Valve corrosion is a common problem in the use of valves, especially in corrosive environments such as chemical, petroleum, and ocean. Corrosion not only shortens the service life of valves, but may also cause leakage, equipment damage, and even safety accidents. The following are the basic knowledge and preventive measures of valve corrosion:
I. Basic knowledge of valve corrosion
1. Definition of corrosion
Corrosion refers to the chemical or electrochemical reaction of metal materials under the action of the environment (such as moisture, chemical media, etc.), resulting in the degradation or destruction of material performance.
2. Types of corrosion
According to the mechanism and manifestation of corrosion, valve corrosion is mainly divided into the following categories:
Local corrosion: Corrosion is concentrated in certain areas of the metal surface, such as pitting and crevice corrosion. Common in environments containing chloride ion media or damaged passivation films.
Electrochemical corrosion: Corrosion caused by the potential difference between different metals. Common in environments where dissimilar metals are in contact or electrolytes exist.
Wear corrosion: Corrosion caused by the combined action of corrosive media and mechanical wear. Commonly seen in high-speed fluids or media containing solid particles.
3. Factors affecting corrosion
Medium characteristics: acidity, alkalinity, oxidizability, chloride ion concentration, etc. of the medium.
Material characteristics: chemical composition, surface state, heat treatment process, etc. of the metal.
Environmental conditions: temperature, pressure, flow rate, humidity, etc.
Design factors: whether the valve structure design is reasonable, and whether there are dead corners or gaps.
2. Preventive measures for valve corrosion
1. Reasonable material selection
Choose appropriate valve materials according to the corrosiveness of the medium:
Stainless steel (such as 304, 316L): Suitable for general corrosive media.
Duplex stainless steel: Suitable for high chloride ion environments.
Hastelloy and titanium alloys: Suitable for highly corrosive media.
Lined valves: Such as fluorine lining and rubber lining, suitable for strong acid and strong alkali media.
2. Surface treatment
Improve the corrosion resistance of valves through surface treatment:
Electroplating: such as chrome plating and nickel plating.
Spraying: such as spraying ceramics and epoxy resins.
Passivation treatment: Improve the corrosion resistance of stainless steel.
3. Optimize design
Avoid dead corners and gaps in the valve structure to reduce the accumulation of corrosive media.
Use streamlined design to reduce the erosion and corrosion of the valve by the fluid.
4. Control environmental conditions
Control the temperature, pressure and flow rate of the medium to avoid accelerated corrosion under extreme conditions.
Add corrosion inhibitors to the medium to reduce the corrosion rate.
5. Cathodic protection
Protect the valve from electrochemical corrosion by means of impressed current or sacrificial anode.
6. Regular maintenance
Regularly check the valve surface for signs of corrosion, and clean and repair it in time.
Repair or replace the coating on the easily corrosive parts.
7. Use anti-corrosion coating
Apply anti-corrosion coating (such as epoxy coating, polyurethane coating) on the valve surface to isolate the corrosive medium.
8. Avoid contact between dissimilar metals
When connecting the valve to the pipeline, avoid direct contact between dissimilar metals to prevent electrochemical corrosion.
IV. Summary
Valve corrosion is a complex process affected by many factors. Through reasonable material selection, optimized design, control of environmental conditions and regular maintenance, corrosion can be effectively prevented and slowed, the service life of the valve can be extended, and the safe operation of the system can be ensured. In practical applications, appropriate anti-corrosion measures need to be selected according to specific working conditions.