invention. Thws, the elastomeric seal ring described need not be included in thc connector where the metal-to- metal seal provides adequate sealing. The connector may also be employed to join pipe sections other than drill pipe joints. The threads of the lock collar and box may be right- hand threads where the drilling operation does 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 conventiona) 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.