Corrosion Fatigue Failure of a Gray Cast Iron Water Main

Abstract

A failure investigation was conducted on a 30.5-cm diameter gray cast iron water main that failed in Anchorage, Alaska, due to a longitudinal fracture. Nearby pressure transducers recorded very modest system pressures at the time of the failure and the pipe did not show signs of advanced graphitization or significant mechanical damage. Mechanical testing and microanalysis were performed on the pipe material. The cause of the failure was determined to be brittle fracture which initiated at a subcritical corrosion fatigue (CF) crack approximately 40.6 cm in length. The corrosion fatigue crack nucleated from a casting defect on the inside surface of the pipe. The findings of the research reported in this paper suggest that subcritical CF crack growth may be a threat to gray cast iron water pipes. Corrosion fatigue mechanisms in gray cast iron have not been documented previously and may be a contributing factor for anomalous fractures showing evidence of multistage failure.