With a capacity of 600 MW, Reuter West is the most powerful heat and power plant in Berlin, Germany. It consists of two equal units, each with an output of 300 MW (block D and E), which were put into operation in 1987 and 1989 respectively and located next to the existing old power plant, Reuter.

During recent routine maintenance checks it was noticed that two of the four return pipes connecting the side coolers with the main cooling return line between the cooling tower and unit E were showing leakages caused by pitting corrosion. The leaking pipes are made of welded steel, with a nominal diameter of 600 mm and are operated with a maximum pressure of 29 psi. The pipeline had been partly assembled by welding half pipes together on site, causing tolerances in diameter, an unusual trait for steel pipelines.

The return lines, together with many other lines, are installed in a service duct below a pavement designed for heavy-duty trucks. The replacement of larger pipe sections would have required the opening of the pavement, digging a trench and removing the reinforced concrete floor. This method was rejected from the beginning; primarily due to the obstruction it would cause to internal plant traffic, but also for cost reasons. The replacement of small sections inside the closed service duct by hand was also discussed as a possible alternative. However, the cost would have been quite high. In either case, the replacement could never have been executed within the time frame.

BKP Berolina Polyester GmbH & Co offered to install the new Berolina-LP-Liner, the first field test of the product. This renovation solution promised cost advantages for the power plant’s owner Vattenfall Europe. Plant management decided to renovate a test section using the liner and await a result before making a final decision about the method of renovation or replacement.

Preparation

As the condition of the leaking pipes — except the pitting holes — was generally still good, the final decision on method was postponed for several months. The leakages were closed by welding steel plates over the holes. A 40 metre test section was left for the liner renovation test. This section was limited by a 90 degree bend with a wall duct that followed on one side. On the other side of the section, and an additional 90 degree bend led into an extension section.

The distance between the upper pipe, which had to be renovated, and the ceiling measured only 3 to 5 cm. First the bends were removed because the liner installation, and subsequent curing by using UV-light, required reasonably straight sections. Afterwards the section was scheduled to be cleaned by high pressure jetting. Unfortunately this was not sufficient as the pipe was encrusted with a hardened build-up that could have damaged the liner. An intensive cleaning and levelling of the pipe’s inner surface was carried out using a special scraper known as a ‘go-devil’ (pictured).

Installation of the liner

The liners were fibre reinforced plastics (FRP), using several layers of glass-fibre mesh reinforcement together with polyester resin which is cured by using UVA-light. So far the Berolina-Liners have been used for renovation of storm water or sewer pipes. The water tightness test in those cases followed the procedures of EN 1610 with a maximum test pressure of 7.25 psi when using water and 1.45-2.90 psi when using air as a pressure medium. Based on the existing liner products the company ventured into a new product line to enable the renovation of pressure pipes.

In this project, the liner for low pressure pipes was chosen to complete the test. Following the pipe cleaning, a polyethylene gliding foil was pulled in the pipe to protect the liner from damage by welding burrs or any remaining hardened build-up when being pulled in.

Then the liner was pulled into the pipe with a hydraulic winch and closed with end caps.

The liner was then inflated by air pressure in order to insert the UVA-light source. The light source consisted of a light train with eight metal halide lamps. The light spectrum was synchronised to the photo catalysts in the polyester resin. A curing unit, type Compact and made by HC PipeTech, was used for curing the liner. Due to the very small external dimensions of this equipment, the installation crew was able to bring the unit into the service duct by hand and through a door only 90 cm wide.

After the insertion of the light train, the liner was expanded close fit to the inner wall of the host pipe. The special design of the liner allows it to dialate over a relatively wide range of diameters – from 5 per cent under measurement up to 5 per cent over measurement compared with the specified size of the host pipe. Therefore, the large tolerances in diameter of the host pipe were not an issue for the liner.

After dilatation, the light source was ignited and pulled through the liner at a defined speed. The UVA-light enabled the polymerisation of the polyester resin.

After the curing had been completed the liner ends were cut with precision and the installed liner could be examined. The smoothness of the inner liner surface was striking. In a public sewer system the job would have been completed by this stage. In this case, the connection to the existing pipeline had to be made. Flange collars, also made of FRP, were bonded to the protruding liner ends and the continuing pipeline components with flange joints attached. This design was necessary for two reasons. Firstly, the design allowed for the opening of the test section for future inspections without destroying any part of the pipeline. Secondly, a joint by laminating was not possible because of the very narrow distance between the pipeline and the reinforced concrete ceiling. Even for the flange type of connection used in this project, the concrete cover had to be removed at some locations to allow enough working space.

Summary

The project described above has been accomplished in an extremely short time frame, especially considering the very tight working space. The renovation of the straight section, including cleaning with the ‘go-devil’, pulling in of gliding foil and liner, curing and exact cutting was done in a single day. The replacement of the pipe section with half pipes would have taken three to four weeks. The time taken for connecting the liner with the rest of the pipeline, as well as for the preparing works for removing the old steel bends, was within the normal time frame for this kind work. The pipe section renovated by using the Berolina-LP Liner has been in full and unrestricted operation for over six months at the time of writing. From testing so far the Berolina-LP-Liner can be rated as reliable for this kind of pipeline renovation in power plants and other low pressure pipes.