Valve Surface Treatment: Key to Enhance Performance

In the industrial field, valves, as important components in pipeline systems, directly affect the operating efficiency and safety of the entire system through their performance and service life. Valve surface treatment technology, as an effective means of significantly enhancing valve performance, is attracting more and more attention. This article will introduce in detail several common valve surface treatment methods, including electroplating, electroless plating, thermal spraying, coating, and nitriding treatment, helping readers better understand the importance and advantages of these technologies in practical applications.

Electroplating: Putting a "Metal Coat" on Valves

Electroplating is a method that uses the principle of electrolysis to deposit a layer of metal or alloy on the valve surface. Specifically, the valve is used as the cathode and placed in an electrolyte containing metal ions to be plated. After the power is turned on, the metal ions gain electrons on the valve surface and are reduced to metal atoms, gradually forming a uniform and dense coating. This process not only improves the corrosion resistance and wear resistance of the valve but also enhances its appearance.

1. Nickel Plating

Nickel plating is one of the most common types of electroplating. It has good corrosion resistance, wear resistance, and luster. In many media, nickel coatings can effectively protect the valve substrate, especially in some non-oxidizing acids and alkali solutions, where it shows good stability. For example, in chemical pipelines, media are often corrosive, and nickel-plated valves can effectively resist corrosion and ensure normal valve operation. At the same time, the nickel plating layer can increase the hardness of the valve surface and enhance its scratch resistance.

Nickel plating processes can be divided into dull nickel, bright nickel, and electroless nickel plating according to the characteristics of the nickel layer. Among them, electroless nickel-phosphorus alloy plating has a porosity of less than 0.1/cm², providing extremely high corrosion resistance. In marine engineering, valves treated with electroless nickel-phosphorus alloy plating showed no obvious corrosion after 1000 hours of salt spray testing, while ordinary galvanized valves could only withstand 240 hours. This fully demonstrates the excellent performance of the electroless nickel-phosphorus alloy layer in harsh environments.

2. Chromium Plating

Chromium plating is known for its high hardness, good wear resistance, and excellent corrosion resistance. A chromium-plated layer can form a hard protective film on the valve surface, effectively preventing wear and corrosion. In addition, chromium-plated valves are bright and attractive, often used in applications with higher appearance requirements, such as building water supply and drainage systems and high-end sanitary equipment.

For example, in hard chromium plating, the process includes degreasing → pickling → pre-copper plating → chromium plating → post-treatment, with each step having a decisive impact on coating quality. In the aerospace field, titanium alloy valves after hard chromium plating had their surface hardness increased from HV300 to HV1000, improving wear resistance by 5 times, effectively solving the wear problem of valves in aviation fuel systems. This not only extended the service life of the valves but also ensured the safe operation of aerospace equipment.

Electroless Plating: Uniform Coating Without Current

Electroless plating is a plating method in which metal ions in the solution are reduced and deposited onto the valve surface using a reducing agent without external current. It relies on specific chemical reactions, where metal ions are reduced to metal elements under the catalytic action of the valve surface, forming a coating. The advantage of this process is its excellent coating uniformity. Regardless of how complex the valve shape is, a uniform coating thickness can be achieved. Moreover, electroless plating does not require an external power supply, is relatively simple to operate, and is suitable for various valve materials.

1. Electroless Nickel-Phosphorus Alloy

The electroless nickel-phosphorus alloy layer is an important application of electroless plating. This coating has low porosity and good corrosion resistance and wear resistance. In some high-temperature, high-pressure, and corrosive pipelines in the petrochemical industry, some valves are treated with electroless nickel-phosphorus alloy plating. This treatment enables valves to maintain good performance in harsh working environments, effectively preventing corrosion and erosion of the valve surface, extending valve service life, and reducing accidents and maintenance costs caused by valve damage.

2. Other Electroless Alloy Layers

In addition to nickel-phosphorus alloys, electroless plating can also form other alloy layers, which often have special physical and chemical properties. For example, some electroless alloy layers can replace electroplated hard chromium in specific environments, providing higher hardness and better corrosion resistance to meet the needs of different industrial scenarios.

Thermal Spraying: Strong Protection from High-Temperature Molten Coatings

Thermal spraying is a process in which metal or non-metal powder is heated by a thermal source to a molten or semi-molten state and then sprayed onto the valve surface by high-speed airflow to form a coating with specific properties. Common thermal sources include flame, electric arc, and plasma arc. This process uses a high-temperature thermal source to melt the coating material and spray it onto the valve surface, forming a metallurgical bonding layer to provide strong protection.

1. Zirconia Ceramic Coating

Plasma-sprayed zirconia ceramic coatings can have a porosity controlled below 3%. In high-temperature flue gas pipelines of waste incineration power plants, valves with this coating had their surface temperature reduced by 50℃ and erosion life extended by 4 times. This indicates that zirconia ceramic coatings can significantly improve valve performance in high-temperature environments and reduce operating costs.

2. Tungsten Carbide Coating

Tungsten carbide coatings prepared by high-velocity oxygen fuel (HVOF) spraying have a hardness of up to HV1300. Applied to high-pressure choke valves in shale gas extraction, the service life increased from 3 months to 18 months. The high hardness and wear resistance of this coating make it an ideal choice for high-pressure and high-wear environments.

3. Metal Coatings

Metal coatings such as sprayed zinc and aluminum have good corrosion resistance and conductivity. In atmospheric environments, zinc coatings can form a dense zinc oxide protective film that provides cathodic protection to the valve substrate; aluminum coatings have high-temperature resistance and oxidation resistance, effectively protecting valves in high-temperature environments. These metal coatings not only prevent corrosion but also provide additional functions such as conductivity in specific environments.

Coating: Protective Film Formed by Paint

Coating refers to applying paint on the valve surface, which then forms a protective film after drying and curing. The film-forming substances in the paint form a continuous thin film on the valve surface, providing isolation, protection, and decoration. This process is simple and easy to apply, relatively low cost, but highly effective.

1. Anticorrosive Coating

Anticorrosive coatings, mainly using epoxy resin and polyurethane as film-forming substances, have good corrosion resistance, adhesion, and mechanical properties. They can form a tough protective film on the valve surface, effectively resisting the erosion of corrosive media such as acids, alkalis, and salts. For example, in wastewater treatment plant pipelines, valves are usually coated with epoxy resin anticorrosive paint to prevent harmful substances in wastewater from corroding the valves.

2. High-Temperature Resistant Coating

These coatings use heat-resistant materials such as organosilicon as film-forming substances, maintaining stable performance in high-temperature environments and preventing valve surface oxidation and deformation. In pipelines of high-temperature kilns, valves coated with high-temperature resistant coatings can work normally under long-term high-temperature conditions, extending their service life.

3. Decorative Coating

In building HVAC systems, valves are usually coated with anticorrosive paints in various colors. On the one hand, anticorrosive coatings protect valves from corrosion by moisture, oxygen, and other substances in the air; on the other hand, different colors of coatings can be used to distinguish pipes and valves with different functions, making installation, maintenance, and management more convenient. At the same time, some coatings with special functions, such as fireproof coatings, can improve valve safety in emergencies such as fires.

Nitriding Treatment: Improving Surface Hardness & Wear Resistance

Nitriding treatment is a heat treatment process in which nitrogen atoms penetrate the valve surface, forming a nitrided layer with high hardness, good wear resistance, and strong corrosion resistance. Under certain temperature and medium conditions, nitrogen atoms form nitrides with metal elements in the valve material, thereby changing the microstructure and properties of the valve surface.

1. High Hardness and Wear Resistance

After nitriding treatment, the hardness of the valve surface is greatly improved, generally reaching HV900–1200, much higher than ordinary steel. This gives the valve good wear resistance and scratch resistance, enabling it to withstand higher pressure and harsher working conditions. For example, in aerospace hydraulic systems, valves need to maintain good performance under high-pressure and high-frequency working conditions. Nitrided valves can meet these requirements, with high hardness and wear resistance ensuring the valve is not easily worn during frequent opening and closing, and good corrosion resistance adapting to long-term effects of hydraulic oil and other media, ensuring valve reliability and stability and guaranteeing the safe operation of aerospace equipment.

2. Corrosion Resistance

The nitrided layer also has good corrosion resistance, effectively preventing valve failure in corrosive media. In marine environments, containing large amounts of salt, moisture, and various microorganisms, valves are highly susceptible to corrosion. Chloride ions easily damage the valve’s passivation film, causing pitting, crevice corrosion, and other localized corrosion, while seawater erosion accelerates wear and corrosion of valve surfaces. To deal with marine corrosion, valves often adopt a combination of surface treatments. First, thermal-sprayed zinc or aluminum coatings are applied, using the sacrificial anode protection of zinc and aluminum to provide cathodic protection for the valve substrate. Then, a layer of high-performance anticorrosive coating such as polyurethane is applied on top of the thermal-sprayed coating to further enhance corrosion resistance and impermeability. In addition, some critical valves can also be plated with highly corrosion-resistant nickel-phosphorus alloy layers and sealed to prevent seawater from penetrating coating pores, improving valve protection.

Application Cases: Solutions for Complex Conditions

In practical industrial applications, valves often face various complex working environments, and a single surface treatment method may not meet all requirements. Therefore, comprehensive application of multiple surface treatment technologies has become a common solution.

1. Comprehensive Protection in Marine Environments

In offshore oil drilling platform pipeline systems, valves need to be exposed to the marine environment for long periods. Valves with thermal-sprayed zinc-aluminum coatings combined with anticorrosive coatings can effectively resist seawater corrosion and erosion, ensuring long-term stable operation in harsh marine environments and reducing safety accidents and economic losses caused by valve corrosion and leakage.

2. Reinforced Treatment in High-Temperature and High-Pressure Environments

In high-temperature and high-pressure environments, valves not only need to withstand great pressure but also resist high-temperature oxidation and thermal fatigue. Therefore, valve materials are usually made of high-temperature, high-strength alloy steels such as chromium-molybdenum alloy steel. For surface treatment of such valves, in addition to high-temperature resistant coatings, nitriding treatment or boriding is often used to further improve surface hardness, wear resistance, and high-temperature performance. In hydrocracking reactors and other high-temperature, high-pressure equipment in the petrochemical industry, valves must work at temperatures of hundreds of degrees Celsius and pressures of tens of megapascals. Chromium-molybdenum alloy steel valves treated with nitriding or boriding can maintain good performance under these extreme conditions, ensuring valve sealing and reliability and providing security for the safe and stable operation of petrochemical production processes.

Conclusion

Valve surface treatment technology plays a vital role in modern industry. Through methods such as electroplating, electroless plating, thermal spraying, coating, and nitriding treatment, the corrosion resistance, wear resistance, hardness, and appearance quality of valves can be significantly improved, thereby extending valve service life and enhancing system efficiency and safety. In practical applications, depending on different working environments and requirements, selecting appropriate surface treatment methods or comprehensively applying multiple technologies can provide optimal protection for valves to meet various complex conditions. With continuous technological progress, valve surface treatment technology is also constantly developing and innovating, providing more reliable and efficient solutions for industrial production.