When watermains in distribution systems spring a leak, the result is usually a relatively minor inconvenience to businesses and residents who might see some excess water on roads and lawns and in the worst situations, a bit of basement flooding. When a major transmission line fails, the amount of water released can be catastrophic, due to the larger-diameter pipes used and the high water pressures involved, which can sometimes be triple the pressure found in a typical watermain and up to 100 times the volume of water.
In 2012, such a break occurred in the transmission system for the Lake Huron and Elgin region of Ontario, an area serving 14 municipalities and a population of half a million people, including the City of London.
A sudden drop in pressure indicated a major pipe failure had occurred, sending a torrent of water gushing onto nearby farmland. The water from this 1,200-mm pipeline inundated over 28 hectares and eroded a two-hectare patch of land up to a metre-and-a-half deep.
The region had to build a temporary access road to complete the transmission pipeline repair, and subsequently bring in over 265 tractor-trailer loads of top soil to replace the soil that had been washed away from the farmland. When the restoration work was complete, the total bill to the region totalled $1.5 million in repair, restoration and damages. The damage was limited to an area with low development, and the costs and impacts of such an event would have been significantly larger if it had occurred in one of the more developed areas along the pipeline.
It’s those kinds of devastating line breaks that municipalities and regions obviously hope to prevent, and one way to do that is through a monitoring system that tells water managers when a pipe has deteriorated to the point where a rehabilitation or repair needs to take place.
Real-time monitoring of pipeline conditions using fibre-optic cables is an effective means of pinpointing problem pipes, the Lake Huron and Elgin Region found when it researched a fibre-optic monitoring system used to detect and locate wire failures in prestressed concrete cylinder pipe (PCCP).
Encompassing around 5,000 square kilometres of southern Ontario – about the same size as Prince Edward Island – the Lake Huron/Elgin water supply area has close to 155 kilometres of transmission pipelines ranging in diameter from 400 mm to 1,200 mm.
The 47-kilometre, 1,200-mm Lake Huron primary transmission pipeline was originally constructed in the mid-1960s using PCCP. Transmission line failures in 1983 and 1988 resulted in 21 kilometres of the pipeline being twinned in 1996 in higher-pressure, failure-prone areas, using 7 km of steel pipe and 14 km of prestressed concrete cylinder pipe. Another 9 km of twinning was undertaken in 2013.
To assess the current state of these pipelines, a detailed condition assessment was undertaken in 2012 and 2013 using the Smart Ball and Pipe Diver technologies from Pure Technologies Ltd. The assessment identified five pipe sections that were in poor condition and required immediate repair.
To monitor the ongoing condition and real-time deterioration of the transmission system, acoustic fibre-optic cables were deployed in the pipeline this past November and December. According to Pure Technologies, the job was the largest deployment of acoustic fibre-optics technology in Canada, and the third biggest in North America.
The installed fibre-optic cables will allow the region to proactively monitor and respond to deteriorating conditions as they occur in real time before a catastrophic pipe failure occurs.
“Other than those five high-risk pipes identified, the system is in remarkably good condition given its age. The final results of the condition assessment shows that only 0.5 percent of the pipes in the system which were installed in 1965 are ‘slightly or moderately deteriorated’ but still in good condition,” said Andrew Henry, regional water supply manager for the region, speaking to CUI about the results of the assessment. “That’s out of nearly 10,000 pipe pieces that were originally installed in 1965.”
Understanding that only a few specific pipes are bad along the pipeline allows the utility to address the specific pipes of concern without having to replace large sections of the pipeline. This savings far exceeds the value of the condition assessment inspections. Replacing large sections of the pipeline would be akin to repaving between two intersections each time a crack or pothole appears in the pavement.
Noises in the pipes
Reinforced concrete pressure pipe is a composite product comprised of an inner steel cylinder, with a layer of concrete on the inside and outside. Pre-stressed, tensioned wire is wound around the outside of the concrete-steel cylinder to reinforce the unit. Over time, largely due to corrosion, the wires can break which weakens the pipe at that location. Several wire breaks occurring within the same area can result in a failure, as there isn’t enough strength to resist the water pressure from inside the pipe.
When a wire breaks, it makes a specific noise that can be detected. Acoustic fibre-optic cables deployed inside the pipe can “hear” the sound of the wire breaking. That sound is collected by data units which correlate its location through an analysis process. All this “noise” data is monitored and when a series of wire breaks occur it is typically a precursor to a catastrophic failure.
During the installation process, string is floated down the pipeline using a parachute while the pipeline is in service. Once the string is in place, it is then used to pull the cable into the pipeline.
“It’s essentially pulled and anchored between the access and egress points, and those can’t be any more than five kilometres apart,” Henry explained. “The cable rests on the bottom of the pipe, and when a wire breaks, the reinforcing wire that’s part of the pipe makes a specific sound.”