Watertightness barrier for a wall of a tank

A watertight and thermally insulating tank arranged inside a bearing structure comprising a bearing wall, the tank comprising a tank wall positioned along the bearing wall, the tank wall comprising a watertightness barrier and a thermally insulating barrier positioned between the watertightness barrier and the bearing wall, the thermally insulating barrier having a flat support surface for the watertightness barrier,

• the watertightness barrier having a repeated structure comprising alternately strips of sheet metal arranged on the support surface and elongate welding flanges connected to the support surface, projecting with respect to the latter and running parallel to the strips of sheet metal over at least part of the length of the strips of sheet metal, the strips of sheet metal comprising lateral edges which are turned up with respect to the support surface, arranged against the adjacent welding flanges,
• each of the two strips of sheet metal arranged on either side of a welding flange comprising a first longitudinal portion in which the turned-up lateral edge of the respective strip of sheet metal is watertightly welded to the welding flange by a straight welded seam parallel to the support surface, the straight welded seam being each time arranged beneath an upper ridge of the turned-up lateral edge of the respective strip of sheet metal,
• characterized in that each of the two strips of sheet metal arranged in either side of a welding flange furthermore comprises:
• a second longitudinal portion in which the turned-up lateral edge is watertightly welded to the turned-up lateral edge of the other adjacent strip of sheet metal by an edge corner weld, and
• an intermediate portion in which the edge corner weld of the second portion and the straight welded seam of the first portion are connected watertightly, the welded seam each time having an end portion which is deviated with respect to the support surface in the direction of the upper edge corner and meeting the upper edge corner of the turned-up edge in the intermediate portion of the respective strip of sheet metal, the edge corner weld being continued in the intermediate portion of each of the two strips of sheet metal in such a way as to create a watertight joint with the end portion of the respective welded seam of each of the two strips of sheet metal.