Ammonia corrosion resistance of surface-treated aluminum materials

Abstract

A plate heat exchanger (PHE) is used as an evaporator in ocean thermal energy conversion systems to generate electricity using seawater. A commonly used material for the PHE is titanium owing to its high corrosion resistance for seawater and ammonia, which are used as heat source and working fluid. To reduce the cost of the PHE, the authors propose using aluminum instead of titanium. However, as sufficient information on ammonia tolerance in aluminum materials is not available, a tolerance test was performed. A total of 15 test-pieces, including 5 aluminum pieces without coating (A1050, A3003, A5052, A5182, A6061), 7 coated aluminum pieces (PEEK film, WINKOTE film, Anodized, Anodized composite film), and 3 pieces made of other materials (Type 304 and 316 Stainless Steel, Titanium), were tested. The time taken to complete the test was approximately one hour, and the changes in mass and surface conditions were recorded. Pitting corrosion appeared on all test pieces without coating on the 7th day, and the A1050 experienced maximum mass reduction. However, the A1050 test pieces with anodized film exhibited no changes in mass and surface conditions for the duration of a year. Hence, anodized aluminum can be used in an ammonia-boiling environments.