AFLAS O-Rings (FEPM)
The high-performance choice for steam, sour gas, amines and caustic environments where FKM compounds fail.
Overview
AFLAS is a tetrafluoroethylene propylene copolymer (FEPM) that occupies a unique position in the high-performance sealing market. It delivers exceptional resistance to steam, hot water, strong bases (alkalis), amines and sour gas (H₂S) — media that rapidly degrade standard FKM compounds through dehydrofluorination.
With a continuous operating temperature range of -5°C to +230°C, AFLAS is widely specified in oil and gas downhole tools, geothermal wellheads, power plant water treatment systems, and chemical processing plants handling caustic soda and amines. Its resistance to phosphate ester hydraulic fluids also makes it suitable for aerospace and industrial hydraulic systems using Skydrol.
AFLAS is not compatible with aromatic hydrocarbons, ketones or chlorinated solvents. In these environments, FKM or FFKM should be selected instead. For applications involving hot water, steam, bases and sour gas in SAGD (Steam-Assisted Gravity Drainage) oil sands operations, AFLAS is the standard industry choice over HNBR or FKM due to its combined steam and amine resistance.
Compression set (ASTM D395 Method B, 70 h/200°C) is typically 20–35%, acceptable for most static applications. NACE MR0175 / ISO 15156 compliant grades available for sour gas service.
Lead time: 10–20 days standard. MOQ: 1 piece. ISO 9001 certified.
The molecular structure of AFLAS is a copolymer of tetrafluoroethylene (TFE) and propylene in an approximately 50:50 molar ratio, polymerized to create an alternating or pseudo-alternating structure. Unlike FKM, which contains vinylidene fluoride (VDF) units with C-H bonds, AFLAS has no VDF — the backbone alternates between perfluorinated ethylene segments (-CF₂-CF₂-) and hydrogenated propylene segments (-CH₂-CH(CH₃)-). This unique structure provides two key benefits: the TFE segments contribute chemical resistance and thermal stability, while the propylene segments provide elastomeric flexibility and, critically, resistance to dehydrofluorination because there are no adjacent C-H and C-F bonds that can eliminate HF. The copolymer is cured using peroxide vulcanization, typically with triallyl isocyanurate (TAIC) as a co-agent, forming C-C crosslinks that are stable to approximately 250°C. The absence of dehydrofluorination reactivity explains AFLAS's exceptional performance in steam, caustic, and amine environments where FKM fails.
Quantified performance comparisons versus FKM highlight AFLAS's specific advantages. In steam resistance testing (continuous saturated steam at 200°C, 168 h), AFLAS maintains tensile strength retention >70% and shows minimal surface cracking, while standard FKM hardens, cracks, and loses >50% tensile strength due to dehydrofluorination. In caustic soda resistance (ASTM D471, 50% NaOH at 100°C, 70 h), AFLAS shows volume change <3% and hardness change <5 Shore A, while FKM swells >30% and hardens by >15 Shore A. In amine resistance (ASTM D471, diethanolamine at 100°C), AFLAS volume change is <5% versus FKM's >40% — an 8× improvement. However, in aromatic hydrocarbon resistance (ASTM D471, toluene at 23°C), FKM shows volume change <10% while AFLAS swells >40%, confirming that AFLAS is not a general replacement for FKM but a specialist for base/amine/steam service. The compression set of AFLAS at 200°C (20–35%) is slightly higher than FKM's (≤ 20%), reflecting the trade-off between chemical resistance and elastic recovery. Tensile strength of 10–18 MPa is comparable to FKM's 10–16 MPa.
A practical grade-selection decision tree: if your application is an oilfield SAGD wellhead seal exposed to 200°C steam, sour gas (H₂S), and amine-based corrosion inhibitors, specify NACE MR0175 compliant AFLAS at 80 Shore A — this is AFLAS's signature application and the reason it dominates Canadian oil sands operations. If your application is a geothermal wellhead valve seal handling 180–230°C brine with dissolved CO₂ and H₂S, specify AFLAS 75–80 Shore A with peroxide cure and full sour gas documentation. If your application is an aerospace hydraulic system using phosphate ester fluid (Skydrol 500B-4), specify 70 Shore A AFLAS — it is the industry standard for Skydrol compatibility, outperforming FKM which swells in phosphate esters. If your application is a power plant boiler feedwater valve seal at 150°C and 10 bar with caustic soda treatment, specify AFLAS 70 Shore A. If your application involves aromatic hydrocarbons (toluene, xylene), ketones (MEK, acetone), or chlorinated solvents, do not use AFLAS — specify FKM or FFKM. If your application requires cold-start sealing below 0°C, verify actual cold-start compression force with hardware testing; AFLAS's TR10 of approximately -5°C means it stiffens significantly near freezing.
Storage of AFLAS follows the same principles as other peroxide-cured elastomers. Store in opaque, airtight packaging below 25°C, away from direct sunlight, ozone sources, and strong oxidizers. The recommended shelf life is 5–7 years for peroxide-cured AFLAS. AFLAS's saturated TFE-propylene backbone provides good ozone resistance, though not as exceptional as fully saturated EPDM or VMQ. Specific gravity of 1.55–1.60 provides easy field identification — AFLAS is noticeably heavier than NBR (1.00–1.25) and lighter than FKM (1.80–1.95). A common error is selecting AFLAS based solely on its high temperature rating (+230°C) without considering its low-temperature limit: at -5°C, AFLAS is already near its TR10 flexibility limit, and at -15°C it becomes effectively rigid. Another frequent mistake is confusing AFLAS with FKM in inventory because both are black and high-performance; specific gravity measurement (1.55–1.60 vs 1.80–1.95) is the fastest field distinction, followed by FTIR spectroscopy for definitive identification.
Material Properties
| Temperature Range | -5°C to +230°C (+23°F to +446°F) |
| Hardness Range | 60–90 Shore A (ASTM D2240) |
| Tensile Strength | 10–18 MPa (ASTM D412) |
| Elongation at Break | 150–300% (ASTM D412) |
| Compression Set (70 h/200°C) | 20–35% (ASTM D395 Method B) |
| Steam Resistance | Excellent to +200°C continuous |
| Base/Amine Resistance | Superior vs. FKM; resists concentrated NaOH and oilfield amines |
| Color (standard) | Black |
| Standards | ASTM D2000 CH, API 6A, NACE MR0175 / ISO 15156 |
Typical Applications
Oil & Gas / SAGD
Downhole packer seals, SAGD wellhead equipment, and BOP seals in sour gas and high-pH amine-treating environments. Standard choice over HNBR where H₂S + steam + amines coexist.
Geothermal
Wellhead and valve seals exposed to high-temperature brine (180–230°C) and steam where FKM compounds fail by acid dehydrofluorination.
Power Generation
Steam turbine seals, boiler feedwater valves and high-pH water treatment system O-rings.
Chemical Processing
Reactor seals, agitator seals and pump seals handling caustic soda (NaOH), amines, and hot water where FKM is degraded by alkaline conditions.
Aerospace
Phosphate ester hydraulic fluid seals (Skydrol) and engine hot-section gaskets requiring phosphate ester compatibility.
Chemical Compatibility Summary
Compatible With
- - Steam and hot water
- - Strong bases and caustic soda
- - Amines and oilfield chemicals
- - Sour gas (H2S)
- - Aliphatic hydrocarbons
Incompatible With
- - Aromatic hydrocarbons
- - Ketones and chlorinated solvents
- - Strong oxidizing acids
- - Some automotive fuels (high aromatic)
- - Polar solvents
Compare Nearby Materials
Further Reading
AFLAS vs FKM
The clearest comparison for amines, steam, sour gas, and aggressive process duty.
Read articleBest Material for Oil and Gas
How AFLAS competes with HNBR, FKM, and FFKM in field applications.
Read articleKey Advantages
Exceptional Steam and Hot Water Resistance
AFLAS maintains sealing integrity in continuous steam service up to +200°C, outperforming FKM (which is attacked by steam above 150°C) and HNBR in wet heat environments.
Superior Base and Amine Resistance
Strong alkalis, caustic soda and oilfield amines (MEA, DEA, MDEA) that attack FKM by dehydrofluorination have minimal effect on AFLAS compounds.
Sour Gas (H₂S) Compatibility
NACE MR0175 / ISO 15156 compliant AFLAS grades are used in sour gas wellheads and downhole tools where H₂S concentrations are high.
Cost-Effective High Performance
AFLAS delivers critical advantages over FKM at a fraction of FFKM cost for steam, base and amine applications — typically 20–40% of FFKM pricing for equivalent sizes.
Quantified Chemical Superiority Over FKM in Alkaline and Steam Media
In ASTM D471 testing with 50% NaOH at 100°C, AFLAS shows volume change <3% and hardness change <5 Shore A, while FKM swells >30% and hardens by >15 Shore A. In diethanolamine at 100°C, AFLAS volume change is <5% versus FKM's >40%. In continuous steam at 200°C for 168 hours, AFLAS retains >70% tensile strength while FKM loses >50% due to dehydrofluorination. These quantified differences make AFLAS the rational choice whenever bases, amines, or steam are present.
Industry-Standard Aerospace Phosphate Ester Compatibility
AFLAS is the specified sealing material for phosphate ester hydraulic fluids (Skydrol 500B-4, LD-4, IV) used in commercial aircraft hydraulic systems. ASTM D471 immersion in Skydrol at 150°C shows AFLAS volume change <5% and tensile retention >80%, while FKM swells >20% and NBR is completely incompatible. All major aerospace OEMs (Boeing, Airbus, Bombardier) list AFLAS compounds on their qualified materials lists for Skydrol service, with full lot traceability and material certification.
Frequently Asked Questions - AFLAS
What is AFLAS and how is it different from FKM?
AFLAS (FEPM) is a tetrafluoroethylene-propylene copolymer, a distinct polymer family from FKM (fluorocarbon). The key difference is in alkaline resistance: FKM is vulnerable to dehydrofluorination by strong bases, amines, and steam above 150°C — AFLAS resists all three. In aromatic hydrocarbons, ketones, and chlorinated solvents, FKM outperforms AFLAS. Choose AFLAS for steam, alkali, and amine service; choose FKM for aggressive hydrocarbon and acid service.
Where is AFLAS commonly used?
AFLAS is specified in oil and gas SAGD operations (steam injection at 180–230°C with amine-based sour gas treatment), geothermal wellheads exposed to high-temperature brine, power plant steam seals, and chemical processing plants handling concentrated caustic soda. In the aerospace sector, AFLAS handles phosphate ester hydraulic fluids (Skydrol) that attack standard FKM.
Can AFLAS handle sour gas (H₂S)?
Yes. AFLAS exhibits excellent resistance to sour gas, oilfield amines, and high-pH environments that degrade FKM. NACE MR0175 / ISO 15156 compliant grades are available with supporting test documentation for oil and gas applications. AFLAS is particularly valued in SAGD environments where H₂S, steam, and amines are present simultaneously — a combination that eliminates most other elastomer options.
What is the temperature range of AFLAS O-rings?
AFLAS operates from approximately -5°C to +230°C continuous. Steam resistance is excellent up to +200°C. The -5°C lower limit is a critical consideration: AFLAS has poor low-temperature flexibility compared to EPDM or HNBR. For applications that require cold-start sealing below 0°C, specify a low-temperature AFLAS compound or consider alternative materials for cold-side sealing.
Is AFLAS more expensive than FKM?
AFLAS is generally comparable to or slightly more expensive than standard FKM 75 Shore A — typically 1.2–1.8× the FKM price for equivalent sizes, depending on grade and quantity. For applications that fall within AFLAS's performance profile (steam, bases, amines), AFLAS is far more economical than FFKM (which costs 10–50× FKM). The business case for AFLAS is: FKM is inadequate, but FFKM is over-specified and cost-prohibitive.
When should I choose AFLAS over FFKM for steam service?
Choose AFLAS when your service conditions are steam (up to 200°C), alkaline media, or amines, without simultaneous exposure to aromatic hydrocarbons, ketones, or temperatures above 230°C. FFKM is required when: temperature exceeds 230°C; chemistry includes ketones, esters, or concentrated oxidising acids; semiconductor purity (low outgassing, particle generation) is needed; or explosive decompression at very high pressures demands maximum compound integrity. AFLAS typically costs 10–30% of equivalent FFKM — a significant operational cost saving for large downhole or geothermal seal programs.
What is AFLAS's low-temperature limitation in practice?
The -5°C lower temperature limit means AFLAS seals can become stiff and leak at cold-start in outdoor or sub-zero environments. If your equipment starts up in ambient temperatures below 0°C, verify cold-start compression force with actual hardware testing — do not rely on datasheet ratings alone. For systems that combine cryogenic or cold-ambient startup with high-temperature operation, an alternative seal architecture (e.g., spring-energized PTFE) or a low-temperature AFLAS compound (available by special order) may be required.
Do AFLAS compounds have NACE MR0175, API 6A, or aerospace certifications?
Yes. For oil and gas, NACE MR0175 / ISO 15156 compliant AFLAS grades are supplied with NACE TM0177 sulfide stress cracking test reports and NACE TM0297 explosive decompression (RGD) qualification for downhole and wellhead applications. API 6A PSL-level material certification is available for wellhead and Christmas tree equipment. For aerospace Skydrol service, AFLAS compounds are qualified to Boeing BMS, Airbus AIMS, and SAE AMS specifications with lot-specific material test reports including Skydrol immersion data at 150°C. Full material traceability from polymer batch to finished O-ring is standard for all certified grades.
How is batch consistency ensured for AFLAS compounds?
AFLAS batch consistency is controlled through: (1) Polymer feedstock testing — every TFE-propylene copolymer lot is tested for Mooney viscosity, comonomer ratio (TFE:propylene 50:50 ±2 mol%), and molecular weight distribution. (2) Compounding — carbon black, plasticizer (if used), peroxide curative, and TAIC co-agent are weighed to ±0.1%; mixed compound is tested for rheometry (MDR tS2, t90). (3) Slab testing — every batch is tested for hardness (±3 Shore A), specific gravity (±0.03), tensile (±10%), elongation (±15%), and compression set at 200°C (20–35%). (4) Application-specific testing — for sour gas grades, NACE TM0177 and TM0297 tests are performed on representative batches; for Skydrol aerospace grades, immersion testing in Skydrol 500B-4 at 150°C is conducted (volume change <5%, tensile retention >80%). (5) SPC tracking — hardness and compression set are monitored on control charts with Cpk ≥ 1.33. Lot-specific CoCs document all test parameters.
Can AFLAS from different suppliers be used interchangeably?
Dimensionally, AS568 and ISO 3601 AFLAS O-rings are interchangeable. Material equivalence requires verifying the TFE:propylene ratio (should be near 50:50 for standard grades), cure system (peroxide with TAIC co-agent is standard), and filler system (carbon black type and loading). AFLAS from AGC (the original manufacturer) and licensed compounders is chemically identical at the polymer level. However, compound formulations vary in plasticizer content, filler loading, and curative level, which can affect compression set (by 5–10 percentage points) and low-temperature flexibility. For critical sour gas or aerospace applications, request comparative test data (compression set, fluid immersion, TR10) from both suppliers before switching. NACE and aerospace certifications are supplier-specific and cannot be transferred — the new supplier must have their own qualification test reports.
What color conventions are used for AFLAS O-rings?
Black is the standard color for AFLAS O-rings across all suppliers and grades. Because AFLAS is primarily used in oil and gas, power generation, and aerospace applications where functional performance outweighs color-coding needs, custom colors are rarely specified. In facilities that stock both AFLAS and FKM, specific gravity is the primary field identification method (AFLAS 1.55–1.60 vs FKM 1.80–1.95). Some aerospace Skydrol applications use green AFLAS as a color code for phosphate ester compatibility, but this is supplier-specific rather than industry-standard. If color coding is required for your facility's material management system, custom pigmented AFLAS is available with minimum order quantities of 500 pieces and 2–3 week additional lead time.
What is the environmental impact and recyclability of AFLAS?
AFLAS production involves fluorinated monomers (TFE) and requires energy-intensive polymerization, giving it a higher per-kilogram environmental footprint than commodity elastomers. However, AFLAS's exceptional durability in steam, caustic, and sour gas environments (5–10 year service life in SAGD wellheads versus 1–2 years for alternative materials) reduces total material consumption and replacement waste. AFLAS is REACH and RoHS compliant. The polymer is chemically inert and does not release harmful substances during service. Post-industrial AFLAS scrap is collected and ground for use in lower-grade fluoropolymer products and industrial gaskets, achieving recycling rates of 10–15%. We provide material safety data sheets (MSDS) and environmental handling guidelines for all AFLAS compounds. For large oilfield seal programs, we offer take-back programs for end-of-life seals to ensure proper disposal or recycling.