How to Improve the Durability of Ultra-High Pressure Valve

Ultra-high pressure valves are widely used in high-pressure and high-velocity fluid environments, particularly in industries such as oil, chemical, and energy. However, these industrial valves often face challenges related to cavitation and erosion wear during operation. Understanding the causes of these failures and their influencing factors, as well as taking effective measures to improve the valves' resistance to cavitation and erosion, is essential for ensuring the safety and stability of systems.

Analysis of Failure Causes

Ultra-high pressure valves play a crucial role in high-pressure fluid environments, yet they are often at risk of cavitation and erosion wear in practical applications. These failure phenomena can affect valve performance and pose overall safety risks to the system.

1. Cavitation

Cavitation occurs when fluid pressure drops, leading to the formation of bubbles that subsequently collapse and violently impact the valve material. The occurrence of cavitation is typically related to the following factors:
Fluid Velocity: High flow rates can cause local pressure drops, accelerating bubble formation. These bubbles rapidly collapse when pressure is restored, generating shock waves.
Fluid Characteristics: Factors such as temperature, viscosity, and gas content of the fluid can also influence cavitation. For instance, low-temperature fluids may increase the likelihood of bubble formation.
Cavitation can cause microscopic damage to the valve material's surface, potentially leading to macrostructural failure and, in severe cases, valve failure.

2. Erosion Wear

Erosion is wear caused by the high-speed impact of fluid particles against the valve surface. The main factors influencing erosion wear include:
Particle Characteristics: The size, shape, and hardness of solid particles directly affect the severity of erosion. Larger or harder particles cause more significant wear.
Operating Pressure: Higher operating pressures result in greater impact forces on the valve, increasing the extent of wear. Especially under high-pressure conditions, the kinetic energy of the fluid increases, making erosion more pronounced.

3. Overview of Influencing Factors

Material Mechanical Properties: The hardness, yield point, and fatigue strength of valve materials are key indicators of wear resistance. Different materials may perform significantly differently in various environments.
Fluid Dynamics: The design of the valve and the characteristics of fluid flow significantly impact cavitation and erosion. Uneven flow or localized turbulence can exacerbate wear.
Environmental Effects: External factors like temperature and chemical composition can also affect valve performance. For example, corrosive environments may accelerate valve aging and failure.

Methods to Improve Resistance to Cavitation and Erosion

To enhance the resistance of ultra-high pressure valves to erosion wear, various methods and technologies can be employed, primarily including material selection, alloying and heat treatment, surface treatment techniques, and new structural designs.

1. Material Selection

Choosing the right materials is fundamental to improving the valve's resistance to cavitation and erosion.

Corrosion-Resistant Materials: Selecting materials with high hardness and acid-resistant protective films, such as titanium alloys or special alloys, can enhance wear resistance.
High Yield Point Materials: Using materials with high yield strength and stability can effectively improve the valve's pressure-bearing capacity and fatigue resistance.
High Fatigue Strength Materials: Selecting materials with high fatigue strength ensures stability under high-frequency vibrations.
Additionally, alloyed materials (such as chromium-molybdenum and tungsten alloys) can offer excellent corrosion and wear resistance.

2. Alloying and Heat Treatment

Two important methods to enhance material performance include:

Alloying: By changing the chemical composition of steel, new materials with special properties can be developed. For example, adding elements like molybdenum and nickel can improve corrosion resistance and strength while enhancing high-temperature performance.
Heat Treatment: Different heating, holding, and cooling processes can alter the microstructure of materials. This process must avoid oxidation and decarburization to ensure material quality. For instance, W18Cr4V materials significantly improve impact toughness and service life after vacuum heat treatment.
Specific heat treatment methods include quenching, tempering, and normalizing. Proper treatment processes can significantly enhance the overall performance of materials.

3. Surface Treatment Techniques

Surface treatment is an important means of improving a valve's wear resistance, commonly involving methods such as:

Surface Hardening: Techniques like flame heating and medium-frequency heating enhance surface hardness, making it more wear-resistant under high-pressure impacts.
Carburizing and Nitriding: These processes improve surface hardness and wear resistance, creating a wear-resistant surface layer that significantly boosts erosion resistance.
Laser Hardening and CVD/PVD Technologies: Utilizing laser techniques and chemical vapor deposition methods can enhance surface properties, improving both corrosion and wear resistance.
These surface treatment methods can greatly extend the lifespan and performance of valves without altering the overall material properties.

4. New Structural Design

Optimizing valve structures can further enhance their performance.

Self-tightening Replaceable Seat Design: This design prevents the valve disc from being directly impacted by the medium, significantly reducing erosion wear. When the valve is closed, the disc is only subject to a small spring force, minimizing the impact on the seat and enhancing sealing performance and lifespan.

Venturi Nozzle Design: Adopting a Venturi shape for the valve seat and outlet can effectively reduce cavitation and flashing phenomena, decreasing fluid impact forces.
Flow Restriction Hole Design: Installing flow restriction holes before or after the valve absorbs some pressure drop, reducing the pressure differential across the valve and mitigating cavitation effects. This design can also reduce pressure fluctuations, enhancing stability.

Mechanical Analysis and Valve Stability

From a mechanical perspective, cone valves are prone to vibration and fatigue failure under the impact of high-pressure and high-velocity fluids. The design of cone valves makes them susceptible to vibration and fatigue failure under strong impacts. In contrast, wedge valves have a valve core designed with a sloped cylindrical shape, providing better stability during operation. The lower end of the valve disc tightly contacts the seat, minimizing vibration amplitude and reducing the risk of failure due to vibration.

1. Structural Stability Analysis

Wedge valves, due to their unique structure, effectively reduce stress concentration and minimize fatigue damage caused by vibrations under high-pressure fluids. Additionally, the design of wedge valves can lower the risk of cavitation, further extending valve life.

2. Methods to Mitigate Cavitation

Installing flow restriction holes before or after the valve absorbs some pressure drop, thereby reducing pressure differential and mitigating cavitation effects. If flashing occurs, designs that avoid bottom-near-side outflow should be preferred to minimize valve impact. Reasonable design of flow paths can significantly improve fluid flow conditions and reduce instability.

Conclusion

In summary, addressing the causes of failure in ultra-high pressure valves through appropriate material selection, alloying and heat treatment, surface treatment technologies, and innovative structural designs can effectively enhance their resistance to cavitation and erosion. As working pressures increase, valve designs should be simplified to ensure stability and reliability under extreme conditions. Implementing these measures not only extends the service life of ultra-high pressure valves but also enhances their overall performance, providing stronger safety guarantees for the operations in related industries.