Comparison between PTFE And Metal-to-Metal Hard Seals: Selection Strategy for DN300 High-Pressure Trunnion Ball Valves in 450°C Steam Pipelines

I. INTRODUCTION
In industrial pipeline systems, BALL VALVES are widely used due to their simple structure and convenient operation. However, in high-temperature and high-pressure working conditions, the choice of sealing materials directly affects the reliability and service life of the valves. This paper will mainly discuss the performance differences between PTFE and metal-to-METAL HARD SEAL materials and their applicability in 450°C steam pipelines.

II. CHARACTERISTICS OF PTFE SEALING MATERIALS
Advantages:

· Strong corrosion resistance: PTFE has excellent chemical stability and can resist most corrosive media.

· High temperature resistance: The maximum service temperature can reach 232°C (450°F), suitable for medium-temperature environments.

· Low friction coefficient: The friction resistance of the PTFE sealing surface is small, which helps to reduce the operating force.

· Good sealing performance: PTFE materials have good sealing properties, but it is necessary to keep the seat surface clean to avoid leakage.

Disadvantages:

· Poor wear resistance: PTFE materials have low mechanical strength and are prone to wear, especially in high-pressure environments.

· High coefficient of thermal expansion: Temperature changes may lead to a decline in sealing performance and thus cause leakage.

· Plastic deformation: Cold flow may occur at high temperatures, resulting in seal failure.

III. CHARACTERISTICS OF METAL-TO-METAL HARD SEALS
Advantages:

· Strong wear resistance: Metal-to-METAL HARD SEALS adopt materials such as chromium-based hard alloys and cobalt-based hard alloys, with a hardness of over HRC60, suitable for high-wear environments.

· High temperature resistance: Metal-to-metal hard seals can withstand temperatures as high as 540°C or even higher.

· Strong sealing stability: The metal-to-metal sealing method is not easily affected by temperature and pressure changes and is suitable for high-pressure working conditions.

Disadvantages:

· High cost: The manufacturing process of metal-to-metal hard seals is complex, and the cost is higher than that of PTFE seals.

· High requirements for the processing of the sealing surface: Precision processing is required to ensure the sealing effect.

IV. COMPARATIVE ANALYSIS OF THE TWO SEALING MATERIALS IN 450°C STEAM PIPELINES
Characteristics PTFE Sealing Materials Metal-to-METAL HARD SEALS
Temperature range ≤232°C (450°F) ≥450°C
Wear resistance Poor High
Sealing performance High, but the seat surface needs to be clean Stable, suitable for high-pressure working conditions
Cost Low High
Applicable scenarios Low-pressure and medium-temperature environments (such as water and gas transmission) High-temperature and high-pressure environments (such as steam and oil-gas transmission)

V. SELECTION STRATEGY
Analysis of applicable scenarios:

· If the working temperature of the steam pipeline is lower than 232°C (450°F) and the requirements for wear resistance and sealing stability are not high, PTFE-sealed ball valves can be selected.

· When the working temperature exceeds 232°C (450°F) and it is necessary to withstand high-pressure and high-wear environments, metal-to-metal hard-sealed ball valves are a better choice.

Comprehensive considerations:

· Cost budget: If the budget is limited, PTFE-sealed ball valves can be prioritized.

· Working conditions: If the working conditions are high-temperature and high-pressure and contain solid particles or dust, metal-to-metal hard seals are more reliable.

VI. Conclusion
In the application of DN300 HIGH-PRESSURE TRUNNION BALL VALVES, both PTFE and metal-to-METAL HARD SEALS have their own advantages and disadvantages. For 450°C steam pipelines, metal-to-METAL HARD SEALS are a better choice due to their excellent high-temperature resistance and wear resistance. However, in the case of a limited budget or when the working temperature is lower than 232°C (450°F), PTFE-sealed ball valves still have certain applicability. Therefore, a comprehensive evaluation should be carried out according to specific working conditions and requirements during the selection process.