In general, the corrosion rates of all the alloys exposed either 

 adjacent to or partially embedded in the bottom sediments at the 5,500 

 foot depth decreased asymptotically with time and became constant at 

 rates between 0,5 and 1.0 MPY after three years of exposure. The 

 corrosion rates of the alloys in the bottom sediments at the 2,350 

 feet depth tended to increase with time. 



The corrosion rate of steel was not affected by nickel additions 

 to 9 percent at either depth, 



Silicon and silicon-molybdenum cast irons were immune to 

 corrosion in deep ocean environments. 



Type 502 steel was selectively attacked resulting in broad 

 shallow pits and crevice corrosion, and its mechanical properties 

 were impaired. 



The mechanical properties of the other alloys were not impaired. 



None of the steels were susceptible to stress corrosion crack- 

 ing at stresses equivalent to 75 percent of their respective yield 

 strengths o 



The corrosion products of the alloys were composed chiefly of 

 alpha iron oxide, ferric oxide hydrate, ferrous hydroxide and Beta 

 iron (III) oxide-hydroxide. 



Zinc (hot-dipped) (1.7 mils) and titanium-cadmium coatings failed 

 to protect sheet steel for one year of exposure. 



A hot-dipped aluminum coating (4 mils) protected sheet steel for 

 a minimum of one year whereas a sprayed aluminum coating (6 mils, 

 sealed) protected sheet steel for three years. 



The mechanical properties of anchor chains were unimpaired. 

 However, sea water penetrated the forged sockets of one type of 

 chain as evidenced by corrosion at the bottoms of the sockets. 



The mechanical properties of Type 304 stainless steel cables 

 in sizes 0.094, 0.125 and 0,187 inch diameter were decreased by a 

 minimum of 85 percent due to corrosion of the internal wires while 

 those of the larger diameter wires were unaffected. 



The breaking strength of a Type 304 stainless steel cable coated 

 with 90 percent copper-10 percent nickel was not affected. 



The breaking strengths of the aluminum coated steel wire ropes 

 were unaffected. 



The bare steel, zinc and alum.inum coated steel and stainless 

 steel wire ropes were not susceptible to stress corrosion cracking 

 when stressed at 20 percent of their respective breaking loads. 

 However, the Type 316 stainless steel wire rope lost 40 percent 

 of its breaking strength due to corrosion of the internal wires. 



The breaking strengths of bare steel, zinc and aluminum coated 



14 



