Abstract: There is provided a seal structure which surely maintains sealing performance of a pressure vessel including a bottomed tubular vessel body with an opening end and a lid closing the opening end. In this seal structure of the pressure vessel, annular grooves 11a, 11b and ridges 21a, 21b fitted to each other are formed on both of the inner and outer sides at the joining faces of opening end 11 of the vessel body 10 and the lid 20, and an annular vent hole 30 is formed between the inner ridge 21a and the outer ridge 21b. An air supply hole 31 for supplying an inert gas to the vent hole 30 is formed in the lid 20. The joining faces on the inside of the inner groove 11a and inner ridge 21a are in metal-to-metal contact. Furthermore, gaskets 51a, 51b are held between the ridges 21a, 21b and the grooves 11a, 11b.

Abstract: There is provided a bellows for a pressure vessel that would not rupture due to thermal expansion and contraction, avoiding stagnation of a raw material. The bellows 40 for a pressure vessel is adapted to realize ring-shaped sealing between an open end 11 of a bottomed tubular vessel body 10 into which a raw material is caused to flow, and an outer peripheral portion of a dispersion board 30 closing the open end 11 so as to permit downflow of the raw material toward the bottom of the vessel body 10. The bellows 40 is provided with a flexure portion 41 flexing radially so as to permit thermal expansion and contraction without being depressed for avoiding of stagnation of the raw material. The flexure portion 41 has a concave curved surface 42 and a convex curved surface 43 which are continuously formed to have a wave shape.