December 28, 2001 — The Institute for Research in Construction (IRC) has undertaken a three-year, collaborative research project with the American Water Works Association Research Foundation (AWWARF) 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 U.S. experience thousands of failures in small, gray cast-iron pipes. Over 80% 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% 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 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.
Working with researchers at the National Research Council's (NRC) Steacie Institute for Molecular Sciences (SIMS), IRC researchers will validate the modeling data using SIMS's neutron diffraction instruments at Atomic Energy of Canada Limited's Chalk River Laboratories. These instruments will help them to understand the strain on the pipe under different stresses, loads and deflections. The major benefit of the technique is that it allows non-destructive stress measurements to be made all through the pipe wall, rather than just at the surface.
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 will be of particular interest to users of pipe inspection technology and utility managers responsible for making decisions about repairing and replacing water mains.
For more information, contact Dr. Jon Makar at (613) 993-3797, fax (613) 952-8102, e-mail [email protected], or visit www.nrc.ca.
© National Research Council of Canada, Institute for Research in Construction (from Construction Innovation newsletter, Summer 2001)
