Analyzing the aging profile of serviced GIS O-ring seals under 30-year long-term field aging condition

•The aging profiles of GIS O-ring seals were analyzed from the field-aged samples with an operating year of 8, 9, 18, 25 and 30, rather than traditional ways of the accelerate aging tests.•The surface morphology, element migration on the surface, and carbonyl absorbance of O-ring samples from the fault phase and the non-fault phase were compared.•Deformation recovery ratio (DRR) was proposed and justified as useful index characterizing the deformation of aged O-rings. Based on several simple assumptions, the degradation of CR GIS O-rings was estimated to be a 9.6-order reaction.