depths of crevice corrosion are shown graphically in the figures to 

 provide an overall picture of the corrosion of the stainless steels. 



The corrosion rates, maximum pit depths, maximum lengths of tun- 

 nel corrosion, depth of crevice corrosion and types of corrosion are 

 given in Tables 3 through 7 and all except tunnel corrosion are shown 

 graphically in Figures 6 through 44. 



AISI Type 200 Series Stainless Steels 



The AISI 200 Series stainless steels are 300 Series stainless 

 steels modified by substituting manganese for about half of the nickel. 

 This modification does not hinder the corrosion resistance of the iron- 

 chromium-nickel alloys in many environments. 



The corrosion rates, maximum pit depths, depths of crevice corro- 

 sion and types of corrosion are given in Table 3. The corrosion rates, 

 maximum pit depths and depths of crevice corrosion are shown graphically 

 in Figures 6 and 7 . 



Corrosion of AISI Type 201 stainless steel, Figure 6, after 6 

 months of exposure was more severe at the 2,500-foot depth than at the 

 surface or at a depth of 6,000 feet because of crevice corrosion. After 

 1 year at the surface, there was severe edge corrosion and at the 2,500- 

 foot depth there was crevice corrosion. There was only incipient 

 crevice corrosion in seawater after 2 and 3 years of exposure at the 

 6,000-foot depth. The bottom sediments at both depths were no more 

 corrosive than the seawater except after 3 years of exposure at the 

 6,000-foot depth where the specimen was perforated by pitting corrosion. 



AISI Type 202 stainless steel was attacked more severely in the 

 seawater by pitting and crevice corrosion after 6 and 12 months of 

 exposure at the surface than at depths of 2,500 and 6,000 feet, Figure 

 7. The 64-mil thick material was perforated both by pitting and crevice 

 corrosion within 6 months at the surface as contrasted to incipient or 

 no corrosion at depth. After 1 year crevice corrosion had penetrated 

 to a depth of 17 mils at a depth of 2,500 feet with no attack at the 

 6,000-foot depth. 



There was neither pitting corrosion nor incipient crevice corro- 

 sion after 2 and 3 years of exposure at the 6,000-foot depth. 



Corrosion in bottom sediments at both depths was about the same as 

 in the seawater. 



The rapidity of the progress of pitting and crevice corrosion at 

 the surface as contrasted to the progress at both depths (2,500 and 

 6,000 feet) indicates that the surface environment was more aggressive 

 to AISI Type 202 stainless steel than were the environments at depth. 

 Variables at the surface which differ from those at depth, to which 

 could be attributed the more rapid corrosion, are higher oxygen concen- 

 tration and the attachment of fouling organisms. 



AISI Type 205 stainless steel exposed in the Tongue-of-the-Ocean, 

 Atlantic Ocean, for 111 days at a depth of 5,600 feet corroded much 

 more rapidly than did the two Cr-Mn-Ni steels at depths of 2,500 and 



