Unplanned rotation of drilling machinery

A large diameter subsea drill had completed drilling operations and was returned to the vessel’s deck for planned maintenance. Part of the maintenance programme required the drill support system to be energised. As the system was energised, the drill bit unexpectedly started rotating for around 40 seconds.

The retention fastenings, used to secure the drill during maintenance, parted, tangling in the rotating drill-bit. Nobody was in the vicinity at the time and there were no injuries.

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