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This paper briefly describes the types and influencing factors of metal corrosion, and discusses the protection methods and necessity of corrosion in detail. At the same time, some common chemical coatings are pointed out, and their principles and functions are briefly explained. In addition, it is also demonstrated that the protection methods of metal corrosion are not single, but diversified. Finally, some suggestions are put forward in the field of protection to minimize the adverse consequences caused by metal corrosion.

Keywords: metal corrosion; Factors; protected mode

In chemical industry, petrochemical industry, atomic energy and other fields, material corrosion will not only cause huge losses to society, but also lead to the leakage of a large number of harmful substances and even radioactive substances, which will cause irreparable harm to the environment and further threaten people's health. Some substances will not disappear in a short time and pose a threat to the environment and people for a long time. At the same time, catastrophic accidents caused by metal corrosion will endanger people's lives and property, such as hydrogen embrittlement, stress corrosion fracture, etc., which will generally lead to major accidents such as explosions and fires, causing great losses to people's lives and property.

1, metal corrosion category

The corrosion of metals is mainly caused by the destruction and deterioration under the influence of the environment. According to the corrosion process, it mainly includes chemical corrosion and electrochemical corrosion; According to the state of metal corrosion damage and the layout of corrosion area, it mainly includes comprehensive corrosion and local corrosion; In addition, according to the corrosion situation. Emphasis includes high temperature corrosion and normal temperature corrosion; Dry corrosion and wet corrosion, etc.

2. Factors affecting metal corrosion

① Relative humidity of air and critical relative humidity of metal corrosion. There is always enough oxygen in the air, and the rate of corrosion reaction is mainly based on the generation of moisture. If it reaches or exceeds a certain relative humidity, corrosion will occur and deteriorate at a faster rate. Generally speaking, the critical relative humidity of steel is about 75%.

② The influence of pollutants in the air. Usually we can see SO2, CO2, Cl-, dust and so on, most of which are acid gases.

③ temperature. The environmental temperature and its changing law affect the reaction rate of water condensation and electrochemical corrosion on the metal surface.

4 acid, alkali and salt. The key point is to affect the electrolyte concentration and H+ concentration of water film, and then accelerate the corrosion rate.

3. Protection methods

There are various protection methods for metal corrosion, focusing on the essence of metal, isolating the protected metal from corrosive medium, or manipulating the surface of metal to change corrosion conditions and electrochemical protection.

3. 1 improves the properties of metals.

According to different uses, using different materials to form corrosion-resistant alloys, or adding alloying elements to metals to improve their corrosion resistance, can prevent or reduce the speed of metal corrosion. For example, adding nickel to steel to make stainless steel can enhance corrosion resistance.

3.2 constitute a protective layer

It is the best way to prevent metal corrosion by setting various protective layers on the metal surface to isolate the protected objects from corrosive media.

3.2. 1 metal phosphating treatment

After degreasing and rust removal, iron and steel products are soaked in a phosphate solution with certain composition, which can form a water-insoluble phosphating film on the metal surface, which is called phosphating operation. Phosphating film is dark gray to dark gray, and its thickness is usually between 5-20 μm, so it has strong corrosion resistance in air.

3.2.2 Metal oxidation treatment

When iron and steel products are melted into NaOH mixed solution and heated, a blue oxide film (mainly Fe3O4) with a thickness of 0.5 ~1.5 micron can be formed on its surface, thus achieving the purpose of steel corrosion protection. This process is called bluing treatment. This oxide film has strong elasticity and lubricity, and will not have any negative impact on the accuracy of parts. Therefore, precision instruments and optical components usually choose this operation.

Nonmetallic coating

Non-metallic coatings can also be coated with non-metallic materials such as paint, spray paint, asphalt, etc. on the metal surface to produce a protective layer and achieve the purpose of anticorrosion. Such as a hull, a carriage, a bucket, etc. Usually painted, and the surface of the vehicle is often painted.

Metal protective layer

It is a protective coating produced by plating a metal or alloy with high corrosion resistance on the surface of the protected object. The coating can be produced not only by electroplating and electroless plating, but also by hot dip plating, infiltration plating and vacuum plating.

3.3 Improve corrosion conditions

Improving conditions is necessary to reduce and avoid corrosion. For example, we can choose to add substances that can reduce the corrosion rate, that is, buffers, to reduce and avoid corrosion. Buffer is a chemical substance. If it is properly mixed into corrosive medium, the corrosion rate of metal can be greatly reduced. Because the amount of buffer is small, it is convenient and cheap, and it is also an important anti-corrosion method.

3.4 Electrochemical Protection Law

This method is based on the electrochemical principle, operating on metal equipment, making it the cathode of corrosion battery, and then becoming a method to prevent or slow down metal corrosion.

cathodic protection

In addition, the metal is protected by an external power supply. Connect the object to be protected to the negative electrode and turn it into a cathode to prevent corrosion. At the same time, some iron blocks are selected to be connected to the anode, so that it becomes the anode and is corroded, that is to say, the anode is sacrificed. This method is mainly used in some acid storage tanks or pipelines, underground water pipes and oil pipelines in chemical plants.

4. Conclusion

No matter in any field of society, metal corrosion is of great significance and will have a serious impact on the environment, economy and safety. Anti-corrosion measures should be taken for new petrochemical facilities such as oil depots, pipelines and large petrochemical production equipment. However, there are various ways of anti-corrosion and its forming factors, which is a great challenge for all personnel in this field and deserves their corresponding efforts.

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