What are the main aspects of qualitative inspection and recording of atmospheric exposure test coatings?

       (1) Color and shape of coating and base metal corrosion products.



    (2) Corrosion rate. The corrosion rate (the ratio of the coating penetrated to the corrosion point of the base metal) is the main content for evaluating the protective performance of cathodic coatings, which can be observed and calculated in the following ways.

    Cover the surface of the tested coating sample with a transparent plexiglass plate with squares (5mmx5mm), count the total number of squares on the coating surface, denoted by N, and then count the squares with corrosion points. number, expressed as n, the corrosion rate is expressed as

               Corrosion rate=n/Nx100%

    (3) Gloss. The gloss of a coating after atmospheric exposure refers to the degree to which the coating is oxidized when it is corroded as a film. During inspection and evaluation, it should be compared with the original sample preserved in isolation, and divided into:

     1 Good ------ no change or no obvious change;

     2 dim ------ the gloss changes slightly, but still retains the gloss;

     3 Dull ------ the color is dark and dull.

     4 cracked. Calculate the percentage of cracked area, the same as calculating the percentage of corrosion rate area.

     5 Determine the corrosion grade from the qualitative evaluation results. The corrosion grade of the coating is determined by the qualitative evaluation result, which is generally divided into 5 grades.

     Grade 1: No change in the coating surface, or only a dim gloss;

     Level 2: The coating has corrosion spots or film-like oxides, or the gloss is dull, but there is no corrosion spot of the base metal;

     Grade 3: There are base metal corrosion spots, but less than 10% of the total area;

     Grade 4: The base metal corrosion point area is less than 30% of the total area, or the coating cracking area reaches the same extent;

     Grade 5: The corrosion point area of the base metal exceeds 30% of the total area, or the cracking area of the coating reaches the same extent.

     Coatings that have reached level 5, have been severely corroded and can terminate the test.