Statistical Analyses of Field Corrosion Data for Ductile Cast Iron Pipes Buried in Sandy Marine Sediments

Abstract

Field corrosion studies were conducted on bare, ductile cast iron pipes buried 17 y in sandy marine sediment classified as sandy soil and containing iron bacteria, sulfate-reducing bacteria (SRB), and other bacteria. Chemical and biochemical analyses of the sediment were performed in the laboratory. Correlation between the maximum corrosion depth (P_max) and 21 environmental factors was evaluated by applying a correlation analysis. On that basis, the factors controlling corrosion damage were considered by quantification theory analysis. A corrosion mechanism was presented to explain the corrosion phenomena. The corrosion site had a positive correlation with the anaerobic site, characterized by particularly high levels of water content (Wc) and ferrous sulfide (FeS) generated by SRB. Corrosion was classified as graphitic and attributed to formation of extensive tubercles resulting from high activity of iron bacteria in the bicarbonate (HCO₃⁻)-enriched soil.