f H21 Phase 2B: Finding and Accessing Leaks

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 GB gas distribution network to 100% hydrogen. 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 distribution networks to transport 100% hydrogen.
Phase 2 consisted of several project phases, which evaluated operational procedures, identifying which of these are suitable for a 100% hydrogen network and those that may require adjustments. To achieve Phase 2a aims, a gas demonstration network was built at DNV Spadeadam Research and Testing to accommodate full scale network OPERATIONS and typical network components. Phase 2b continued from Phase 2a with demonstrations undertaken in a public setting. A section of existing NGN gas distribution network was adopted and developed utilising existing buried ductile iron gas mains, which once served now demolished terrace housing. These mains were interconnected by installing new 180mm PE pipe sections at South Bank, Middlesbrough. A Master Test Plan (MTP) was subsequently developed by NGN in collaboration with the Health & Safety Executives Science & Research Centre (HSE S\&RC) and DNV to address various aspects of existing network procedures and operations including:
♦ Emergency Response and bad practice demonstrations (ER)
♦ Finding leaks (FL)
♦ Accessing leaks (AL)
♦ Assessment of repair techniques (R)
♦ Planned live gas operations (LG)
♦ Isolation techniques (IS)
♦ Commissioning and decommissioning activities (PU)
♦ Pressure regulation and maintenance procedures (MA)
♦ Pressure and flow validation modelling (MO)
This report details the work conducted in relation to the finding (FL) and accessing leaks (AL) tasks within Phase 2b of the MTP. The NGN procedures reviewed and demonstrated being EM72 and EM74 respectively. The programme included manned operational demonstrations of leak finding operations (bar holing/rock drilling) prior to accessing leaks operations (using various excavation techniques) on hydrogen gas-saturated ground locations near to live leaks. In a change to current, natural gas procedures; the initial excavations were conducted away from the live leak location following recommendation from the HSE S\&RC's procedural review conducted during H21 Phase 2a¹. The recommendation is such that no work should be conducted in flammable atmospheres on hydrogen distribution networks where the potential for ignition is unknown and likely greater than that of natural gas. After completion of various finding leaks operations and exploratory excavations around the live leaks had been carried out, excavations directly onto the leak were carried out in the gas-saturated ground after remote isolation of the buried pipework.
All testing was conducted at Middlesbrough Test Site (MTS), South Bank, Middlesbrough, TS6 6LF which was constructed specifically for the H21 Phase 2B program.
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.