Testing subsea air bags with SmartLoad® load monitoring technology

Unique Seaflex Ltd, manufacturers of underwater air lift bags commonly used in the offshore oil and gas industry, contacted Scotload to support some full scale load monitoring safety trials.

The issue:

Subsea air bags are commonly used to support divers installing, re-positioning or removing subsea pipelines and manifolds. There have been several incidents in the offshore industry where the air lift bags have been accidentally released from the seabed and entered a Dive Support Vessel's thruster causing it to lose power and ultimately its position over the diver.

The International Marine Contractors Association (IMCA) has issue guidance notices relating to a multitude of offshore activities and equipment and their Guidance D016 covers air lift bags. Within Guidance D016 information is provided to manufacturers detailing the safety features air lift bags must contain, one of which is the inverter line attachment point on the very crown of the bag. The purpose of this is to provide a tie off point for a rope to be connected back to the load, so that in the event of rigging failure between the air lifting bags and the load, the bag is prevented from ascending to the surface. The line arrests the bag, and then turns it upside down to allow the air to escape before the bag gently settles back on the seabed. 

IMCA asked Unique Seaflex to carry out some full scale trials in an 8m deep tank at the National Hyperbaric Centre in Aberdeen to measure the load experienced by the inverter line while inverting an air lift bag, in order to provide advice to air lift bags uses on which breaking strain of line to use.

The solution:

"Unique Seaflex approached Scotload who quickly understood the nature of the problem and within a week supplied a 17t subsea load shackle with a 10m cable and SmartLoad® transmitter. The load shackle transmitted the loads back to a laptop computer with SmartLoad® software installed at a rate of 200Hz which provided superb data in both graphic and numerical outputs." Commented Graham Brading, managing director of Unique Seaflex.

Most commercially available alternative systems have a relatively low sample and transmit rate rendering them unsuitable for dynamic measurement, but SmartLoad® is designed for speed data acquisition and transmission. This is achieved by incorporating a data-logger in the sensor interface, enabling the data to be sampled at 200 Hz and then transmitted to the receiving station immediately after the test. The signal is bi-directional, enabling the monitoring and telemetry to be configured and controlled from the remote station.

Graham remarks further: "Unique Seaflex and IMCA were extremely pleased with the performance, accuracy and reliability of the SmartLoad® equipment and will no doubt be using it again in all subsequent trials."