| Popis: |
A total of 1300 specimens of 47 iron base alloys were exposed at depths of 2,340, 2,370, 5,300, 5,640 and 6,780 feet at two sites in the Pacific Ocean for 197, 402, 1064, 123, 751 and 403 days respectively to determine the effects of deep ocean environments on their corrosion behavior. Corrosion rates, pit depths, types of corrosion, changes in mechanical properties, effects of stress, and analyses of corrosion products are presented. The corrosion rates of all the alloys, both cast and wrought, decreased asymptotically with duration of exposure and became constant at rates varying between 0.5 and 1.0 mils per year after three years of exposure in sea water and partially embedded in the bottom sediments at a nominal depth of 5,500 feet. These corrosion rates are about one- third those at the surface in the Atlantic Ocean. At the 2,350 foot depth, the corrosion rates in sea water also decreased with duration of exposure but tended to increase slightly with duration of exposure in the bottom sediments. The corrosion rates at the 2,350 foot depth were less than those at the 5,500 foot depth. The mechanical properties were unimpaired. Silicon and silicon-molybdenum cast irons were uncorroded. A sprayed 6 mil thick coating of aluminum protected steel for a minimum of three years and a hot dipped 4 mil thick coating of aluminum protected steel for a minimum of 13 months while a hot dipped 1.7 mil thick coating of zinc protected steel for about 4 months. |
