AWWA ACE68558

This powerpoint presentation investigates the mechanism(s) of corrosion on ductile iron pipe (DIP) with polyethylene encasement (PE) in accordance with AWWA C105 standard. Methodology included the following: simulate small gap between DIP and PE surface and where moisture is trapped; PE test of 3 DIP conditions; annealing oxide coating; removed annealing oxide coating (Bare); asphaltic coating (as manufactured); and, sample and chemically analyze trapped fluid as a function of time. Presentation conclusions indicate that: asphaltic DIP showed little to no signs of corrosion, protective asphaltic coating prevents contact between corrosive pore fluid and DIP, and no semi-volatile organics were detected; annealing oxide DIP acts as a protective layer and pitting rings at top caused by greater dissolved oxygen; bare DIP offered no protective layer with pitting near top rings and uniform corrosion at lower portion; corrosion mechanism is strongly influenced by dissolved oxygen, PE deprives system of oxygen, and dissolved oxygen increases corrosion; pH increases as corrosion proceeds; LPR readings indicate general corrosion; and, semi-volatile organics are not a factor in corrosion control. Includes tables, figures.