Note: Descriptions are shown in the official language in which they were submitted.
" ~15~Z3~
BACK-UP POWER TONGS AND METHOD
_ackground
This invention relates to means and methods for
securing a pipe member and the like against axial rotation, and
more particularly relates to ilnproved back-up means and methods
for connecting and disconnecting drill pipe of the sort
commonly employed to drill oil and gas wells.
It is well known that oil and yas is found in subsurface
eartll formations, and that boreholes are drilled into these
formations to recover these substances. What is not so well
known, however, are the problems and difficulties which attend
the drilliny of such boreholes, and consequently the peculiarities
and requirements which must be met.
In the first place, such wells are often thousands
of feet deep in the earth, and therefore t'ne mere drilling
of such wells is a technological challenge, not only with
respect to cutting away rock and soil of various character at
different depths, but also the need to remove the drill
cuttings being produced at the bottom of the borehole. Accordingly,
it is now conventional to drill such wells usiny a bit or
cutting tool which is suspended at the end of a tubular string
of lengths of pipe. More particularly, the drill bit is rotated
at the bottom of the borehole by rotation of the string of drill
pipe at its upper end, while suitable drilling fluids or "muds"
are pumped down the interior of the drill string and out
through apertures in the drill bit.
The drilling mud or slurry serves various essential
purposes, in addition to lubrication of the cutting surfaces of
the drill bit. The mud which flows down the interior of the
drill string, returns to the surface by way of the annular space
between the wall of the borehole and the outside surface of the
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234
dril1 striny, to carry away the drill cuttings which would
otherwise accumulate in the borehole. Thus, the drilling mud
also serves as a lubricant between the wall of the borehole
and the striny of revolving drill pipe. Furthermore, the
weight of the column of drilling mud in the borehole provides
a back-pressure in the event that the drill bit unexpectedly
encounters a formation containing fluids under an abnormally
high pressure.
The string of drill pipe is necessarily assembled at
the surface on a piece-by-piece basis, wherein each length or
"joint" of drill pipe is selectively connected to the upper
end of the last joint previously added, as the string is
proyressively lowered into the borehole. Similarly, each
time it becomes necessary to repair or replace the drill bit,
(which occurs many times during the drilling of deeper boreholes),
the string of pipe is progressively lifted out of the borehole
as the topmost joint of pipe is removed.
Although there are many difficulties attending
the drilliny of a borehole in the earth, there are particular
difficulties which relate to the making and breaking of the
threaded couplings between the joints of drill pipe. Since
drill pipe tends to lose wall thickness as it is revolved in
the borehole, it is undesirable to apply any significant
gripping force to a joint of drill pipe lest this effect a
crushing which, in turn, tends to produce a longitudinal weakening
in the pipe. On the other hand, it is essential that sufficient
torque be applied to the pipe to achieve a fluid-tight connection
between each two joints of pipe, to avoid a pressuri%ed discharge
of drilling fluid which erodes the wall of the borehole, and
this in turn necessitates the application of a heavy gripping
force. In an atternpt to compromise these two conflicting needs,
1151~234
most drill pipe is now formed with a box-like portion at one
end, the "box" being provided with extra-heavy wall thickness
and with inside threads, and with an extra-heavy wall thickness
immediately adjacent the exterior threads at the other end.
Provision of a wall thickness of this magnitude will, even for
drill pipe haviny a severely eroded exterior, permit the pipe
to resist compressional forces which might otherwise crush
the pipe but which are necessary to apply adequate torque to the
pipe in making and breaking the threaded connections between
two joints of drill pipe. Nevertheless, this has further
necessitated that the pipe be seized only at the two end
portions having an extra-heavy wall thickness, and under no
circumstances at any other place along each joint of drill pipe.
Originally, the drill string was assembled and
disassembled using two sets of manually operated pipe tongs,
wherein one set was applied to the "box" portion of the pipe
at the upper end of the drill string in the borehole, and the
other set was applied to the lower end (immediately above the
threads) of the pipe being added or removed from the drill string.
The upper set of tongs was conventionally interconnected by a
cable and torque gauge to a powered winch, and the lower set
of tongs was connected oppositely thereof through a cable to
a point of anchorage on the drilling rig. When the winch was
activated, the connecting cable would turn the so-called
"pipe tongs" to rotate the upper joint until the torque
gauge registered the torque considered to effect a fluid-tight
seal, (during make-up of the drill string), or to break the
threaded connection in the case of disassembly of the drill
string. The snubbing cable attached to the lower tongs
would, of course, secure the lower tongs and thus the box
portion of the lower joint of drill pipe from rotation during
this process.
3~51:)~34
It will readily be apparent that such a process
was time consuming and therefore expensive. More particularly,
however, it was o~ten extremely dangerous because of the possibility
of cable breakage, and this possibility was increased when the
so-called "manual" tongs used to rotate the upper pipe joint
were replaced by hydraulically-actuated rotating tongs of the
type depicted in U.S. Patent No. 4,084,453, in order to achieve
even higher torques prescribed for threaded connections in
deeper boreholes.
Another disadvantage to such techniques, even after
hydraulically-actuated rotary tongs came into widespread use,
arose out of the inaccuracy of the measurement being provided
by the torque gauge now interconnected with the snubbing
cable. More particularly, it was long recognized that the
torque gauge would accurately indicate the torque on the pipe
only when the two cables were positioned to define force vectors
which, in turn, were positioned at exactly 90 degrees of each
other, and that this condition would only exist momentarily
as the upper pipe was revolved. Thus, the problem of
achieving a fluid-tight seal between adjacent lengths of
drill pipe continued to exist even after the adoption
of powered rotary tongs.
In so~e instances it has been found useful to
couple the so-called "manual" back-up tong to the powered
rotary tong assembly, whereby the two sets of tongs might
be handled and operated as a unit, and whereby the drill
string could be more quickly and conveniently connected and
disconnected. In such an arrangement, of course, the two
tongs tend to be snubbed together whereby at least one of the
two cables were eliminated. Even this has become impractical
'q ~Sq;~Z34
with the need to develop increasingly higher torques by the
rotary tong assembly, however, which were beyond the yripping
capability of conventionally designed "manually-operated" tongs.
Accordingly, there has long existed a need for powered back-up
tongs which can develop a gripping force on the box portion of
the drill pipe which is capable of immobilizing the drill
string against the torques now required to obtain a fluid-tight
pipe connection.
There have, of course, been many attempts to develop
powered back-up tong assemblies having this capability,
although all such attempts have been less than completely
successful. One significant problem, which has prevented
the use of designs similar to those incorporated in the rotary
powered tong asse-,nbiies, has been the need to locate the back-up
tongs at the box of the lower drill pipe and therefore immediately
below and in close proximity to the lower surface of the rotary
powered tongs. Another problem arises from the fact that,
although a combination of the rotary and back-up tongs may
eliminate the snubbing cables, the combined tong assembly is
itself a hazard in the event of unscheduled vertical movement of
any portion of the drill string.
These and other disadvantages of the prior art are
overcome with the present invention, and improved powered
back-up tongs are herewith provided for interconnection and
use with powered rotary tongs.
Summary of Invention
In a preferred embodiment of the present invention,
a powered back-up tong assembly is provided having a pair of
oppositely movable jaw members which are arranged to be radially
~l~Z34
driven into grippiny enyayement with the box portion of a joint
of drill pipe. ~ore particularly, the two jaw members are
supported by a pair o~ upper and lower plate members shaped
substantially in conformance with the general configuration
of the rotary tong assembly, and having an open throat portion
~or receiving and fitting the two jaw members about the pipe
member sought to be secured against rotation.
Each jaw member is interconnected with its own
separate driving assembly which, in a particularly suitable
form, includes a hydraulic cylinder pivotally anchored at lts
rearward end between the two plate members, and having its
piston rod hingedly connected to one end of a pivotally anchored
lever having its other arm urged against the jaw member. Since
both cylinders are sought to be cooperatively actuated, whereby
both jaw members are driven in synchronism, hydraulic power
is supplied to the cylinders through a flow divider so that
both piston rods are extended in unison and through the same
distance. Thus, both jaw members are extended exactly the
same distance so as to avoid warping or misalignment of the
drill pipe at the same time the rotary tong assembly (which
is linked to the back-up tongs) is applying tor~ue to the
pipe assembly.
It will be apparent that, although the back-up
and rotary tong asser,lblies are intended to be interlinked
as a unit, the connection between the two must be flexible
within prescribed limits. Furthermore, such flexibility
must not only perMit limited movement in the direction of
application of the torque to the pipe member, but also limited
movement between the two tong assemblies along the longitudinal
axis of the drill string.
115~234
Referriny more particularly to the matter of linkage
of the two tong assemblies, the rotary tong assembly is
preferably provided with three downwardly extending rod members
which, in turn, are each preferably provided with a plurality
of pin apertures at various locations along their length.
The back-up tony assembly, in turn, is conveniently provided
with corresponding apertures through which these rods will
extend when the back-up tony assembly is positioned immediately
below the rotary tong assembly. A shear pin is inserted
through the aperture in each rod, which thereby selects the
maximum vertical spacing sought to be maintained, and the
back-up tong assembly then rests on these three shear pins.
In addition, a spring or other resilient means is preferably
disposed between the shear pin and the under surface of the
top plate of the back-ùp assembly, to absorb impact when the
back-up tong assembly is drawn against the rotary tong assembly
as the two sections of drill pipe are screwed together.
Similarly, the springs tend to soften the reaction when the
two tong units separate, as by removal of a section of drill
pipe from the drill string.
With respect to lateral movement between the two
units, the holes to be provided in the back-up tong assembly
are preferably formed in the manner of arcuate slots having
a radius of curvature and position corresponding to rotation
about the pipe string. More particularly, each unit is also
provided with a rearwardly extending bracket member which tend
to be urged toward each other when the rotary tong assembly
applies torque to the pipe member, and thus a suitable torque
sensor may be arranged to be compressed between th&se two
brackets to provide an extremely accurate measurement of the
torque applied to the pipe member unless the rods move against
the ends of the slots.
--8--
1~5~234
It sometimes happens that the operator of the winch
(not depicted), which supports the upper joint of drill pipe 4,
will activate and lift that joint of drill pipe after it has
been unscrewed from the box yripped by the back-up tongs, but
before it has been released by the rotary tong assembly.
Similarly, it will sometimes happen that the slips in the
rotary table will fail to hold the drill string, and if the
tong assemblies are gripped to the drill string, or even if
only the back-up tongs are then gripped to the drill string,
this may cause both tong units to be carried away from their
suspension means. In both cases, this creates an extreme
risk to personnel in the vicinity r by virtue of the collapse
of several thousand pounds of equipment onto the drilling
platform, and is another reason why powered back-up tonys
have not previously been considered desirable.
In the present invention, this disadvantage is
substantially overcome by the fact that, in either of these
cases, the shear pins will sever to separate the back-up
tong assembly from the rotary tong assembly. If the operator
has inadvertently prematurely activated his winch, as in
the first example, this will merely lift the rotary tong
assembly free of the back-up tongs without other misadventure.
If the drill striny begins to collapse into the borehole,
as in the other example, this may carry the back-up tong
assembly to the floor of the drilliny rig, but the rotary
tong assembly will be freed to remain in its normal positon.
Accordingly, one aspect of the present invention seeks
to provide improved back-up tongs and method for securing
a pipe member ayainst rotation by powered rotary tongs and
the like.
5~Z34
It is also an aspect of the present invention to
provide improved hydraulic powered back-up tongs and method.
It is further an aspect of the present invention to
provide improved hydraulically-actuated back-up tongs for
securing drill pipe and the like against a high rotational
torque.
It is further an aspect of the present invention to
provide improved back-up tong means and method for cooperating
with powered rotary tongs to develop a more accurate measurement
of torque being applied to a pipe member and the like.
It is also an aspect of the present invention to
provide improved back-up tong means releasably interconnectable
with powered rotary tongs and the like.
In its broadest aspect the invention pertains to an
apparatus for securing a pipe member against axial rotation,
comprising a body member having an open throat portion for
receiving the pipe member, first and second gripping members
within the body member each linearly and radially movable toward
a pipe member received in the throat portion and first and
~0 second powered cylinder means, each operationally interconnected
with one of the gripping members for urging the gripping
members into engagement with the pipe member. Power supply
means are connected to both the first and second cylinder means
for simultaneous activation of the gripping members, and first
and second pivotally mounted lever means is each respectively
interconnected between the gripping members and the first and
second powered cylinder means for increasing the force exerted
on the pipe member by the gripping members in response to
activation by the power supply means.
These and other aspects and features of the present
invention will become apparent from the following detailed
description, wherein reference is made to the Figures in the
accompanying drawings.
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Z34
In The Drawings
Figure 1 is a simplified pictorial representation
of powered rotary and back-up tongs embodying one form of
the present invention.
Figure 2 is a sirnplified pictorial top view,
partly in cross section, of the back-up tongs depicted
generally in Figure 1.
Figure 3 is a similar side view of the same
back-up tongs depicted in Figure 2.
Figure 4 is a similar bottom view of the same
back-up tongs depicted in Figures 2 and 3.
Figure 5 is a pictorial view, partly in cross
section, of a selected portion of the apparatus depicted
in Figure 3.
Figure 6 is another pictorial view, partly in
cross section, of another different portion of the apparatus
depicted in Figure 3.
f Figure 7 is a schematic diagram of the hydraulic
circuits and components depicted in part in Figure 2.
-- 11 --
- ~5~234
Detailed Description
_
Referring now to Figure l, there may be seen a
simplified pictorial side view of apparatus embodying at least
one concept of the present invention, and including a suitable
rotating power tong assembly 2 disposed about an appropriate
location along the length of a joint of drill pipe 4. In
addition, and located immediately below, there is provided a
back-up power tong assembly 3 of the type hereinafter described
in detail. The rotating power tong assembly, which operates to
apply rotational torque to the length of drill pipe 4, is
preferably provided with a plurality of support rods 5 which,
in turn, extend fixedly down in parallel with the drill pipe.
The back-up power tong assembly 3, therefore, will preferably
be provided with suitable apertures whereby it may be disposed
about these support rods 5, to provide for a minimum gap 14 or
spacing between the rotating power tongs 2 and the back-up
power tong assembly 3.
At the lower end of each of the support rods 5, there
is preferably provided a plurality of suitably spaced-apart
apertures through which a shear pin 6 may be inserted. Between
the shear pin 6, and the back-up power tong assembly 3, there
is preferably provided a suitable washer 9 or other appropriate
retaining means, and a suitable spring means 7, whereby the
back-up power tong assembly 3 is supported in close proximity
to the underneath surface of the rotating power tong assembiy 2.
Referring again to Figure l, it may be seen that the
back-up power tong assembly 3 is preferably provided with a
rearwardly extended bracket ll which supports an appropriate
torque sensor lO. In addition, the rotating power tong assembly 2
is also provided with an appropriate bracket 12 which extends
down to drive laterally and rotatably against the torque sensor lO
-12-
~5~Z34
whenever the rotating power tong assembly 2 is actuated to apply
rotational force or torque to the joint of drill pipe 4. Since the
back-up power tong assembly 3 is designed to immobilize the length
of drill pipe 4, each of these brackets 10 and 12 tend to be
driven together, to not only cooperatively snub both the rotating
power tong assembly 2 and the back-up power tong assembly 3,
whereby they do not revolve dangerously about, but whereby they
cause the torque sensor 10 to provide an appropriate indication
of the amount of torque being applied therebetween, (and also
consequently to the length of drill pipe 4).
It should be noted that the function of the shear pin 6
is not only to provide for coupling of the back-up power tong
assembly 3 to the rotating power tong assembly 2, but also to
act as a safety release in the event these two components
inadvertently separate. More particularly, it sometimes happens
that the drill string (in this case represented by the portion
of the drill pipe 4 which is gripped by the back-up power tong
assembly 3) tends to drift downwardly into the bore hole due to
failure of the slips in the rotary table ~not depicted). Although
the rotating power tong assembly 2 is appropriately supported
by suspension from above (by means not depicted in Figure 1), such
suspension cannot carry the weight of the drill string, and thus
there is an immediate danger that two power tong assemblies 2 and 3
may be brought down with attendant risk of injury to personnel
in the immediate vicinity. However, the shear pins 6 are intended
to sever in such an eventuality, thereby relieving the rotating
power tony assembly 2 from the weight of the drill string represented
by the length of drill pipe 4, whereby only the back-up power tong
assembly 3 will descend to the floor of the drilling platform
(not depicted). If the back-up power tong assembly is then
actuated to engage the length of drill pipe 4, the rate of descent
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~S~234
of the back-~p power tong assembly 3 will be no more rapid than the
rate of descent of the drill pipe 4 into the bore hole.
. Similarly, it sometimes happens that the operator of the
winch (not depicted) which supports the upper end of the drill pipe 4
will actuate and raise the pipe after it has been unscrewed from
the lower yortion oE the pipe 4 which is gripped by the back-up
power tong assembly 3, but beEore the rotating power tong assembly 2
has been disconnected from the upper end of the pipe 4. In this
event, both of the power tong assemblies 2 and 3 would be carried
dangerously upwardly except that the shear pin 6 will sever to
disengage the back-up power tong assembly 3 from the rotating
power tong asseMbly 2. Since the winch'(not depicted) is easily
capable of supporting the rotating power tong assembly 2, as well
as the single joint of drill pipe 4 being gripped thereby, this
greatly minimizes the risk of injury to the adjacent personnel.
Referring now to Figures 2-6, there may be seen simplified
pictorial views of the back-up power tong assembly 3 generally
depicted in Figure 1, and further showing that this assembly
includes a suitable top plate 20 with elongated arcuate
slots 15 for containing the three support rods 5. In addition,
there is a washer 8 or other suitable retaining means interposed
between the upper end of each spring 7 and the lower surface
of the top plate 20, for the purpose of engaging the upper plate 20.
It will be noted that the elongate arcuate configuration
of the slots 15 provide for sufficient movement of the rods 5,
whereby the brackets 11 and 12 may be brought toyether to cause
the plunger lOA, of the torque sensor 10, to provide an accurate
indication of the torque developed between the power tong assemblies
2 and 3 when the rotating power tong assembly 2 is actuated to
rotate the pipe member 4, but not such that slots 15 will limit
such travel prior to reaching the torque desired, and to then provide
a false reading of the torque actually applied to the pipe member 4.
-14-
~5g~234
Referring ayain to Figures 2-6, it may be seen that the
back-up power tong assembly 3 is provided with an open throat
portion 21 whereby the rotating tong assembly 2 may be inserted
about the pipe member 4. ~ore particularly, the throat portion 21
is a space formed by the upper and lower plates 20 and 54, and rnore
particularly by the spacing between the guide blocks 21A-B which, in
turn, cooperate with a bracing block 42 to provide slidable support
and guidance for a pair of jaw members 22 and 23 adapted to
be driven into gripping engagement with the pipe member by
levers 28 and 29. More particularly, the left jaw member 22 may
be seen to be provided with a pin 26 and rotatable bushing 24
which, in turn, is urgeably engaged by the lever 28 which, in turn,
is pivotally interconnected with the left hand end of the bracing
block 42 by means of pivot pin 30. Rotation of the lever 28
about pivot pin 30 is affected by the driving assembly composed
of the hydraulic cylinder 38 having its piston rod 36 and clevis
member 34 interconnected with the opposite end of the lever 28
by hinge pin 32. In addition, cylinder 38 is hingedly fixed
between the upper and lower plate members 20 and 54 by hinge pin 40,
whereby extension of the piston rod 36 will rotate the lever 28
in a counterclockwise direction to drive the left hand jaw member 22
against the pipe member 4.
Similarly, the right-hand jaw member 23 is provided
at its opposite end with a rotatable bushing 25 which, in turn,
is disposed about pin 27, whereby the right-hand jaw mernber 23
may be driven against the pipe member 4 by clockwise rotation
of the right-hand lever 29 about pivot pin 31 which, in turn,
is interconnected with the opposite end of the bracing block 42.
More particularly, rotation of lever 29 is affected by the driving
assembly composed of the hydraulic cylinder 39 which is pivotally
fixed between the upper and lower plate members 20 and 54 by
~5~23~
pivot pin 41, and which has its piston rod 37 interconnected with
the opposite end of the right-hand lever 29 by means of clevis
member 35 and hinge pin 33.
Operation of the back-up power tong assembly 3 may be
achieved by an actuating valve 61, which is schematically shown
in Figure 7, to connect hydraulic power through fluid supply
line 60A and 48, -to an appropriate flow divider or equalizer
device 47, and thence equally through check valves 45 and 46 to
extend lines 43 and 44 leading to the extend ports of the hydraulic
cylinders 38 and 39. Extension of piston rods 36 and 37 will,
of course, be accompanied by return flow of the hydraulic fluid
through return lines 49 and 50, and thence by way of the fluid
supply line 51 to the hydraulic fluid supply 60 which is shown
schematically in Figure 7.
It should be noted that the jaw members 22 and 23 are
not only driven slidably between the bracing block 42 and the left
and right-hand guide blocks 21A-B to securely engage the pipe
member 4, but that such engagement is maintained by the check
valves 45-46 unless and until the actuating valve 61 is intentional-
ly repositioned. More particularly, it is the function of the checkvalves 45 and 46 to trap hydraulic fluid within the extend lines
43 and 44 whereby the piston rods 36 and 37 are maintained in
their extended position regardless of whether hydraulic pressure is
present in lines 43 and 44. Alte~natively, however, when it is
intended to retract the piston rods 36 and 37 to release the jaw
members 22 and 23 from the pipe member 4, it will be seen in Figure
7 that the actuating valve 61 may be positioned so as to apply hyd-
raulic power through intake line 51 r and to reconnect line 48 to
the return line 60B leading to the hydraulic power source 60 as
indica-ted in Figure 7. Accordingly, the arrival of hydraulic
power through line 51 will not only connect hydraulic fluid through
lines 49 and 50 to the return ports of cylinders 38 and 39, such
power will also be applied through lines 52 and 53 to release the
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234
check valve 45 and 46, whereby hydraulic fluid may now returnthrough lines 43 and 44 to line 48, and may thereafter flow
through the actuating valve 61 to the return line 60s of the
hydraulic power supply 60.
As hereinbefore stated, it is essential that maximulll
travel of the jaw members 22 and 23 be provided for, due to the
fact that the pipe member 4 (and especially that type of pipe
employed to compose a drill string), be securely engayed against
rotation by the rotating power tong assembly 2. It will thus be
noted that the travel limits of jaw members 22 and 23 will not
only be determined by the configuration of the bracing block 42
and the left and right-hand guide blocks 21A-B, but also by the
position of the pivot pins 30 and 31 between the opposite ends
of the two levers 28 and 29. In other words, the greater the
spacing be~ween pins 30 and 32 in the lever 28, and also between
pins 31 and 33 in lever 29, the lesser the travel of the two
jaw members 22 and 23 upon extension of the piston rods 36 and 37.
More particularly, however, the greater the spacings between
pins 30 and 32, and between pins 31 and 33, the greater the
driving force which may be applied to jaw members 22 and 23 by
levers 28 and 29, to thereby reduce the size of the hydraulic
cylinders 38 and 39 needed to affect back-up engagement of pipe
meMber 4.
As hereinbefore stated, it is a primary function of the
bracing block 42 to provide for slidable support for the jaw members
22 and 23. In addition, however, the bracing block 42 also
interconnects the two forkedly extending portions of the top and
bottom plate members 20 and 54 which define the throat portion 21
of the back-up power tong assembly 3, whereby these portions are
prevented from spreading when the jaw members 22 and 23 are
subjected to an opposing force from the rotating power tong
assembly 2, and whereby the jaw members 22 and 23 may become
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1~5~Z34
disenyaged from the pipe member 4. It should be noted, however,
that maximum spacing between pins 30 and 32, and between pins 31
and 33, may require that the bracing block member 42 be provided
with concave aperture 21C to accommodate the pipe member 4.
Referriny now to Figure 4, it will be noted that the
bottom plate 54 does not extend about the two rods 5 on the
opposite sides of the open throat portion 21, and that the
arcuate aperture 55, which surrounds the rearward rod 5, is
substantially larger than its corresponding aperture 15 in the
upper plate. The reason for this is that it is the upper plate
20 which carries the entire weight of the back-up tong assembly 3,
therefore there is no need to extend the lower plate 54 about
any portion of the front pair of rods 5. Further, since the
back-up tony assembly 3 is intended to be released entirely
from the rods 5 upon severing of the shear pins 6, it is
essential that the arcuate aperture 55 in the lower plate 54
be larger than the washer 8, whereby the back-up tong assembly 3
may drop free of all portions of the rotary tong assembly 2.
As hereinbefore stated, it is intended that the levers
28 and 29 function to drive the jaw members 22 and 23 into
gripping engagement with the pipe member 4, upon e~tension of
the piston rods 36 and 37. It will therefore be noted, in
Figure 4, that a suitable spriny means is preferably included
to retract the jaw members 22 and 23, upon retraction of the
piston rods 36 and 37 into the cylinders 38 and 39. More
particularly, the spring means is indicated by spring 56,
which is shown in Figure 4 as interconnected at one end to
pin 27, and at its other end to an appropriate portion of
either the upper or lower plates 20 and 54. Accordingly, when
lever 29 is rotated to drive jaw member 23 into engagement
with the pipe member 4, this will elongate the spring 56.
--1~3--
~ 15S3234
When lever 29 is rotated away from bushing 25, however, spring
member 56 will contract to withdraw jaw member 23 from engagement
with the pipe member 4. A similar spring means is preferably
interconnected with jaw member 22, but is not specifically
indicated in Figure 4.
Referring ayain to Figure 2, it will be noted that,
in this type of back-up tong assembly, no rotational force or
torque is inherently developed merely by engagement of the
pipe member 4 by the jaw members 22 and 23, inasmuch as the
gripping force is generated, in the first instance, by extension
of piston rods 36 and 37. In the case of the rotary tong
assembly 2, however, this unit will develop a tendency to
revolve oppositely the direction of torque which is applied
to the pipe member 4, and in the case where a section of
pipe is sought to be added to the drill string, this torque
will tend to develop in a counterclockwise direction. Accordingly,
in such an operation the rearward bracket 11 tends to snub the
revolving rotary tong assembly 2, and further to support the
sensor 10 against compression of the sensor piston lOA by the
bracket 12 of the rotary tong assembly 2.
This will, of course, be reversed during break out
length of drill pipe from the drill string, since the rotary
tong assembly 2 will tend to revolve in an opposite direction
when unscrewing drill pipe. Thus the two bracket members 11
and 12 will tend to separate, rather than to draw together,
and thus no torque measurement will be provided by the sensor 10.
This is inconsequential, however, since a torque measurement is
only required to indicate when sufficient torque has been
generated during interconnection of the length of drill pipe
in the drill string, and since torque is only required in a
magnitude sufficient to break apart a threaded joint when the
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Z34
drill string is being disconnected. It will also be noted that,
during disassembly of the drill string, the two bracket members
11 and 12 will no longer snub each other toyether. However, this
~unction will be performed by the rods 5 moving within the
arcuate slots lS in the top plate 20.
As hereinbefore stated, a back-up tong assembly of the
type hereinbefore discussed is particularly suitable for use
with drill pipe which, although relatively small in outside
diameter, requires applications of very high torque both to
interconnect and disconnect the threaded connections, by reason
of the particular arrangement of levers and hydraulically
actuated piston rods. However, a back-up tong assembly of
this type is clearly not limited to use with only drill pipe,
but is particularly useful with any type of threaded members sought
to be connnected or disconnected, and especially with respect
to well tubing joints and lengths of sucker rod and the like.
In addition, embodiments of the invention may be often useful
for many larger sizes of tubing or pipe, such as threaded well
casing, line pipe, and the like.
It will be readily apparent from the foreyoing
description that modifications and substitutions of components
may be made without departure from concept of the present
invention. Accordingly, it should be understood that the
structures and techniques hereinbefore depicted and described
are intended as examples only and are not intended as limitations
on the scope of the invention.
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