National Grid has completed the insertion of a 5-kilometre steel gas pipeline through a new tunnel under the River Humber.
The tunnel, measuring 3.65 metres in diameter, was built 30 metres below the river to replace an old trench-laid pipe that had become exposed over time.
Eight 620-metre pipe sections, each weighing 850 tonnes, were driven through the tunnel one after another on rollers by two “hydraulic thrust machines”.
Once one section had been inserted, the next was lined up at the entrance to the tunnel and they were welded together before the pushing continued. The process was repeated until all five kilometres had been laid.
The pipes were pushed from the Goxhill side of the river at a rate of around one metre per minute. To aid the insertion, the tunnels were flooded with 50,000 cubic metres of purified water – enough to fill 16 Olympic swimming pools.
National Grid said the Feeder 9 project, which will transport up to 25 per cent of Britain’s gas supplies, has broken the record for the world’s longest hydraulically inserted pipeline. The work began on 23 June and was completed around two weeks later on 9 July.
Steve Ellison, senior project manager for capital delivery at National Grid, said: “Completing the installation of the pipeline under the Humber is a major milestone for both the project team and partners. We will now begin work to connect the pipeline to the network, ready for gas to begin flowing towards the end of the year.”