Tools – Tool jaw – Jaw-actuating means
Reexamination Certificate
2000-10-11
2002-01-01
Smith, James G. (Department: 3723)
Tools
Tool jaw
Jaw-actuating means
C081S057340, C081S057360
Reexamination Certificate
active
06334376
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the application of torque forces to an object engaged by a wrench. More particularly, the present invention relates to the application of angular torque forces to a pipe that is being threadedly engaged to, or disengaged from, another pipe with the use of a hydraulic power tong.
2. Description of the Prior Art
Long strings of joined pipe sections are required for the drilling and completion of oil and gas wells. The pipe string is assembled by screwing together pipe sections, or “joints,” typically 30-40 feet in length to make a long, continuous string of pipe that is lowered into the well as the joints are added. The joints are typically equipped with male “pin” threads at one pipe end and female “box” threads at the other pipe end. The string is extended by screwing the pin of the joint being added into the box at the top of the string.
During the early days of the drilling industry, the pipe string was screwed together in a two-step process using a “spinning rope” and a wrench called a “rig tong.” One end of the spinning rope was wrapped around the joint being added to the string, and the opposite end was loosely wrapped around a rotating “cathead” powered by the drilling rig. An operator pulling on the tail end of the rope increased the friction of the wraps around the cathead causing the rope to spool over the cathead, pulling the rope away from the joint. A second operator simultaneously restrained the tail end of the rope wound on the pipe to force the pipe to rotate as the rope pulled toward the cathead, spinning the joint pin into the string box. The final makeup torque was applied to the connection using the rig tong, which was also pulled around the joint by the cathead rope.
Hydraulically powered wrenches, called “power tongs,” were developed to replace the spinning rope and manual rig tongs. Power tongs typically include a tong body that surrounds the pipe to be rotated. The tong body carries a hydraulic motor driving a gear transmission connected to a rotary drive that engages and rotates the pipe. The rotary drive is generally equipped with appropriately sized jaws that are selectively actuated by the tong operator to grip the pipe to force the pipe to rotate with the rotary. The tong body is prevented from rotating around the pipe by attaching a restraint, or “snub line,” between the tong and a support structure that is fixed relative to the angular motion of the joint being added to, or removed from, the string. In some cases, the support structure is the pipe string extending into the well, in which case an “integral backup tong,” designed to grip the string to provide the required restraint, is also carried by the power tong body.
The torque generated by the power tong is monitored by measuring the force required to restrain the tong from rotating. If the snub line and the centerline of the tong are at a right angle with respect to each other, the torque applied to the pipe is equal to the measured force times the “tong arm” length. The tong arm length is the distance between the point of attachment of the snub line (or integral backup tong) to the tong body and the centerline of the engaged pipe. The power of the motor and the gear ratio of the transmission connecting the motor to the rotary determine the maximum torque that can be generated by a conventional rotary power tong.
In a typical application, the hydraulic power tong is used to rotate a pipe joint to screw the threads at one end of the joint into mating threads on another joint. Pipe sections having threads such as employed in many proprietary thread designs may be screwed together with very little initial torque until the shoulders in the thread profiles of the two connections engage. Once shoulder engagement occurs, the torque required to properly secure the connection increases substantially above the torque required to rotate the connection to the point of shoulder engagement. Following engagement of the shoulders, very little additional rotation occurs until the desired torque for the connection is obtained.
Most conventional systems used to automatically operate the tongs employ a control signal that bypasses, or “dumps,” the hydraulic fluid pressure acting on the tong motor to disable the tong drive system when a desired torque value is sensed. Usually, the dump signal occurs suddenly while the tong motor is generating a high torque force. The weight and momentum of the typical tong prevent it from reacting instantaneously to the dump signal so that the torque applied to the engaged tubular body will frequently exceed the desired minimum torque value.
Another problem with conventional hydraulic power tongs is that the tongs may not provide sufficient power to release (break out) a connection that is made up to a high torque value. This may occur, for example, because the breakout torque of the connection is greater than its makeup torque. When specifying the type of tong to employ for such an application, it is necessary to specify a tong with a higher torque capacity than that required only to make up the pipe. Generally, the greater the torque required for a given job, the larger and more expensive the tong required to perform the job. A related factor is that the space available on most drilling or workover rigs is limited, and it is desirable to keep the equipment size as small as possible while still maintaining the ability to perform the required work.
U.S. Pat. No. 4,938,109 to Torres et al., assigned to the inventor of the present invention, discloses a hydraulic tong system that includes a power tong equipped with an auxiliary power mechanism that applies a force to the tong body to apply torque to the pipe through the stalled tong motor and transmission. The auxiliary power mechanism is preferably a hydraulic piston-cylinder assembly that can be extended or retracted to apply, and hold, the desired torque to a pipe gripped in the tong rotary.
While the Torres et al. system may be used to increase the maximum rated output of the power tong, it is generally used for applying torque to a connection where the desired optimum torque value is well below the maximum torque that can be applied by the tong motor. In such applications, the system is very effective in precisely applying the desired torque for most pipe connections; however, when the pipe is being made up to very low torque values, such as are required in the connections of fiberglass pipe and some other special pipe connections, the tong's transmission and motor are sometimes moved in reverse as the auxiliary power mechanism moves the tong body in a direction to increase the torque exerted on the gripped pipe. This typically occurs when the final makeup torque for the pipe is so low that it is necessary to limit the hydraulic pressure driving the motor to a level at which the tong motor stalls at a torque that is too low to resist the reverse forces acting through the transmission.
U.S. Pat. No. 5,161,438 describes a power tong that locks the rotary and the housing to prevent the rotary from turning in reverse as the housing is being pivoted with respect to the rotational axis of the rotary. A bolt (or bolts) is used to inhibit the relative rotation. A piston-cylinder arrangement is used for pivoting the housing. All torque generated in the patented system is transmitted through the main rotary gear of the tong.
SUMMARY OF THE INVENTION
An integral pipe brake mounted on a rotary power tong grips the pipe as a hydraulic piston-cylinder assembly applies angular force to the tong body. The torque applied to the pipe by the piston-cylinder assembly exceeds that internally generated by the tong. The brake isolates the main rotary gear and transmission from the externally generated torque and prevents the tong body from rotating relative to the pipe while the piston-cylinder assembly is angularly displacing the tong body.
The pipe brake may be actuated to engage automatically once the piston-cylinder assembly is actuated, or the brake may
Bushman P.C. Browning
Smith James G.
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