Standing seam metal roofing systems are becoming increasing popular because of lower cost and esthetic appeal. The coating systems most commonly used in metal roofs and metal buildings are galvanized or zinc-aluminum coated steel that are factory-coated with polyvinylidene fluoride (PVF2) or silicone modified polyester (SMP). These coating systems were subjected to ASTM D 5894 testing in the laboratory, which combines the environmental effects of salt fog and ultraviolet exposure,
alternately. The ASTM D 5894 exposure was used to simulate corrosive conditions of the field, and samples were evaluated using electrochemical impedance spectroscopy (EIS). Analysis of EIS
measurements on specimens exposed to the ASTM D 5894 accelerated laboratory weathering provided a means of modeling the equivalent circuit parameters, and detecting the on-set of incipient corrosion
(coating degradation). Results indicated that both of these systems (galvanized vs. zinc-aluminum coatings) provide the same corrosion protection, and that E!S can be used to predict one coating system's long-term service life relative to another coating system, based on short-term laboratory tests.