An ingenious idea from Saab Seaeye customer, Stinger Technology, has found a way to penetrate the labyrinth inside offshore production tanks in search of environmental contaminates prior to decommissioning.

They managed to squeeze a unique underwater robotic systems configuration loaded with sampling technology through a 150 cm square hatch to search the tank’s internal maze of baffles, and navigate along 25.5 cm diameter pipe-runs of curves and bends.

2Tank 2Tank layout showing entrance for mothership.

Stinger’s idea turned the already compact Saab Seaeye Falcon into a ‘mother ship’ from which is launched an even smaller fly-out VideoRay and tiny fly-out Stinger Nano.

The Norwegian company dubbed the trio, Mother, Daughter and Little Sister.

With the market expecting 1800 wells to be decommissioned over the next 10 years, in Norway and the UK alone, the new ‘little family’ is set to be busy.

Importantly for offshore operators, is that sampling investigations on installations still in production, but planned for decommissioning, are not interrupted.

Saab Seaeye were pleased to collaborate with Stinger who are known for finding innovative ways to work in confined underwater spaces and chose the Falcon as the smallest and most powerful option on the market.

The Falcon’s five-thruster strong precise manoeuvrability, and the plug and play configurability of its intelligent distributed control system, meant Stinger were confident it would be an ideal mothership for the two fly-off resources.

Measuring just 1 x 0.5 x 0.6 metres in size, Stinger knew the Falcon could pass through the 150cm hatch and into the ‘nose tank’, even when fully configured, ready for launching the daughter and sister from their integrated tether management system on their extended sampling missions.

The entire Falcon mother ship configuration, with its fly-out 120m TMS, its docking station for fly-out daughter and sister, a subsea toolbox, tailor-made subsea interchangeable tools using manipulator, and docking-inclusive cleaning device in its tool basket – all fitted into a total system dimension of 1000x1000x850mm.

Saab Seaeye engineers were keen to assist in Stinger’s technological achievement, which included Stinger developing their own miniature robotic system in the form of the Nano - the smallest and most advanced plugin fly-out on the market.

Once into the tank and embarking upon the data-gathering mission, two operators work in tandem – one, piloting the Falcon, the other piloting the daughter and sister.

The environmental sampling strategy involved seeking out various residues expected within the tank from a lifetime of production cycles. These included oil, oil and water emulsion, wax, scale, sediment and sludge, sand, and possibly smaller gas pockets.

The VideoRay and Stinger Nano were fitted out with a range of tools including a deposit depth rule tool for measuring sediment and deposits on base and walls, a scraper tool for measuring the thin layer of hydrocarbon wax deposits on the tank wall and a scoop sampler. Included was a water quality sensor for measuring dissolved oxygen, temperature, conductivity, salinity, specific conductance, resistivity, pH and ORP. A bottle sampler with a manipulator operated release mechanism was also included and a camera to verify successful sample taking.

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