Pig launchers are used at the start of the pipeline, while pig receivers are located at the end of the pipeline. Both are collectively known as pig traps, and the type to be used will depend on the design conditions of the pipe and the pig that will be run. The station design should take into consideration the handling of pigs and for debris brought in by the pigs.
Typically, pipeline pigging operations follow a certain sequence, and only trained operators should perform pipeline pigging-related tasks. The information in this article in no way substitutes pigging system operator training. Operating procedures and training may vary from one service provider to another. This article provides a high-level basic overview of the process in order to be used as a guideline for developing custom operating procedures.
Some companies will isolate the pig launcher, while others will leave it on stream. However, it is up to the operator to verify whether it is isolated and depressurized before the procedure commences.
Launching a pipeline pig:
- Verify that the kicker valve and isolation valves are closed.
- On a natural gas system, open the vent to allow it to reach atmospheric pressure. In a liquid system, open the drain valve and allow the liquid to be displaced by opening the vent valve.
- Leaving the valves open, allow it to drain completely (0 psi), and then open the closure door.
- Now, install the pipeline pig, allowing firm contact between the reducer, which is situated between the nominal bore section of the launcher and the barrel.
- Clean all sealing surfaces and the closure seal. Apply lubricant if necessary, and secure the door.
- Close the drain valve and slowly fill the trap by gradually opening the kicker valve, allowing venting through the vent valve.
- Once it is filled, close the vent valve and allow pressure to equalize across the isolation valve.
- Once you open the isolation valve, your pig is ready to be launched.
- Partially close the main line valve to increase flow behind the pig and through the kicker valve. Continue closing the main line valve until the pig signal indicator shows that the pig has left the trap and made its way into the main line.
- Once the pig has left the trap and entered into the main line, it is time to open the main line valve, and to close the kicker valve and isolation valve.
Receiving a pipeline pig:
Verify whether there is any pressure inside the receiving trap before starting receiving procedures.
- Ensure that the receiver is pressurized.
- Fully open the bypass valve.
- Fully open the isolation valve while partially closing the main valve.
- Monitor the pig signaller to determine it’s arrival.
- Close the bypass and isolation valves.
- Open the vent valve and the drain valve.
- Check whether the trap is being depressured.
- Open the trap closure and remove the pipeline pig.
- Clean and seal the pig closer and closure box, and remove it from your receiver
- Clean the sealing surfaces as well as any other sealing surfaces. Lubricate as needed and secure the closure door.
- Return the pig receiver to its original condition.
- Ensure all launchers are primed.
- Ensure all launchers are hydrostatically tested.
- Ensure valves on launchers and receivers are round.
- Ensure the full port has a 100% pipe size opening.