Reinhart 



There was no measurable corrosion of the silicon and silicon- 

 molybdenum cast irons at either depth. 



In sea water at both depths the other cast irons behaved 

 similarly to the steels as is clearly shown by comparing the curves 

 in Figure 5 with those in Figure 10. 



The corrosion rates of the austenitic cast irons in sea 

 water are shown graphically in Figure 11. The corrosion rates of 

 these alloys in sea water also decrease with time of exposure at both 

 depths with the rates at 2,350 feet being lower than those at 5,500 

 feet. 



The median curves for the two groups of cast irons and the 

 alloy steels are shown in Figure 12 for sea water and in Figure 13 

 for bottom sediments. These curves (Figure 12) show that in sea 

 water at a depth of 5,500 feet corrosion behavior of these three 

 groups of alloys was the same after 750 days of exposure. There was 

 a slight decrease in the corrosion rates of the three groups of alloys 

 with time at a depth of 2,350 feet and the corrosion rate of each 

 group was lower than that of its companion group at a depth of 5,500 

 feet. In the bottom sediments the behavior of the alloys was some- 

 what erratic. The lower corrosion rates after 400 days at a depth 

 of 6,780 feet is attributed to the fact that a greater proportion of 

 each specimen was embedded in the bottom sediment than during the 

 other three exposure periods at the nominal depth of 5,500 feet. 

 The corrosion rates at 2,350 feet tended to increase slightly with 

 time for the steels and austenitic cast irons while those for the 

 cast irons increased sharply. The type of behavior for the cast and 

 wrought alloys can only be attributed to their proximity to the 

 water- sediment interface or the percent embedment in the bottom 

 sediment. 



SUMMARY AM) CONCLUSIONS 



The purpose of this investigation was to determine the 

 effects of deep ocean environments on the corrosion of irons, steels 

 and cast irons. To accomplish this, specimens of 47 different alloys 

 were exposed at nominal depths of 2,350 and 5,500 feet for periods 

 of time varying from 123 to 1,064 days. 



The corrosion rates of all the alloys, both cast and 

 wrought, decreased asymptotically with time and became constant at 

 rates varying between 0.5 and 1.0 MPY after three years of exposure 

 at a nominal depth of 5,500 feet in sea water. These corrosion rates 

 are about one-third those of wrought steels at the surface in the 

 Atlantic Ocean at Harbor Island, North Carolina. The corrosion rates 

 of these same alloys in sea water at a depth of 2,350 feet were lower 

 than those at the 5,500 foot depth and decreased with time. 



In general, the corrosion rates of all the alloys exposed 

 either adjacent to or partially embedded in the bottom sediments at 

 the 5,500 foot depth decreased asymptotically with time and became 

 constant at rates between 0.5 and 1.0 MPY after three years of ex- 

 posure. The corrosion rates of the alloys in the bottom sediments 

 at the 2,350 feet depth tended to increase with time. 



272 



