Pipe Tongs

Abstract

A pair of tongs are suspended above the rotary table of an oil well, their jaws aligned to grip pipe which is screwed together, or unscrewed, in sections. The jaws of the tongs are actuated by a fluid-powered mechanism to obviate manual manipulation. The tongs are mounted and arranged so they may be swung with the pipe sections and kelly between a rotary table and a mousehole.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to powered tongs for the sections of well drill pipe to be threaded together or unthreaded. More specifically, the invention relates to automation of certain functions of the tongs which increase their effectiveness and ease of operation.

2. Description of the Prior Art

Abortive attempts have been made to produce a power system for automation operation of well pipe tongs which will be generally acceptable in the industry. The only use of power generally accepted has been applied with driving cables or chains between tongs and catheads on the drawworks, or hoist. It remains preferable to manually manipulate tongs into position for the break-out and make-up operations of the tongs.

Conventional tongs depend upon a compound-over-center lever system to furnish the gripping power necessary for torque in the range of 5 to 50,000 ft./lbs. Counterweight suspension of the tongs is helpful to personnel, but one man is required for each tong for basic positioning. However, the dies of the tong jaws which actually grip the pipe surface are not applied uniformly from their rigid mounting in jaws of fixed dimensions. It is seldom that tong jaws and pipe dimensions match to give the uniform application of tong force which will minimize the crushing effect of their force on the pipe. Then, when the pipe size varies so greatly from the jaw size that it is necessary to change jaws, two men are required to lift the jaw parts and manually make the change.

There is need for tong structure which will apply its dies uniformly to the pipe. There is need for the dies to be mounted in jaw structure which provides articulation of the die structure in the tong to gain uniform contact with the pipe and ready replacement of one size die with another by one man to accommodate various pipe sizes. The dies of prior art tongs are not readily changed to accommodate pipe of various diameters, but are mounted rigidly upon the tong jaws to accommodate limited ranges of pipe diameters.

The prior art tongs have also not been adapted and arranged to be bodily transported with the pipe sections. In other words, the section to which a new section is to be joined, or broken off, could not have prior tongs kept about it in preparation for the make-up or break-off operation. By and large, prior art tongs have been mounted at a fixed location to which new sections of pipe must be brought for make-up to other sections or from where broken-off sections must be moved.

There is need for a mounting structure for tongs which will apply the tongs from one side of the pipe to obviate a bending moment on the pipe as held by the slips which will bend and notch the pipe.

There is need to provide lead tongs which can be wrenched in either of their two directions from a cable linked to a single cathead at a fixed location.

There is need for a hydraulic system to automatically vary the tong force on the pipe during the break-out and make-up wrenching by the tongs.

SUMMARY OF THE INVENTION

A principal object of the invention is to adjust, or articulate, the die positions in tong jaws to enable the dies to uniformly contact the pipe gripped by the tongs.

Another object is to readily replace one size of die with another to preserve the uniform contact between the dies and pipes of varying diameters.

Another object is to mount powered tongs so they may swing with a pipe section between more than one location for make-up and break-off operations with other sections.

Another object is to operate powered tongs from one side of pipe sections made-up and broken-off to obviate the pipe being damaged.

Another object is to provide an arrangement including a powered cathead at one location, a cable and vertical member with which a wrenching force can be applied to the movable tong in either of two directions from the cathead.

Another object is to provide fluid force for setting tong dies which fluid force is automatically adjusted when the tongs make-up and break-off connections.

The present invention contemplates one tong, or a pair of tongs, mounted to pivot between two laterally-spaced locations. The tongs can be opened to release or grip pipe sections at either location or remain about a kelly bar which is swung to disconnect from a pipe section at one location to connect with a pipe section at a second location. In oil well drilling, the tongs can be used to make mousehole connections between a kelly bar and a pipe section which is to be added to a string of drill pipe.

The invention provides a vertical member located relative to a pulling source of power in order to provide a means with which a cable between the source and movable tong can be arranged to reverse the direction with which a wrenching force can be applied from the source to either make-up or break-off pipe sections.

The invention contemplates that the make-up, or break-off, tong be rotated with power from a piston-cylinder link which generates a fluid pressure force on the tong dies proportional to the make-up, or break-off, torque applied to the tong.

The invention further contemplates the dies being mounted in holders which are linked together with a resilient member. The holders are held by this resilient in recesses of shoes which are an integral part of the tong jaws. The retaining force of the resilient member can be manually overcome to remove the dies and their holders for service, repair or replacement.

Other objects, advantages and features of this invention will become apparent to one skilled in the art upon consideration of the written specification, appended claims, and attached drawings, wherein;

FIG. 1 is a plan view of a tonging machine in which the present invention is embodied;

FIG. 2 is a front elevation of the tonging machine in which both lead tong and the back-up tong grip pipe sections threaded together;

FIG. 3 is a plan view of the tonging machine with the top frame plate of the back-up tong removed and the tong gripping a pipe section with its dies;

FIG. 4 is a plan view of the lead tong with its jaws open and moving into engagement with the pipe;

FIG. 5 is a diagrammatic representation of the fluid-actuated control circuit for the tonging machine;

FIG. 6 is a plan view of the tonging machine positioned to break-off the kelly and swing with the kelly to a pipe section in the mousehole boot;

FIG. 7 is the plan view of FIG. 6 with the lead tong cocked and ready to be wrenched up;

FIG. 8 is a plan view of the tong jaw dies engaging a pipe section of relatively large diameter;

FIG. 9 is a sectioned elevation along lines a--a in FIG. 8;

FIG. 10 is a plan view of the tong jaw dies engaging a pipe section of relatively small diameter; and

FIG. 11 is a perspective elevation showing an alternate arrangement for retaining dies in tong jaws.

DESCRIPTION OF THE PREFERRED EMBODIMENT

General Plan of the Disclosure

Compatible with universal practice, I utilize two tongs to make-up and break-out pipe in an oil well. FIGS. 1 and 2 show the lead tong 1 and back-up tong 2 positioned to make-up or break-out pipe sections 3 and 4. The tongs are pivoted in parallel planes about the vertical axis of a cable 5. This support structure, including the cable 5, will be described in more detail infra.

The tongs are pivoted between laterally spaced locations. FIGS. 6 and 7 show the tongs pivoted between the well and mousehole. In this way the kelly can be broken-off a section of drill pipe in the slips and kelly and tongs pivoted to make-up to a section in the mousehole. The tongs then, although automated in their movement and operation, are flexible in being adapted for use at different laterally spaced locations. Sections threaded together can be tonged to make-up and break-off at each of the laterally spaced locations.

Although some vertical movement is provided for the tongs pivoting in their parallel planes, the range is limited. It is desirable that both powered tongs grip the pipe to be broken-off from the same side of the pipe. If the sidewise stress of tonging with tongs spread too far apart, the pipe section 4 could be bent and notched. This damage could cause immediate failure of the pipe section or subsequent failure when far below the ground surface.

FIGS. 3 and 4 disclose the tongs have essentially the same actuating mechanism for latching their jaws to grip pipe sections and set the dies on the pipe sections with the required force. FIG. 3 shows the back-up tong 2 gripping pipe section 4. FIG. 4 shows the lead tong 1 with its jaws open to receive pipe section 3. At this place in the disclosure, the feature emphasixed is the arrangement for wrenching tong 1.

Tong 1 is either wrenched from the position disclosed in FIG. 4 and FIG. 6 or from the cocked position disclosed in FIG. 7. The present invention enables a cable from a single cathead (indicated at 7 in FIG. 1) to wrench tong 1 in either direction. The direct pull of FIG. 6, or the indirect pull of FIG. 7, can be carried out from the single cathead 7.

The jaws are powered from fluid-actuated cylinders. These cylinders are disclosed in FIGS. 3 and 4. Latching cylinder 10 of back-up tong 2 opens and closes the tong jaws. Die set cylinder 11 places the desired force on the closed jaws to set the dies on the surface of pipe section 4. Comparable cylinders function in lead tong 1 to accomplish similar latching and die setting. The control system to actuate the cylinders is disclosed in FIG. 5.

The dies of the tong jaws are disclosed in FIGS. 8-11. The dies 12, 13 and 14 are each fitted into recesses of the tong jaws. The dies have a range of movement within these jaw recesses which enable them to adjust their actual contact with the surface of the pipe section. The contact becomes uniform, even, to give the jaws a highly efficient and consistent grip on the pipe surface.

FIG. 11 illustrates how each die could be retained in its jaw recess by a pin. However, it presently appears advisable to provide a resilient spring member connected to each set of dies. The force of this spring member is directed to maintain the dies in their respective recesses yet the spring and attached dies be manually removable for dies of different size when desirable.

Tong Suspension

FIGS. 1 and 2 disclose the tong suspension in detail. FIG. 2 discloses the rotary table 20. Slips 6 are in position about pipe section 4. On this level, a support frame 21 is indicated for cable 5. Journalled over cable 5 is a rider post 22.

Post 22 forms a pivot base for the tongs 1 and 2. Back-up tong 2 is connected to post 22 through a slotted bracket 23. Tong 2 is basically supported by a hanger 24 attached to the post 22 at one end and extending its other end to beneath the tong 2 at about its center of gravity. A lift cable 25 extends up to a counterweight above.

Tong 1 is also supported from a cable 26, counter-weighted and attached to tong 1 over its center of gravity. The post end 27 of tong 1 is shaped to engage post 22 as disclosed in FIG. 1.

Control of End 27

The end 27 of tong 1 is also controlled from a cable 28. With the powered cathead 7, jerk cable 28 exerts a force on tong 1 which wrenches it in either of the two directions required to cooperate with back-up tong 2 in breaking out and making up pipe sections 3 and 4. Attaching cable 28 to tong end 27 and pulling end 27 away from its FIG. 1 position is easily understood. Movement of end 27 from post 22 will break-off pipe section 3 threaded to section 4. Cathead 7 is powered from drawworks not necessary to disclose in FIG. 1. Cable 28 turned about cathead 7 will pull cable 28 and tong end 27 away from post 22. FIG. 4 and FIG. 6 both disclose this simple wrenching movement of tong 1.

How is the one cathead 7 then utilized to move cocked tong 1 toward post 22? FIGS. 1, 2, 4 and 7 all disclose how the invention provides this powered movement of tong end 27. The same cable 28 is led from cathead 7 around post 22 and attached to tong end 27. A snub line 29 is connected to post 22 to counter the force cathead 7 exerts on post 22 through cable 28. Then the cathead 7 will pull tong end 27 from its cocked position of FIG. 7 to the FIG. 1 position. Pipe section 3 will thereby be made-up to section 4 through their threaded engagement.

General Tong Movement

The suspended tongs move relative to post 22 in planes parallel to the drilling floor. They are very heavy, bulky objects, but suspended as they are they can be manually swung into position to engage pipe sections as required.

Of course there is always need for some vertical adjustment of the tongs in getting them coupled to, and uncoupled from, pipe sections. The height required over the well might not precisely match the height required over the mousehole. Slotted bracket 23 provides a limited range of vertical adjustment for tong 2 relative to tong 1. Rider post 22 positions vertically over the limited range provided by cable 5 to give the desired position of both tongs above the slips 6. With the tong height above the slips limited, and both tongs actuated from one side of the pipe, the sidewise stress placed upon the pipe by the tongs is minimized. The result is small opportunity for the pipe to be damaged by bending and/or notching in the slips.

Also, it is to be noted that, contrary to prior art power tongs, the tongs 1 and 2 move from over the well to over the mousehole to make-up and break-off pipe. The tongs move from one lateral location to another lateral location under the suspension provided. No prior art power tong has provided this degree of flexibility in use at different lateral locations.

Basic Jaw Arrangement

FIGS. 3 and 4 disclose the power structure for jaw actuation. FIG. 3 discloses the jaws of tong 2 closed and latched about pipe section 4. FIG. 4 discloses the jaws of tong 1 open to receive pipe section 3. The jaws of both tongs operate in the same manner with the same arrangement of parts.

In final analysis, the jaw structure of the tongs engages the outer surface of their pipe sections with the teeth of dies 11, 12 and 13. These dies are placed uniformly about the circumference of the pipe section and forced into the pipe surface as hard as necessary to hold the pipe during the wrenching operation of the lead tong.

The dies are held in jaw parts which are pivoted to open and close relative to the pipe sections. More specifically, long dieholder jaw 40 is pinned at 41 to the frame 42 of tong 2. When the dies are set into pipe surface, the far end of jaw 40 is against pin 43. So braced, this long die-holder jaw is formed with the strength to match the force exerted by short jaw dieholder 44 which sets die 11 into the opposite surface of the pipe section. Jaw 44 is pivoted about pin 45 to engage and disengage die 11. Pin 45 is mounted on frame 42, giving both pivot pin 41 and pivot pin 45 a common base.

There is no reason to separately designate the tong jaw parts as between tong 1 of FIG. 4 and tong 2 of FIG. 3; both sets perform the same function in the same way. The jaws are open in FIG. 4 and they are closed in FIG. 3. The basic jaw arrangement and function can be understood by comparing the two drawings.

Jaw Actuation

The tong jaws are opened and closed by fluid pressure. This source of power is utilized through cylinder-piston combinations to actuate the jaws.

FIG. 4 discloses short jaw dieholder 44 pivoted to its extreme clockwise position about pin 45 to carry die 11 away from a pipe section surface within the jaws. Latch member 46 is pinned at its intermediate section to the lower end of short jaw 44. Latching cylinder 10 rotates latch 46 about its pin 47; in FIG. 4 latch 46 has been rotated clockwise to carry hooked end 48 away from engagement with pin 49 of latch link 50.

Latch link 50 is pinned to latch lever 51 near pivot pin 52. Pin 53 is placed but a short distance from pivot pin 52 in order to develop a large mechanical advantage by die set cylinder 11 which is connected to the opposite end of latch lever 51.

Once latching cylinder 10 is powered to extend its piston and rotate latch 46 into engagement with pin 49 of latch link 50, the jaws are closed. FIG. 3 discloses this arrangement. Die set cylinder 11 is then actuated to extend its piston and rotate latch lever 51 clockwise about pivot pin 52 to carry latch link 50 and its pin 49 to the right as viewed in FIG. 3. It is the force exerted by cylinder 11, through the mechanical advantage of the lever system, that provides the desired force on the dies in their engagement with the pipe section.

The jaws are unlatched by first powering cylinder 11 to retract its piston, shorten the combination. Connected latch lever 51 is rotated counterclockwise about pivot pin 52. Latch link 50 is carried to the left, as viewed in FIG. 4. Next, the cylinder-piston 10 may also be shortened and latch 46 pulled from the FIG. 3 position to the FIG. 4 position. The jaws are thereby opened, opened to release a pipe section or to receive a pipe section. Thus, the tong jaws are actuated automatically by applying fluid power to cylinders 10 and 11 in the proper sequence. FIG. 5 discloses the control of the fluid power source. Further, the added control feature is disclosed wherein the power applied to the die set cylinders of the tongs is automatically increased as cable 28 is pulled by cathead 7 to wrench the lead tong.

Increased Die Force During Wrenching

Heretofore, I have spoken of the control of tong end 27 as being from a cable linked to a cathead. However, it could well be feasible to mount a powered piston-cylinder to exert the required force on this tong end. I want it clearly understood that my invention is not limited to a cable-cathead embodiment of this power source.

Returning to the cable-cathead disclosure, a piston-cylinder combination 60 is included as a link to end 27. Cable 28 is connected to the cylinder and cable 28 is, in effect, continued to connection with tong end 27. This continuation of cable 28 is designated as 28A to avoid confusion.

In further clarity, cable 28 has been provided with alternate connections to tong end 27. The piston of 60 can be connected directly to end 27 as disclosed in FIGS. 4 and 6. The piston can be connected to one end of cable 28A and the other end of cable 28A can be connected to tong end 27 as disclosed in FIGS. 1, 2 and 7. In both events, piston-cylinder 60 is a link to which the cathead force is applied in trying to extract the piston from the cylinder.

As the piston of 60 is drawn from the cylinder, fluid beneath the piston is forced out of the cylinder and applied to the die set cylinders 11 of both tongs. This additional force, proportional to the force applied by the cathead, is applied through the linkage of 51, 50 and 46, to short jaw dieholder 44. The result is that the force applied by the dies in the jaws is increased during wrenching of the tongs proportional to the wrenching force applied to the tongs.

Fluid Control Circuit

Up to now, I have disclosed the piston-cylinder combinations and their relations with the tongs' components. The actuation of the cylinder-piston combinations has been generally referred to as by a source of fluid pressure. FIG. 5 brings the source and cylinder-piston combinations into a system for analysis.

Latching cylinder 10 and die set cylinders 11 are manifolded together so that fluid pressure can be simultaneously applied to the ends of each set of cylinders to extend or retract the pistons of each set as desired in the required sequence.

A source of air pressure is connected to line 61. Manually controlled valve 62 controls this fluid pressure to either side of the pistons of 10 to latch and unlatch the jaws of both tongs.

Manually controlled valve 63 is also connected to the fluid pressure source. Valve 63 is connected to cylinder-piston combination 11 to retract their pistons. Line 64 is manifolded to the cylinders 11 to carry out this retraction. However, the valve 63 is also connected to the other side of the cylinders 11 through a system which includes a reservoir of liquid 65. The liquid of reservoir 65 is connected to the second side of cylinder 11 and when fluid flows from the reservoir to the cylinders 11, their pistons are extended. In general, then, valve 63 is manually operated to withdraw the pistons of 11 as part of the unlatching of the jaws. The valve 63 also extends the pistons after the jaws are latched to apply the desired force to the dies.

The hydraulic fluid of reservoir 65 is a link to piston-cylinder 11 which can also be linked readily to the cylinder-piston 60 in cable 28. This connection is clearly disclosed in FIG. 5. Check valve 66 between 65 and 60 prevents 60 from forcing hydraulic fluid up into 65 when the wrenching of cable 28 places additional force on the dies through cylinders 11.

It is evident, from the drawing, that valve 63 directs the air pressure of conduit 61 to the top of cylinder 65 when it is desired to extend the pistons of 11 to apply die force. It is not so evident what happens, when valve 63 is operated to apply air to 11 to retract the pistons. The hydraulic fluid must be vented from the cylinder of 11. Check valve 66 must be unseated to allow passage of the hydraulic fluid from 11 to 65. This unseating is done by the air pressure of conduit 64. A line 67 is indicated as connected between conduit 64 and valve 66 to upset the element of valve 66 and vent fluid from 11 back into cylinder 65.

Die Force Intensified

Piston-cylinder 60 is disclosed to best advantage in FIGS. 6 and 7. As disclosed in those Figs., 60 always functions to intensify, or increase, the force on the dies by piston-cylinder 11. As force is applied to cable 28 by cathead 7, the piston is withdrawn from 60. The fluid beneath the piston is forced from the cylinder and applied to the pistons of 11.

The piston-cylinder 60 may be connected directly to end 27 as disclosed in FIG. 6 or it may be connected between cable 28 and 28A. In both cases, the force applied to 11 is the same; a force proportional to the wrenching force from cathead 7. In FIG. 7, cable 28A is led around rider post 22 to wrench the lead tong 2 in the makeup of the pipe sections.

In all events, rider post 22 is braced against displacement by the wrenching. In FIGS. 6 and 7, it can be clearly seen how cable 29 is connected to post 22 to resist its displacement by the force applied by cathead 7 through cable 28. Cable 29 is connected between some stable anchor point not shown and post 22. The length of cable 29 is great enough to permit the tongs to move over their vertical range without becoming a factor in its sole functions of keeping post 22 stable against the stresses of cable 28 transmitting the cathead force.

Dies

FIGS. 8-11 disclose the specific die form used here to demonstrate a broad principle. FIG. 8 disclosed the tong jaws with recesses therein to receive dies 11-13. Basically, the dies are round in their cross-sections; FIG. 8 discloses this clearly. The dies do not have a tight fit in their recesses, but are free to rotate as viewed in FIG. 8. This articulation, a possible rocking motion, enables the dies to accommodate a large range of pipe section diameters.

By accommodate, I mean the teeth of the dies that actually contact the pipe section surface are positioned to evenly contact the pipe surface and give maximum gripping between the two. At the same time, accommodation is provided while cable 70 is connected to the back of each die. The cable 70 is flexible to the degree necessary to provide the accommodation, yet stiff enough to positively urge the dies into seating within their respective recesses.

FIG. 9 discloses cable 70 as it fits between jaw halves while connected to the dies. FIG. 10 discloses how the cable permits the die 11 to move with jaw 44 while being urged into seating within its recess of jaw 44. Also, FIG. 10 illustrates how dies for a smaller diameter of pipe section for a smaller diameter of pipe section than disclosed in FIG. 8 can be connected to a cable 70 and be carried in the same jaw recesses as the FIG. 8 dies. The cable 70 is flexible enough for one man to bend and remove one set of dies from the jaws and replace the dies by another size. The FIG. 8 dies can be readily replaced by one man with the dies of FIG. 10. No longer is it necessary for more than one man to change the entire jaw. The dies can simply be changed.

However, I do not want to transmit the impression that only a cable 70 is employed to provide removable dies. FIG. 11 discloses how a die 71 can have a bracket 72 mounted on its back surface and a pin 73 can capture the die bracket, the pin held by holes in the jaw. I have not yet concluded the most practical form of die retention structure for the invention. However, the more desired form will provide articulation with retention and yet be readily replaceable.

CONCLUSION

I want to emphasize what should now be some obvious features of my invention. Although I have disclosed a pair of tongs to grip pipe sections in the make-up and break-off operations, a single tong could be used. The slips could function as a holding structure while a single tong is wrenched in alternate directions by the source of power.

All of the unique features described in association with one of the pair of tongs disclosed could be embodied in a single tong. The reversible direction of wrenching from a single power source, the hydraulic system for increasing jaw force as wrenching force increased and the die-jaw arrangement; all these and other features disclosed are useful with a single tong, the pipe section being held by slips, or equivalent structure.

From the foregoing it will be seen that this invention is one well adapted to attain all of the end and objects hereinabove set forth, together with other advantages which are obvious and inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the invention.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted in an illustrative and not in a limiting sense.

Claims

The invention having been described, what is claimed is:

1. A pair of pipe tongs, including,

a base member vertically extended and connected with the back-up tong of the pair of pipe tongs so as to enable the back-up tong to pivot in a horizontal plane and to at least two laterally spaced locations where there are pipe sections to be threaded together and unthreaded,

a support structure for the lead tong of the pair of pipe tongs which is provided and arranged for the pivot of the tongs about the base member as the tongs wrench pipe sections to make-up and break-off the sections at each of the laterally spaced locations,

a source of power capable of wrenching the lead tong in make-up and break-off; and

a link adapted and arranged with the power source and lead tong and including a flexible cable detachably connected by one end to the lead tong and to a powered cathead as a source of power by the other end, the cable being selectively connected directly between the tong and cathead and conducted from the cathead around the vertical base member to the tong, such arrangement enabling the tong to be wrenched in either of its two directions of movement relative the back-up tong.

2. The tongs of claim 1, including,

a piston-cylinder combination included in the link; and

a hydraulic system to actuate the jaws of the tongs and connected to the piston-cylinder combination to develop a setting force on the tong dies proportional to the wrenching force applied to the lead tong from the power source.

3. A pipe tong, including,

a pair of jaws,

means for actuating the jaws to grip and release a pipe section between the jaws,

dies mounted in the pair of jaws, the dies shaped to fit recesses of the jaws so as to provide a range of articulation for each die in a horizontal plane to accomodate pipe sections of various pipe diameters as the dies engage each of the pipe sections; and

a flexible cable connected to all the dies so as to exert a seating force on the dies in the jaw recesses loosely enough to permit the articulation of the dies but maintain the dies in their recesses during the complete cycle of gripping and releasing pipe sections, the dies and connected cable being manually removable and replaceable as as a unit.

4. The tong of claim 3, including,

means connected to the jaws for hydraulic actuation of the jaws of the tong through the complete cycle of gripping and releasing pipe sections as the sections are made-up and broken-off.

5. The tong of claim 4, in which the means for hydraulic actuation include,

a first cylinder-piston combination connected to one jaw and a latch to open and close the jaws on a pipe section and open and close a latch for the jaws,

and a second cylinder-piston combination connected to the latch to place a desired force on the dies through the latch as a link.

6. A pipe tong, including,

a frame member in the form of a flat plate,

a pair of jaw members pivoted on the frame toward and away from a pipe section to be gripped by the jaw members,

a first piston-cylinder mounted between the frame and one of the jaw members so that reciprocation of the piston will move the one jaw member toward and away from the other jaw member,

a second piston-cylinder mounted on the frame member; and

a latch between the one jaw member and the second piston-cylinder which latch is engaged when the first piston-cylinder moves the one jaw member toward the other jaw member to grip a pipe section, extension of the second piston-cylinder increasing the gripping force by the jaws through the latch.

7. The tong of claim 6, including,

a fluid control system for the first and second piston-cylinder combinations which can be manually controlled to sequentially latch the jaws to grip a pipe section and increase the gripping force of the jaws followed by relief of the gripping force and unlatching of the jaws.