How to detect film corrosion?

After the metal surface is corroded, it shows up through cracks or small holes in the paint film. In the atmospheric aging test, the evaluation method of corrosion is expressed as a percentage of the area of ​​the sample plate. Generally divided into five levels, namely o.1%, o.2%, o.5%, l%, 2%.

Here, the concept of accumulative area needs to be introduced, that is, for the convenience of estimating the sample area occupied by corrosion, the rust spots on the sample plate are all calculated together, so sometimes there are more rust spots on the sample plate, and the accumulated area is still small. It should be noted that sometimes the rust generated on the surface of the base layer does not appear on the surface of the paint layer.