CORROSION OF MATERIALS IN HYDROSPACE - PART VI - STAINLESS STEELS 



Technical Note N-I172 



YF 38.535.005.01.004 



by 



Fred M. Reinhart 



ABSTRACT 



A total of 1,750 specimens of 57 different stainless steels were 

 exposed in seawater at the surface and at depths of 2,500 and 6,000 feet 

 in the Pacific Ocean for periods of time varying from 123 to 1,064 days 

 in order to determine the effects of the seawater environments at dif- 

 ferent depths on their corrosion resistance. 



Corrosion rates, type of corrosion, pit depths and stress corrosion 

 cracking resistance are presented. 



Cast stainless steel, Ni-Cr-Mo-Si, was uncorroded. 



AISI Types 317 and 329 stainless steels were attacked by incipient 

 (less than 1 mil deep) crevice corrosion. Stainless steel 20Cb-3 was 

 attacked by both incipient crevice corrosion and incipient pitting cor- 

 rosion. Most of the corrosion on AISI Type 325 stainless steel was of 

 the general surface type. 



All the other stainless steels, AISI Types 200, 300, 400 and 600 

 series and miscellaneous alloys, both cast and wrought, were attacked 

 by pitting, tunneling and crevice types of corrosion varying in inten- 

 sity from depths of 1 mil to complete perforation of the thickness of 

 the material and tunnels to 12 inches long. 



In general, corrosion in surface seawater was more severe than in 

 the deep seawater and in the bottom sediments at depths of 2,500 and 

 6,000 feet for equivalent periods of exposure. 



Sensitization decreased the corrosion resistance of AISI Types 304 

 and 316 stainless steels. 



Stainless steel wire ropes were also attacked by the pitting and 

 crevice types of corrosion. 



Precipitation hardening stainless steels 630-H925, 631-TH1050 and 

 RH1050, 632-RH1100, 15- 7AMV- annealed, RH950 and RH1150 and PH14-8Mo- 

 SRH950 failed by stress corrosion cracking. 



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