f H21 Phase 2: Assessment of Repair Techniques

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 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 components 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 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 technical note details the work conducted in the H21 demonstration grid, herein referred to as “Microgrid”, in relation to assessment of repair techniques. Six used cast iron (CI), spun iron (SI) and steel (ST) assets purposedly made to present leaks or leak paths were repaired using six commonly used techniques in the current natural gas network including: muffed encapsulation, anaerobic repair, two-part joint injection, polyform repair, clamp repair and heat shrink repair. The repairs were then leak checked with nitrogen, buried and connected to the H21 microgrid and commissioned with hydrogen. Weekly over the course of five months, whilst the rest of the testing programme was being carried out, the assets were individually isolated and checked for re-appearance of leakage over time and under service conditions by means of pressure decay tests.
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.