INTRODUCTION 



Corrosion is the deterioration of materials tlirougli diemical and 

 electrochemical attack. It is a very complex form of material deterioration. 

 Despite intensive research and experimentation,'"'^ there is a lot to learn about 

 corrosion processes of metals and metal alloys submerged in the sea. Corrosion 

 in the hostile hydrospace environment will continue to be a problem of major 

 importance to marine engineers and designers. 



When materials are submerged in the sea, the submerged object soon 

 becomes covered with marine growth.-^ LaQue and Clapp^ have found that 

 certain species of marine organisms accelerate corrosion. The attachment of 

 marine organisms on the surface of metals and metal alloys could be an impor- 

 tant contributing factor in the complex corrosion process by producing local 

 changes in dissolved oxygen concentration, pH, and oxidation— reduction 

 potential. For example, pitting occurs under barnacle shells as a result of a 

 difference in oxygen concentration,^'^ and sulfate-reducing bacteria associated 

 with anaerobic corrosion^'^ are known to produce hydrogen sulfide under 

 (1) corrosion products formed over metal surfaces, (2) deteriorating paint 

 film, and (3) decaying organisms. Various species of microorganisms are also 

 found to be responsible for the corrosion of metals and metal alloys in the 

 marine environment.^''"^ 



In order to study the importance of fouling organisms and their effects 

 on corrosion rates of metals, an experimental method must be devised whereby 

 the control panels exposed in the sea will be free of marine growth during the 

 exposure period. The corrosion rate of the fouling-free test panels could then 

 be compared to test panels which were exposed to maximum marine growth 

 in the sea. 



Himmelfarb and others" have conducted a short-term (1-week) marine 

 exposure study to determine the effects of bacterial slime growth on corrosion 

 of aluminum and copper. The control panels were kept free of any bacterial 

 slime growth by placing the test panel inside a plastic dish filled with sterile 

 distilled water and sealed with a 0.45-micron porosity membrane filter. Refer- 

 ence 1 1 states that a sterile condition can be maintained inside the plastic dish 

 and that seawater will quickly replace the distilled water by diffusion through 

 the membrane filter. 



