The corrosion rates and other pertinent information on control and 

 exposed test specimens submerged in the sea for 64 and 92 days are presented 

 in Table 3. The information on corrosion rates is also shown graphically in 

 Figures 33 and 34. Examination of the control and exposed panels after 

 these were chemically cleaned showed that the panels corroded similarly to 

 panels in Exposure Test No. 1 . Since the corrosion of various metals and 

 alloys in seawater is greatly dependent on the amount of dissolved oxygen 

 supplied to the metal surface, seawater samples from the initially sterile test 

 chambers sealed with membrane filters (control) and also seawater from 

 10 feet below the surface were collected at high tide and analyzed. The results 

 obtained on seawater analysis are presented in Table 4. The dissolved oxygen 

 concentration in test chambers containing control carbon steel and aluminum 

 alloy panels was lower than in seawater collected from 10 feet below the sur- 

 face at Point Mugu Pier. This could be one of the reasons for the low corrosion 

 rate experienced by the carbon steel and aluminum alloy control panels. 



Exposure Test No. 3 (23 and 43 Days). The test panels were exposed 

 in the sea during the summer months, whereas in Exposure Test Nos. 1 and 2, 

 the panels were exposed in the sea during the winter months. The procedure 

 for submerging the test panels in the sea was similar to that for Exposure 

 Test No. 2. The initially sterile test cylinders sealed with membrane filters 

 were filled with filtered seawater in the laboratory prior to exposing them in 

 the sea. The risk of rupturing the thin membrane filter is reduced using this 

 method. 



When the carbon steel and aluminum alloy exposed panels were 

 recovered and examined, the panels were covered primarily with a very light 

 growth of hydroids, and branching and encrusting bryozoans. Only a trace 

 oi Ectocarpus (brown algae) growth was present on these panels. The control 

 panels were free of marine growth. However, microorganisms were again 

 found in seawater samples containing the control panels inside cylindrical 

 chambers sealed with membrane filters. The morphology of these bacteria 

 was similar to that of the bacteria found in previous exposure tests. The 

 effect of these microorganisms on corrosion rates is not known. The dissolved 

 oxygen concentration of the seawater in which the control panels were exposed 

 was low compared to the concentration in the seawater samples collected 

 10 feet below the surface of the sea at Point Mugu Pier. Other pertinent infor- 

 mation on the seawater environment is presented in Table 4. Such information 

 is helpful in evaluating corrosion rates of test panels which were exposed in 

 the sea under varying conditions. 



32 



