Gas release as blockage cleared from a pressure transmitter blow down line

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Alert ID: 
Description of Task: 

Gas release as blockage cleared from a pressure transmitter blow down line

During plant operation it was noted that a well head pressure transmitter reading was incorrect. To alleviate this situation the pressure transmitter was blown down to relieve the blockage, this subsequently released and resulted in a high pressure although short term gas release as the valves were lined out to the well head pressure.

The pressure released from the wellhead into the pipework caused it to become dislodged from the designated vent point (below the deck plate) to inside the wellbay module. A work party had been present at this location seconds before the incident. However there were no injuries during this event.

Lessons Identified: 


  • Various improvements are to be made to the design and security of the vent pipework as well as the procedural controls for the venting of well annulus pipework.
  • Ensure operator tasks (such as the blowdown of instruments) are covered by an appropriate risk assessment.
Information source: 
Contact Details: 
Andrew Miller, Centrica Storage Limited
Specific Equipment: 

Common pressure transmitter and well annuli blow down pipework

Incident consequence: 
Hydrocarbon release
Production operations
Fixed Installation
Cause of accident or incident: 
Uncontrolled release of a flammable gas or liquid