Low-Temperature Leakage in Metal-seated Ball Valves: Causes and Countermeasures

Abstract: This paper investigates the failure mechanisms of metal-seated ball valve seals under low-temperature conditions and examines how factors such as deformation and shrinkage of sealing materials, sealing pair quality and surface finish, sealing pressure ratio, and the physical properties of the working medium affect sealing performance. Based on these mechanisms, countermeasures are proposed, including appropriate material selection and cryogenic treatment, structural optimization with elastic sealing elements, thermal insulation strategies, and the application of heating devices. By integrating technical solutions with practical considerations, this study aims to ensure the reliable operation of metal-seated ball valves in low-temperature environments. The findings provide both theoretical support and practical guidance for the sealing design of ball valves under cryogenic conditions.

Introduction

Low-temperature environments pose considerable challenges to the sealing performance of metal-seated ball valves. Under these conditions, sealing materials are prone to deformation and shrinkage, which may result in seal failure. Additionally, factors such as the quality and surface finish of the sealing pair, the sealing pressure ratio, and the physical properties of the medium further impact sealing effectiveness. Therefore, it is essential to thoroughly investigate the failure mechanisms of metal-seated ball valves operating under low-temperature conditions and to develop effective countermeasures. This paper addresses these issues from two main perspectives: the mechanisms of sealing failure and the corresponding engineering solutions.

1. Failure Mechanism of Metal-seated Ball Valve Seals Under Low-Temperature Conditions

1.1 Deformation and Shrinkage of Sealing Auxiliary Materials

Under low-temperature conditions, the deformation and shrinkage of sealing auxiliary materials in metal-seated ball valves are major contributors to sealing failure. These auxiliary materials, whether metallic or non-metallic, undergo significant changes in physical properties at low temperatures. Metal contract at low temperatures, leading to dimensional shrinkage and increased clearance between sealing surfaces, which compromises the original sealing condition. In cryogenic environments, non-metallic materials like polymers and elastomers often become rigid and brittle, compromising their elasticity and sealing effectiveness. The extent of deformation and shrinkage depends not only on the intrinsic properties of the material but also on the rate of temperature change. Rapid cooling can cause uneven internal stress distribution, leading to thermal stress that further aggravates material deformation. Additionally, phase transformations at low temperatures can adversely impact sealing performance. For example, certain metals may undergo martensitic transformation, causing volumetric changes that compromise the dimensional fit and precision of the sealing surfaces.

1.2 Sealing Pair Quality and Surface Processing

The quality of the sealing pair and the precision of surface finishing are critical factors influencing the sealing performance of metal-seated ball valves in low-temperature environments. The quality of the sealing pair directly determines its resistance to pressure, temperature fluctuations, and corrosion caused by the working medium, while the precision of surface finishing affects the tightness and effectiveness of the sealing interface. In low-temperature environments, any quality issues in the sealing pair become more pronounced. As the temperature drops, material toughness decreases, allowing even minor defects or cracks to propagate rapidly and potentially cause sealing failure. Additionally, changes in the physical properties of the working medium at low temperatures can accelerate corrosion and wear, further degrading the sealing performance. Surface processing accuracy mainly affects how well the sealing surfaces fit together. If the surfaces are uneven or have defects such as scratches or pits, they will fail to form a tight seal, creating potential leakage paths. Furthermore, material shrinkage at low temperatures can exacerbate minor machining imperfections, significantly affecting the overall sealing effectiveness.

1.3 Influence of Sealing Specific Pressure and Physical Properties of the Medium

Sealing specific pressure and the physical properties of the medium are two additional critical factors that influence the sealing performance of metal-seated ball valves under low-temperature conditions. Sealing specific pressure refers to the pressure per unit area between the sealing surfaces, which determines the extent of surface contact and the overall sealing effectiveness. The physical properties of the medium—such as density, viscosity, and thermal conductivity—directly impact lubrication and heat transfer between the sealing interfaces. Under low-temperature conditions, variations in sealing specific pressure can significantly affect sealing performance. As the temperature drops, the elastic modulus of the sealing materials generally increases, which changes the distribution of contact stress between the sealing surfaces. If the sealing pressure is too low, the sealing surfaces may fail to maintain adequate contact, resulting in leakage. Conversely, excessive sealing pressure can cause severe wear or even mechanical damage to the sealing surfaces. The physical properties of the medium also change significantly at low temperatures. For example, the viscosity of liquids tends to increase, which reduces lubrication efficiency between the sealing surfaces. Gas density increases at low temperatures, which can accelerate flow through leakage paths and worsen leakage. Additionally, the thermal conductivity of most media decreases, reducing heat transfer across the sealing surfaces and further compromising sealing reliability.

2. Countermeasures for Sealing Failure of Metal-seated Ball Valves Under Low-Temperature Conditions

2.1 Material Selection and Cryogenic Treatment

Sealing failure in metal-seated ball valves under low-temperature conditions presents a significant challenge for material selection. To effectively address this issue, it is essential to thoroughly evaluate the cryogenic properties of the materials, including their toughness, strength, thermal expansion coefficient, and corrosion resistance. First and foremost, it is essential to select materials with excellent low-temperature toughness. In cryogenic environments, materials tend to become brittle and rigid, increasing the risk of cracking or deformation, which can compromise sealing performance. Due to their superior toughness in cryogenic environments, special alloys such as austenitic stainless steels and nickel-based alloys are commonly employed in the construction of cryogenic valves. In addition to toughness, material strength and thermal expansion characteristics are also critical considerations. While strength generally increases at low temperatures, changes in the thermal expansion coefficient may alter the clearance between sealing surfaces, potentially compromising the seal. Therefore, both properties must be considered together to ensure a consistent and reliable fit under cryogenic conditions. Cryogenic treatment is another effective method for enhancing material performance. Deep cryogenic processing helps relieve residual internal stress, improve structural stability, and enhance long-term durability. Additionally, it refines the grain structure of the material, thereby increasing its resistance to brittle fracture at low temperatures. For non-metallic sealing components such as elastomers and polymers, specialized low-temperature modification techniques can be employed to enhance their elasticity and sealing performance in cryogenic environments. In practical applications, material selection and processing techniques must be tailored to specific operating conditions and service requirements to ensure the reliable performance of metal-seated ball valves in low-temperature environments.

2.2 Structural Design Optimization and Elastic Sealing

Structural design plays a crucial role in the sealing performance of metal-seated ball valves under low-temperature conditions. To optimize the sealing structure, careful attention must be paid to the geometry and matching accuracy of the sealing surfaces. Adopting spherical or conical sealing designs can increase both the contact area and surface conformity, thereby improving the sealing performance. During manufacturing, it is essential to strictly control dimensional tolerances and surface roughness to ensure precise surface matching and consistent sealing performance. In addition to optimizing the sealing surface geometry, incorporating elastic sealing elements is crucial for maintaining effective sealing under cryogenic conditions. Elastic sealing elements retain their flexibility and resilience at low temperatures, enabling them to accommodate minor deformations and displacements between sealing surfaces while maintaining a stable seal. When selecting these components, factors such as material composition, structural design, and dimensional specifications must be carefully evaluated to ensure their reliability and durability in cryogenic environments. Further improvements in sealing performance can be achieved by optimizing the overall valve structure. For instance, incorporating a double-seal configuration or a multi-layer sealing design can enhance redundancy and overall reliability. Additionally, guide mechanisms or positioning devices can be integrated into the valve assembly to ensure precise alignment and contact of sealing components under low-temperature conditions.

2.3 Insulation Measures and Application of Heating Devices

In low-temperature environments, sealing failure in metal-seated ball valves is often directly caused by temperature-induced material degradation. To effectively mitigate this issue, insulation measures and heating devices can be used to maintain the valve’s internal temperature within an optimal functional range. One approach is to apply insulation layers or covers around the valve to minimize heat loss and help stabilize its internal temperature. The selection of insulation materials should consider properties such as thermal conductivity, density, and low-temperature resistance to ensure both durability and effectiveness. In addition to passive insulation, active heating is an effective method to raise the valve temperature and prevent sealing materials from becoming brittle or contracting. Heating elements, such as electric heating wires or heating tapes, can be installed at critical locations to provide targeted thermal input. The design of these heating systems should take into account power output, temperature control accuracy, and operational safety. Excessive heating power can cause the valve to overheat, compromising its performance, while insufficient power may fail to prevent seal degradation. Accurate temperature control is essential: excessively high temperatures may accelerate the aging or damage of sealing materials, while temperatures that are too low may fail to prevent shrinkage and leakage. Therefore, integrated temperature monitoring and control systems should be implemented to maintain optimal operating conditions. In practice, the implementation of insulation and heating systems must also take into account cost-effectiveness, energy efficiency, and ease of maintenance. The proper selection and integration of these measures can markedly improve sealing performance and extend the service life of metal-seated ball valves in cryogenic environments. Furthermore, routine inspection and maintenance are essential to ensure continued effectiveness. For instance, the insulation layer and heating elements should be regularly checked to verify that they remain intact and fully operational. Valve temperatures should be continuously monitored to ensure they remain within the desired range, and any aging or damaged sealing or heating components should be promptly replaced.

3. Technical Implementation and Practical Considerations

3.1 Valve Selection and Adaptability to Operating Conditions

Proper valve selection is a critical step in the technical implementation of metal-seated ball valves under low-temperature conditions. Valve selection must thoroughly consider actual operating conditions such as medium temperature, pressure, corrosiveness, and fluid properties. To ensure reliable performance in cryogenic environments, valve materials must exhibit excellent low-temperature toughness and resistance to corrosion. Specialized alloys and cryogenic elastomers are often preferred for such applications. In low-temperature applications, the valve’s structural design must be carefully considered. Configurations such as dual seals or elastic sealing elements can significantly enhance sealing reliability and operational stability. In addition to material and structural considerations, factors such as valve size, weight, installation method, and operational convenience must be carefully evaluated. These considerations help ensure that the valve is compatible with the process system, thereby enhancing overall system efficiency and safety.

3.2 Regular Inspection and Maintenance

To maintain long-term stability and reliability of metal-seated ball valves in cryogenic environments, regular inspection and maintenance are critical. To mitigate the risk of critical failure, a thorough inspection plan should prioritize components such as sealing surfaces, flexible sealing elements, valve stems, and actuation mechanisms. Prompt identification and remediation of wear or corrosion are vital. To maintain optimal performance, valves should be regularly cleaned and lubricated. For those operating continuously in low-temperature environments, it is crucial to inspect the condition and performance of insulation layers and heating elements. Regular inspection and maintenance help extend valve lifespan while simultaneously enhancing system reliability and safety.

3.3 Emergency Response and Contingency Planning

During operation, metal-seated ball valves in cryogenic environments may occasionally experience unexpected failures. Developing a comprehensive emergency response plan is essential to ensure system safety and operational continuity. The plan should explicitly specify procedures for fault diagnosis, emergency response actions, switching to backup valves, and personnel evacuation. Regular emergency drills should be held to strengthen the staff’s response capabilities and teamwork. An effective contingency plan helps minimize downtime, mitigate failure impacts on system performance, and safeguard personnel and equipment.

4. Conclusion

In summary, the failure mechanisms of metal-seated ball valve seals in low-temperature environments are mainly attributed to material brittleness, deformation of the sealing structure, and temperature-induced stress. Addressing these challenges requires a comprehensive approach that includes appropriate valve selection, material treatment, optimized structural design, and the application of insulation and heating measures. The sealing performance and operational reliability of metal-seated ball valves in low-temperature conditions can be significantly improved through the selection of cryogenically suitable materials, optimization of sealing structures, enhancement of routine inspection and maintenance practices, and the establishment of effective emergency response plans.