alloy was anodic to the parent nickel in the sea water but not in the 

 bottom sediment. 



Nickel 200 was not susceptible to stress corrosion cracking when 

 exposed at a depth of 2,370 feet for 402 days at tensile stresses 

 equivalent to 50 and 75 percent of its yield strength (12,500 and 

 18,700 psi, respectively). 



Exposures for periods of time as long as 1064 days at a depth 

 of 5,300 feet were not detrimental to the mechanical properties of 

 nickel 200, Table 4. 



NICKEL-COPPER ALLOYS 



The chemical compositions of the nickel-cooper alloys are given 

 in Table 5, their corrosion rates and types of corrosion in Table 6 

 and changes in mechanical properties in Table 1 . 



The nickel-copper alloys have excellent corrosion resistance in 

 sea water except that in slowly moving or stagnant sea water they 

 are subject to pitting. This is particularly true if fouling orga- 

 nisms are present and attach themselves to the metal. They are 

 inherently passive, hence in environments deficient in oxygen this 

 passivity is destroyed locally and they pit at these local anodes or 

 corrode by oxygen concentration cell type of corrosion in crevices. 



The corrosion rates of nickel-copper 400 alloy at depth and at 

 the surface in both the Atlantic and Pacific Oceans are shown in 

 Figure 5. Even though there was both pitting and fouling of specimens 

 in all surface exposures, the corrosion rates decreased with increase 

 in duration of exposure. However, due to the higher average tempera- 

 ture at the Panama Canal Zone, the corrosion rates there were three 

 times as great as those at Port Hueneme, California and at Harbor 

 Island, North Carolina. 



The corrosion rates at nominal depths of 2,500 and 6,000 feet 

 irs. the Pacific varied with duration of exposure so that it was not 

 possible to construct smooth curves. This vacillation of the cor- 

 rosion rates is attributed to the pitting and crevice types of 

 corrosion. The pitting of nickel-copper alloy 400 after 1064 days 

 of exposure partially embedded in the bottom sediment at a depth of 

 5,300 feet is shown in Figure 6. The unpitted portion on the right 

 was embedded in the bottom sediment; the pitted portion extended 

 above the sediments. For this reason the corrosion rates at both 

 depths in sea water are shown as a band in Figure 5 which encompasses 

 all but three of the 17 values. For duration of exposure longer 

 than 400 days this band is between the two curves for surface cor- 

 rosion rates. The low oxygen concentration environment (2,500 foot 



