Tests were made to determine whether soil microorganisms could alter the insulating value of coatings intended for use on cathodically protected buried pipe. The microbial corrosion of bare metal also is considered.
Data tabulated from more than 150 bell-holes show that a pipe line ditch represents a definite alteration of natural undisturbed soil equilibrium conditions. Moisture was found to be present in greater amounts in the bottom of pipe line ditches than in undisturbed soil. The presence of aerobic conditions and the high bacterial populations adjacent to coated pipe lines suggest the importance of microbial decomposition of coating materials. An experimental setup with data was presented to show electrical potentials developed by common soil bacteria in contact with bare steel and carrying on normal metabolism.
Data reported include soil bacteria count per gram of soil, percent soil moisture at ditch bottoms adjacent to pipe lines, comparison of moisture present at soil surfaces and equivalent pipe line depths, and moisture in coatings samples removed from pipe after years of underground service. The significance of these data in relation to cathodic protection is considered. 3.3.4
