The membrane filter coverings over cylindrical test chambers in 

 which the control panels were placed were found to be ruptured when the 

 test chambers were recovered after 268 days in the sea. The acrylic plastic 

 cylinders were covered primarily with branching and encrusting bryozoans 

 and hydroids (Figure 23). The steel panels which had been placed inside 

 one of these cylinders were covered uniformly with a paperlike thin film of 

 red rust instead of the powderlike flaky red rust found on control panels 

 exposed 70 and 1 12 days (Figure 24). The aluminum alloy panels were 

 relatively free of corrosion products. However, there were a few calcareous 

 tubeworms growing on the panels (Figure 24). The chemically cleaned 

 exposed and control panels are shown in Figures 25 through 27. The corro- 

 sion rates of the panels exposed for 70, 1 12, and 268 days in the sea are 

 presented in Table 2 and shown graphically in Figure 28. 



Exposure Test No. 2 (64 and 92 Days). The test panels were exposed 

 in the sea beginning in the month of November. The corrosion rates were 

 obtained by exposing the test panels in four different ways as follows: 



1. Placed inside initially sterile cylindrical test chambers sealed with 

 membrane filters (control panels). The sealed chambers with test specimens 

 were filled with seawater by carefully submerging them in the sea at the expo- 

 sure test site. 



2. Placed inside cylindrical chambers with both ends covered with a 

 nylon screen (Figure 29). 



3. Placed inside cylindrical chambers with ends left open (Figure 30). 



4. Placed on 2-inch-wide phenolic plastic strips (exposed panels). 



After 64 days the steel and aluminum alloy control panels were free 

 of any fouling growth, however, these panels were exposed to microorganisms 

 that invaded the initially sterile cylinders sealed with membrane filters. The 

 bacteria were morphologically similar to those isolated in Exposure Test No. 1 . 

 The exposed aluminum alloy panels (Figure 31) were covered with branching 

 bryozoans and numerous small mussels (1/16-inch). The steel panels were 

 covered with layers of loose corrosion products on which there were a few 

 small mussels. Other marine organisms may have been washed off together 

 with the loose corrosion products by currents. The panels placed inside 

 cylinders with ends open were similarly affected. 



25 



