Resistance to corrosion of galvanized steel covered with an epoxy-polyamide primer coating

The resistance to corrosion provided by an epoxy-polyamide primer attached to a galvanized steel panel was assessed by electrochemical impedance spect roscopy. Three different coating thicknesses were tested in this work, name ly 100, 200 and 500 mum, which were applied on panel sections cut-off from overhead electrical transmission-line towers. Corrosion tests were performe d by exposing the painted coupons to a 3.08 NaCl aqueous solution in a hori zontal flat-cell. Changes in the impedance characteristics of the systems w ere found to occur as a function of the exposure time in all the three case s, though their evolution with time showed marked differences which derived directly from the different thicknesses of the coatings. With the thinnest coating considered, the primer film could not provide an effective protect ion for the metal that underwent corrosion asa result of the delamination p rocess. On the contrary, when the coating film was sufficiently thick, effe ctive protection of the metallic substrate was provided by the epoxy-polyam ide film. (C) 2001 Elsevier Science B.V. All rights reserved.