Rigging failure during riser recovery – soft slings parted

During recovery of a 10m riser section with buoyancy modules attached, the riser section dropped 2.5m to deck when the soft slings parted after rubbing on the sharp edge of the Deadman Anchor (DMA). During decommissioning activities, the riser was cut into approximately 10m long sections.

The section had been weighted down with a DMA prior to cutting. On completion, the DMA was recovered along with the riser section suspended below the DMA.  When slewing the riser section inboard, the riser section (3.8Te) fell approximately 2.5m to deck when the slings parted after rubbing on the sharp edge of the DMA.

Control measures were being followed with all personnel standing clear of the lifting area, behind the barriers as stipulated by the risk assessment.

What went wrong – findings

• A pendulum effect occurred whilst the product was draining before recovery onboard, which resulted in the riser section suspended below the DMA moving against the sharp edges on the DMA, and thus cutting the soft slings;
• The sharp edges of the DMA had not been identified as a potential hazard in relation to the use of soft slings.

Lessons learned/actions

• Wire rope slings should be used where slings connect with a DMA;
  • The exception would be, unless the use of soft slings has been fully risk assessed with specific consideration given to the possible contact with the edges of the DMA;
• Consider the use of rounded DMAs where there is a potential for sharp edges to connect with the rigging;
• Consider having pad eyes welded along the bottom profile of the DMA to mitigate against fouling with the rigging.

Members may wish to refer to:

• High potential near-miss – Lifting equipment failure  
• Failure of lifting equipment: Dropped ROV  
• Parting of slings causing fall of heavy object onto seabed