In the past, the UK received plentiful natural gas from reserves from the North Sea, but with reserves slowly declining, the country has transitioned from the role of a major gas exporter to being an importer of LNG from overseas.

The $US1.6 billion South Wales Gas Pipeline is the largest scale infrastructure project National Grid has ever undertaken, taking three years to construct, with completion achieved in 2007.

The 48 inch diameter steel pipeline was built to transport gas between two LNG terminals located near Milford Haven– including the proposed South Hook LNG Plant, which will be the world’s largest LNG terminal when completed – to National Grid’s existing national transmission system in Thirley, Gloucestershire.

The pipeline project includes a compressor station, which is one of the largest in the UK's energy network.

Meeting greenhouse targets

The UK Government’s carbon reduction will require large organisations to contribute to reducing carbon dioxide emissions by 32 per cent by 2020. In addition to meeting this requirement, National Grid has committed to reducing its greenhouse gases by a further 48 per cent by 2050. The company has gone beyond standard environmental impact assessment obligations to assess the pipeline project’s carbon footprint.

National Grid said it wanted to understand how much carbon dioxide was being produced – directly and indirectly – by the pipeline project during construction and operation to ensure that environmental impacts were minimised. It commissioned RSK to quantify the climate impacts associated with the construction, commissioning and operation of a section of the pipeline running between Felindre and Thirley. The company then used the information collated to develop a carbon budget.

Carbon budgeting for beginners

A carbon budget measures and sets targets for the total greenhouse gas emissions that can be linked to a project over time, and includes direct impacts such as tree removal and the quantity of gas burnt, as well as indirect effects such as the supply chain’s carbon footprint. The carbon-related emissions over the life of the project are then evaluated.

RSK began with a review of the carbon intensity of the materials used to construct the pipeline, tracking their lifecycles from raw materials through to final disposal. The company assessed how much ‘embodied’ energy had been consumed during the production of the raw materials (for example, during quarrying), in processing them (for example, during steel manufacture) and the amount of energy used in transportation and their use and final disposal.

The data was sourced through suppliers and commonly used databases. Wherever possible, source-specific information was acquired, but RSK said that at times, such data were often unavailable in this emerging assessment field.

RSK also calculated the transport emissions associated with the project site using information from the lead contractor such as project schedules.

Analysing carbon risks

The natural carbon systems in the affected areas that would be most at risk of impacts from the pipeline’s construction were also analysed. RSK concentrated particularly on areas where the pipeline route traversed the national parks in the South Wales region. The analysis took particular account of the effects of the pipeline on peat bogs, as these, like trees, act as carbon sinks. Pipeline construction can affect the drainage of the peat bogs through the excavation of carboniferous material critical to peat bog ecosystems.

The data gathered were entered into computer models to calculate the carbon generated through commissioning, operating and decommissioning the pipeline. It was found that the development, including its embodied energy and the impacts on natural systems, would only cause a 0.2 per cent increase in the greenhouse gas emissions associated with the combustion of the natural gas supplied by the pipeline.

The future means optimal design, minimal CO2

The South Wales Pipeline project highlighted how pipeline design and construction can be optimised to minimise carbon dioxide releases while still taking into account the exacting specifications required to ensure safety is not compromised. Lifecycle analysis provided an important opportunity to encourage greener materials selection and production methods during the design phase of future pipeline projects.