Lift bag lost when rigging parted

The lift bag was of the open bottomed parachute type. In order to provide additional buoyancy to a pipeline, two five-ton lift bags were secured to the pipe in between pre-installed foam buoys. The buoys were secured by the traditional method of steel straps and bandit clamps. A ‘strip-out’ wire was in place and was run underneath the straps along the length of the pipe to assist removal of the foam buoys once the pipe was in position.

The lift bags were rigged and secured to the pipe with appropriately selected and certified rigging. It was determined that the additional ten tons of lift was not sufficient force to cause a loss of control of the pipe. The inverter line was secured to the pipeline and ‘snugged-up’ to avoid a snatch load in the event of failure or an unplanned release of the rigging. Later, upon up-hauling of the strip-out wire to remove the buoys, one of the two bags was found to have parted and was floating on the surface.

Schematic diagram of pipeline and lift bags illustrating incident

Further inspection revealed that the webbing strops of the bag had been cut through when the strip-out wire was pulled at an acute angle across the plane of the pipe relative to the bag. It was also discovered that the inversion line had pulled the attachment points away from the crown of the bag. These strops remained secured to the inverter line which in turn remained attached to the pipeline.

It was further determined that the strops at the top of the bags used for attaching the inversion lines were intended for handling purposes only and were not designed as inversion line attachment points.