FLEXWELL district heating cable (FHK) – the flexible, double-walled steel-casing pipe system

The FLEXWELL district heating cable (FHK) is a flexible, self-compensating and monitorable steel-casing pipe system for district heating, district cooling and domestic hot water or condensate – and it is 100% diffusion-tight. Developed for underground installation, this pipe system has proven itself over many years in a wide range of applications, even under extreme conditions. Thanks to flexible installation options, it is safe and economical during the planning and construction phases, and reliably durable in operation.

An extremely reliable district heating pipe for all applications

The FLEXWELL district heating cable (FHK) is highly corrosion-resistant, making it ideal for transporting various media: heating water, domestic hot water, drinking water or condensate. Its reliability is largely due to the intelligent construction of the pipe composite. The core consists of a flexible carrier pipe made of corrugated steel, which compensates for temperature-induced length changes within itself, eliminating the need for expansion joints. U-bends, L-legs, and fixed points are not necessary. The inner pipe is encased in a layer of CFC-free polyurethane foam insulation, which also contains monitoring wires. This is surrounded by a corrugated steel casing for corrosion protection, and finally, a PE-LD jacket. Delivered in continuous lengths with flexible bending radii, FLEXWELL-FHK enables exceptionally reliable district heating pipelines through underground installations, always following the shortest possible path – with no welding, without interrupting the corrosion protection and with minimal trench dimensions.

Unbeatable advantages for planning and installation

Specifically, the FLEXWELL district heating cable (FHK) can usually be laid in continuous lengths without the need for couplings. This shortens the construction times, as welding or re-insulation is unnecessary and even enables trenchless installation by means of ploughing, as well as simultaneous installation with other pipelines. This means that old or damaged pipe networks can be quickly and easily replaced. Safe installation is also possible in wet soil, high groundwater areas or when crossing rivers and bodies of water. Overall, FLEXWELL keeps the excavation costs low thanks to narrow trench widths, direct routes and minimal earthworks – shallow laying depths are also sufficient. Obstacles can be crossed over or under without additional expense thanks to the system’s flexibility. FLEXWELL is therefore not only cost-effective and quick but also environmentally friendly, as the routes can be adapted to the local terrain, protecting trees, forests and shrubs. The system is also self-ventilating, self-compensating and flexible.

Ideal for installation using the horizontal directional drilling method

What if you need to cross a road? Or a traffic route that mustn’t be disrupted? Or a strip of land that can’t be excavated for nature conservation reasons? In such cases, horizontal directional drilling (HDD) is the solution. Due to its product-specific advantages, the FLEXWELL district heating cable (FHK) is ideal for this surface-friendly installation technique. In a nutshell: you first need to create a precise connection between your starting pit and the intended target pit using a mobile drilling rig and a three-dimensionally steerable drilling lance. This connection is stabilised with flexible steel pipe sections and flushed with an environmentally friendly drilling suspension. In the target trench, the drilling lance is replaced by an expansion head connected to the FLEXWELL district heating cable (FHK). The cable is then pulled back through the newly created connection, aided by a bentonite drilling suspension. Done! Sure, it may sound simple, but not every district heating pipe can handle this process. By contrast, the FLEXWELL-FHK ensures outstanding results.

The range of FLEXWELL district heating cables (FHK) and accessories

Our FLEXWELL district heating cables (FHK) are available in nine nominal diameters from DN 15 to 150, with lengths ranging from 1,000 to 230 metres. We offer both welded and weld-free connection options. The system’s corrugated steel casing is designed to withstand significant ground and traffic loads. Expert opinions have confirmed that for FLEXWELL district heating cables (FHK) of the type series 22/55–200/310 (inner/outer pipe diameter), a coverage height of 0.2 metres is sufficient to withstand the SLW 60 traffic load, which accounts for heavy vehicle traffic.

All key data at a glance


  • Operating temperature: -170°C to +150°C
  • Operating pressure: 16/25 bar
  • Dimensions: DN 25–150
  • Carrier pipe: Stainless steel
  • Exterior pipe: Stainless steel
  • Insulation: Polyurethane (PUR)

Is this the solution you’re looking for? Contact us

Convinced? Is the FLEXWELL district heating cable (FHK) with its multi-layer corrosion protection, continuous monitoring and universal connection options exactly the solution you need for your district heating project? Then take a look at our reference projects. We can provide numerous application examples that demonstrate the many advantages of our steel-casing pipe system. Feel free to contact us directly – you can reach us here. We will be happy to advise you.


Type DN Stainless steel inner pipe External diameter Min. bending radius max. Delivery lengths*
    d1 x s2 D
  mm mm m m
FHK 30/91 25 30.0 x 0.3 94 1.0 1000
FHK 39/116 32 38.9 x 0.4 121 1.2 640
FHK 60/148 50 60.0 x 0.5 156 1.5 590
FHK 75/171 65 75.8 x 0.6 178 2.0 480
FHK 98/171 80 98.0 x 0.8 178 2.0 480
FHK 98/220 80 98.0 x 0.8 233 4.0 270
FHK 127/220 100 127.0 x 0.9 233 4.0 270
FHK 147/220 125 147.0 x 1.0 233 4.0 250
FHK 200/310 150 197.5 x 1.2 313 5.0 230