Above-ground pipe with flexible aramid liner
paper mill in southern Germany was looking for a suitable solution to return its treated wastewater to a river above ground. Rädlinger primus line GmbH realised the task with its self-developed and reusable Primus Line® Overland Piping system.
Low water levels and aquatic ecology are a major issue throughout Europe. The constraints on companies that rely on water extraction from rivers, streams and lakes are increasing. This also affects a paper mill in southern Germany.
The mill operator takes out water from a mid-mountain stream for paper production and returns it to a canal several hundred metres below the point of withdrawal. For environmental reasons, the paper mill was instructed to return the purified process water to the extraction spot.
The company approached Rädlinger primus line GmbH who were able to offer a suitable solution with the Primus Line® Overland Piping system.
What is Primus Line® Overland Piping?
Primus Line® Overland Piping is a reusable solution specifically designed for above-ground pipelines in order to be able to safely transport demanding and potentially hazardous media such as industrial wastewater, brine, process water etc. The system consists of two components: an aramid-reinforced liner and specially developed connectors.
Up to 4,000 metres of the flexible pipe are supplied on a reel, unrolled from it and laid directly – even in difficult terrain. (Figure 1) The pipe naturally conforms to the surface structure. Depending on the diameter (nominal widths from DN 150 to DN 350), the maximum operating pressure ranges from 56 to 20 bar. The inner layer is made of thermoplastic polyurethane (TPU), which is corrosion resistant and offers a high abrasion and chemical resistance that even withstands contact with highly corrosive hydrocarbons. The Kevlar® fabric reinforcement gives Overland Piping its high tensile strength, enabling it to absorb even very high operating pressures completely. The TPU outer layer protects against UV radiation and abrasion and provides the flexibility required for multiple installations and the ability to roll up the reusable system.
The connectors ensure a leak-free joint. Specially designed high-pressure end fittings with flanges or special quick couplers are used to connect the pipework. They can also be connected to pumps or other pipework.
Project planning for wastewater recirculation with Primus Line®
The wastewater recirculation line of the South-German paper mill has a total length of 690 metres and was to be installed above ground via a raft water canal. The volume of recirculated wastewater varies between 600 and 1,200 cubic metres per hour. Due to its temporary use during the summer and autumn months, the original plan was to roll up the system, store it for the rest of the year and then roll it out again – a classic use case for the reusable Primus Line® Overland Piping system.
However, during an on-site visit, the project team decided to leave the pipeline permanently in the canal due to the difficult access in some areas. The Primus Line F-Liner that is used as Overland Piping system was also suitable for this case of application and met all the requirements in terms of service life, temperature, UV and abrasion resistance. It also withstands the alternation between several months of operation and shutdown. In addition, its shape remains stable whether the canal is filled with water or not.
As a result of the flow rate calculation, an F-Liner with a nominal diameter of DN 350 was selected, operating at a pressure rating of PN 10. Due to its low friction coefficient (k = 0.028 millimetres), it can also handle the highest flow rates.
One of the challenges of project planning was determining the installation sections. The curved course of the canal as well as structures that had to be passed such as a lock and a building containing the mill’s own hydropower plant prevented installation in one section. Primus Line’s engineers also had to take into account the ongoing operation and traffic on the mill site which had to be maintained during placing the winch and reels. In the end, three sections with lengths of 440, 200 and 50 metres were defined.
Pipeline in the river bed
After intensive preplanning, the safety training for the installation team from Rädlinger primus line GmbH and setting up the construction site, work could begin.
In order to place the liner in a safe and stable manner, both during installation and in future operation, the Primus Line installation team first of all removed timber from the canal (logs and branches). This clearing work was done using a boat and a winch.
A boat and a winch were also used to lay the pipeline. The team placed the end of the liner with the installed connector in the boat and attached the end of the winch line to the connector. In this way, the pull of the winch gradually unwound the liner and placed it in the canal. In this way, Primus Line laid the three sections one after the other: 200 metres under the hydropower plant, 50 metres near the lock and 440 metres up to the wastewater intakes.
A total of six connectors was necessary to link and connect the pipelines. (Figure 4) Some were mounted on pontoons and some were pre-installed before the liner was laid. The liner was then pressurised with water, set up and brought into its circular shape. (Figure 5) This allowed the liner to sink to the bottom of the canal. After a final pressure test, the pipeline was returned to service after a three-week construction period. About half of this time was taken up with the removal of the timber.
Advantages over HDPE pipes
Primus Line® Overland Piping is the consistent further development of a technology that Rädlinger primus line GmbH has been using for more than 20 years for the trenchless rehabilitation of pressure pipes. The Bavarian company’s above-ground solution is now also being used all over the world, for example in France, Canada and Norway, to reliably transport brine, domestic sewage and process water.
In all of these projects, the flexible pipeline based on the aramid-reinforced liner has prevailed over above-ground HDPE pipes, albeit for different reasons.
These include significant advantages in terms of mobilisation and equipment requirements. The fabric-reinforced liner is transported on reels, saving space. Installation requires a mini-excavator or winch and simple hand tools. There is no need for machinery, manpower or time spent on complex welding to make the connection. Installation and dismantling times are correspondingly shorter. Primus Line normally take one or two days to lay six kilometres of their liner. Lengths of 1,000 metres and more in one section reduce the number of joints and weak points. The liner easily adapts to the unevenness of the surface. By comparison, installing the same length of HDPE pipe takes about 25 to 30 days, with increased additional labour costs. Dismantling the same length of pipe also takes only one to two days with Primus Line® Overland Piping, as the liner is simply rolled up, compared with seven to ten days for HDPE. The subsequent storage requirements for HDPE pipes are up to ten times greater than for liners on reels. In addition to storage and transport costs, operating costs are on average also lower due to minimal mobilisation and demobilisation costs and lower manpower requirements.
In addition to cost and efficiency, the low use of machinery also contributes to the environmental friendliness of the Overland Piping system. It can be 
installed in sensitive environments such as protected areas, nature parks or rivers without major environmental impact. This avoids emissions and reduces the carbon footprint.
The middle layer of the three-layered Primus Line® Overland Piping system ensures the safety of the flexible pipe: It is made of seamlessly woven Kevlar®. This synthetic fibre is up to ten times stronger than steel and twice as strong as glass fibre or nylon. The flexible pipe therefore has a very high factor of safety (FoS). The burst pressure is at least 2.5 times higher than the allowable operating pressure. The entire production process is closely monitored. Sensors and cameras continuously capture the process parameters and provide the basis for extensive wall thickness and consistency control mechanisms. In addition, every liner produced is subjected to an in-house pressure test before being delivered to the construction site.
Fast installation in emergency cases
Primus Line® Overland Piping also provides a solution in the event of catastrophes such as landslides, floods or forest fires that cause pipeline damage or failure. A single container can hold two to four kilometres of flexible pipe with the appropriate fittings. In case of an emergency, the flexible and spoolable Primus Line® above-ground pipe can be installed immediately and depending on the environmental conditions – within a short period of time. In addition, the Primus Line® Overland Piping system has a very long service life – depending on the type of use and the conditions.