Abstract
Localized corrosion on buried ductile cast iron pipes was investigated placing the main emphasis on the morphology of corrosion attack and the action of microorganisms. The form of corrosion was classed as selective leaching attack commonly referred to as graphitic corrosion. It was found that each nodular graphite was supported by amorphous silica and iron carbonate, thereby constituting a porous graphite mass that is characteristic of graphitic corrosion. Microbial enumeration and electrochemical observations strongly suggested a possibility that a symbiotic proliferation of iron bacteria and iron oxidizing bacteria was primarily responsible for accelerated localized selective leaching as well as tubercle formation. Results of EPMA analysis indicated that amorphous silica was formed as a result of metabolism of such bacteria to form both porous graphite mass and tubercles.
