The companies were recognised for the outstanding rehabilitation project in Sofia, Bulgaria, at the 29th International No-Dig Conference and Exhibition, held in Berlin.

International Sekisui SPR Europe (SSPRE) Group Chief Executive Officer Edmund Luksch said “The ISTT has honoured one of the most exciting construction projects with its renowned award. That makes us and our partners very proud.”

Using the Nordipipe pressure line, the team renewed a steel water pipe with a working pressure of 7 bar and a diameter of 1,220 mm, within the space of only a few weeks. A new inversion vessel, with a diameter of 3,000 mm, was specially developed for the purpose.

Project scope

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Stroitelna Mehanizatsia rehabilitated an 850 m section of a 30 year old pipeline below narrow streets of an old residential district in Sofia, which included a crossing underneath a railway. Population pressure meant that the pipeline could not be taken out of service for an extended period.

Construction could not start until December, but had to be completed by mid-January. In view of the large diameter and the thin 8 mm walls, SSPRE used the Nordipipe pressure liner as a semi- structural solution.

The severe cold hindered not only jet cleaning the host pipe with pressure water, but the impregnation, because it was difficult to keep the resin fluid. A further challenge was that due to minimum thickness requirements of the impregnated liner, only sections up to 90 m could be rehabilitated.

Stroitelna Mahanizatsia developed a new inversion vessel for the liner – likewise within the extremely tight deadline – tailor-made for rehabilitating sections of up to 110 m in length in this project.

This enabled the inversion to be completed successfully in all nine sections.

Maximum performance from man and technology

Stroitelna Mehanizatsia General Manager Stefan Zhelyazkov said “The biggest challenge with this project was to motivate my team to complete the work in the short time and to believe in themselves.”

“Our employees did a great job and we were able to count on the full support of SSPRE. Our success is thus thanks to the complete family of SSPRE companies, who gave optimum cross-border support for the installation of the Nordipipe liner.”

Successful co-operation

A total of 45 tonnes of liners and resin were installed in only 35 days, including both the Christmas and New Year holidays.

“Due to the complexity of the construction project we had, of course, hoped for the recognition of the ISTT,” Mr Zhelyazkov said. “Nevertheless, the announcement of the award came as a surprise and we are absolutely thrilled.”