>>GAS TRANSMISSION<<

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Gas Transmission is the supply of gas at high pressure along steel pipelines. On the UK mainland pressures are generally between 7bar and 100bar. Transmission pipelines deliver gas from gas fields to Local Distribution Networks which supply gas at much lower pressures to our Homes and Industry. As gas flows along a pipeline it loses pressure due to the friction of the gas against the walls of the pipeline.

Compressor Stations installed at strategic points along the pipeline
recompress the gas back up to pressure. The gas used by homes and industry varies throughout the day and is usually at a peak at evening tea time, this is known as 'diurnal swing', however gas flows into a pipeline from a gas field at a fairly constant rate.Gas has to be
stored in pipelines during periods of of low demand to maintain supplies when
the demand is higher. This is achieved by allowing pipelines to increase in
pressure at times of low demand and reduce when the demand is higher.
This is known as 'line pack'.

Pressure Reduction Stations are installed at the ends of the Transmission system to reduce the gas to a lower pressure and deliver the volumes of gas needed to supply Local Distribution Networks. Pressure reduction stations are designed to ensure that the pressure in the pipeline they are supplying does not exceed the design pressure of the pipeline and that a failure to supply could only happen in exceptional circumstances. Transmission pipelines must be designed to contain gas at high pressure and be positioned so that they do not present a risk to the community in the unlikely event of failure. Transmission pipelines must be designed to meet the requirements of the Pipeline Safety Regulations. Pipeline operators must also ensure that they comply with the Pressure Systems Safety Regulations.
Much of the high pressure Transmission system on the UK mainland is owned by National Grid Transco, There are a number of pipelines owned by companies supplying gas to large plant such as power stations. Transco will normally only allow connections to its national transmission system for gas loads in excess of 58,600,00 kWh per annum (2milllion therms.p.a.) Any company who is intending to operate a Transmission pipeline must satisfy the requirements of the Gas Safety Management Regulations by submitting a Safety Case to the Health a nd Safety Executive. They must construct, operate and maintain the pipeline in accordance with internationally recognised Standards.

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