Inadequate planning and execution led to a 35.2-ton slip joint unintentionally dropping from Odfjell Drilling's offshore drilling rig to an offshore supply ship before ending up on the seabed offshore Norway in March this year, an investigation by the Petroleum Safety Authority Norway has shown.
The incident, that happened on March 8, 2022, occurred in connection with a lifting operation from the Stril Mar supply ship to Deepsea Atlantic, which is operated by Odfjell Drilling. During a lift from ship to facility, the load dropped out of control before striking the Stril Mar’s bulkhead and landing on the seabed.
"The PSA’s investigation shows that planning and execution of the lifting operation was inadequate. In addition to having the wrong settings, the crane was operated outside its design criteria," the PSA Norway said.
The direct cause of the incident was crane overload.
"Overloading of the crane occurred when lifting the slip joint from the supply ship. The load exceeded the crane’s capacity, which in turn activated the crane’s APOS and the load was rapidly lowered," the PSA said.
"The slip joint was specified to weigh 32 tonnes, but proved to be 35.2 tonnes," the PSA said.
"The slip-joint weight specified in the manifest, and which formed the basis for planning the lift, did not accord with its actual weight. The slip joint weighed 33 286 kilograms on delivery from the manufacturer, but two modifications had subsequently been made. Lifting clamps had been retrofitted, which added 856 kilograms, plus two melons for mechanical protection, which amounted to 1 304 kilograms.
In addition, hydraulic control lines totalling about 100 kilograms had been removed. The manifest from the logistics base, which formed the basis for planning the lift, specified 32 tonnes. The actual weight of the slip joint was subsequently measured to 35.2 tonnes. According to a manifest from 2021 used with a slip-joint lift, the weight was 33 tonnes. The riser, including slip joint, is part of the facility’s equipment and is owned by Odfjell," the PSA said in its report.
The lifting incident resulted in material damage to the offshore crane, the slip joint and the ship’s bulwark. After the incident, the starboard offshore crane was out of action for a time, the PSA said.
Under slightly different circumstances, the load could have fallen with full force against the ship’s deck or the bulwark and caused greater material damage to the ship, the PSA said. The ship is owned Simon Møkster Shipping.
This field comprises two subsea templates for production and one for water injection. Deepsea Atlantic had completed activities on well E-4. In connection with the operation, the wells in the template were shut down and the subsea systems depressurised.
According to the PSA, it is considered unlikely that the slip joint could have caused damage to subsea structures. The incident did not pose a potential for personal injury, the PSA added.
The PSA has identified the following nonconformities in connection with the incident: inadequate safety clearance of activities; safety system for offshore crane; deficiencies in weight information for the slip joint; use of offshore crane. The PSA has also identified an improvement point: design of the procedure for heavy lifting.
The incident occurred on the Statfjord North satellite field in the North Sea, where Equinor is the operator.