Valve Sealing Surface Damage and Material Selection

In industrial piping systems, valves, as important equipment for controlling fluid flow, have sealing performance that directly affects the safety and reliability of the system. The valve sealing surface, as the key part for achieving sealing, directly impacts the valve's service life and operational efficiency. With the increasing complexity of industrial working conditions, sealing surfaces are prone to damage during long-term operation, which may not only cause medium leakage but also lead to equipment shutdowns and production accidents. Therefore, deeply understanding the causes of sealing surface damage and mastering the key points of material selection are of great significance for ensuring reliable valve operation and extending service life. This article will start from the various causes of sealing surface damage and, combined with material selection principles under different working conditions, provide comprehensive guidance for the design, manufacturing, installation, and maintenance of valve sealing surfaces.

During actual use, sealing surfaces face various complex working conditions, making them prone to damage. The following sections will detail the multiple causes of sealing surface damage, to better understand the underlying mechanisms and provide reference for subsequent material selection and maintenance.

Design Oversights: Negligence during the design stage is an important cause of sealing surface damage. If a valve design does not fully consider actual working conditions, such as the properties of the medium, temperature, and pressure, the sealing surface may not withstand the real working environment. For example, failing to select appropriate sealing surface materials according to the corrosiveness of the medium, or not considering wear resistance and fatigue resistance in structural design, can easily cause the sealing surface to be damaged during use.

Manufacturing Defects: Quality issues in manufacturing can also damage sealing surfaces. These include cracks, pores, and inclusions on the sealing surface, which may result from improper overlay welding and heat treatment selection, as well as poor operation during these processes. For example, if the base metal is blown to the surface during overlay welding, diluting the alloy composition of the sealing surface, it may lead to uneven hardness and poor corrosion resistance. In addition, excessive or insufficient hardness of the sealing surface may also be caused by material selection errors or improper heat treatment.

Improper Material Selection: Material selection is a key factor affecting sealing surface quality. If the material is improperly selected, even with precise design and manufacturing, the sealing surface may not meet actual use requirements. For example, using a cut-off valve as a throttling valve can lead to excessive closing stress and fast or incomplete closure, causing erosion and wear on the sealing surface. Moreover, the corrosion resistance, scratch resistance, and erosion resistance of the sealing surface material must match the actual working conditions, otherwise damage is likely.

Improper Installation: If the sealing surface is not installed correctly, it can lead to abnormal operation and subsequent damage. For example, loose contact between the sealing surface and the valve body or other components, or failure to follow the correct installation sequence and method, can cause the sealing surface to bear additional stress during use, accelerating damage.

Improper Use: Certain improper operations during use can also damage the sealing surface. For example, frequent valve operation, especially under high-temperature and high-pressure conditions, can impose significant mechanical stress on the sealing surface, leading to fatigue damage. Additionally, closing the valve too fast or too slow can cause erosion and wear on the sealing surface.

Inadequate Maintenance: Untimely or improper maintenance can also result in sealing surface damage. If problems occur during use and are not promptly addressed, or if incorrect repair methods and materials are used, the damage to the sealing surface will be further aggravated, shortening its service life.

Medium Corrosion: Corrosion from the medium is one of the main causes of natural sealing surface damage. The medium around the sealing surface can chemically react with it, even without electric current, causing corrosion. For example, acidic or alkaline media may chemically react with the sealing surface material, destroying the surface. In addition, electrochemical corrosion can also damage the sealing surface. When sealing surfaces contact each other, or contact the closure member and valve body, and differences in medium concentration or oxygen concentration exist, a potential difference arises, causing electrochemical corrosion that corrodes the anodic sealing surface.

Medium Erosion: Flowing medium can erode the sealing surface, which is another important factor of natural damage. At certain velocities, suspended fine particles in the medium can collide with the sealing surface, causing local damage. High-velocity medium directly scouring the sealing surface can also cause local damage. Additionally, when the medium mixes or locally vaporizes, bubble collapse impacts the sealing surface, causing further local damage. The alternation of erosion and chemical corrosion strongly corrodes the sealing surface.

Mechanical Wear: During valve opening and closing, the sealing surface can suffer scratches, dents, and extrusion damage. Under high-temperature and high-pressure conditions, atomic diffusion occurs between two sealing surfaces, causing adhesion. When the sealing surfaces move relative to each other, adhesion points are easily torn. Higher surface roughness makes this more likely. Moreover, during valve closure or disc reseating, the sealing surface can be dented or scratched, causing local wear or indentation.

Fatigue Damage: Long-term use under alternating loads can cause the sealing surface to fatigue, resulting in cracks and delamination. For example, rubber and plastic sealing surfaces tend to age over prolonged use, resulting in decreased performance and accelerated damage.

The performance of sealing surface materials directly affects their durability and reliability under various working conditions. Therefore, understanding key points in material selection is critical for improving overall valve quality. The following factors should be carefully considered.

Sealing surface materials must have excellent corrosion resistance to ensure the surface is not damaged by the medium. Corrosion resistance depends mainly on composition and chemical stability. When selecting sealing surface materials, factors such as medium type, temperature, and pressure should be considered. For acidic media, acid-resistant stainless steel or alloys can be selected; for alkaline media, nickel-based alloys or similar materials are suitable.

During relative motion, friction-induced damage is unavoidable. Therefore, sealing surface materials must have good scratch resistance, especially for valves requiring frequent operation, such as gate valves. Scratch resistance is determined by internal material properties. Materials with moderate hardness and smooth surfaces should be selected to reduce friction damage.

High-velocity media can erode the sealing surface, which is especially pronounced in throttling valves, safety valves, and high-temperature, high-pressure steam media, significantly affecting sealing performance. Materials with high hardness, toughness, and erosion resistance should be selected according to flow velocity, temperature, and pressure.

Sealing surface materials should have sufficient hardness and maintain it at the specified working temperature. Moderate hardness effectively resists erosion and wear, while ensuring wear resistance and fatigue resistance. Materials should be selected based on actual working conditions, ensuring hardness does not significantly decrease at operating temperatures.

The thermal expansion coefficient of the sealing surface and the body should be similar, particularly for embedded sealing ring designs. Large differences can create additional stress at high temperatures, causing loosening or damage. Materials with thermal expansion coefficients close to the body material should be selected to reduce stress under high temperatures.

For high-temperature applications, sealing surface materials must have sufficient oxidation resistance, thermal fatigue resistance, and thermal cycling performance. High temperatures can change material properties, such as hardness decrease and reduced oxidation resistance. Materials with good high-temperature performance should be selected to ensure reliability and stability.

Different working environments require different sealing surface materials to ensure long-term stable valve operation.

Valves used in high-velocity media should focus on erosion resistance. For example, throttling valves and safety valves operating under high-temperature, high-pressure steam require materials with high hardness, toughness, and excellent erosion resistance, such as hard alloys or ceramics, which can resist erosion and prolong service life.

When the medium contains solid impurities, the sealing surface is prone to wear and erosion. High-hardness materials should be selected to improve wear and erosion resistance. Examples include hard alloys and stainless steel, which resist abrasion and reduce damage.

For corrosive media, corrosion resistance is crucial. For valves operating in acidic or alkaline media, acid-resistant or alkali-resistant materials should be selected. Common corrosion-resistant materials include stainless steel, nickel-based alloys, and titanium alloys, which have excellent chemical stability and can maintain sealing performance.

For valves operating under high-temperature and high-pressure conditions, sealing surface materials must have high-temperature performance and fatigue resistance. High-temperature alloys, such as nickel-based or cobalt-based alloys, are suitable. These materials maintain hardness and oxidation resistance under high-temperature, high-pressure conditions, and resist fatigue under alternating loads, prolonging sealing surface life.

Damage to valve sealing surfaces is a complex issue with multiple causes, including human-induced damage, such as design oversights, manufacturing defects, improper material selection, incorrect installation, improper use, and inadequate maintenance, and natural damage caused by medium corrosion, erosion, mechanical wear, and fatigue. To extend sealing surface life and improve valve sealing performance, material selection should focus on corrosion resistance, scratch resistance, erosion resistance, hardness, thermal expansion coefficient, and high-temperature performance, according to different working conditions. Only by selecting appropriate materials and strictly controlling design, manufacturing, installation, operation, and maintenance can sealing surface damage be effectively reduced, ensuring valve reliability and stability.