f H21 Phase 2A Testing - Part A: Planned Live Gas Operations and Isolation Techniques

In line with the UK government’s de-carbonisation strategy, Northern Gas Network’s (NGN) H21 project aims to demonstrate the feasibility of converting the existing <7barg gas distribution network to 100% hydrogen. After conversion of the gas networks, hydrogen could be 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 was proposed to build on the knowledge acquired to provide further quantified safety-based evidence on the suitability of the GB networks to transport 100% hydrogen. Phase 2 consisted of a number of Project Phases. Phase 2a evaluates network operational 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 Development to accommodate full scale network parameters including typical network components. A Master Test Plan (MTP) was subsequently developed by NGN in collaboration with the HSE Science and Research Centre (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 (i.e. purging)
♦ 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 on the H21 demonstration grid, herein referred to as “Microgrid”, in relation to planned live gas operations and isolation techniques. The programme included assessing the effectiveness of existing flow stopping techniques by measurement of the let-by rate downstream of the flow stopping device. The flow stopping techniques demonstrated included: a metallic stopple, squeeze off, ALH bag off, and an MLS bag off. These techniques were performed by third parties according to Method Statements and Risk Assessments modified for the application to hydrogen. Principally, the outcome of the Procedural Review conducted by HSE S\&RC1 was that flammable atmospheres within and around the tools, pipework and vents as currently operated could not be tolerated as for hydrogen operations. As such, the techniques were all conducted with the introduction of nitrogen inerting steps to avoid hydrogen and air mixing within any confined geometries.
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.