Abstract:
A pumping unit is provided that controls fluid pressure in a pipe being traversed according to the degree of resistance encountered by a pig traversing the pipe under fluid pressure. Increasing fluid pressure in constricted areas enables an intelligent pig to traverse the pipe with a more uniform speed by controlling the fluid velocity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119(e) of provisional application No. 61/025,149 filed Jan. 31, 2008. 
    
    
     FIELD OF THE INVENTION 
     Pipe cleaning methods and apparatus. 
     BACKGROUND 
     Oil refineries frequently include many kilometers of pipes that require cleaning, as for example in fired heaters, where oil is heated during the refining process. One well established cleaning technique is to run a pig through the pipes under hydraulic pressure to clean the pipes. Pigs are typically polyurethane or strangulated foam cylinders or balls that are studded with scraping elements. The inventor has been a pioneer in the art of pigging, and has obtained U.S. Pat. No. 6,569,255 for a Pig and method for cleaning tubes, U.S. Pat. No. 6,391,121 for a Pig and method for cleaning tubes, U.S. Pat. No. 6,359,255 for a Pipe inspection device and method, U.S. Pat. No. 6,170,493 for a Method of cleaning a heater, U.S. Pat. No. 5,685,041 for a Pipe pig with abrasive exterior, U.S. Pat. No. 5,379,475 for a Scraper for a Pipe Pig, U.S. Pat. No. 5,358,573 for a Method of cleaning a pipe with a cylindrical pipe pig having pins in the central portion, U.S. Pat. No. 5,318,074 for a Plug for a furnace header, U.S. Pat. No. 5,265,302 for a Pipeline Pig and U.S. Pat. No. 5,150,493 for a Pipeline Pig. 
     Intelligent pigs that carry sensors are run through pipes, as for example the pipes in fired heaters, to inspect the pipes with the sensors. It is preferred that the intelligent pigs run at a constant speed. However, the intelligent pigs tend to slow down when encountering obstacles in the pipe. This can cause problems for the operator of the intelligent pig. 
     SUMMARY 
     A pumping unit and method are provided that control fluid pressure in a pipe being cleaned according to the degree of resistance encountered by a pig traversing the pipe under fluid pressure. Increasing fluid pressure in constricted areas enables an intelligent pig to traverse the pipe with a more uniform speed. 
     These and other aspects of the device and method are set out in the claims, which are incorporated here by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which: 
         FIG. 1  is a graph showing a pressure recording chart for a pigging operation; 
         FIG. 2  is a schematic showing details of an engine driving two pumps, each pump being connected into a respective pumping circuit that is connected into a pipe to be cleaned; and 
         FIG. 3  is a simplified diagram of a controller for controlling flow in a pumping circuit. 
     
    
    
     DETAILED DESCRIPTION 
     In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite article “a” before a claim feature does not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims. 
     Referring to  FIG. 1 , pressure on a pig is sensed while it traverses a pipe. A pressure recorder generates a trace  10  that records the pressure in the pipe on the high pressure side of the pig. When the pig encounters bends in the pipe, it encounters resistance, which produces pressure spikes  12  in the trace  10 . The pressure spikes  12  can be used to detect the location of the pig since the bends in the pipe are usually known. When the pig encounters an area of low contamination, the pressure increases as indicated at  14  and when the pig encounters an area of high contamination, the pressure increases as indicated at  16 . To maintain the pig at constant speed, when the pressure as recorded by the pressure recorder exceeds a pre-set pressure, a throttle valve (variable flow control valve) is opened to temporarily increase pressure on the pig and thus help maintain pig speed at a constant level. 
     Referring to  FIG. 2 , an engine and pump configuration is shown that may be used to increase pressure on a pig temporarily as it passes obstructions in the pipe. While  FIG. 2  depicts a double-pass unit, it will be understood that the teachings herein may be applied to a single-pass unit, a four-pass unit, etc. In situations where there is more than one pass, and the teachings are used primarily as an inspection tool, it may be more economical to implement the teachings on only one path. However, the teachings may be used for more than just inspection purposes, and may be applied to each path in a unit. In  FIG. 2 , engine  24  has an integral clutch  26  from which extends a drive shaft  28 . The drive shaft  28  is connected to drive pump  30 A (P 1 ). The engine  24  is shown with only one integral clutch, but has a main shaft  32  that extends from the end of the engine  24  opposite to the clutch  26 . Main shaft  32  is connected through a stand alone clutch  34  to drive pump  30 B (P 2 ). Other clutch and drive shaft configurations may be used to configure a single engine to drive two pumps. In this way, for example, engine  24  may be connected to drive two pumps. Each pump P 1 -P 4  is connected into a valved pumping circuit. An exemplary configuration of two such valved pumping circuits  38 A,  38 B associated with engine  24  is shown in  FIG. 2 . The valved pumping circuits  38 A and  38 B may be constructed in the same way, and thus in the detailed description that follows, only valved pumping circuit  38 A is described, the description for valved pumping circuit  38 B being the same, except replacing the suffix A with the suffix B in the reference characters. 
     Pump  30 A has an inlet conduit  42 A with valve  44 A that extends into the clean water tank  20  to provide a supply of clean water to pump  30 A. In practice, pump  30 A may have one or more such inlets, with different sizes, for example 4 inch or 12 inch inlets. The inlet conduit  42 A may be made of a suitable combination of rigid pipe and flexible hoses. Pump  30 A has a power outlet conduit  45 A with valve  46 A that leads to a valve bank  48 A. Valve bank  48 A has suitable connections  50 A,  52 A for connecting to either end of a pipe  54 A to be cleaned. The pipe  54 A may be a pipe in a fired heater. In a fired heater, the pipe typically passes through a radiant heating section  56 A (denoted red side) and a convection heating section  58 A (denoted blue side). The valve bank  48 A itself is conventional and typically comprises four valves for routing fluid either direction through the pipe  54 A, and operates together with a bypass valve  49 A on bypass line  47 A for returning fluid directly back to the clean water tank  20 . The bypass line  47 A is used for example when using the valve bank  48 A to switch between flow directions in the pipe  54 A. The valve bank  48 A has a return conduit  60 A for routing water back to either the dirty water tank  18  or clean water tank  20  through valve  62 A and diverter valve  64 A. Diverter valve  64 A operates to discharge water that has passed through the pipe  54 A into either the dirty water tank  18  or clean water tank  20 . The return conduit  60 A may be any suitable combination of piping and hoses. 
     The connections  50 A,  52 A are each provided with valves  66 A,  68 A and a pig launcher/receiver  70 A. The pig launcher/receivers  70 A may be placed in parallel or in series with the connections  52 A,  54 A, and various configurations of pig launcher/receiver may be used. One or more pressure sensors are included in the pumping circuit, such as pressure sensor  71 A between the pump  30 A and the connection  50 A, and pressure sensor (not shown) between connection  52 A and dirty and clean water tanks  18  and  20 . Alternatively, a differential pressure sensor (not shown) may be included to determine the difference in pressure between heater sections  58 A and  56 A. This may be positioned at any convenient location. 
     The valved pumping circuit  38 A is provided with at least one variable flow control valve. The variable flow control valve or valves regulate flow in the valved pumping circuit  38 A and may for example be incorporated into the valved pumping circuit  38 A in various ways, such as into the pump  30 A, or as a stand alone valve or valves in the valved pumping circuit  38 A. At least one variable flow valve should be placed between the pump  30 A and the pipe  54 A. For example, valve  46 A may be a variable flow valve. Valve  46 A may also be referred to as a throttle valve. Valve  62 A on return conduit  60 A between the valve bank  48 A and the clean/dirty water tanks  18 ,  20  may also be a variable flow control valve. More than one variable flow valve may be used for each the valves  46 A and  62 A. In one embodiment, the valve  62 A may be located at the dirty/clean water tanks  18 ,  20  on the return conduit  60 A and may be supported by the tanks  18 ,  20 . The return conduit  60 A may be provided with a flow meter  72 A. Valves  66 A or  68 A may be variable flow control valves. 
     Referring to  FIG. 3 , a controller  74 A is connected to receive signals from the pressure sensors including pressure sensor  71 A, and is connected to control at least the one or more variable flow control valves, for example valve  46 A and valve  62 A, and may also control the valve bank  48 A, and the valves  44 A,  46 A,  49 A and  64 A. In some cases, it may be desirable to have separate control inputs for the throttle or other valves, where one input is the coarse adjustment, which allows for rapid changes in pressure such as when initially applying the pressure, and another input that allows for fine adjustment which is used to maintain the system within a desired pressure range. The controller  74 A may for example be at a console in an operator&#39;s cabin, and may be manual, partly manual and partly automatic, or fully automatic. Automatic controllers for hydraulic systems are well known and need not be described in detail here, but generally include a processor with inputs and outputs that runs on instructions implemented through hardware or software that is connected to a memory unit, and may be programmed or otherwise configured to control the pump circuit in the manner described here. In particular, due to desirability of fast response, the variable flow control valves  46 A and  62 A are automatically controlled in response to the controller  74 A receiving pressure signals from the pressure sensor  71 A. 
     As will be recognized by those in the art, controller  74 A may have a control box portion for receiving manual inputs, and a control circuitry portion with a process that is programmed to make decisions based on the inputs. The control circuitry portion may also include automatic control circuitry, which would reduce the need for manual inputs and supervision. 
     Each pumping circuit and pump is operated in conventional manner, with modifications described here. Operation of circuit  38 A is described, but the same principles apply to circuit  38 B. Initially, clean water is passed through the pipe  54 A and returned to the clean water tank  20  to ensure a free flow path. Pipe  54 A is first connected into the pumping circuit  38 A including pig launchers  70 A. Engine  24  is used to drive the pump  30 A. Fluid flow in the pumping circuit  38 A is controlled by the variable flow control valves such as throttle valves  46 A and  62 A. The engine for the pump  30 A may be operated at constant speed, with flow control provided by the variable flow control valves such as valves  46 A and  62 A. A second engine with two additional pumping circuits and pumps may likewise be used to clean third and fourth pipes. 
     The pipe  54 A may be cleaned by running pigs through specific sections repeatedly by reversing flow using the valve bank  48 A operated by controller  74 A. In addition, the pipe  54 A may be inspected by running an intelligent pig through the pipe  54 A with the variable flow control valves, such as valves  46 A and  62 A, partly closed. Flow bypass and diversion may also be accomplished by control from the controller  74 A in a conventional manner. Location of the pigs may be determined from the upstream pressure recorder  71 A in the manner described above in relation to  FIG. 1 . As the pigs pass bends or other obstructions in the pipe being cleaned, the pressure spikes, which may be sensed by the controller  74 A comparing the pressure as sensed by the upstream pressure sensor  71 A with a pre-set value. Upon the fluid pressure in the pipe  54 A exceeding the pre-set value, which may be determined experimentally, the variable flow control valve or valves are opened beyond the partly closed state for at least a period of time, that is, temporarily, to increase fluid pressure on the pig. 
     At the end of the period of time, the one or more variable flow control valves are returned to a partly closed state. The period of time may be determined in various ways. For example, the period of time may be a pre-set time, or may end when the fluid pressure in the pipe returns to the pre-set value or a second pre-set value, or may be determined by the rate of pressure increase when the fluid pressure exceeds the pre-set value. 
     Opening the one or more variable flow control valves temporarily increases pressure on the pig in the pipe  54 A. The pig, having slowed down at the obstruction (such as obstruction  12 ,  14  or  16 ), then speeds up. If automatic control is used, the speeding up is almost immediate. Upon exiting the obstruction, the return of the at least one variable flow control valve to the partly closed state reduces pressure on the pig, and the pig will not be speeded up past the obstruction. By operation of the variable flow control valves temporarily closing while the pig encounters an obstruction, the pig is maintained at a more uniform speed. Although a single variable flow control valve between the pump  30 A and the pipe  54 A may suffice, it is preferred to use a second variable flow control valve between the pipe  54 A and the clean/dirty water tanks  18 ,  20 . 
     In situations where it is desirable to have the pig travel at a more constant velocity, such as when the pipe  54 A is being inspected by an intelligent pig, valve  62 A may be used as a second variable flow control valve, such that a back pressure is applied in addition to the motive force behind the pig. The back pressure helps reduce any undesired increases in speed when the motive force behind the pig is increased to compensate for an increase in friction. In other words, applying a back pressure prevents the pig from surging forward more rapidly than desired when pressure is applied to increase its speed, by maintaining the pig within a desired pressure differential range. It will be understood that since it is the pressure differential that controls the speed of the pig, the motive force may also be increased by decreasing the back pressure. For example, it has been found that the pig requires a minimum pressure differential of about 100-150 psi to initiate movement of the pig. Thus, it is useful in this embodiment to measure the pressure differential between the pressure sensor  71 A upstream from the pig and an additional pressure sensor (not shown) downstream from the pig. Alternatively, a differential pressure sensor may be included to measure the differential pressure, rather than having to compare the two pressure sensor readings. This would also be more useful if automatic controls were used. For example, a differential pressure sensor may be contained within valve bank  48 A to measure the pressure difference between the blue output to section  58 A and the red output to section  56 A of the valve bank  48 A, or any other convenient location. The flow meter  72 A can be used to provide information for the fluid flow velocity required for optimum operation of the intelligent pig. In addition, instead of monitoring the pressure readings to maintain the desired speed, an operator may instead monitor the flow meter to maintain a proper fluid velocity, and use the pressure readings to ensure that the pressures are in an appropriate range. Other sensors may also be included to monitor the system. 
     A single operator may manage two pipes being cleaned at a time, so that two operators in a single pumping unit may manage four pipes being cleaned at a time. A single pig handler may be used for all four pumping circuits, so that the total staff required to perform four passes at a time is three and only a single pumping unit is required. 
     Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.