in Figure 43. The corrosion rates in sea water and in the bottom sedi- 

 ments at the 5,000 foot depth were comparable and decreased gradually 

 with increasing time of exposure. The corrosion rates at the 2,500 

 foot depth were lower than those at the 6,000 foot depth and those in 

 the bottom sediments were lower than those in sea water. The corrosion 

 rate after 181 days of exposure at the surface in the Pacific Ocean at 

 Point Mugu was about the same as in the sea water at the 6,000 foot 

 depth. The corrosion of this alloy was of the uniform type. 



The corrosion rates in sea water at the 2,500 and 6,000 foot depths 

 of all the copper-nickel alloys given in Table 14 and shown in Figures 

 35 through 43 are shown within bands in Figure 44, At the 6,000 foot 

 depth, the band narrows and decreases asymptotically with increasing 

 time of exposure to a width of 0.5 MPY after 1064 days. The arithmeti- 

 cal average curve is located about the midpoint of the width of the 

 band. The band for the 2,500 foot depth is practically constant with 

 time and the average curve practically bisects it. From these bands 

 it can be concluded that the corrosion rates of the copper-nickel alloys 

 in sea water can be expected to decrease with increasing duration of 

 exposure and to corrode at between 0,5 and 1 MPY at depth in the 

 Pacific Ocean after about 3 years at a depth of 6,000 feet and after 

 about 1 year at a depth of 2,500 feet. The only alloy whose corrosion 

 rates did not come within these bands was the 70 copper-30 nickel alloy 

 which contained 5 percent iron. However, at the 6,000 foot depth its 

 corrosion rate increased when the protective film failed locally and 

 after 751 days it was nearly as great as those of the other alloys. 



Similar bands encompassing the corrosion rates of the copper- 

 nickel alloys when partially embedded in the bottom sediments are shown 

 in Figure 45. The lines within the bands are the average curves. At 

 the 6,000 foot depth the band narrows and decreases asymptotically with 

 increasing time of exposure to a width of about 0.3 MPY after 1064 days 

 of exposure. From this band it can be concluded that the corrosion 

 rates of the copper-nickel alloys partially embedded in the bottom 

 sediments can be expected to decrease with increasing duration of ex- 

 posure and to corrode at between 0.2 and 0.5 MPY after about 3 years 

 of exposure. At the 2,500 foot depth there was a slight increase in 

 the width of the band between 200 and 400 days of exposure and the 

 average corrosion rate curve also increased slightly. After 1064 days 

 of exposure at a depth of 6,000 feet, the copper-nickel alloys par- 

 tially embedded in the bottom sediments corroded at slower rates than 

 in the sea water as shown by comparing Figures 44 and 45. 



Stress Corrosion 



Five of the copper-nickel alloys were exposed in the stressed con- 

 dition to determine their susceptibility to stress corrosion cracking. 

 Table 16. They were stressed at values equivalent to 35, 50 and 75 

 percent of their respective yield strengths. None of the alloys were 



17 



