We have recently learned of a crane whip line, on an offshore crane, parting when lifting a concrete mat weighing 4.5 tonnes from the vessel deck. The load being lifted was well within the safe working load of the wire and the crane. Fortunately no-one was injured and no damage was sustained.
After investigation it was concluded that the wire rope parted due to internal corrosion which had been generated from lack on internal lubrication of the first, approximately, 22m of the wire from the hook end. This allowed corrosion of the internal strands generating a fatigue failure of the internal wire and a tensile failure of the external wire which resulted in a contribution of fatigue and loss of metallic areas. This conclusion was further substantiated when the wire was visually inspected at the contractor’s premises, where it was found that the first 16m was heavily corroded with its condition gradually improving to the 22m mark.
There had been inspection, greasing and destruct tests of the wire rope during its service. A 100% NDT inspection and high pressure lubrication of the wire had been undertaken a couple of months prior to the incident. It was subsequently found that, although the wire should have had a 100% inspection, NDT and high pressure lubrication, this was not achieved. When the wire rope was reeled off the crane onto a reel sited on the quayside and the NDT and pressure lubricating equipment positioned on the crane jib approximately 25m of the wire was omitted from the inspection. This was the section of wire that failed.
The company involved has contacted the inspection company to verify that it has changed its quality procedures to include a method statement to ensure 100% NDT inspection and high-pressure lubrication.
The planned maintenance for the inspection of vessel crane wires is to be reviewed to determine if the frequency and mechanism is sufficient to actively monitor the condition of crane wire ropes in use.
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