Reverse pig movement during shutdown causing pipeline ESD valve to not close on demand.

Who could be interested:

Operations teams, shutdown planners, integrity engineers, pipeline engineers, and personnel involved in pigging, valve testing, and simultaneous operations (SIMOPS)

 What is this all about? 

During a planned shutdown, downstream pressure increased due to unrelated testing activities.

Check valves passed sufficiently to create reverse flow, mobilising a cleaning pig backwards from the receiver into a safety-critical valve, preventing full closure.

The hazard—reverse pig transit—had not been adequately considered in procedure development, especially under SIMOPS conditions. 

Key learnings relate to understanding system-wide pressure interactions, configuring pig receivers appropriately, and validating pig positions.

Some things to consider

 • Consider whether the risk can be eliminated entirely. The most effective way to prevent reverse pig movement is to remove pigs from receivers prior to entering shutdown scopes. 

While this may not be practicably achievable for all operations, it should be the first consideration during shutdown and SIMOPS planning.

 • Where elimination is not practicable, consider reviewing shutdown, pigging, and testing procedures together to capture SIMOPS interactions. 

• Consider assuming check valves will pass and designing isolation and pressure control philosophy accordingly.

• Consider placing pig receivers in bypass mode where credible reverse flow exists. 

• Consider using reliable pig position detection and validating pig location prior to shutdown activities.