Procedures for launching a pig in a gas flow line

1. Ensure the pig receiver at the other end of the line is set up to receive the pig. Depending upon the length of the line being pigged and the fluid velocity in the line, there is always a chance the pig will reach the receiver before the operator can get there to set it up. The receiver should be set up with the main pig trap (receiver) and bypass valve open, and the blowdown line valve closed.

Prior to opening these valves, the pig trap end closure should be checked that it is closed securely. If the main flow tee upstream of the pig trap main block valve is not equipped with pigging bars, the block valve on this line should be closed and the flow routed through this pig trap. This will prevent the pig from entering the flow tee and getting stuck in the plant inlet lines.

2. Ensure the pig trap and bypass valve on the pig launcher are closed and the main flow line valve on the tee downstream of the pig launcher is open. Make the necessary adjustments if the valves positions are not as described above.

3. Open the blowdown valve to depressure the launcher. Some sour facilities may have a line from the pig trap to flare for depressuring the trap and a second line from a sweet gas system to purge the trap before it is opened. If this is the case, follow your company's recommended procedures to ready the trap for launching the pig.

4. Open the end closure and insert the pig until the front of the pig reaches the reducer. Depending upon the type of pig and design of the pig launcher, you may require some type of rod or stick to push the pig into the trap until it reaches the reducer section.

Always stand to the side of the pig trap when opening the end closure. This ensures you do not get hit by the pig cap should there be pressure in the pig barrel which was not detected before attempting to open the closure.

5. Close the end closure.

6. Open the bypass valve slightly to purge the air from the trap.

7. Close the blowdown valve, slowly bring the launcher up to line pressure.

8. Open the pig trap valve.

9. If the launcher is equipped with a pig signal device, monitor it to determine if the pig leaves the trap. If it didn't or you do not have any indication that it left the trap, slowly close in on the main flow line valve on the tee downstream of the pig trap. This will force the fluid to flow through the bypass valve and push the pig out of the trap.

10. After you are sure the pig has left the trap, the trap isolation and bypass valve can be closed, the main flow line valve can be opened, and the pig trap may be depressured.

Дата добавления: 2015-11-14