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Ce medii corozive poate rezista pompa magnetică anticorozivă din oțel inoxidabil?

Timpul: 2023-01-18

Stainless steel magnetic pump has anti-corrosion performance. Stainless steel materials include 304, 316L, etc. These two materials are commonly used in stainless steel magnetic pumps. For the delivery of strong corrosive liquids, where is the limitation of the anti-corrosion performance of stainless steel? The medium to be transported There are eight main types of corrosion on metal magnetic pump materials: electrochemical corrosion, uniform corrosion, intergranular corrosion, pitting corrosion, crevice corrosion, stress corrosion, wear corrosion, and cavitation corrosion.

1. Pitting corrosion
Pitting corrosion is a kind of localized corrosion. Due to the local destruction of the metal passivation film, hemispherical pits are rapidly formed in a certain local area of the metal surface, which is called pitting corrosion. Pitting corrosion is mainly caused by CL ̄. To prevent pitting corrosion, Mo-containing steel (usually 2.5% Mo) can be used, and with the increase of CL ̄ content and temperature, the Mo content should also increase accordingly.

2. Crevice corrosion
Crevice corrosion is a kind of local corrosion, which refers to the corrosion caused by the local destruction of the metal passivation film due to the decrease of oxygen content and (or) pH decrease in the crevice after the crevice is filled with corrosive liquid. Stainless steel crevice corrosion often occurs in CL ̄ solution. Crevice corrosion and pitting corrosion are very similar in their formation mechanism. Both are caused by the role of CL ̄ and the local destruction of the passivation film. With the increase of CL ̄ content and the rise of temperature, the possibility of crevice corrosion increases. The use of metals with high Cr and Mo content can prevent or reduce crevice corrosion.

3. Coroziunea uniformă
Uniform corrosion refers to the uniform chemical corrosion of the entire metal surface when a corrosive liquid contacts the metal surface. This is the most common and least harmful form of corrosion.
The measures to prevent uniform corrosion are: adopt suitable materials (including non-metallic), and consider sufficient corrosion allowance in pump design.

4. Cavitation corrosion
The corrosion caused by cavitation in the magnetic pump is called cavitation corrosion. The most practical and simple way to prevent cavitation corrosion is to prevent cavitation from occurring. For pumps that often suffer from cavitation during operation, in order to avoid cavitation corrosion, cavitation-resistant materials can be used, such as hard alloy, phosphor bronze, austenitic stainless steel, 12% chromium steel, etc.

5. Stress corrosion
Stress corrosion refers to a kind of localized corrosion caused by the joint action of stress and corrosive environment.
Austenitic Cr-Ni steel is more prone to stress corrosion in CL~ medium. With the increase of CL ̄ content, temperature and stress, stress corrosion is more likely to occur. Generally, stress corrosion does not occur below 70~80°C. The measure to prevent stress corrosion is to use austenitic Cr-Ni steel with high Ni content (Ni is 25%~30%).

6. Coroziune electrochimică
Electrochemical corrosion refers to the electrochemical process in which the contact surface of dissimilar metals forms a battery due to the difference in electrode potential between metals, thereby causing corrosion of the anode metal.
Measures to prevent electrochemical corrosion: First, it is best to use the same metal material for the flow channel of the pump; second, use sacrificial anodes to protect the cathode metal.

7. Intergranular corrosion
Intergranular corrosion is a kind of local corrosion, which mainly refers to the precipitation of chromium carbide between stainless steel grains. Intergranular corrosion is extremely corrosive to stainless steel materials. The material with intergranular corrosion loses its strength and plasticity almost completely.
The measures to prevent intergranular corrosion are: annealing stainless steel, or using ultra-low carbon stainless steel (C<0.03%).

8. Wear and corrosion
Abrasion corrosion refers to a kind of erosion corrosion of high-speed fluid on the metal surface. Fluid erosion erosion is different from the erosion caused by solid particles in the medium.
Different materials have different anti-wear and corrosion properties. The order of wear and corrosion resistance from poor to good is: ferritic Cr steel<austenitic-ferritic steel<austenitic steel.


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