Abstract: A weldment heat exchanger having at least the surfaces contacted by the fluids between which heat is exchanged of stainless steel and comprising a tube bundle having spaced tubes through which one of the fluids flows and over the outer surfaces of which tubes a second fluid flows for exchange of heat between the fluids through the walls of the tubes, a first header-tank at one end of the bundle and a second header-tank at the opposite end of the bundle, the joints of the parts including those of the two header-tanks and the tubes being welded.