As gas comes ashore in Great Britain from a gas field (such as the North Sea or Morecambe Bay) it will enter a natural gas processing plant where the gas is purified. The gas is cleaned and contaminants such as water, sulphur and mercury are removed so that it can then be safely distributed around the country to homes, factories and offices. Processing plants in the UK include: Rampside (Barrow-in-Furness), Easington (East Riding), Bacton (Norfolk), and Theddlethorpe (Lincolnshire).
Where gas is imported by sea and a tanker, the gas may enter a terminal where it is converted from a liquid to a gas. Other supplies coming by gas pipe under the sea may be compressed and stored underground or in liquid natural gas (LNG) storage.
Once gas is ready to be consumed, it needs to be transported around the country. To do this, there is a complex network of gas pipes and offtakes from higher pressure parts of the network. To safely deliver gas, the pressure must be reduced from ‘high‘ or ‘intermediate‘ to ‘medium’ or ‘low’. This process is carried out at pressure reduction stations and govenors.
The materials used for gas pipe transportation vary depending on the range of pressures they transport and local ground conditions.The most common pipe material used is Polyethylene (PE) which is a type of plastic. It is the preferred material for gas networks in low pressure areas. Plastic gas pipes are made from the same material used to make plastic bags and shrink wrap. PE is used to replace older metal pipes where possible due to it’s non-corrosive properties. Other benefits include durability and flexibility.
Where pressue is high (above 7 bar), you would be likely to find a high quality protected steel pipe. Intermediate pressure (up to 7 bar) pipes are usually made from HDPE (high density polyethylene). Medium pressure (up to 2 bar) and low pressure (up to 75 mbar) gas pipes are often made from MDPE (medium density polyethylene). Low pressure parts of the gas mains network are the most sizeable and around 50% of the National Grid are still iron pipes which is reducing over time as they are replaced with plastic.