Posted on 22 July 2014

Basic valve interlock configurations in pipeline pigging

In pipeline pigging procedures, different valve interlock configurations can be distinguished, depending on the complexity of the pigging procedure. In this article, 3 basic configurations are described in detail.This article can also be viewed and downloaded as an infographic.

Pipeline pigging configuration 1

Application field

This configuration is applicable:

  • when the drain and vent are connected to an open system;
  • when no venting to a closed system is required prior to opening the atmospheric vent.

Valve interlocks safeguard pipeline pigging procedures

Symbol index

The following symbol index applies to all configuration schematics in this article:

Legend for valve interlock configurations

 Basic functionality

  • All main and kicker valves to the vessel are locked closed before the closure door can be opened;
  • The atmospheric vent and open drain have to be opened before the closure door can be opened.

To start the pigging procedure, start key A is taken from the control room and used for (a)  opening the atmospheric vent before opening the closure door or (b) opening the main line and proceeding with pressurizing the vessel.

Basic valve interlock configuration for pipeline pigging operations

Sequence specifics

This safety level can be achieved with the use of a linear interlocking sequence. All valves are operated in a linear order and reverse-operated in the reverse order.

Pipeline pigging configuration 2

Application field

This configuration is applicable:

  • when the drain is connected to a closed system;
  • when venting to a closed systems is required before atmospheric venting is allowed.

Basic functionality

  • All main and kicker valves to the vessel are locked closed before the closure door can be opened;
  • Before the vessel is opened, the draining and venting procedure is performed at least once;
  • The atmospheric vent has to be opened before the closure door can be opened;
Safety levels in pipeline pigging procedures

In pipeline pigging procedures, various valve interlock configurations can be distinguished

To start the pigging procedure; Start key A is taken from the control room and used for (a) opening and closing vents and drains; only after that, the atmospheric vent and the closure door can be opened or (b) opening the main line and proceeding with pressurizing the vessel.

 

Sequence drawing of pipeline pigging configuration

Sequence specifics

This particular configuration can be achieved by using a ‘mini-MPCU’ in pigging operations. This device is used to affirm opening and closing of the vent and drain. Only after opening and closing of these valves, the key is released that opens the atmospheric vent, after which the key is released to open the closure door.

Pipeline pigging configuration 3

Application field

This advanced configuration is applicable:

  • when the vent and drain is connected to a closed system;
  • when one or more purging cycles are required to degas the vessel before it can be opened safely.

Basic functionality

  • All main and kicker valves to the vessel are locked closed before the closure door can be opened;
  • The vents and drains are opened and closed again, the purge is opened and closed again, then vents and drains are opened and closed once more;
  • Above cycle may have to be repeated several times before the closure door can be opened;
  • The atmospheric vent has to be opened before the closure door can be opened;
  • After launching, the vessel is guaranteed to be vented and drained.

pipeline-pigging-procedure-safety-level-3

Sequence specifics

This configuration can be achieved by using a Mechanical Process Control Unit (MPCU). The MPCU is a mechanically-programmed key exchange system where sequence steps need to be confirmed before one can proceed to the subsequent step. After venting and draining key D is released and inserted in the MPCU, confirming that vents and drains have been opened. The same key is released and drains and vents are closed again, resulting in the release of key B from the vent, which is entered in the MPCU to confirm the closing of vents and drains. Similarly, the opening and closing of the purge valve is confirmed in the MPCU. After that, the venting and draining is repeated. If required, purging, venting and draining is repeated several times using the MPCU. After the required number of repeated steps of venting, draining and purging, the key is released to open the closure door.

More complex configurations

Over the years, Netherlocks has designed hundreds of valve interlock configurations, of which many for pipeline pigging. Often, these configurations are more complex as the ones as described in this article. Procedures for more complex configurations can include:

  • Hot oil flushing
  • Chemical flushing
  • Purging and flushing
  • Portable pig launchers
  • Hydrotesting
  • Dewatering
  • Bi directional pigging
  • Gas pigging

Please contact Netherlocks staff for examples and detailed information on these configurations.

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