did not decrease progressively with increasing depth. The corrosion 

 rate of zinc, on the other hand, was much greater at the 6,000-foot 

 depth than at either the surface or the 2,500-foot depth. 



The effect of the concentration of oxygen in seawater on the cor- 

 rosion rates of the miscellaneous alloys is shown in Figure 33. The 

 corrosion rates of lead, tin, lead-tin solder, molybdenum and tungsten 

 were lower at the lower oxygen concentrations than at the highest, but 

 the decreases were not linear. Since there were only two points for 

 the molybdenum and tungsten curves, there is no assurance that the 

 curves would be linear with more points at intermediate oxygen concen- 

 trations. The corrosion rate for zinc was definitely not dependent 

 upon the oxygen concentration of seawater; it was the same at the low- 

 est as at the highest concentration of oxygen in seawater and twice as 

 high at the intermediate oxygen concentration. 



The effect of time of exposure at the surface on the corrosion rate 

 of molybdenum and tungsten are shown in Figure 34. The corrosion rate 

 of molybdenum decreased with increasing time of exposure while that of 

 tungsten definitely increased. 



SUMMARY 



The purpose of this investigation was to determine the effects of 

 surface seawater on the corrosion of different types of alloys for com- 

 parison with their deep ocean corrosion behavior. To accomplish this 

 1,134 specimens of 189 different alloys were exposed 5 feet below the 

 lowest tide level in the Pacific Ocean at Point Mugu, California (Site 

 V, Figure 1) for from 366 to 763 days. 



Aluminum Alloys 



In general the corrosion rates of the aluminum alloys were greater 

 at depth than at the surface in the Pacific Ocean after one year of 

 exposure, except for 5086-H34 whose corrosion rate was slightly lower. 



The maximum pit depths of the aluminum alloys were greater at depth 

 than at the surface, except for 5086-H34 whose maximum pit depths were 

 less than at the surface. 



The corrosion rate of 5086-H34 decreased slightly with the oxygen 

 concentration of seawater, those of 2219-T81 and 6061-T6 increased with 

 decreasing oxygen concentration and those of 1100-H14, 5083-H113 and 

 3003-H14 were higher at the lower oxygen concentrations, but not pro- 

 gressively. The corrosion rate of 2024-0 appears to be independent of 

 the oxygen concentration of seawater. 



The maximum pit depths of alloys 2024-0, 2219-T81 and 6061-T6 in- 

 creased with decreasing concentration of oxygen in seawater, while those 

 of 5086-H34 decreased with the oxygen concentration. The maximum pit 

 depths of 3003-H14 were deeper at the lower oxygen concentrations, but 



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