Aluminum Alloys as Potential O.T.E.C. Heat Exchanger Materials

Data for well over 800 days of corrosion testing at the Natural Energy Laboratory of Hawaii are reported. Tube samples are exposed in once-through test loops at flow velocities of 1.35 and 1.85 m/s. To date, the alloys tested in the warm (25-28°C) surface seawater show only uniform corrosion at a very low rate of n/yr. In the cold (7-9°C) deep ocean water, which is taken from 600 m depth, co-extruded 7072 cladding on alloy 3003 tends to corrode by localized attack. The base metal is not affected, however, and the overall corrosion rate is low. The attack increases at lower flow velocities. Other alloys, notably alloy 5052, have so far shown excellent resistance to pitting and general corrosion. Implications of the results on future alloy development efforts and on heat exchanger applications are discussed.