Torque-controlled pipe-thread tightener

[57] ABSTRACT

A device for threading lengths of drill pipe together with predetermined maximum 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.

Claims, 1 Drawing Figure

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PATENTEDMAR27IS73

3,722.331

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3,7ί 1

TORQUE-CONTROLLED PIPE-THREAD TIGHTENER

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 welldrilling 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 25 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 &gt;2,331 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 inter⁵ posed between the cathead and the tongs for generating a hydraulic signal representing the force applied by the cathead to the tongs and, consequently, the totque applied by the latter to the pipe, and a hydropneumatic relay connected to the cathead and responsive to the ¹⁰ 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 ₂₀ signal is applied counter to the spring, the spring being of adjustable precompression to establish the torquecutoff 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 per30 mits 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 ³⁵ 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 40 f°^{rce tlle} 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 ₄₅ 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 50 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 55 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 mechani^υ cal 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 ₆₅ 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 2ά having a handle 2b which may be gripped by the operator, jaws 2c which

3,722,331 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 5 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, ¹⁰the pneumatic cathead 3 is connected with a hydraulic transducer A by a flexible element 4 here shown to be a cable whose eye 4α engages the shackle 4b of a piston rod 6 of the hydraulic transducer A.

The transducer A comprises a cylinder 7 closed at its ¹⁵left-hand end by a threaded cap 8 whose eye 8α 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 ₂₀piston 5 mounted upon rod 6 and defining a chamber 7α 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 25 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 7α. It will be apparent that the gauge 11 indicates the instantaneous torque. 30

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 12α behind a cup-shaped piston 13 ³⁵which is urged to the left against a shoulder 12h 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 24α 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 24h and is provided with a wheel 25 having index markings 25α co-operating with a pointer 26 to indicate the torque setting of the relay. ₄₅

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 50 formed with a sealing ring 21 which is engageable by a lip 15α 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 / 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 15α to the orifice d and hence to the cathead 3 which is thereby placed in operation to tighten the pipe. When, however, the lip 15α 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 2α of the tongs. Since the force is applied through the liquid in chamber 7α, 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/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.