Patent Application
20100193197
This invention relates to well site pipe string assembly operations, and bucking units used in plants. More particularly, it pertains to the control of such as the speed, torque, and turn variables used when making up threaded collar and pipe connections.
Pipe strings for installation in wells can be made useless by only one faulty connection. The need for quality control of materials and machining has been recognized. The product is inspectable after each step in the preparation for use. When the pipe is assembled into pipe strings in wells the last inspection has to do with the manner of assembly. After that point the pipe is not accessible for quality assurance.
Turn, as used herein, comprises rotation of one pipe joint relative to the mating joint or fitting. One turn is one revolution. But any rotational movement is turn. Advance is turn toward completion of a connection. Thread run is the number of turns from first thread engagement to final make-up.
Pipe threads are usually tapered but they often have shoulder surfaces or the equivalent in the form of sealing surfaces. A threaded pipe connection may require many turns. The first few turns require little torque but the last few degrees of turn may engage the sealing surfaces and ramp up the torque required for further advance. At that point, only a few degrees of excess turn may ruin a connection. Ruin usually involves compromised sealing surfaces and inward forging of pipe material. Inward forging, or deforming, reduces the bore diameter and may prevent the installation of pipe bore traversing apparatus. In recognition of the critical nature of the pipe connecting process, many pipe sources have provided torque limitations, relative to accumulated turn, in the form of graphs. Such graphs are specific for particular pipe connections. There are several special forms of pipe connections.
Graphs provided by pipe sources are usually torque allowed versus accumulated turns. Lower torque is usually allowed and final torque is defined between limits.
Specific turn and torque requirements sometimes define a few revolutions to be done by hand. That is sometimes defined as a percentage of the final torque allowed, often ten percent. Damaged threads can often be found that way. Damaged or defective threads usually announce themselves by requiring more, or less, than a specific torque to advance after a preselected amount of turn.
Investigations following pipe connection failures often find evidence of human errors or instrument failures. Excess torque damage is often indicated.
Most power tongs are fluid powered and should be capable of maximum torque settings. Torque ramps up suddenly when shoulders are encountered and human operators may need to be fully prepared to limit torque if the tong settings enable overtorque errors.
There is a need to reduce the dependence upon operator alertness to limit torque that often damages pipe connections.
There is also a need to provide a graph reader that can compare standard data to incoming data from torque sensors to automatically limit torque being applied to pipe connections.
Of the parameters usually recorded in real time, temperature and actual flow and pressure of the tong related operating system seems to be neglected. If fluid pressure is used as a redundancy in torque measurement, the temperature, actual flow, and pressure of the torque motor fluid supply should not be neglected. The torque and fluid pressure relationship seems to vary somewhat with temperature. Further, the temperature may be an indicator of impending maintenance problems. Torque reading and recording systems do fail at times and the record of temperature can elevate confidence in pressure related torque readings.
A fluid powered pipe tong fluid supply has a shunt that fluidly connects the tong input fluid line to the tong output fluid line. A flow control valve is installed in the shunt and is open when pipe joint make-up begins. The valve is slowly closed and the resulting fluid power made available to the tong causes it to make the low-resistance turns required of the pipe during the thread run. As the valve continues to close, the resulting pipe turn increases the resistance and causes the tong motor to demand more pressure, to achieve more turn. Torque demand continues to develop as the valve continues to close. If acceptable, the tong can be allowed to race through the low resistance turns. Increasing torque requirements of the connection will stop the race rate. The valve has a pre-set limit to its ability to cause pressure build-up and the tong will provide a maximum torque related to the pre-set pressure limit. Excess torque is never developed and no additional valve shut off is required to limit torque. There are no inertia problems. Options include computer control, a graph reader to direct the computer, a recorder is usually required, a manually set by-pass relief valve to parallel the flow control valve as a secondary pressure limit assurance, and a minor by-pass valve to reduce the torque output for preselected time, then, by re-closing, reapply the previously highest torque. Some users prefer a brief hold at the maximum torque achieved, then a brief drop in torque, held for a short time, then a return to maximum torque achieved. If nothing has changed in the make-up of the connection by those excursions, the connection is acceptable.
From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.
In the drawings wherein like features have like captions,
In the formal drawings some details are omitted in the interest of descriptive clarity. Most complex systems such as computers are “black boxed” in the general relationship to associated parts of the system. The power tong is symbolic, and well known in the art. The pump and related sump are symbolic with many possible options well known to those skilled in the art.
Signal level electric lines (s) near the tong are not usually considered an ignition potential. The computer is usually some distance from the rotary table and the remote data station RDS allows safe on-site communication for control. In some cases, there are fewer safety concerns and the lines labeled s may carry greater power loads. The lines with the enclosed s will probably remain electric but data can be communicated by fluid lines. Piezo detectors and strain gages have reduced signal level flow to near zero and data can move at near the speed of sound in the fluid media. The media is usually liquid, and the fluid signal lines can be quite small and flexible. In cases of higher risk, the data committed communication lines will likely go to fluid systems. That is anticipated by and is within the scope of the claims.
The graph reader is optional and usually feeds comparison data to the computer. Such data is usually provided by pipe suppliers, in graph form, relating maximum allowable torque at accumulated turn positions. Graph readers are available commercially. The computer may contain a graphic recorder.
If the pump is a system committed fluid source, it will feed only a fluid rate that will drive the power tong at an acceptable rate. If the pump is a larger, general purpose, pump it will likely have such capacity that the flow delivered to the tong motor requires flow rate control. The flow control valve FC is optional.
The motor valve MV is controlling a shunt between high pressure HP lines and low pressure LP lines from the pump. The computer controls the motor valve through the controller C, which may be within the computer. The controller responds to signals from the computer to control the motor valve. Ideally, the motor valve will be wide open at the start of a connection make-up and will close as required to allow fluid to be delivered to the tong. The tong cannot develop torque until adequate pressure is supplied by closing the motor valve. Normally the motor valve will be set such that excess torque, as defined by the computer, cannot develop.
If a connection requires too much torque, after a selected amount of turn, two problems are responsible for most such cases. One is thread damage, the other is mis-alignment of the pipe being mated. If the problem is just misalignment, the computer can be programmed to halt proceedings until the suspended pipe can be “wobbled” about to clear the alignment problem. When the problem was encountered, the tong could not develop thread damaging energy. Once cleared, the existing torque will automatically advance the connection. The computer can find that an indication that the connection process can proceed.
If the manual valve is erroneously adjusted and excess torque could be delivered, the pre-set valve PV will open to sap the pump output through the related shunt. No excess torque can be developed.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.
It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims.
As many possible embodiments may be made of the apparatus of this invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
