Power tongs and control system

Abstract

A control system for power tongs comprises two tongs torque limiters, one of which limits tongs torque to a very low (hand-tight) level; the other limits torque at full makeup to, for example, 2000 ft. lb. The hand-tight torque limiter is manually or automatically disabled after the hand-tight level is reached. The system enables the operator to verify that the threads are properly engaged before applying full torque to the connection. The tongs have a very high reduction ratio, so that torque rises very slowly and can be more accurately controlled.

Description

of to tongs operation, and does not interfere with high torque operation during the final stage of makeup.

The snub line 54 also has mounted therein a second load transducer 61 which communicates via conduit 62 with a Bourdon tube 64 supported within the recorder module B. The free end of the Bourdon tube is connected to the stylus 65 of a conventional chart recorder 66 having a spring-driven motor 68. The stylus has a small blade 70 attached thereto capable of interrupting flow of air through a normally open air gap unit 72, which can be moved toward or away from the stylus by means of threaded support 74 to adjust the threshold makeup torque. The air gap unit is supplied with air regulated to a very low pressure, e.g. 5 psi, so as not to affect stylus position. The output signal is amplified and inverted by the pneumatic logic unit 76, details of which are shown in applicant's copending application Ser. No. 526,611, the disclosure of which is incorporated by reference. The logic unit 76 thus generates a high pressure output in conduit 78--provided the second override valve 80 is open--when the stylus blade 70 enters the air gap as the tongs reach maximum makeup torque. Conduit 78 leads to one input of a two-way check valve 82, the other input of which is from the hand-tight transducer 56. A high pressure at either input is thus delivered via conduit 84 to a second pneumatically actuated shunt valve 86, which when actuated halts tongs operation.

The valve 60, first transducer 56 and shunt valve 86 together provide means for halting tongs operation at a preset hand-tight torque level. Lever 34, linkage 62 and valve 60 function as means for disabling this first means. This general terminology is used in the claims below. The second transducer 61, recording module B and shunt valve 86 comprise means for halting tongs operation at a preset fuel full makeup torque level.

Turning to the torque control module C, it can be seen that the tongs exhaust line 44 is directly connected to return line 22, while the tongs inlet line 42 is variably regulated as to both pressure and flow rate. Fluid entering the module from supply line 20 first encounters a three-way pneumatically actuated valve 88, whose position is ultimately determined by the position of gear selector lever 34. In high gear, fluid is directed to line 90, which is regulated to very low pressure in the range of 25-200 psi by the adjustable pressure regulator 92, which relieves excess pressure back to the return line 22.

When the tongs are in low gear, and valve 60 blocks delivery of control pressure to valve 88, the supply line 20 is connected to a unregulated high pressure line 94 having therein a manually adjustable flow rate controller 96. This valve enables the operator to control maximum tongs speed during the final makeup stage, without affecting the maximum torque obtainable. The variable restriction 98 shunting supply and return lines 20 and 22, on the other hand, enables the operator to limit the pressure deliverable to the tongs. Maximum tongs torque can thus be limited, providing a measure of redundancy over the automatic control system defined between transducer 61 and shunt valve 86.

In operation, as a drill string is supported by slips or the like on a rig deck, a new joint is brought into mating contact with the next lower joint, Once the threads are engaged, the tongs operator, having placed the gear selector in high, throws throttle 50, thereby closing shunt valve 46 to apply regulated pressure from line 42 to the tongs motor, which rotates the pipe slowly at about twenty rpm hand tight. Note that compressed air passes through valve 60 to valve 88, which directs all hydraulic fluid flow past low pressure regulator 92, substantially limiting the torque capacity of the tongs. Furthermore, air pressure is supplied to first transducer 56. When the preset threshold snub line load is reached, air passes through transducer 56, override valve 58 and check valve 82 to open the second shunt valve 86 and automatically stop the tongs. In the event of improper thread engagement, this sequence of events disables the tongs before thread damage occurs, regardless of the operator's attentiveness or reaction time, and corrective action can be taken. It is not necessary, with this system, to count turns of pipe rotation or the like.

Provided the connection is properly run up to hand tight, and the operator can see that the sealing shoulders have come into contact, he then places the gear selector lever in "low", automatically obstructing the high pressure control signal to the second shunt valve 86, which thereupon closes so that tongs operation can be resumed. Simultaneously, the valve 88 reverses position, so that fluid at full pressure is delivered to the tongs. Now developing high torque, the tongs rotate the pipe very slowly--at five rpm or less, and this speed can be regulated by means of valve 96--until the desired makeup torque is reached. At the present cutoff torque level, stylus blade 70 enters the air gap unit, causing logic unit 76 to deliver a high pressure signal to open the second shunt valve 86, thereby automatically halting tongs operation.

The embodiment of the invention described above has proven extremely reliable in testing. The absence of sophisticated electronic monitors, alarms, and the like is attractive from a cost and repairability standpoint, and in fact the torque record charts have demonstrated unequaled consistency from connection to connection.

The foregoing is a description of but one embodiment of the invention, whose full scope is described by the following claims. Various modifications within the scope of the invention may occur to those of skill in the art. For example, electronic components could be substituted for the pneumatic components described. A fully pneumatic system is presently preferred, however, because many rig operators understandably prefer to keep electrical devices of all types away from the rig deck.

Claims

1. A control system for a power tongs comprising a snub line for restraining the tongs,

a first snub line tension transducer for generating signals proportional to tongs torque in the hand-tight range,

a second snub line tension transducer for generating signals proportional to tongs torque in the full makeup torque range,

first means responsive to said first transducer for halting tongs operation at a preset hand-tight torque level,

second means responsive to said second transducer for halting tongs operation at a preset full makeup torque level, and

means for disabling said first means.

2. The system described in claim 1 wherein said tongs have high and low speeds and a gear selector for choosing between said speeds, and

said disabling means is controlled by said gear selector.

3. The system described in claim 2 wherein said disabling means is actuated to disable said first means only when the tongs are operated in the lower of said two speeds.

4. The system described in claim 3 wherein the ratio between said high and low speeds is at least 4:1.

5. The system described in claim 4 wherein the overall gear ratio between the tongs motor and the tongs jaws is about 250:1 in low speed and about 60:1 in high speed.

6. A control system for a power tongs comprising

means for restraining the tongs from rotation,

a first transducer operatively connected to said restraining means for generating signals proportional to tongs torque in the hand-tight range,

a second transducer operatively connected to said restraining means for generating signals proportional to tongs torque in the full makeup torque range,

first means responsive to said first transducer for halting tongs operation at a preset hand-tight torque level,

second means responsive to said second transducer for halting tongs operation at a preset full makeup torque level, and

means for disabling said first means.