Figure 20. Crevice corrosion in seawater was more prevalent than pit- 

 ting corrosion and ranged from incipient to perforation of the 30-mil 

 thick specimens after exposure for 1 year at a depth of 2,500 feet. 

 Pitting corrosion was the same in the bottom sediments as in seawater 

 at both depths but crevice corrosion was less intense than in the 

 seawater. 



Forgeson, et al. .Reference 15, reported perforation (270 mils) by 

 pitting of AISI Type 321 stainless steel after 1 year of exposure in 

 seawater at the surface at Fort Amador, Panama Canal Zone in the Pacific 

 Ocean as compared to a maximum pit depth of 22 mils after 1 year of 

 exposure at the surface at Port Hueneme in the Pacific Ocean. This 

 performance at Fort Amador is considerably greater than the corrosion 

 of this alloy at both depths in the Pacific Ocean at Port Hueneme. 

 These differences can be attributed to the higher temperature and oxygen 

 concentration at Fort Amador. 



AISI Type 325 stainless steel differed from the other 300 Series 

 stainless steels in its corrosion behavior in that the types of corro- 

 sion were general or pitting associated with higher calculated corro- 

 sion rates, Figure 21. On the basis of corrosion rates calculated from 

 weight losses the seawater at depth was more corrosive than the bottom 

 sediments , and seawater at the surface was more aggressive than that at 

 depth. 



Except for perforation of the 50-mil thick specimens of AISI Type 

 330 stainless steel exposed at the surface for 6 months and 1 year, 

 there was no pitting corrosion of this alloy, Figure 22. Crevice corro- 

 sion in the seawater was more prevalent than pitting corrosion ranging 

 from incipient to perforation of the 50 mil thick specimens after 6 

 months of exposure at the surface and of the 30-mil thick specimens 

 after 1 year of exposure at the 2,500-foot depth. The aggressiveness 

 of the bottom sediments was about the same as that of the seawater at 

 depth. 



Pitting and crevice corrosion were much more severe on AISI Type 

 347 stainless steel in seawater at the surface than at depth, the 50 

 mil thick specimens being perforated by both types of corrosion as shown 

 in Figure 23. There was no pitting in seawater at either depth, 2,500 

 or 6,000 feet, while crevice corrosion ranged from none to 10 mils deep. 

 Crevice corrosion in the bottom sediments was more severe than in the 

 seawater at depth, the 50-mil thick specimens were perforated after 3 

 years of exposre at the 6,000-foot depth. Pitting corrosion in the 

 bottom sediments was of the same severity as in seawater at depth. 



The predominate types of corrosion on the AISI 300 Series stainless 

 steels were crevice, tunneling and pitting corrosion. The one exception 

 was AISI Type 325 stainless steel which contained only 9.0 percent 

 chromium and 23.5 percent nickel, which was chiefly attacked by general 

 corrosion with some pitting and crevice corrosion. 



The surface seawaters were more aggressive than the seawater at 

 either depth. The rates of penetration of pitting, tunneling and crevice 



