Oil-based coatings can be used to enhance the corrosion resistance of metals and therefore increase their lifetime. Such oils can be applied either by spraying or by using a brush on metal substrates in their real application environments. Recently we performed an accelerated corrosion test on several oil-based coatings for our client Sia Auto Truck Studio, who were particularly interested in the performance of a spray-type oil based coating – an NHOU Rust Prevention Spray. As the name suggests, the coating can be sprayed on the substrate directly from the bottle, which creates an uniform coating. This is achieved by using a proper combination of oil viscosity and spray bottle design, which creates an expanding cone of expelled oil particles, that create a defect free coating on the metal substrate. The corrosion test was performed on 90×90 mm low carbon steel plates, that are extremely vulnerable to corrosion. For testing, the Machu test was used, which is essentially an accelerated corrosion test in an acidified salt solution with hydrogen peroxide. This test allows to obtain results already within 48 hours, which is useful for quickly gaining feedback on the performance of materials and coatings before carrying out long-term immersion or salt spray tests. As can be seen from the photo in Figure 1, the coated sample remained relatively unharmed after the test, exhibiting only a few individual sites of corrosion in the central area. Only the edge of the sample suffered damage from corrosion as it was problematic to coat for this particular test. Overall, the coating exhibited good performance and should therefore be tested further with long-term immersion and salt spray tests, electrochemical techniques and finally in real application environment.
Need to test the corrosion resistance of your material or a protective coating?
In collaboration with the University of Tartu we can do both chemical and electrochemical tests to simulate real or even extreme conditions in order to evaluate the performance of your sample.
Contact us if you are interested in corrosion testing!
Chemical tests – Studied substrates are exposed to a corrosive environment similar to the real conditions where it will be used later on. We can also alter the conditions of the environment to make it more corrosive by adjusting the pH and temperature or include UV light. A common example would be a test of series to compare the quality of stainless steel samples obtained from different suppliers. Another example would be the evaluation of different protective coatings on metal substrates.
Electrochemical tests – Corrosion can electrochemically be accelerated and this allows to quickly obtain reliable information about a materials or protective coatings corrosion resistance. For instance, certain metal alloys can be immersed in a salty water for years before it corrodes while electrochemically we can evaluate its long-term performance within a hour.
Microscopy – In addition to corrosion tests we also do microscopy studies of the tested substrates in order to get additional information about the type of corrosion. For example, Pitting corrosion often occurs undetected as it stats as a tiny hole on the surface and forms a network of tunnels inside the substrate, thus greatly degrading its mechanical properties. In contrast, uniform corrosion initially affects the aesthetic appearance of a material and mechanical properties are not much affected if the problem is dealt with.
One of the most widely used methods to counter the degradation of a materials mechanical properties to due to corrosion is to use more material. If the speed of uniform corrosion is known (mm per year), then it is possible to calculate the required thickness of the material, so that it can serve its purpose during its expected lifetime. The Steel Bridge in Portland (USA) is just one example where this method is used. Protective coatings are also often applied in order to slow down the corrosion of the construction material even more.