HSE: Motor Failure Caused Drill Rig to Drop a Blowout Preventer
The drawworks on the drill rig Deepsea Atlantic dropped a blowout preventer and 400 feet of riser onto the seabed in an uncontrolled lifting failure in April, all because of a single motor failure, according to the UK Health and Safety Executive (HSE).
On April 18, Deepsea Atlantic's crew was running a blowout preventer riser on Drawworks A, one of two identical drawworks on the vessel. At about 2100 hours, one motor on the drawworks tripped, followed shortly after by the remaining three motors. At the time, the drawworks had about 650 metric tonnes on the hook.
The loss of the motors caused loss of control of the top drive and the main brake system. The emergency disc brakes kicked in, but were not adequate to prevent the runaway descent of the load. The BOP and riser headed for the seafloor fast enough to pull the wire rope off the main winch drum and flail it about the upper levels of the drawworks, causing damage to equipment and the structure itself.
No one was injured in the accident, but HSE concluded that the incident caused "a significant risk of harm to persons from falling debris."
The rig was not endangered in the incident, operator Odfjell Drilling said. The BOP itself was resting on the seabed in about 1,100 meters of water, and work on Deepsea Atlantic was paused while awaiting its retrieval.
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The 2009-built Deepsea Atlantic is a sixth-generation drillship equipped for the rigors of the North Sea. She has had one previous lifting incident: in 2022, one of her cranes dropped a 35-tonne slip joint while hoisting, damaging a platform supply vessel below. Norway's PSA determined that that casualty was caused by an inaccurate weight on the cargo manifest and repeated lift attempts, which prompted the crane's automatic overload protection system to activate. "The lifting operation was not cleared, managed and conducted in a prudent manner after the crane became overloaded . . . even though overload alarms were activated," PSA concluded in its 2022 analysis.
Top image: Deepsea Atlantic (Geir Vinnes / VesselFinder)