Apparatus and method for spinning pipe

Abstract

A pipe spinner and method for spinning pipe used in oil wells. The pipe is engaged simultaneously by a chain and by friction-drive rollers. Both the chain and the rollers are driven. The beneficial results thus achieved include increased torque, and greatly extended chain life. The chain is a silent chain, and has an inverse internal portion which mounts around the pipe without any necessity for latching of jaws or for breaking of the chain. Tightening of the chain is effected by power cylinders which close the jaws on which are mounted (a) sprockets for the chain, and (b) the friction-drive rollers associated with such sprockets.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of my copending patent application Ser. No. 238,069, filed Mar. 27, 1972, for Pipe-Spinning Apparatus and Method.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of apparatus and methods for rotating substantially cylindrical objects, particularly drill pipe, drill collars, casing, etc. The word "cylindrical" is employed in this specification in its ordinary or common sense, namely to define objects which have a circular or substantially circular exterior cross-sectional shape.

2. Description of Prior Art

The cited copending application sets forth much background, and specifies much prior art, all relating to the long-standing effort to replace the dangerous and unsatisfactory spinning chain. The cited application also describes and claims an apparatus and method which are greatly superior to those of the prior art. In the present application, there are described and claimed an apparatus and method which have the same superiorities over the prior art and, in addition, are characterized by an even greater driving torque and by a much extended chain life.

There are large numbers of prior-art pipe-spinner devices wherein the pipe is engaged and driven by a chain (or other flexible drive element) only, or by friction-drive rollers only. There is no such device known to applicant wherein both a chain (or other flexible drive element) and friction-drive rollers simultaneously engage and drive the pipe. Such simultaneous use of the chain and of friction-drive rollers achieves the surprising benefit of increasing the drive torque, as well as increasing greatly the chain life. The torque increase and the life increase occur without losing any of numerous benefits of chain-type devices over devices which have rollers only.

In order to be highly practical and fast-acting, a pipe spinner should operate from only one side of the pipe. From such one side, the spinner should grab the pipe, then spin it, then let loose. The apparatus described herein and in the cited copending application are of such type, and are to be contrasted with prior art apparatus of types wherein the chain had to be broken each time the tool was mounted on the pipe, or wherein a latching means had to be closed on the side of the pipe remote from the main portion of the spinning apparatus, or wherein there were no power-operated jaws, or wherein the pipe was not engaged directly. Some prior art tools of these last-mentioned types are shown in the following patents: U.S. Pat. Nos. 1,760,167; 1,805,007; 1,925,970; 2,460,671; and 2,573,212.

SUMMARY OF THE INVENTION

The present invention provides pipe-engaging rollers at the ends of power-operated jaws which close toward the pipe with great force. Furthermore, there is provided a chain having an inverse internal portion, the ends of which bend around sprockets located at the jaw ends. The diameters of the rollers are sufficiently large that they engage the pipe and relieve the loads on the bent chain portions which extend around the indicated sprockets. Such bent portions are, therefore, not compressed between the sprockets and the pipe, despite the great force of the jaws. Accordingly, the lives of the chain and sprockets are very greatly extended. The chain should be a silent chain, as described and claimed in the cited patent application, to achieve numerous advantages relative to (for example) gripping the pipe without damaging the same, and relative to achievement of a desirable clutching action when the joint seats.

According to one important aspect of the present invention, the rollers are connected to the sprockets in such manner that the rollers are forcibly and positively driven thereby. The rollers are thus friction-drive rollers which engage and drive the pipe. The friction between rollers and pipe is great, because of the great closing power created in the jaws. The rollers thus engage the pipe and friction-drive it at a plurality of points about the pipe circumference, and the silent chain engages the pipe and friction-drives it at a large number of other points around such circumference. There should be no teeth on either rollers or chain, all gripping being instead frictional and resulting from the forcible closing of the jaws and from the resulting great tension created in the chain.

Since there is no need to break the chain when the tool is mounted on the pipe, or to latch the jaws together, the apparatus and method are operated on only one side of the pipe and are therefore extremely practical and fast acting. The described combination of power-closed jaws, friction-drive rollers, and silent chain having an inverse internal portion achieves many advantages. Such advantages include (for example) high torque, long chain life, great adaptability to fit on pipes of different diameters, ability to grip effectively on oily and dirty pipes, minimized damage to the pipe, and ability to work on surfaces which are not perfectly cylindrical. Surprisingly, the present tool with driven rollers creates more torque than the same tool with no rollers--this despite the fact that roller-type tools normally create less drive torque than do chain-type tools.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the present apparatus, said view corresponding substantially to FIG. 1 of the above-cited patent application, but showing the friction-drive rollers mounted in the jaws and also showing a different form of suspension;

FIG. 2 is a bottom plan view, corresponding generally to FIG. 4 of the cited application, and showing the present apparatus when in the pipe-gripping position;

FIG. 3 is a vertical sectional view on line 3--3 of FIG. 2 and which corresponds generally to FIG. 6 of the cited application;

FIG. 4 is a horizontal sectional view which corresponds generally to FIG. 7 of the cited application, the jaws being shown in an open position permitting introduction of the pipe;

FIG. 5 is a horizontal section view on line 5--5 of FIG. 3 and corresponding generally to FIG. 8 of the cited application, the jaws being shown closed on the pipe;

FIG. 6 is an enlarged fragmentary vertical sectional view on line 6--6 of FIG. 5, and illustrating the drive means between the sprockets and the associated friction-drive rollers; and

FIG. 7 is an enlarged fragmentary isometric view illustrating a portion of the silent chain.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Except as specifically stated in the present specification, the apparatus and method described herein are identical to those described in the above-cited patent application Ser. No. 238,069. Said application Ser. No. 238,069 is hereby incorporated by reference herein, as though set forth in full.

To summarize briefly the various basic components of the present apparatus, an elongated closed-loop flexible drive element 33 is so mounted that it has an external portion 33a, an inverse internal portion 33b, and two return-bent portions 33c which connect the external portion to the internal portion.

The flexible drive element should be a silent chain as described and claimed in the cited patent application. Such chains are well known in other arts, one example (suitable for use as the flexible drive element 33) being given by U.S. Pat. No. 3,661,025 for a Silent Chain and Method of Assembly Thereof, which patent is hereby incorporated by reference herein as though set forth in full.

"Silent chain" is a recognized term for an inverted-tooth chain made up of a large number of corresponding planar leaf links 36 the ends of which overlap each other in alternating relationship as shown in FIG. 7. Each leaf link has an inner bearing edge 37 adapted to engage the pipe 34, and also has at each end thereof (and on the side opposite edge 37) a pair of sprocket teeth 38 which are shaped to mesh with the various sprocket wheels. The bearing edges 37 of the various links are shown as being substantially straight, but they may also be slightly concave in order to conform more closely to the exterior surface of pipe 34.

In the illustrated silent chain 33, the various leaf links 36 are disposed in pairs, such as 36a and 36b, which are coextensive, parallel and in surface contact with each other. Large numbers of such pairs are disposed in what may be termed layers, in the alternating relationship shown in FIG. 7. Pivot pins 39 extend through the end portions of the leaf links to hold the chain together in pivotal relationship.

The silent chain 33 (and the sprocket wheel teeth) are preferably constructed in accordance with American Society of Automotive Engineers Standard B29.2. Such chain is well known in industry, being desirable for various purposes because of its silent operation, strength, durability, etc. In accordance with the present apparatus and method, the relatively silent operation of the chain is not a factor, the purpose being instead to create large bearing areas at the inner leaf edges 37 and which engage the external cylindrical surface of the pipe 34 to be spun.

When a chain is employed having the indicated leaf edges 37, and the large bearing area, it is not necessary to provide teeth on the inner surfaces of the chain (the pipe-engaging surfaces thereof), so that there is a minimum possibility of damage to the pipe. Furthermore, when no pipe-engaging teeth are employed, the chain may more readily slip relative to the pipe when the joint bottoms out.

The use of the silent chain in combination with the very large jaw-closing pressures indicated below, permit the spinning apparatus to create a sufficient torque to spin large pipes at high speed, despite the presence of water, oil, etc., on the pipe. One advantage of the silent chain is that it is substantially incapable of being stretched. Furthermore. it is a primary advantage that the pipe is spun without any substantial damage thereto.

The chain 33 extends around sprocket wheels 24 which are fixedly mounted at the front end of the main housing of the apparatus (such housing constituting a "support" for various components of the apparatus). Pivotally connected to the main housing at the axes of sprocket wheels 24 are the jaws 16a and 17a, such jaws respectively corresponding to jaws 16-17 of the cited application except as specified hereinafter. The jaws have sprocket wheels (described below) at the outer ends thereof and around which the chain 33 bends at the return-bent portions 33c.

When jaws 16a-17a are in the opened condition of FIGS. 1 and 4, the apparatus may be mounted around a vertical pipe 34 to be spun. Then, the jaws are closed with much force, for example to the position of FIGS. 2 and 5, thereby creating a large amount of tension in the inverse internal portion 33b to cause such portion to frictionally engage the exterior pipe surface with great bearing pressure. The inverse internal portion engages the exterior pipe surface about a majority of the circumference thereof but not about the full circumference. When the jaws are thus in closed condition, they maintain the pipe in position in the inverse internal portion of the chain.

Opening and closing of jaws 16a-17a is effected by power means best shown in FIGS. 2 and 3, namely, pneumatic cylinders 61 the pistons of which connect to the jaws through cranks and linkages as described in detail in the cited application. The cranks and linkages include crank arms 56 which are fixedly associated with the jaws 16a-17a.

When the jaws are closed, the distal ends thereof do not touch each other (and thus act as mutual stops). Instead, the chain 33 acts as the sole means to limit the degree of jaw closing, the result being that closing of the jaws creates much tension in the chain. The jaws are so constructed that, if there were no chain, the jaw ends would (when the jaws are closed) touch each other.

After the jaws are closed to grip the chain portion 33b on pipe 34, the chain is driven in order to effect rapid spinning of the pipe. Such driving is effected by a pneumatic motor 42 which operates through a gear box 47 to rotate a shaft 51 (FIGS. 3 and 4) on which is mounted the drive sprocket 32 for chain 33. Thus, when a control valve is operated to admit air into the motor 42, the shaft 51 is driven to thus drive the sprocket wheels 32 and thereby drive chain 33 to rotate pipe 34.

The motor 42 and gear box 47 are movable toward and away from the pipe 34, thus moving the axis of shaft 51 and of sprocket wheel 32. Such movement is not effected except when it is desired to adapt the apparatus for driving a substantially different diameter of pipe 34. To achieve the indicated adjustment, a chain guide and lock element 41 are shifted in response to rotation of an adjustment screw 52. After the adjustment is completed, lock screws 48 (which extend through a flange portion of the gear box 47, and are threaded into element 41) are tightened in order to lock element 41 (and thus elements 42, 47 and 51) in position. In order that the described adjustment may occur, the upper portion of the housing of the apparatus is suitably slotted, as illustrated, to receive the lock screws.

The apparatus is suspended, adjacent the wellhead of an oil well, by means of an inverted V-shaped suspension bar 110 the lower ends of which connect to the housing of the apparatus. At the upper or apex portion of bar 110 is provided a mounting means 111 by which the bar may be connected to the lower link of a suspension chain 112. The mounting means 111 is so constructed that the chain may be connected at different axial points therealong, thus permitting balancing of the spinning apparatus in generally a horizontal condition.

In order to facilitate manipulation of the apparatus, suitable handles 113 are provided below each jaw 16a-17a as illustrated (relative to jaw 16a) in FIG. 1.

DETAILED DESCRIPTION OF THE FRICTION-DRIVE ROLLERS AND ASSOCIATED SPROCKET WHEELS

As best shown in FIGS. 3 and 6, each jaw 16a-17a is enlarged at the outer portion thereof in order that it may incorporate two friction-drive rollers 116 and one sprocket wheel 117. Since the elements at the outer ends of the two jaws 16a-17a are identical, only the elements incorporated in jaw 16a are shown and described in detail.

Referring to FIG. 6, the two rollers 116 are disposed on opposite sides of (above and below) the sprocket wheel 117, all of the elements 116 and 117 being mounted coaxially of each other on a vertical shaft. More specifically, such shaft is illustrated as being bolt 118 which extends through collars 119 welded on the upper and lower walls of the housing portion of jaw 16a, there being nuts 121 provided to maintain bolt 118 fixedly in position. Mounted around bolt 118, between the upper and lower housing walls of the jaw, is a sleeve 122 around which are provided a plurality of sets of antifriction bearings (for example, needle bearings) 123. The rollers 116 and sprocket wheel 117 are mounted in encompassing relationship to such bearings 123 in order that such elements 116-117 will rotate freely relative to the shaft or bolt 118.

Sprocket wheel 117 (and the other sprocket wheels) is of the type conventionally employed with a silent chain, having vertical teeth which mesh with the tooth portions of the chain 33 as described in the cited patent application and also in said U.S. Pat. No. 3,661,025. Each sprocket wheel may be termed a "silent chain" sprocket wheel.

It is pointed out that the teeth of the silent chain do not engage the pipe 34, engagement instead being effected at a multiplicity of untoothed bearing edges as described above. As is known and conventional in many silent chains, guiding of the chain is effected by means of guide links which pass through a circumferentially grooved central region of the sprocket wheel 117. Such guide links are indicated at 124 in FIG. 6, and are extended through the circumferential groove 126 in wheel 117. The other sprockets of the apparatus have similar circumferential grooves for reception of the guide links 124.

As shown in FIG. 6, the cylindrical peripheral surfaces of rollers 116 are in direct bearing engagement with the exterior cylindrical surface of pipe 34. Such rollers 116 have diameters sufficiently great to insure that neither the chain nor the sprocket wheels will be damaged due to the pressure engagement with the pipe 34. Stated more specifically, the roller diameters are sufficient that the return-bent portions 33c of chain 33 will not be crushed or compressed between sprocket wheels 117 and the exterior pipe surface. It has been found that, if such crushing or compression is permitted to occur, it results in "brinelling" of the chain links and/or of the sprocket wheels, with consequent stiffening of the chain and reduction in chain life.

As an example, in the illustrated embodiment, a small gap (for example, 0.030 inch) is provided at 127 (FIG. 6) between each return-bent chain portion 33c and the exterior pipe surface. The presence of such gap assures that even substantial wearing on the rollers, so as to reduce the diameters thereof, will not cause the chain 33 to be compressed between sprocket wheels 117 and the pipe to thereby cause wear and stiffening of the chain.

It is emphasized that each gap 127 is only present at a relatively small region immediately between sprocket wheel 117 and the pipe, and that the chain portion 33b is in direct engagement with a major portion of the circumference of the pipe. Thus, there are two important areas of frictional engagement between the drive elements and the pipe 34. One of such areas is at the rollers 116, and the other of such areas (which is much larger than the first) is along a major portion of the circumference of the pipe and at which the silent chain frictionally engages the pipe.

Stated in another manner, the chain frictionally engages the pipe along a long arc of the circumference thereof, whereas the friction-drive rollers frictionally engage the pipe at about (or between) the ends of such long arc. The word "circumference" is presently employed to denote only one circumferential region along the length of the pipe.

Applicant has discovered that, if the rollers 116 are not driven but instead are permitted to rotate freely in the manner of antifriction bearings for the pipe 34, then the amount of drive torque created by the spinning apparatus is drastically reduced. If, on the other hand, the rollers are positively driven with or by the sprockets 117, then the drive torque created by the present spinning apparatus is increased in comparison to the torque which would be created if no rollers were employed. Such an increase was not to be expected, particularly because the rollers are only in line contact with the pipe whereas the chain portion (which was lifted, by the rollers, off the pipe) was in surface contact with the pipe.

To summarize, therefore, the presence of the driven rollers 116 creates two major benefits relative to the construction described in the cited application, wherein no such rollers are employed. These benefits are increased drive torque and greatly increased chain life.

The driving of the rollers 116 on each jaw 16a-17a is effected by means of drive pins 128 which extend into registered apertures in the ends of the sprocket and of the rollers. Since each sprocket 117 is driven by the chain 33 (which chain is in turn driven by the drive sprocket wheel 32 in response to operation of motor 42 and gear box 47), and since the rollers 116 are connected to the sprocket 117 by means of drive pins 128, it follows that the rollers 116 are driven positively, and operate as friction-drive rollers for the pipe 34.

DESCRIPTION OF THE METHOD

The jaws 16a-17a are first opened by operation of the pneumatic cylinders 61, for example to the position shown in FIGS. 1 and 4. The amount of opening is enough to permit the apparatus to be swung toward the pipe 34 so that the pipe enters the space between the return bent portions 33c of the chain and becomes largely surrounded by the inverse internal portion 33b thereof.

The cylinders 61 are then operated to close the jaws 16a-17a, with great force, for example to the positions shown in FIGS. 2 and 5. The jaws do not close to positions such that they engage each other and serve as mutual stops, the degree of closing being instead determined by the length of the chain. Thus, the jaws close until the chain tension is so great that it counter-balances the jaw-closing force. The described jaw closing and chain tension cause strong pressure engagement between the rollers 116 of the pipe, and between the inverse internal chain portion 33b and the pipe. Such pressure engagements create great friction, without damaging the pipe, which friction is operative to spin the pipe after the motor 42 is started to drive (by means of gear box 47) the shaft 51 and thus the drive sprocket wheel 32 and chain 33.

Driving is effected until the desired joint is either made or broken, at one end of the pipe 34, following which the cylinders 61 are operated to open the jaws and permit the operation to be repeated with a different length of pipe.

As described in detail above, the driving of the chain effects driving of the rollers 116 so that they operate as friction-drive rollers and cooperate with the inverse internal chain portion 33b in driving and spinning the pipe without damage thereto.

The apparatus may operate on pipes of slightly different diameters, without effecting any adjustment in the position of the drive sprocket wheel 32. When a pipe of substantially different diameter is to be driven, the position of the axis of wheel 32 is adjusted as described heretofore and in the cited application. Briefly, this adjustment is effected by loosening the lock screws 48, turning the adjustment screw 52 until the position of the shaft 51 is such that the chain is adjusted to the desired length, and then re-tightening the screws 48. The method is then repeated in the manner described above but with the pipe of substantially different diameter.

If desired, very high torques may be created with the present apparatus, particularly if the silent chain is caused to be very wide and if there is a very large gear reduction between the pneumatic motor 42 and the drive sprocket wheel 32. It is also pointed out that the pneumatic motor 42 could be replaced by hydraulic means in order to increase torque capabilities.

The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.

Claims

I claim:

1. Apparatus for spinning pipe, which comprises:

a. a support,

b. first and second jaws movably mounted on said support,

c. power means to close said jaws with a large amount of force,

d. an elongated closed-loop flexible drive element,

said flexible drive element having an external portion and an inverse internal portion disposed within said external portion,

said inverse internal portion being adapted to receive and engage the pipe to be spun,

e. first and second wheels mounted, respectively, on said jaws,

said wheels having extended therearound the return-bent portions at which said external portion of said flexible drive element connects to said internal portion thereof,

f. roller means mounted on said jaws to engage the pipe in response to forcible closing of said jaws by said power means, and to prevent said flexible drive element or said wheels from being damaged or worn due to forcible engagement with said pipe in the vicinity of said wheels; and

g. means to drive said flexible drive element, and thus effect spinning of said pipe, after said jaws have been closed by said power means,

said drive means also being connected to effect driving of said roller means in such direction that said roller means serve as drive elements for aiding said flexible drive element in spinning said pipe,

said driving of said roller means being such that said roller means impart driving torque to said pipe through the regions of engagement between said roller means and said pipe.

2. The invention as claimed in claim 1, in which said power means comprise cylinder means and associated piston means, and also comprise means to introduce pressurized fluid into said cylinder means.

3. The invention as claimed in claim 1, in which said flexible drive element is a chain, and in which said wheels are sprocket wheels meshed with said chain.

4. The invention as claimed in claim 3, in which said chain is a silent chain, in which said sprocket wheels are shaped to mesh with the teeth of said silent chain, in which the untoothed bearing edges of said chain are on the interior side of said inverse internal portion so that said bearing edges will engage the exterior cylindrical surface of said pipe when said jaws are closed, and in which said roller means prevent said chain from being compressed between said pipe and said wheels.

5. The invention as claimed in claim 1, in which said flexible drive element has such length that it prevents said jaws from closing into engagement with each other, said flexible drive element constituting when said pipe is disposed in said inverse internal portion the sole means for counterbalancing the force exerted by said power means, whereby said inverse internal portion is tensioned greatly and therefore bears with great force against said pipe.

6. The invention as claimed in claim 1, in which said flexible drive element is a chain comprising a large number of planar leaf links the ends of which overlap each other in alternating relationship, said overlapped ends being pivotally connected to each other by pivot pins, each of said leaf links having at one side thereof an untoothed bearing edge disposed at said inverse internal portion and adapted to forcibly engage the exterior surface of said pipe without damaging the same, at least some of said links incorporating protuberances on the side thereof opposite said untoothed bearing edges, said protuberances forming part of said drive means recited in clause (g).

7. The invention as claimed in claim 1, in which said jaws are pivotally mounted on said support, and in which said jaws are devoid of any latch means for connecting said jaws to each other on the side of said pipe remote from said support.

8. The invention as claimed in claim 1, in which said roller means comprise rollers mounted on said first jaw in axial alignment with said first wheel, in which said roller means further comprise rollers mounted on said second jaw in axial alignment with said second wheel, and in which the diameters of said rollers are sufficiently large that said rollers engage said pipe when said jaws are closed and therefore relieve the pressures tending to damage said flexible drive element or said wheels.

9. The invention as claimed in claim 8, in which said diameters of said rollers are sufficiently large that said flexible drive element is, at the portion thereof adjacent said wheels, spaced away from said pipe.

10. The invention as claimed in claim 8, in which said rollers are connected to said wheels and therefore rotate therewith, whereby said rollers serve as drive rollers for aiding said flexible drive element in spinning said pipe.

11. The invention as claimed in claim 1, in which said means to drive said flexible drive element comprises a power-driven wheel drivingly engaged with said flexible drive element, and means to mount said power driven wheel in such manner that the axis thereof is fixed in position at all times when the apparatus is being employed to spin pipe having a fixed predetermined diameter.

12. Apparatus for rotating pipe about the longitudinal axis thereof, which comprises:

a. an elongated flexible drive element adapted to engage a pipe along a substantial arc of the exterior surface thereof, to thereby rotate the pipe about the longitudinal axis thereof,

said flexible drive element being a closed loop having an external portion and an inverse internal portion,

the interior surface of said inverse portion engaging the exterior surface of said pipe around a major portion of the pipe circumference,

b. drive roller means adapted to engage said pipe to rotate the same about the longitudinal axis thereof, said flexible drive element and said drive roller means engaging said pipe simultaneously with each other,

said drive roller means engaging said pipe adjacent the return-bent portions at which said external portion of said flexible drive element connects to said inverse internal portion thereof,

said return-bent portions being respectively mounted around wheels,

said roller means comprising rollers drivingly related to said wheels for driving thereby, and

c. means to forcibly drive said flexible drive element and said rollers to thus effect rotation of said pipe about the longitudinal axis thereof due to the conjoint operation of said flexible drive element and said rollers,

said drive means being such that said flexible drive element imparts driving torque to said pipe through the arc of engagement between said flexible drive element and said exterior surface, said drive means also being such that said rollers impart driving torque to said pipe through the regions of engagement between said rollers and said exterior surface.

13. The invention as claimed in claim 12, in which said rollers are coaxial with said wheels and are rigidly connected thereto for conjoint rotational movement.

14. The invention as claimed in claim 13, in which the diameters of said rollers are sufficiently large to prevent damage to said flexible drive element or said wheels due to forcible engagement with said pipe.

15. The invention as claimed in claim 12, in which said flexible drive element is a silent chain.

16. A pipe-spinning apparatus for spinning pipe at the wellheads of oil wells, which comprises:

a. a movable support,

b. first and second jaws pivotally mounted on said support for pivotal movement in such manner that the distal ends of said jaws move toward and away from each other as said jaws close and open,

said distal ends being so related to each other that, unless restrained, they would touch upon closing movement of said jaws,

c. piston and cylinder means connected to said jaws to forcibly close the same and thereafter open them,

d. first and second "silent-chain" sprocket wheels rotatably mounted, respectively, at end portions of said first and second jaws,

e. a silent chain having an external portion and an inverse internal portion,

said external and internal portions connecting to each other at return-bent portions which bend around and mesh with said first and second sprocket wheels,

said internal portion being adapted to receive the pipe to be spun,

f. a drive sprocket wheel mounted on said movable support and meshed with said chain,

the length of said chain being such that when said inverse chain portion encompasses a pipe of predetermined diameter said jaws may not be closed sufficiently far to cause said distal ends thereof to touch each other,

g. means mounted on said support to drive said drive sprocket wheel,

h. first and second roller means respectively mounted at said end portions of said first and second jaws,

said first and second roller means being respectively coaxial with said first and second sprocket wheels,

said roller means having diameters sufficiently large to prevent said return-bent chain portions from being compressed between said pipe and said first and second sprocket wheels, and

i. means provided to drivingly connect in positive manner said first roller means to said first sprocket wheel, and said second roller means to said second sprocket wheel,

whereby said roller means constitute friction-drive rollers which cooperate with said inverse internal portion in spinning said pipe.

17. The invention as claimed in claim 16, in which means are provided to adjust the position of the axis of said drive sprocket wheel, and to lock said axis in adjusted position, whereby to adapt the apparatus for spinning pipes of different diameters.

18. The invention as claimed in claim 16, in which additional sprocket wheels for said silent chain are respectively mounted at the pivot axes of said first and second jaws, said additional sprocket wheels being meshed with said chain.

19. A method of rotating pipe adjacent the wellhead of an oil well, to thereby make or break threaded joints between coaxial pipe sections, which comprises:

a. wrapping a section of a flexible drive element around at least a major portion of the circumference of said pipe to be rotated, and in engagement with the exterior surface of said pipe,

b. engaging roller means with said exterior surface of said pipe in the general region of said flexible drive element,

c. creating great tension in said flexible drive element to force it into pressure engagement with said exterior surface,

d. creating large bearing pressure between said roller means and said exterior surface, and

e. simultaneously driving both said flexible drive element and said roller means to thereby rotate said pipe,

said driving of said flexible drive element imparting driving torque to said pipe through the area of engagement between said flexible drive element and said exterior pipe surface,

said driving of said roller means imparting driving torque to said pipe through the area of engagement between said roller means and said exterior pipe surface.

20. Apparatus for rotating about the longitudinal axis thereof a pipe which has a substantially cylindrical exterior surface, which apparatus comprises:

a. a support,

b. first and second jaws mounted on said support and movable between an open position in which said first and second jaws are relatively remote from each other and a closed position in which said first and second jaws are relatively close to each other,

c. an elongated closed-loop flexible chain,

said chain comprising a large number of planar leaf links the ends of which overlap each other in alternating relationship, and pivot pins pivotally connecting said overlapped ends together, said leaf links being in a relatively high density such that there is a close spacing between adjacent links at the central portions thereof intermediate adjacent ones of said pivot pins,

said leaf links having on one side thereof untoothed bearing edge portions adapted to forcibly engage the substantially cylindrical exterior surface of the pipe without damaging the same, and having protuberance means on the other side thereof,

d. wheel means comprising a plurality of wheels including first and second wheels mounted, respectively, on said first and second jaws,

said chain being mounted around said wheel means in such manner that, when said jaws are in said closed position, there is an external chain section, an inverse internal chain section disposed within said external section, and junction regions between said external and internal chain sections return-bent and extending respectively around said first and second wheels,

said internal chain section being adapted to receive said pipe and being so oriented that said untoothed bearing edge portions of said leaf links in said internal chain section engage said substantially cylindrical exterior surface of said pipe,

said internal chain section engaging, when said jaws are in said closed position, said substantially cylindrical exterior surface of said pipe about a majority of the circumference thereof but not about the full circumference,

e. rollers mounted on said jaws to engage said substantially cylindrical exterior surface of said pipe adjacent said junction regions,

said rollers having peripheral surfaces which are closer to said exterior pipe surface than are said leaf links and said first and second wheels so that said rollers engage said exterior pipe surface and prevent said leaf links and said first and second wheels from being damaged or worn due to forcible compression of said leaf links between said exterior pipe surface and said first and second wheels,

f. power means selectively operable for moving said jaws to said open position thereof and for moving said jaws to said closed position thereof, such that said internal chain section so engages said substantially cylindrical surface of said pipe, and for causing a large tension to be created in said chain, thereby causing said untoothed bearing edge portions of said leaf links in said internal chain section to engage with great force said substantially cylindrical exterior surface of said pipe so received,

said jaws operating, when in said closed position, to hold said pipe in position in said internal chain section, and

g. means to drive said chain, and thus effect rotation of said pipe about the longitudinal axis thereof, when said jaws are in said closed position and said chain has thus been tensioned,

said means to drive said chain including at least one of the wheels in said wheel means,

said one wheel incorporating protuberance means meshing with said protuberance means of said leaf links on said other side of said leaf links,

said means to drive said chain further including power means for rotating said one wheel for causing said protuberance means thereof to react with said protuberance means of said leaf links on said other side of said leaf links and thus advance said chain.

21. A method of rotating cylindrical pipe sections adjacent the wellhead of an oil well, to thereby make or break threaded joints between coaxial pipe sections, which method comprises:

a. providing a closed-loop flexible drive chain comprising a large number of planar alternated leaf links the ends of which are pivotally connected to each other by pivot pins, such leaf links having at one side thereof untoothed bearing edge portions adapted to forcibly engage the pipe surface without damaging the same, and having at the other side thereof protuberance means adapted to be engaged by a driving means,

b. then causing said chain to assume a shape in which it has an external section, an inverse internal section disposed within said external section, and bent portions between said external and internal sections, and has said untoothed bearing edge portions of said leaf links on the inner side of said internal chain section,

c. disposing a cylindrical pipe section in said internal chain section,

d. causing said chain to engage a majority of the circumference of said pipe section, but less than the entire circumference thereof, in such manner that said pipe section is constrained by said internal chain section and prevented from moving out of the same, and creating great tension in said chain to thereby cause said untoothed bearing edge portions of said leaf links in said internal chain section to forcibly engage said pipe section about a majority of the circumference thereof,

e. engaging and moving said protuberance means of said leaf links to thus drive said chain with consequent rotation of said pipe section about the longitudinal axis thereof,

said step of engaging and moving said protuberance means being performed by causing protuberance means on at least one power-operated drive wheel to engage and drive said protuberance means on said leaf links, and

f. preventing from forcibly engaging said pipe section said bent portions of said chain which connect said external chain section and said internal chain section.