Case Studies in Graphitic Corrosion of Cast Iron Pipe

Throughout many parts of the world, cast iron pipe has been and continues to be used for utility piping (water and sewage) and gaseous media piping. Gray cast iron is known to have a limited life in service but is often left in place beyond its reasonable service life. Therefore, end of life is then left to be defined as a rupture or a crack and a subsequent leak, often at an unpleasant time with unpleasant results. The controlling mechanism involved is time dependent and known as graphitic corrosion. This paper provides a review of the phenomenon of graphitic corrosion in the form of key characteristics. Several references are cited that further explore the mechanism involved and corrosion prevention/mitigation. Two case studies are presented that explore graphitic corrosion in gray cast iron pipe from a failure analysis point-of-view. Both case studies feature conditions that further aid in the interpretation of graphitic corrosion and an appreciation for when and how this phenomenon occurs.