The technicians of Zoomlian Pumps found that the main reason for the failure of the water pump is corrosion. Whether it is a mixed flow pump or a centrifugal pump, or a stainless steel corrosion-resistant pump, fluoroplastic pump, or ordinary cast iron pump, corrosion will occur during use. We cannot prevent the water pump from being corroded, but can only reduce the degree of corrosion as much as possible. In order to reduce the degree of corrosion of water pumps, it is necessary to understand what corrosion phenomena exist, and then solve them according to these phenomena. How to solve the acid corrosion of the pump?
What are the types of water pump corrosion?
Localized corrosion: Localized corrosion is also called non-uniform corrosion. Its characteristic is concentrated in a certain area of the surface, while other parts are not corroded or slightly corroded.
general corrosion: general corrosion is also called uniform corrosion, which is characterized by corrosion in the surface area. Comprehensive corrosion is easy to be found or detected, so the risk of this occurrence is relatively small.
There are usually 8 types of water pump corrosion phenomena:
1. Abrasion corrosion: refers to the erosion and corrosion of metal surfaces by high-speed fluids. Fluid erosion erosion is different from the erosion caused by solid particles in the medium.
Water pumps will wear out 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 wear and corrosion resistance.
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 the anode metal to corrode.
The measures 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 local corrosion, which mainly refers to the phenomenon of precipitation of chromium carbide between stainless steel grains. Intergranular corrosion is extremely corrosive to stainless steel materials.
The measures to prevent intergranular corrosion are: annealing the stainless steel, or using ultra-low carbon stainless steel (C<0.03%).
4. Uniform corrosion: Uniform corrosion refers to uniform chemical corrosion on the entire metal surface when corrosive liquid contacts the metal surface.
This is the most common type of corrosion, and it is also the least harmful one. The measures to prevent uniform corrosion are: adopt suitable materials (including non-metals), and consider sufficient corrosion margin when designing the 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 of oxygen content in the crevice and/or the decrease of pH value after the crevice is filled with corrosive liquid.
The use of metals with high Cr and M0 content can prevent or reduce the occurrence of crevice corrosion.
6. Pitting corrosion: Pitting corrosion is a localized corrosion. The partial destruction of the metal passive film causes the rapid formation of hemispherical pits in a local area of the metal surface. This phenomenon is called pitting corrosion. Pitting corrosion is mainly caused by Cl-.
"M0 steel (usually 2.5% Mo) can be used to prevent pitting corrosion, 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 local corrosion caused by the combined action of stress and corrosion environment.
The measure to prevent stress corrosion is to use austenitic Cr-Ni steel with high Ni content (Ni; >25%-30%).
8. Cavitation corrosion: The corrosion caused by cavitation in the pump is called cavitation corrosion. The most practical and simple way to prevent cavitation corrosion is to prevent cavitation.
Water pump cavitation cannot be prevented. Cavitation occurs more or less during pump operation. For those pumps that often produce cavitation corrosion, cavitation resistant materials can be used to increase their cavitation resistance.
