National Transmission System

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 terminals situated on the coast and to gas distribution companies that supply commercial and domestic users.

History

Origins

The National Transmission System (NTS) originated in the construction during 1962-3 of the 200 mile (320 km) long high-pressure methane pipeline from Canvey Island to Leeds.[1] Imported liquified natural gas (LNG) from Algeria was regasified at the Canvey terminal and supplied to the pipeline, this provided eight of the twelve Area Boards with access to natural gas.[2] 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 process.

The pipeline was 18-inch (460 mm) in diameter and operated at 1,000 pounds per square inch (69 bar). The pipeline had 150 miles (240 km) of spur lines, supplying gas to area boards.[3]

Methane pipeline spur lines
Area Board Supply to Diameter (inches) Length (miles)
North Thames Bromley/East Greenwich 'Tee' 14 15.5
Bromley 10 2.5
Slough (from Reading spur line)
South Eastern East Greenwich 12 3
Southern Reading 8 49
Eastern Hitchin 8 7
Dunstable 6 8.5
West Midlands Coleshill 14 10.5
East Midlands Sheffield 12 10
North Western Manchester 14 24
North Eastern Leeds 12 8

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 gas works as feedstock to a reforming plant.[4]

UK natural gas

Natural gas was discovered on the UK continental shelf in 1965 and production started in 1967.[5] 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.

UK sources of offshore natural gas, 1967-1985
Field Field type Licensee or operator Discovered First gas onshore Shore terminal
West Sole Gas BP September 1965 March 1967 Easington
Leman Gas Shell/Esso, Amoco/Gas Council, Arpet Group, Mobil April 1966 August 1968 Bacton
Hewett Gas Phillips Petroleum, Arpet group October 1966 July 1969 Bacton
Indefatigable Gas Shell/Esso, Amoco/Gas Council June 1966 October 1971 Bacton
Viking Gas Conoco/BNOC May 1968 July 1972 Viking (Theddlethorpe)
Rough Gas Amoco/Gas Council May 1968 October 1975 Easington
Forties Oil + associated gas BP October 1970 September 1977 St Fergus
Frigg (Norway) Gas Elf/Total June 1971 September 1977 St Fergus
Frigg (UK) Gas Elf/Total May 1972 September 1977 St Fergus
Piper Oil + associated gas Occidental group January 1973 November 1978 St Fergus
Tartan Oil + associated gas Texaco December 1974 January 1981 St Fergus
Brent Oil + associated gas Shell/Esso July 1971 1982 St Fergus
Morecambe Bay Gas + condensate Hydrocarbons (GB) September 1974 1985 Barrow

With the assured availability of natural gas a government White Paper on fuel policy[6][7] 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.[8]

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 (NTS).[9]

Feeder pipelines - England

Gas from the West Sole field was first dispatched from the Easington terminal 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.[10]

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.[11][12][13][14]

Initial feeder pipelines of the NTS
Feeder No. Diameter Length From To Operational
1 24-inch (600 mm) 90 miles (144 km) Easington terminal Scunthorpe and Totley near Sheffield, where it connected to the original methane pipeline. July 1967/ July 1968
2 36-inch (900 mm) 123 miles (197 km) Bacton terminal Brisley, Peterborough and Churchover near Rugby, where it connected to the original methane pipeline. August 1968
3 36-inch 107 miles (171 km) Bacton terminal Roudham Heath, Cambridge, Whitwell near Hitchin, where it connected to the original methane pipeline. October 1969
4 36-inch 154 miles (246 km) Bacton terminal Great Ryburgh, King's Lynn and Alrewas near Lichfield. Autumn 1970
5 36-inch Bacton terminal Yelverton, Diss, Chelmsford and Horndon, where it connected to the original methane pipeline Autumn 1971
6 30-inch (750 mm) 91 miles (146 km) Paull Pickering (see note), Westwood and Little Burden near Darlington Autumn 1971
7 36-inch Wisbech Hatton and Scunthorpe 1972
8 30-inch Former Viking (Theddlethorpe) terminal Hatton July 1972

The No. 6 feeder runs via Pickering which received gas from a treatment plant for the onshore Lockton gas field.[14]

Feeder pipelines - Scotland

North Sea gas first reached Scotland in Spring 1970 at Coldstream, this was 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 liquification plant was constructed.[14]

A major set of pipelines were constructed in Scotland in preparation for arrival of gas from the Frigg gas field in 1977. From the St Fergus terminal in Scotland, two 36-inch (900 mm) 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 595 miles (950 km). These lines were commissioned in 1976 and cost £140 million. Initially these pipelines carried gas from southern England into Scotland until the Frigg field began production via St Fergus in September 1977. Compressor stations are provided at 40 mile (65 km) intervals along the pipelines. A third 36-inch pipeline from St Fergus (Feeder No. 12) was completed in 1978, and a fourth 40-inch (1050 mm) pipeline (Feeder No. 13) in 1982.[15]

Growth of the NTS

The NTS was extended from Leeds to Newcastle upon Tyne in early 1969.[14] 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 from 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).[14]

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).[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 the Feeder No. 5 runs from Horndon-on-the Hill, crosses the Thames at Tilbury and runs via Shorne to connect to Mogador, thus completing the South London ring main, this became operational in early 1972.[14]

In addition to these distribution pipelines in 1971 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.[14]

Most of the NTS was built from the late 1960s to the early 1980s, the growth of the system is shown in the following table.[16]

Growth of the NTS 1966–1983
Years NTS mileage Operational Gas Terminals Compressor stations
1966/7 320 Canvey 0
1968/9 688 Canvey Easington Bacton 0
1970/1 1898 Canvey Easington Bacton 1
1972/3 2199 Canvey Easington Bacton Theddlethorpe 4
1974/5 2308 Canvey Easington Bacton Theddlethorpe 9
1976/7 2915 Canvey Easington Bacton Theddlethorpe St. Fergus 10
1978/9 3047 Canvey Easington Bacton Theddlethorpe St. Fergus 11
1983 3200 Canvey Easington Bacton Theddlethorpe St. Fergus 14

Later (post-1983) feeder mains not described above include.[17]

NTS Feeder pipelines built after 1983
Feeder No. From To Year commissioned
9 Easington East Ilsley 1983-86
15 Longtown Warburton 1984
16 Barrow Lupton 1983
17 Theddlethorpe Hatton 1988
18 Peterborough Cambridge 1988–94
Isle of Grain Gravesend 2008
Matching Green Tilbury 1990
19 Easington Paull 1991
20 Ilchester Choakford 1989
21 Mawdesley Alrewas 1992–2001
Carnforth Burscough 1992
Elworth Deeside power station 1994
22 Goxhill Peterborough 1993
23 Churchover Honeybourne 1998-2001
Peterstow Gilwern 2000
Wormington Corse 2000
24 St Fergus Lochside 2001
Easington Paull 2010
Hatton Silk Willoughby 2001
25 Bridge Farm Mickle Trafford 2001
26 Huntingdon Steppingley 2001
27 Bacton King's Lynn 2003
Cambridge Matching Green 2002
28 Herbrandston Corse 2007
29 Easington Nether Kellett 2006–08

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 NGL storage sites were constructed from the late 1960s.[18] 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 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.

NTS Liquefied Natural Gas (LNG) Sites. Gas volumes at standard conditions.
Site LNG storage tank capacity Commissioned Decommissioned Operations
Canvey Island, Essex 6 × 4,000 tonnes, 2 × 1,000 tonnes, 4 × 21,000 tonnes[19] (underground) 1959, 1964, 1968, 1975 1984[20] Import of LNG from Arzew Algeria, original contract for 1 billion m3 (35 billion cu ft) per year of gas. Liquefication 205 tonnes/day, vapourisation 6 × 50 tonnes/hour.[21]
Ambergate, Derbyshire 5,000 tonnes (1 × 12,000 m3) [22][21] 1967-1970[19] 1985[23] Import of LNG by road tanker from Canvey, output 72 million cu ft (2.0 million m3) per day.[24]
Glenmavis, Lanarkshire 20,000 tonnes (2 × 47,800 m3),[22][21] 1972, 1974[21] 2012 Liquefication 100 tonnes per day, vapourisation 250 million cu ft (7.1 million m3) per day
Partington, Cheshire 4 × 20,000 tonnes (4 × 49,800 m3)[22][21] 1972[19] 1972, 1974[21] March 2012 Liquefication 10 million cu ft (280 thousand m3) per day,[25] vapourisation 8 × 75 tonnes/hour[21]
Dynevor Arms, (Hirwaun) Rhondda Cynon Taf 2 × 20,000 tonnes[22] 1972 March 2009 Liquefication 10 million cu ft (280 thousand m3) per day,[25] vapourisation 2 × 75 tonnes/hour[21]
Avonmouth, Bristol 3 × 50,000 m3 1974-1980;[19] 1978, 1979, 1983[21] April 2016[26] Short-term storage, liquefication 205 tonnes/day, vapourisation 6 × 75 tonnes/hour[21]
Isle of Grain, Kent 4 × 50,000 m3, 4 × 190,000 m3 1980-2010 Operating Vapourisation 58 million m3/day. See Grain LNG Terminal

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.[27]

  • Isle of Grain, six 'bullets', 12 ft (3.6 m) diameter, 250 ft (76.2 m) long, capacity 8 million cubic feet (226,000 m3) of gas, operating at up to 1,000 psi (69 bar).
  • Beckton gas works, eight 'bullets', 13.5 ft (4.1 m) diameter, 263 ft (80.1 m) 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’, 13 ft 6 in (4.1 m) diameter, 311 ft 8 in (95 m) long, total capacity 13 million cubic feet (368,000 m3), pressure cycle 450-40 psi (31-2.76 bar).
  • Biggin Hill Kent, seventeen, 42-inch (1.07 m) diameter buried pipes, 1,040 ft (317 m) long, capacity 10 million cubic feet (283,000 m3), operating up to 1,000 psi (69 bar).

Operation

NTS is the starting point for UK gas distribution. The pipeline system for 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[28] bar and 1050 mm[28] 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 0.625-inches (18mm).

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 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 LNG; Milford Haven (South Hook and Dragon). The Canvey Island gas terminal ceased importing LNG in 1984.[20]
  • Storage facilities. These include a mixture of salt cavity storage, onshore LNG storage sites, depleted onshore gas fields and the depleted offshore gas field at Rough (via Easington terminal). Storage facilities include: Holford Cheshire; Garton/Aldborough East Yorkshire; Hornsea East Yorkshire; Stublach Cheshire; Holford Cheshire; Hole House Farm Cheshire; Saltfleetby Lincolnshire; Hatfield Moor South Yorkshire; and Barton Stacey/Humbly Grove Hampshire. 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).[26]
  • There is a salt cavity storage facility at Hornsea, East Yorkshire. Seven cavities at a depth of 1800 m each store up to 60 million m3 of gas at a maximum pressure of 240 bar. 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.[21]

Gas specification and composition

The specification of gas transported within the NTS is typically within the following parameters.[29][30][31][32]

Specification of gas in the NTS
Content or Characteristic Value
Gross Calorific Value 37.0 – 44.5 MJ/m3
Wobbe Number* 47.2 – 51.41 MJ/m3
Water Dewpoint <-10 °C @ 85barg
Hydrocarbon Dewpoint <-2 °C
Hydrogen Sulphide content* ≤5 mg/m3
Total Sulphur content (including H2S)* ≤50 mg/m3
Hydrogen content* ≤0.1% (molar)
Oxygen content* ≤0.2% (molar)
Carbon Dioxide content ≤2.0% (molar)
Nitrogen content <5.0% (molar)
Total Inerts <7.0%
Incomplete Combustion Factor* ≤0.48
Soot Index* ≤0.60

Parameters marked * are specified in the Gas Safety (Management) Regulations 1996.

The composition of natural gas in the NTS is typically as follows.[33]

Composition of natural gas
Component Volume %
Methane 93.63
Ethane 3.25
Propane 0.69
Butane 0.27
Other hydrocarbons 0.20
Nitrogen 1.78
Carbon Dioxide 0.13
Helium 0.05

Compressor stations

There are twenty five (mostly gas turbine driven) compressor stations and over 25 pressure regulators. Gas moves through the NTS at speeds up to 25 mph (40 km/h) depending on pressures and pipeline diameters. Compressor stations generally operate at a pressure ratio of 1:1.4, this ratio is 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 40 mile (65 km) intervals; each compresses the gas from about 48 bar at 5 °C to 65 bar at 45 °C.[34]

Compressor stations include:

Initial NTS compressor stations[21]
Station Gas turbines Power rating (MW) Commissioned
Alrewas 2 Rolls-Royce Avons 21.6 1970
Peterborough 3 Rolls-Royce Avons 35.4 1972
Churchover 3 Orendas 18.4 1972
Scunthorpe 2 Rolls-Royce Avons 23.6 1973
Chelmsford 2 Rolls-Royce Avons 23.0 1973
King's Lynn 4 Rolls-Royce Avons 47.2 1973
Cambridge 2 Rolls-Royce Avons 23.0 1974
Bishop Auckland 2 Orendas 14.4 1974
Kirriemuir 4 Rolls-Royce Avons 47.2 1977
Bathgate 4 Rolls-Royce Avons 47.2 1977
Diss 3 Rolls-Royce Avons 34.5 1977
St Fergus I 4 Rolls-Royce Avons 47.2 1977
St Fergus II 2 Rolls-Royce Maxi Avons, 3 Rolls-Royce RB211s 65.3 1978
Moffat 2 Rolls-Royce RB211s 38.6 1980
Wisbech 1 Rolls-Royce RB211, 1 Rolls-Royce Maxi Avon 32.6 1980

Offtakes

Offtakes from the NTS include those supplying industrial users, local distribution networks, storage sites and export pipelines.

  • Offtakes to about 71 large users such power stations and industry either those on multi-business sites such as Billingham and Runcorn or to individual companies such as INEOS Teesside.
  • NTS offtakes to inland storage sites (see 'Entry') and to the offshore Rough field storage site via the Easington gas terminal.
  • The NTS supplies the Irish interconnectors; the 24-inch 135 km Scotland-Northern Ireland Pipeline (SNIP) to Ballylumford Northern Ireland and the two 24-inch UK-Eire Interconnectors to Dublin, they are supplied from an NTS offtake at Moffat. Gas can also be exported to Belgium and the Netherlands via the Interconnector UK and the BBL pipelines both via the Bacton terminal.
  • Offtakes to the Gas Distribution Network of Local Distribution Zones.[35]
NTS Gas Distribution Network offtakes
National Grid Area Number of LDZ offtakes
Scotland 19
Northern 15
South West 13
East Midlands 13
West Midlands 12
North West 11
East Anglia 11
North East 9
Southern 8
North Thames 5
South East 5
Wales 3
Total 124

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 England, Scotland and Wales within eight distribution networks. The network covers 275,000 km (171,000 mi). The LTS is managed from Hinckley, Leicestershire (former headquarters of the NTS). Financial transactions between gas transporters are managed by Xoserve, based in Solihull, which was a department of National Grid before it became an independent company.

For retail distribution, Cadent owns the network in North West England, the West Midlands, the East Midlands, the East of England 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 of the NTS

The changing ownership of the NTS reflects developments and corporate changes in the UK 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 – 10 October 2005
  • National Grid Gas plc, part of National Grid plc, since 10 October 2005

NG is administratively based in Warwick. NG owns and operates the gas transmission system in all of Great Britain; in comparison it only owns the electrical transmission system in England and Wales but operates it for all of Great Britain.

Northern Ireland

Northern Ireland is not part of the NTS per se 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.

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See also

References
  1. Williams, Trevor I. (1981). A History of the British Gas Industry. Oxford University Press. pp. 147.
  2. "Origins and growth of the British Gas Plant Operations Department" (PDF).
  3. Wilson, D. Scott (1969). The Modern Gas Industry. Edward Arnold Ltd. p. 43.
  4. Falkus, Malcolm (1988). Always under Pressure: A History of North Thames Gas since 1949. Macmillan. pp. 63 & 74.
  5. Falcus, Malcolm (1988). Always under Pressure: A history of North Thames Gas since 1949. Macmillan. pp. 76 & 108.
  6. Fuel Policy, Cmnd. 3438, HMSO, London (1967).
  7. Williams, Trevor I. (1981). A History of the British Gas Industry. Oxford University Press. pp. 210–11.
  8. Williams, Trevor I. (1981). A History of the British Gas Industry. Oxford University Press. pp. 182–9.
  9. John Ellis 'The Origins and Growth of the British Gas Plant Operations Department', 2014.
  10. Tiratsoo, E.N. (1972). Natural Gas. Beaconsfield: Scientific Press Ltd. pp. 216, 221, 222.
  11. "Origins and growth of the British Gas Operations Department" (PDF).
  12. Williams, Trevor I. (1981). A History of the British Gas Industry. Oxford University Press. pp. 177–8.
  13. Wilson, D Scott (1974). North Sea Heritage: the story of Britain's natural gas. British Gas. p. 27.
  14. Tiratsoo, E.N. (1972). Natural Gas. Beaconsfield: Scientific Press Ltd. pp. 221–2.
  15. Cassidy, Richard (1979). Gas: Natural Energy. London: Frederick Muller Ltd. pp. 39–47.
  16. Williams, Trevor I. (1981). A History of the British Gas Industry. Oxford University Press. pp. 225–30.
  17. "NTS feeder mains".
  18. Tiratsoo, E.N. (1972). Natural Gas. Beaconsfield: Scientific Press Ltd. pp. 159, 183, 224.
  19. "Whessoe LNG tanks".
  20. "Methane gas terminal Canvey Island".
  21. McHugh, J (1983). "The engineering of the national transmission system of the British Gas Corporation". Proceedings of the Institution of Mechanical Engineers. 197A: 179–96.
  22. Tiratsoo, E.N. (1972). Natural Gas. Beaconfield: Scientific Press Ltd. p. 183.
  23. "Testing of redundant LNG tank" (PDF).
  24. Tiratsoo, E.N. (1972). Natural Gas. Beaconfield: Scientific Press Ltd. p. 162.
  25. Tiratsoo, E.N. (1972). Natural Gas. Beaconsfield: Scientific Press Ltd. p. 224.
  26. "UK's Avonmouth LNG storage site to stop operations on April 30".
  27. Tiratsoo, E.N. (1972). Natural Gas. Beaconsfield: Scientific Press Ltd. p. 174.
  28. "The domain nationalgrideducation.com is registered by NetNames" (PDF). nationalgrideducation.com.
  29. "Gas Safety (Management) Regulations, 1996".
  30. "Shell Bacton Infrastructure" (PDF).
  31. "Perenco Bacton & Dimlington Infrastructure" (PDF).
  32. "Gas Ten Year Statement (GTYS) | National Grid". www2.nationalgrid.com. Retrieved 20 September 2016.
  33. Cassidy, Richard (1979). Gas: Natural Energy. London: Frederick Muller Limited. p. 14.
  34. Cassidy, Richard (1979). Gas: Natural Energy. London: Frederick Muller Limited. pp. 46–47.
  35. "Gas Transportation Charges Tables 3&5".
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