Abstract:
A method and system for launching a pipeline pig includes the steps of compressing a modulating bypass valve of a pipeline pig and installing a locking means to temporally maintain the bypass valve in the compressed state. Once the pig has travelled a predetermined distance through the pipeline, the locking means is released and retrieved through the launch trap door. The locking means is preferably a launching pin having a clip attachment that receives the clips of a retractable lead. The lead is housed by a retraction device that is detachably secured to the launch trap door. The modulating valve has sufficient mass and aerodynamic drag to overcome the force of a gas spring. The valve moves between a retracted and compressed position substantially instantaneously upon the pipeline pig stalling and between the compressed and retracted position substantially instantaneously upon the pipeline pig accelerating.

Description:
FIELD OF INVENTION 
     This invention relates to devices and methods for launching pipeline pigs. More specifically, the invention relates to systems and methods for controlling pressure differential across the pig during its launch into a pipeline. 
     BACKGROUND 
     Pipeline pigs perform various pipeline maintenance, cleaning and inspection operations while the pipeline continues to operate under pressure and transport product. The pig is introduced into the pipeline by way of a trap (the “pig launcher”) connected to the pipeline. Once the pig is placed inside the launcher, the closure door of the launcher is closed and pipeline flow is used to push the pig into and through the pipeline. The pig continues to travel through the pipeline until the pig reaches a receiving trap (the “pig catcher”). 
     In order to launch itself properly into the pipeline, the pig must experience an adequate pressure differential across the pig body. The ability to control bypass flow through the pig body, therefore, is critical to providing sufficient acceleration of the pig during its launch into the pipeline and controlling the speed of the pig as it travels through the pipeline. In many cases—such as those where minimal flow is available to push the pig out of the launcher and into the pipeline—it is desirable to have minimum bypass flow through the pig during the initial launch phase, that is, up until the time at which the pig passes the first mainline valve and bypass tee. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and system for launching a pipeline pig includes the steps of compressing a modulating bypass valve of the pig so that the valve is in a compressed position and installing a locking means to temporally maintain the bypass valve in the compressed position. Once the pig has travelled a predetermined distance through the interior of the pipeline, the locking means is released and retrieved through the launch trap door as the pig continues travelling in an opposite direction through the pipeline. The locking means is preferably a launching pin having a clip attachment that receives the clips of a retractable lead. The lead is housed by a retraction device that is detachably secured to the launch trap door. The length of the lead is such that it allows the pig to travel past the first mainline valve and bypass tee before the lead runs out of length. 
     The system for use in launching the pipeline pig includes a modulating bypass valve effective for controlling bypass flow through the pipeline pig and a locking means for temporarily securing the modulating valve in a compressed position. The locking means is in communication with a retrieval means such as a retractable lead. The lead has a length L effective for allowing the pipeline pig to travel past the first mainline valve and bypass tee downstream of the pig launcher. When the lead reaches the end of its length, the locking means is retracted and retrieved through the launch trap door. The modulating valve then operates in a normal operating mode as the pig continues to travel through the pipeline. The locking means may be in the form of a launch pin and a ball detent arrangement may hold the modulating valve in its compressed state. 
     The modulating bypass valve may be located rearward of an inlet side of the venturi. A gas spring controls the response of the valve and the valve has sufficient mass and aerodynamic drag to overcome the force of the gas spring. The initial position of the modulating valve may be adjusted by an adjustment screw and the output force of the gas spring may be adjusted by an adjustment screw. The modulating valve has a first (retracted) position and a second (compressed) position. When in the first position, the modulating valve allows a predetermined maximum bypass flow through venturi. When in the second position, the modulating valve allows a predetermined minimum bypass flow through the venturi. The valve moves between the first position and the second position substantially instantaneously upon the pipeline pig stalling and between the second position and the first position substantially instantaneously upon the pipeline pig accelerating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a pipeline pig prior to launch preparation. The pig includes a modulating bypass valve for regulating the speed of the pig by controlling bypass flow through the pig as the pig travels through a pipeline. A gas spring holds the modulating valve in an open position and provides a means for adjusting the response of the modulating valve. The gas spring has a preload capacity selected to match pipeline conditions. Spring preload capacity or output force may be adjusted by way of a spring valve or by providing a shorter or longer spring adjustment screw. 
         FIG. 2  is a view of the pipeline pig taken along section line  2 - 2  of  FIG. 1 . The maximum bypass flow through the venturi may be manually adjusted prior to launching the pig by replacing a rearward adjustment screw with a longer substitute to prevent the modulating valve from reaching a fully opened position. 
         FIG. 3  is another view of the pipeline pig prior to launch preparation. A longer spring adjustment screw compresses the gas spring, thereby increasing the output force of the gas spring in comparison to the shorter spring adjustment screw of  FIG. 1 . 
         FIG. 4  is a cross-sectional view of the pipeline pig after a bolt has been installed to compress the modulating valve between the open position and a closed (fully compressed) position. In the closed position, the modulating valve provides for minimum bypass flow through the pig. A launch pin provides a locking means for holding the modulating valve in the closed position. 
         FIG. 5  is a view of the pipeline pig taken along section line  5 - 5  of  FIG. 4 . 
         FIG. 6  is a cross-sectional view of the pipeline pig after the bolt has been removed. The launch pin actuates a ball detent arrangement that locks the modulating valve into its closed position. The rearward adjustment screw may then be re-inserted if desired. Retractor clips at the end of a retractable lead are attached to a clip receiver of the launch pin. 
         FIG. 7  is a view of the pipeline pig within the pig launcher. The retractor device is held to the closure door by a strong magnet and includes a retractor means such as a lead. The retractable lead extends from the retractor device and holds the pig in a starting position. 
         FIG. 8  is a view of the pipeline pig after the pig has launched and entered the pipeline. Once the pig passes the first mainline valve and bypass tee downstream of the pig launcher, the retractable lead reaches the end of its length. 
         FIG. 9  is a view of the pipeline pig as the retractable lead reaches the end of its length and pulls the launch pin free while the pig continues travelling through the pipeline. As the launch pin is pulled free, the ball detents are released and the modulating valve is free to move between the closed position and the open position. 
         FIG. 10  is a view of the launch pin as it is travels back to the pig launcher. The retraction device automatically reels the launch pin back to the closure door for easily removal. 
         FIG. 11  is a view of the retraction device. Two retractable leads with clips are housed by the retraction device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of a pipeline pig launch pin and retraction device will now be described by making reference to the drawings and the following elements illustrated in the drawings: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 10 
                 Launch pin 
               
               
                 12 
                 Body/pin portion 
               
               
                 14 
                 Top end/head 
               
               
                 16 
                 Bottom end 
               
               
                 18 
                 Clip attachment 
               
               
                 20 
                 Bolt 
               
               
                 30 
                 Retractor device 
               
               
                 32 
                 Housing 
               
               
                 34 
                 Lead 
               
               
                 36 
                 Clip 
               
               
                 40 
                 Pipeline pig 
               
               
                 42 
                 Body 
               
               
                 44 
                 Forward end 
               
               
                 46 
                 Rearward end 
               
               
                 48 
                 Passageway 
               
               
                 50 
                 Radial sealing discs 
               
               
                 52 
                 Radial sealing discs 
               
               
                 54 
                 End plate 
               
               
                 55 
                 Central hub with spokes 
               
               
                 56 
                 Venturi 
               
               
                 58 
                 Inlet side 
               
               
                 60 
                 Modulating bypass valve 
               
               
                 62 
                 Valve/head stopper 
               
               
                 64 
                 Adjustment screw 
               
               
                 66 
                 Cylindrical recess 
               
               
                 68 
                 Balls 
               
               
                 70 
                 Housing 
               
               
                 72 
                 Forward bracket 
               
               
                 74 
                 Valve sleeve 
               
               
                 76 
                 Detents 
               
               
                 78 
                 Plunger 
               
               
                 80 
                 Gas spring 
               
               
                 82 
                 Adjustment screw 
               
               
                   
               
             
          
         
       
     
     Referring first to  FIGS. 1 to 3 , in a preferred embodiment a pipeline pig  40  includes a longitudinal, cylindrical body  42 , a forward end  44 , a rearward end  46 , and a venturi-shaped passageway  48  therethrough. A set of radial discs  50  and  52  provide sealing engagement with the inner wall surface of the pipeline in order to propel pig  40  forward under differential fluid pressure. The venturi-shaped passageway  48  increases the amount of bypass flow though the pig, which helps minimize the pressure drop across the pig  40  and thus maximize the reduction in traveling speed of pig  40  in high velocity flow pipelines. Centralized bypass  48  includes a venturi  56  that preferably has a long shallow taper toward the forward end  44  in order to avoid turbulence and thus improve the efficiency of bypass flow. Minimizing the pressure drop, however, increases the likelihood of stalling should pig  40  encounter some higher friction portions of the pipeline such as increased wall thickness, bends, or accumulated debris at the forward end  44  of pig  40 . An anti-stalling feature, therefore, is required. 
     Modulating bypass valve  60  prevents stalling and regulates the bypass flow through pig  40 . In a preferred embodiment, valve  60  includes a frustoconical-shaped valve head or stopper  62  that has substantially the same shape as a portion of an interior surface of venturi  56 . Stopper  62  is attached to a plunger  78  and held in an open position at rearward end  46  by a gas spring  80 . A spoke-and-rim style end plate  54  located at rearward end  46  limits the rearward movement of stopper  62  and, therefore, helps maintain valve  60  within the body of pig  40 . An adjustment screw  64  may be employed to hold valve  60  in a less than fully opened positioned in order to provide a predetermined maximum bypass flow. 
     Stopper  62  has sufficient mass and/or aerodynamic drag to overcome the spring force of gas spring  80  which holds valve  60  in the open position. Gas spring  80  is contained within a hollow valve stem housing  70 . Housing  70  is oriented coaxial to the central longitudinal axis of pig  40  and is received and supported by spoke-shaped bracket  72  at forward end  44 . A valve sleeve  74 , which is connected to stopper  62 , slides over housing  70 . 
     Gas spring  80  is used to hold modulating valve  60  in the open position by providing neutralizing resistance to the pipeline flow, thus keeping valve  60  open under normal pipeline conditions. Gas spring  80  may be replaced by a traditional coil compression or tension spring but gas spring  80  is preferred over these mechanical springs because of its wide range of output forces, low spring rate, and ease of adjustment. 
     Gas springs suitable for use as gas spring  80  are available in a wide range of preload capacities to match pipeline conditions. Output force may be adjustable by way of a spring bleed off valve that provides fine-tuning field adjustment to match pipeline conditions. The internal damping feature of the gas spring  80  ensures smooth motion of valve  60 , avoiding instability. The output force of gas spring  80  may be adjusted in the field prior to launch by replacing spring adjustment screw  82  with one that is longer or shorter. For example, screw  82  shown in  FIG. 3  further compresses gas spring  80  thus increasing the output force whereas screw  82  shown in  FIG. 1  does not provide any additional spring compression. 
     The maximum bypass through the venturi  56  may be manually adjusted prior to launching pig  40  by replacing a rearward adjustment screw  64  with a longer substitute to prevent valve  60  from reaching a fully opened position. For example, adjustment screw  64  in  FIG. 1  allows valve  60  to open to the fully extended position whereas the longer screw  64  in  FIG. 3  limits the rearward travel of valve  60 , thereby restricting the maximum allowable bypass flow. The maximum bypass is adjusted based upon such factors as pipeline flow rate and pig drag. 
     Valve  60  uses a combination of mass/inertia and increased flow rate during stalling to ensure that stopper  62  chokes down instantly upon sudden stalling of pig  40 , thus starting pig  40  instantly moving again before significant pressure builds up behind pig  40  (and therefore control surging). The ability of stopper  62  to instantly open again, due to inertia, when pig  40  surges forward minimizes the tendency of pig  40  to surge to speeds even higher than the average fluid flow velocity in the pipeline. 
     In a preferred embodiment, gas spring  80  holds stopper  62  in a withdrawn or open position relative to the inlet side  58  of venturi  56 , thereby allowing a predetermined maximum bypass flow through venturi  56 . Immediately upon pig  40  stalling, stopper  62  does not close completely but reduces the bypass flow area through venturi  56  to a predetermined minimum bypass flow to ensure that the pig will start and run. The predetermined minimum bypass flow is effective for causing an acceleration of pig  40  to a speed below that of an average speed of a pipeline product flow. If the friction of pig  40  increases somewhat due to changes in the internal diameter of the pipeline or the accumulation of debris, stopper  62  will tend to close slightly as flow rate through venturi  56  increases, thereby creating more driving pressure drop across pig  40  and keeping pig  40  moving at a desirable rate of travel. The predetermined maximum bypass flow is effective for causing a speed reduction of pig  40  below that of an average speed of a pipeline product flow. In a preferred embodiment, the speed reduction is in a range of 30% to 90% of the average speed of the pipeline product flow. 
     In a cleaning pig application, this minimum bypass area will still allow flow through pig  40  which will tend to clear away any forward debris and allow pig  40  to start running again. In a dispersal pig application, the venturi-shaped bypass  48  will create smooth, high velocity flow which maximizes the suction vacuum and energy of the gas/liquid mixture being sprayed out the front of a nozzle while functioning as previously described to minimize velocity, stalling, and surging of pig  40 . 
     Referring now to  FIGS. 4 to 6 , modulating bypass valve  60  includes a ball  68  (or balls  68 ) located within a cylindrical recess  66  of stopper  62 . A ball detent  76  for receiving ball  68  is located about an external surface of housing  70 . In preparation for launch, adjustment screw  64  is removed and modulating valve  60  is compressed with a bolt  20  so that valve  60  is positioned and held in a closed (fully compressed) position. In a preferred embodiment, the closed bypass valve  60  restricts bypass flow to 3%. A locking means, preferably in the form of a launch pin  10 , is inserted into cylindrical recess  66 . Launch pin  10  includes a body or pin portion  12 , a top end or head  14 , and a bottom end  16 . In a preferred embodiment, body  12  accommodates the spokes of end plate  54  and is in coaxial alignment to the central hub or opening  55  in end plate  54  (see  FIG. 2 ). Head  14  is oversized relative to central hub  55  and helps retain pin  10  relative to end plate  54 . Bottom end  16  engages each ball  68  and pushes each ball  68  into its respective detent  76 , thereby locking valve  60  in the closed position. Bolt  22  may then be removed and adjustment screw  64  may be replaced. 
     Launch pin  10  is a retractable launch pin. A retractor clip  36  is attached to a clip receiver  18  located on the head  14  of pin  10 . Retractor clip  36  is connected to the distal end of a lead  34 . 
     Referring to  FIGS. 7 to 10 , lead  34  is a retractable lead having a length L and housed within and released from a retractor device  30 . Length L is preferably a length that accounts for the total distance that pig  40  must travel from the pig launcher in order to pass the first mainline valve and bypass tee of the pipeline. Retractor device  30  includes a housing  32  that is detachably secured to the inside closure door of the launcher. In a preferred embodiment, housing  32  includes a set of magnets for this purpose. 
     After pig  40  leaves the launcher and passes the mainline valve and bypass tee, retractable lead  34  reaches the end of its length L and pulls launch pin  10  away from the rearward end  46  of pig  40  as pig  40  continues travelling through the pipeline. Retraction device  30  automatically reels launch pin  10  back to the closure door for removal. Because modulating valve  60  is no longer retained in a compressed state by launch pin  10 , the valve  60  opens and continues normal operation. 
     While a launching pin and retraction device and method for its use has been described with a certain degree of particularity, many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. A launching pin and retraction device according to this disclosure, therefore, is limited only by the scope of the attached claims, including the full range of equivalency to which each element thereof is entitled.