During the process of transporting media, the corrosiveness of the medium being transported by a magnetic drive pump varies, and the corrosiveness of the same medium to different materials also varies. Therefore, selecting suitable metal and non-metal materials based on the properties of the medium and the operating temperature is related to the service life of the magnetic pump. Therefore, when selecting a magnetic drive pump, it is necessary to determine whether to choose a metal material magnetic drive pump or a non-metal material magnetic drive pump based on the medium being transported.
The corrosion of metal pump materials by the transported medium mainly includes the following eight types: electrochemical corrosion, uniform corrosion, intergranular corrosion, pitting corrosion, crevice corrosion, stress corrosion, wear corrosion, and cavitation corrosion.
1、 Electrochemical corrosion
Electrochemical corrosion refers to the electrochemical process in which the contact surface of heterogeneous metals forms a battery due to the difference in electrode potential between metals, resulting in corrosion of the anode metal. So it is best to use the same metal material for the flow channel of the magnetic pump, such as dedicating the anode and maintaining the cathode metal.
2、 Uniform corrosion
Uniform corrosion refers to the uniform chemical corrosion of the entire metal surface when a corrosive liquid touches it. This is the most common and least harmful corrosion method. Adopting appropriate materials (including non-metallic materials) may effectively address this issue by considering the required corrosion allowance during design.
3、 Intergranular corrosion
Intergranular corrosion is a type of partial corrosion, mainly referring to the appearance of chromium carbide separating between the grains of stainless steel. Intergranular corrosion is highly corrosive to stainless steel materials. The data of intergranular corrosion shows a complete loss of strength and plasticity. Generally, stainless steel is annealed or ultra-low carbon stainless steel is selected.
4、 Point corrosion
Spot corrosion is a type of partial corrosion. Due to partial damage of the metal passive film, a certain area of the metal surface quickly forms hemispherical pits, which is called point corrosion. Point corrosion is mainly caused by Cr. To avoid pitting corrosion, Mo containing steel (usually 2.5% Mo) can be used, and with the increase of Cr content and temperature, Mo content should also be added accordingly.
5、 Crevice corrosion
Gap corrosion is a type of partial corrosion, which refers to the corrosion caused by the partial damage of the metal passivation film due to the decrease in oxygen content and/or pH in the gap after it is filled with corrosive liquid. Stainless steel often experiences crevice corrosion in Cl - solution. The mechanisms of crevice corrosion and pitting corrosion are very similar. Both are due to the effect of Cl -
6、 Stress corrosion
The reason for the occurrence of stress corrosion is that the corrosive liquid touches the surface of the pump, and the contact surface is subjected to stress.
Austenitic Cr Ni steel in Cl liquid is prone to stress corrosion. The temperature at which stress corrosion occurs is above 80 degrees, and using austenitic Cr Ni steel with high Ni content can avoid stress corrosion.
7、 Wear and corrosion
This corrosion is caused by the high-speed movement of liquid eroding the surface of the water pump during overcurrent. Each type of data has different resistance to wear and corrosion. The order from poor to good is: ferritic Cr steel, austenitic ferritic steel, austenitic steel.
8、 Cavitation corrosion
There are many manifestations of cavitation in magnetic pumps, and cavitation can also cause corrosion of the magnetic pump. Advocating the use of cavitation resistant materials for pumps, including austenitic stainless steel, 12% chromium steel, hard alloys, and phosphor bronze.

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