Pig receiver explodes

Gas and a good deal of the oil from North Sea platforms are transported to land by pipelines. These need to be cleaned internally at regular intervals. This is done by introducing a cleaning ?pig? at the intake end of the line. Gas or liquid is then led via a valve system behind the pig, which is driven by the pressure through the line to the pig receiver where it can be removed.

On that September day, the hatch on a TCP2 receiver for pigs from DP2 came loose. The pipeline was under full pressure of 170 bar. The hatch cover vanished through the platform wall and out into the sea, while the pipe and its attachments were torn loose and deformed. The whole pipeline system around the pig receiver shook and was thrust backwards.

Safety systems on TCP2 functioned faultlessly. Crew rapidly mobilised and sprayed foam over the area around the site to remove possible residual gas. The leak was halted within less than two minutes. There was never any immediate danger of fire, since the gas under high pressure escaped to the open air. Because Frigg had two parallel production systems, and only one was shut down, deliveries to the UK continued without interruption.

The accident was caused by poor design and a faulty locking mechanism on the hatch. Both pig receivers from DP2 were subsequently modified to prevent a recurrence.