|Client:||City of Calgary|
|Project Date:||May 2013 - ongoing|
|Type of Pipeline:||Water Transmission Main|
|Pipe Material:||Bar-Wrapped Pipe|
The City of Calgary provides water and wastewater services for over 1 million people in the Greater Calgary area. For many municipalities, accurate and regular condition assessment of large-diameter pressure pipelines has become more important in recent years as these assets continue to age and risk of failure increases. The Memorial Feedermain is a 30-inch (750-mm) Bar-Wrapped Pipe transmission main that supplies potable water to residents in Calgary.
City of Calgary's Challenge
In an annual condition assessment program, the City of Calgary inspects its Prestressed Concrete Cylinder Pipe (PCCP) and Bar-Wrapped Pipe (BWP) for deterioration.
By identifying isolated pipe sections with deterioration, the City is able to make selective repairs in favor of full-scale replacement, which carries a high cost and may replace pipe sections with significant remaining useful life.
Pure Technologies’ data from over 8,000 miles of pressure pipe condition assessment indicates that only a small percentage of pipes (less than 5 percent) are in need of repair and therefore have a significant remaining useful life. Condition assessment data also suggests that pipe distress is localized and a significant ROI can be achieved by locating and addressing isolated problems through structural inspection.
Results at a Glance
- 3 out of 232 inspected pipes were identified with bar breaks
- City of Calgary verified and repaired 1 high-risk BWP section
- Data analysis showed 3 additional BWP pipe sections with cylinder anomalies
What was the Solution?
To inspect the Memorial Feedermain, the City used PureRobotics™, which is a powerful robotic system equipped with PureEM™ technology that can be configured to inspect a variety of pipelines and materials with different operational conditions.
In BWP, the technology identifies and locates broken bars and areas of corrosion on the steel cylinder, which are the main indication this type of pipe will eventually fail.
Although BWP looks similar to PCCP in cross section, their design and materials are significantly different. PCCP is a concrete pipe that remains under compression because of the prestressing wires with the thin-gauge steel cylinder acting as a water membrane. With BWP, the cylinder plays a much larger role in the structural integrity of the pipe. BWP is essentially designed as a steel pipe with mild steel used to manufacture the steel cylinder and steel bars.
PCCP utilizes mild steel for the cylinder, but high strength steel is utilized for the wire, which is wrapped under high tension. As a result, the bar in BWP and wire in PCCP respond differently to environmental conditions that facilitate corrosion. The high strength steel wire in PCCP is smaller in diameter and wrapped under higher tension, therefore corrosion makes it quite vulnerable to breakage.
The mild steel bars in BWP are thicker in diameter and wrapped under less tension, therefore corrosion takes significantly longer to lead to breakage. The type of failure is also much different; PCCP tends to fail suddenly with a large dispersion of energy.
This type of failure is less likely in BWP where failures are similar to steel pipe with long periods of leakage occurring prior to rupture. Because of the differences in make-up, BWP and PCCP are inspected using unique methods to determine their structural condition.
In May 2013, the City inspected 1.6 miles (2.2 km) of the 30-inch (750-mm) BWP Memorial Feedermain using PureRobotics. In August 2013, the City verified the results with Pure Technologies by excavating a pipe section that was identified as distressed during data analysis.
The results from the inspection identified 3 of 232 BWP pipe sections with evidence of bar breaks, as well as 3 additional pipe sections with evidence of cylinder anomalies.
In August 2013, the most distressed pipe section was excavated for verification. The results had predicted bar breaks and cylinder corrosion, which can eventually lead to pipe failure if not repaired or replaced. The validation confirmed the broken bars and a large area of cylinder corrosion.
The City of Calgary was pleased with the results, and through condition assessment, has been able to identify and address individual distressed pipe sections on an otherwise serviceable transmission main. This has allowed the City to avoid a potential rupture of the main in a high consequence area while increasing service reliability and the useful life of the Memorial Feedermain.
The other sections identified in the inspection have been prioritized and will be verified in a future repair cycle.