HNBR O-Rings (Hydrogenated Nitrile)
Hydrogenated nitrile for high temperatures, ozone resistance, and sour gas service
Overview
HNBR (Hydrogenated Nitrile Butadiene Rubber) is the premium upgrade to standard NBR. By hydrogenating the nitrile polymer chain, virtually all double bonds are removed, giving HNBR significantly improved temperature resistance, ozone and weathering resistance, and mechanical strength — while retaining excellent petroleum oil and fuel compatibility.
HNBR is the material of choice for oil and gas downhole seals (NACE MR0175 / ISO 15156 compliant grades for H₂S sour gas service), automotive air conditioning and fuel injection systems where ozone resistance is critical, and high-pressure hydraulic cylinders where standard NBR would fail due to heat or fatigue.
Acrylonitrile content in HNBR ranges from 18% to 43%. Higher ACN content (36–43%) improves oil and fuel resistance but reduces low-temperature flexibility. Lower ACN (18–26%) provides better cold performance but lower swell resistance in aromatic fuels. Standard industrial grades typically use 34–36% ACN, balancing both properties.
Compression set performance (ASTM D395 Method B, 22 h/150°C) of 15–25% makes HNBR a reliable long-service static and dynamic seal in hot environments. ASTM D471 immersion in IRM 903 oil at 150°C shows volume change of 5–15%, confirming stability in high-temperature petroleum service.
Lead time: 7–15 days standard; 3–5 days for stocked compounds. MOQ: 1 piece. ISO 9001 certified. NACE MR0175 / ISO 15156 documentation available.
The hydrogenation process is the defining transformation: standard NBR contains approximately 18% carbon-carbon double bonds (unsaturation) in its butadiene segments. Through catalytic hydrogenation — typically using palladium or rhodium catalysts in solution — these double bonds are saturated to single C-C bonds, reducing unsaturation to below 0.5%. The degree of hydrogenation is critical: partially hydrogenated grades (5–10% residual unsaturation) allow sulfur vulcanization but retain some ozone vulnerability; fully hydrogenated grades (<0.5% unsaturation) require peroxide or resin curing and achieve maximum ozone and heat resistance. The ACN content interacts with hydrogenation level: high-ACN (36–43%) HNBR has a glass transition temperature (Tg) of approximately -20°C to -25°C, while low-ACN (18–26%) grades achieve Tg of -40°C to -45°C. For sour gas service, specific hydrogenation catalyst residues must be controlled below 50 ppm to prevent stress corrosion cracking of adjacent metal components.
Quantified performance improvements over NBR are substantial and justify the 3× cost premium in demanding applications. Tensile strength increases from NBR's 10–20 MPa to HNBR's 15–25 MPa — a 25–67% improvement that directly translates to better extrusion resistance and longer dynamic seal life. Compression set at elevated temperature shows the most dramatic difference: at 150°C (ASTM D395 Method B, 22 h), HNBR achieves 15–25%, while NBR at the same temperature exceeds 50% and is effectively unusable. In Taber abrasion testing (ASTM D4060, H-18 wheel, 1000 g load, 1000 cycles), HNBR exhibits wear losses of 80–150 mg versus NBR's 200–400 mg — a 2–3× improvement that extends service life in contaminated hydraulic fluid. Ozone resistance is fundamentally different: NBR cracks in 24–48 hours at 50 pphm ozone (ASTM D1171), while HNBR shows no cracking after 1000+ hours, placing it in the same ozone-resistance class as EPDM and VMQ. In IRM 903 oil at 150°C (ASTM D471), HNBR volume swell is 5–15% versus NBR's 35–50% — enabling reliable sealing at temperatures where NBR would soften and extrude.
A practical selection decision tree: if your application is an automotive under-hood fuel injector seal with ozone exposure and temperatures to +150°C, specify 70 Shore A high-ACN (36–40%) HNBR with peroxide cure and automotive OEM approval (e.g., VW 2.8.1, GM 6031M). If your application is an oilfield downhole packer in sour gas (H₂S > 1000 ppm) at 120°C and 70 MPa, specify NACE MR0175 / ISO 15156 compliant HNBR with 34–36% ACN, hardness 80–90 Shore A, and NACE TM0297 explosive decompression qualification. If your application is a high-pressure hydraulic cylinder (>35 MPa) operating above +120°C in an outdoor construction machine, specify 80 Shore A HNBR for the combination of extrusion resistance, ozone immunity, and heat stability. If your application involves aromatic fuels (E85, biodiesel blends) at temperatures below +100°C, high-ACN HNBR (39–43%) provides better swell resistance than standard grades. If budget is the primary driver and temperature never exceeds +100°C with no ozone exposure, NBR remains the correct economic choice.
Storage of HNBR follows the same principles as NBR but with longer allowable shelf life due to the saturated backbone. Store in opaque, airtight packaging below 25°C, away from ozone sources (electric motors, UV lamps, welding equipment). Peroxide-cured HNBR grades have a recommended shelf life of 7–10 years; sulfur-cured partial hydrogenation grades are stable for 5–7 years. HNBR's specific gravity (1.15–1.25) provides easy field distinction from NBR (1.00–1.25 overlap at the low end) and FKM (1.80–1.95). A critical but common error is specifying HNBR for continuous steam or hot water service above 80°C: while HNBR resists moisture better than NBR, hydrolysis of the nitrile groups at elevated temperature degrades the polymer over time. For steam, specify EPDM or AFLAS; for hot water above 80°C, EPDM is the proven choice. Another frequent mistake is using low-ACN HNBR (18–26%) in fuel systems expecting the same aromatic resistance as high-ACN grades — volume swell in aromatic fuels can be 2–3× higher for low-ACN compounds.
Material Properties
| Full Name | Hydrogenated Nitrile Butadiene Rubber |
| Temperature Range | -40°C to +150°C (-40°F to +302°F); short-term peaks to +160°C |
| Hardness Range | 50–90 Shore A (ASTM D2240) |
| Tensile Strength | 15–25 MPa (ASTM D412) |
| Elongation at Break | 150–400% (ASTM D412) |
| Compression Set (22 h/150°C) | 15–25% (ASTM D395 Method B) |
| Acrylonitrile Content | 18–43% ACN (34–36% standard industrial grade) |
| Specific Gravity | 1.15–1.25 |
| Color | Black or green (custom colors available) |
| Price Index | 3× NBR base cost |
| Standards | ASTM D2000 DH, SAE AMS3216, NACE MR0175 / ISO 15156 |
Typical Applications
Oil & Gas
Downhole packers, BOP seals, and wellhead seals in sour gas (H₂S) environments. NACE MR0175 / ISO 15156 compliant grades with NACE TM0297 explosive decompression test reports available.
Automotive
Fuel injection systems, air conditioning compressor seals, and power steering where ozone and heat up to +150°C are present. Preferred over NBR for under-hood applications.
Hydraulics
High-pressure cylinder seals, pump shaft seals, and accumulator seals in mobile and industrial hydraulics operating above 120°C or in ozone-rich environments.
Aerospace
Fuel system seals and actuator seals requiring improved thermal stability and fatigue resistance over standard NBR.
Chemical Compatibility Summary
Compatible With
- - Mineral oils
- - Hydraulic fluids
- - Gasoline and diesel fuels
- - Aliphatic hydrocarbons
- - Silicone oils and greases
Incompatible With
- - Polar solvents (ketones, esters)
- - Aromatic hydrocarbons
- - Chlorinated hydrocarbons
- - Steam and hot water
- - Strong acids
Compare Nearby Materials
Further Reading
HNBR vs NBR O-Rings
Mechanical strength, heat capability, and the real upgrade path over standard nitrile.
Read articleKey Advantages
High Temperature Performance
HNBR extends the useful temperature range from NBR's +120°C limit to +150°C continuous, making it ideal for under-hood automotive, hot hydraulic oil systems, and oilfield downhole tools operating in elevated geothermal gradients.
Ozone and Weather Resistance
Unlike standard NBR, which cracks within months in ozone-rich environments, the saturated HNBR backbone resists ozone and UV degradation for long-term outdoor and marine service without protective coatings.
Sour Gas Compliance
NACE MR0175 / ISO 15156 compliant HNBR grades are qualified for oil and gas environments containing hydrogen sulfide (H₂S). Test reports including NACE TM0297 explosive decompression qualification available on request.
Mechanical Robustness
Tensile strength 15–25 MPa and tear resistance superior to NBR support demanding dynamic reciprocating and rotary seal applications, including high-cycle hydraulic cylinders and automotive compressors.
Quantified Performance Advantage Over NBR in Hot Oil and Dynamic Service
At 150°C in IRM 903 oil, HNBR shows volume swell of only 5–15% versus NBR's 35–50% — a 3× improvement in dimensional stability that eliminates extrusion failures. In Taber abrasion testing, HNBR wear is 80–150 mg per 1000 cycles versus NBR's 200–400 mg, extending seal life by 2–3× in contaminated hydraulic systems. Compression set at 150°C is 15–25% for HNBR versus >50% for NBR, ensuring sustained sealing force in hot static joints.
Full NACE Qualification and Oilfield Traceability Documentation
NACE MR0175 / ISO 15156 compliant HNBR compounds are supplied with comprehensive documentation packages including compound test reports per NACE TM0177 (sulfide stress cracking), NACE TM0297 (explosive decompression RGD), hardness certification (±3 Shore A), and full lot traceability from polymer batch to finished O-ring. Material certificates reference the specific NACE standard edition and are accepted by all major oilfield operators and OEMs for wellhead, BOP, and downhole equipment.
Frequently Asked Questions - HNBR
What is the difference between HNBR and NBR?
HNBR is produced by hydrogenating NBR, which removes the double bonds in the polymer chain that make NBR vulnerable to ozone attack and high-temperature degradation. The result is improved continuous temperature resistance from +120°C (NBR limit) to +150°C, full ozone and UV resistance, higher tensile strength (15–25 MPa vs. 10–20 MPa for NBR), and better compression set at elevated temperatures. Oil and fuel resistance is retained. Cost is approximately 3× NBR.
Is HNBR NACE MR0175 / ISO 15156 compliant?
Yes. We supply HNBR compounds specifically formulated and tested to meet NACE MR0175 / ISO 15156 for sour gas (H₂S) service in oil and gas applications. Compliance documentation including the compound test report and certificates of conformance are available on request. For downhole applications subject to explosive decompression (RGD), we also have compounds with NACE TM0297 qualification test reports.
When should I choose HNBR over FKM?
Choose HNBR when you need oil and fuel resistance plus mechanical toughness at temperatures up to +150°C, or when NACE MR0175 sour gas compliance is required. FKM is the correct choice for continuous service above +150°C, in highly aromatic or oxygenated fuels (E85, biodiesel), or when chemical resistance to acids and amines is needed. HNBR is typically 2–3× less expensive than FKM for comparable sizes, making it the cost-effective choice at the +120–150°C operating range.
Can HNBR be used with steam or hot water?
HNBR is not recommended for steam or continuous hot water service. While HNBR resists moisture better than NBR, hydrolysis at elevated temperatures degrades the polymer over time. For steam applications up to 150°C, EPDM is the correct material. For steam above 150°C, PTFE or metal seals are required.
How does acrylonitrile content affect HNBR performance?
Higher ACN content (36–43%) improves resistance to petroleum oils, fuels, and non-polar solvents, but reduces flexibility at low temperatures (TR10 around -25°C for 43% ACN). Lower ACN (18–26%) provides better cold-temperature performance (TR10 to -45°C) but less resistance to fuel swell. The standard 34–36% ACN grade used in most industrial HNBR O-rings balances oil resistance and cold-weather flexibility. Specify ACN content when ordering for applications at temperature extremes.
What hardness grades are available for HNBR O-rings?
We stock and manufacture HNBR O-rings from 50 to 90 Shore A. 70 Shore A is standard for most static and low-pressure dynamic applications. 80 Shore A is preferred for hydraulic seals above 100 bar, where extrusion resistance is critical. 90 Shore A is used for backup ring replacements or high-pressure pneumatic applications. Softer grades (50–60 Shore A) are available for low-pressure, low-temperature static sealing.
How do I confirm HNBR quality on receipt?
For critical applications (oil and gas, automotive OEM), incoming verification should follow three levels: (1) Review the certificate of conformance (CoC) for compound designation, Shore A hardness, compound date, and lot number. (2) Spot-check hardness with a calibrated durometer per ASTM D2240 — accept ±5 Shore A from nominal. (3) For sour gas service, verify that the compound lot matches the NACE MR0175 test report on file. FTIR spectroscopy ($80–200/sample) provides definitive polymer family confirmation if material identity is uncertain.
Do HNBR compounds meet automotive IATF 16949 and aerospace AMS specifications?
Yes. For automotive, HNBR compounds are available from IATF 16949-certified facilities with full PPAP documentation (Levels 1–5), material test reports per AIAG standards, and specific OEM approvals including VW 2.8.1, GM 6031M, and Ford WSB-M2G341-A2. For aerospace, HNBR is supplied to SAE AMS3216 (standard hydrogenated nitrile, 75 Shore A) with lot-specific test data including hardness, tensile strength, elongation, compression set, and fluid immersion per the AMS test protocol. Full material traceability from polymer lot to finished O-ring is standard for both automotive and aerospace grades. NADCAP-accredited testing is available for flight-critical applications.
How is batch consistency controlled for HNBR, particularly for NACE MR0175 grades?
HNBR batch consistency is ensured through five control layers: (1) Polymer feedstock testing — every HNBR polymer lot is tested for Mooney viscosity, ACN content (±1%), degree of hydrogenation (residual unsaturation <0.5% for fully saturated grades), and catalyst residue (Pd or Rh <50 ppm for NACE grades). (2) Compounding control — carbon black, plasticizer, and curative batches are tested and weighed to ±0.1%; mixed compound is tested for Mooney viscosity and cure rheometry (MDR tS2, t90). (3) Slab testing — every batch is tested for hardness (±3 Shore A), specific gravity (±0.02), tensile (±10%), elongation (±15%), and compression set at 150°C (15–25%). (4) Fluid immersion — ASTM D471 in IRM 903 at 150°C (volume change 5–15%). (5) NACE-specific testing — for sour gas grades, NACE TM0177 sulfide stress cracking and TM0297 explosive decompression tests are performed on representative batches and retained for lot correlation. Statistical process control with Cpk ≥ 1.33 is maintained on hardness and compression set.
Can HNBR from different suppliers be interchanged in critical applications?
Dimensionally, AS568 and ISO 3601 HNBR O-rings are interchangeable. Material equivalence requires deeper verification: specify the same ACN content range (34–36% standard, 36–43% high-ACN), the same degree of hydrogenation (fully saturated <0.5% vs partially saturated 5–10%), and the same cure system (peroxide vs sulfur). Peroxide-cured fully saturated HNBR from major suppliers (Zeptol, Therban, Zetpol) is broadly equivalent for general industrial service. However, NACE MR0175 compliance and explosive decompression resistance are compound-specific and supplier-specific — switching suppliers for sour gas service requires the new compound to have its own NACE test reports at the relevant H₂S partial pressure, temperature, and decompression rate. For automotive OEM applications, supplier change typically requires customer notification and re-qualification per the OEM's supplier change request process.
What color conventions are used for HNBR O-rings?
Black is the standard color for most HNBR O-rings. Green is widely used to denote NACE MR0175 / ISO 15156 sour gas grades in oil and gas inventory systems — a visual safeguard against installing standard industrial HNBR in critical downhole service. Blue may indicate peroxide-cured fully saturated grades in some supplier systems. Custom colors are available with 1–2 week additional lead time. Because HNBR specific gravity (1.15–1.25) overlaps with NBR at the lower end, color coding combined with specific gravity measurement provides reliable field identification. Some facilities require all HNBR inventory to be green as a mandatory color-coding policy for BOP and wellhead seal traceability.
What is the environmental impact and recyclability of HNBR?
HNBR production requires hydrogenation of NBR polymer using precious metal catalysts, which adds energy and processing complexity versus NBR. However, HNBR's extended service life in demanding applications (3–5× longer than NBR in hot oil or ozone-rich environments) reduces total material consumption and replacement waste over the equipment lifecycle. HNBR is REACH and RoHS compliant. Post-industrial HNBR scrap is ground and used as filler in lower-grade rubber compounds and anti-vibration products, achieving recycling rates of 10–20%. Unlike thermoplastics, HNBR cannot be remelted. We are evaluating bio-based and recycled-content feedstocks as they become available, and we provide lifecycle assessment (LCA) data on request for customers with sustainability reporting requirements. The environmental business case for HNBR is durability: fewer seal replacements mean less waste, less downtime, and lower total resource consumption.