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.

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.

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.