PURPOSE: To prevent gas leakage from the flange weld zone of the cooling plate of a blast furnace when such leakage arises by covering the circumferential edge part of the flange with an annular cylindrical body, welding the side edge part thereof to the shell of the flange and pressing further the flange by means of retaining metals and bolts.

CONSTITUTION: When a crack arises in the weld zone 5 between the flange 2 of a cooling plate 10 for cooling the wall of a blast furnace and a shell 3 and gas leakage from the inside of the furnace arises, the circumferential edge part of the flange 2 is covered with an annular cylindrical body 7 and the inside edge part 7a thereof is welded to the flange 2. The side edge part 7b of the body 7 is then welded to the shell 3 and retaining metals 8 are welded to the shell 3. Tap bolts 9 are screwed to the tips 8a of said metals 8 and the flange 2 is pressed by the bolts 9. Even if the strength decreases owing to the crack in the weld zone 5, the flange 2 is securely pressed and therefore the plate 10 is prevented from jumping to the outside of the furnace. The gas leaking from the crack does not leak to the outside of the furnace as the inside of the body 7 is hermetically sealed.