uniformly decreased. The corrosion rates of AISI 430 and 18Cr-14Mn- 

 0.5N stainless steels, although lower at the lower oxygen concentra- 

 tions than at the highest oxygen concentration, were not uniformly 

 affected by the oxygen concentration. 



Examination of the pitting, tunneling and crevice corrosion data 

 for these stainless steels in Tables 13, 15 and 17 shows only a general 

 relationship with corrosion rates. These types of corrosion were, in 

 general, more severe or just as severe in the surface seawater (high- 

 est oxygen concentration) than at depths of 2,500 and 6,000 feet. 

 However, it is more realistic to assess the performance of these 

 stainless steels on their localized types of corrosion performance 

 than upon calculated corrosion rates. 



The corrosion rates of the 300 Series stainless steels as affec- 

 ted by depth are shown in Figure 28. Only the corrosion rates of the 

 AISI 304 and 304L stainless steels decreased with increasing depth. 

 The corrosion rates of AISI 301, 302, 316, 316 (sensitized), 330, 347, 

 304 (sensitized) and 325 stainless steels were lower at depth than at 

 the surface, but they did not decrease progressively with increasing 

 depth. In addition, the shape of the corrosion rate curve for AISI 

 325 was similar to the oxygen concentration curve. 



The effect of changes in the concentration of oxygen in seawater 

 on the corrosion rates of the 300 Series stainless steels are shown in 

 Figure 29 . The corrosion rates of the alloys shown in Figure 29 de- 

 creased with decreasing oxygen concentration, although not uniformly. 



Examination of the pitting, tunneling and crevice types of corro- 

 sion in Table 14 for the alloys whose corrosion rates were plotted in 

 Figures 28 and 29 shows that, in general, there is no definite correla- 

 tion between their corrosion rates and the severity of these types of 

 corrosion. For example, the corrosion rates of AISI 304L varied from 

 1.0 to 0.4 to <0.1 MPY at the three depths, while pitting corrosion 

 was to perforation (115 mils) in all exposures while crevice and tun- 

 neling corrosion was more severe at the 6,000-foot depth where the 

 corrosion rate was the lowest (<0.1 MPY). 



Oxygen and depth apparently had no effect on the corrosion of the 

 following 300 Series stainless steels: AISI 309, 310, 311, 316L, 317, 

 321 (slightly affected) and 329. 



The effect of depth on the corrosion rates of some of the 600 

 Series precipitation hardening stainless steels is shown in Figure 30. 

 The corrosion rate of 631-TH1050 and 635 decreased with increasing 

 depth of seawater. The corrosion rates of 630-H925 and 632-RH1100 were 

 lower at depth than at the surface but they did not decrease progress- 

 ively with increasing depth. 



The effect of changes in the concentration of oxygen in seawater 

 on the corrosion rates of the 600 Series precipitation hardening stain- 

 less steels is shown in Figure 31. The corrosion rate of AISI 632- 

 RH1100 decreased progressively with the oxygen content of seawater. 

 The corrosion rates of AISI 630-H925, 6 31-TH1050 and 635, although 



