f H21 Phase 2A: Commissioning and Decommissioning Operations

In line with the UK government's de-carbonisation strategy, Northern Gas Network's (NGN) H21 project aims to enable the conversion of the UK gas networks to pure hydrogen. After conversion of the gas networks, hydrogen is transported from various sources through new and existing gas networks to industrial and domestic customers.
Following progress on Phase 1 of the H21 programme, Phase 2 consisted of a number of Project Phases. Phase 2a evaluates network operations, tools and procedures, identifying which of these are suitable for a 100% hydrogen network and those that may require adjustments. To achieve this, a gas demonstration network was built at DNV Spadeadam Research and Testing to accommodate full scale network parameters and typical network components. A Master Test Plan (MTP) was subsequently developed by NGN in collaboration with the HSE S&RC and DNV to address various aspects of existing network procedures and operations including:
♦ Emergency Response and bad practice demonstrations
♦ Finding leaks
♦ Accessing leaks
♦ Assessment of repair techniques
♦ Live gas operations
♦ Isolation techniques
♦ Commissioning and decommissioning activities
♦ Pressure regulation and maintenance procedures
♦ Pressure and flow validation
Each of these areas of testing and assessments were then divided in individual tests or tasks and identified with a unique ID name.
The current report details the work conducted in the H21 demonstration grid at Spadeadam, herein referred to as ""Microgrid"", in relation to commissioning and decommissioning activities. The programme included commissioning and decommissioning of straight mains, branched networks, and service pipes in each of the pressure tiers in the microgrid (IP, MP, and LP). In line with recommendations by the HSE S\&RC in their procedure review conducted earlier in Phase 2a; pipe diameters above 32 mm were commissioned or decommissioned indirectly (by displacing air with inert fluid followed by displacement of the inert fluid with hydrogen or vice versa). Pipe diameters under 32 mm (service pipe tests) were purged directly (air displaced by fuel gas or vice versa) according to a bespoke test procedure employing exclusion zones around pipes and vents.
Conversion style commissioning was also carried out in IP, MP, and LP mains, i.e., converting pipes previously commissioned with Natural Gas to contain 100% hydrogen. This was also carried out by direct displacement of one fuel gas for the other.
This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating, which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.
Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.