contrast to none at depth; (3) corrosion rates, pitting and crevice 
corrosion of alloys Ni-Cu 400, Ni-Cu K-500 and Ni-Cr-Fe 600 were 
greater at the surface than at a depth of 6,000 feet after 6 months of 
exposure. 
Steels, Cast Irons and Stainless Steels 
The chemical compositions of the steels, cast irons and stainless 
steels are given in Table 6, and their corrosion rates and types of 
corrosion in Table 7. 
The corrosion of the high strength steels (HS) and the 18 Ni 
maraging steel was uniform except for pitting in the circular weld 
beads of HS numbers 1 and 4 and crevice corrosion of the 18 Ni marag- 
ing steel. In all cases the corrosion rates were greater in the sea- 
water than in the bottom sediments. 
The pits in the weld bead of HS #4 were not typical of corrosion 
pits in steels. Their sides were nearly parallel and normal to the 
plane of the plate and were larger in diameter underneath the surface. 
A transverse section was cut through the weld bead to examine these 
voids in more detail. A section through the weld after polishing and 
etching is shown in Figure 3. The clean, smooth walls of the cavities 
and those which had no access to the surface indicate that they were 
due to entrapment of gas during the welding operation. 
The corrosion rates of two of these steels (HS #1 and 18 Ni marag- 
ing, the only ones available for comparison) were considerably higher 
during exposure in surface seawater for the same period of exposure 
than at depth, as can be seen by comparing the data in Table 12, Ref- 
erence 11, with that in Table 7. 
The two austenitic cast irons corroded uniformly and at slower 
rates in the bottom sediments than in the seawater approximately 4 
feet above the water-sediment interface. Their corrosion rates at 
depth were less than those at the surface for equivalent periods of 
exposure, Table 15, Reference 11. 
Specimens of AISI Type 316 stainless steel tubing with fittings 
on each end and with a zinc anode attached to the end of one specimen 
were exposed in the seawater. There were rust stains and incipient 
crevice corrosion at the junctures of the tubes with the fittings, and 
at the junctures of the end caps with the nuts on the specimens with- 
out zinc anodes. There was no observable corrosion on the specimen to 
which the zinc anode was attached, indicating that the anode had pre- 
vented the inception of corrosion. The zinc anode was about 25 per- 
cent consumed. 
The 20Cb-3 stainless steel was attacked by incipient crevice and 
pitting corrosion in the seawater and by severe crevice corrosion to a 
maximum depth of 40 mils in the bottom sediment. This alloy was at- 
tacked by incipient crevice corrosion during 6 months of exposure in 
surface seawater. 
