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Quality leap for TRM cast iron pipes

Innovative coating technology

For the traditional manufacturer of ductile iron pipes based in the Tyrol – Tiroler Rohre GmbH – the emphasis is consistently placed on innovation and further development. For two years, the TRM research department was working together with an Austrian cement producer on a new type of fibre cement mortar for the external coating of pipes. Since autumn 2018, two machines have been set up in the factory in Hall, Austria which make the almost fully automatic wrapping of pipes with the new type of fibre cement mortar possible. With this new type of coating, the pipe system offers not only the highest level of chemical and mechanical protection, but also some tangible economic advantages.

The so called “ZMU-Austria” (ZMU is the German abbreviation for cement mortar coating) is a technique developed by the company for applying the coating to the pipe using the extrusion process. This has made it possible to develop a cement mortar which, on the one hand, offers the highest degree of external protection for the pipe and, on the other hand, is easily implemented in production.

TRM cast iron pipes with innovative fibre cement coating

Together with a partner from the Austrian cement industry, TRM has developed an innovative fibre cement coating. Meaning that, once again, the Tyrolean company is setting the standard in matters of resistance and durability.

Adhesion without adhesives

The fact that the new pipes with the “ZMU-Austria” cement mortar coating are produced entirely without bonding agents is so far a unique selling point on the market. In its production, the special cement mortar is extruded over a mesh bandage on the pipe and smoothed out at the same time. Special machines were acquired for this production step, and these were adapted to the needs of the production process in close collaboration between TRM and the Austrian machine manufacturer.

Complex composition – profound protection

TRM cast iron pipes: fibre cement coating applied in a fully automatic extrusion process

The fibre cement coating is applied in a thickness
of 5 mm in a fully automatic extrusion process.

TRM cast iron pipes: attaching the tapping sleeve

The cement mortar layer is partially removed for attaching the TRM tapping sleeve.

If we consider the ductile iron pipe with the new ZMU-Austria cement mortar coating in terms of its composition, we can talk about three layers which go around the pipe: on the inside it is lined with a cement mortar produced from Portland, blast furnace, alumina or plastic-modified cement. Outside this, the first layer consists of a fine zinc overlay applied at in 200 g/m2. The outermost protective layer now presents the new, 5 mm thick fibre cement mortar coating. The socket end-face and spigot end remain free of cement mortar and instead are provided with the tried and tested PUR or epoxy coating.

Obviously, they did not want to have one of the greatest strengths of the ductile iron pipe – namely its flexibility – restricted by the cement coating. Even in the ZMU-Austria version, the pipes still have an elastic deformability of 3 % to 5 %, depending on the diameter.

Chemical resistance

Another important characteristic which they wanted to give the new fibre cement mortar is found in its chemical resistance. Specifically, this concerns a highly alkaline composition which, beyond a pH value of 10, prevents corrosion of the iron. ”The fibre cement mortar which we have developed also has a very high sulphate resistance. This means that the new pipe system offers maximum protection in very aggressive, contaminated soils with a high sulphate content”, explains Christof Mairinger. Thanks to its safe electrochemical properties, the ZMU-Austria pipe can also be used in the area of influence of stray currents.

Mechanical protection

However, the obvious quality lies in the mechanical protection provided for the pipe. The 5 mm thick layer of fibre cement mortar makes sure that the pipe does not suffer any damage during storage, transport and, naturally, also during installation. The last point also has a role to play with trenchless installation above all – The cement mortar coating surface protects it against damage.

The multitalented ZMU-Austria is absolutely predestined for use in Alpine and mountainous areas. Thanks to its high mechanical robustness, almost any excavation material can be used for the bedding zone, where the inclusion of stones in sizes up to 100 mm are permissible. The advantages:

– no additional bedding or filling material necessary
– no disposal costs for the excavated material (because it is recycled)
– by recycling the original excavated material, the natural soil structure is preserved

Because of its outstanding suitability for pipeline construction in Alpine areas, the ZMU-Austria is the pipe of choice when it comes to pressure pipelines for hydropower stations, but also for snowmaking equipment.

Urban applications

But, of course, it is not only for the construction of pipelines in mountainous areas that extreme resistance and long working life are advantages which are increasingly in demand. “There is one thing here which should not be forgotten: naturally it makes a difference whether trees are cleared in a forest area because a pipeline has to be replaced after just 20 years or perhaps only after 100 years. But the question becomes more delicate in highly built-up urban areas. One only has to think about the fact that simple plastic pipes in urban areas often need to be replaced after less than 20 years – with all the consequences which that brings for traffic and the entire infrastructure. Therefore, in this area too, the kind of durability offered by the TRM pipe plays an important role”, argues Christof Mairinger.

In the urban environment, the very useful application for the new pipes could be the “sponge city principle”, which is a solution model for cooling in the increasingly hot urban centres (see also article “Implementation of the sponge city principle”). Of course, only pipes which are 100 % root resistant can be used here – such as the new ZMU-Austria pipe. A pilot project of this kind should be launched in the near future in a large city in Austria.

Improved ecological footprint

With all innovations in the TRM company, questions of sustainability and the ecological footprint play a major role. Of course the new ZMU-Austria pipe also sets standards in this respect. Basically, for their ductile iron pipes, TRM  exclusively uses recycling material which is obtained from the immediate vicinity. In addition, thanks to its photovoltaic system with a 9,000 m² collector surface (the largest rooftop system in the Tyrol), TRM uses the energy generated itself, thus making a considerable contribution to environmental protection. Any by-products are utilised: the waste heat is fed into the Hall district heating system.

All dimensions available

The most recent result of this research and development work, the new ZMU-Austria pipe is, thanks to its high resistance, ideally suited for both pressurised and gravity applications. All approvals and certificates are available for this. At the moment, the factory in Hall has two coating units at its disposal: one for dimensions DN 300 to DN 1000 and the other for DN 80 to DN 600. Since the middle of the year, all pipe sizes within this range are available with ZMU-Austria coating.

Also new here is an improvement in traceability and the recording of process data. Currently, each individual pipe which leaves the factory in Hall bears its own QR code, which makes automatic identification possible. This means that there is seamless documentation and traceability providing information on when and in which series the pipe was produced. The ZMU-Austria pipe from Tiroler Rohre GmbH is a further milestone in the technical development of the cast iron pipe in Austria.

Roland Gruber, Editor-in-chief at zek HYDRO


The article was slightly shortened by the editors. You can find the complete article with various illustrations as a PDF in the download area under Downloads Annual Issues EADIPS FGR.