Norrenergi renewed a pipe section in the Stockholm district heating network without excavating or replacing the old pipes. The energy company identified a leaking district heating pipe situated under a road in Stockholm. To replace this pipe section using traditional methods – traffic, including several bus lines, would have been heavily affected, as a large road section would require excavation. Faced with this problem, Norrenergi turned to Pressure Pipe Relining Sweden AB (“PPR”) and decided to use CarboSeal®, a new solution to rehabilitate district heating pipes by relining them.

Fjärrvärmeprojekt Sverige AB was engaged in the project to support planning and execution. Installation company Pollex AB was appointed to install the CarboSeal® liner. They were supported by PPR engineers who overlooked the process. The team was challenged, as the leaking section included two compensators and a 12-degree bend.

In connection to the leaking section, a reduction in diameter from DN 400 to DN 300 had already been made, so the team devised a solution where CarboSeal® would be cured in a DN 300 sleeve inside the leaking DN 400 pipes. This solution also made it possible to reline through the compensators and the 12-degree bend. To assure relining through these obstacles would be viable, the PPR team made a test rig mimicking the diameter change, the two compensators and the bend. After a successful test on the ground, the team installed CarboSeal® in the leaking section.

A standard installation of CarboSeal® takes between one and two days; however, as this was a new solution, the team decided to follow a conservative time plan and dedicate three days for renewal of each pipe (feed and return). The pipe renewal was completed in five days. The pipes have been welded together, recommissioned and in service with no issues since the end of May 2021. The old pipes were given new life, without needing to dig out, refill or recycle. Furthermore, no permits were needed to dig up streets, change bus routes or redirect traffic. On top of the reduced time and effort spent, by avoiding excavation and replacement, the carbon footprint was reduced by 80%.

The patented CarboSeal® system has been developed by an experienced group of district heating network owners, relining companies, and material experts, with valuable support from research institutes and district heating associations. Thorough testing and evaluation have confirmed that the system can withstand the high temperatures and pressures in district heating networks over long periods, which has proved impossible for conventional relining solutions.