Metal valve can be said to be a key component structure that can easily corrode failure in engineering equipment. Generally, the seal, valve stems, film, small spring and other valves of the metal valve generally use first -level materials, valve body, valve cover, etc. Or three materials, for high-voltage, toxic, flammable, explosive, radioactive media valves, they use small corrosive materials.

Under the complex working conditions such as atmosphere or solution, the metal valve not only occurs uniformly corrosion on the metal surface at all times, but also is prone to etching, gap corrosion, crystal corrosion, delay corrosion, stress corrosion, fatigue corrosion, and fatigue corrosion in the local location of the metal. Selective corrosion, wear and corrosion, air blister corrosion, vibration corrosion, hydrogen erosion, and other local corrosion.

Anticorrosive measures for metal valves

1. Select corrosion-resistant materials according to the corrosive medium
   In the actual production, the corrosion of the medium is very complicated. Even the valve materials used in the medium, the concentration, temperature, and pressure of the medium are different, and the medium is not as corrosive of the material. Each increase of the medium temperature increases by about 1 to 3 times. The concentration of the medium has a great impact on the corrosion of the valve material. For example, in the small concentration of sulfuric acid with a small concentration, the corrosion is small. When the concentration exceeds 96%, the corrosion rises sharply. In contrast, carbon steel is severely corrosive when the concentration of sulfuric acid is about 50%. When the concentration increases to more than 6%, the corrosion decreases sharply. For example, aluminum is very corrosive in concentrations of more than 80%, but corrosion is severe in medium and low concentrations of nitric acid. Although stainless steel has strong corrosion resistance to dilute nitrate, corrosion in more than 95%of concentrated nitric acid is aggravated.

From the above cases, it can be seen that the correct selection of valve materials should be analyzed according to the specific situation, analyzing various factors that affect corrosion, and selected materials according to the relevant anticorrosive manual.

2. Use non -metallic materials
   Non -metallic corrosion resistance is good. As long as the valve uses temperature and pressure meets the requirements of non -metallic materials, it can not only solve the problem of corrosion, but also save valuable metals. The valve body, valve cover, lining, lining, cover and other commonly used non -metallic materials. As for the pads, the fillers are mainly made of non -metallic materials. Plastics such as polytimonia, chloride polyether, etc., as well as rubber such as natural rubber, chlorine rubber, chip Qing rubber as a valve lining, and the main body of the valve body and valve cover is made of cast iron and carbon steel. That is to ensure the strength of the valve and the valve is not corroded. The pipe valve is also designed based on the good corrosion performance and mutation performance of the rubber. Now more and more right plastics such as nylon, polytefloxyl dilute, use natural rubber and synthetic rubber as a variety of seals, sealing rings, for all kinds of valves, these non -metals used for sealing surfaces are used as a seal surface. Materials are not only resistant to corrosion, but also have good sealing performance, especially suitable for use in particle media. Of course, their strength and heat resistance are low, and the scope of application is limited. The emergence of flexible graphite has entered the high temperature domain, solving the problem of long -term difficulty in fillers and pads, and it is a good high -temperature lubricant.
3. Metal surface treatment
   Valve connecting snails are commonly used with galvanized, chrome -plated, oxidation (blue) treatment to improve the ability to resist atmosphere and agglomerate corrosion. In addition to the above methods, other fasteners are also treated with surface treatment according to the situation.

Close -cover and low -caliber closure pieces often use surface processes and other surface processes such as nitrogen and boron, improve its corrosion resistance and abrasion resistance. The valve petals made by 38CRMOALA, the nitrogen seepage layer ≥0.4mm.

Valvers’ anticorrosive anti -corruption uses surface treatment processes such as nitrogen, boron, chrome, nickel -plating, etc., to improve its erosion resistance, erosion resistance and rubbing scratching performance. Different surface treatment should be suitable for different valve stem materials and working environments. Valves that are contacting with asbestos and asbestos in the atmosphere and water vapor media can be used. The valves in the hydrogen sulfurization atmosphere have better protective performance with electroplating high phosphorus nickel plating layers; 38CRMOALA can also resist with ions and gas nitride, but it is not advisable to use a hard chromium plating; The carbon steel with gas nitrogen can also resist the corrosion of ammonia, while all phosphate coating is not ammonia corrosion; it has a good corrosion resistance and comprehensive performance through the gas nitride 38CRMOALA material.

Small diameter valves and hand wheels are often chrome -plated to improve their corrosion resistance and decorate valves.

4. Hot spray coating
   Thermal spray is a process block for coating, which has become a new technology for material surface protection. It uses high -energy density thermal source (gas burning flames, arcs, plasma arcs, electric heating, gas explosion, etc.) to heat and melt metal or non -metallic materials, and spray it into the basic surface of the processing in the form of atomization to form a spray coating. , Or heat the basic surface at the same time, make the coating melt again on the surface of the substrate, forming the surface reinforcement process method of the spray layer. Most metals and alloys, metal oxide ceramics, metal ceramic complexes, and hard metal compounds can be used to form coatings on metal or non -metal matrix.

Thermal spraying can improve its surface corrosion resistance, abrasion resistance, high temperature resistance and other performance, and extend the service life. The special function coating of thermal spray has special properties such as heat insulation, margin (or heterodine), grinding sealing, self -lubrication, thermal radiation, and electromagnetic shielding; the use of thermal spray can be repaired.

05, spray brush paint
Coatings are widely used for anticorrosive methods, and it is an indispensable anticorrosive material and identification logo on valve products. Coatings are also non -metallic materials. It is usually prepared by synthetic resin, rubber pulp, vegetable oil, solvents, etc., covering the metal surface, interval and atmospheric atmosphere to achieve the purpose of anticorrosion. Coatings are mainly used in environmentally corrosive environments such as water, salt water, seawater, and atmosphere. Anticorrosive paint is commonly used in the inner cavity of the valve to prevent medium such as water and air from corrosion of the valve. There are different colors in the paint to indicate the materials used by Fan. Valve spraying paint coatings, in half a year to year.

6. Add a corrosion agent
   The mechanism of the corrosion control of corrosion is that it promotes the batteryization. The corrosion agent is mainly used for media and fillers. Adding a corrosion agent in the medium can slow down the corrosion of the equipment and valves. For example, chromium nickel stainless steel becomes a large solubility range in a large soluble range in a non-oxygen sulfuric acid, and the corrosion is severe, but a small amount of copper sulfate or nitrate is added. The oxidant can turn stainless steel into a dull state, generate a layer of protective film on the surface, and prevent the erosion of the medium. In hydrochloric acid, if a small amount of oxidant is added, it can reduce the corrosion of titanium. Valve tests are commonly used as a medium for test pressure, which can easily cause corrosion of the valve. Adding a small amount of sodium nitrite to water to prevent water from corrosion of the valve. Asbestos contains chloride, which has a large corrosion of the valve stem. If the washing method of steamed water can be used to reduce the content of chloride, but this method is much more difficult in implementation. It cannot be generally promoted. The ester is suitable for special needs.

In order to protect the valve stems and prevent the corrosion of asbestos filler, in the asbestos filler, apply the composite and sacrifice metal on the valve stem. The corrosion agent can generate layer passivation film by sodium nitrite and sodium chromate, which improves the corrosion resistance of the valve stem; the solvent can slowly dissolve the corrosion agent, and it can lubricate the effect; in the asbestos; in the asbestos Add zinc powder as sacrificing metals. In fact, zinc is also a corrosion agent. It can first combine with chloride in asbestos to reduce the chance of contact with the metal with valve stem metal, thereby achieving the purpose of anti-corrosion. If the coatings are added with a corrosion agent such as Hongdan and calcium lead, spraying brushes on the surface of the valve can prevent the atmosphere from corrosion.

7. Electrochemical protection
   There are two types of electrochemical protection: yang and yin protection. If zinc is used to protect iron, zinc is corroded, zinc is called sacrifice metal. In production practice, Yang Yang protection is less, and more yin protection is used. The large-scale valve and important valve adopt this yin protection method, which is a method of economically simple and effective. Zinc is added to asbestos, and the protection valve stem also belongs to the yin protection method.
8. Control the corrosion environment
   The so-called environment has two types: broad and narrow sense. The broad environment refers to the surrounding environment and its internal circulation medium around the valve installation area; the narrow environment refers to the conditions of the valve installation area. Most environments cannot be controlled, and the production process cannot be changed arbitrarily. Only in the absence of damage to products, processes, etc., the method of controlling the environment can be used, such as boiler water oxygen removal, alkali regulating pH value in the refining process, etc. Starting from this view, the above -mentioned additives and electrochemical protection are also controlling the corrosive environment.

The atmosphere is full of dust, water vapor, and smoke. Especially in the production environment, such as toxic gases and micro-powder emitted by smoke and equipment, it will cause different degrees of corrosion of the valve. The operator shall regularly clean, blow off the valve, and refuel regularly in accordance with the provisions of the operating regulations. This is an effective measure to control the environmental corrosion of the environment. The valve stem installation protective cover, the ground valve set the ground, the surface of the valve surface spray paint, etc. This is a method to prevent corrosive material erosion valves. The increase in ambient temperature and air pollution, especially the equipment and valves in the closed environment, will accelerate its corrosion. Try to use an open plant or ventilation and cooling measures to slow down environmental corrosion.

9. Improve processing process and valve structure form
   The anti-corrosion protection of the valve is a problem that starts from design. A valve product with reasonable structural design and correct process and methods. It is undoubtedly good for slowing the corrosion of the valve.

Therefore, the design and manufacturing departments respond to those components that are unreasonable, incorrect in the process and methods of the structural design, and corrosive components. It should be improved and it should be suitable for the requirements of various conditions under different operating conditions.

10. Corrosion type of different valve components

Prevent stainless steel valve parts from generating crystal corrosion methods for “solid-soluble quenching”, that is, heating to about 1100 ° C about water quenching, using Octoba stainless steel with titanium-containing and cymbal, and carbon content below 0.03%to reduce chromium carbonization Express.

Stress corrosion occurs under the action of corrosion and stress at the same time to prevent stress corrosion. It eliminates or reduces welding through heat treatment or reduces the stress produced in cold processing. Spray anti -corrosion coating. Add measures such as a corrosion agent and pressure stress.

The corrosion of wear and corrosion is the corrosion form produced by fluids on metal wear and corrosion alternation. It is a common seed corrosion of valves. This corrosion occurs on the cover. Methods: choose corrosion-resistant and wear-resistant materials, improve structural design, and use in protection.

Modern corrosion is the two parts of mutual contact with each other to withstand loads at the same time, and the contact surface is damaged due to vibration and sliding. Capitated corrosion occurs at the bolt connection, and the valve stem and the closure part are connected to the connection, between the pearl bearing and the shaft. You can use coating lubricating oil, reduce friction, surface phosphorus, use hard alloys, and use spray tile treatment or cold processing to improve the surface hardness method.

After welding, we should try to use corresponding protection measures such as annealing treatment to improve the roughness of the surface of the valve stem processing and the roughness of other valve parts. The higher the surface roughness, the stronger the resistance. Improve the processing process and structure of fillers and pads, use flexible graphite and plastic fillers, as well as flexible graphite stickers and adhesive pads and polyfluoro Barbilit pads, which can improve the sealing performance, reduce ground valve stems and flang sealing Corrosion.