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There are many methods for identifying the corrosion products of metals, which generally include physical and chemical methods. The initial methods employed include: 1. Visual inspection (through photography or recording); for example, in the case of rust on steel components, it is possible to distinguish between (1) initial rusting (minor rusting), during which the metallic luster disappears and only dark signs are visible ； ⑵Surface rust (light rust): The metal appears yellow or light red, with fine powdery deposits ； ⑶Trace rust (moderate rust): The surface appears reddish-brown, light ochre, or yellow, in the form of a powdery deposit ； ⑷Layered rust: The surface shows black, flaky layers of rust or raised rust spots. The severity of rust can be expressed as mild, moderate, severe, or very severe. The advantage of this method is its simplicity and feasibility, but its drawback is that it is affected by visual errors and is only suitable for qualitative assessment ； 2. Chemical reagent method: Appropriate reagents are used to conduct chemical analysis and identification of metal cations ； 3. Macroscopic analysis: By using a magnifying glass or a stereomicroscope, it is possible to observe the characteristics of corrosion, the depth of pits, and the distribution of corrosion products. Rust on steel appears as irregular, linear patterns under a microscope; this is different from mechanical damage and fatigue phenomena. Detailed analysis can be carried out by comparing typical samples and diagrams, providing a more in-depth and accurate assessment than the first two methods ； 4. The weight change measurement method is divided into two types: measuring weight loss and measuring weight gain. The former is applicable to cases where corrosion products can be removed. The latter is applicable when the corrosion products are insoluble and adhere tightly to the sample. This method is typically used when the corrosion rate is uniform. Its advantages are simplicity, quantitativeness, and directness; however, it is affected by errors in sample cleanliness, cannot be applied to special types of chemical corrosion (such as intergranular corrosion), and requires multiple samples ； Microscopic analysis methods involve the use of modern testing techniques such as metallographic microscopes, X-ray diffractometers, scanning electron microscopes, electron probes, infrared spectrometers, laser microanalysis instruments, and ellipsometers for inspection and analysis. It is possible to analyze the depth, characteristics, composition, and properties of corrosion pits, and even observe the corrosion process in progress. In addition, it is also possible to measure changes in the physical properties of the metal after corrosion (such as hardness and impact toughness), as well as changes in electrical resistance ； The changes in the surface’s ability to reflect light are used to determine its corrosion characteristics. During the testing process, the tools and instruments used include: magnifying glasses, binocular stereomicroscopes, internal cavity inspection devices, metallographic microscopes, scanning electron microscopes, electron probes, X-ray diffractometers, laser microanalysis instruments, ellipsometers, infrared spectrometers, Auger spectrometers, and more.