STAINLESS STEELS 



The chemical compositions of the stainless steels are given in 

 Table 17; their corrosion rates and types of corrosion in Table 18 and 

 the effects of exposure on their mechanical properties in Table 19. 



The alloys which were least corroded were AISI Types 310, 317 and 

 329; 20Cb; 20Cb-3 and; AM350. They were not entirely uncorroded in 

 that there was incipient crevice corrosion evident on all of them even 

 though their corrosion rates were less than 0.1 mils per year. 



All the other alloys were attacked by pitting, crevice, edge or 

 the tunnel types of corrosion or combinations of these types. The 

 crevice and tunnel types of corrosion were the most prevalent and they 

 are also the most insidious types. 



Crevice corrosion occurs in the small space between two contacting 

 surfaces and usually its severity is not evident from visual examination 

 unless there is perforation of the alloy: generally the mating sur- 

 faces must be separated from each other to evaluate the degree of 

 severity. 



The tunnel type of corrosion usually appears as a tiny pin hole on 

 the surface or on the edge of the material. However, once corrosion 

 penetrates the surface it spreads out in a tunnel like configuration 

 extending for a considerable distance underneath the surfaces of the 

 material. 



In general, the Type 300 stainless steels were less corroded than 

 either the 200 or 400 Type alloys. The precipitation hardening stain- 

 less steels, except AM350, were severely attacked by the edge and the 

 tunnel types of corrosion and were judged to be about as corrosion re- 

 sistant as the 200 and 400 Type alloys. The precipitation hardening 

 stainless steels are: PH14-8Mo, PH15-7Mo, 17-7PH, 17-4PH, 17Cr-14Ni- 

 Cu-Mo, 18Cr-14Mn, AM350 and 17Cr-7Ni. 



In general, crevice corrosion was more severe after 181 days of 

 exposure at the surface than after comparable periods of exposure at 

 depths of 2,500 and 6,000 feet. 



The effects of exposure in sea water on the mechanical properties 

 of some of the stainless steels are given in Table 19. The mechanical 

 properties of the alloys were not adversely affected. 



TITANIUM ALLOYS 



The chemcial compositions of the titanium alloys are given in 

 Table 20, their corrosion rates in Table 21 and the effect of exposure 

 in sea water on their mechanical properties in Table 22. 



The corrosion rates and types of corrosion of the titanium alloys 

 are given in Table 21. There was neither any significant weight losses 

 nor visible corrosion on any of the welded or unwelded alloys except 

 stress corrosion cracking of the 13V-llCr-3Al alloy containing a 

 circular weld. 



