Abstract
Laboratory experiments were conducted to determine the role of microorganisms in the pitting of mild steel flooring which had been overlaid with plywood. Experimental setups consisting of 4.8 mm (3/16 inch) mild steel plates covered with a 12.7 mm (1/2 inch) thick pieces of plywood were exposed to several different aqueous media supplemented with various combinations of a soil suspension and selected inorganic and organic compounds. Half of the replicate metal-wood-water setups were sterilized and aseptically maintained during incubation, after which they were checked for the presence of viable microorganisms and pitting of the mild steel. The initial experiments showed that pitting of the mild steel specimens in many of these setups occurred after a reasonably short incubation period (3 to 6 months). However, the method used to exclude microorganisms by sterilizing the components separately was unsuccessful. In a second set of experiments, setups were sterilized by exposure to gamma irradiation after they had been assembled. The sterilized setups remained sterile throughout the experiments while those which were not originally sterile still contained viable microorganisms at the end of the experiments. Pitting of the mild steel specimens was more severe when they were exposed to sterile conditions than when viable microorganisms were present. These experiments showed that while microorganisms are known to enhance corrosion processes in some circumstances, their presence can reduce corrosion in others.
