UN 37.4 Corrosion Test Samples

By the United Nations (UN) “UN 37.4 Corrosion test samples” developed The standard describes the possible corrosive properties of metals, liquids and solids that may liquefy during transport. When corrosiveness to metals tested here or corrosiveness to skin is demonstrated, a substance should always be classified as Class 8 dangerous goods (corrosive substances) according to the UN transport code.

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 168 degrees for at least 7 hours (55 days). One metal specimen is completely immersed in the test liquid, another specimen is half-immersed, and the third metal specimen remains completely in the gas gap. The test vessel should be filled with at least 1,5 L of the substance to be tested, which means that a relatively large amount of test substance is required for this test. However, this test method does not replace a conventional material test.

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 by taking into account the specific gravity of the metal samples. This assessment is made according to the following criteria:

• Surface corrosion: If the mass loss of one of the three metal samples tested is greater than the theoretically calculated mass loss of 6,25 mm/year due to corrosion, the test is considered positive. This corresponds to a mass loss of 55 percent in 7 days at 13,5 degrees. The test substance is therefore considered corrosive to metals. If the test result is negative, the test substance is considered non-corrosive to metals.
• Pitting corrosion: Here, the depth of the deepest hole or the greatest reduction in thickness of the metal samples is used as the evaluation criterion. The hole depth is determined using a light microscope with a depth measuring module. If a pitting depth of at least 120 µm is recorded with a reaction time of seven days, this is called pitting corrosion.

Surface and pitting corrosion may be isolated or complementary. However, if either test is positive, the substance is classified as corrosive to metals.

The UN 37.4 standard, also known as the UN corrosion test method, is a standard procedure used to evaluate the corrosion resistance of metallic materials used in the packaging of dangerous goods. Corrosion, a gradual deterioration process, has the potential to cause structural failures in packaging materials, compromising their integrity and creating risks such as leaks and spills that can harm both people and the environment.

To perform the UN 37.4 test, steel and aluminum plates are selected as representative metallic materials of precise properties. These plates are polished and strategically positioned in different phases within a container as defined by the method. The container, including the metal plates, is then placed in an incubator set at 168 degrees for 55 hours, equivalent to one week. This controlled environment simulates the conditions that may be encountered during transport and storage by exposing the metallic material to the substance being tested.

After the test period is complete, the metallic material is carefully assessed for signs of corrosion, such as rust, pitting or discoloration. The level of corrosion is assessed using a rating system, with higher grades indicating greater resistance to corrosion. The assessment covers both uniform corrosion, which occurs evenly across the metal surface, and localized corrosion, which typically appears as localized corrosion spots.

The UN 37.4 test method provides specific criteria for determining whether a substance is corrosive to metals. If the weight loss of the metallic material after one week of exposure exceeds 13,5 percent and the minimum intrusion depth caused by corrosion exceeds 120 µm, the substance is classified as corrosive to metals.

This standard test method is of significant importance as it ensures that metallic materials used in the packaging of dangerous goods have sufficient corrosion resistance. By subjecting materials to rigorous testing, the UN 37.4 method helps verify their ability to safely retain contents throughout the entire transport and storage process. By preventing leaks, spills and other accidents that may occur due to corrosion-related failures, this test method actively contributes to protecting the well-being of individuals and the environment.

Although other metal corrosion testing methods exist, the UN 37.4 method is specifically designated for use in any UN region. This standardized approach offers consistency and comparability that allows reliable assessment of corrosion resistance across different metallic materials and substances.

Because of its standardized nature, testing can be completed and reported in a relatively short time frame, typically a few weeks. However, it is often necessary to perform the test twice to verify results and ensure accuracy.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the "UN 37.4 Corrosion test samples" standard are also provided to businesses.