The Corrib gas pipeline is 20 inches (50 centimetres) in diameter. The wall of the pipeline is more than one inch thick (27 millimetres) and is made of high-grade carbon steel. By way of comparison, Bord Gais Eireann pipelines running throughout the country are 9 millimetres thick.
The outside of the pipeline will have several layers of protective coating, including plastic and concrete, to protect it from external corrosion.
Internal corrosion is controlled by the continuous injection of corrosion inhibitor via the umbilical. Corrosion is monitored in real time by a subsea corrosion monitoring spool. An internal inspection tool, referred to as a ‘smart pig’, will be pushed through the pipeline at intervals to gather data on the internal condition of the pipeline and monitor the integrity of the pipeline throughout.
As a safety measure, the pipeline was originally designed to withstand 345 bar in the highly unlikely event of pressure increasing above the normal operating pressure.
Advantica were commissioned by the Department of Communications, Marine and Natural Resources, to carry out an independent safety review of the Corrib gas pipeline.
The findings of this review were published in May 2006 and concluded that “proper consideration was given to safety issues in the selection process for the preferred design option and the locations of the landfall, pipeline route and terminal.
Advantica recommended a system be put in place to ensure that the onshore pipeline pressure could not exceed 144 bar, suggesting this to be a practical and effective measure to reduce risk in light of societal concerns that had been expressed.
As part of the design of the onshore pipeline, which was approved by An Bord Pleanála in January 2011, the maximum allowable operating pressure (MAOP) within this section will now be 100 bar. Its MAOP under the 2002 design was 150 bar. However, the normal operating pressure in the onshore pipeline will be approximately 85 bar and the pressure reduced as gas in the Corrib reservoir naturally depletes.
In addition, a Landfall Valve Installation has been incorporated into the design, which automatically shuts off the pressure from offshore in the very unlikely event that the pressure in the onshore pipeline should rise towards 100 bar.
Over 7,000 lengths of pipe were welded together onboard the Solitaire pipelay vessel during summer 2009. The pipeline was laid on the seabed from the shore out to the wells in the Corrib gas field, 83 kilometres away.
The onshore pipeline route is now 234 metres from the nearest occupied house - more than three times as far away from occupied housing compared to the originally approved route. The route will have minimal impact on the local environment and designated conservation sites such as Special Areas of Conservation (SAC) and Special Protection Areas (SPA).
The onshore pipeline will be underground along its entire route.