Hygenic Seal Material Guidelines

This information has been carefully prepared to help in selecting the correct elastomer or perfluorocarbon utilized in high purity sanitary hygienic seals where critical pure water, process fluids (both ambient and hot), and SIP environments exist. The intention is to consider the different uses, applications and conditions to determine the most favorable hygienic seal material for each application.

The following criteria is used in determining correct hygienic seal materials:
  • U.S. Pharmacopeia Class VI Certification
  • Cytotoxicity Criteria
  • CFR Title 21 Section 177.1550
  • CFR Title 21 Section 177.2600
  • Traceability: Lot and Batch
  • Certification: Lot and Batch
  • ASME-BPE Standards
  • USDA Standards
  • 3-A Sanitary Standards
  • Current Good Manufacturing Practices (CGMP)
  • Manufacturer data and specifications
  • Consultation with various pharmaceutical users
  • Animal Derived Ingredient Free

The gasket materials considered are Tuf-Steel® (PTFE/Stainless Steel), Tuf-Flex,® PTFE, Silicone (platinum), FKM Fluoroelastomer, EPDM and Buna.

The 3 main goals are:
  • To protect products from contamination, spalling, particulates and TOCs resulting from the use of improper hygienic seal material.
  • To protect facilities from unnecessary downtime associated with hygienic seal failure and replacement from use of improper hygienic seal material.
  • To provide a standard of consistency for hygienic seal selection between multiple facilities.

Most decisions driving seal type selection are based on chemistry, temperature, exposure limits, USP, FDA qualifications, and curing methods. The following briefly addresses each of these issues.

Exposure Limits

It is important to define the operating parameters of a new or existing processing sanitary system. The user specifications for exposure limits and reactivity to process fluids are compared with process operating parameters. All materials are acceptable for steam excluding Buna.

All materials should meet process fluid reactivity parameters. Even though all compound exposure limits fall within operating parameters, the service life of some compounds will be different under certain conditions. This must be considered when selecting a compound.

FDA and USP Qualifications

CFR’s define the criteria for extractables and for compounds used in the manufacture of rubber and plastic articles. The two applicable categories are; rubber articles (Buna, EPDM, FKM Fluoroelastomer, Silicone) and perfluorocarbon resins (PTFE). USP defines the criteria for testing biological reactivity and the amount/type of extractables. The hygienic seals in service must meet USP Class VI specifications, and be manufactured using the proper compounds as stated in the CFR, Title 21, Sections 177.1550 and 177.2600 respectively.

Note: Not all hygienic seals meet these requirements.

Curing Methods

Curing agents have an affect on the amount and type of extractables a material will emit. Typically, the hygienic seal group in service uses three methods; sulfur cured*, peroxide cured and platinum cured. When dealing with elastomers, peroxide cured is the most favorable method. When dealing with silicone, platinum cured is the most favorable. All gaskets shall be post cured. Using these methods minimize potential reactions with the respective process fluid applications and can uphold pure water and process fluid standards.

* Sulfur cured elastomers can significantly alter a process fluids integrity and negatively affect mammalian cell yields.

Note: Hygienic seal identification for curing methods. For example, EPDM: one green dot (•) means sulfur cured and three green dots (•••) means peroxide cured. EPDM Hygenic Seals are all peroxide cured.

What Material(s) Can Be Used

By reviewing manufacturer data and compiling information regarding regulatory requirements, it appears that any of the aforementioned compounds are suitable for both utility and process equipment use. However, you must ensure that all hygienic seals and compounds meet the CFR and USP requirements, and have a certificate to verify compliance.

What Material(s) Should Be Used
  • Tuf-Steel® is the material of choice when purity, long service life performance, chemical and heat resistance is required. Leak free when torqued correctly. Minimum creep and cold flow. Non-stick, ultra-low absorption and no pigmentation. Maintains seal integrity in applications where large temperature variations occur frequently. It can remain in service for extended periods of time in both water and frequent SIP use. The Torque-Rite® is recommended for use with clamps (See Torque-Rite literature for complete details).
  • PTFE is the material of choice whenever low temperature flexibility or hygienic seal memory is not required (not recommended where large temperature variations occur frequently, leakage can occur). PTFE has almost no extractables, has a low absorption rate and excellent resistance to process fluids. It can remain in service for longer periods of time in both water and steam for continuous use, high pressure clamps are recommended to prevent leakage resulting from temperature variations. A PTFE envelope hygienic seal with an FKM Fluoroelastomer inner core should be used if slight misalignment is observed.
  • Platinum cured silicone is the material of choice in sanitary water systems when PTFE is not feasible due to severely misaligned fittings, or if the cost of high pressure clamps does not outweigh the benefits of PTFE (extended service life).
  • FKM Fluoroelastomer, EPDM and Buna compounds are specified by many of our process equipment manufacturers. They are generally suitable for these applications, however, service life must be considered and a preventative maintenance program be implemented to mitigate degradation. They are not recommended for continuous use in SIP procedures.
  • Color coding - identification of hygienic seal materials

Hygienic Seal Material Guidelines

Download the Hygienic Seal Material Guidelines chart. (pdf 59kb)

  • Tuf-Flex®: Tuf-Flex is the world’s only unitized gasket, setting new standards for purity, performance and flexibility. A Tuf-Flex Gasket’s contact surface is a layer of PTFE unitized to an EPDM rubber inner core. This totally bonded construction provides a PTFE gasket with the mechanical characteristics, including memory, of an elastomer gasket. Designed to meet critical requirements in biopharmaceutical, ultra-pure water, WFI (water for injection) and difficult food and beverage processing, Tuf-Flex out performs other gaskets while eliminating costly process interruptions. Achieve higher performance under SIP/CIP conditions.
  • Tuf-Steel®: A unique 50/50 blend of nonpigmented PTFE and 316L, water atomized and passivated, delivers leak-proof performance. Tuf-Steel is the choice for leak-proof, perfect surface performance and outstanding durability in SIP (steam in place) and WFI (water for injection) applications. Tuf-Steel is ideal for sanitary steam pipe connections in extreme temperatures ranging from -20°F to 500°F. The superior strength of Tuf-Steel eliminates cold flow and creep to prevent maintenance problems and system downtime.
  • PTFE is the material of choice whenever low temperature flexibility or gasket memory is not required (not recommended where large temperature variations occur frequently, leakage can occur). PTFE has almost no extractables, has a low absorption rate and excellent resistance to process fluids. It can remain in service for longer periods of time in both water and steam for continuous use, high pressure clamps are recommended to prevent leakage resulting from temperature variations. PTFE envelope gaskets with a FKM Fluoroelastomer inner core should be used if slight misalignment is observed.
  • Platinum Cured Silicone is the material of choice in sanitary water systems when PTFE is not feasible due to severely misaligned fittings, or if the cost of high pressure clamps does not outweigh the benefits of PTFE (extended service life).
  • FKM Fluoroelastomer and EPDM compounds are specified by many of our process equipment manufacturers. They are generally suitable for these applications, however, service life must be considered and a preventative maintenance program be implemented to mitigate degradation. They are acceptable, but not recommended for continuous use in SIP procedures.
  • Buna is the last choice in most applications due to temperature limitations and does not pass U.S. Pharmacopeia Class VI Certification and Cytotoxicity.

This sheet indicates general preferences. Unique applications may require further considerations and analysis. When selecting hygienic seal materials it is important to consider many factors: resistance to heat, resistance to SIP, resistance to chemicals like; hydrocarbons, ethanol, ketones, etc, tear strength, and flexibility. The service life of a material depends on the application. Many of the materials are acceptable if the expected service life is very short in duration, however, in extended exposure situations the material can degrade quickly rendering it ineffective or less desirable overall. This analysis was intended for hygienic seal applications specifically. Sanitary gasket applications are inherently static and can be dynamic. When different performance attributes are a consideration in dynamic applications, Tuf-Steel may be the material of choice.