New technique fixes district heating leak

When Navirum Energi was hit by a district heating leak under the railway in Örebro Sweden, the solution was to reline the pipe. This is a new technique for district heating pipes, and FVB coordinated the project.

The leak began in the early autumn at an unknown location under the railway in the centre of Örebro, where there are a number of other pipes in the ground.

“It wasn't just a matter of digging and repairing the pipe or laying new pipes. We looked at various alternatives such as guided drilling and hammer drilling, but they would have been tricky because of the other pipes down there and would also have been expensive and difficult to do,” explains Olof Jörstad, Construction Manager for the distribution division at Navirum Energi, a wholly-owned subsidiary of E.ON.

“We had a presentation on relining district heating pipes at a distribution conference in which a new technique developed by Swedish company Pressure Pipe Relining Sweden had been used. So, we contacted them to see if relining was an option for the pipe under the railway, which we then decided to use,” says Olof Jörstad.

The carbon fibre lining had to be carefully rolled out to prevent it getting abraded and therefore damaged.

Relining entails laying a new soft pipe (the liner), also referred to as a ‘liner’ through the old pipe. The liner is then inflated and hardened to a new, hard pipe which can cope with the pressure even at points where the old pipe has rusted away. Relining is used a lot in the water and sewage industry but has never been used for district heating before. This is mainly because there were no products suitable for this purpose on the market. But it’s also harder to perform relining within district heating than for water and sewage as district heating runs at considerably higher pressure and temperatures. Steel district heating pipes expand and contract at different temperatures, which means a liner has to be able to do the same.

Sealing with carbon fibre liner
Pressure Pipe Relining Sweden, based in Borås, have developed a composite carbon fibre liner for district heating. And this was the one we decided to use in Örebro. To be able to lay the carbon fibre liner, the existing pipe was drained and inspected using video.

“We were able to see that the welds on the existing steel pipe had ragged edges and that there was a risk of ripping the carbon fibre liner during the installation phase, so Pollex, the contractor that carried out the job, ran in a robot that ground down the sharp edges inside the pipe,” says Dennis Hild-Walett of FVB, the Project Manager.

The soft carbon fibre liner was then pulled through the supply and return pipes using a winch. It extended to a total of two lengths of 60 metres each. The liner was totally flat to begin with. Pollex then inflated and hardened it into a pipe shape using steam. The hardening process in this instance took eight hours per pipe.

“There are a number of advantages to using relining as a method. In Örebro we didn't have the option of digging up the pipe as it lay under a railway right in the town centre along one of its busiest streets. Hammer drilling was a possibility, but because it lay under the railway, we would have been forced to take a number of safety precautions and drill several metres under the railway, which would have been very expensive. This alternative was cheaper,” says Dennis Hild-Walett.

“Using relining also meant the job was done very quickly. We were finished within six weeks, and only two small shafts had to be dug,” he adds.

“We did the job in October, and it all went very smoothly. It’s been in use ever since, during a period with a lot of rain and during times of peak demand, without any problem at all. It's a totally new and simple technique that presents a number of new options, especially in areas where it is going to be difficult to replace the pipe,” concludes Olof Jörstad.

Risks with a new technique
But using a new technique implies several uncertainties, and both Dennis Hild-Walett and Olof Jörstad point out the risks involved with the lifespan of the carbon fibre liner. According to the manufacturer, based on simulated tests it should be at least 30 years.

They also point out that heat loss will be higher as the relined pipes were laid in the 1960s when heat loss was much higher compared to more recent pipes. Neither are there any sensor wires in relined pipes to indicate humidity.

“But overall, relining is a good method for repairing and updating district heating pipes, and I think we’re going to see more relining in the industry,” states Dennis Hild-Walett, and Olof Jörstad concurs.

This is what the relined pipe looks like inside after installation. The liner stiffens after hardening and is now ready for use.

FVB
Both in Sweden and internationally, FVB is a leading consultant in the Energy, Industry, Property, Electrical & Automation and Water & Sewage sectors.

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