86 Insight | UUVs Tank inspections As well as exploring strange new waters, some uncrewed systems are now operating in entirely different fluid mediums. Since 2019, Massachusetts and Texas-based Square Robot has completed over 250 commercial tank inspections worldwide using the SR-1 and SR-3 autonomous submersible robots. These inspections have involved tanks containing a variety of fluid products, including fuels, lube oils and alcohols. Square Robot’s three founders previously worked for a defence contractor, developing UUVs for military applications such as MCM, with one underwater robotic system in particular being used in scanning the exterior of ship hulls. “Somewhere along the line, an oil and gas industry veteran saw the ship-hull inspection robot, and queried that if it was possible to inspect the outside of a ship hull while it was still in the water, we ought to be able to inspect the inside of a fuel storage tank while it is still in service,” says Ross Jarvis, technical director of sales and marketing at Square Robot. The SR-1 was therefore engineered from day one as a solution specialising entirely on inspecting the interior of above-ground atmospheric storage tanks, and enduring and navigating through chemicals of varying temperatures, densities and viscosities. After four years of real-world operations with the SR-1, Square Robot analysed extensive feedback, field experience and the hard lessons learned (as well as vast amounts of data) to develop the SR-3, its flagship inspection system. The SR-3 measures 1.70 x 0.51 x 0.45 m and weighs 120 kg in air. As well as integrating a plethora of sensors (including cameras complemented by illuminators), the robot’s hull holds eight thrusters, a 256-element phased array ultrasonic (PAUT) sensor, rollers for navigating along the inside of tank walls, and an auger brush for moving sediment on the tank bottom out of the path of the PAUT sensor. “A large part of the design choices and improvements that went into SR-3 focused on material compatibility. Our engineering team’s work required not just choosing structural materials that would be strong enough and light enough, but also materials that wouldn’t degrade in harsh products, like naphtha and methanol,” Jarvis notes. The SR-3 typically operates at a maximum speed of 15 cm/s while inspecting; that being the operating limit for the PAUT sensor integrated principally for measuring plate thicknesses to a high degree of accuracy, which allows for the identification of defects, corrosion and pitting. The PAUT sensor is able to collect 96,000 individual UT data points for every square metre of tank bottom inspected. Significant work was done to ensure appropriate sealing of the system to protect electrical and electronic systems against the pressures and corrosive properties of the surrounding fluids. The SR-3 can work in pressure up to 275 kPa (40 psig) as atmospheric storage tanks can reach 15 m in height. “Meanwhile, the fact we’re working in GNSS-denied spaces means we needed a high-quality inertial navigation, supported by our onboard acoustic sensors suite for localisation. Our system has a navigational accuracy to within 0.153 m anywhere within the tank,” Jarvis says. While the SR-3 inspects autonomously 90% of the time, Square Robot always has a trained field engineer as the operator at its GCS, to constantly monitor but also assist the autonomy system in the most complex scenarios, when invariably it is faced with a new and unexpected obstacle – one that even a well-trained AI system would struggle to determine the optimal response to (for now). Summary While the use-cases documented here cover a broad mix of operating locations, from lakes and tunnels to 10,000 m-deep seafloors, they all share the property of targeting cost-effectiveness, either in their use, construction or both. With the leading but highly expensive UUVs of the world now sharing space with lower-priced systems, democratised access to ocean data can gradually be expected to boost demand for UUV units. Within the next 10-15 years, one should not be surprised to see factories dedicated to series production of these new UUVs springing up. Production of complementary systems, such as subsea autopilots, marine batteries and marine actuators, can be expected to increase around them as part of a real, dedicated UUV manufacturing boom – much like what is happening around UAVs today. February/March 2025 | Uncrewed Systems Technology Extensive material compatibility studies were key to optimising the SR-3 for navigating and surveying through fuels, lube oils, alcohols and other chemicals (Image courtesy of Square Robot)
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