The patent's inventors are Pruett, Rick D. (
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "Pipeline pigs for inspecting, servicing, and maintaining pipelines are typically moved along the interior of the pipeline under pressure. Absent any speed control, the pig travels at essentially the same rate of speed as the pipeline fluid propelling it. In many cases, the speed of the pipeline fluid exceeds the desired range in which the pig is most effective for its intended use. In addition, pipeline debris and build-up may slow the pig below a desired minimum speed, thereby requiring means for increasing pig speed. Therefore, various speed control means have been developed. Some are 'passive' control devices, using only pressure flow. Others are 'active' control devices, using electronics or electrical actuators.
"Prior art passive speed control devices may be classified into two broad categories: valve-actuated control devices and passageway-adjusted control devices. Both categories of speed control devices work by altering the amount of bypass flow through the body of the pig. An example of an early valve-actuated control device is disclosed in U.S. Pat. No. 2,860,356. A hollow valve member having a front and rear set of ports is received by a sleeve located at a forward end of the pig. If the pig encounters resistance to its movement and slows, a pressure increase at the rearward end of the pig causes the valve member to move farther into the sleeve, thereby blocking the front ports and reducing flow through the valve and, therefore, increasing bypass flow though the pig. The reduced flow through the valve further increases the pressure differential across the pig and, therefore, the speed of the pig increases. By allowing more bypass flow through the pig when the pig stalls, debris may be flushed out of the way to allow the pig to start again. The valve, however, does not prevent the pig from stalling, nor does it prevent speed surges above that of the pipeline fluid propelling the pig.
"Other valve-actuated control devices employ increasingly sophisticated active control means for operating the valve. None of those control means, however, prevent the pig from stalling or controlling speed surges. For example, U.S. Pat. No. 3,495,546 discloses the use of a valve that is opened or closed by a large piston coupled to a solenoid responsive to changes in line pressure. Actuation of the piston moves the valve, thereby controlling the degree of opening in a bypass port. A more sophisticated control means, such as that disclosed in U.S. Pat. No. 6,098,231 places a sleeve-type valve in communication with a microprocessor. The microprocessor monitors pig speed and, when speed falls outside a predetermined range, the microprocessor sends a signal to extend or retract a hydraulic actuator connected to the valve. By controlling the actuator, a portion of the sleeve is drawn over, or removed from, a set of circumferential exit ports, thereby increasing or decreasing flow through the pig.
"As to the second category of speed control devices, passageway-adjusted, U.S. Pat. No. 4,769,598 provides a typical example. Two perforated discs rotatable in relation to one another are mounted external to the pig body in an annular space between the front sealing elements. The degree of alignment in the perforations in the two discs permits the speed of the pig to vary by allowing more or less fluid to flow through the interior passageway of the pig. Similar to the above patent is U.S. Pat. No. 6,190,090, which discloses the use of a first and second bonnet. Each bonnet has several openings and is mounted to a forward end of the pig. A stepper motor and controller vary the degrees of alignment in the bonnets and, therefore, regulate bypass flow through the pig.
"Another example of an active passageway-adjusted device is found in U.S. Pat. No. 5,208,906, which discloses the use of a set of longitudinal passageways through the interior of the pig and a set of movable plates that adjust the flow through the passageways. The plates are typically adjusted by a step motor and controller which are, in turn, controlled by a comparator circuit that compares the actual speed of the pig with the desired speed.
"With the exception of U.S. Pat. No. 2,860,356, all of the above speed control devices rely upon sophisticated control means for either varying the position of the valve or the alignment or size of the passageways to shunt bypass flow. U.S. Pat. No. 2,860,356, however, requires the use of multiple valves in large pigs and in high velocity pipeline applications; therefore, it--along with the other prior alt devices--is not optimized for maximum speed reduction of the pig. Additionally, none of the prior art devices prevent stalling or surging. When the pig stalls, significant pressure may build up behind the pig and cause the pig to surge to speeds even higher than the average fluid flow through the pipeline. This is problematic, for example, in dispersal-type pigs.
"A dispersal pig is configured to move fluid (gas and liquid) forward in advance of the pig and includes one or more nozzles located at a forward end of the pig. Differential pressure across the pig allows the gas flow to draw liquid into the nozzle and a spray of liquid is formed and ejected from the nozzle opening. Although the dispersion method generally results in an improved coating application of the interior cylindrical wall of the pipeline, an inability to control the amount of bypass flow, and therefore control the maximum flow rate through the nozzle, erodes the effectiveness of the dispersion. The high velocity of product passing through the nozzle may stall the pig, resulting in pressure buildup behind the pig that causes the pig's speed to surge far above the speed at which it effectively disperses the liquid. Therefore, a need exists for a device to provide maximum speed reduction and prevent stalling and surging of the pig without reliance upon sophisticated control means.
"Likewise, in the case of a cleaning type pig, optimum speed for effective cleaning may be significantly slower than the average flow in high-flow pipelines. A large amount of bypass may slow the pig and cause it to stall, especially as debris builds up in front of the pig. This stalling may result in pressure build-up and surging (as described above), resulting in high pig velocity and skating over portions of the debris. Again, a means to minimize the duration of stalling, pressure build-up, and surging is needed."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "A pipeline pig made according to this invention has a longitudinal pig body with a forward end, a rearward end, a central passageway, and a plurality of external circumferential seating elements in sealing engagement with a pipeline. The central passageway includes a venturi preferably concentric to the pig body. The venturi may be provided by a nozzle affixed to the forward end of the pig. A modulating valve, which is also preferably concentric to the pig body, is located rearward of the inlet side of the venturi. The venturi, modulating valve, or both may be non-concentric to the pig body. The modulating valve has an open or withdrawn position and a closed (or partially closed) or extended position relative to the venturi. When the modulating valve is in the open position, a predetermined maximum bypass flow is allowed through the venturi. If this maximum bypass is exceeded due to the pig stalling, the valve substantially instantly moves to the closed position. The closed position allows a predetermined minimum bypass flow through the venturi in order to substantially immediately start the pig moving again before significant pressure builds up behind the pig. The valve then substantially instantly moves to the open position. This prevents the pig from surging to speeds higher than the average fluid flow.
"The predetermined maximum bypass flow may result in a speed reduction of the pipeline pig to a relatively small percentage of the average fluid flow velocity in the pipeline. Larger body pigs are likely to have greater speed reduction possibility than smaller body pigs. The predetermined minimum bypass flow may be set to cause an acceleration of the pig to a speed below that of the average fluid flow.
"The modulating valve may be a poppet-style valve having a compression or tension spring, a plate, and an insert. The plate and the insert each has a plurality of ports that allow bypass flow through the plate and insert, respectively. The face of the plate may be substantially flat or substantially the same shape as an interior surface of the venturi. When the valve is closing, the plate extends toward the inlet side of the venturi to reduce bypass flow to the minimum bypass flow.
"The modulating valve may also be a frusto-conical shaped valve or stopper. The stopper has sufficient mass to overcome the spring force holding the modulating valve in its open position. When the pipeline pig stalls, the valve closes and the stopper chokes bypass flow through the venturi to the predetermined minimum bypass flow. The peripheral surface of the stopper preferably has substantially the same shape as the interior surface of the venturi. When the pig starts running again, the valve opens as inertia forces the stopper away from the inlet side of the venturi. The use of a mass damper device may also minimize any 'bouncing' effect of the stopper.
"A better understanding of the invention will be obtained from the following detailed description of the preferred embodiments taken in conjunction with the drawings and the attached claims."
For the URL and additional information on this patent, see: Pruett, Rick D.; Strong, Robert F.; Freeman,
Keywords for this news article include: Electronics, Microprocessors,
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