THE final section of a gas transmission pipeline has been successfully pushed through a tunnel beneath Gladstone harbour to the Santos GLNG plant on Curtis Island.
The 120 pipeline segments, each measuring 36m in length, were welded and pushed gradually through the 4.3km tunnel over the past month, using a large hydraulic jack.
The tunnel was filled with seawater to buoy the 42-inch diameter pipeline as it was pushed through.
Santos vice-president downstream GLNG Rod Duke said the delivery of the first under-sea crossing for Queensland's CSG to LNG industry was in its final stages of completion.
"This year is about delivering milestones across Santos GLNG," Mr Duke said.
"We're particularly proud of this achievement, given the innovation and expertise required to achieve a marine crossing like this one.
"Our under-sea tunnel has allowed us to cross The Narrows without disturbing the local marine environment and with minimal impact to the surrounding coastal environments.
"In the coming weeks the marine crossing pipe will be connected to the rest of Santos GLNG's 420km pipeline.
"This is already buried on the mainland and Curtis Island."
Pipeline pre-commissioning works are well underway.
Clean and gauge activities are nearing completion and about half of the required hydrotesting has been completed.
The pipeline route will be fully rehabilitated.
Initial reinstatement works are now more than 90 per cent complete.
The 3.45m internal diameter under-sea tunnel was a feat in itself. It runs about 8m below the sea bed.
The under-sea tunnel was constructed using a 100m long, 277 tonne tunnel boring machine.