Aging Characteristics of GIS seal ring (O-ring)

The properties of the rubber seal ring determine the gas-tightness of the GIS. Previous research used the compression set as an important mechanical property to evaluate the aging of vulcanized rubber, but it is hard to be applied on retired seal ring sample due to its inaccessible initial data and non-standard shape. This paper proposed a test method for retired seal ring based on a new index, deformation recovery rate (DRR). Twenty-nine retired neoprene GIS seal ring samples including 4 from a faulty GIS, which have been in operation for $8 \tilde 30$ years were obtained and tested. Five new samples were also tested as a control. The results showed an exponential plot between DRR and operating time. Then, the ATR-FTIR was applied to identify the main chemical change during the aging process. The results showed a decrease of -CH3 and an increase of C=O, illustrating the chain scission and the oxidation of the rubber. The relation between carbonyl index and operating time was exponential function, too. Besides, EPDM rubber show stronger deformation recovery ability and antioxidant ability than CR. Faultage appeared on the surface and the increase of oxygen atom were detected, which demonstrated that oxidation and chain scission happened during the aging process. Compared the SF6 side to the air side of the seal ring, less protrusions and pits were observed on the surface, and significantly less C, more Si, F, and a small amount of Al, Fe, Zn were detected. The findings demonstrated that the seal ring may react with the flange, SFi gas or its decomposition gas.