Many oil and gas offshore facilities use heat exchangers cooled with seawater. Titanium is widely used for seawater plate heat exchangers, but its availability for this market depends on other large demand from other markets like the aerospace industry. Thus, it is vital to find alternative materials in seawater heat exchangers' applications. High-alloyed stainless steels and nickel-base alloys are used for different marine and offshore applications, but have not been widely used for seawater plate heat exchangers. Most of the corrosion data available in the literature on these alloys have been obtained from laboratory experiments. Thus, there is a need to determine the corrosion resistance of these alloys under real service conditions. This is important as heat transfer, flowing and geometrical conditions of plate heat exchangers may be difficult to simulate based upon simple laboratory exposure. Therefore, a test program has been developed to test selected materials in actual plate heat exchanger conditions using natural sea water during one year and more. These materials are nickel-based alloys UNS N06625, N10276, N06059, N06200 and N06686, along with a special steel UNS N08031. The study was performed in chlorinated natural sea water from 30°C up to 60°C. The result data from this test program are presented and discussed in this paper.