Corrosion in Gas-Insulated Switchgear and Circuit Breakers with Respect to Gas Leakage: Causes, Prevention, Lifecycle Impact, Field Experience, Laboratory Studies, and Recommendations

Field inspections revealed several corrosion mechanisms across operational equipment.

Uniform corrosion was commonly found on stainless‑steel enclosures but was not directly associated with leakage, though progression may affect long‑term durability. Galvanic corrosion was prominent at bolted joints where dissimilar metals were present, accelerating localised attack. Crevice corrosion emerged as the primary mechanism leading to gas leakage.

Stagnant electrolytes trapped within flange interfaces produced oxygen‑depleted, acidic conditions that drove autocatalytic metal dissolution, which in some cases penetrated the O‑ring groove and compromised the gas seal. Other types of degradation were also observed including pitting corrosion, hydrogen embrittlement, and microbiologically influenced corrosion (MIC).

To reproduce field‑observed behaviours and evaluate mitigation measures, a laboratory experiment was carried out using 420 kV GIS aluminium flanges. Four samples were prepared:

an uncoated control and three coated variants using epoxy and polymeric systems. Each sample incorporated two hardware types—galvanised steel and stainless steel—to examine the influence of material selection. Neutral salt spray testing was conducted in accordance with ISO 9227, with an extended duration of 3000 hours selected to align with long‑term service expectations derived from ISO 12944 for C4 and C5 atmospheric categories. This exposure duration was intended to approximate 50‑year performance in C4 conditions and 25‑year performance in C5 conditions.

The paper also evaluates the suitability of Non‑Destructive Testing (NDT) for detecting early‑stage corrosion within flange assemblies. Total Focusing Method (TFM) was used to assess the laboratory samples during and after the salt-spray test. Preliminary findings are summarised, demonstrating promising capability for future development.

A meteorological‑based atmospheric corrosion map is presented as a modern alternative to the 2001 Zinc Millennium Map (ZMM). This ongoing work seeks to refine corrosivity estimates using site‑specific corrosion data and contemporary meteorological modelling. The updated map is expected to provide a more reliable basis for design, siting, and maintenance decisions than the legacy ZMM, with further results to be reported in a future CIGRE document.

The paper concludes by outlining a new corrosion-protection specification for AIS and GIS equipment. Informed by field experience, laboratory testing, and the meteorological-based corrosion map, it sets C4 requirements for indoor installations and C5 for outdoor installations.

The specification introduces extended salt-spray testing—2000 hours for C5 and 1440 hours for

C4—followed by gas-tightness testing and inspection to ensure no corrosion that could lead to gas leakage, addressing the inadequacy of the 168-hour IEC 62271-203 requirement. It also provides guidance on corrosion protection measures, maintenance, and inspection, with routine checks required during factory assembly, site installation, and post-repair.