The project
The 516 km long Greenstream gas pipeline (Libyan Gas Transmission System - LGTS), running from Mellitah, Libya to Gela in Sicily, is still the longest sealine laid in the Mediterranean Sea and one of the biggest challenges ever faced in terms of design and complexity. The depth and slope of the seabed, the close attention paid to the environment, and a tight schedule made the Greenstream project a challenge. The sealine crosses points near Malta where the depth reaches 1,127 m, an achievement for a large-diameter pipe laid in S-lay mode. With the Greenstream project, Saipem set a record for deepest pipelaying with anchors. Gas produced at the desert Wafa field, and the offshore Bahr Essalam field is sent via pipeline to Mellitah, on the Libyan coast, for treatment; a part is compressed and exported to Sicily through the Greenstream pipeline, while the rest goes to the local market.
An extraordinary project
To operate in deep water, modifications were made to the Castoro Sei and the entire mooring system. A front pushing tug provided constant forward force, while two lateral Anchor Handlers— with anchors connected to Castoro Sei via mooring cables— provided stability by keeping and pulling the force needed for Castoro Sei to perform pipelaying operations at that depth. This would have been impossible to achieve with a standard traditional anchoring system. Innovative pipeline integrity monitoring systems, still in use today, provided real-time data on the pipeline’s stress and strain conditions during pipelay operations. The production line was also upgraded to optimize timing and increase average daily production. Greenstream was the first project in which Saipem’s PRESTO welding system was used as a substitute for Saipem’s historical PASSO welding system.
