Successfully performed works on connecting the Zabok – Lučko and Kozarac – Sisak gas pipelines

Within the scope of completing the construction of the Zabok - Lučko DN 700/75 gas pipeline and the Kozarac - Sisak DN 800/100 main gas pipeline, the works on connecting the new gas pipelines to the gas transmission system have been successfully performed.



The works were performed within the announced period of 96-hour long interruption in transmission, that is, from Thursday 23 April (at 6:00 o'clock) to Monday 27 April (at 6:00 o'clock).  The Zabok - Lučko gas pipeline was connected to the gas transmission system at the Lučko gas node while the Kozarac - Sisak gas pipeline was connected to the Zagreb Istok - Kutina DN 600/75 gas pipeline in the immediate vicinity of the Kozarac gas node.



During the four-day long activities it was necessary to prepare the existing and newly constructed installations for works in a safe manner. For this purpose, natural gas was evacuated from the existing installations respecting the strict conditions prescribed by the Regulation 2024/1787 on the reduction of methane emissions, and after that nitrogen (N₂) inerting of the existing and newly constructed installations was performed.
After the preparation, the physical connection of the installations was carried out by employees of the Monter company and other members of the group of contractors for the construction of both gas pipelines. Upon the completion of works and obtaining the positive results of supporting documentation, experts from Plinacro repeated inerting of the installation, replaced the nitrogen in the installation with natural gas and filled the installation up to the operating pressure of the system.


35 Plinacro employees, about twenty employees of contractual partners and more than 80 employees of the group of contractors were engaged in the works.



Works at both gas pipelines were carried out simultaneously at two locations to avoid additional interruptions in gas transmission. However, such organization of works represented one of the most demanding challenges for Plinacro in the field of transmission system supervision and operation.
During the four-day disruption, it was necessary to significantly adjust the transmission system operation regime. In this period, the dominant gas entry into the system from the LNG terminal was completely suspended. At the same time, south of Zagreb the transmission system was separated from other gas sources, except for production from the north Adriatic fields. In addition, almost 90 kilometres of gas pipeline between the two locations where the works were carried out, were temporarily isolated from the transmission, which is why this part of the system could not contribute to transmission or the flexibility of the gas transmission system.



Due to the complexity of the stated circumstances, the preparation of the transmission system for such operating conditions was planned in detail in advance and coordinated with all business partners. The LNG terminal operator (the LNG Croatia Company), the storage system operator (the Underground Gas Storage Company), the Hungarian transmission system operator (FGSZ) , the Slovenian transmission system operator  (Plinovodi), the INA Company, and the users of the transmission service who are also users of the LNG terminal services — HEP, MVM, PPD and MET significantly contributed  to the successful implementation of the works, which was carried out in accordance with the plan and without unexpected additional disruptions in the transmission system operation.