Tool joint clamp

A tool joint clamp which includes a clamp assembly and a stop ring. The clamp assembly has at least two die carriers, with each die carrier having a translating and pivoting link between the die carriers such that the die carriers may move toward and away from a centerline of the clamp assembly. The stop ring includes a ring body having a central aperture forming an internal sidewall, with at least a portion of the internal sidewall having splines. A cam surface and cam follower are positioned between the clamp assembly and the stop ring, with the cam surface and cam follower configured to urge the die carriers toward the clamp assembly's centerline when relative torque is applied between the clamp assembly and the stop ring.

BACKGROUND OF INVENTION

The present invention relates to methods and apparatuses used to maintain and protect the integrity of threaded connections, particularly threaded connections between tubular members used in the oil and gas industry.

Ensuring that threaded connections are made up to a proper torque value and then maintained at that torque value is often critical for connecting many different types of tubular members used in the oil and gas industry. Using a drilling rig employing a top drive as one example, the top drive is equipped with a quill and various other tubular members to be rotated are connected to the quill. One common device or tool connected to the pin threads of the quill is a mud saver valve, which is made up with the quill to a predetermined torque value. A further series of tubulars are connected below the mud save valve, including those tubulars being inserted into the wellbore (e.g., drill pipe). This series of tubulars can be referred to collectively as the tubular string. Because the tubular string in the wellbore typically has certain resistance to rotation caused by friction and other forces, torque imparted by the top drive and quill to the other elements of the tubular string will have a tendency impart torque to the connections between tubulars, potentially over-torquing or under-torquing connections, depending on the direction of rotation.

Again using the quill and mud saver valve connection as an example, if this connection becomes over-torqued, it may damage the component threads and/or make the routine breaking apart of the connection excessively difficult. When connections cannot be readily broken, operators may be force to employ expedients such as heating the connection to loosen it. These expedients are problematic for a number of reasons and therefore, it is highly desirable to avoid over-torquing of the connections from the outset. The prior art has developed a class of devices to address this problem, often referred to as “joint clamps.” The prior art joint clamps frequently consist of upper and lower clamp assemblies which may be joined in a manner to prevent relative rotation between the clamp assemblies. After the tubular connection has been made up to the desired torque value, the upper clamp assembly grips the upper tubular just above the connection point and the lower clamp assembly grips the lower tubular just below the connection point. Because the clamp assemblies are fixed against relative rotation, torque applied to the upper tubular is not transferred to the threads of the connection (assuming no slippage of the clamp assemblies), but rather to the flanges of the tubulars engaged by the clamp assemblies, thus preventing over-tightening or loosening of the connection. However, as suggested, the effectiveness of the joint clamps is largely dependent on the ability of clamp assemblies to resist slippage of the tubulars under the very considerable torque loads exerted by the top drive. Devices and methods for reducing or avoiding such slippage can provide an important advance in the art.

SUMMARY OF SELECTED EMBODIMENTS OF INVENTION

One embodiment of the present invention is a tool joint clamp which includes a clamp assembly and a stop ring. The clamp assembly has at least two die carriers, with each die carrier having a translating and pivoting link between the die carriers such that the die carriers may move toward and away from a centerline of the clamp assembly. The stop ring includes a ring body having a central aperture forming an internal sidewall, with at least a portion of the internal sidewall having splines. A cam surface and cam follower are positioned between the clamp assembly and the stop ring, with the cam surface and cam follower configured to urge the die carriers toward the clamp assembly's centerline when relative torque is applied between the clamp assembly and the stop ring.

Another embodiment of the invention is a method of reinforcing a tubular connection with a joint clamp. The method includes positioning a stop ring on a second tubular having external splines. The stop ring includes a ring body having a central aperture forming an internal sidewall, at least a portion of the internal sidewall having internal splines, and where the internal splines of the stop ring engage the external splines of the second tubular. A clamp assembly is positioned on a first tubular. The clamp assembly includes at least two die carriers, each die carrier having a translating and pivoting link between the die carriers such that the die carriers may move toward and away from a centerline of the clamp assembly. The first and second tubular members are threaded together, and the clamp assembly is engaged with the stop ring such that a cam surface and cam follower are positioned between the clamp assembly and the stop ring. The cam surface and cam follower are configured to cause the die carriers to impart an increased radial force on the first tubular when relative torque is applied between the clamp assembly and the stop ring. Then the clamp assembly is closed such that the die carriers engage the first tubular with an initial radial force.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

FIG. 1illustrates one embodiment of the present invention, tool joint clamp1, positioned over two tubular members100and150, whileFIG. 2is an exploded view of theFIG. 1embodiment. In the illustrated example, the first tubular member is a conventional top drive quill100while the second tubular member is a mud-saver valve body150. However, the tubular connection to which the tool joint clamp may be applied could be a connection between many other types of tubular members employed in oil and gas well operations. Reference to a “first” tubular member and a “second” tubular member is intended to convey application of the tool joint camp1to all types of tubular members which are joined by a threaded connection (including those outside the oil and gas industry). As described in more detail below, the second tubular (e.g., a valve body) will typically have a series of external splines152formed at the tubular end having box threads151. Of course, there could also be instances of the external splines being on the end of the tubular just above the pin threads.

In its most general form, the tool joint clamp1is constructed of the clamp assembly3and the stop ring5.FIGS. 3 to 5illustrate one embodiment of the clamp assembly3.FIG. 3shows how this embodiment of the clamp assembly3is formed of three die carriers8which are joined by clevises15and bolts20. However, other embodiments of clamp assembly3could potentially be formed of two die carriers8, four die carriers8, or conceivably more than four die carriers8. The die carriers may also sometimes be referred to as “jaw members” or simply “jaws.” The joining of the die carriers8with the clevises15and bolts20creates an enclosed area or central passage29capable of receiving a tubular member.

As best seen inFIG. 5, the basic body of die carrier8will include clevis ears11with pin apertures12formed there through. On the side of the die carrier body opposite clevis ears11is the carrier bolt bore24. Carrier bolt bore24has a diameter sized to allow the passage of the threaded shaft of bolt20, but not its head21. The rear access bore28seen inFIG. 3is large enough to accommodate bolt head21. The front central section of the die carrier body will have the die insert slot9and the retaining screw aperture10. In the assembled state seen inFIG. 4, the clevis15is secured to the die carrier body by the clevis pin aperture17being positioned between clevis ears11and clevis pin13being inserted therebetween and secured in place with pin retainer14. Similarly, the carrier bolt20will extend through bolt bore24with a lock washer26positioned in front of bolt head21and an internal retaining ring22following bolt head21in rear access bore28. Retaining ring22will act to prevent carrier bolt20from falling out of the rear access bore while the multiple die carriers8are connected into the clamp assembly3. In one embodiment, carrier bolt20is a torque indicating bolt such as a MaxBolt™ load indicating fastener available from Valley Forge & Bolt Mfg. Co., of Phoenix, Ariz.

The die insert30will be secured in die slot9with retaining plate or clip31being engaged by die retaining screw33advancing into screw aperture10(with lock-ring washer32between the retaining screw head and retaining plate31). As is well known in the art, die insert30will have a curved face which matches of the curvature of the tubular member diameter die insert30is sized to grip. The front face of die insert3will typically be modified to grip the tubular member with minimum slipping. For example, the die insert face may have a conventional knurled tooth pattern, a granular particle surface, or one of many other die surface patterns known in the art.

Viewing againFIG. 3, it may be seen how the threaded shaft of carrier bolt20will engage the internally threaded aperture16of clevis15. The carrier bolt20of each die carrier8will engage the clevis15of an adjacent die carrier8, ultimately forming the closed ring configuration of the clamp assembly3. The spacer23on the shaft of carrier bolt20will be sized to limit the degree which bolt head21can move backward in bolt bore24and maintain the approximate spacing of the die carriers from one another in order that a tubular of intended diameter can be position through the central passage29of clamp assembly3. However, it will be understood that the bolt head21is capable of a small degree of translational movement (i.e., in a direction along the centerline of the bolt) within bolt bore25between a front shoulder of bolt bore25and the internal retaining ring22. This allows the clamp assembly's central passage to initially be large enough for the first tubular to pass between the die insert faces and then for the dies carriers to move inward sufficiently for the die insert faces to firmly engage the tubular. Although largely hidden from view inFIGS. 3 to 5, the lower surface of die carriers8will include a triangular boss35which is better seen inFIG. 8and whose function will be described in more detail below.

FIG. 6illustrates the other main component of tool joint clamp100, stop ring5, which may also sometimes be referred to as the “spline ring” or “splined stop ring.” In the illustrated embodiment, stop ring5has a generally triangular shape along its external sidewalls45. Similar to clamp assembly3, stop ring5has a central passage46sized to engage the second tubular member of the connection on which the tool joint clamp is positioned. The internal wall of the central passage is further lined with splines50running parallel to the direction of central passage46. Formed at the corners of stop ring5are the boss slots52. Boss slots52extend through the upper portion of the external walls45into the central passage46. It can be seen that boss slots52are substantially triangular in shape with the straight line side walls53forming an angle β if extended to their intersecting point (as suggested by the dashed lines inFIG. 6). This angle β may vary considerably from embodiment to embodiment, for example between 2.5° and 80°. In a preferred embodiment seen inFIG. 6, β is approximately 45°. It will also be noted that the portions of the internal sidewall forming central passage46will have longer splines50than the sidewall portions below boss slots52. AlthoughFIG. 6shows three boss slots, it will be understood that the number of boss slots is not critical and generally will follow the number of die carriers forming the clamp assembly3. While also not critical, it can be seen theFIG. 6embodiment of stop ring5is formed of a continuous section of material, not as an assembly of parts as clamp assembly3. Forming stop ring5of a continuous section of material is often advantageous when the stop ring incorporates cam surfaces such as provided by the boss slots.

FIGS. 7 to 9better illustrate how the tool joint clamp1will engage the connection of quill100and valve body150. The internal splines50on stop ring5will engage the external splines152on valve body150. As best seen inFIG. 8(showing stop ring5removed), valve body150will include an increased diameter153at the base of external splines152on which stop ring5will come to rest after sliding over external splines152. It will be understood that the engagement of internal splines50with external splines152prevents any relative rotation between stop ring5and valve body150. As suggested above, the location of bosses35on a lower surface of die carriers8is clearly seen inFIG. 8. As seen inFIG. 10, the bosses are substantially triangular in the sense that they are essentially a triangle with a curved base and a truncated apex.

FIGS. 10 to 12best illustrate the interaction between bosses35and boss slots52.FIG. 10is a cross-sectional view taken at the section line Y-Y seen inFIG. 1.FIG. 10shows the vertical centerline70of the tool joint clamp, which is also the vertical centerline of clamp assembly3and stop ring5.FIG. 10further shows the radial axis75extending from the die carrier (or boss) center to tool centerline70.FIG. 11illustrates an enlarged view of boss35and boss slot52.FIG. 11shows boss35position rearward in boss slot56such that die insert30is not engaging the tubular surface.FIG. 11also shows the angle formed by the boss sidewalls36, i.e., angle α.FIG. 12similarly shows the boss slot angle β, which will generally be slightly larger than α. In many embodiments, β is between 1° and 10° larger than α and in preferred embodiments, β is between 1° and 3° larger than α. This difference in angles will contribute to the “cam effect” described below between boss35and boss slot52.

To mount tool joint clamp1over the connection between quill100and valve150, prior to the connection being made, the spiral retaining ring154and then stop ring5are lowered over the external splines152on valve150such that the internal stop ring splines50engage the external splines152. Spiral retaining ring154will act as a spacer to prevent the bottom of stop ring5from directly resting on the shoulder where external splines152terminate on valve150. Next, the assembled clamp assembly3can be slid over and positioned above the pin threads101on quill100, allowing the pin threads101to then engage the box threads151on valve150, after which the quill/valve connection is made up to its specified torque load (e.g., 40,000 ft-lbs). Alternatively, the quill/valve connection could be made up prior to positioning clamp assembly3on quill100. In this alternative, clamp assembly3would be partially disassembled (e.g., by removing a clevis pin), thereby allowing the clamp assembly3to be “opened up” and “wrapped around” quill100before being reassembled in its closed ring configuration by reinsertion of the clevis pin.

Once the quill/valve connection is made up and claim assembly3is positioned around quill100, clamp assembly3is moved onto the stop ring5such that bosses35engage boss slots52. Thereafter, the carrier bolts are gradually and sequentially tightened to draw the die carriers8together in order to have the die inserts place an initial radial load on quill100. In one example, the carrier bolts are tightened to about 1000 ft-lbs, placing an initial radial force between each die insert and quill100.

After this assembly procedure, the tool joint clamp1is in its assembled state as suggested inFIG. 10. The connection125between quill100and valve150has been made up and torqued to a predetermined load. Stop ring5is engaging external spines152on valve150and die inserts30are engaging quill100. The bosses35on die carriers8are positioned rearward in the boss slots52as suggested byFIG. 11. During normal drilling operations, a top drive will transfer torque through the quill100, valve150(and possibly other tubulars not illustrated such as a sub-saver) to the tubular being worked into the wellbore, e.g., a stand of drill pipe attached to the drill string already in the wellbore. Where the drill string provides substantial resistance to being rotated, that torque would normally (i.e., in the absence of the tool joint clamp) be transferred through quill100to the connection125, introducing an undesirable additional torque tending to tighten connection125, or additional torque tending to loosen connection125(depending on the direction of rotation). However, because in theFIG. 10embodiment, quill100transfers torque to die carriers8, then through bosses35to stop ring5, and finally from stop ring5to external splines152on valve150, connection125does not experience any additional torque load.

Most significantly, when die carriers8initially receive a torque load from quill100, die carriers8will urge bosses35into active engagement with boss slots52. This causes the sidewall36(acting as a cam follower) of bosses35to engage the slightly larger angled sidewall53(acting as a cam surface) of boss slots52. This will cause a camming action whereby the torque acting on the die carriers will be transferred into a radial force acting in the direction of the centerline of the clamp assembly3, thus increasing the gripping load applied by the die inserts30. Those skilled in the art will grasp that the greater the differential torque load applied between quill100and valve150, the greater the radial gripping force applied by die inserts30onto quill100.

In theFIG. 11embodiment, the bosses35(and boss slots52) are generally symmetrical around the radial axis75which extends through the bosses and boss slots. For example, the angles ϕ and γ on the bosses35are the same on opposing sides of the radial axis75, as are the corresponding angles on the boss slots. This symmetry around radial axis75results in equal torque-to-radial-force ratios regardless of whether clockwise or counter-clockwise torque is exerted on the clamp assembly.

It will be clear that the cam surface (boss slot sidewall53) is configured to urge the die carriers toward the clamp assembly's centerline when relative torque is applied between the clamp assembly and the stop ring. Naturally, other cam surface/cam follower configurations could be employed in place of the illustrated triangular boss/boss slot structure. For example, some type of roller cam follower could act against a arcuate cam surface.

FIGS. 13 to 16illustrate an alternative embodiment of the tool joint clamp. The most notable change in theFIG. 13embodiment is the stop ring5, which is now circular in shape rather than triangular as seen in theFIG. 1embodiment. As best seen inFIG. 16, boss35and boss slot52of this embodiment are essentially truncated triangles similar to that seen inFIG. 10. However, the boss35inFIG. 16has both a curved base and a curved truncated opposite side, with the curved opposite side generally conforming to the curvature of the stop ring outer circumference. B for theFIG. 16embodiment is generally the same as described above for theFIG. 12embodiment.

TheFIG. 14clamp assembly3illustrates a few modifications from that seen inFIGS. 1-12. Typically, the height “h” of the die carriers8is someone less than in earlier embodiments and will accommodate die members30having a height of “h1” between about 2.5″ and about 3″. Additionally, the die members30will be retained in the die slots by cotter pins34extending through apertures at the top of the die slots. Further, the clevis pins13will be completely recessed in pin apertures12. As seen inFIG. 15, the internal retaining rings22engage an internal ring groove in order to hold the head of clevis pins13within the pin apertures12. The term “about” will typically mean a numerical value which is approximate and whose small variation would not significantly affect the practice of the disclosed embodiments. Where a numerical limitation is used, unless indicated otherwise by the context, “about” means the numerical value can vary by +/−5%, +/−10%, or in certain embodiments +/−15%, or even possibly as much as +/−20%. Similarly, “substantially” will typically mean at least 85% to 99% of the characteristic modified by the term. For example, “substantially all” will mean at least 85%, at least 90%, or at least 95%, etc. Although the invention had been described in terms of certain specific embodiments illustrated in the drawings, those skilled in the art will see many obvious modification and variations which are intended to be encompassed by the scope of the following claims.