for steels shows that corrosion of steels is not 

 affected by depth (pressure), at least to a depth of 

 6,000 feet (2,700 psi) for a period of 1 year of expo- 

 sure. The shape of this curve is practically identical to 

 that of the oxygen concentration curve. The identical 

 shape of these curves indicate that the concentration 

 of oxygen in seawater exerts a major influence on the 

 corrosion of steels in this environment. 



2.1.3. Concentration of Oxygen 



The effect of the variation in the concentration of 

 oxygen in seawater on the corrosion of steels after 1 

 year of exposure is shown in Figure 6. The curve for 

 the average corrosion rates of the steels after 1 year 

 of exposure versus the concentration of oxygen is a 

 straight line. This indicates that the corrosion of 

 steels in seawater is proportional to the concentration 

 of oxygen. 



2.1.4. Nickel 



The effect of the variation of the concentration 

 of nickel on the corrosion of steels is shown in Figure 

 7. Variations of from 1.5 to 9% in the nickel content 

 were ineffectual with respect to the corrosion of steel 

 both at the surface and at depth. However, the cor- 

 rosion rates in surface exposures were higher than at 

 depth by about a factor of 7. 



2.1.5. Type of Corrosion 



All the steel, except AISI Type 502, in general, 

 corroded uniformly except for some slight pitting in 

 surface seawater which was caused by fouling. The 

 corrosion rates of AISI Type 502 steel (5% Cr-0.5% 

 Mo) were erratic- and higher than those of the other 

 steels. This behavior is attributed to the broad, 

 shallow pitting and the severe crevice corrosion 

 caused by the chromium content of the steel. 



2.1.6. Metallic Coatings 



Zinc, aluminum, sprayed aluminum, titanium- 

 cadmium, cadmium, copper, and nickel-coated steel 

 specimens were exposed at depth. 



A 1 oz/sq ft of zinc on galvanized steel sheet 

 exposed at a depth of 2,500 feet protected the steel 



for from 3 to 4 months in the seawater and for about 

 7 months when partially embedded in the bottom 

 sediments. 



A 1 oz/sq ft of aluminum on aluminized steel 

 sheet exposed at a depth of 2,500 feet protected the 

 steel for at least 1 3 months in the seawater and when 

 partially embedded in the bottom sediments. 



A 6-mil-thick hot-sprayed aluminum coating over 

 steel, which had been subsequently primed and 

 sprayed with two coats of clear vinyl sealer, protected 

 the underlying steel from corroding for 1,064 days at 

 the 6,000-foot depth. After removal from exposure 

 the aluminum coating was dark gray and speckled 

 with pin-point size areas of white corrosion products. 

 Since no red rust was present, it is evident that this 

 coating would provide added protection to the steel 

 for an additional period of time, possibly another 3 

 years. 



A titamium-cadmium coating on AISI 4130 steel 

 was completely sacrificed, and the underlying steel 

 was covered with a layer of red rust after 402 days of 

 exposure at a depth of 2,500 feet. Such a coating 

 would not provide satisfactory protection for sea- 

 water applications. 



An electrolytically applied cadmium coating on 

 steels, both stressed and unstressed, did not provide 

 adequate protection for 1 year of exposure at depths 

 of 2,500 and 6,000 feet. 



Electrolytically applied copper and nickel 

 coatings on steels, both stressed and unstressed, failed 

 within 6 months after exposure at the 2,500-foot 

 depth and caused galvanic corrosion of the underlying 

 steels. 



2.1.7. Inorganic Coatings 



A few steels were coated with selected paint 

 coatings to determine their performance at depths in 

 the Pacific Ocean. Table 6 shows the results of this 

 test. 



The multicoat epoxy systems exhibited, in 

 general, satisfactory performance, while the multicoat 

 polyurethane system behaved erratically, varying 

 from cracked and blistered paint to no paint failures. 

 The single-coat, zinc-rich primer coating did not 

 afford satisfactory protection for a period of 6 

 months at a depth of 6,000 feet. 



