Watertight and thermally insulating tank with an improved corner structure, built into the bearing structure of a ship

Watertight and thermally insulating tank built into the bearing structure of a ship, the said tank comprising two successive watertightness barriers, one being a primary one (17) in contact with the product contained in the tank, and the other being a secondary one (13) located between the primary barrier and the bearing structure, the said bearing structure comprising, for each tank, on the one hand, walls (1) which are substantially parallel to the axis of the ship and form the internal sides of its double hull and, on the other hand, two transverse bulkheads (2) substantially perpendicular to the axis of the ship, these two watertightness barriers alternating with two thermally insulating barriers, the primary insulating barrier being held pressed against the secondary watertightness barrier by fastening means (12) arranged substantially continuously in a straight line and mechanically joined to the secondary insulating barrier (4, 104), the corner connection of the primary and secondary barrier elements in the zones where the transverse bulkheads (2) meet the internal sides (1) of the double hull, being achieved in the form of a connecting ring, the structure of which remains substantially constant along the entire length of the solid angle (3) of intersection between a transverse bulkhead and the internal sides of the double hull, characterized in that each connecting ring comprises a prefabricated composite girder (20) made up of a rigid metal formwork (21) incorporated in a thermally insulating material (22), the said rigid formwork defining a central fixed anchorage zone (29) substantially at the intersection between the plane bisecting the connection corner starting from the solid angle of intersection and the extension of the secondary watertightness barrier (13), on each side of the said solid angle of intersection, for mechanically securing the secondary watertightness barrier to the said fixed central anchorage zone of the formwork, the opposite ends (23) of the said formwork being secured to the bearing structure by fixing means (26) borne respectively by a transverse bulkhead and by an internal side of the double hull.