Corrosion of the valve is usually understood as the damage to the metal material of the valve under the action of a chemical or electrochemical environment.
Since the “corrosion” phenomenon occurs in the spontaneous interaction between the metal and the surrounding environment, how to isolate the metal from the surrounding environment or use more non-metallic synthetic materials is the focus of corrosion prevention.
The valve body (including the bonnet) of the valve occupies most of the weight of the valve and is in constant contact with the medium, so the selection of the valve often starts from the valve body material.
The corrosion of the valve body usually be 2 types – Chemical corrosion & Electrochemical corrosion.
The corrosion rate can be divided into six levels as below:
1. Complete corrosion resistance: the corrosion rate is less than 0.001 mm/year;
2. Extremely resistant to corrosion: the corrosion rate is 0.001 to 0.01 mm/year;
3.Corrosion resistance: the corrosion rate is 0.01 to 0.1 mm/year;
4. Still corrosion resistant: the corrosion rate is 0.1 to 1.0 mm/year;
5. Poor corrosion resistance: the corrosion rate is 1.0 to 10 mm/year;
6. Not corrosion resistant: the corrosion rate is greater than 10 mm/year.
How to prevent valve corrosion?
The anti-corrosion of the valve body is mainly based on the correct selection of materials. Although there are abundant anti-corrosion materials, it is not easy to choose the right one, because the problem of corrosion is very complicated.
For example, sulfuric acid is very corrosive to steel when the concentration is low, and when the concentration is high, it will produce steel.
Hydrogen is very corrosive to steel only under high temperature and high pressure.When chlorine is in a dry state, it is not very corrosive, but when there is a certain humidity, it is very corrosive, and many materials cannot be used.
The difficulty in selecting the valve body material is that it can not only consider the corrosion problem, but also must consider the pressure and temperature resistance.
The second is to take lining measures, such as lining lead, lining aluminum, lining engineering plastics, lining natural rubber and various synthetic rubbers. If the media conditions permit, this is an economical method.
The third is the main material of the fluorine-lined valve can often be very effective in preventing corrosion when the pressure and temperature are not high.
In addition, the outer surface of the valve body is also corroded by the atmosphere, and generally steel materials are protected by painting.
