Volume 17, Number 2, June 2012
Almost 15% of water distribution pipes in service in Canada and the United States are constructed of asbestos cement (AC). In some towns and cities, these make up the majority of the pipe inventory. Most AC pipes were installed from the 1950s to 1970s, which means that they have been in service for 40 to 60 years. As these pipes age they deteriorate, resulting in increase of failure frequency. The deterioration and failure frequency, however, vary significantly with local environmental and operational conditions.
Water utilities need a comprehensive strategy for maintenance, rehabilitation and replacement of their AC water mains. Such a strategy would require the ability to assess a pipe’s present condition, forecast its deterioration, and devise an effective method to manage condition monitoring and pipe renewal.
To help address this need, NRC Construction conducted an extensive study of AC pipes through the participation of 20 water utilities and municipalities, which provided data, samples and a technical review.
What was investigated?
- Factors contributing to AC pipe deterioration were identified by analyzing pipe breakage data and working environment information provided by the participating utilities. These factors include mechanical and chemical properties of the soil, which can affect external deterioration, and the chemical properties of the conveyed water, which can affect internal deterioration.
- A set of chemical and mechanical test methods were evaluated for their capability to either measure the extent of deterioration, or to test the remaining pipe strength.
- Pipe degradation depths were correlated with the environmental parameters (water quality and surrounding soil characteristics) to develop models that can be used to forecast future pipe deterioration.
What the research found
- Water quality, pipe age and soil movement were identified as major contributing factors in the deterioration and failure of AC pipes.
- Internal degradation is more severe for conveyed waters with low Aggressiveness Index (AI is an index used to measure the chemical aggressiveness of water) and low alkalinity.
- Faster deterioration occurs where the water in the soil pores has a pH below 7.
A pipe will fail when the loads acting on it exceed its remaining strength. The models to forecast pipe deterioration can be used to predict the remaining strength of the pipe. The external loads (overburden, traffic, frost) as well as internal (pressure) loads acting on the pipe can be estimated. The remaining strength of, and loads acting on, the AC pipe are then used to assess and forecast its remaining service life.
This procedure was presented and demonstrated with case studies. Based on the expected remaining service life of each pipe, utilities can make proactive decisions and improve their priority planning to ensure that maintenance and renewal budgets are allocated where they are most needed.
Partial funding for the project was provided by the Water Research Foundation. NRC researchers are producing a detailed research report and a concise guidance document which will be published by the Foundation towards the end of 2012. The report will describe the research and methods developed, while the guidance document will encapsulate these methods into a practical what-to/how-to manual.
For more information
Visit www.nrc-cnrc.gc.ca/eng/projects/irc/long-term.html or contact Yafei Hu at email@example.com or 306-780-5432.