THE SALT SPRAY CORROSION OF POLYMER COATING ON STEEL

Abstract

This study reports on the salt spray corrosion of polymer coating on steel substrate. In the process, firstly, steel coupons are sand blasted, chemically cleaned, and phosphated in different time periods, then the surface of steel is coated with an epoxy-polyester layer at different thicknesses which range from 50 to 180 mu m and then they are Cured at 200 degrees C for 20 min. in a liquid petroleum gas atmosphere. The corrosion test was performed in salt solution, which consists of 5% NaCl, for over 2000 hours. The relative humidity of cabinet was 100% and the temperature of it was 35 degrees C. The corroded samples were examined with a high resolution camera and a stereo microscope. The pH of sprayed and collected water changed between 6.5 and 7.2. The conductivity of water used were arranged as 10 mu S by filtration and the formation time of red rust are determined during testing for each samples. The corrosion of samples is measured in terms of ratio of scribed and unscribed areas of coating quantitatively. It was found that the best results are obtained for sand blasted, phosphated, and coated for 3 seconds. The scribed, unscribed, and average corrosion values are 10, 10, and 10, respectively. It was observed that polymer coating increases the corrosion resistance of steel substrate.