U.S. patent number 3,722,331 [Application Number 05/154,746] was granted by the patent office on 1973-03-27 for torque-controlled pipe-thread tightener.
This patent grant is currently assigned to IPCUR-Institutul De Proiectari Si Cercetari Pentru Utilaj Petrolier. Invention is credited to Valentin C. Radulescu.
United States Patent |
3,722,331 |
Radulescu |
March 27, 1973 |
TORQUE-CONTROLLED PIPE-THREAD TIGHTENER
Abstract
A device for threading lengths of drill pipe together with
predetermined imum torque or tightening moment to form a drill
string. A mechanical tongs engages the pipe and is angularly
displaced by a pneumatic cathead, a hydraulic transducer being
provided between the cathead and the tongs for generating a
hydraulic signal representing the applied torque. A hydraulically
controlled pneumatic relay is responsive to this signal to release
the cathead when the predetermined torque is attained.
Inventors: |
Radulescu; Valentin C.
(Bucharest, RU) |
Assignee: |
IPCUR-Institutul De Proiectari Si
Cercetari Pentru Utilaj Petrolier (Bucharest,
RU)
|
Family
ID: |
22552609 |
Appl.
No.: |
05/154,746 |
Filed: |
June 21, 1971 |
Current U.S.
Class: |
81/467;
173/164 |
Current CPC
Class: |
E21B
19/166 (20130101); E21B 19/162 (20130101) |
Current International
Class: |
E21B
19/16 (20060101); E21B 19/00 (20060101);
B25b () |
Field of
Search: |
;81/52.4,57.33 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jones, Jr.; James L.
Claims
I claim:
1. A torque-limiting pipe-tightening system, comprising:
mechanical tongs engageable with a length of pipe adapted to be
tightened with predetermined torque;
a pneumatically controlled cathead operatively connected to said
tongs for engularly displacing same;
a hydraulic transducer interposed between said cathead and said
tongs for generating a hydraulic signal representing force applied
by said cathead to said tongs; and
a hydraulic pneumatic relay connected in a control path with said
cathead and connected with said transducer for inactivating said
cathead upon said signal attaining a predetermined value
representing limiting torque.
2. The system defined in claim 1 wherein said relay comprises:
a valve housing provided with a first orifice connected to a source
of compressed air, a second orifice open to the atmosphere, and a
third orifice connected to said cathead, a piston shiftable in said
housing under hydraulic pressure generated by said transducer for
blocking communication between said first and third orifices and
establishing communication between said second and third orifices;
and
a coil spring in said housing bearing upon said piston against the
force of said hydraulic pressure for maintaining communication
between said first and third orifices prior to attainment of the
predetermined value of said signal, said cathead having a clutch
for driving same upon application of compressed air to said
cathead.
3. The system defined in claim 2 wherein said source of compressed
air includes a distributor having a first port connected to a
compressor, a second port connected to said first orifice and a
third port opening into the atmosphere, and means for selectively
connecting said first and second ports and said second and third
ports.
4. The system defined in claim 3 wherein said relay further
comprises a tubular slide received in said housing and
spring-biased in the direction of said piston, said first, second
and third orifices being spaced apart in the direction of
displacement of said piston by said hydraulic pressure, said first
and third orifices communicating through said tubular slide, said
tubular slide having an annular formation adapted to seat against
said housing for blocking flow between said first and third
orifices, said piston axially engaging said slide upon displacement
by said hydraulic pressure.
5. The system defined in claim 4 wherein said relay is provided
with a spindle threaded into said housing opposite said piston and
forming an adjustable seat for said spring, said spindle having an
end extending out of said housing and provided with an adjustment
wheel and indicator means co-operating with said wheel for
displacing the preset limiting torque of the system.
Description
FIELD OF THE INVENTION
The present invention relates to a system for tightening pipe and,
more particularly, to a torque-responsive pipe tightener for
lengths of drill pipe forming a well-drilling string.
BACKGROUND OF THE INVENTION
In the tightening of lengths of drill pipe to form a drill string,
it is a common practice to seize the uppermost length of drill pipe
of the drill string and to position the next length thereover,
while screwing the added length to the previously formed drill
string. The pipe-tightening arrangement includes mechanical tongs
which engage the rotatable pipe length and displace it angularly
with a force generated by a cathead coupled to the tongs, usually
by a flexible member, e.g. a cable.
The pipe joints of lengths of the drill string must be tightened
with a maximum torque which is generally indicated in catalogs and
specifications for the various sizes, configurations and materials
of the drill string to prevent undue stress which may result in
breakage of the string or loosening when the tightening torque is
significantly below the aforementioned maximum. Hence it has been
proposed to provide moment limiters or torque control devices which
permit some slip, lost motion or an interrupted force transfer when
the torque or tightening moment reaches a certain value. For the
most part, these devices have included resilient elements displaced
by the cathead and bearing upon the tongs so as to yield when the
predetermined maximum torque is attained. It has also been
suggested to provide a pneumatic torque limiter for preventing
excess tightening moments from being generated, the pneumatic
system including pneumatic valves which are manually released to
terminate operation of the tongs. These systems have been limited
commercially by their intricacy.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide an
improved system for tightening the pipe of a drill string,
especially an oil-drilling string, with a predetermined tightening
moment or maximum torque.
It is another object of the invention to provide a device,
including a cathead and pipe-engaging tongs, for limiting the
tightening torque applied by the latter to the pipe of a drill
string.
Still another object of the invention is to provide a device for
the purposes described which is of simple and inexpensive
construction, which is highly versatile and adapted to many
existing pipe-tightening installations, which is relatively simple
and free from complex constructions and intricate arrangements of
fluid circuitry, which is accurate and capable of adjustment for
maximum torques within a wide range.
SUMMARY OF THE INVENTION
These objects and others which will become apparent hereinafter are
attained, in accordance with the invention, in a torque-limiting
tightening system for the added lengths of a drill string,
particularly an oil-well drill string, which comprises a set of
mechanical tongs releasably engageable with the pipe lengths to be
tightened, a cathead having a flexible element connected to the
tongs for actuating same and controlled by pneumatic pressure, a
hydraulic transducer interposed between the cathead and the tongs
for generating a hydraulic signal representing the force applied by
the cathead to the tongs and, consequently, the torque applied by
the latter to the pipe, and a hydropneumatic relay connected to the
cathead and responsive to the hydraulic signal for terminating
operation of the cathead when the hydraulic signal attains a preset
value.
According to a more specific feature of the invention, the control
system is constituted by a torque-limiting relay mounted between a
hydraulic transducer located at the point at which the flexible
element of the cathead is applied to the tail of the tongs. The
relay comprises a spring-biased piston to which the hydraulic
signal is applied counter to the spring, the spring being of
adjustable precompression to establish the torque-cutoff threshold.
Advantageously, the relay is a valve having three ports or orifices
including an inlet port at one end of the piston stroke connected
to a source of compressed air, a central port, and a port which, at
the other end of the piston stroke, is connected to a pneumatic
cathead. The central port is open to the atmosphere and constitutes
a vent. The valve arrangement normally blocks the central or vent
port and permits communication between the other ports so that
compressed air is fed to the cathead and the latter is operated to
swing the tongs. As hydraulic pressure develops in the transducer,
representing increasing torque, the piston is biased against the
spring force until it first blocks the compressed-air inlet and
then opens the outlet to the vent port. The valve may consist of
the aforementioned piston and a tubular slide, each biased by a
respective coil spring against the hydraulic force of the
transducer. A threaded spindle arrangement is provided in the relay
for adjusting the prestress of the spring and, therefore, the
torque threshold; the spindle may have a knob or wheel extremity of
the relay housing co-operating with a pointer to indicate the
torque setting of the relay.
DESCRIPTION OF THE DRAWING
The above and other objects, features and advantages of the present
invention will become more readily apparent from the following
description, reference being made to the accompanying drawing in
which the sole FIGURE is a fluid-circuit diagram, illustrating the
principles of the present invention and showing some of the
components of the system in axial section.
SPECIFIC DESCRIPTION
In the drawing, there is shown a length of drill pile 1 adapted to
be screwed onto a drill string by a mechanical tongs generally
represented at 2 and of conventional construction. The tongs 2 and
the cathead 3 are devices conventional in the petroleum-well field
and reference may be had to U.S. Pat. No. 3,021,739, the art cited
therein and the patents of its class for structure relating to
these elements. In brief, the mechanical tongs 2 comprise a tail or
arm 2a having a handle 2b which may be gripped by the operator,
jaws 2c which are articulated to each other and to the handle 2a
and catches 2d which lock the tongs around the pipe. The cathead 3
is of the pneumatic type and may comprise a windlass drum 3a which
may be driven by a shaft 3b from the usual engine or motor. Between
the shaft and the drum, there is provided a pneumatic clutch 3c
which is engaged when the compressed air is introduced into the
chamber 3d through an orifice a. When the air is released, the
clutch is disengaged.
According to the principles of the present invention, the pneumatic
cathead 3 is connected with a hydraulic transducer A by a flexible
element 4 here shown to be a cable whose eye 4a engages the shackle
4b of a piston rod 6 of the hydraulic transducer A.
The transducer A comprises a cylinder 7 closed at its left-hand end
by a threaded cap 8 whose eye 8a is articulated to the arm or tail
2a of the tongs. A port 8b vents the left-hand compartment of
cylinder 7 to the atmosphere. Within the cylinder 7, there is
provided a piston 5 mounted upon rod 6 and defining a chamber 7a in
which the hydraulic control pressure or "signal" is generated. This
signal is transmitted via an orifice b to a line 10 having a
pressure indicator or manometer and running to the orifice c of the
hydropneumatic relay B. Hydraulic fluid may be added to the system
from a reservoir not shown, through a check valve 9 which opens
when the negative pressure is generated in chamber 7a. It will be
apparent that the gauge 11 indicates the instantaneous torque.
The relay B comprises a housing or cylinder 12 which is closed at
its left-hand end and is provided with a cover 19 held by bolts 20
through its flanges, at the right-hand end. The orifice c connects
line 10 with a cylinder chamber 12a behind a cup-shaped piston 13
which is urged to the left against a shoulder 12b of the housing
via a compression coil spring 17 seated against the base of the
cup. The other seat for spring 17 is a shoulder 24a of a threaded
spindle 24 received in the cover 19 and sealed at 22 to prevent
loss of pressure in the relay. The spindle extends outwardly from
the housing at 24b and is provided with a wheel 25 having index
markings 25a co-operating with a pointer 26 to indicate the torque
setting of the relay.
Within the cylinder 12, there is also provided a tubular slide 15
having seals 16 to prevent leakage therepast, the slide 15 being
biased to the left by a spring 18 seated against the cover. A seal
23 prevents leakage past the cover while the face of the cover 19
is formed with a sealing ring 21 which is engageable by a lip 15a
of the slide 15 when the latter is in its extreme right-hand
position. The seal of the piston 13 is represented at 14. Seals 14,
16, 22 and 23 may be conventional O-rings.
The cylinder 12 is formed with three orifices d, e, f, the central
orifice f opening into the atmosphere. The orifice d is connected
via an air line 50 with the orifice a of the pneumatic cathead
while the orifice e is connected by the pneumatic line 51 to a
pneumatic distributor or valve arrangement 27. The distributor is
of conventional construction and is not the subject of the present
invention, but has ports or orifices h, i, j, as shown in the
drawing. The orifice i is connected by a pneumatic line 52 with a
compressed air source while orifice j is connected by line 51 to
orifice e to supply the relay with compressed air. Orifice h is
open to the atmosphere and in one position of the distributor 27
connects line 51 to the atmosphere. It will be apparent that, with
the valve B in the position illustrated in the drawing, compressed
air is delivered via orifice e to the relay B and passes through
the tubular slide 51 around the lip 15a to the orifice d and hence
to the cathead 3 which is thereby placed in operation to tighten
the pipe. When, however, the lip 15a engages the seal 21,
communication between orifice e and orifice d is broken. In this
position, moreover, a channel 15c in the periphery of the slide 15
connects orifice f with orifice e to vent the relay.
In operation, compressed air from source 53 enters the distributor
27 through orifice i and is delivered via orifice j to the relay B
through orifice e and is passed to orifice d to the cathead 3. The
compressed air thus clutches the pneumatic cathead 3 drawing the
cable 4 to the right and rotating the arm 2a of the tongs. Since
the force is applied through the liquid in chamber 7a, a
corresponding pressure is generated in line 10. The hydraulic
pressure is applied to the relay B through the orifice c and is
indicated by the manometer 11. At a predetermined pressure level,
established by the prestress on the spring 17, the piston 13 is
displaced to the right to engage piston 15 and shift the latter
against the seal 21. Communication between the orifices e and d is
interrupted and the orifices d and f are connected to vent the air
to the atmosphere. The release in pressure at the cathead
declutches the latter and prevents application of further
torque.
The spring 17 returns the piston 13 to its original position and
the sleeve 15 enabled to return by connected line 51 to orifice h
by manipulation of the distributor 27.
The system described has been found to be particularly effective
for the uniform and reproducible tightening of threaded joints and
can be used with existing equipment.
* * * * *