Patent Publication Number: US-2011061681-A1

Title: Pipeline Pig with Rupture Disc

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to a pipeline pig that services a pipeline and moves forward through the interior of the pipeline by the flow of pressurized gas or liquid. More specifically, this invention relates to a pipeline pig that is designed to locate a previously launched but completely stuck pipeline pig yet allow a certain percentage of flow through the pipe past the stuck pig. 
     Pipeline pigs for inspecting, servicing, and maintaining pipelines are typically moved along the interior of the pipeline under pressure. In some pigging applications, a certain amount of pipeline product may be allowed to flow through a central longitudinal passageway of the pig. Pipeline debris and build-up ahead of the pig may slow the pig below a desired minimum speed or completely prevent the pig from moving forward through the pipeline. Therefore, various passive and active speed control devices have been developed to regulate the amount of this bypass flow and therefore control the pig&#39;s speed. 
     Debris and build-up within the interior of a pipeline is problematic. Not only can it prevent the passage of pigs and other tools inspecting and servicing the pipeline, it reduces product flow, thereby increasing the pressure on valves and pumping equipment. If a pig encounters a partial blockage that stops the pig and pressure buildup behind the pig is not sufficient to get the pig moving forward again, the pig serves to restrict product flow through the pipeline downstream of the pig until the pig can be located and removed from the pipeline. 
     In an attempt to eliminate the build-up of ferrous debris within the pipeline, cleaning pigs have been developed that typically include a nose bumper with embedded magnets. However, debris and build-up can also prevent the passage of cleaning pigs. Unlike pigs used in other cleaning applications—such as inhibitor dispersal—or used in other pigging applications such as inspection operations, some cleaning pigs with their solid nose bumper (or other central obstruction) do not allow for bypass flow through the pig body. If the cleaning pig encounters a partial blockage that stops the pig and pressure buildup behind the pig is not sufficient to get the pig moving forward again, the cleaning pig serves to completely block product flow through the pipeline downstream of the pig until the pig can be located and removed from the pipeline. The longer that this no flow situation occurs, the more cost or lost revenue the pipeline operator incurs. Therefore, there is a need for a recovery pig that can remove ferrous debris ahead of the pig yet provide for continued bypass flow when a partial blockage causes the pig to become stuck in the pipeline. There is also a need for a recovery pig that can locate (or dislodge) a previously launched but stuck pipeline pig—in cases in which the stuck pig is still allowing for a certain percentage of bypass flow through the pig body—and provide continued product flow downstream of the obstruction until the pipeline operator performs a hot tap, bypass, and section removal procedure and removes the stuck pig. The recovery pig will also hold on to any metallic components on the stuck pig, allowing for accurate location of the stuck pig. 
     Pig designers have attempted to temporarily block bypass flow through the body of the pig by various active and passive speed control means as discussed above and through the use of temporary seals. For example, Freyer et al. (U.S. 2007/0286682) discloses a pipeline tool having a temporary seal illustrated in the form of a plug and located in the central bypass flow passageway of the tool. The tool is pushed along the interior of the pipeline by differential pressure contacting the body of the tool (as the primary means) and the temporary seal and guide discs disposed about the body (as secondary means). Once the tool is positioned at its intended location, a swellable component expands against the inner pipe wall to anchor the pipeline tool. The temporary seal, which is in the form of a plug body, permits isolation of the pipeline section upstream or downstream of the temporary seal. When the required maintenance, repair or upgrade operation is completed, the temporary seal is selectively opened to permit product flow to resume through the pipeline. 
     Freyer et al.&#39;s temporary seal may be a rupture disc designed to burst open and relieve an over-pressure at a predetermined differential pressure. However, because the disc must remain intact for at least as long as it takes the swellable component to swell and sealably engage the pipeline wall, the rupture pressure must be well above the normal operating differential pressure experienced by the disc when the tool is moving forward through the interior of the pipeline. Because of this requirement, Freyer et al.&#39;s rupture disc cannot rupture at the point in time when the tool comes to a dead stop. If the disc ruptures at this point, the purpose of the invention is defeated. Therefore, the tool cannot maintain product flow in the event that it encounters an obstruction that would cause it to stall. Furthermore, the tool cannot locate or adhere to a stuck pig body (or the metallic components of a stuck pig body) nor is it configured to remove ferrous debris ahead of the pig. 
     SUMMARY OF THE INVENTION 
     A pipeline pig according to this invention includes a longitudinal body having at least two elastomeric sealing cups and a central bypass flow passageway extending between a forward and rearward end of the longitudinal body. A rupture disc is located in the central bypass flow passageway that prevents product flow from flowing through the flow passageway as the pig travels forward under differential pressure through the interior of a pipe or pipeline. The rupture disc may be held in place by a first and second flange half of the longitudinal body. The amount of product flow entering the central bypass flow passageway rearward of the rupture disc is limited by means such as a set of rear standoff spacers. When the pig comes to a complete stop because of debris—or because it has encountered a previously launched but stuck pipeline pig—the rupture disc ruptures substantially immediately. When the rupture disc ruptures, pipeline product flow entering the central bypass passageway is allowed to flow through the body of the pig while the pig waits to be retrieved by a pipeline operator. 
     The pig preferably includes a nose bumper located at a forward end that includes at least one embedded magnet. The nose bumper removes ferrous debris ahead of the pig and allows the pig to stick to the body of the previously stuck pig. A transmitter module towed by the pig transmits signals is used to pinpoint the exact location of the obstruction or blockage. 
     A method for locating an obstruction in a pipeline includes the steps of:
         (a) launching a pipeline pig into a pipeline;   (b) limiting an amount of pipeline product flow entering a central bypass flow passageway of the pipeline pig;   (c) preventing the amount of pipeline product flow entering the central bypass flow passageway from flowing through the central bypass flow passageway when the pipeline pig is moving forward under differential pressure;   (d) encountering an obstruction ahead of the pipeline pig that stops the forward travel of the pipeline pig; and   (d) releasing the amount of pipeline product flow through the central bypass flow passageway when a pressure produced by the amount of pipeline product flow is at least as great as a predetermined differential pressure.       

     The pig preferably has a magnetic nose bumper for removing ferrous debris ahead of the pig and for sticking to the body of a previously launched but stuck pig that lies ahead of the pig. The releasing step may occur by way of a rupture disc located within the central bypass flow passageway of the pig. The rupture disc ruptures substantially instantaneously with the pig stopping because of the obstruction. The differential pressure at which the rupture disc ruptures is greater than a normal operating differential pressure but less than the cup blow over pressure and maximum pump pressure. The pig, as well as the obstruction encountered, may then be located and retrieved from the pipeline. However, product flow may still flow through the pig body while it waits to be retrieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of a preferred embodiment of a pipeline pig made according to this invention and located within a section of piping or pipeline. The pig includes two cylindrical-shaped body flange halves bolted together that provide for a predetermined amount of product flow to flow through the pig. The pig, which is moved forward within the pipeline by differential pressure, may tow an optional transmitter module that assists an operator in locating the pig should the pig become stuck in the pipeline and require retrieval. 
         FIG. 2  is a cross-sectional view of the pipeline pig of  FIG. 1  taken along section line  2 - 2 . The pig includes a centrally located rupture disc that prevents pipeline product flow through the pig body when the disc is in its intact (not ruptured) state. 
         FIG. 3  is a cross-sectional view of the transmitter module of  FIG. 1  taken along section line  3 - 3 . The transmitter module allows a predetermined amount of product flow to flow past it and to the pig body. 
         FIG. 4  is a view of the pipeline pig of  FIG. 2  taken along section line  6 - 6 . 
         FIG. 5  is a view of the pipeline pig of  FIG. 1  illustrating the centrally located rupture disc in its ruptured state. When ruptured, the disc allows a predetermined amount of bypass flow through the pig body. 
         FIG. 6  is a view of the pipeline pig of  FIG. 5  taken long section line  6 - 6 . 
         FIG. 7  is a view of the pipeline pig of  FIG. 2  taken along section line  7 - 7 . 
         FIG. 8  is a view of the pipeline pig of  FIG. 2  taken along section line  8 - 8 . The nosepiece of the pig includes two magnets for use in removing ferrous debris as the pig moves forward through the pipeline. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of a pipeline pig with rupture disc will now be described by making reference to the drawings and the following elements illustrated in the drawings: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 10 
                 Pipeline pig 
               
               
                 11 
                 Cylindrical body 
               
               
                 13 
                 Forward end 
               
               
                 15 
                 Rearward end 
               
               
                 17 
                 Central bypass flow passageway 
               
               
                 19 
                 Driving or sealing cups 
               
               
                 21 
                 Nose bumper 
               
               
                 23 
                 Magnet 
               
               
                 25 
                 First body flange half 
               
               
                 27 
                 Second body flange half 
               
               
                 29  
                 Towing means 
               
               
                 31 
                 Rear standoff spacers 
               
               
                 33 
                 Bypass flow area provided by 31 
               
               
                 35 
                 Front standoff spacers 
               
               
                 37 
                 Bypass flow area provided by 35 
               
               
                 40 
                 Transmitter module 
               
               
                 50 
                 Rupture disc 
               
               
                 51 
                 Rupture disc retaining flanges 
               
               
                 53 
                 Bypass flow area provided by 50 when ruptured 
               
               
                   
               
            
           
         
       
     
     Referring to the drawings and first to  FIGS. 1-4 , a preferred embodiment of a pipeline pig  10  made according to this invention has a longitudinal cylindrical body  11  with a central bypass flow passageway  17  therethrough. Cylindrical body  11  may have a nose bumper  21  located at its forward end  13  and an optional towing means  29  located at its rearward end  15 . Nose bumper  21  is preferably a plastic nose bumper with one or more embedded magnets  23  (see also  FIG. 8 ) for picking up ferrous debris as pig  10  travels through the pipeline. Mounted at forward end  13  and rearward end  15  are driving or sealing cups  19  that provide sealing engagement with the inner wall surface of the pipeline in order to propel pig  10  forward under differential fluid pressure. Towing means  29 , such as a universal joint, may be connected to a transmitter module  40  that is then towed behind pig  10 . Transmitter module  40  is of a type well known in the art and includes means for locating pig  10  within a pipeline. 
     Cylindrical body  11  may be constructed of two separate body flange halves  25 ,  27  that, when bolted together, secure a pair of rupture disc retaining flanges  51  in between the two halves  25 ,  27 . Retaining flanges  51 , in turn, retain a rupture disc  50 . Rupture disc  50 , which may be a metallic foil disc or a urethane disc (see  FIG. 7 ), prevents pipeline product flow that enters central passageway  17  through the bypass flow area  33  provided by spaced-apart rear standoff spacers  31  from flowing completely through central bypass flow passageway  17  and exiting the bypass flow area  37  provided by front standoff spacers  35 . Rupture disc  50  is such that the driving pressure of pig  10  is not a sufficient pressure to rupture the disc  50 . 
     Referring now to  FIGS. 5 &amp; 6 , pig  10  may become stuck within the pipeline and stop moving forward. As pig  10  encounters a blockage or a previously launched but stuck pipeline pig (not shown) pig  10  stops completely and differential pressure builds rearward of rupture disc  50  until it reaches a level of differential pressure that rupture disc  50  can no longer withstand (the “burst pressure”). This burst pressure occurs substantially immediately upon pig  10  stopping, allowing the exact location of the blockage or other pig to be pinpointed by the signal transmitted by transmitter module  40 . The burst pressure is set above normal operating differential pressure, below the blow over pressure of sealing cups  19 , and below the maximum pressure capacity of the pipeline product pump (not shown). A pipeline operator can be confident that when a pressure spike is observed—up to a predetermined value followed by a drop in pressure to a previous pressure reading—that either pig  10  is stuck or pig  10  has encountered a previously launched but stuck pipeline pig. In cases in which a stuck pipeline pig is encountered, the nose bumper  21  sticks to the body of the stuck pig (or some other metallic component of the pig) so that the blockage may be located by tracking the signal transmitted by transmitter module  40 . 
     Once the burst pressure is reached, rupture disc  50  ruptures and a disc bypass flow area  53  through disc  50  is created. The portion of the pipeline product flow that enters through bypass flow area  33  and into central bypass flow passageway  17  may now flow downstream of disc bypass flow area  53  and through bypass flow area  37 . 
     Disc bypass flow area  53  provides for a predetermined amount of bypass flow through pig  10  that may be substantially equal to the amount of bypass flow area  33 ,  37  provided by the front and rear standoff spacers  31 ,  35 , respectively and individually. In a preferred embodiment designed for a 10-inch pig  10 , front and rear standoff spacers  31 ,  35  each provide about a 25% bypass flow area  33 ,  37 , respectively, and rupture disc  50  when ruptured provides about a 25% disc bypass flow area  51 . Therefore, a 25% bypass flow is maintained throughout the length of pig  10 . This design may be scaled up for larger sizes of pipe or scaled down for smaller size pipe (e.g. 2-inch size pipes). 
     While a pipeline pig with rupture disc 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 pipeline pig made 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.