Slovenia finishes M6 DN400 pipeline link between Ajdovščina and Sežana ahead of schedule, designed for later hydrogen use

Slovenia’s M6 DN400 gas pipeline between Ajdovščina and Sežana has been completed ahead of schedule, a milestone aimed at modernizing the country’s gas transmission infrastructure. The project also stands out for its long-term design: the pipeline is intended to be converted for hydrogen transport after the necessary certifications and regulatory approvals are secured.

Built through steep terrain under difficult geological conditions

Construction took place in one of the most technically challenging areas of southwestern Slovenia, where crews had to work across steep terrain and difficult geological conditions. The complexity of the environment shaped both the engineering plan and the execution approach.

Testing completed; commissioning and initial injection next

After construction works were finished, the pipeline underwent pressure testing and drying procedures. It is now described as fully prepared for commissioning and initial gas injection, moving the project from build phase into operational readiness.

Engineering scope included long pressure tests and slope installations

The construction process included multiple complex operations. These comprised calibration works along pipeline sections, pressure testing over a continuous 8.5-kilometer stretch, and installation on slopes with inclinations reaching up to 65 degrees—where cable transport systems were used. Crews also laid a 500-meter section on terrain with a steep 45-degree gradient.

Contractor Monter delivered amid operational constraints

The demanding conditions highlighted the technical expertise of local contractor Monter, which carried out the installation works. The company relied on specialized engineering solutions to complete the project safely while meeting an accelerated timeline despite terrain-related constraints.

With construction complete and readiness steps already undertaken, investors and market participants will be watching how quickly Slovenia moves into commissioning and whether certification processes for hydrogen conversion progress in line with its broader energy transition strategy.