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Load exceeding safe working load (SWL) leads to overstressed and damaged rigging

What happened?

During a recent decommissioning operation, shears were used to cut a pipeline. The shear tool was rigged to the crane in a vertical fashion. The shear tool was placed on the pipeline at the cut location and when the shear jaws closed around the pipe to make the cut, the shear tool was pulled downward due to the ‘bird’s beak’ design of the jaws.

As a result, the load quickly increased the tension on the rigging over the safe working limit (SWL) of the rigging resulting in damage (deformation) to the rigging. The crane operator was instructed to immediately reduce load to an acceptable level.

The shear tool was placed on the seabed and the damaged rigging was removed from the arrangement. The shear tool was then re-rigged to the whip line for recovery to the surface.

This incident resulted in damage to property (hook and shackle) but could easily have been a good deal more serious, having the potential to have harmed the diver who was working close to the shear tool.

What were the causes?

The immediate causes of the incident were:

  • Failure to recognize the hazard of the shear tool pulling downward during cutting operations;
  • Inadequate preparation/planning.

The root causes were found to be:

  • Lack of knowledge;
  • Inadequate communication.

Lessons learnt

  • Placement of the shear tool and the amount of ‘slack’ available to make a cut will have an impact on the outcome;
  • Ensure SWL of rigging arrangement is communicated to crane operator prior to lifting operations;
  • Ensure rigging drawings are available. If not, a hand sketch should be prepared locally and reviewed/approved prior to lifting operations.

Members may wish to refer to the following incident (search phrase: ‘overstressed’):

Safety Event

Published: 21 December 2017
Download: IMCA SF 32/17

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