Crane wire failure

Weather conditions were fair with an estimated 0.5 m significant wave height on top of a 1.5m swell.

During recovery of the ROV, the supervisor could hear the crane hydraulics bypassing the pressure relief valves – indicating an overload.

On trying to lift again, the crane wire parted and the ROV was released to sea.

The company’s investigation revealed:

• scuffing/gouging of the spelter socket
  
  
• recent and historical damage on the inside face of the swivel sheave cheek plates – indicative of a wire scraping along the plates
  
  
• the cheek plates had been distorted outwards by approximately 30 mm
  
  
• damage to the outer face of the sheave wheel
  
  
• crushing and mechanical damage to the broken ends of the crane wire.

The company has concluded that the crane wire had been over-recovered in the past, to the extent where the conical end of the spelter socket had forced itself between the sheave assembly cheek plates, wedging them apart by circa 30 mm. This, in turn, allowed the wire rope to come off the sheave and jam between the wheel and the cheek plates, causing crushing damage to the wire. The additional impact load on the already damaged wire during the recovery of the ROV through the splash zone ultimately led to the failure of the wire.

The root causes of the failure were noted as:

• inadequate crane inspection ‘routine’s
  
  
• no action had been taken when the existing damage had previously been noted
  
  
• the crane had been previously modified without recourse to a management-of-change procedure or consultation with the manufacturer
  
  
• there was no limit switch fitted to restrict the spelter socket from entering between the cheek plates.