RELATIONSHIP BETWEEN MARINE FOULING AND CORROSION 

 RATE OF CARBON STEEL AND ALUMINUM ALLOY AT THE 

 SURFACE AND AT 6,000-FOOT DEPTH 



Technical Report R-681 



YF 51.543.007.01.001 



by 



J. S. Muraoka 



ABSTRACT 



Carbon steel (1010) and aluminum alloy (7178-T6) panelswere 

 exposed at the surface (23 to 286 days) and at 6,000-foot depth (189 days) 

 in the Pacific Ocean ( 1 ) to determine the effects of fouling organisms on the 

 corrosion rate and (2) to compare the biological corrosion rate of identical 

 test panels submerged at the two depths. Seawater samples obtained at the 

 surface and at depth were analyzed for dissolved oxygen concentration, pH, 

 salinity and temperature. Bacteriological tests were also conducted on seawater 

 samples. The test panels were submerged in the sea as follows to obtain data 

 on corrosion rates; ( 1 ) enclosed inside an initially sterile plastic cylindrical 

 chamber with both ends sealed with membrane filters (control panels), 



(2) placed inside a cylinder covered with 210-mesh nylon screen cloth, 



(3) placed inside a cylinder with both ends uncovered, and (4) attached to a 

 phenolic plastic strip (exposed panels). The control specimens became contam- 

 inated; however, from corrosion data obtained on test panels exposed on the 

 seafloor in 6,000 feet of water, it is concluded that slime films played a signif- 

 icant role in accelerating corrosion of test specimens. Test panels exposed at 

 the surface corroded at faster rates than replicate test panels which were 

 exposed on the seafloor in 6,000 feet of water. The corrosion rates of both 

 steel and aluminum alloy panels approach constancy after extended exposure 

 in the sea. The various environmental factors and their effects on the corrosion 

 rates at the surface of the sea and at great depth on the seafloor are discussed. 



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