crevice corrosion. Thus, the addition of small 

 amounts of columbium to alloy 825 improves its 

 corrosion resistance, at least in seawater. 



All the nickel alloys corroded essentially the same 

 in the bottom sediments as in the seawater above 

 them. 



4.3.1. Duration of Exposure 



The corrosion rates and types of corrosion of the 

 nickel alloys are given in Table 33. Except for the 12 

 alloys above, 13 of the remaining 16 alloys were 

 attacked by crevice and pitting corrosion with crevice 

 corrosion being considerably more predominant. 

 Ni-Be alloy was attacked by pitting corrosion on the 

 ends of the bars. Ni-Mo-Fe alloys B and 2 were 

 attacked by general corrosion. Because of the crevice 

 and pitting types of corrosion, corrosion rates were 

 meaningless for determining effects of duration of 

 exposure on the corrosion behavior of these alloys. 

 These 14 alloys were: Ni-Cr-Fe alloys 600, 610, 

 X-750, and 88, Ni-Fe-Cr alloys 800, 825, 825S, and 

 902, Ni-Sn-Zn 23, Ni-Cr alloys 65-35, 75, and 80-20, 

 Ni-Si alloy D, and Ni-Be. 



4.3.2. Effect of Depth 



The severity and frequency of crevice and pitting 

 corrosion, in general, of the 16 alloys given in the 

 previous paragraph were much greater at the surface 

 than at depth. Also, the average corrosion rates were 

 greater at the surface than at depth, although they 

 did not decrease progressively or constandy with 

 increasing depth, as shown in Figure 16. Although 

 these corrosion rates are unreliable because they are 

 based upon localized corrosion weight losses, they do 

 substantiate the conclusion based upon the frequency 

 and severity of pitting and crevice corrosion. 



4.3.3. Effect of Concentration of Oxygen 



The severity and frequency of crevice and pitting 

 corrosion of the nickel alloys which corroded signifi- 

 cantly, in general, increased with increasing concen- 

 tration of oxygen in seawater. Their average corrosion 

 rates calculated from weight losses increased 

 asymptotically with increasing concentration of 

 oxygen, as shown in Figure 17. 



4.3.4. Effect of Welding 



The weld beads in Ni-Cr-Fe 600 alloy, made by 

 the TIG welding process using filler metal 62, were 

 perforated by line corrosion along their edges after 

 402 days of exposure at the 2,500-foot depth, and 

 540 days of exposure at the surface; the weld bead 

 was attacked by incipient pitting corrosion after 181 

 days of exposure at the surface. 



When Ni-Cr-Fe 600 alloy was TIG welded with 

 filler metal 82, the weld beads and heat-affected 

 zones were perforated after 402 days of exposure at 

 the 2,500-foot depth; the weld bead was pitted after 

 540 days of exposure at the surface; and the weld 

 bead was slightly etched after 181 days of exposure 

 at the surface. 



The weld beads in Ni-Cr-Fe 600 alloy, made by 

 the manual shielded metal-arc process using electrode 

 132, were perforated after 402 days of exposure at 

 the 2,500-foot depth and after 540 days of exposure 

 at the surface. The weld beads were also attacked by 

 tunnel corrosion after 540 days of exposure at the 

 surface. 



Weld beads in Ni-Cr-Fe 600 alloy, made by the 

 manual shielded metal-arc process using electrode 

 182, were perforated after 181 days of exposure at 

 the surface, but were only etched after 402 days of 

 exposure at the 2,500-foot depth. 



Butt welds in Ni-Cr-Fe 718 alloy, made by the 

 TIG process using filler metal 718, were uncorroded 

 after 189 days of exposure in both seawater and 

 bottom sediment at the 6,000-foot depth, in seawater 

 after 402 days of exposure at the 2,500-foot depth, 

 and after 540 days of exposure at the surface. Also, 

 3-inch-diameter, unrelieved, circular weld beads made 

 by the same process were etched after 189 days of 

 exposure in seawater and in the bottom sediment at 

 the 6,000-foot depth. 



The weld beads in Ni-Cr-Fe X-750 alloy, made by 

 the TIG process using filler metal 69, were etched 

 after 402 days of exposure at the 2,500-foot depth, 

 but both the weld beads and heat-affected zones were 

 attacked by crater corrosion after 540 days of 

 exposure at the surface. Weld beads in Ni-Cr-Fe 

 X-750 alloy, made by the manual shielded metal-arc 

 process, were perforated and the heat-affected zone 

 was attacked by tunnel corrosion after 402 days of 

 exposure at the 2,500-foot depth; the heat-affected 



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