Figure 40. Carbon steel and aluminum alloy control panels which were placed 

 inside initially sterile cylindrical chambers sealed with membrane 

 filters were relatively free of corrosion products. 



Examination of the exposed aluminum alloy panels after chemical 

 cleaning revealed that the edges and ends of these panels were severely cor- 

 roded (Figure 41). Crevice corrosion was also found around the holes 

 underneath the nylon nuts and bolts. Only a trace of pitting corrosion had 

 occurred over the surface area of the aluminum alloy panels. The exposed 

 steel panels corroded uniformly without formation of any pits or any crevice 

 corrosion on their surfaces. The control aluminum alloy panels were free of 

 pitting corrosion on the surface and crevice corrosion around the bolt holes; 

 however, there were traces of light corrosion along the edges and ends of 

 these panels. The control steel panels corroded uniformly (Figures 41 and 

 42). The corrosion rates of 1010 carbon steel and 7178-T6 aluminum alloy 

 panels which had been exposed on the seafloor in 6,000 feet of water for a 

 period of 189 days are presented in Table 7. This information is also plotted 

 on Figures 35 and 36 so that the rates of biological corrosion which occurred 

 at the surface and at depth can be compared. The data presented in Table 7, 

 and Figures 35 and 36 show that bacterial slime growth and metabolic prod- 

 ucts may have played a significant role in accelerating corrosion on the deep 

 ocean floor. The corrosion rates for exposed carbon steel panels which were 



47 



