DANGER

Pigging systems are often found in the oil and gas industry. They are designed so that the pig is loaded into the launcher, which is pressurized up to launch the pig into the pipeline through a kicker line. The pig is removed from the pipeline via the receiver at the end of each run.If not operated correctly following a predetermined sequence, opening the vessel to the atmosphere can be very dangerous and care must be taken to ensure that the vessel is depressurized prior to opening. If the vessel is not completely depressurized, the pig can be ejected from the vessel and operators have been severely injured when standing in front of an open pig door.

SOLUTION

To ensure that a predetermined sequence is followed while loading and unloading pig traps a mechanical key interlocking system is crucial.Interlocks can be installed on the Closure doors, Main valves (either MOV or manual), Vent valves, Drain valves, Pressure valves and Kicker valves.The system also ensures that the outlet valves are fully open when a pig passes through.Taking the start key from the control room commences the procedure to launch the pig following the sequence step by step. The design can either be a linear concept or as described in this example a nonlinear sequence through a sequence control box (SCB). The predetermined sequence may vary and is always depending on the client requirements.

PRODUCTS

Lever of handwheel valves:Closure door lock (SDL CD)MOV lockSequence control box(SCB)Key cabinet

- option 1 integral lock- option 2 bolt lock

OPERATION

In this example we will follow all required steps to launch a pig safely. Every step in the sequence is predetermined in the sequence control box following the required procedure step by step. To begin ensure that all valves are locked closed.

Depressurize procedure:

1 Open and close the vent valve. Take key A from the sequence control box (SCB). Insert key A in valve V1 (vent) to unlock the closed position of the valve. Open valve V1 and take out key B. Valve V1 is now locked open with key A trapped. Key B travels back to the SCB. Turn the knob of the SCB one step further. Now take key B again from the SCB and follow the mirrored sequence to close the vent valve again. After completion turn the knob of the SCB one step further.

2 Open and close the drain valve. Take key C from the sequence control box (SCB). Insert key C in valve D1 (drain) to unlock the closed position of the

valve. Open valve D1 and take out key D. Valve D1 is now locked open with key C trapped. Key D travels back to the SCB. Turn the knob of the SCB one step further. Now take key D again from the SCB and follow the mirrored sequence to close the drain valve again. After completion turn the knob of the SCB one step further.

Ensure zero pressure of the vessel or else repeat steps 1 and 2 using the return button on the SCB (Optional).

Line up procedure:

3 Open and close the closure door. Take key E from the sequence control box (SCB). Insert key E in the closure door to unlock the closed position. Open the door and insert the pig. Key E is trapped as long as the door is open. Close the door and lock the door by taking out key E. Key E travels back to the SCB. Turn the knob of the SCB one step further.

4 Open and close the vent valve to release any entrapped air. For procedure see step 1.

5 Open and close the pressure valve. Take key F from the sequence control box (SCB). Insert key F in valve P1 (pressure) to unlock the closed position of the valve. Open valve P1 and take out key G. Valve P1 is now locked open with key F trapped. Key G travels back to the SCB. Turn the knob of the SCB one step further. Now take key G again from the SCB and follow the mirrored sequence to close the pressure valve again. After completion turn the knob of the SCB one step further.

6 Open the kicker valve. Take key H from the sequence control box (SCB). Insert key H in valve K1 (kicker) to unlock the closed position of the valve. Open valve K1 and take out key I. Valve K1 is now locked open with key H trapped. Key I travels back to the SCB. Turn the knob of the SCB one step further.

7 Open the main valve. Take key J from the sequence control box (SCB). Insert key J in valve M1 (main) to unlock the closed position of the valve. Open valve M1 and take out key K. Valve M1 is now locked open with key J trapped. Key K travels back to the SCB. Turn the knob of the SCB one step further.

Pig launching:Slowly close the bypass valve to move the pig until after the barred tee at the downstream than fully open the bypass again. (Normally this is not part of the interlocking sequence)

8 Close the main valve. Take key K again from the SCB and follow the mirrored sequence of step 7 to close the main valve again. After completion turn the knob of the SCB one step further.

9 Close the kicker valve. Take key I again from the SCB and follow the mirrored sequence of step 6 to close the kicker valve again. After completion turn the knob of the SCB one step further.

10 Depressurize the pig trap again by repeating step 1 and step 2.