Abstract: Plate exchanger of the type comprising a plurality of juxtaposed metallic plates defining spaces between them, every other of which spaces receives a flow of a first fluid whereas the other spaces receive a flow of a second fluid, substantially parallel to the first, each plate being joined in tight manner, by its periphery to the two adjacent plates, while inlet or outlet orifices are provided for the fluids, the plates being paired up by straight seam welding in two opposite end parts of the plates of each pair of plates, characterized in that one plate at least from each pair comprises a flange, at least in one of the end parts and close to said welding, which flange is bent substantially at right angle and joined by straight welding of its free bordering part to a plate facing the next pair.