The City of Winnipeg, Manitoba, Canada, chose a modern solution for an aging infrastructure problem.
Pressure pipes running under rivers or lakes present unique challenges when rehabilitation becomes necessary. In particular, network engineers often face problems with pipelines that have multiple bends as these can hardly be accessed due to the location under water. Nevertheless, most trenchless systems are not capable of traversing a large number of bends, particularly when the pipe cannot ever be completely dry due to the holes in the pipe located under a river.
The City of Winnipeg was confronted with exactly this situation: a DN250 fresh water main 175 m in length with three 45-, one 22.5- and one 11.5-degree bend was in need of renovation as it had an active leak.
The steel pipe was originally considered for cured-in-place pipe (CIPP), however, this application was not feasible for several reasons. First, using this widespread trenchless technology under the river with all the bends was not possible in a single shot. Second, the pipe was constantly filled with water due to exterior leakage. This adds another challenge to CIPP that couldn’t be overcome as the curing process turns out to be extremely risky under such circumstances.
By combining flexibility and stability, flexible fiber-reinforced pipes (FFRP) offers various advantages for the trenchless rehabilitation of pressurized pipes. Generally, small construction pits, short rehabilitation times and the low level of impact on the environment make it the ideal technology for the renovation of defective lines in sensitive circumstances.
As such, liners can traverse multiple bends and operate independently from the host pipe, it was presented to the engineering consultant and the City of Winnipeg. After subsequent evaluation, the Primus Line DN 250 medium pressure system was identified as the best option for rehabilitation.
A new player in the trenchless industry came to the rescue aided by Tri-Core Projects Ltd. and directed by AECOM on behalf of the city. There were challenges overcome and lessons to be learned by all involved.
As an experienced contractor in the application of Primus Line overland piping as a bypass in several projects, LV Trenchless from Calgary was chosen as installer for the respective pipe rehabilitation project; being selected for this job as a low bidder made them a new player in the trenchless industry of Canada.
While not its first Primus job, this did present some challenges to its experienced operations. LV Trenchless integrated as a team with the engineer and the city operating as one entity to overcome supply chain issues, unforeseen conditions, and a difficult to access work site.
Prior to any Primus Line installation, the pipeline had to undergo CCTV inspection to identify obstacles such as debris, welding seams or incrustations. In this particular case, several areas showed sharp protrusions that could potentially damage the liner during the process of insertion. These sections required robotic milling.
As with all current-generation rehabilitation technology, preparation is the majority of the work. Given the large size of Canada and Winnipeg’s comparably remote location in Manitoba, it took several days to source the necessary equipment and the milling robot.
Besides the detected obstacles inside the pipe, an unknown 45-degree bend that was less than 20 ft away from the end of the section to be rehabilitated was uncovered during the inspection. Under these new circumstances the low-pressure connector couldn’t be assembled and had to be replaced by a medium pressure connector that was shipped up from the United States.
Time to for the Relining
With all preparations in place, the pipeline being cleaned and the free inner diameter verified by a second camera inspection, LV Trenchless was set for the central step: the insertion of the FFRP. The transportation drum with the U-shaped liner was placed at the start pit and a pulling winch at the destination pit. The rope connection was established by the means a foam pig under air pressure.
The actual insertion of the FFRP only took 30 minutes, as it can be pulled at a speed of 600 m per hour. Once brought in its final position it was inflated with oil-free compressed air and rounded back to its operating configuration. The tapes which keep the liner in its u-shaped form during transportation and insertion burst and simply remain inside the host pipe. The connectors were installed on both sides completing the lining in one day. The connectors were placed with the medium pressure and low pressure connector at either end the system would soon be prepped for service by Tri-Core.
After pressure testing the FFRP system to verify the success of the installation, it was only disinfection that remained in order to guarantee the safety of the drinking water. After that, the lined section was reintegrated to the existing network using spool pieces on both ends and subsequently could go back online.
As a result of this rehabilitation measure, the water main could be handed over to the City of Winnipeg with a minimum extension of its useful life by at least five decades. This span of FFRP design life is derived through verification of long-term strength according to DIN 16887 and DIN EN ISO 9080 in a series of up to 10.000-hour tests extrapolated to 50 years.
Several conclusions can be drawn from this project. First, it became clear that pipe cleaning can bring significant and unforeseen challenges for contractors and thus delay the schedule of a project. In this case, large holes in the pipe became a problem that required extra equipment to be brought in.