The 210-mil thick specimens were perforated by pitting and tunneling 

 after 6 months of exposure at the surface and after 1 year and longer 

 at depths of 2,500 and 6,000 feet. Crevice corrosion was serious but 

 its penetration rate was lower than either the pitting or tunneling 

 rates. The bottom sediments were less aggressive at both depths than 

 was the seawater above them. 



Brown, et. al. (Reference 14), reported that the maximum pit depth 

 of AISI Type 304 was 27 mils after 111 days of exposure in the Tongue 

 of the Ocean at a depth of 5,600 feet. In the NCEL tests there was no 

 pitting of Type 304 after 6 months of exposure at depths of either 2,500 

 or 6,000 feet but there was tunneling, the longest of which was about 1 

 inch at the 2,500-foot depth. 



Sensitized (heated for 1 hour at 1200°F and cooled in air) AISI 

 Type 304 was more susceptible to pitting and crevice corrosion at the 

 surface and at depths of 2,500 and 6,000 feet (Figure 11) than was the 

 unsensitized alloy (Figure 10) . The 50-mil thick specimens were per- 

 forated by crevice corrosion in all three seawater environments after 

 6 months of exposure. The bottom sediments of both depths were not as 

 aggressive as was the seawater at these depths. 



The corrosion of AISI Type 304L stainless steel was comparable with 

 that of AISI Type 304 stainless steel as shown by comparing Figure 12 

 with Figure 10. Pitting and tunneling corrosion were more severe than 

 was crevice corrosion, the 115-mil thick specimens being perforated by 

 the pitting and tunneling types after 1 year of exposure at the surface 

 and at both depths, 2,500 and 6,000 feet. From the standpoint of pit- 

 ting and tunneling corrosion, the seawater at the 2, 500- and 6,000-foot 

 depths was more aggressive than the bottom sediments , but from the 

 standpoint of crevice corrosion the reverse was true. 



As shown in Figure 13, AISI Type 309 stainless steel was free of 

 pitting during surface exposures and at the 2,500-foot depth for 1 year 

 and at the 6,000-foot depth for exposures as long as 3 years. There 

 was only incipient crevice corrosion of this alloy except after 6 months 

 at the surface where it had penetrated to a depth of 33 mils. The 

 aggressiveness of the bottom sediments was the same as the water above 

 them. 



There was no pitting corrosion of AISI Type 310 stainless steel 

 during surface seawater exposures or during exposure at a depth of 2,500 

 feet for 1 year or at a depth of 6,000 feet for 3 years, Figure 14. 

 There was only incipient crevice corrosion except after exposure for 1 

 year at the surface, perforated (50 mils), and at the 2,500-foot depth, 

 14 mils. The bottom sediments were no more aggressive than was the 

 water above them. 



There was no pitting corrosion of AISI Type 311 stainless steel 

 except during the surface exposures, Figure 15. The alloy was pene- 

 trated to a depth of 28 mils after 6 months of exposure with only in- 

 cipient pitting being present after 1 year of exposure. Crevice corro- 

 sion was the most prevalent type, it being incipient or shallow at depth, 

 but perforated the 50-mil thick specimens after 6 months of exposure at 



