Oct 2020
Gas Transmission
Inline Flow Stop - Feasibility
NIA_NGGT0167
Live
Oct 2020
Apr 2021
National Grid Gas Transmission
Dave Hardman, Kirsty McDermott
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Network Innovation Allowance
GT - Reliability and maintenance
Gas Transmission Networks
£109,080.00
Investigate the use of in line isolation tools on the National Transmission system. Work through the requirements for a policy update to allow the tools to be used and understand if a live trial is required based on the pre-work carried out by PRCI.
The objective of this NIA project is to summarise the work completed to date on onshore inline isolation tools and compare this to the requirements of National Grid Gas Transmission with an understanding of how the network was constructed and is managed today. Following this the policies and procedures that need to be amended to allow inline isolation tools to be used will be highlighted and any changes will be proposed to NGGT for inclusion. A live trial of the tools will be proposed if it is needed following this NIA but is not included in the scope of this work.
If inline isolation tools are used on the NTS then the extent of the isolation will be significantly reduced due to the downstream block valves not requiring to be used. With a reduced isolation length the amount of natural gas that is vented to atmosphere will be reduced having an environmental and financial impact each time the tool is used.

Insulation Joint (IJ) replacement example from above
Existing case
  • Assumed 15km between the IJ and the next operational ball valve downstream
  • This would be taken down to 7 bar(g) using a recompression rig ~£80k
  • Venting cost
7bar/km = 4 tonnes of gas/km, total = 60 tonnes
£2,157/km - Cost of gas = £32,355

Use of an Inline flow stop tool
  • Assumed the tool could be stopped 10m downstream of the IJ
  • No requirement for recompression rig
  • Venting cost
Venting cost 70bar/km = 43 tonnes of gas/km, total = 0.43 tonnes
£25.5k/km – Cost of gas = £255

Total savings = 59.57 tonnes of gas and £32,100

According to the RIIO 2 business plan for NGGT it is planned that 41 IJs will be replaced over the 5 year period, therefore across RIIO 2:

Total savings = 2,442 tonnes of gas and £1,316,100, additionally the recompression rig will not be needed for the 41 jobs across RIIO 2 so £3,200,000 could be added as well.