8 types of corrosion phenomena in water pumps

There are usually 8 types of corrosion phenomena in water pumps:

1. Wear corrosion: refers to the erosion and corrosion of metal surfaces by high-speed fluid. Fluid erosion, wear and corrosion are different from the abrasion caused when the medium contains solid particles.

The water pump will produce wear during operation, so we should try our best to use materials with good wear resistance to reduce wear and corrosion. Of course, different materials have different resistance to wear and corrosion.

2. Electrochemical corrosion: 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.

To prevent electrochemical corrosion, one is to use a sacrificial anode to protect the cathode metal; the other is to use the same metal material for the flow channel of the pump.

3. Intergranular corrosion: Intergranular corrosion is a kind of partial corrosion, which mainly refers to the precipitation of chromium carbide between stainless steel grains. Intergranular corrosion is extremely corrosive to stainless steel materials.

Measures to avoid intergranular corrosion are: anneal stainless steel, or use ultra-low carbon stainless steel (C<0.03%).

4. Average corrosion: Average corrosion means that when corrosive liquid contacts the metal surface, uniform chemical corrosion occurs on the entire metal surface.

This is a common type of corrosion, and it is also a less harmful type of corrosion. Measures to avoid uniform corrosion are: use appropriate materials (including non-metals) and consider sufficient corrosion margin when designing the water pump.

5. Crevice corrosion: Crevice corrosion is a kind of local corrosion, which refers to the corrosion caused by the partial destruction of the metal passive film due to the decrease in oxygen content and/or the decrease in pH value in the gap after the gap is filled with corrosive liquid.

The use of metals with high Cr and M0 contents can avoid or reduce the occurrence of crevice corrosion.

6. Pitting corrosion: Pitting corrosion is a kind of partial corrosion. Due to the partial destruction of the metal passive film, hemispherical pits are rapidly formed in certain areas of the metal surface. This phenomenon is called pitting corrosion. Pitting corrosion is mainly caused by Cl.

To avoid pitting corrosion, steel containing M0 (usually 2.5% Mo) can be used, and as the Cl content and temperature increase, the M0 content should also increase accordingly.

7. Stress corrosion: Stress corrosion refers to a kind of partial corrosion caused by the combined action of stress and corrosive environment.

The measure to avoid stress corrosion is to use austenitic Cr-Ni steel with high Ni content (Ni; >25% to 30%).

8. Cavitation corrosion: The corrosion caused when cavitation occurs in the pump is called cavitation corrosion. A practical and simple method to prevent cavitation corrosion is to prevent cavitation from occurring.

Water pump cavitation cannot be prevented. Cavitation will occur more or less during the operation of the water pump. For those water pumps that often produce cavitation corrosion, anti-cavitation materials can be used to increase their cavitation resistance.