In industrial production, the selection of a sealing system not only affects the stable operation of equipment but also impacts safety, cost, and service life. Especially when handling corrosive media, high-temperature environments, high-pressure conditions, or high-viscosity liquids, the risks of seal failure are often magnified: leaks, corrosion, equipment downtime, environmental impact, and personnel safety issues can all be caused by a seemingly minor sealing error. Therefore, one of the most important aspects for companies when designing or selecting equipment is matching the ‘correct sealing material + suitable sealing structure.
Sealing technology itself involves multiple factors such as materials science, fluid mechanics, temperature stress, and chemical compatibility. Coupled with the wide variety of industrial media, engineers often face difficulties in making choices. What materials can withstand acids and alkalis? What structures can withstand high temperatures and pressures? Is it necessary to replace high-viscosity media with special mechanical seals?
Can the material withstand it?
The erosion rates of corrosive media (acids, alkalis, solvents, salts, organic chemicals, etc.) on sealing materials vary greatly. Therefore, the first step is to determine ‘whether the material can withstand it.’ Common high-corrosion-resistant materials for selection can be referenced as follows:
– PTFE (Polytetrafluoroethylene): Exhibits excellent chemical stability against almost all strong acids, alkalis, and solvents, suitable for extremely corrosive media.
– FKM / FFKM Fluororubber: Strong chemical resistance, can withstand oils, solvents, and acidic gases, and has higher temperature resistance than ordinary rubber.
– Metallic materials (Hastelloy, Monel, 2205/2507 duplex steel): Suitable for highly corrosive, chlorine-containing media, or stress corrosion environments.
– Silicon carbide (SiC) / Carbon graphite: Commonly used for mechanical seal end faces, with good chemical stability and high wear resistance.
Structurally, corrosive environments are more suitable for mechanical seals because the sealing surface material can be customized for the medium, avoiding expansion or embrittlement of the rubber O-ring due to long-term immersion.
High-Temperature Structural Design
High-temperature operating conditions (150℃, 200℃, 300℃ or even higher) require materials that are stable, do not soften, and do not carbonize, and also require a structural design that allows for controllable thermal expansion. Therefore, two aspects need to be considered:
● Suitable Temperature-Resistant Materials
Metal Sealing Rings (Metal Gaskets, Corrugated Gaskets): Highest temperature resistance, exceeding 500℃.
-Graphite (Flexible Graphite Packing): High temperature resistance and strong chemical stability; commonly used sealing material for valves and pumps.
-Ceramic/Silicon Carbide Mechanical Seal Faces: Can withstand high temperatures without deformation.
● Stable Sealing Structure
-Metal Spiral Wound Gaskets: Suitable for high-temperature flange sealing applications; good elasticity and strong pressure resistance.
-External Mechanical Seals (e.g., Double-End Face): Avoid direct high-temperature action on the elastic element, extending service life.
General rubber O-rings are not recommended for high temperatures because exceeding their temperature limits (e.g., NBR 120℃, EPDM 150℃) will cause rapid aging and failure.
Prioritize Structural Strength
The challenge of high-pressure environments is not the medium, but the ‘force.’ The material’s hardness and the structure’s ability to withstand pressure differentials become paramount.
● Applicable High-Pressure Sealing Materials
Metal Gaskets (Annular Gaskets, Octagonal Gaskets): Commonly used in high-pressure pipelines and petrochemical plants; strong structure and resistant to compression.
Hard Alloy End Face Mechanical Seals: Can withstand friction and compression under high pressure.
● More Reliable Structures
Double-End Face Mechanical Seals: Balance internal pressure, less prone to being blown open by pressure differentials.
Balanced Seals: Reduce the load on the sealing surface, maintaining low wear even under high pressure.
Metal-to-Metal Seals (Common in Valves and Flanges): Prevent the extrusion of soft sealing materials.
The most common failure in high-pressure applications is ‘extrusion,’ therefore, it is crucial to avoid using soft materials to bear the pressure alone.
High Viscosity? Rely on Structure for Stability
High-viscosity liquids such as resins, colloids, heavy oils, and slurries can cause problems such as wear, blockage, and poor heat dissipation. In these cases, priority should be given to whether the structure is prone to trapping impurities, whether it is easy to cool, and whether it is self-cleaning.
● Recommended Structures
Open or Semi-Open Mechanical Seal Chamber: Reduces the risk of blockage.
Hard End Faces (SiCSiC): Wear-resistant and resistant to particle impact. Mechanical seals with flushing systems: Diluted, cooled, and cleaned with external cleaning fluid.
● Materials: Silicon carbide end face + fluororubber O-ring is a common combination.
For seals containing solid particles or slurries, a metal carbide end face + metal spring protection structure can be used.
In high-viscosity conditions, soft materials wear quickly, so direct contact with the medium should be minimized.
In extreme conditions such as high corrosion, high temperature, high pressure, and high viscosity, no single sealing solution is universally applicable. Truly safe and reliable sealing systems are the result of a combination of factors: operating conditions, material matching, and structural adaptation. In corrosive environments, chemical stability is prioritized; in high-temperature conditions, material thermal stability and structural heat dissipation are crucial; high-pressure scenarios require resistance to compression and high strength; and for high-viscosity liquids, wear resistance and anti-clogging capabilities are important. Many companies’ sealing problems are not due to insufficient material quality, but rather to unclear selection logic, leading to ‘good materials being used in the wrong places, and ordinary materials being subjected to excessive pressure.’ Therefore, it is more important to understand the essential requirements of each operating condition and then combine materials accordingly: PTFE, metal gaskets, graphite, silicon carbide, etc.; balanced, double-end, and metal seal structures, etc. As long as the selection principles are correct, long-term stable operation can be achieved in most extreme media. The ultimate goal is not the ‘strongest seal,’ but the ‘most suitable seal,’ which is safe, economical, and durable.
