FINDINGS AND CONCLUSIONS 



1 . The effect of marine fouling on corrosion of carbon steel and aluminum 

 alloy panels exposed at the surface of the open sea was not definitely estab- 

 lished by the experimental methods used in this current study because the 

 initially sterile control specimens became contaminated with bacteria after 

 immersion in the sea. 



2. Bacterial slime growth and its metabolic products apparently play a 

 significant role in accelerating corrosion on the deep-ocean floor. 



3. The corrosion rates of exposed test panels placed in the sea at the surface 

 were greater than for identical panels which were exposed on the seafloor in 

 6,000 feet of water, 



4. The corrosion rates of both carbon steel and aluminum alloy panels 

 approach constancy after 9 months of exposure in the sea. As shown in 

 Figures 35 and 36 it can be expected that these corrosion rates will continue 

 at this lower rate after extended period of exposure. 



FUTURE PLANS 



Additional test specimens of 1010 carbon steel and 7178-T6 aluminum 

 alloy have been placed on a STU (STU 1-6) to determine the effects of biolog- 

 ical organisms on corrosion. The STU was emplaced on the ocean floor at a 

 depth of 6,000 feet of water on 3 December 1969 during the second quarter 

 of FY 70. 



If further controlled studies of marine corrosion processes (biological, 

 chemical, and physical) are undertaken, microtechniques should be developed 

 to study the various chemical reactions which occur at the microlayer immedi- 

 ately above the surface of test specimens — for example, measure the oxygen 

 concentration, pH, HjS concentration, temperature, current velocity, etc. at 

 the metal-seawater interface. The effects of metabolic products and byprod- 

 ucts of fouling organisms on corrosion should also be investigated. The control 

 panels should be carefully protected from biological factors by specially 

 designed sterile test chambers which would keep the test specimens free of 

 fouling attachment including microorganisms but would continuously expose 

 them to other parameters of the seawater environment. Such a study could 

 be undertaken in the laboratory by pumping filtered seawater through a sterile 

 test chamber sealed with membrane filters and containing test panels. The 

 cylinder should first be tightly fitted inside a plastic tube so that seawater is 

 pumped through the membrane filters. By using this method, the fresh 



50 



