cases each of crevice and pitting attack during surface 

 exposure; 21 mils maximum for crevice corrosion, 

 and 24 mils maximum for pitting corrosion. 



Alloy 20Cb-3, a modified version of 20Cb (4% 

 higher nickel content), was more resistant to cor- 

 rosion by seawater and the bottom sediments than 

 20Cb. There was only one case of crevice corrosion 

 (40 mils deep) at depth. 



The corrosion of two cast versions of 20Cb, 

 Ni-Cr-Cu-Mo numbers 1 and 2, was very similar to 

 that of the 20Cb. There were isolated cases of crevice 

 corrosion, the maximum depth of attack being 27 

 mils. 



There was only incipient crevice corrosion on cast 

 alloy Ni-Cr-Mo during exposure at the surface and at 

 depth. 



Cast alloy Ni-Cr-Mo-Si was not susceptible to cor- 

 rosion by seawater during exposure either at the sur- 

 face or at depth. 



Cast alloy RL-35-100 was attacked by general and 

 uniform types rather than by the localized types of 

 corrosion. The corrosion rates were rather low, the 

 maximum being 0.7 mil per year after 3 years of 

 exposure at the 6,000-foot depth. 



The corrosion behavior of these alloys was not 

 affected by duration of exposure, depth of exposure, 

 or changes in the concentration of oxygen in sea- 

 water. 



As shown in Table 55, alloy 20Cb was not sus- 

 ceptible to stress corrosion in seawater at depth. 



The effects of exposure in seawater on the 

 mechanical properties of alloy 20Cb are given in 

 Table 56. The mechanical properties were not 

 affected. 



135 



