The Institute for Research in Construction (IRC) has undertaken a three-year collaborative research project with the American Water Works Association Research Foundation to build a new understanding of the effect of corrosion pitting on gray cast-iron pipes used in water systems. ("Gray" refers to the color produced by the graphite flakes in the cast iron, which can be seen along the broken surface of these pipes manufactured between 1850 and the early 1970s.)

Each year, cities in Canada and the United States experience thousands of failures in small, gray cast-iron pipes. Over 80 percent of these failures occur when the pipes crack across the center, which is similar to the way in which a twig breaks when it bends.

There are corrosion pits at the broken edges of more than 90 percent of these failed pipes, but, at the present time, not much is known about the exact effect of this pitting on the mechanical strength of the pipes. To help solve this problem, IRC researchers will combine experimental stress measurements with finite element computer modeling to investigate pipe behavior under a wide variety of environmental conditions.

The research is expected to result in estimates of the minimum sizes of corrosion pitting that will increase risk of pipe failure under different soil, loading and pitting conditions. These findings should be of particular interest to users of pipe inspection technology and utility managers responsible for making decisions about repairing and replacing water mains.