Rescue Pig for Stuck Pig Location and Removal
Various methods can be adopted for trying to remove a stuck pig from a pipeline, such as increased differential pressure across the pig or reverse flow. However, in many cases, the final option is to launch a second pig in the hope that it will free the stuck pig and push it out of the pipeline. However, this brings the risk that the second pig may also become stuck in the pipeline. Therefore, careful planning and the correct selection for running a second pig like a Rescue pig is critical for the success of this contingency pipeline pigging procedure. To enable a second pig to be launched, there has to be flow through the pipeline with product being received at the receiver.
A Polly Pig or Foam Pig may be used as a Rescue Pig and ideally it should be fitted with magnets and a transmitter to enable pig tracking and location. Once the Polly Pig reaches the stuck pig it will deform, but will also create a seal around the stuck pig in the pipeline. The stuck pig may then move forward, or both pigs will remain in the pipeline. The advantage with this method is that the exact location of the Polly Pig or Foam Pig can be located and in turn the position of the stuck pig in the pipeline can be determined. However, the disadvantage is that if the stuck pig fails to move, the Polly Pig or Foam Pig will have created a seal around the stuck pig and flow through the pipeline will be prevented, causing a pipeline blockage due to the stuck pigs. Furthermore, if the differential pressure across the pigs is increased sufficiently, the Polly Pig or Foam Pig may be destroyed and whilst this will enable flow to continue, the tracking magnets and transmitter would be left inside the pipeline.
How to Avoid Blocking a Pipeline during Stuck Pig Recovery
An alternative that addresses both the advantages and disadvantages of stuck pig removal is the Pigtek Advanced By-Pass Pig, which can be used as a Rescue Pig. This specialist pig design has one or more bypass valves fitted internally to the pig body, which are set to open at a pre-determined pressure.
Using the Pigtek Advanced Bypass Pig as a Rescue Pig will also either push and remove the stuck pig from the pipeline or will also become lodged behind the stuck pig. However, the Advanced By-Pass Pig is fitted with an internal pressure relief valve and in the event that this type of pig also became stuck in the pipeline, the valve will open to allow flow to continue. The Rescue Pig can easily be fitted with magnets and a transmitter for pig tracking and pig locating so that in the event that the pig did also become stuck, the exact position can be determined. The only modification that needs to be made to an Advanced By-Pass Pig when used for rescuing a pig, for a stuck pig location and removal operation is fitting a protector bumper cage to the front of the pig. As the protector bumper cage makes contact with the rear of the stuck pig, it will prevent the pressure relief valve from receiving any impact damage. The pressure relief valve will then be able to open and operate without restriction, allowing product to flow through the by-pass valves, preventing a complete pipeline blockage, until further remedial action can be taken.
Contact us at Pigtek to know more on how an Advanced By-Pass Pigs can be used as a Rescue Pig in sizes from 4in. through to 56in.