Abstract: A device and process for reinforcing underwater structures of branched joints having a main element (1) and at least one secondary element (2), one end to which is integral with the surface of element (1). The device incorporates a flange (3, 3'), a first portion (3') of which is initially fixed to the secondary element (2), and a second portion (3') of which is thereafter fixed to the first portion. The flange portions define an annular space between the flange and the elements. A liquid composition which generates an elastic polymerized material (4) is introduced into an enclosure to fill the annular space and encapsulate the flange, which enclosure defines the outer boundary of the polymerized material (4).