Pig Trap /Pig Launcher/Intelligent Pig

1. Pig trap dan pig launcher

Pig launchers are used to launch the pig into the pipeline, and pig receivers are used to receive the pigs after they have made a successful run. The launcher and receiver are installed at the upstream and downstream of the pipeline section being pigged, respectively. The distance between the launcher and receiver depends on the service, location of pump (liquid product) or compressor (gas product) stations, operating procedures, and the materials used in the pig. In crude oil pipeline systems, the distance between launcher and receiver can be as long as 500 miles for spheres and 300 miles for pigs. The amount of sand, wax, and other materials carried along the pig can affect the proper distance.

In gas transmission service, the distance between the launcher and receiver can be as long as 200 miles for spheres and 100 miles for pigs, depending on the amount of lubrication used. The launcher and receiver consist of a quick opening closure for access, an oversized barrel, a reducer, and a neck pipe for connection to the pipeline. Pigs can be located using fixed signalers along the pipe or electronic tracking systems mounted inside the pig. A typical configuration of a pig launcher for liquid service is illustrated in figure below. The horizontal barrel holds the pig for loading.

A typical configuration of a pig launcher for liquid services

Source: Offshore pipelines - Dr. Boyun Guo (2005)

 The figure below shows a typical configuration of a pig receiver for liquid service. The horizontal barrel holds the pig for unloading. A barrel diameter 2 inches larger than the diameter of pipeline has been recommended for both launchers and receivers. The barrel length should be 1.5 times the pig length and long enough to hold 10 or more spheres.

A typical configuration of pig receiver for liquid services

Source: Offshore pipelines - Dr. Boyun Guo (2005)

The pigging systems should be designed according to the same design codes as the pipeline to which they are connected. The predominant codes used for pipeline design in many countries are written by ASME. The ASME codes commonly encountered in the pipeline industry are ASME B31.4 which governs the design of liquid pipelines; ASME B31.8 which governs the design of gas pipelines; ASME B31.3 which governs the design of process piping and ASME Section VIII, Div. 1 and 2 which governs the design of pressure vessels (sometimes referred to as the Boiler Code). There are other codes in use that govern the design of pig traps such as CSA Z-662 in Canada or ASME B31.11 for slurry pipelines.

A typical configuration of a pig launcher for gas services

Source: Offshore pipelines - Dr. Boyun Guo (2005)

A typical configuration of a pig receiver for gas services

Source: Offshore pipelines - Dr. Boyun Guo (2005)

The typical of pig launching procedure are:

Pig launcher

Source: http://www.tremcopipeline.com.au/pdf/girard/launching_retrieving_procedures1.pdf

1. Make sure that the isolation valve and the kicker valve are closed.
2. In liquid systems, open the drain valve and allow air to displace the liquid by opening the vent  valve. In natural gas systems, open the vent and vent the launcher to atmospheric pressure.
3. When the pig launcher is completely drained (0 psi), with the vent and drain valves still open, open the trap (closure) door.
4. Install the pig with the nose firmly in contact with the reducer between the barrel and the nominal bore section of the launcher.
5. Clean the closure seal and other sealing surfaces, lubricate if necessary, and close and secure the closure door.
6. Close the drain valve. Slowly fill the trap by gradually opening the kicker valve and venting through the vent valve. 
7. When filling is complete, close the vent valve to allow pressure to equalize across the isolation valve.
8. Open the isolation valve. The pig is ready for launching.
9. Partially close the main line valve. This will increase the flow through the kicker valve and behind the pig. Continue to close the main line valve until the pig leaves the trap into the main line as indicated by the pig signaler.
10. After the pig leaves the trap and enters the main line, fully open the main line valve. Close the isolation valve and the kicker valve.
11. The pig launching is complete.

The typical pig receiving procedures are:

Pig receiver

Source: http://www.tremcopipeline.com.au/pdf/girard/launching_retrieving_procedures1.pdf

1. Make sure the receiver is pressurized.
2. Fully open the bypass valve.
3. Fully open the isolation valve and partially close the main line valve.
4. Monitor the pig signaler for pig arrival.
5. Close the isolation valve and bypass valve.
6. Open the drain valve and the vent valve.
7. Check the pressure gauge on the receiver to assure the trap is depressurized (0 psi).
8. Open the trap closure and remove the pig from t he receiver.
9. Clean the closure seal and other sealing surfaces, lubricate if necessary, and close and secure the trap (closure) door.
10. Return the receiver to the original condition. 

2. Intelligent pig

Intelligent pigs are sophisticated devices that can be inserted into a pipeline at special pig launching chambers and transported along the pipeline with the flow at speeds of between 0.7 and 4 m/s for up to 100 kilometres. Intelligent pigs normally use a technology known as Magnetic flux leakage (MFL) to accurately detect circumferential and longitudinal cracks and metal loss due to corrosion.

Intelligent pig

Source: http://www.ukstt.org.uk/trenchless-technology/location-inspection-a-detection/intelligent-pigging

MFL only works in cast iron and steel pipes as it is based on the use of magnets to induce a D.C. magnetic field in the pipe wall. Wherever corrosion is present, a small amount of magnetic flux leaks from the pipe resulting in slight changes in the local magnetic field that are detected by sensors and recorded as the pig passes down the pipe. Although the technique can provide detailed information about the condition of metallic pipes, it is not feasible for use in water distribution mains for a number of reasons. First of all, because there must be close contact between the pig and the metallic pipe wall, it is not suitable for pipes lined with cement mortar, for example. Secondly as there must be a tight fit between the pipe and the pig any changes in diameter will either stop the progress of the pig or prevent close contact between pig and pipe. Thirdly, the progress of the pipe will also be prevented by control valves, air valves and tee connections. Finally, the cost of carrying out an intelligent pig survey is very expensive - around £400 per metre; whilst this may represent good value for maintaining the integrity of long distance oil pipelines it is unlikely to be economically feasible for water mains.



Source :
Offshore pipelines - Dr. Boyun Guo (2005)
http://www.ukstt.org.uk/trenchless-technology/location-inspection-a-detection/intelligent-pigging
http://www.tremcopipeline.com.au/pdf/girard/launching_retrieving_procedures1.pdf