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In chemical, petrochemical, and refinery joint applications, gasketing products based on flexible graphite have been used successfully to 850/F (455/C) for extended service. In this report, the long-term service temperature predictions that are extrapolated from the use of equivalent aging parameters show the limitation of these materials to 600/F-650/F (315/C-343/C) for a 5-year exposure of a joint under worst-case scenarios of exposure to an air-oxidizing atmosphere. These gasket temperatures have been derived from laboratory test data that were obtained under realistic simulated flange loads and flexibility with accelerated thermal aging. They represent the cumulative effect of thermal conditions at the gasket over time. The life prediction of gasketed joints appears to be delicate, and as a simple attempt to reproduce the aging effect on gasket properties, the air exposure is considered as a valid approach because this environment represents the worst condition encountered by most users in process plants and because most gaskets in process application have one edge that is air exposed. It is believed that steam and liquid exposures are less harsh unless a chemical attack of gasket material components is involved. The calculated long-term service temperatures for the tested flexible graphite gasketing products are significantly less than commonly accepted wisdom. The process temperature of joints equipped with these products may be greater, and it could be required that they be confirmed and/or supplemented by elevated temperature leakage tests. Publication of this document - WRC Bulletin No. 419 was sponsored by the Pressure Vessel Research Council of the Welding Research Council, Inc.