Abstract Spherical flotation units of 99.9% Al2O3 ceramic have been successfully produced by DeepSea Power & Light for application to ocean trench systems, such as the Woods Hole Oceanographic Institution (WHOI) hybrid remotely operated vehicle (HROV) Nereus and other high-performance systems requiring maximum buoyancy with minimum air weight. WHOI successfully operated their HROV in the Mariana Trench Challenger Deep in Summer 2009, scooting across the trench floor for a total of 11 h at 36,000 feet (11,000 m). More than 1,750 3.6-inch (91.45 mm), OD seamless hollow ceramic spheres, each generating 0.6 lb (272 g) of lift, provided Nereus its buoyancy. The spheres, with a 0.34 weight/displacement ratio, withstood proof testing to 30,000 psi (207 MPa), 1,000 h of sustained pressurization to 25,000 psi and 10,000 pressure cycles to 20,000 psi (138 MPa). In addition, each of the WHOI spheres withstood 15 h at 18 ksi static pressure hold. When encased in a 0.2-inch thick buoyant elastomeric boot, they withstood impact on a concrete floor from a 6-foot elevation. An extensive quality assurance (QA) procedure is applied to 100% of manufactured spheres, with strict adherence to tight dimensional and thickness specifications as well as pressure test acoustic emission criteria (Figure 1).
Engineers at WHOI demonstrate the toughness of DSPL’s jacketed hollow ceramic spheres they use to provide lift at extreme pressures for their deep diving HROV, Nereus. (Photo by Tom Kleindinst, WHOI).
DeepSea Power & Light has additionally demonstrated the process for casting larger alumina ceramic spheres with an 8.6-inch (218.4 mm) outside diameter for the whole range of ocean depths from 10,000 feet (3000 m) to 36,000 feet (11,000 m). The larger spheres were successfully used offshore by Scripps Institution of Oceanography/UCSD in summer 2005 in an experimental free vehicle sediment sampler that impacted the seafloor at 2 m/s at a water depth of 2,200 m, dropped a weight, then rebounded to the surface with its cargo of sediment.
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