A sealing element is provided, which sealing element is more particularly intended for the joining of tubes of small diameter of a circuit of fluid at high temperature. It comprises an annular metal core 12 in which is formed at least one circular recess or groove 14 for receiving a lining 16 of expanded graphite which, before compression of the sealing element, projects from each side of the metal. A recess 18 devoid of graphite performs the function of a collector for receiving, as the case may be, the graphite when the sealing element is compressed, in particular in the case of creep of the graphite due to a particularly high pressure. The recess may be provided between two co-axial annular rings, the lining being moulded on the recess from a wound ribbon of graphite. Alternatively the lining may comprise a thermosetting resin containing a filler.