National Transmission System
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The United Kingdom's National Transmission System (NTS) is the network of gas pipelines that supply gas to about forty power stations and large industrial users from
natural gas Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
terminals situated on the coast, and to gas distribution companies that supply commercial and domestic users. It covers Great Britain, i.e. England, Wales and Scotland.


History


Origins

The system originated in the construction during 1962–3 of the high-pressure methane pipeline from
Canvey Island Canvey Island is a town, civil parish and reclaimed island in the Thames Estuary, near Southend-on-Sea, in the Castle Point district, in the county of Essex, England. It has an area of and a population of 38,170.Office for National Statistics. ...
(on the Essex coast) to Leeds. Imported
liquefied natural gas Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled to liquid form for ease and safety of non-pressurized storage or transport. It takes up about 1/600th the volume o ...
(LNG) from Algeria was turned into gas at the Canvey terminal and supplied to the pipeline, providing eight of the twelve area gas boards with access to natural gas. The gas was initially used to manufacture town gas, either as a feedstock in gas reforming processes or to enrich lean gases such as that produced by the Lurgi
coal gasification In industrial chemistry, coal gasification is the process of producing syngas—a mixture consisting primarily of carbon monoxide (CO), hydrogen (), carbon dioxide (), methane (), and water vapour ()—from coal and water, air and/or oxygen. H ...
process. The pipeline was in diameter and operated at 1,000 pounds per square inch (69 bar). The pipeline had of spur lines, supplying gas to area boards. The Gas Council was responsible for this £10 million co-operative scheme and the construction details were a joint effort of the distribution engineers of the area boards. LNG had first been imported to Canvey from Louisiana in February 1959, and piped to Romford gasworks as feedstock to a reforming plant.


UK natural gas

Natural gas was discovered on the UK continental shelf in 1965 and production started in 1967. The development of offshore natural gas fields is shown in the following table. Shore terminals were built to receive, process, blend and distribute the gas. With the assured availability of natural gas, a government
white paper A white paper is a report or guide that informs readers concisely about a complex issue and presents the issuing body's philosophy on the matter. It is meant to help readers understand an issue, solve a problem, or make a decision. Since the 199 ...
on fuel policy in November 1967 proposed that natural gas should be immediately and more extensively exploited. The Gas Council and area boards began a ten-year programme to convert all users and appliances to operate on natural gas and consequently to discontinue the manufacture of town gas at local gasworks. In a pilot scheme, users on Canvey Island had been converted to natural gas in 1966.


Building the NTS

To exploit the availability of natural gas and to provide for more widespread distribution, construction began of a major new transmission network which became the National Transmission System.


Feeder pipelines – England

Gas from the West Sole field was first dispatched from the Easington terminal on the Yorkshire coast in July 1967, via Feeder No. 1 across the Humber to the East Midland Gas Board's gasworks at Killingholme. It was used to enrich low calorific value manufactured gas. Feeder No. 1 was extended to Totley near Sheffield where it connected to the 18-inch methane pipeline. UK natural gas first entered the NTS in July 1968. Feeder lines from the North Sea gas terminals to the spine of the NTS were laid and brought into use as the shore terminals were constructed. The No. 6 feeder runs via Pickering which received gas from a treatment plant for the onshore Lockton gas field.


Feeder pipelines – Scotland

North Sea gas first reached Scotland in Spring 1970 at Coldstream via an extension of the Leeds-Newcastle pipeline. This pipeline was then extended to Glenmavis near Coatbridge Lanarkshire (Feeder No. 12) where a natural gas liquefication plant was constructed. A major set of pipelines were constructed in Scotland in preparation for arrival of gas from the
Frigg gas field Frigg gas field is a natural gas field on Norwegian block 25/1 in the North Sea, on the boundary between the United Kingdom and Norway. The field is named after the goddess Frigg. King Olav V of Norway officially opened production on 8 May 1978. P ...
in 1977. From the St Fergus terminal in Scotland, two pipelines (Feeder No. 10 and No. 11) were laid via Bathgate to Partington and Bishop Auckland to connect to the NTS in England, a total pipeline length of . These lines were commissioned in 1976 and cost £140 million. Initially they carried gas from southern England into Scotland until the Frigg field began production via St Fergus in September 1977. Compressor stations are provided at intervals along the pipelines. A third 36-inch pipeline from St Fergus (Feeder No. 12) was completed in 1978, and a fourth pipeline (Feeder No. 13) in 1982.


Growth of the NTS

The NTS was extended from Leeds to Newcastle upon Tyne in early 1969. This line was extended to Coldstream in spring 1970 and then to Glenmavis, near Coatbridge, Lanarkshire. The Wales Gas Board received natural gas supplies in 1969 through a 24-inch line from Churchover (Rugby) to Swansea via Wormington (an extension to Feeder No. 2). North Wales was also connected in 1969 via a 24-inch/18-inch pipeline from Audley Cheshire to Maelor near Wrexham (an extension to Feeder No. 4). The South Western Gas Board received natural gas at the end of 1970 from a 24-inch/20-inch pipeline from Wormington to Exeter (Feeder No. 14). A 30-inch/24-inch extension of Feeder No. 3 runs to the west of London via Slough to Mogador, Surrey, and was commissioned in 1970. An extension of Feeder No. 5 runs from Horndon-on-the Hill, crosses the Thames at Tilbury and runs via Shorne to connect to Mogador, completing the South London ring main which became operational in early 1972. In addition to these distribution pipelines, in 1971 the area boards began to supply natural gas directly to major consumers. For example, a 24-inch 17 mile 'spine' pipeline was constructed to ICI Ltd at Billingham (designated as part of Feeder No. 6), and the West Midlands Gas Board laid six similar 'spine' mains into industrial districts of Birmingham and the Black Country. Most of the NTS was built from the late 1960s to the early 1980s. Later (post-1983) feeder mains not described above include: The NTS now comprises over 7,600 km of welded steel gas pipelines. The Canvey to Leeds line is no longer part of the NTS.


LNG storage sites

In addition to the Canvey Island liquefied natural gas (LNG) import terminal, further LNG storage sites were constructed from the late 1960s. These were peak-shaving facilities used to support the NTS at times of high demand, and to ensure security of gas supplies at strategic locations. When demand was high,
liquefied natural gas Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled to liquid form for ease and safety of non-pressurized storage or transport. It takes up about 1/600th the volume o ...
was pumped from storage tanks, heated in vapourisers to a gaseous state and delivered into the NTS. When demand was low, gas was withdrawn from the NTS and liquefied by cryogenic cooling to minus 162 °C to replenish the storage tanks.


High-pressure gas storage

In addition to LNG storage for peak-shaving, several sites had storage facilities for high pressure gas that could be released into, and pressurised from, the NTS. The following sites were operational by 1972. * Isle of Grain, Kent: six 'bullets', diameter, long, capacity 8 million cubic feet (226,000 m3) of gas, operating at up to 1,000 psi (69 bar). * Beckton gasworks, East London: eight 'bullets', diameter, long, capacity 5 million cubic feet (142,000 m3) of gas, pressure cycle 350-100 psi (24–6.9 bar). * South Western Gas Board, for Bristol and Cheltenham: eleven 'bullets', diameter, long, total capacity 13 million cubic feet (368,000 m3), pressure cycle 450-40 psi (31–2.76 bar). * Biggin Hill, Kent: seventeen, diameter buried pipes, long, capacity 10 million cubic feet (283,000 m3), operating up to 1,000 psi (69 bar).


Operation

The NTS is the starting point for UK gas distribution. The pipeline system serving houses is not part of the NTS, but is part of the gas distribution network of local distribution zones; the two systems combine to form the UK's gas distribution network. The two types of gas pipelines in the UK are: large diameter high-pressure (up to 85 bar (1200 psi) and diameter) pipelines – the type that the NTS uses – and smaller diameter lower pressure pipelines that connect to users who burn gas for heat. The wall thickness of the high-pressure pipelines is up to .


Entry

Gas currently enters the NTS from a number of sources: * Offshore oil and gas fields on the UK continental shelf. These deliver gas via five (formerly six) UK coastal gas terminals (five in England: CATS Teesside; Easington/Dimlington; Bacton; Rampside Barrow and the former Theddlethorpe terminal; and one in Scotland: St Fergus). Gas from the Liverpool Bay (Douglas) field formerly entered the NTS at Burton Point terminal in Cheshire; this terminal is now identified by National Grid as a NTS offtake to Connah's Quay power station. * Onshore gas fields such as Saltfleetby, Lincolnshire (production was via the former Theddlethorpe terminal); and
Wytch Farm Wytch Farm is an oil field and processing facility in Dorset, England. It is the largest onshore oil field in Western Europe. The facility, taken over by Perenco in 2011, was previously operated by BP. It is located in a coniferous forest on Wytc ...
, Dorset. * Continental Europe. From Norway via the Langeled pipeline and the Easington terminal; from the Netherlands via the BBL pipeline; from Belgium via the Interconnector UK pipeline, both of the latter through Bacton gas terminal. * Imported LNG. Gas is delivered from import terminals at the Isle of Grain and Milford Haven ( South Hook and
Dragon A dragon is a Magic (supernatural), magical legendary creature that appears in the folklore of multiple cultures worldwide. Beliefs about dragons vary considerably through regions, but European dragon, dragons in Western cultures since the Hi ...
). The Canvey Island gas terminal ceased importing LNG in 1984. * Storage facilities. These include a mixture of salt cavity storage, onshore LNG storage sites, and formerly the depleted onshore gas field at Rough (via Easington terminal). The onshore storage facilities are listed below. The NTS was formerly supplied by the following decommissioned LNG sites: Ambergate, Derbyshire (closed 1985); Dynevor Arms, Merthyr Tydfil (closed 2009); Glenmavis, Lanarkshire (closed 2012); Partington, Greater Manchester (closed 2012); and Avonmouth, Bristol (closed April 2016).


Gas specification and composition

The specification of gas transported within the NTS is typically within the following parameters (revised April 2023). Parameters marked * are specified in the Gas Safety (Management) Regulations 1996. As amended by the Gas Safety (Management) Regulations 2023. The composition of natural gas in the NTS in 1979 was typically as shown below. The decline of supply from the UK continental shelf since 2000 and the sharp increase in LNG imports during the 2021 natural gas supplier crisis have made the composition more variable, though still within the calorific value limits.


Natural gas storage

Gas storage is used to manage seasonal and short-term variations in the supply and demand of gas in the UK. Facilities include salt caverns and onshore LNG storage sites (see above). Since 1985, gas has been stored offshore in the depleted Rough gas field, which initially held nine days' supply and was the UK's largest store. This facility, owned by Centrica, was closed in 2017 due to maintenance costs but about 20% of its capacity was reopened in October 2022. The operational onshore gas storage facilities in Britain are as follows. The salt cavity storage facility at Hornsea, East Yorkshire comprises seven cavities at a depth of , which each store up to 60 million m3 (80 million cu. yd.) of gas at a maximum pressure of 240 bar (3500 psi). The releasable volume of gas is about half of the gross volume. During periods of low demand, gas is compressed into the cavities by electrically driven compressors and fed back onto the NTS at times of peak demand. Salt cavern storage facilities at Stublach were created by drilling diameter holes through of rock and of salt. This was followed by inserting metal tubes into the holes and filling the annulus with cement to create a leak-tight seal. Water was injected into the wells to dissolve the salt and create brine which was supplied to local industry for the production of bulk chemicals, such as soda ash and chlorine. The caverns created are about in diameter and tall (each has a volume of 339,300 m3; 443,800 cu. yd.) and are used to hold compressed gas. Stublach is the largest gas storage facility in the UK, containing up to 450 million cubic metres (590 million cubic yards) of gas.


Compressor stations

There are 25 (mostly
gas turbine A gas turbine or gas turbine engine is a type of Internal combustion engine#Continuous combustion, continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas gene ...
driven) compressor stations and over 25 pressure regulators. Gas moves through the NTS at speeds up to , depending on pressures and pipeline diameters. Compressor stations generally operate at a pressure ratio of 1:1.4 – a balance between maintaining pressure and hence flow, and the capital and running cost of the compressors. It also ensures that the temperature rise across the compressors is not high enough to require after-coolers to prevent damage to the pipeline protective coatings. On the pipelines from St Fergus, compressor stations are provided at intervals; each compresses the gas from about 48 bar (700 psi) at to 65 bar (950 psi) at . Compressor stations include: * England – Wooler,
Bishop Auckland Bishop Auckland ( ) is a market town and civil parishes in England, civil parish at the confluence of the River Wear and the River Gaunless in County Durham, England. It is northwest of Darlington and southwest of Durham, England, Durham. M ...
, Carnforth, Nether Kellett,
Warrington Warrington () is an industrial town in the Borough of Warrington, borough of the same name in Cheshire, England. The town sits on the banks of the River Mersey and was Historic counties of England, historically part of Lancashire. It is east o ...
, Hatton, Alrewas, Wisbech,
King's Lynn King's Lynn, known until 1537 as Bishop's Lynn and colloquially as Lynn, is a port and market town in the borough of King's Lynn and West Norfolk in the county of Norfolk, England. It is north-east of Peterborough, north-north-east of Cambridg ...
,
Peterborough Peterborough ( ) is a City status in the United Kingdom, cathedral city in the City of Peterborough district in the Ceremonial counties of England, ceremonial county of Cambridgeshire, England. The city is north of London, on the River Nene. A ...
,
Churchover Churchover is a small village and civil parish in Warwickshire, England. Parish The population of the parish in the 2001 census was 230, increasing to 251 at the 2011 census. It is located around 4 miles (7 km) north of Rugby, Warwickshir ...
,
Huntingdon Huntingdon is a market town in the Huntingdonshire district of Cambridgeshire, England. The town was given its town charter by John, King of England, King John in 1205. It was the county town of the historic county of Huntingdonshire. Oliver C ...
,
Cambridge Cambridge ( ) is a List of cities in the United Kingdom, city and non-metropolitan district in the county of Cambridgeshire, England. It is the county town of Cambridgeshire and is located on the River Cam, north of London. As of the 2021 Unit ...
, Diss,
Chelmsford Chelmsford () is a city in the City of Chelmsford district in the county of Essex, England. It is the county town of Essex and one of three cities in the county, along with Colchester and Southend-on-Sea. It is located north-east of London ...
,
Aylesbury Aylesbury ( ) is the county town of Buckinghamshire, England. It is home to the Roald Dahl Children's Gallery and the Aylesbury Waterside Theatre, Waterside Theatre. It is located in central Buckinghamshire, midway between High Wycombe and Milt ...
, Lockerley and Wormington. * Scotland –
Aberdeen Aberdeen ( ; ; ) is a port city in North East Scotland, and is the List of towns and cities in Scotland by population, third most populous Cities of Scotland, Scottish city. Historically, Aberdeen was within the historic county of Aberdeensh ...
, Avonbridge,
Kirriemuir Kirriemuir ( , ; ), sometimes called Kirrie or the ''Wee Red Toon'', is a burgh in Angus, Scotland, United Kingdom. The playwright J. M. Barrie was born and buried here and a statue of Peter Pan is in the town square. History Some of th ...
, Moffat and St Fergus.


Offtakes

Offtakes from the NTS include those supplying industrial users, local distribution networks, storage sites and export pipelines. * To about 71 large users such power stations and industry, either on multi-business sites such as Billingham and
Runcorn Runcorn is an industrial town and Runcorn Docks, cargo port in the Borough of Halton, Cheshire, England. Runcorn is on the south bank of the River Mersey, where the estuary narrows to form the Runcorn Gap. It is upstream from the port of Live ...
or to individual companies such as INEOS Teesside. * To inland storage sites (see 'Entry') and formerly to the offshore Rough field storage site via the Easington gas terminal. * To the Irish interconnectors; the 24-inch Scotland-Northern Ireland Pipeline (SNIP) to Ballylumford, Northern Ireland, and the two 24-inch UK-Ireland Interconnectors to Dublin, both via an NTS offtake at Moffat, Scotland. * Gas can be exported to Belgium and the Netherlands via the Interconnector UK and the BBL pipelines, both via the Bacton terminal. * To the Gas Distribution Network of Local Distribution Zones, as follows:


Gas distribution network

Companies that own part of this gas network, also known as the Local Transmission System (LTS), are known as gas transporters. Gas enters this network via the NTS through a pressure reduction station to the twelve gas distribution zones in Great Britain within eight distribution networks. The network covers . The LTS is managed from Hinckley,
Leicestershire Leicestershire ( ) is a Ceremonial counties of England, ceremonial county in the East Midlands of England. It is bordered by Derbyshire, Nottinghamshire and Lincolnshire to the north, Rutland to the east, Northamptonshire to the south-east, Warw ...
(former headquarters of the NTS). Financial transactions between gas transporters are managed by Xoserve, based in
Solihull Solihull ( ) is a market town and the administrative centre of the Metropolitan Borough of Solihull, in the West Midlands (county), West Midlands, England. Solihull is situated on the River Blythe in the Arden, Warwickshire, Forest of Arden ar ...
, which was a department of National Grid before it became an independent company. For retail distribution, Cadent owns the network in
North West England North West England is one of nine official regions of England and consists of the ceremonial counties of England, ceremonial counties of Cheshire, Cumbria, Greater Manchester, Lancashire and Merseyside. The North West had a population of 7,4 ...
, the West Midlands, the East Midlands, the
East of England East is one of the four cardinal directions or points of the compass. It is the opposite direction from west and is the direction from which the Sunrise, Sun rises on the Earth. Etymology As in other languages, the word is formed from the fact ...
and North London. In the North of England, local distribution is owned by Northern Gas Networks; in the Wales and West by Wales and West Utilities; and in Southern England and Scotland by SGN.


Ownership

The transmission network is owned by National Gas, which is owned by Macquarie Asset Management (80%) and National Grid plc (20%). Agreement was reached in July 2024 for Macquarie to buy National Grid's stake, giving Macquarie full ownership in the first quarter of 2025 subject to regulatory approval. The changing ownership of the NTS reflects developments and corporate changes in the UK's gas and energy industries. * Gas Council and area boards, 1962 – 31 December 1972 * British Gas Corporation, 1 January 1973 – 24 August 1986 * British Gas plc, 24 August 1986 – 1994 * Transco plc, part of British Gas plc, 1994 – 17 February 1997 * Transco plc, part of BG plc, 17 February 1997 – 1999 * Transco plc, part of BG Group plc, 1999 – 23 October 2000 * Transco plc, part of Lattice Group plc, 23 October 2000 – 21 October 2002 * Transco plc, part of National Grid Transco plc, 21 October 2002 – 31 January 2023; renamed National Grid Gas plc on 10 October 2005 * National Grid Gas plc, owned by Macquarie, BCI and National Grid, from 31 January 2023; renamed National Gas Transmission plc on 6 February 2023


Northern Ireland

Northern Ireland Northern Ireland ( ; ) is a Countries of the United Kingdom, part of the United Kingdom in the north-east of the island of Ireland. It has been #Descriptions, variously described as a country, province or region. Northern Ireland shares Repub ...
is not part of the NTS and gets its gas via the Scotland-Northern Ireland pipeline (SNIP), owned by Premier Transmission and built between 1994 and 1996. The gas network in Northern Ireland is split, with one area owned by Phoenix Natural Gas and the other by Firmus Energy.


See also

* Humber Gas Tunnel * Central Area Transmission System * United Kingdom–Ireland natural gas interconnectors


References


External links


Gas Transmission System Operations

Map of the NTS at National Grid



Instantaneous gas flows into the NTS

Pipeline projects at National Grid plc

Ownership of the gas distribution network
archived in 2008
Society of British Gas Industries
archived in 2012
Xoserve

GCSE PDF factsheet about the NTS
archived from ''www.energynetworks.org'' in 2011
Origins and Growth of the British Gas Plant Operations Department (including pipeline maps)
''www.oldflames.org.uk''
Statement of Gas Transmission Transportation Charges Table 3 & 5
{{Energy in the United Kingdom, sources Natural gas pipelines in the United Kingdom