Abstract: A heat exchanger in which a plurality of tubes are supported by tube sheets within a shell having inlet and outlet heads connected to its ends. One of the heads and tube sheets are secured directly to one end of the shell while the other tube sheet and head form a floating head assembly which is connected to the other end of the shell by an expansion joint to permit relative movement between the head assembly and the shell. A first heat exchange fluid is passed into the inlet head and through the tubes before discharging from the outlet head, and a second heat exchange fluid is passed through the shell in a heat exchange relation to the first heat exchange fluid. A load is applied to the head assembly in the direction of the shell to preload the tubes in compression, and movements of the head assembly relative to the shell in excess of a predetermined amount are prevented.