National Grid has chosen Costain as programme manager for its £100m project to replace its gas pipeline across the Humber estuary.

Above: The Humber Estuary

National Grid intends to lay the replacement pipeline in a tunnel under the river to provide a more robust long-term engineering solution.  Currently, the pipeline runs in a covered trench along the river bed and is susceptible to tides and erosion, requiring regular maintenance.

Planning consent for the replacement pipeline, from the Planning Inspectorate, is expected in September 2016.

The River Humber pipeline is 5.4km long and runs between Paull, on the north bank of the Humber, and Goxhill, on the south bank.

The current pipeline was built in 1984 and runs in a trench on the riverbed between above-ground installations. Over time, tidal patterns have eroded the riverbed covering the pipeline, leading to parts of it becoming exposed. To protect it, exposed areas were filled with gravel-filled bags and concrete ‘mattresses’ placed over the top, with plastic fronds to mimic seaweed and encourage the settlement of sand and silt. This solution ensured the pipeline could continue to operate normally in the short term. But the long-term solution had to be replacing the pipeline.

The replacement pipeline will be constructed in a tunnel to be dug beneath the River Humber. This will minimise the impacts on the river and surrounding habitats, and ensure the continued operation of the UK gas transmission network.  The project has been designed by Capita.

Costain will be providing a full range of project services to National Grid. The works will span across multiple disciplines including health, safety, project management, project controls and planning, commercial management, engineering, risk management and other specialist tunnelling disciplines.

Costain power sector director Nigel Curry said: “The award of this contract demonstrates Costain’s ability to meet its customers’ needs through our broadened consultancy and advisory project service offering.”

Length of pipeline:       5.4km / 3.3 miles

Diameter of pipeline:  48 inches (1,220mm)

Length of pipeline tunnelled:   5km / 3.1 miles

Depth of tunnel:           35 metres

Width of tunnel:           3-4 metres

Length of construction:            35 months (approx.)

Length of time spent tunnelling:         12 months (approx.)

Gas pressure:   70 barg

Cost:     Upwards of £100m