Replacing Titanium in Sea Water Plate Heat Exchangers

The use of titanium plate heat exchangers is widespread for Offshore and Coastal installations where seawater cooling is required. Several years ago difficulties to supply titanium Grade 1 for this application triggered the need for qualification of other alloys for this application. Hot seawater is a very corrosive medium in particular as regards crevice corrosion for passive alloys. Titanium is known to be the most corrosion resistant alloy in seawater. This means that only a few alloys could be candidate for this use. In addition only ductile alloys that are easily shaped into plates by cold pressing can be used. This narrows even further candidate alloys for plate heat exchangers. In this study nickel chromium molybdenum alloys and a highly alloyed stainless steel were tested between 30 and 70°C in natural seawater with up to 1 ppm free chlorine. Rather than using short electrochemical testing that is often difficult to compare with service performance long term exposure tests (up to 18 months) of real plate heat exchangers were carried out. These tests are considered to be more representative of actual service conditions. The results of these tests and their significance are discussed in the light of previous reported work.