In a study of the effects of earthquakes on water and sewer pipe, ductile iron pipe with restrained joints proved superior to other pipe materials, according to a paper by Michael Tucker, senior sales engineer with American Cast Iron Pipe in Tulsa, Okla. The paper was published in the May 2010 issue of the Journal of the American Water Works Assn.
“Pipelines that deliver clean water and remove wastewater are essential to the well being of our communities,” Tucker said. “Some utilities may have only one source--one lifeline--into a community. In areas of seismic activity, utilities need to consider how best to protect these lifelines from failure.”
The study reviewed data about pipe failures during modern-day earthquakes, including the following earthquakes in the U.S.: Prince William Sound, Alaska, 1964; Loma Prieta, Calif., 1989; and Northridge (San Fernando Valley), Calif., 1994.
“Earthquakes like these have demonstrated time and again the need for high-strength, flexible pipe with flexible joints,” Tucker said. “Whether the pipe and joints are flexible or rigid determines the ability of the pipeline to resist the motion and energy associated with earthquakes.”
The study showed that ductile iron pipe and joints performed the best, sustaining only minimal structural damage. Asbestos-cement pipe had the worse failure rate, and plastic pipe was more likely to pull apart at the joints.
“Most mid- to large-size utilities in seismic zones in this country use ductile iron pipe and joints designed for river crossings,” Tucker said. “This application has proven very effective in withstanding the effects of earthquakes. It uses locking joints with 15 degrees deflection.
“Utilities in seismic zones need to evaluate the lifelines critical to their systems and give these lifelines top priority for retrofitting or replacement to ensure the greatest seismic resistance.”
For new developments, the time to consider system reliability is during initial planning. “While the cost of an earthquake-resistant system may be more on the front end, in addition to protecting a utility’s lifelines, it may offer considerable savings in the long run,” Tucker said.
