A PTFE gasket is a sealing component made from polytetrafluoroethylene (PTFE) — a fluoropolymer prized for its chemical inertness, wide temperature range, and non-contaminating surface. PTFE gaskets are the default choice wherever a flange connection has to handle aggressive chemicals, maintain product purity, or operate reliably across extreme temperatures, from chemical plants and refineries to pharmaceutical and food-processing lines.
This guide breaks down the three main PTFE gasket types, how they compare on chemical resistance, temperature, pressure, and cold flow, and how to pick the right one for your flange. It’s written by Asian Sealing Products, an ISO 9001:2015, ISO 14001:2015, and ISO 45001:2018 certified gasket manufacturer with API 6A and API 17D licenses, operating a 15,000 sq.m facility in Chennai, India, and supplying PTFE and CNAF gaskets to the oil & gas, petrochemical, and process industries worldwide.
What Is PTFE and Why Is It Used for Gaskets?
PTFE (Polytetrafluoroethylene), commonly known by DuPont’s trade name Teflon™, is a synthetic fluoropolymer with a carbon backbone fully shielded by fluorine atoms. That molecular structure is what gives PTFE gaskets their defining properties:
- Chemical inertness — resists nearly every industrial acid, base, solvent, and hydrocarbon
- Wide temperature range — performs from -260°C (-436°F) up to 260°C (500°F) continuous, with short excursions to 315°C (600°F)
- Non-stick, non-contaminating surface — prevents media buildup and product contamination
- Low coefficient of friction — among the lowest of any solid material
- High dielectric strength — excellent electrical insulator
- Physiologically inert — safe for food, pharmaceutical, and medical contact (FDA 21 CFR 177.1550, USP Class VI)
The trade-off is cold flow (creep) under sustained bolt load; PTFE slowly deforms and loses sealing stress. Which gasket type you choose determines how big a problem that is.
How Does a PTFE Gasket Work?
A PTFE gasket works by filling the microscopic irregularities between two flange faces when compressed during installation. Once sufficient bolt load is applied, the gasket forms a tight seal that prevents fluid or gas leakage.
Unlike elastomeric gaskets that rely mainly on elasticity, PTFE uses controlled deformation to create an effective seal. Its excellent creep resistance, particularly in filled PTFE grades, helps maintain sealing performance over extended operating periods.
Proper installation, correct bolt torque, and selecting the appropriate gasket thickness are essential for achieving optimal sealing efficiency.
Key Features of PTFE Gaskets
PTFE gaskets offer several features that distinguish them from conventional sealing materials:
Outstanding Chemical Resistance
PTFE is resistant to almost every industrial chemical, including:
- Sulfuric acid
- Hydrochloric acid
- Nitric acid
- Sodium hydroxide
- Chlorine compounds
- Solvents
- Alcohols
- Organic chemicals
This makes PTFE the preferred gasket material for chemical processing industries.
High Temperature Performance
PTFE maintains its physical properties across a broad temperature range, typically from -260°C to +260°C, making it suitable for both cryogenic and high-temperature environments.
Low Friction
Its naturally low coefficient of friction minimizes wear during installation and allows easier disassembly during maintenance.
Non-Contaminating
PTFE does not leach contaminants into process media, making it suitable for pharmaceutical, food, beverage, and biotechnology industries.
Excellent Electrical Insulation
PTFE also possesses outstanding dielectric properties, allowing it to be used in specialized electrical and electronic applications.
Types of PTFE Gaskets
1. Virgin PTFE Gaskets
Made from 100% pure, unfilled PTFE resin. Virgin PTFE gaskets offer the highest chemical resistance and purity of any PTFE type, along with excellent electrical insulation — but they’re the most prone to cold flow, especially at elevated temperature and pressure.
Best for: highly corrosive chemical service, pharmaceutical and food-grade applications, semiconductor manufacturing, and lower-pressure duty where purity matters more than mechanical strength.
2. Filled PTFE Gaskets
Virgin PTFE reinforced with glass fiber, carbon, graphite, bronze, or mineral fillers to reduce cold flow and increase mechanical strength. The filler determines the performance profile:
| Filler | What It Improves | Typical Use |
|---|---|---|
| Glass fiber (15–25%) | Compressive strength, creep resistance | General chemical processing, moderate-to-high pressure, steam |
| Carbon (10–35%) | Hardness, wear resistance, thermal conductivity | High-pressure service, hot water, steam |
| Graphite (5–15%) | Chemical resistance near virgin PTFE, low friction | High-temperature service, aggressive chemicals |
| Barium sulfate / silica microspheres | Creep resistance without major chemical trade-off | Caustics, hydrogen peroxide, fragile flanges |
Best for: general industrial sealing where higher pressure or reduced retorquing is needed, but purity requirements are less strict than pharma or food-grade.
3. Expanded PTFE Gaskets (ePTFE)
Made by mechanically expanding 100% virgin PTFE into a fibrillated, multi-directional microstructure — no fillers or binders added. This gives ePTFE a rare combination: it keeps the universal chemical resistance and purity of virgin PTFE while resisting cold flow far better, and it seals effectively at much lower bolt loads on rough or damaged flange surfaces.
Best for: fragile or irregular flanges (glass-lined, FRP, ceramic), low bolt-load applications, and services demanding both purity and creep resistance.
Quick Comparison
| Property | Virgin PTFE | Filled PTFE | Expanded PTFE (ePTFE) |
|---|---|---|---|
| Chemical resistance | Excellent | Good–Excellent (filler dependent) | Excellent |
| Cold flow / creep | High | Low | Low–Moderate |
| Mechanical strength | Moderate | High | Low–Moderate (biaxially strong) |
| Conformability to rough flanges | Moderate | Low | Excellent |
| Purity | Highest | Reduced by filler | High (100% PTFE) |
| Continuous temperature | Up to 260°C (500°F) | Up to 260°C (500°F) | Up to 260°C (500°F) |
| Max pressure @ 20°C | ~80 bar | ~150 bar | ~120 bar |
| Required bolt/seating stress | Moderate | High | Very low |
Physical Properties of PTFE Gaskets
| Property | Typical Value |
|---|---|
| Material | Polytetrafluoroethylene (PTFE) |
| Color | White (Virgin), Various (Filled Grades) |
| Density | 2.1–2.3 g/cm³ |
| Operating Temperature | -260°C to +260°C |
| Melting Point | Approximately 327°C |
| Water Absorption | Less than 0.01% |
| Coefficient of Friction | 0.05–0.10 |
| Tensile Strength | 20–35 MPa |
| Elongation at Break | Up to 300% |
| Chemical Resistance | Excellent |
| UV Resistance | Excellent |
| Electrical Insulation | Excellent |
How to Choose the Right PTFE Gasket
Selecting the correct PTFE gasket comes down to four questions:
- What’s the media? Strong acids, caustics, halogens, or solvents are all handled well by any PTFE type. For food, pharma, or semiconductor purity requirements, go virgin PTFE or ePTFE — fillers can compromise purity.
- What’s the flange condition? Smooth, standard-finish flanges (Ra 3.2–6.3 µm) work well with virgin or filled PTFE. Rough, corroded, glass-lined, or plastic flanges need ePTFE’s conformability (up to Ra 12.5 µm).
- What’s the pressure and bolt load? High-pressure service favors filled PTFE. Limited bolt-load capacity (fragile equipment) favors ePTFE.
- How much retorquing can the application tolerate? Virgin PTFE typically needs a retorque after the first thermal cycle. Filled and ePTFE gaskets hold load significantly better over time.
Still unsure? Contact our engineering team with your pressure, temperature, chemical, and flange details and we’ll recommend the right grade including our range of PTFE and CNAF gaskets.
Installation Best Practices
Proper installation matters as much as material selection:
- Never use sealant or grease on the gasket face. PTFE’s sealing mechanism relies on the material conforming to the flange; lubricants create a slip plane and accelerate cold flow.
- Use a controlled, star-pattern tightening sequence in at least three passes (30%, 60%, 100% of final torque), always with a calibrated torque wrench.
- Lubricate bolt threads and nut faces only, so applied torque translates accurately into clamping force.
- Plan for a retorque on virgin and some filled PTFE gaskets after the first thermal cycle. ePTFE typically needs little to none.
- Use the thinnest practical thickness — 1.5 mm or 3.0 mm are standard, and thinner gaskets creep and extrude less than thicker ones.
- Prefer recessed (ring) gasket designs on raised-face flanges over full-face designs, since confinement significantly reduces extrusion risk.
Common Causes of PTFE Gasket Failure
| Failure Mode | Typical Cause | Fix |
|---|---|---|
| Leakage | Under-torquing, cold flow, damaged flange face | Verify torque, retorque after thermal cycle, inspect flange |
| Extrusion | Over-torquing, insufficient confinement, gasket too thick | Use recessed design, thinnest practical gasket, correct torque |
| Premature failure | Wrong PTFE grade for the pressure/temp/chemical, mechanical damage in storage | Re-verify application parameters, store per guidelines, replace (never reuse) |
Industries That Rely on PTFE Gaskets
- Chemical & petrochemical processing — pipelines, reactors, distillation columns, valves handling acids, caustics, and solvents
- Oil & gas (upstream & downstream) — wellheads, pipelines, refineries, especially sour gas and corrosive hydrocarbon service
- Pharmaceutical & biotechnology — sanitary connections, bioreactors, API production (FDA 21 CFR 177.1550, USP Class VI)
- Food & beverage — processing and packaging lines requiring FDA-compliant, non-contaminating seals
- Semiconductor manufacturing — ultra-high purity gas and liquid delivery systems
- Power generation & water treatment — steam lines, cooling systems, and purification equipment
In the demanding world of industrial processes, reliable sealing solutions are paramount. Leaks can lead to significant financial losses, safety hazards, and environmental damage. Polytetrafluoroethylene (PTFE) gaskets have emerged as a cornerstone in sealing technology, offering an unparalleled combination of chemical inertness, temperature resistance, and non-contaminating properties. This comprehensive guide is designed to equip our industrial customers with an in-depth understanding of PTFE gaskets, enabling them to make informed decisions for their specific applications.
What is PTFE?
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene, famously known by its DuPont brand name, Teflon™. Discovered accidentally by Roy Plunkett in 1938, PTFE is a high-performance plastic distinguished by its exceptional properties. Its unique molecular structure, featuring a carbon backbone completely shielded by fluorine atoms, imparts remarkable chemical stability, thermal resistance, and a very low coefficient of friction.
Key Properties of PTFE Relevant to Gasketing
- Exceptional Chemical Inertness: Resists attack from nearly all chemicals, solvents, and corrosive agents, making it ideal for aggressive media.
- Wide Temperature Range: Maintains structural integrity and performance from cryogenic temperatures (as low as -260°C / -436°F) up to high continuous operating temperatures (around 260°C / 500°F), with short excursions possible to 315°C (600°F).
- Low Coefficient of Friction: Possesses one of the lowest friction coefficients of any solid material, which is beneficial in dynamic applications and prevents material adhesion.
- Non-Stick Surface: Its inherent non-stick property prevents process media buildup and facilitates easy cleaning, reducing contamination risks.
- Excellent Electrical Insulator: Exhibits high dielectric strength and a low dielectric constant, providing superior electrical insulation.
- Non-Hygroscopic: Does not absorb moisture, maintaining dimensional stability in humid environments.
- UV and Weather Resistant: Highly resistant to degradation from ultraviolet (UV) radiation and weathering, ensuring longevity in outdoor or exposed applications.
- Physiologically Inert: Virgin PTFE is non-toxic and biocompatible, making it safe for use in sensitive applications such as food, pharmaceutical, and medical industries.
Why Choose PTFE Gaskets?
PTFE gaskets offer a multitude of advantages that make them the preferred choice in critical industrial sealing applications where other materials may fail.
Superior Chemical Resistance
PTFE is virtually impervious to almost all industrial chemicals. This includes strong acids (e.g., concentrated sulfuric acid, nitric acid, hydrochloric acid), strong bases (e.g., sodium hydroxide), corrosive solvents (e.g., acetone, toluene, MEK), and hydrocarbons across a wide range of concentrations and temperatures. This broad compatibility makes it the go-to material for sealing aggressive and hazardous media.
Excellent Temperature Range
PTFE gaskets can perform reliably in extreme temperature environments, from intensely cold cryogenic conditions down to approximately -260°C (-436°F) and up to continuous high temperatures of 260°C (500°F). Some specialized grades and short-term exposures can even withstand up to 315°C (600°F). While mechanical properties may be affected at temperature extremes, its chemical stability remains largely intact.
Low Friction and Non-Stick Properties
The extremely low coefficient of friction of PTFE is a significant advantage, particularly in applications where sliding or rotational motion occurs. Its non-stick surface prevents adherence to process materials, facilitating easier disassembly, reducing material buildup, and minimizing the potential for product contamination.
Purity and Non-Contamination
Virgin PTFE is inherently pure and contains no fillers, binders, or additives that could leach into sensitive process fluids. This makes it an essential material in industries where product purity is paramount, such as pharmaceutical, food & beverage, and semiconductor manufacturing.
Weatherability and UV Resistance
PTFE exhibits exceptional resistance to environmental degradation, including long-term exposure to UV radiation and various weather conditions. This makes it highly durable for outdoor installations and ensures its performance remains consistent over extended periods.
Electrical Insulation
With high dielectric strength and a low dielectric constant, PTFE serves as an outstanding electrical insulator. This property is crucial in applications requiring electrical isolation, preventing current leakage and ensuring system safety.
Types of PTFE Gaskets
The selection of a PTFE gasket type is critical and depends on the specific application’s pressure, temperature, chemical media, and the need to address cold flow characteristics.
Virgin PTFE Gaskets
- Description: Manufactured from 100% pure, unadulterated PTFE resin, typically skived from billets or molded.
- Pros: Offers the highest degree of chemical resistance, unparalleled purity, excellent electrical insulation, and the lowest coefficient of friction among PTFE types.
- Cons: Most susceptible to cold flow (creep) under continuous compressive load, especially at elevated temperatures. It is softer and has lower mechanical strength compared to filled PTFE.
- Applications: Ideal for highly corrosive chemical services, pharmaceutical production, food processing, semiconductor manufacturing, and lower-pressure general industrial applications where purity is a prime concern.
Filled PTFE Gaskets
To enhance the mechanical properties of virgin PTFE and significantly reduce its susceptibility to cold flow, various fillers are homogeneously incorporated into the PTFE matrix. The choice of filler is determined by the specific property enhancements required.
| Filler Type | Properties Enhanced | Typical Applications |
|---|---|---|
| Glass Fiber (e.g., 15-25%) | Increased compressive strength, significantly reduced creep and cold flow, improved wear resistance, and better thermal conductivity. | General chemical processing, petrochemical, moderate to high pressure applications, and steam. |
| Carbon (e.g., 10-35%) | Enhanced hardness, superior wear resistance, improved thermal conductivity, excellent creep resistance, and antistatic properties. | High-pressure applications, steam, hot water, chemical processing, and applications requiring electrical conductivity. |
| Graphite (e.g., 5-15%) | Excellent chemical resistance (often comparable to virgin PTFE), improved wear resistance, good thermal conductivity, reduced friction. | High-temperature applications, steam, and aggressive chemicals, where low friction is still desired. |
| Bronze (e.g., 40-60%) | Substantially increased wear resistance, high hardness, excellent thermal conductivity, and improved dimensional stability. | High-pressure hydraulic and pneumatic systems, bearing pads, are less common for static gaskets due to reduced chemical resistance. |
| Molybdenum Disulfide (MoS2) | Provides excellent lubricity, reduced friction, and improved wear characteristics. | Low-friction sliding applications, bearings, and some dynamic seals. |
| Silica / Glass Microspheres | Improved creep resistance, good chemical resistance, and better recovery than virgin PTFE. | Fragile flanges (e.g., glass-lined) due to enhanced conformability and sealing at lower loads. |
- Pros (General for Filled PTFE): Dramatically reduced cold flow/creep, increased mechanical strength (e.g., tensile strength, hardness), improved wear resistance, and often higher pressure capabilities.
- Cons (General for Filled PTFE): Chemical resistance may be slightly reduced depending on the filler’s compatibility with the specific media. Purity may be compromised for ultra-high purity applications.
Expanded PTFE (ePTFE) Gaskets
What is ePTFE? Expanded PTFE (ePTFE) is a material derived from 100% pure virgin PTFE through a unique manufacturing process involving controlled expansion and stretching. This process transforms the dense, crystalline structure of virgin PTFE into a highly fibrillated, microporous material with a node-and-fibril microstructure. This intricate network provides multi-directional strength, making ePTFE distinct from virgin or filled PTFE. It typically comes in sheet form, joint sealant tape (cord), or pre-cut gaskets.
Unique Microstructure and Its Benefits:
The key to ePTFE’s superior performance lies in its microstructure. Unlike solid PTFE, ePTFE consists of a web of PTFE fibrils connected by nodes. This structure offers:
- Multi-Directional Strength: The controlled expansion process results in a material with nearly equal tensile strength in all directions (biaxially oriented), eliminating the “grain” effect found in skived virgin PTFE. This enhances dimensional stability and resistance to creep.
- High Porosity: The microporous nature gives ePTFE a lower density than virgin PTFE (ranging from 0.6 to 1.0 g/cm³ compared to ~2.2 g/cm³ for virgin PTFE). This porosity contributes to its softness and conformability.
- Softness and Flexibility: Despite its strength, ePTFE is significantly softer and more flexible than other PTFE types, allowing it to easily conform to irregular or damaged flange surfaces.
Key Performance Advantages of ePTFE
- Exceptional Conformability and Sealability: Its softness and flexibility enable ePTFE to fill minute surface imperfections, scratches, and pitting on flange faces. This allows for excellent sealing even with low bolt loads, making it ideal for fragile flanges (e.g., glass-lined, FRP, plastic) or applications where bolt load is limited.
- Superior Creep and Cold Flow Resistance: While it is still PTFE and can experience some cold flow, the multi-directional fibrillated structure of ePTFE significantly restricts creep and cold flow compared to virgin PTFE. This helps maintain bolt load and seal integrity over time, reducing the need for retorquing.
- Universal Chemical Resistance: Since it’s made from 100% virgin PTFE, ePTFE inherits the universal chemical resistance, making it compatible with almost all chemicals across the entire pH range (0-14), with the only exceptions being molten alkali metals and elemental fluorine at high temperatures and pressures.
- Wide Temperature Range: Maintains performance from extreme cryogenic temperatures (down to -268°C / -450°F) up to 260°C (500°F) continuously, with short excursions to 315°C (600°F).
- High Purity and Non-Contamination: As it contains no binders, fillers, or additives, ePTFE is extremely pure and physiologically inert, making it ideal for pharmaceutical, food & beverage, and semiconductor applications. It often complies with FDA 21 CFR 177.1550 and USP Class VI.
- Good Blow-out Resistance: Despite its softness, the biaxial strength provides good blow-out resistance.
- Easy Installation and Removal: Its flexibility simplifies installation, and it typically removes cleanly from flanges without leaving residue.
Technical Data for ePTFE
| Property | Unit | Typical Value Range for ePTFE | Test Method (Approx.) | Notes |
|---|---|---|---|---|
| Material | 100% Expanded Virgin PTFE | No binders or additives | ||
| Temperature Range (Continuous) | °C (°F) | -268 to 260 (-450 to 500) | Short excursions up to 315°C (600°F) possible | |
| Pressure Range (Max) | bar (psi) | Vacuum up to 200 (3000) | Depends heavily on temperature, flange design, and media. | |
| pH Range | 0-14 (universal) | Except molten alkali metals & elemental fluorine | ||
| Density | g/cm³ | 0.6 – 1.0 | ASTM D792 | Significantly lower than virgin PTFE |
| Tensile Strength | MPa (psi) | 10-20 (1450-2900) | ASTM F152 | Across grain, often consistent due to the biaxial nature |
| Compressibility | % | 45-68 | ASTM F36 | High compressibility for excellent conformability |
| Recovery | % | 12-15 | ASTM F36 | Good recovery helps maintain the seal |
| Creep Relaxation (24h @ 100°C) | % | 15-35 | ASTM F38 | Much lower than virgin PTFE at elevated temps |
| Sealability (Nitrogen) | ml/hr | <0.16 | ASTM F37B | Excellent low leakage rates |
| Color | White | |||
| FDA Compliance | Yes (21 CFR 177.1550) | Safe for food and pharmaceutical contact | ||
| TA-Luft | Yes | VDI 2440 | Certified for low fugitive emissions (up to 230°C) |
Skived PTFE Gaskets
- Description: Produced by skiving (peeling) a continuous thin sheet from a molded or ram-extruded billet of virgin PTFE. This process creates a material with a distinct “grain” or directional strength.
- Pros: Good surface finish, excellent electrical properties, good chemical resistance (for virgin PTFE).
- Cons: Higher tendency for cold flow along the grain direction, can be prone to extrusion if not properly confined, typically limited to virgin PTFE properties.
- Applications: General purpose sealing, electrical insulation, and diaphragms.
Molded PTFE Gaskets
- Description: Formed by compressing PTFE powder in a mold and then sintering it at high temperatures. This allows for the creation of complex shapes or thicker sections directly.
- Pros: Can create intricate geometries, suitable for very thick gaskets, and can incorporate fillers.
- Cons: Can be more costly for standard flat gaskets, may have internal stresses.
- Applications: Custom parts, valve seats, and seals requiring specific geometries.
Comparison of Key PTFE Gasket Types
| Property | Virgin PTFE | Filled PTFE (e.g., Glass) | Expanded PTFE (ePTFE) |
|---|---|---|---|
| Chemical Resistance | Excellent | Good to Excellent (filler dependent) | Excellent |
| Cold Flow/Creep | High | Low | Low to Moderate (excellent for PTFE) |
| Mechanical Strength | Moderate | High | Low to Moderate (biaxially strong) |
| Conformability | Moderate | Low | Excellent |
| Purity | Highest | Reduced (due to filler) | High (100% PTFE) |
| Seating Stress Req. | Moderate | High | Very Low |
| Flange Imperfection Tolerance | Low | Low | High |
| Cost | Moderate | Moderate to High | Moderate to High |
Key Performance Characteristics
Understanding the technical data is crucial for selecting the correct PTFE gasket for your application.
Chemical Compatibility Chart
Disclaimer: This chart provides general guidelines. Always consult specific chemical resistance charts from gasket manufacturers and conduct testing for critical applications. Concentration, temperature, and pressure can significantly affect compatibility.
| Chemical Class | Examples | Virgin PTFE | Filled PTFE | ePTFE | Notes |
|---|---|---|---|---|---|
| Acids (Strong) | Hydrochloric Acid, Sulfuric Acid, Nitric Acid | Excellent | Excellent | Excellent | Fuming nitric acid at high temperatures may affect some fillers. |
| Bases/Alkalies (Strong) | Sodium Hydroxide, Potassium Hydroxide | Excellent | Excellent | Excellent | |
| Solvents (Organic) | Acetone, Toluene, Benzene, MEK, DMSO | Excellent | Excellent | Excellent | |
| Hydrocarbons | Oils, Gasoline, Kerosene | Excellent | Excellent | Excellent | |
| Halogens | Chlorine (wet/dry), Bromine, Fluorine | Excellent | Good | Excellent | Highly reactive with many fillers. Virgin/ePTFE preferred. |
| Oxidizing Agents | Hydrogen Peroxide, Bleach, Ozone | Excellent | Good | Excellent | Some fillers may degrade. |
| Steam | Saturated/Superheated Steam | Good | Excellent | Good | Filled PTFE (e.g., carbon, graphite) often preferred for long-term steam service due to better creep resistance. |
| Molten Alkali Metals | Sodium, Potassium | Not Recommended | Not Recommended | Not Recommended | The only common chemicals that attack PTFE. |
| Elemental Fluorine | (at high temperature/pressure) | Not Recommended | Not Recommended | Not Recommended | Reacts under these specific conditions. |
Temperature vs. Pressure
| PTFE Type | Max. Pressure @ 20°C (68°F) | Max. Pressure @ 100°C (212°F) | Max. Pressure @ 200°C (392°F) | Max. Pressure @ 250°C (482°F) | Max. Temp (Continuous) |
|---|---|---|---|---|---|
| Virgin PTFE | 80 bar (1160 psi) | 30 bar (435 psi) | 10 bar (145 psi) | 5 bar (75 psi) | 260°C (500°F) |
| Filled PTFE (25% Glass) | 150 bar (2175 psi) | 80 bar (1160 psi) | 40 bar (580 psi) | 20 bar (290 psi) | 260°C (500°F) |
| Expanded PTFE (ePTFE) | 120 bar (1740 psi) | 60 bar (870 psi) | 30 bar (435 psi) | 15 bar (220 psi) | 260°C (500°F) (Short term up to 315°C) |
Mechanical Properties
| Property | Unit | Virgin PTFE | Filled PTFE (e.g., 25% Glass) | Expanded PTFE (ePTFE) (Sheet) | Test Method (Approx.) |
|---|---|---|---|---|---|
| Tensile Strength | MPa (psi) | 15-30 (2175-4350) | 20-40 (2900-5800) | 10-20 (1450-2900) | ASTM D638 / F152 |
| Elongation at Break | % | 200-400 | 100-250 | 50-150 | ASTM D638 |
| Durometer Hardness | Shore D | 50-65 | 60-75 | 30-45 | ASTM D2240 |
| Compression Set (24h @23°C) | % | 10-20 | 5-10 | 8-15 | ASTM D395 |
| Density | g/cm³ | 2.14-2.20 | 2.20-2.30 (can be higher with heavy fillers) | 0.6-1.0 | ASTM D792 |
| Compressibility | % | 10-20 | 5-15 | 45-68 | ASTM F36 |
| Recovery | % | 5-10 | 5-10 | 12-15 | ASTM F36 |
| Creep Relaxation (ASTM F38) | % | High (e.g., 20-30%) | Low (e.g., 5-15%) | Low (e.g., 15-35% at elevated temps) | ASTM F38 |
Creep and Cold Flow
Understanding the Phenomenon: Creep, also known as cold flow, is the permanent deformation of a material under continuous mechanical stress over time. For PTFE, particularly virgin PTFE, this thermoplastic characteristic is pronounced. When a gasket is compressed by bolt load, the material slowly flows away from the area of highest stress, leading to a reduction in gasket thickness and a loss of bolt load. This effect is exacerbated at elevated temperatures.
Impact on Gasketing:
- Loss of Seal Integrity: As the gasket creeps, the effective sealing stress decreases, potentially leading to leakage.
- Gasket Relaxation: The initial compression force diminishes, requiring re-tightening (re-torquing) of bolts to maintain the seal.
- Gasket Extrusion: In applications with insufficient confinement (e.g., full-face gaskets on raised face flanges, or improper sizing), the material can extrude into the pipe bore.
Mitigation Strategies:
- Material Selection:
- Filled PTFE: The most effective way to combat cold flow. Fillers mechanically strengthen the PTFE matrix, significantly reducing its tendency to creep.
- ePTFE: Offers excellent resistance to cold flow compared to virgin PTFE due to its multi-directional fibrillated structure, which provides inherent dimensional stability.
- Controlled Bolt Torque: Adhere strictly to the gasket manufacturer’s recommended torque values. Over-torquing does not necessarily improve sealing and can accelerate cold flow and lead to gasket damage or extrusion.
- Retorquing: For virgin and some filled PTFE gaskets, an initial retorque of the bolts after a few hours of operation or after the first thermal cycle (when the system reaches operating temperature and cools down) is highly recommended to compensate for initial creep. ePTFE often requires less or no retorquing due to its superior creep resistance.
- Flange Design: Utilize raised face flanges with confined gasket designs (e.g., ring gaskets) which physically restrict the outward flow of the gasket material.
- Gasket Thickness: Use the thinnest practical gasket thickness. Thinner gaskets exhibit less total cold flow than thicker ones under the same compressive stress.
Permeability
PTFE, in all its forms (virgin, filled, ePTFE), possesses extremely low permeability to most gases and liquids. This characteristic is vital for applications requiring tight seals to maintain vacuum, contain hazardous or valuable media, or prevent ingress of contaminants. The microporous structure of ePTFE does allow for some gas permeability (like water vapor), while remaining liquid-impermeable (hydrophobic), a property leveraged in filtration membranes, but for static sealing, its overall leakage rates remain exceptionally low.
Recommended Flange Surface Finishes
| Gasket Material | Recommended Ra (µm) | Recommended RMS | Notes |
|---|---|---|---|
| Virgin PTFE | 3.2 – 6.3 | 125 – 250 | Spiral serrated finish is advantageous. |
| Filled PTFE | 3.2 – 6.3 | 125 – 250 | Spiral serrated finish is advantageous. |
| Expanded PTFE (ePTFE) | Up to 12.5 | Up to 500 | Ideal for irregular, damaged, or fragile flanges. |
Standards and Certifications to Look For
Reputable PTFE gaskets are tested and certified against recognized standards:
- ASTM F104, F36, F37, F38, F152 — gasket classification, compressibility, sealability, creep, and tensile testing
- ISO 13000 — PTFE molding and extrusion materials
- FDA 21 CFR 177.1550 — food-contact compliance
- USP Class VI — biocompatibility for pharmaceutical use
- TA-Luft (VDI 2440) — low fugitive-emissions certification
Always request a Certificate of Conformance for critical applications. Asian Sealing Products’ PTFE and CNAF gaskets are manufactured under our ISO 9001:2015-certified quality system, with material traceability and test documentation provided on request; see our full certifications.
Troubleshooting Common Issues
While PTFE gaskets offer exceptional reliability, understanding potential issues and their remedies can minimize downtime and improve operational efficiency.
Leakage
- Causes:
- Insufficient Bolt Load/Under-torquing: The most common cause. The gasket was not compressed enough to create an effective seal or maintain it under pressure.
- Cold Flow/Relaxation: The gasket material (especially virgin PTFE) creeps over time, leading to a loss of bolt load and seating stress.
- Improper Installation: Gasket misalignment, pinching, or damage during installation.
- Damaged Flange Surfaces: Scratches, gouges, or warping on the sealing face can create leak paths that the gasket cannot fully bridge.
- Incorrect Gasket Type: Using virgin PTFE where a filled or ePTFE gasket is required due to high pressure, temperature, or cold flow concerns.
- Excessive Vibration or Thermal Cycling: Can cause bolts to loosen over time, reducing clamping force.
- Chemical Incompatibility (Rare for PTFE base, but possible with fillers): While the PTFE base is highly resistant, some fillers might degrade with specific media, leading to seal failure.
- Solutions:
- Verify Bolt Torque: Re-torque bolts to the manufacturer’s specified values using a calibrated torque wrench and a proper tightening sequence.
- Implement Retorquing: For virgin and certain filled PTFE gaskets, plan for an initial retorque after system start-up or the first thermal cycle.
- Review Installation Procedure: Ensure all personnel are trained on proper gasket handling and installation techniques.
- Inspect Flanges: Check flange faces for damage. If severe, re-machine or replace the flange. Consider ePTFE for its ability to seal on imperfect surfaces.
- Select Correct Gasket: Re-evaluate application parameters (pressure, temperature, media, flange condition) and choose the appropriate PTFE gasket type (e.g., switch from virgin to filled or ePTFE for better creep resistance).
- Maintain Bolt Load: Consider using spring washers or disc springs in applications with high vibration or frequent thermal cycling.
Gasket Extrusion
- Causes:
- Excessive Bolt Load/Over-torquing: Applying too much compressive force can cause the soft PTFE material to flow outward beyond the flange OD or inward into the pipe bore.
- Insufficient Gasket Confinement: Using a full-face gasket on a raised face flange, or a gasket that is too wide for the flange sealing area.
- Too Thick a Gasket: Thicker gaskets have more material volume, making them more prone to extrusion.
- Insufficient Flange Rigidity: Flanges that bow or deflect under high bolt load can create gaps that allow the gasket to extrude.
- Solutions:
- Control Bolt Torque: Strictly adhere to recommended torque values; avoid over-torquing.
- Optimize Gasket Design: Use recessed (ring) gaskets on raised face flanges for better confinement. Ensure gasket dimensions match flange specifications precisely.
- Reduce Gasket Thickness: Use the thinnest practical gasket (1.5mm or 3.0mm are standard).
- Improve Flange Rigidity: Ensure flanges meet design standards and are sufficiently rigid for the application’s pressure and temperature.
- Select Filled PTFE or ePTFE: These materials offer improved extrusion resistance compared to virgin PTFE due to their enhanced mechanical strength and creep resistance.
Premature Failure
- Causes:
- Material Mismatch: Selecting a PTFE gasket that is not suitable for the application’s specific pressure, temperature, or chemical environment. (e.g., using virgin PTFE in a high-pressure steam application, or a filled PTFE where the filler is incompatible with the media).
- Temperature Excursion: Operating the system beyond the gasket’s maximum continuous or short-term temperature limit.
- Chemical Attack (of fillers): While the PTFE base is highly inert, some fillers can be attacked by specific aggressive chemicals, leading to gasket degradation.
- Mechanical Damage: Gaskets can be damaged during shipping, storage, handling, or installation (e.g., nicks, cuts, scratches).
- Improper Storage: Exposure to UV light, extreme temperatures, or contaminants during storage can degrade gasket performance.
- Solutions:
- Thorough Application Review: Conduct a detailed review of all operating parameters (P, T, C – Pressure, Temperature, Chemical) and select the PTFE grade that best meets all requirements. Consult with your gasket supplier.
- Process Control: Ensure the system operates within the specified temperature limits of the gasket material.
- Verify Chemical Compatibility: Double-check compatibility charts, especially for filled PTFE, to ensure the filler material is also resistant to the process media.
- Proper Handling: Train personnel on careful handling and inspection of gaskets before installation. Discard any damaged gaskets.
- Adhere to Storage Guidelines: Store gaskets in a cool, dry place, away from direct sunlight and contaminants, in their original packaging.
Why Source PTFE Gaskets from Asian Sealing Products
- ISO 9001:2015, ISO 14001:2015, and ISO 45001:2018 certified manufacturing across our Chennai facility
- API 6A and API 17D licensed, with EIL approval for oil & gas and process applications
- 15,000 sq.m production facility with in-house testing and quality control
- Global reach — supplying gasket solutions to the UAE, Saudi Arabia, the USA, and Southeast Asia, with a dedicated USA & Mexico distribution hub
- Recognized as a top-ranked gasket manufacturer by TradeIndia and Hindustan Times
Request a quote or explore our PTFE and CNAF gasket range to get engineering support for your application.
FAQs
What is a PTFE gasket used for?
PTFE gaskets seal flange connections in applications with aggressive chemicals, extreme temperatures, or strict purity requirements — common in chemical processing, oil & gas, pharmaceutical, food, and semiconductor industries.
What are the three main types of PTFE gaskets?
Virgin PTFE (pure, highest chemical resistance, most prone to cold flow), filled PTFE (reinforced with glass, carbon, or graphite for strength and creep resistance), and expanded PTFE / ePTFE (fibrillated structure that resists cold flow while keeping virgin-grade purity).
What temperature range can a PTFE gasket handle?
PTFE gaskets operate continuously from -260°C to 260°C (-436°F to 500°F), with short excursions up to 315°C (600°F).
What is cold flow in a PTFE gasket, and how is it prevented?
Cold flow (creep) is the gradual deformation of PTFE under sustained bolt load. It’s minimized by choosing filled or ePTFE gaskets, using correct torque values, confined (recessed) gasket designs, and retorquing after the first thermal cycle.
Can PTFE gaskets be reused?
No. Once compressed, a PTFE gasket takes a permanent set and won’t reseal reliably. Always fit a new gasket at every maintenance interval.
Are PTFE gaskets safe for food and pharmaceutical use?
Yes — virgin PTFE and ePTFE are physiologically inert and typically comply with FDA 21 CFR 177.1550 and USP Class VI.
Do PTFE gaskets need sealant or grease?
No. Never apply sealant or grease to a PTFE gasket face — it interferes with the sealing mechanism. Only lubricate bolt threads and nuts.
Which PTFE gasket is best for a damaged or irregular flange?
Expanded PTFE (ePTFE) — its soft, conformable structure seals effectively on flange surfaces up to Ra 12.5 µm, including glass-lined, FRP, and corroded flanges.
