The corrosion rates, maximum pit depth, maximum tunnel length, 

 maximum depth of crevice corrosion and types of corrosion are given in 

 Table 7 and shown, except for tunneling, graphically in Figures 39 

 through 44. 



Wrought stainless steel 20Cb which was developed to resist reducing 

 conditions was susceptible to some pitting and crevice corrosion, Figure 

 39. The only case of pitting occurred during 398 days of exposure at 

 the surface where the maximum depth was 14 mils. There was no pitting 

 at either depth for as long as 3 years of exposure. The deepest crevice 

 corrosion in seawater was 26 mils after 2 years of exposure at the 6,000- 

 foot depth. Except for these isolated cases of corrosion the alloy was 

 not attacked. 



A slightly modified version of 20Cb, (4 percent higher nickel) 

 designated 20Cb-3, was more resistant than 20Cb to seawater and the 

 bottom sediments. There was only incipient pitting and incipient 

 crevice corrosion after exposure at the surface for 1 year and at depth 

 for 3 years, Figure 19. 



The corrosion of two cast versions of 20Cb , Ni-Cr-Cu-Mo numbers 

 1 and 2, are shown in Figures 40 and 41. There were isolated cases of 

 crevice corrosion and pitting corrosion similar to the behavior of 20Cb. 

 For both cast Ni-Cr-Cu-Mo alloys crevice corrosion during surface expo- 

 sure was more rapid than at depth. Their behavior in the bottom sedi- 

 ments was the same as in the seawater immediately above the sediments. 



A cast Ni-Cr-Mo stainless alloy was free of pitting corrosion 

 during exposure at the surface and at depth both in seawater and in 

 the bottom sediments, Figure 42. Crevice corrosion was slight, the max- 

 imum depth being 1 mil after 1 year at the 2,500-foot depth. 



A cast stainless steel containing Ni-Cr-Mo-Si was free of any type 

 of corrosion both during surface exposure and during exposure at depths 

 of 2,500 and 6,000 feet. This was the only stainless steel which was 

 not corroded insome manner. 



Cast alloy RL- 35-100 was free from both pitting and crevice corro- 

 sion in seawater and the bottom sediments, Figure 43. The type of 

 corrosion was surface etching or general surface attack which is com- 

 pletely different from any of the other stainless steels used in this 

 program. 



An alloy containing 18Cr-14Mn-0 .5N is a modified 300 Series stain- 

 less steel in which 14 percent Mn and 0.5N were substituted for the 

 nominal 8 percent Ni to conserve the use of nickel. The substitution 

 did not improve the corrosion resistance of the 300 Series stainless 

 steels; its corrosion behavior is shown in Figure 44. It was rapidly 

 attacked by pitting, crevice and tunneling types of corrosion, both at 

 the surface and at depth, both in seawater and the bottom sediments. 



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