RFQ Today
Certifications: EN 10204 3.1 / 3.2 material test certificates (where applicable), ASTM F104 gasket classification data, and complete export documentation packages.
PTFE
A world-class technical reference for EPC contractors, piping engineers, procurement heads, and TPI inspection agencies specifying the gaskets, envelope gaskets, expanded PTFE tape, filled/reinforced PTFE compounds, and PTFE pipe thread sealant products — covering material properties and forms, gasket design per ASME B16.21, chemical and temperature compatibility, filler selection logic, and the QC and documentation discipline required for critical EPC flange and threaded joint sealing supply.
Forms & Application
Selection Logic
As a bulk gasket, seal, and thread sealant material, PTFE (polytetrafluoroethylene) provides the same fundamental chemical inertness and low-friction characteristics discussed in RR Hydraulic’s PTFE coating reference — applied here to sealing applications where it forms the entire sealing element rather than a surface coating on a metal substrate.
1.1 — Why PTFE Is the Default Non-Metallic Gasket and Sealing Material
PTFE’s combination of near-universal chemical inertness, wide service temperature range (-200°C to +260°C continuous), excellent dielectric properties, and inherently non-stick, low-friction surface makes it the default choice for non-metallic gasket, seal, and thread sealant applications wherever the process fluid is aggressive, the sealing surface must resist adhesion to the mating flange faces (easing disassembly for maintenance), or a wide operating temperature range must be accommodated without material degradation. Unlike elastomeric gasket materials (rubber, EPDM, Viton), it does not swell, soften, or chemically degrade in contact with the vast majority of industrial process fluids — this chemical universality is the single most compelling reason PTFE gaskets and seals are specified across chemical processing, pharmaceutical, food and beverage, and general industrial piping wherever a broad-spectrum, “safe default” non-metallic sealing material is required without performing an extensive elastomer compatibility study for every process fluid the joint may encounter over its service life.
1.2 — Product Forms
Skived/Cut PTFE Gasket Sheet
PTFE sheet produced by skiving (thin slicing) from a sintered PTFE billet, or by direct sheet moulding — cut into flat gaskets to the flange bolt pattern and bore per ASME B16.21 or the applicable flange standard. The standard form for full-face and ring-type flat gaskets on RF and FF flanges in general process piping.
Envelope Gaskets
A thin PTFE “envelope” or jacket wrapped around a softer, more compressible core material (typically a compressed non-asbestos fibre or rubber core) — combines the chemical resistance and non-stick sealing face with the core material’s superior compressibility and gasket seating characteristics, providing better sealing performance at lower bolt load than solid PTFE alone while retaining full chemical resistance at the process-fluid-contacted surface.
Expanded (ePTFE) Tape and Gaskets
PTFE processed through an expansion process that creates a microporous, highly conformable structure with substantially improved compressibility and creep resistance compared to conventional skived PTFE sheet — expanded PTFE gasket tape (wound around the flange bolt circle by the installer) and pre-formed expanded the gaskets provide superior sealing performance, particularly on imperfect or slightly damaged flange faces, compared to standard PTFE sheet gaskets.
PTFE Pipe Thread Sealant Tape
Thin PTFE tape wound around male NPT/BSPT threaded pipe connections before assembly, providing both a lubricating and sealing function that fills minor thread imperfections and prevents fluid leakage through the thread’s helical clearance path — the standard sealing method for threaded pipe joints in general plumbing, pneumatic, and low-to-moderate-pressure hydraulic connections, per DIN 3535 or equivalent thread sealant tape standards.
Filled and Reinforced PTFE Compounds
Virgin PTFE compounded with fillers (glass fibre, carbon, graphite, bronze, or other materials) to improve specific mechanical properties — reduced cold flow/creep, improved wear resistance, increased load-bearing capacity, or enhanced thermal conductivity — at some trade-off in chemical inertness or dielectric properties depending on the specific filler. Used for gaskets, valve seats, bearing/wear components, and packing rings requiring properties beyond virgin baseline mechanical performance.
Valve Seats and Packing Rings
Machined or moulded (often filled) components used as valve seat rings (providing the soft-seat sealing surface in ball and other valve types) and as packing rings in stem sealing and pump shaft sealing applications — leveraging PTFE’s low friction, chemical inertness, and self-lubricating characteristics for dynamic sealing service.
1.3 — Filler Selection Logic
| Filler | Typical Loading | Property Improvement | Trade-Off |
|---|---|---|---|
| Glass fibre | 15–25% | Reduced cold flow/creep; increased compressive strength | Some reduction in chemical resistance to strong alkalis; slightly abrasive to mating metal surfaces |
| Carbon / graphite | 15–25% | Improved wear resistance and thermal conductivity; reduced friction in dynamic sealing | Electrically conductive (loses dielectric insulation property); some chemical resistance trade-off |
| Bronze | 40–60% | High load-bearing capacity; excellent thermal conductivity; good wear resistance | Reduced chemical resistance (bronze filler susceptible to acid attack); electrically conductive |
| Molybdenum disulphide (MoS₂) | 1–5% (often combined with glass) | Further reduced friction and improved wear resistance in dynamic applications | Minor cost increase; typically combined with another primary filler |
ASME B16.21, Standards
& Sealing Characteristics
It gasket dimensions, classification, and sealing performance are governed by specific ASME and ASTM standards. Full detail on the flange standards gaskets are designed against is available in our ANSI B16 reference.
Submit form, thickness, size, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — Governing Standards
ASME B16.21 — Non-Metallic Flat Gaskets for Pipe Flanges
Defines the dimensional standard for non-metallic flat gaskets (including PTFE) sized to mate with ASME B16.5 flanges — inside diameter, outside diameter, and bolt hole pattern (for ring-type or full-face gaskets) matched to the corresponding flange NPS and pressure class.
ASTM F104 — Non-Metallic Gasket Materials Classification
Provides a standardised classification system for non-metallic gasket materials (including PTFE) based on key properties — compressibility, recovery, tensile strength, and other characteristics — allowing gasket materials to be specified and compared using a consistent classification code independent of manufacturer or brand.
ASTM D1710 / D4894 / D4895 — PTFE Material Specifications
D1710 covers extruded PTFE rod and tube stock; D4894 covers granular (moulding) PTFE resin; D4895 covers fine powder (paste-extrudable) PTFE resin — the base polymer material specifications underlying finished gasket, seal, and sealant products.
DIN 3535 — PTFE Thread Sealant Tape
The European standard governing PTFE thread sealant tape dimensions (width, thickness, roll length) and density/quality classifications by application category (Part 1: general purpose; Part 2: oxygen service and other specialized applications with restricted lubricant/filler content requirements).
2.2 — Gasket Sealing Mechanics: Why PTFE Requires Careful Bolt-Load Management
Unlike compressed fibre or rubber gaskets, PTFE exhibits a characteristic called “cold flow” or creep relaxation under sustained compressive load — the material continues to deform slowly over time at the applied bolt preload, gradually relieving some of the compressive stress originally applied at installation torque. This behaviour means a PTFE gasket joint that was correctly torqued at installation can experience gradual preload loss over weeks to months of service, potentially reducing the sealing gasket stress below the minimum required to maintain the seal — particularly relevant for thermal cycling service, where repeated heating/cooling cycles accelerate this creep relaxation. This is the primary engineering reason expanded PTFE (Section 1.2) — engineered specifically to reduce creep and improve long-term stress retention compared to conventional skived PTFE sheet — is increasingly specified over standard PTFE sheet gaskets for critical, long-term, or thermally-cycled flanged joints, and why periodic re-torque inspection is a recommended maintenance practice for PTFE-gasketed critical joints in cyclic service.
2.3 — PTFE Gasket vs. Alternative Non-Metallic Gasket Materials
| Material | Chemical Resistance | Temperature Range | Creep Resistance | Cost |
|---|---|---|---|---|
| PTFE (skived sheet) | Excellent — near-universal | -200°C to +260°C | Moderate — susceptible to cold flow under sustained load | Moderate |
| Expanded PTFE (ePTFE) | Excellent — near-universal | -200°C to +260°C | Good — engineered for improved stress retention | Moderate-high |
| Compressed non-asbestos fibre (CNAF) | Good — moderate chemical range | Up to ~230°C | Moderate | Low |
| Rubber (EPDM/Viton/NBR) | Fluid-specific — requires elastomer compatibility check | Elastomer dependent, typically -40°C to +200°C | Good — elastomeric recovery | Low-moderate |
| Spiral wound metallic gasket | Metal-and-filler dependent | Broad — up to 600°C+ depending on filler/metal | Excellent — metallic winding provides robust spring-back | Moderate-high |
Service Limits
& Thread Sealant Practice
Correct PTFE gasket and sealant selection requires understanding both the material’s broad chemical compatibility and its practical mechanical limits — as well as correct application technique for PTFE thread sealant tape on threaded pipe connections.
3.1 — Chemical Compatibility Overview
As discussed in RR Hydraulic’s PTFE Coating reference, PTFE resists virtually the entire practical range of industrial process fluids — acids, alkalis, solvents, and most aggressive chemicals — with the small number of documented exceptions being molten or dissolved alkali metals, elemental fluorine and closely related aggressive fluorinating agents, and certain conditions involving highly concentrated oxidizing acids at elevated temperature. For virtually every standard EPC process piping application — hydrocarbon processing, general chemical manufacturing, pharmaceutical, food and beverage, and water treatment — PTFE gaskets and seals provide reliable chemical compatibility without requiring the fluid-specific elastomer compatibility verification needed for rubber gasket alternatives.
3.2 — Temperature and Pressure Service Limits
3.3 — PTFE Thread Sealant Tape Application Practice
Correct Winding Direction
PTFE thread tape must be wound in the same direction as the thread’s tightening rotation (typically clockwise when viewed from the pipe end being threaded in) — winding in the wrong direction causes the tape to unwind and bunch during assembly rather than compressing smoothly into the thread root, compromising the seal and potentially causing tape fragments to enter the fluid stream.
Number of Wraps and Tension
Typically 2–4 wraps applied with moderate tension (enough to seat the tape into the thread profile without excessive stretching that thins the tape beyond its effective sealing thickness) — starting one to two threads back from the pipe end to avoid tape fragments entering the bore.
Density and Application-Specific Tape Grades
Standard-density PTFE tape is adequate for general water, air, and non-critical fluid service; higher-density tape (or tape specifically rated for gas service) is recommended for gas, oxygen, and higher-pressure applications where the standard tape’s sealing margin may be inadequate — verify the tape’s specific rated application per its DIN 3535 classification or manufacturer’s technical data before use on gas or oxygen service.
Not a Substitute for Correct Thread Engagement
PTFE thread tape seals minor thread clearance imperfections and reduces installation friction, but does not substitute for correct thread engagement length, correct thread form/class matching between mating components, or adequate installation torque — a joint with insufficient thread engagement will leak regardless of tape application, since the tape cannot compensate for fundamentally inadequate mechanical thread contact.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability and dimensional/material verification for PTFE gasket, seal, and thread sealant product supply, from raw resin lot through finished product testing to final dispatch documentation.
4.1 — Inspection & QC Protocol
4.2 — Documentation Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| Material certificate of conformance | PTFE resin type, filler content, ASTM F104 classification code | Mandatory — all EPC supply | All gasket and seal product supply |
| Dimensional inspection report | ASME B16.21 or applicable flange standard tables | Mandatory | All gasket product supply |
| Compressibility/recovery test report | ASTM F36 / F38 | Conditional — critical service gaskets | High-consequence or safety-critical joints |
| Food/pharmaceutical compliance declaration | FDA 21 CFR 177.1550 or equivalent | Conditional — food/pharma-contact applications | Food, beverage, and pharmaceutical process service |
4.3 — Applications by Industry
Chemical Process Flange Sealing
PTFE and expanded PTFE gaskets as the default non-metallic gasket choice across chemical process plant flange connections — the near-universal chemical compatibility eliminates the need for fluid-specific elastomer selection studies on the large majority of process lines, simplifying gasket specification across a plant with diverse process fluid services.
Pharmaceutical and Food-Grade Process Equipment
PTFE gaskets and seals meeting FDA food-contact compliance (21 CFR 177.1550) for pharmaceutical and food/beverage process piping, where both chemical inertness and hygienic, non-stick, cleanable surface characteristics are simultaneously required — non-porous surface resists bacterial adhesion and simplifies cleaning validation compared to more porous gasket alternatives.
General Threaded Pipe Joint Sealing
PTFE thread sealant tape as the standard sealing method for NPT/BSPT threaded pipe connections across plumbing, pneumatic, and general low-to-moderate-pressure hydraulic fitting applications — the default, universally available thread sealing solution for the vast majority of threaded pipe joint sealing requirements outside of high-pressure or gas-critical applications requiring a specifically rated tape grade.
4.4 — Export Packaging Specification
- PTFE gaskets individually packed flat or in protective sleeves to prevent creasing, cutting, or damage during transit — This sheet gaskets are relatively soft and can be permanently deformed by improper stacking or handling
- Cartons labelled with gasket size (per NPS/PN class), thickness, material composition (virgin/filled type), and, where applicable, the ASTM F104 classification code
- PTFE thread sealant tape supplied in standard roll packaging, labelled with tape width, thickness/density, and DIN 3535 classification or application-specific grade designation
- Documentation in a waterproof pocket: material certificate of conformance, dimensional inspection report, compressibility/recovery test report (where applicable), food/pharma compliance declaration (where applicable), and packing list with form/size/composition breakdown per item
- Standard export cartons for international shipment, with country of origin and HS tariff code documentation matched to the product category
Submit your form, thickness, size, and quantity to RR Hydraulic for a complete, certified commercial offer.