The City of Calgary’s location in southern Alberta, close to one of the world’s largest oil deposits, has granted Canada’s third largest municipality access to innovative pipeline technologies first developed for the oil and gas industry. For more than 20 years, the City of Calgary has managed an industry-leading watermain inspection and cathodic protection program.
The City operates a water distribution and transmission main network that spans more than 5,300 km and serves 1.4 million people. Within this network, more than 460 km of pipe are classified as feedermains, ranging from 500 mm up to 3 m in diameter. This network of large-diameter pressure pipe supplies water to pump stations, reservoirs, and distribution mains and consists primarily of prestressed concrete cylinder pipe (PCCP/AWWA C301), bar-wrapped pipe (BWP/AWWA C303), and steel pipe (AWWA C200).
The City of Calgary initially focused its inspection program on corrosion-induced metallic distribution main failures. However, in 2004, the scope of its program expanded to include feedermains after a catastrophic break on McKnight Boulevard. Failure of the 1,200-mm PCCP feedermain disrupted service to more than 100,000 customers, released more than 20 megalitres of water, and flooded McKnight Boulevard, shutting down a portion of this critical east-west transportation corridor for days. The failure occurred due to degradation of the pipeline’s concrete coating, which enabled corrosion of the steel wires that provide PCCP with its strength. Investigations into the root cause of failure revealed a combination of factors, including local soils high in sulphates.
To prevent similar catastrophic failures, the City of Calgary responded to the McKnight pipeline failure by adopting a proactive condition assessment program for high-risk feedermains. To start, the City categorized its feedermains and assigned each category a probability of catastrophic failure. The categories are based on year of construction, known condition, failure history, soil parameters, location, material, and cathodic protection. In the next phase, the City will assign risk scores to each pipe by evaluating its hydraulic importance in the system, its ease of repair, and by understanding the social, environmental, and financial consequences of potential failures.
The City’s initial risk evaluation revealed that concrete feedermains were generally most at risk when accounting for both the probability of failure and the consequences. Due to these results and other failure investigations, the City’s feedermain condition assessment program is focused primarily on concrete pipelines. The program includes annual soil sampling to check for corrosive ground conditions and proactive internal pipeline inspections.
Since the start of the City’s feedermain inspection program, Pure Technologies, a Xylem brand, has assessed more than 100 km of the network with proprietary acoustic and electromagnetic technologies. These inspections have helped the City proactively manage its large-diameter mains by providing a pipe-by-pipe understanding of their condition. The City can use this data to target damaged pipe sections and make informed repair or replacement decisions that prolong the useful life of its buried assets.
Exemplifying this approach, the City of Calgary partnered with Pure Technologies to conduct three leak detection inspections on two critical feedermains in 2018 and 2019. The team located five leaks that were quickly repaired to prevent a catastrophic failure.
Pinpointing Leaks Proves Challenging
The City of Calgary set out to locate and address at least two watermain leaks after finding chlorinated water surfacing on roadways and infiltrating valve and utility chambers. However, detecting and accurately locating leaks in large-diameter mains is challenging using conventional methods and tools. The City ruled out leaks on its distribution mains but was unable to pinpoint the location of leaks on its feedermains with standard acoustic correlators.
Both feedermains investigated for leaks are buried beneath busy roads in urban areas, and one main crosses below a railway line. Coupled with the size and criticality of the mains, a failure would be catastrophic, damaging property, threatening public safety, harming the City’s reputation, and resulting in costly repairs.
Detecting Leaks with Inline Acoustic Technology
Calgary investigated the suspected leaks using Pure Technologies’ SmartBall platform, an inline, free-swimming inspection tool. The tool travels with the flow of water and can be inserted and extracted from a live pipeline, through existing features. This enabled the City of Calgary to inspect its feedermains while limiting shutdown time and avoiding the expense and public disruption of excavating in a dense urban area.
The SmartBall platform has a sensitive acoustic sensor that detects leaks and air pockets in pressurized pipelines. The sensor always passes within one pipe diameter of a leak, making it highly effective for inspecting large-diameter mains. As the tool approaches a leak, the acoustic signal increases to a crescendo. Analysts cross-reference this acoustic data with continuous tracking information to pinpoint the leak location.
The first of three inspections conducted by Pure Technologies in 2018 and 2019 covered 2,600 m of the 14th Street Southwest Feedermain. This main is comprised of 900-mm PCCP and BWP and 750-mm steel pipe, with sections ranging from 40 to 60 years old. The inspection revealed one large leak estimated to be greater than 37.5 litres per minute.
Pure Technologies also assessed 3,300 m of the 52nd Street Southeast Feedermain, which is comprised of 1,200-mm PCCP installed in 1976. Over two inspections, the SmartBall platform found four leaks including one caused by a circumferential crack in the PCCP that could be heard by SmartBall 250 m away. This leak was located on the pipe barrel, indicating significant structural damage. The leak never surfaced or formed a sinkhole, so it likely would have gone unnoticed until evolving into a catastrophic failure. Another leak, found at a pipe joint, would have continued to grow by eroding the steel joint ring until eventually compromising the structural integrity of the pipe.
Prolonging Useful Life and Preventing Failure
To date, the City of Calgary has inspected and developed a condition baseline for nearly 25 per cent of its feedermain network using acoustic leak detection, electromagnetic technology, and other inspection tools. The City has proactively repaired or replaced more than 30 pipe sections based on inspection data and was able to carefully plan those repairs, reduce capital and operational costs, limit shutdown time, and reduce public disruption. Pinpointing anomalies on the 14th Street Southwest and 52nd Street Southeast Feedermains enabled the City to repair the leaks and prevent another large failure promptly and efficiently.
Russ Dueck, P.Eng, is senior asset planning engineer, water resources at City of Calgary; Rita Zhang, P.Eng, is infrastructure planning engineer, water resources at City of Calgary; Justin Hebner is business development manager at Pure Technologies; and Kristina Twigg is product marketing specialist at Pure Technologies.