Calgary water pipes are vulnerable to failure

The infrastructure network that transports safe, clean water around Calgary contains 187 kilometres of pipe similar to the line that suffered a catastrophic break more than two weeks ago, forcing the city’s residents and businesses to cut back on water use and prompting a massive emergency fix-it job.

The city’s Bearspaw South Feedermain, which ruptured June 5, is a prestressed concrete cylinder pipe (PCCP), a design used elsewhere in Calgary and across North America. This type of pipe is known to be vulnerable to major failures, although its engineering has improved since the late 1970s and determining what, precisely, caused the feedermain to crumble may be impossible.

Calgary mayor Jyoti Gondek, in an interview, said the fallout from her city’s water woes should ripple across the country. She and other city officials insist the June rupture happened without warning, although Calgary and other jurisdictions have long known about the risks associated with PCCP. San Diego County Water Authority, for example, started rehabilitating its PCCP infrastructure in 1982 after suffering a major failure in 1979.

“It is going to be a call for action for everyone that has this type of infrastructure, to better understand its condition,” Ms. Gondek said. Officials need to work with experts in the oil and gas industry, the tech sector, and other industrial water users to better understand how to monitor the pipes and predict problems, she said. Calgary’s infrastructure, Ms. Gondek noted, is not very old given most of the city’s growth happened after 1975.

“If this can happen to a young city, then others need to be aware.”

Calgary’s potable water infrastructure consists of 5,385 kilometres of pipeline, according to the city. Michael Thompson, Calgary’s general manager of infrastructure services, this week reiterated that 98 per cent of these pipes are in “good or very good condition.” But he also acknowledged the Bearspaw South Feedermain, the city’s largest and most important line, was rated in good condition before it broke. After it busted, an inspection robot later indicated five more spots on the line were at risk of catastrophic failure and in need of urgent repair.

The city has finished fixing the original break, is in the midst of repairing the five hot spots, and this week predicted service will return to normal July 5, in time for the first day of the Calgary Stampede. To cope, Calgary and neighbouring cities imposed a ban on outdoor watering and asked residents to cut their indoor use by a quarter.

The San Diego County Water Authority sent Calgary two lengths of solid steel pipe to use in the repairs. Martin Coghill, the asset management program manager at the SDCWA, said the deal came together after a friend, who used to work in San Diego for a technology firm that inspected water lines and is now employed by Calgary, called to see if his organization had spare parts.

The pieces are “close” to a perfect fit for the Calgary job, Mr. Coghill said.

PCCP consists of a concrete core, a thin steel cylinder, high-tensile prestressed steel wires for reinforcement, and a mortar coating. Calgary officials believe the Bearspaw South Feedermain failed in part because too many of the prestressed steel wires, encased in a concrete sleeve and essentially coiled around the pipe to provide stability, snapped.

SDCWA has roughly 128 kilometres of pipe comparable to the line that failed in Calgary, Mr. Coghill said. His organization has “rehabilitated” about 77 kilometres of this infrastructure by inserting steel cylinders inside the PCCP.

“That can take decades,” he said.

SDCWA overhauled its first eight kilometres of PCCP between 1982 and 1985, with another burst of upgrades in 2001, he said. Until all the pipes are refurbished, the SDCWA will lean heavily on monitoring the problematic lines. It scans the insides of its lines with electromagnetic technology to identify broken wires in the PCCP. When SDCWA finds troublesome sections, it installs acoustic fibre optic cable to listen for more wires breaking. This allows the agency to identify spots in need of repair, before a break occurs.

The SDCWA spends about US$1,000 a month per 1.6 kilometres on its acoustic monitoring, and the agency monitors about 42 kilometres of its PCCP with this technology, Mr. Coghill said.

But the monitoring technology can only pick up on about two-thirds of potential problems, he said.

“We could have a similar pipe failure to Calgary.”

Problems with PCCP, first manufactured in 1942, are well-documented. Calgary’s 2019 standards handbook on feedermain design and construction flagged the pipes as subject to “catastrophic failure” and prone to accelerated “deterioration and corrosion in Calgary soils.” In 2004, a PCCP feedermain on McKnight Boulevard ruptured, which investigators attributed in part to soil high in sulphates, which chewed into the pipe’s concrete coating and allowed the steel wires to corrode, according to a 2020 report in Trenchless Technology, an industry publication. The report’s authors included experts employed by Calgary.

Roughly 48 per cent of Calgary’s 187 kilometres of PCCP was installed prior to 1979, according to data provided by the city.

Kerry Black, a professor and Canada Research Chair in the University of Calgary’s department of civil engineering, said the existence of PCCP does not necessarily mean the city should expect future failures. It is possible Calgary’s planned third-party investigation into what went wrong with the Bearspaw line will identify a swath of contributing factors.

“I don’t think you will have a smoking gun,” she said.