SF6 is the insulating medium gas used in GasInsulated Switchgear (GIS) across the electricity transmission network. While it provides excellent electrical insulation performance, SF6 is also a high impact greenhouse gas, and leaks can occur as assets age. Effective leak sealing is essential for environmental protection, regulatory compliance, and asset reliability.
Challenge
Preventive maintenance or SF6 leak repair on GIS typically requires taking equipment out of service, removing the SF6 gas, completing the repair, and then refilling the system. Even small leaks in ancillary pipework can require several days of outage, increasing operational disruption and environmental risk.
To reduce emissions and minimise downtime, National Grid Electricity Transmission (NGET) sought a technology capable of safely sealing SF6 leaks while assets remained in service.
Solution
RW Seals’s M3 technology, using low melting point bismuth alloys, enables operators to seal flowing leaks directly—without removing SF6 or interrupting operations. M3 seals are fully reversible, suitable for both temporary and longer term repairs.
Working collaboratively with NGET through two Network Innovation Allowance (NIA) projects and follow on contracts, M3 was tested across a wide range of leak scenarios. RW’s M3Cast system using specially designed reusable moulds achieved an average 98% leak-rate reduction when deployed against a 7 bar flowing leak in lab testing. Additional controlled testing at NGET’s Deeside Centre of Innovation further validated the deployability and reversibility of the method.
To confirm safety and asset integrity, RW and Cardiff University collaboratively performed further assessments to address potential alloy or gas ingress. Testing confirmed no change to SF6 composition or GIS electrical performance following an M3 repair.
For the pilot deployment at Dinorwig Substation, two leaking elbow connectors were selected. M3Cast was used to cast the molten alloy around the leak locations, after which the reusable moulds were removed.
Outcome
Both SF6 leaks were successfully sealed while the asset remained live, gas filled, and under pressure. No leaks were detected following deployment, and the seals remained in place for periodic monitoring.
This pilot demonstrated that M3 is a credible, safe, and effective solution for sealing SF6 leaks in small bore pipework without the need for outages.
Rawwater extends thanks to NGET for the collaborative approach that supported the progression of this technology from concept to successful onsite deployment in just 14 months.
