In view of the burst of rupture disc for 500 kV circuit breaker

it is found through the physical and chemical inspection of the burst rupture disc that the material of the failed rupture disc is gray cast iron with microporous on the surface

with sealing and protection with rubber layers on both sides and without corrosion. Electron microscopy analysis shows that the material is of high brittleness. By replacing the rupture disc of the same type of circuit breaker and comparing the performance of the new and old rupture discs

it is found that the old rupture disc has deformation and the rubber layer of outer side of the most of old rupture discs is aged and cracked

causing water ingress and corrosion of rupture disc. Moreover

it is still found by the blasting test that the blasting pressure of some old rupture discs is reduced but not the samples with severe corrosion. The result shows the corrosion is not the key cause of the blasting pressure drop of the rupture disc. The rupture disc is of flat type and cast-iron material with high brittleness

insufficient fatigue resistance and microporous defects on the surface

which are the root cause of the failure.