A self-supporting case suitable for supporting and thermally insulating a sealed membrane intended to contain a fluid, the case comprising: a bottom panel, lateral webs (24, 27) fixed to the bottom panel and protruding at right angles on one side of the bottom panel to delimit the outline of an internal space of the case, a cover panel supported and fixed on a top edge of the lateral webs parallel to the bottom panel and at a distance from the bottom panel to close the internal space of the case, the cover panel comprising a top plate and a bottom plate superposed on and fixed to one another, at least one groove formed in the cover panel and emerging on a top surface of the cover panel to receive a weld support intended to retain a sealed membrane on the cover panel, at least one supporting partition (26, 126, 226) extending longitudinally vertically in line with the groove parallel to the groove, the supporting partition being arranged at right angles to the bottom panel and to the cover panel, the supporting partition extending between said lateral webs so as to divide the internal space into a plurality of compartments intended to receive a heat-insulating packing, the supporting partition (26, 126, 226) having a top surface in contact with the bottom plate of the cover panel and a bottom surface in contact with the bottom panel, and fasteners engaged at right angles in the bottom plate and the top surface of the supporting partition (26, 126, 226) to fasten the supporting partition to the cover panel, characterized in that the groove has a section comprising, in succession in a thickness-wise direction of the top plate, a wider bottom part and a narrower orifice part, and that the top surface of the supporting partition (26, 126, 226) is wider than the bottom part of the groove, the fasteners being engaged in a zone of the bottom plate offset laterally with respect to the bottom part of the groove. a bottom panel, lateral webs (24, 27) fixed to the bottom panel and protruding at right angles on one side of the bottom panel to delimit the outline of an internal space of the case, a cover panel supported and fixed on a top edge of the lateral webs parallel to the bottom panel and at a distance from the bottom panel to close the internal space of the case, the cover panel comprising a top plate and a bottom plate superposed on and fixed to one another, at least one groove formed in the cover panel and emerging on a top surface of the cover panel to receive a weld support intended to retain a sealed membrane on the cover panel, at least one supporting partition (26, 126, 226) extending longitudinally vertically in line with the groove parallel to the groove, the supporting partition being arranged at right angles to the bottom panel and to the cover panel, the supporting partition extending between said lateral webs so as to divide the internal space into a plurality of compartments intended to receive a heat-insulating packing, the supporting partition (26, 126, 226) having a top surface in contact with the bottom plate of the cover panel and a bottom surface in contact with the bottom panel, and fasteners engaged at right angles in the bottom plate and the top surface of the supporting partition (26, 126, 226) to fasten the supporting partition to the cover panel, characterized in that the groove has a section comprising, in succession in a thickness-wise direction of the top plate, a wider bottom part and a narrower orifice part, and that the top surface of the supporting partition (26, 126, 226) is wider than the bottom part of the groove, the fasteners being engaged in a zone of the bottom plate offset laterally with respect to the bottom part of the groove.