In an article published last month (https://big-media.ca/pipe-problems-a-detailed-examination-of-what-lies-beneath-us/), I outlined issues with municipal infrastructure and focused on city pipes. In my Canadian home city of Calgary, things had improved since the break in a major water main curtailed water use in the city for most of June:
- The water main break was repaired
- Five additional spots on the same main line were pre-emptively replaced
- Water restrictions were gradually relaxed as volumes ramped up to near-normal levels
Closer to home, there was another water-main event in late July. A minor water main broke and shut off all water access for approximately 500 homes for almost 24 hours. Calgary experiences more than 200 water-main breaks per year, so this was not a news-worthy event. It was, however, immediately outside my home.
(Photo by author)
Out of curiosity, I checked on the details of the wounded water pipe. This water main is a 150-mm cast-iron pipe installed in 1910 https://data.calgary.ca/Services-and-Amenities/Public-Water-Main-Locations, which is a common breed for areas near the city centre. In fact, cast iron was a very common replacement for wooden (yes, wooden) pipes, and new installations from 1910 to 1968. Considering that this particular pipe is over a century old, I wondered if my front street was destined to become a water feature.
City data confirms the last major install of cast iron in 1968 https://data.calgary.ca/Services-and-Amenities/Public-Water-Main/w6h9-w33i/about_data, and subsequent use is assumed to be repairs of existing lines, given short install lengths. The City of Calgary provides a handy timeline of water-pipe material use:
Iron-based pipe makes up about one-third of the 5.3 million metres of water mains in Calgary, but 14% (743,174 m) of the total system is cast iron. Cast iron is an older, less-resilient material versus ductile iron, and generally more susceptible to corrosion and failure. The installs of cast-iron pipe length were charted by age of original installation to expand the perspective of the system timeline.
Most of the cast-iron water system is approximately 55-80 years old. An anomalous amount of installation (~11%) is recorded as having occurred in 1910, which is an improbable amount of construction for that time. This is also the first data input year, so the data point is more likely a default input to reflect earlier years or unknown install date. Regardless of the validity of some of the data, most of the cast-iron system is 50-100 years old.
How is it holding up?
Unfortunately, open portal City datasets do not overlap main installation data (which includes material type) with main breaks (which exclude material type). The data allows for a broad look at water-main breaks for all materials, which, as charted below, indicates substantial reduction in breaks and break ratio after the 1980s, and relative levelling of both measures after 2010.
This change in break ratio coincides with introduction and general replacement of PVC as material of choice (cast iron went from 90% of system in 1960 to 35% by 1980, and sits at 11% in 2023, while PVC went from 3% in 1980 to 55% of the system in 2023). The trends support the use of PVC and similar materials for lower failure rates, but also highlight the much higher failure rates of materials used in 1980s and before.
The remaining question – how long can older materials such as cast iron hold out with regular repairs before reaching the end of useful life and are fully replaced? Stay tuned.
(Reference Data: Contains information licensed under the Open Government Licence – City of Calgary)
