Mechanical seals prevent leaks in pumps and other rotating equipment. Selecting the right seal material is critical for optimal performance and reliability.
This guide provides an overview of common mechanical seal materials and their properties.
Seal Faces
Carbon (CAR) – Graphite
Carbon and graphite are common seal face materials. They have good lubricity and heat dissipation properties. Carbon/graphite is resistant to a wide range of chemicals. It is often used as a mating face with ceramic or tungsten carbide.
Ceramic (CER)
Ceramic is a hard, wear-resistant seal face material. It has excellent chemical resistance and can withstand high temperatures. Ceramic is brittle and can be prone to cracking under mechanical shock. It is often used as a mating face with carbon/graphite or PTFE.
Silicone Carbide (SiC)
Silicon carbide is an extremely hard and wear-resistant seal face material. It has excellent chemical resistance and can handle high pressures and velocities. SiC is brittle but has higher strength than ceramic. It is often used in demanding applications as a mating face with SiC, carbon/graphite or tungsten carbide.
Tungsten Carbide (TC)
Tungsten carbide is a hard, tough, and wear-resistant seal face material. It has good chemical resistance and can handle high pressures and velocities. TC has higher strength and impact resistance than ceramic and SiC. It is often used in heavy-duty applications as a mating face with carbon/graphite.
PTFE
PTFE (polytetrafluoroethylene) is a soft, low-friction seal face material. It has excellent chemical resistance. PTFE has low wear resistance and is limited to low pressure and velocity. It is often used as a mating face with ceramic or stainless steel when a low-friction seal is required.
Stainless Steel
Stainless steel is a ductile and durable seal face material. It has moderate wear resistance. The chemical resistance depends on the grade of stainless steel. Stainless steel can gall and seize if not lubricated properly. It is sometimes used as a low-cost alternative to hard face materials in non-demanding applications.
Secondary Seal – Elastomers
Nitrile (NBR)
Nitrile (NBR) is a common elastomer for secondary seals. It has good resistance to oils, fuels, and hydraulic fluids. NBR has moderate temperature range from -30°C to 110°C. It is not suitable for oxidizing acids, ozone, and aromatic hydrocarbons.
EPDM (EPR)
EPDM (EPR) is a versatile elastomer with excellent resistance to ozone, sunlight, and weathering. It has good chemical resistance to acids, alkalis, and polar solvents. EPDM has a wide temperature range from -50°C to 150°C. It is not recommended for oils and fuels.
Viton (FKM, FPM)
Viton (FKM, FPM) is a high-performance elastomer with excellent chemical resistance. It is suitable for a wide range of fluids including oils, fuels, and many chemicals. Viton has a wide temperature range from -20°C to 200°C. It is more expensive than NBR and EPDM.
AFLAS (TFE/P)
AFLAS (TFE/P) is a specialty elastomer with excellent chemical resistance and high-temperature performance. It is suitable for aggressive chemicals and high-temperature steam up to 230°C. AFLAS is more expensive than Viton.
FEP Silicone
EP-encapsulated silicone combines the chemical resistance of FEP with the elasticity of silicone. It has excellent resistance to acids, bases, and polar solvents. FEP silicone has a wide temperature range from -60°C to 200°C. It is not recommended for dynamic applications.
FEP Viton (FKM, FPM)
FEP-encapsulated Viton combines the chemical resistance of FEP with the performance of Viton. It has excellent resistance to a wide range of chemicals and high temperatures up to 200°C. FEP Viton is suitable for dynamic applications.
Kalrez (FFKM)
Kalrez (FFKM) is a high-end elastomer with exceptional chemical resistance and high-temperature performance. It is suitable for the most aggressive chemicals and temperatures up to 327°C. Kalrez is significantly more expensive than other elastomers.
Metal Components
304 Stainless Steel
304 stainless steel is a common alloy for mechanical seal components. It has good corrosion resistance in mild environments. 304 SS is suitable for water, steam, and non-aggressive chemicals. It is not recommended for seawater, chlorides, and acidic conditions.
316L Stainless Steel
316L stainless steel is an upgraded alloy with improved corrosion resistance. It contains molybdenum for better resistance to chlorides and acids. 316L SS is suitable for seawater, mild chemicals, and food processing. It has better pitting and crevice corrosion resistance than 304 SS.
Duplex and Super Duplex Stainless Steel
Duplex and super duplex stainless steels are high-performance alloys. They have excellent corrosion resistance in aggressive environments. Duplex and super duplex are suitable for seawater, acidic conditions, and high chloride content. They have higher strength and wear resistance than 304 and 316L SS.
Hastelloy
Hastelloy is a family of nickel-based superalloys. They have exceptional corrosion resistance in severe environments. Hastelloy alloys are suitable for highly aggressive chemicals, acidic conditions, and high temperatures. They are significantly more expensive than stainless steels.
FAQs
What factors should be considered when selecting mechanical seal materials
When selecting mechanical seal materials, consider factors such as the fluid being sealed (chemical composition, temperature, pressure), the operating conditions (speed, load, vibration), the environmental conditions (abrasive particles, corrosive atmospheres), and the required seal life.
Can I use the same seal material for both the primary and mating rings
In most cases, it is recommended to use dissimilar materials for the primary and mating rings to prevent binding and ensure proper lubrication. For example, a carbon graphite primary ring is often paired with a ceramic or tungsten carbide mating ring.
What is the maximum temperature for mechanical seals?
Standard seals typically handle up to 400°F (204°C). Specialized high-temperature seals can operate at 600-800°F (315-427°C) or higher.
In conclusion
Selecting the optimal materials is critical for mechanical seal performance and reliability. Evaluate your application’s requirements carefully to make the best choice.
For expert guidance on mechanical seal material selection for your specific needs, contact our knowledgeable team today to discuss customized solutions.
