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Cause and Effect of Corrosion of Pneumatic Ball Valves (Part 3)

 6. Add corrosion inhibitor
The mechanism by which the corrosion inhibitor controls corrosion is that it promotes the polarization of the battery.
Corrosion inhibitors are mainly used in media and fillers. Adding a corrosion inhibitor to the medium can slow down the corrosion of equipment and valves. Such as oxidant, can make the stainless steel into a passive state, and a protective film is formed on the surface to prevent the corrosion of the medium. In hydrochloric acid, if a small amount of oxidant is added, the corrosion of titanium can be reduced.
Water-sealed globe valve pressure test often uses water as the pressure test medium, which is easy to cause corrosion of the valve. Adding a small amount of sodium nitrite to the water can prevent water from corroding the valve.
The asbestos packing contains chloride, which greatly corrodes the valve stem. If the method of washing with distilled water is used, the chloride content can be reduced. However, this method is much more difficult to implement and cannot be generalized. The ester is suitable for special needs.
In order to protect the valve stem and prevent the corrosion of the asbestos filler, the valve stem is filled with corrosion inhibitor and sacrificial metal in the asbestos filler. The corrosion inhibitor consists of sodium nitrite and sodium chromate can make the valve stem surface passivation Membrane to improve the corrosion resistance of the valve stem; the solvent can slowly dissolve the corrosion inhibitor and can play a lubricating role; adding zinc powder to asbestos as a sacrificial metal, in fact, zinc is also a corrosion inhibitor, it can Firstly, it is combined with chloride in asbestos, so that the chance of chloride contacting with the stem metal is greatly reduced, so as to achieve the purpose of anticorrosion. If corrosion inhibitors such as red lead and calcium lead acid are added to the paint, spraying on the valve surface can prevent it Atmospheric corrosion.

Water-Sealed Globe Valve
Water-Sealed Globe Valve

7. Thermal spraying
Thermal spraying is a type of process box for preparing coatings, and has become one of the new technologies for surface protection of materials.
It uses a high-energy density heat source (gas combustion flame, electric arc, plasma arc, electric heating, gas explosion, etc.) to heat and melt metal or non-metallic materials and spray it onto the pretreated basic surface in the form of atomization to form a spray coating , Or heating the basic surface at the same time to make the coating melt again on the surface of the substrate to form the surface strengthening process method of the spray welding layer.
Most metals and their alloys, metal oxide ceramics, cermet composites, and hard metal compounds can be coated on metallic or non-metallic substrates by one or several thermal spraying methods.
Thermal spraying can improve its surface corrosion resistance, wear resistance, high temperature resistance, etc., and extend its service life. Thermal spray special functional coating, with special properties such as heat insulation, insulation (or different electricity), wearable sealing, self-lubrication, heat radiation, electromagnetic shielding, etc .; parts can be repaired by thermal spraying.
8. Control the corrosive environment
The so-called environment is broadly defined and narrowly defined. The broadly defined environment refers to the environment around the aerodynamic ball valve installation and its internal circulation medium; the narrowly defined environment refers to the conditions around the valve installation.
Most environments cannot be controlled and the production process cannot be changed arbitrarily. Only in the case of no damage to products, processes, etc., environmental control methods can be used, such as deoxidation of boiler water, adjustment of PH value by alkali in oil refining process, etc. From this point of view, the above addition of corrosion inhibitors, electrochemical protection, etc. also belong to the control of corrosive environments.
The atmosphere is full of dust, water vapor, smoke, especially in the production environment, such as smoke halogen, toxic gases and fine powder emitted by the equipment, will produce different degrees of corrosion to the valve.
The operator should regularly clean and purge the valve and refuel regularly according to the provisions in the operating regulations. This is an effective measure to control environmental corrosion. The valve stem is installed with a protective cover, the ground valve is provided with a ground well, and the surface of the valve is sprayed with paint, etc. This is a method to prevent the corrosive substances from eroding the valve.
Increased ambient temperature and air pollution, especially equipment and valves in a closed environment, will accelerate their corrosion. Open plants should be used as much as possible, or ventilation and cooling measures should be adopted to reduce environmental corrosion.
9. Improve processing technology and valve structure
The anti-corrosion protection of the valve is a problem that has been considered from the design. A valve product with a reasonable structural design and a correct process method will undoubtedly have a good effect on reducing the corrosion of the valve.
Therefore, the design and manufacturing department should improve the components that are unreasonable in structural design, incorrect in the process and easily cause corrosion, and be adapted to the requirements of various working conditions.

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