Tube-to-tube and gasketed plate heat exchangers are used for a variety of applications on
ships, offshore oil platforms, and at coastal locations where seawater is employed as a
cooling medium and marine corrosion is likely. The corrosivity of the seawater is often
increased by the addition of chlorine to control marine life in such systems. While
commercially pure (C.P.) titanium and titanium alloys offer excellent resistance in this type of
equipment, these materials are currently in very limited supply. Thus, designers are being
forced to consider alternate corrosion-resistant materials. Nickel-chromium-molybdenum
corrosion-resistant alloys such as 625 (N06625), C-276 (N10276), 22 (N06022), and 686
(N06686) and super-austenitic stainless steels such as alloys 25-6MO (N08926) and 27-7MO
(S31277) offer high strength and formability along with resistance to corrosion. This paper
presents data developed from testing of actual heat exchangers as well as laboratory coupon
exposures in sea water at elevated temperature. The corrosion resistance of these alloys
under typical marine heat exchanger conditions along with details of their mechanical
properties and fabricability are described. By taking advantage of the excellent corrosion
resistance and mechanical properties of these alloys, it is shown that they are cost-effective
candidates for this application and offer long, reliable service.