ANSI/NEMA 62321-7-1:2015

This part of IEC 62321 describes a boiling water extraction procedure intended to provide a qualitative determination of the presence of hexavalent chromium (Cr(VI)) in colourless and coloured corrosion-protection coatings on metallic samples.

Due to its highly reactive nature, the concentration of Cr(VI) in a corrosion-protection coating can change drastically with time and storage conditions. Since storage conditions prior to sample submission are not often known or provided with the samples, this procedure determines the presence of Cr(VI) based on the levels detected in the coatings at the time of testing. For testing of freshly coated samples, a minimum waiting period of 5 days (after the coating process) is necessary to ensure the coatings have stabilized. This waiting period allows potential post-process oxidation of Cr(III) to Cr(VI) to occur prior to testing.

The presence of Cr(VI) is determined by the mass of Cr(VI) per surface area of the coating, in μg/cm2. This approach is preferred since corrosion-protection coating weights are often difficult to measure accurately after production. From a coating technology perspective, the industry as a whole has transitioned to either using the non-Cr(VI) based chemistries – where little to no Cr(VI) should be present – or using the traditional Cr(VI) based chemistries – where significant levels of Cr(VI) are present and can be detected reliably. Given this industry shift, the presence or absence of Cr(VI) is often sufficient for compliance testing purposes.

In this procedure, when Cr(VI) in a sample is detected below the 0,10 μg/cm2 LOQ (limit of quantification), the sample is considered to be negative for Cr(VI). Since Cr(VI) may not be uniformly distributed in the coating even within the same sample batch, a “grey zone” between 0,10 μg/cm2 and 0,13 μg/cm2 has been established as “inconclusive” to reduce inconsistent results due to unavoidable coating variations. In this case, additional testing may be necessary to confirm the presence of Cr(VI). When Cr(VI) is detected above 0,13 μg/cm2, the sample is considered to be positive for the presence of Cr(VI) in the coating layer.