Metallic Coatings 



Zinc, aluminum, sprayed aluminum and titanium-cadmium coated 

 steel specimens were exposed at depth „ 



The galvanized steel (1.0 oz per sq ft) was covered with a layer 

 of flaky red rust after 402 days of exposure at a depth of 2,370 feet. 

 The corrosion rates were 0.9 MPY for the specimens exposed in the sea 

 water and 0.4 MPY for the specimens partially embedded in the bottom 

 sediment. The corrosion rate for bare steel (AISI 1010) in sea water 

 under the same conditions was 1.2 MPY indicating that the zinc coat- 

 ing was removed within a short period of time (3 to 4 months). The 

 difference in corrosion rates in the bottom sediment was 0„7 MPY 

 which shows that the zinc coating protected the steel in the bottom 

 sediment for at least twice as long as it did in the sea water. 

 There was no loss in the mechanical properties of the galvanized 

 steel. 



The aluminized steel (1.03 oz per sq ft) was covered with white 

 corrosion products, spotted with a few specks of red rust after 402 

 days of exposure at a depth of 2,370 feet. About 22 percent of the 

 aluminum coating was corroded from the specim.ens exposed in the sea 

 water and 40 percent was corroded from the specimens partially 

 embedded in the bottom sediment; the underlying steel had not 

 corroded. Therefore, it can be concluded, on a weight basis, that 

 1 oz per sq ft of aluminum will protect steel for a longer period 

 of time than 1 oz per sq ft of zinc; about 4 times as long in sea 

 water and about 2 times as long when partially embedded in the bottom 

 sediment . 



A titanium-cadmium coating on AISI 4130 steel was completely 

 sacrificed and the steel was covered with a layer of red rust after 

 402 days of exposure at a deptti of 2,370 feet, 



A 6 mil thick, sprayed aluminum coating which had been primed 

 and sprayed with 2 coats of clear vinyl sealer protected the under- 

 lying steel for 1,064 days of exposure at a depth of 5,300 feet. 

 After removal from exposure the aluminum coating was dark gray in 

 color, speckled with pin point size areas of white corrosion products. 



Cast Irons 



The chemical compositions of the cast irons are given in Table 

 1 and their corrosion rates in Table 4, 



The corrosion rates for the gray, nickel, nickel-chromium, silicon, 

 silicon-molybdenum and ductile cast irons at the two nominal depths in 



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