For more than two decades breaks and replacements of water mains in the City of Calgary, Alberta climbed alarmingly. At its peak, the City was coping with a break rate of 70 per 100 km and main replacement surged from about 3 km per year in the early 1970s to more than 30 km by the late 1990s.
“We had areas where the pipes were being eaten alive,” says Roy Brander, who was Calgary’s senior infrastructure engineer until 2015. “In the worst cases, water mains that should have lasted for more than 50 years were being replaced after only seven to 10 years of service.”
Corrosive soil was the culprit. The city was growing rapidly during those years and much of the new development and water infrastructure was built in soil that aggressively attacked metallic pipelines. The City quickly found itself spending about $27 million per year to replace and repair water mains, even as construction costs were skyrocketing during the Alberta oil boom.
Choosing its Battles
Brander and the City fought back, turning to technologies such as PICA SeeSnake condition assessment to help identify the most vulnerable water mains and implement cost-effective management strategies that are contributing to annual savings of about $2 million in averted pipeline repair cost.
SeeSnake is a non-destructive, inline condition assessment tool that uses remote field testing (RFT) technology to measure the actual remaining wall thickness from the inside and outside of a pipeline. The tool precisely locates areas of wall thinning, pitting, holes and cracks along the entire length of pipeline and around the circumference.
In the 1980s and 1990s water mains were replaced in Calgary based on the age of the line and the number of breaks experienced over a set period of time. It wasn’t unusual for four or five breaks to trigger the replacement of the water main for an entire block. Often, Brander says, once the pipeline was removed, corrosion was isolated to only a few sections and the majority of the line could have provided many more years of reliable service.
“SeeSnake condition assessment data gave us the courage to not replace pipelines,” Brander says.“Especially in areas where the pipelines carry a high consequence of failure.”
Over 115 km of 6- and 8-in. diameter water mains have been inspected by SeeSnake since the program began in 1998. “You can’t go more than three or four blocks in any direction before coming across a street where the water main has been inspected by SeeSnake,” Brander says. Since SeeSnake can be inserted into these mains through a hydrant, inspections can be conducted quickly and easily with little disruption to the neighbouring community and businesses.
Data from SeeSnake condition assessment was incorporated into detailed maps that show areas of pitting, corrosion and wall thinning. These maps also show soil resistivity, soil acidity, chloride levels, sulfate levels and redox potential, which was obtained from hundreds of thousands of soil tests taken around the City’s metallic pipe network. This information was used to identify pipelines that were at the greatest risk of failure, predict where breaks would occur and respond proactively.
“Pipeline corrosion occurs at a linear pace,” Brander says. “We can extend the data to predict when a pipe will fail and experience through holes.”
This strategy enabled Brander and his team to identify areas that were more susceptible to failure and, in some cases, conduct additional SeeSnake inspections to verify localized corrosion in a water main and make repairs to small sections. The savings were huge since the City could avoid the early replacement of the entire main on a street, which sometimes stretched up to 400 m long.
SeeSnake’s precision was part of the reason Calgary’s program worked so well. Each run of the tool would not only reveal holes, but also the precise locations of pits and the actual amount of pipeline that remained, expressed as a percentage.
This is a major advantage over other technologies that are limited to leak detection or measurements of average remaining wall thickness. Measuring average remaining wall thickness can reveal how much of a pipe section has corroded, but doesn’t show how it is distributed across the pipe or if corrosion is concentrated in a particular area.
Even when holes exist, Brander says that replacement may not be needed immediately. For example, SeeSnake may show graphitization and through holes in a section of thick-walled cast iron pipeline that is buried in heavy clay soil. The heavy soil often holds the graphite plug in place for quite some time so repair is not urgently required. Brander says that farther down the same length, defects may be in looser soil so he will address those sooner because he knows they are more likely to leak.
Program Pays for Itself
Calgary’s approach to water main risk assessment and management is paying off in a big way. Pipeline condition assessment data provided by SeeSnake has enabled the City to proactively target problem areas and address breaks before they happen. Using this strategy, breaks in metallic pipelines dropped continually during Brander’s term at the City and went from 600 per year to less than 250 per year. SeeSnake inspections have also assisted the City to dramatically reduce the amount of pipeline that is replaced — cutting the work from about 35 km annually to only 6 km in recent years.
“The program paid for itself,” Brander says. “In Calgary, condition assessment was about one tenth the cost of replacement, so if we averted or delayed replacement once out of every ten inspections, we were breaking even.”
But Calgary was doing much better than that. “SeeSnake helped the City to maintain a pipeline replacement budget at $10 million per year for several years despite skyrocketing construction costs,” Brander says.
SeeSnake’s biggest benefit for Calgary, according to Brander, was in helping to decide where to apply cathodic protection to prevent corrosion and extend the life of water mains. Cathodic protection is widely used in Alberta’s oil and gas industry to protect pipelines and Brander believed that the proven technology could have a big impact in helping Calgary win its battle against corrosion in its water mains.
“We used SeeSnake to identify pipelines that were just about to fail. Those that had pits with about five percent remaining wall thickness., Brander says. These pipelines, according to Brander, had about two to five years of life left and would reap the greatest economic benefit from cathodic protection. Once the anode was applied, it would prevent corrosion to the pipe and extend its life by 20 years, deferring construction costs and disruption to the community.
SeeSnake also found many areas where pipelines were experiencing heavy corrosion, but not to a degree that warranted immediate anode retrofit. “We made notes to revisit those sites in a decade or two and attach anodes then,” Brander says.
Anodes also became a standard component for metallic water mains in new development and were attached every time a water main was repaired. Though the City now uses PVC pipe for new development and pipe replacement, hundreds of kilometres of metallic pipe is still in service. SeeSnake will continue to play an important role in managing that infrastructure, according to Brander, though he has doubts as to whether many of those pipes may actually be removed.
He says that new technologies to refurbish pipelines may make more economic sense than replacement. This approach, combined with SeeSnake condition assessment and accurate soil maps may help Calgary and other cities with aging pipelines reduce the cost of water main replacement even more.
Bill Jappy is director of sales and marketing for PICA Corp.