Corrosiveness to metals


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Corrosiveness to metals

For classification according to UN transport law (UN Recommendations on the Transport of Dangerous Goods), we offer a test procedure for the classification of Class 8 substances that are corrosive to metals.

UN Test C.1 as defined in Section 37.4 [1] aims to determine possible corrosive properties with respect to metals of liquids and of solids which could liquefy during transport. A substance must always be classified as Class 8 dangerous goods (corrosive substances) according to UN transport law when corrosiveness to skin or corrosiveness to metals tested here has been demonstrated.

In this test procedure, aluminum and steel test specimens of defined type and size are placed in a test vessel filled with the substance to be tested at a temperature of 55 °C for at least 168 hours (7 days). One metal sample must be completely immersed in the test liquid, another sample must be halfway immersed, and the third metal sample remains entirely within the gas space. The test vessel must be filled with at least 1.5 L of the substance to be tested, which means a comparatively large quantity of the test substance is required for this test. This test method is not a substitute for a traditional material test, however.

After the test is completed, the metal samples are cleaned and dried, then weighed and examined under a microscope. The corrosion rate is thus determined while taking the specific mass of the metal samples into account. This is assessed according to the following criteria:

Surface corrosion

If the decrease in the mass of one of the three tested metal samples is greater than the theoretically calculated decrease in mass due to corrosion of 6.25 mm/year, the test is assessed as positive. This corresponds to a decrease in mass of 13.5% within 7 days at a temperature of 55 °C. The test substance is thus considered to be corrosive to metals. If the test result is negative, the test substance is assessed as non-corrosive to metals.

Pitting corrosion

Here, the depth of the deepest hole or the greatest reduction in the thickness of the metal samples is used as the assessment criterion. The hole depth is determined using a light microscope with a depth measurement module. If a pitting depth of >120 µm is registered with a reaction time of seven days, this is referred to as pitting corrosion.

Surface and pitting corrosion may be isolated or complementary. If one of the two tests is positive, however, the substance is classified as corrosive to metals.