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Is there an easy way to test for chromates on hot-dip galvanized steel?


ASTM B201, Standard Practice for Testing Chromate Coatings on Zinc and Cadmium Surfaces, discusses standard practices for testing chromate coatings on zinc and cadmium surfaces. Testing for the type of chromate coatings most often applied in the galvanizing industry is included in Section 6.3 of this specification. To test for a chromate coating on a galvanized coating, simply place one drop of lead acetate testing solution on the surface and wait five seconds. (Directions for preparing the lead acetate testing solution are included in Section 6.3.2 of ASTM B 201.) Remove the remaining testing solution by gently blotting it and ensuring not to disturb the deposit that may have formed under the liquid. If a dark or black deposit or stain has developed, there is no chromate on the galvanized coating in that area. To verify test results, the lead acetate testing solution can be applied to a galvanized coating that was known not to have chromates applied to its surface. A negative test result showing a chromate coating is not on the galvanized coating does not necessarily mean chromates were not applied. Chromates tend to last up to six weeks on the galvanized coating. In very wet or humid environments chromates can be consumed much quicker. If the chromates have been consumed, the chromate test described above would show a negative result for chromates being on the galvanized coating.

Passivation Testing 

The specification to determine the presence of chromate on zinc surfaces is ASTM B201. This test involves placing drops of a lead acetate solution on the surface of the product, waiting 5 seconds, and then blotting it gently. If this solution creates a dark deposit or black stain, then there is unpassivated zinc present. A clear result indicates the presence of a chromate passivation coating.

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Mohammed Khaja Nazeeruddin

I want to know what is the test method to calculate weight of chromate in gm/m2 surface area on galvanized surface. what is the standard to follow?


Mohammed, Coating weight is varied by immersion time. Calculating coating weight is not typically required by most chromate conversion coating application standards and other test methods are used to ensure quality. Instead, refer to the chromate conversion coating specification you are using, and then follow all of the inspection and test criteria provided in the standard.

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