SELECTION OF CORROSION TEST METHODS BASED ON MECHANISM PRINCIPLES

Six coatings, including an epoxy ester copolymer, aliphatic oil-modifi ed urethane, short-oil alkyd, short-oil alkyd with silicate, water-red ucible alkyd, and acrylic emulsion were tested and compared at three f ilm thicknesses to measure or predict corrosion resistance. Performanc e of the coatings changed at different film thicknesses. This has been associated with mechanisms prevalent in each test as well as relative mechanism rates. The coating types were rated as best, intermediate, and poor according to three basic causes of corrosion: water permeabil ity, ion mobility, and wet adhesion/undercutting. This study showed th at although a single test cannot adequately compare the corrosion char acteristics of a group of coating types, a suitable test method can be selected. This is based on a major cause of corrosion that may be exp ected in a specific application.