A corrosion-resistant alloy metal tube sheet used to construct a shell and tube heat exchanger (50) for cooling fluids with sea water passing through corrosion-resistant alloy tubes (25) contained in a horizontal carbon steel outer shell (1) that are supported and sealed at each end by passing them through holes (27, 30) in a carbon steel tube sheet (28, 31) and axially aligned holes (36, 37) in alloy tube sheets (34, 35) that cover and protect the adjacent interior carbon steel tube sheets from sea water corrosion. The walls of the holes (27, 30, 36, 37) have at least one annular groove (45, 46) and the ends of each tube are radially expanded to form circumferential ridges (40, 41) on the outside of each tube at a mating location with each of said annular grooves (45, 46) where they are forcibly driven into the grooves to form a circumferential joint having good mechanical strength and water tightness, thereby eliminating the need for welding the external joint between the alloy tube sheets and alloy tubes.