Rehabilitation of sewer rising mains with Primus Line^®: a custom-fit solution

30 Mar 2023

Sewerage systems are one of the most significant achievements of our modern civilisation – and lead a hidden existence. We rarely think about how our wastewater gets to the sewage treatment plant and what effort is needed to clean it. Many of the sewerage systems are already in need of rehabilitation and especially the rehabilitation of sewer rising mains in the sewerage systems confronts cities and municipalities with numerous challenges. The trenchless rehabilitation method Primus Line^® offers a custom-fit solution for this.

Many sewer rising mains have one thing in common: They are part of the operators’ critical infrastructure. Leakages have to be eliminated, because seepage from untight sewer rising mains carries the danger of environmental damage as well as of compromising traffic and building safety. This is associated with considerable costs. A permanent rehabilitation is therefore essential.

However, sewer rising mains that need to be rehabilitated are often difficult to access. They run in densely populated inner-city areas, in ecologically valuable or even protected areas, under rivers, railway tracks or main roads. In case of rehabilitation, it is laborious to take these pipelines out of service. Therefore, a short installation time and fast recommissioning have top priority for operators. New sewer rising mains are usually already designed redundantly in order to be able to maintain sewage transport in the event of failure or repair. This is not the case for older mains. During the rehabilitation period, the sewage has then normally to be pumped out and transported to the sewage treatment plant by lorries.

Failures of pressure pipelines arise by external or internal corrosion as well as by mechanical defects such as untight connectors or longitudinal cracks. In many cases, the pipeline can still withstand the traffic load, but no longer the internal pressure load. Rehabilitation with other trenchless methods is often not an option: Their execution is more time-consuming, installation lengths are restricted and bends can only be traversed to a limited extent.

In view of these challenges, operators of sewer rising mains are increasingly using lining with inserted hoses for their rehabilitations. This method leaves an annular space between liner and host pipe. As with Primus Line^®.

Flexible and fast: Primus Line^®

Due to its product properties, Primus Line^® is predestined for use in the rehabilitation of sewer rising mains. The system consists of the liner and particularly developed connectors. The three-layer structure of the liner – inner and outer layer made of polyethylene (PE) or thermoplastic polyurethane (TPU) with a reinforcement of aramid fibres in between – make the liner flexible and at the same time extremely strong. Thanks to its flexibility, the liner can pass bends up to 45° in the line run by standard.

Since sewer rising mains usually have no service connections, long insertion lengths are required. With Primus Line^®, up to 2,500 metres at a stretch are possible. Liner and connectors are installed via small excavation pits, generally at start and end point of the section to be rehabilitated. Existing shafts can also be used for liner insertion. This has only a minor impact on the environment – traffic can continue to flow or protected natural areas are hardly touched. The insertion speed of up to ten metres per minute reduces the total installation time to a minimum. Once the connectors have been installed and the integrity of the system has been successfully tested, the pipeline can be reconnected to the network.

If it is not possible for the operators to take the sewer rising mains out of operation for a limited period due to time and cost reasons, Rädlinger primus line GmbH offers another solution: Primus Line^® Overland Piping can be deployed as temporary bypass and re-used afterwards.

Tested quality

Safety is important when transporting contaminated water. Rädlinger primus line GmbH promises a service life of at least 50 years for their system of liner and connectors in rehabilitations and backs up this statement by vigorous qualification testing, such as cyclical load or abrasion tests.

In the load test according to the ISO 15306 standard, a cyclic load of 75 to 125 per cent of the maximum operating pressure is applied to the liner and connectors under test to check their effect on the burst pressure. The result after one million unrestrained cycles: An effect of the varying internal pressure load on the burst pressure of the Primus Liner is not verifiable. The material did not show any aging after this test.

In the abrasion test following the DIN EN 295 standard, appendix 1, the so-called “Darmstadt Procedure”, a mixture of water and materials of different grain sizes is moved back and forth on the liner’s inner layer. For this purpose, a half-shell of the liner to be tested is fixed in a tipping trough. Here, too, the result after 600,000 cycles is convincing: The inner layer of the Primus Liner, which is made of polyethylene, is abrasion-resistant.

By means of the material tests in combination with a continuous factory quality control, the operator gets a safe and high-quality product for his application.

Time- and cost-saving alternative

Trenchless systems with annular space such as Primus Line^® are a time- and cost-saving alternative to the rehabilitation of sewer rising mains with conventional dig-and-lay. Product and material properties relieve the operators of sewer rising mains through short installation times and fast recommissioning.

The benefits of the Primus Line^® technology are also transferable to rehabilitations in the drinking water sector. The system is approved for drinking water applications in more than twenty countries.

Special situation in Germany: Pressure test of sewer rising mains mandatory in Bavaria as of 2024

About 10% of the sewers, combined sewers and storm sewers in Bavaria are sewer rising mains. According to the currently applicable self-monitoring regulation, they would already have to be checked for leaks. Until now, however, there has been no appropriate testing procedure. The potential of undetected leaks is therefore high – with the known effects on the environment.

The Augsburg University of Applied Sciences (HSA) has developed a standardised procedure on behalf of the Bavarian State Office for the Environment, the so-called HSA standard procedure. When the new version of the self-monitoring regulation, which will be published in 2024, explicitly requires the testing of the tightness of sewer rising mains, a corresponding testing procedure will now be available. Other German federal states, such as North-Rhine Westphalia, are also working on adapting the corresponding state-specific self-monitoring regulations.