Institute Investigates Cast-Iron Pipe Failure

Sponsored by

A program of the National Research Council of Canada has been investigating water pipe failures. The research suggests that substantial damage occurs before a pipe fails ? damage that current techniques such as leak detection may not discover.

The research is being conducted by the Urban Infrastructure Rehabilitation Program of the Institute for Research (IRC). The IRC?s goal is to learn enough about the way pipes break to develop or improve techniques for detecting the early warning signs of failure.

Most gray cast-iron pipe failures were thought to occur as single events when a pipe snaps across the middle, splits at the bell or along the length. IRC research found this is not always the case. The circumferential breaks and bell splits examined by researchers show evidence that the breaks can occur in several stages.

Each of the failure stages can be identified by differences in the color and chemistry of the rust deposits along the surface of the fracture. Sometimes the shape of the fracture surface also reveals the failure stages, which vary in number.

The research was conducted on piping in Canada. In Toronto, some pipes showed evidence that three different cracking episodes occurred without the pipe breaking across. A blown-out 6-inch pipe from the Regional Municipality of Ottawa-Carleton showed the metal along the edge of the blow out hole was paper-thin at the time of failure. Although the pipe had a protective coating, it appeared to have been scratched during installation, likely by dragging it on the ground. Corrosion pits formed along the scratches.

When an unexpectedly high failure rate occurs in a specific group of pipes, failure analysis can determine whether it is a statistical fluke or due to a cause that will continue producing a large number of pipe failures. In the case of large main breaks, determining the cause is important to ensure that no further failures take place.

Failure analysis examines the ?fracture surface,? the material exposed when the break took place. Water flowing over the fracture surface builds up a coating of corrosion products that hides the causal evidence, but visual examination and chemical analysis of the corrosion products can lead to answers.

Sand blasting removes the corrosion products and exposes the extent of any corrosion pitting. Since sand blasting destroys evidence from the failure, only one of the two fracture surfaces should be cleaned. The other surface remains intact for future examination. Mechanical properties, likely loads and metal quality also need to be considered during a full failure analysis.

Acknowledgement:

Construction Innovation, a quarterly publication of the National Research Council of Canada, Institute for Research in Construction provided this article. The National Research Council of Canada provided the diagram and photographs. For further information contact Dr. Jon Makar at (613) 993-3793; fax (613) 993-5984 or by e-mail: . HYPERLINK mailto:jon.makar@nrc.ca ..jon.makar@nrc.ca..

About the Author:

Dr. Jon Makar is a research officer with the National Research Council Canada. He obtained Master?s and Ph.D. degrees from Queen?s University (Kingston, Ontario) and a B.A.Sc. from the University of British Columbia in Vancouver. Currently his research interests include metallurgy and failures of cast iron pipes, non-destructive testing techniques for the water industry and intelligent buildings and infrastructure.

Sponsored by

TODAY'S HEADLINES

Washington DOE approval granted to HaloSource for hybrid water treatment technology

HaloSource recently announced that it has received the Washington State Department of Ecology's General Use Level Designation for its BHR-P50 hybrid polymer used in conjunction with Chitosan Enhanced Sand Filtration system.

Case Study: Filter reduces flood-induced suspended solids in New Orleans heat exchangers

In New Orleans, fooding from Hurricane Katrina led to an in­crease in TSS, which caused fouling of the heat exchangers, resulting in a loss in efficiency and increase in maintenance costs. As such, Vortisand cross-flow microsand filter provided submicron filtration and high-quality water.

Tanks and Water Storage

US based manufacturer Fibrelite has seen a tremendous increase in inquiries for their lightweight composite access covers ...

Meeting Abu Dhabi's High Water Demands

Spurred on by a buoyant economy and population growth, the GCC countries are looking to invest $130 billion over the next decade to meet future demand and introduce new measures to achieve long-term sustainable water and energy supplies.

FOLLOW US ON SOCIAL MEDIA