AWARD-WINNING CORRIB TUNNEL GAS PIPELINE

Award-winning Murphy project, delivering Europe’s longest service tunnel installation

Project outline

This project won the 2016 Land-Based Pipeline Projects Award, awarded by the worldwide Pipeline Industries Guild, in recognition of the work by Murphy on the largest single infrastructure project ever carried out in the history of the Irish state.

The construction of a 4.9km tunnel under Sruwaddacon Bay, County Mayo in the Republic of Ireland, forms an integral part of the Corrib gas field project. The tunnel, the longest of its kind in Ireland and the longest service tunnel in Europe, was built on behalf of Shell E&P Ireland. The mechanical installation was awarded to Murphy International Ltd.

Key challenges

The works were awarded in two stages – the first in January 2013 for the 3.2km land section from Aghoose to Bellanboy, in collaboration with Roadbridge, preparing the spread, backfilling and reinstating it following pipe laying. The second phase involved the installation of a 500mm diameter pipeline in the tunnel from May to November 2015.

Murphy was engaged as the specialist pipeline contractor to weld, non-destructive test (NDT) and install the pipeline in single pipe lengths, in a trench wide enough to fit a side boom. The first five months of the project were spent developing the weld procedures and gaining approval. Following the removal of the tunnel boring machine (TBM), works commenced on the tunnel fit-out, which involved the installation of 5km of 20” gas pipeline, 10km of wastewater lines, 18km of HDPE back grout lines, 10km of signal cable and 25km of fibre-optic cables.

A major challenge was to provide a welding habitat that could fit over the pipe, be transportable, and also protect the welding process from the extremes of north-west Mayo weather. Murphy International developed a self-contained lightweight aluminium shelter for placement over the pipe-support of the Scorpion welding equipment. This was designed to be lifted into position using either a crane or backhoe, for ultimate manoeuvrability. The normal pipeline plant for handling pipe and equipment was unsuitable for the geography and condition of the spread, deemed too disruptive to welding production. The second challenge was therefore to develop plant and equipment specifically for use on a narrow spread, weight and mobility being key considerations.

Project delivery and innovations

Extensive early engineering and design work was required by the Murphy team to propose, test and approve the various systems required to install the pipework. This process took four months to gain all approvals, involving the construction of a life-sized tunnel mock-up, to prove the installation methodology. The working platform was 72m long and on it were mounted bespoke designed and engineered work stations - providing welfare, lifting, welding, NDT and coating operations, as well as transport for the tunnel crews. All of these elements were designed based upon the first principles developed by Murphy International and manufactured at the Murphy workshop in Newbridge, County Kildare.

Murphy, with considerable research and development applied by its welding engineers, used its Scorpion automated welding equipment to develop a system and set of welding procedures to work consistently in the field. The approval process was both exhaustive and rigorous, marrying the requirements of numerous specifications, approval agencies and designers into one approval regime. In short, it represented a weld engineering process never before attempted prior to Corrib.

Murphy International designated key people to ensure project milestones were met throughout the contract, with the adherence to detail demanded of the project, including: the design; planning; safety; quality and environmental challenges; as well as meeting the budget forecasts.

Murphy completed the tunnel installation works exactly two months ahead of schedule in early November 2014. The tunnel was handed back on 7 November 2014. Once hydro-testing of the pipeline was carried out, Murphy completed the final golden weld at the LVI in Glengad, on 15 December.

Key facts

• 70 front line staff and 15 supervisors with 200,000 Murphy hours worked accident free
• 30,000m signal and fibre optic cables were installed in just three days
• At peak times, Murphy installed four stings in a 24 hour day with six welders
• Murphy completed the final ‘golden weld’ at the LVI in Glengad on 15 December 2015, two months ahead of schedule.

Client

Shell E&P Ireland

Location

Ireland

Completion Date

December 2015

Value

Undisclosed

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