Failure of a Cast Iron Water Pipe due to Graphitic Corrosion
A 25.4 cm (10 in.) diam gray cast iron water main pipe was buried in the soil beneath a concrete slab. The installation was believed to have been completed in the early 20th century. A leak from the pipe resulted in flooding of a warehouse. Once removed, the pipe revealed through-wall perforations and cracking along its axis. The perforations and the crack were at the 6 o'clock position. Investigation (visual inspection, radiography, unetched macrographs, and tensile testing) supported the conclusion that the failure occurred as result of years of exposure to ground water in the soil resulting in graphitic corrosion. Soils containing sulfates are particularly aggressive. Recommendations included pipe replacement. The wall thickness had been sufficiently reduced that the pipe could no longer support the required load. Water mains are designed for more than 100 years life. Ductile iron or coated and lined steel pipe, generally not susceptible to graphitic corrosion, were suggested as suitable replacement materials, and cathodic protection was also considered as a possibility.