Relative and controlled sealing between a pipe (1) and a ceramic tube (7) utilizes a cylindrical chamber (5) that is attached in a sealed manner to the pipe (1), and to one end of the ceramic tube that is placed inside the chamber. At least two sets of sealing fixtures (3, 3') are placed in an annular space between the ceramic tube and the chamber. A crosspiece (4) is interposed between the two sets sealing of fixtures (3, 3'). A metal mating flange (6) is pressed against a compression ring (4') to compress the sealing fixtures (3, 3'). Injection of a fluid (8) between the two sets of sealing fixtures (3, 3') applies a pressure differential that is determined on each of the fixtures.