O-Rings by Industry: Which Compound Where

The fastest route to the right seal is knowing what your industry already runs. Decades of field failures have already sorted the winners from the losers in every major application, and the survivors are remarkably consistent: hydraulics runs nitrile, water runs EPDM, semiconductor fabs run white FFKM. Start with your industry’s default, then check the exceptions and traps below before you order. When in doubt, the compatibility chart settles arguments.

Hydraulics and Pneumatics

The bread and butter of the O-Ring world, and Nitrile (Buna-N) owns it: excellent resistance to petroleum hydraulic oils at low cost, in 70 duro for general service and 90 duro where pressure climbs. The trap here is extrusion. Above roughly 1,500 psi, a 70-duro ring starts flowing into the gland gap and nibbling itself to death; step up to 90 duro or add back-up rings and the problem disappears. For rod and piston seals taking abrasion and shock loading, cast polyurethane outwears nitrile several times over. Port sealing has its own hardware: SAE ORB straight-thread ports take 90-duro boss O-Rings, not standard AS568 rings. We stock the whole range: Hydraulic and Pneumatic Seals, Hydraulic Boss O-Rings, OSK™ Hydraulic Cylinder Seal Kits, and the OSK™ Boss Seal Kit for the service truck.

Automotive and Heavy Truck

Under the hood is a fluid-by-fluid decision. Nitrile still handles engine oil and older fuel systems, but modern engine bays run hotter and the fuels got nastier, so FKM (Viton®) is the call for fuel injection and anything touching today’s blended gasoline. Air conditioning is its own world: the green HNBR O-Ring is THE A/C compound, built for R134a (and commonly run with R1234yf) and happy in underhood heat to +300°F where nitrile cooks. The two traps that ruin brake jobs and oil seals alike: glycol brake fluid destroys nitrile and FKM, so brake systems get EPDM only, and EPDM in turn swells and fails in any petroleum oil. Never swap those two. Shop HNBR O-Rings, OSK™ OEM Replacement O-Rings, and the Max Truck kit for heavy-duty service.

Aerospace

Aerospace does not pick compounds, it picks specifications, and the part number tells you the material: M83248/AMS7276 FKM for fuels and lubricants, M25988 fluorosilicone for fuel systems needing low-temperature flexibility, M83461/MS28775 nitrile for petroleum-based hydraulic fluid, NAS1611 ethylene propylene for Skydrol phosphate-ester hydraulics, and Simriz® 501 to AMS7257 where FFKM performance is called out. Our mil-spec cross reference decodes the whole system. The traps are paperwork, not chemistry: cure dates, batch traceability, and a certificate of conformance are part of the product, and an uncertified ring of the right rubber is still the wrong part. Note the Skydrol case especially: it attacks nitrile and FKM alike, so the spec exists for a reason. Shop Mil-Spec FKM O-Rings and M25988/1 fluorosilicone.

Oil and Gas

Downhole service stacks every killer at once: sour gas, high pressure, high heat, and amine-based inhibitors. Hydrogen sulfide (H2S) hardens and cracks standard nitrile and attacks FKM, so the sour-gas workhorses are HNBR and Aflas® (FEPM), which also shrugs off the amine corrosion inhibitors that swell FKM. The second killer is rapid gas decompression (RGD): high-pressure gas saturates the elastomer, pressure drops fast, and the ring blisters from the inside out. The answer is a 90-duro RGD-rated grade such as Simriz® 134, NORSOK M-710 certified, or Simriz® 502 when temperatures run to +325°C. Steam injection and SAGD flip the chemistry again: EPDM, Aflas, or FFKM for steam, never nitrile. Start with Aflas® O-Rings and step up as the well gets uglier.

Food and Beverage

Food contact starts with the paperwork: FDA 21 CFR 177.2600 compounds for anything touching product, NSF/ANSI 61 where potable water is involved, and 3-A Sanitary in dairy. The trap most plants hit is cleaning chemistry, not the food itself: CIP/SIP caustics, acids, and steam cycles chew up ordinary rubber long before the product does, so match the compound to the sanitation regime. HACCP lines increasingly spec metal-detectable O-Rings so a lost ring trips the detector instead of shipping in a jar. We stock the full FDA lineup: white FDA nitrile, FDA EPDM, FDA silicone, FDA/3-A FKM, sanitary and brewery gaskets, and Simriz® 484 FFKM when CIP/SIP kills everything else.

Medical and Pharmaceutical

The default here is USP Class VI silicone: clean, inert, biocompatible, and comfortable across the temperature swings of medical devices and pharma equipment. The trap is sterilization. Repeated autoclave and steam-in-place cycles are harder on a seal than the process fluid, and gamma or chemical sterilization each have their own casualties, so qualify the compound against your actual sterilization method, not just the drug contact. Where steam cycles or aggressive process chemistry defeat silicone, Simriz® 484 FFKM carries FDA, USP Class VI, and 3-A approvals with FFKM durability. The other half of the job is documentation: lot traceability and a certificate of conformance are standard expectations in validated processes, so ask for the paperwork with the quote. Start with FDA silicone O-Rings and tell us what your validation package needs.

Water and Plumbing

EPDM is the water king: hot water, steam, chlorinated municipal supply, and outdoor weathering are all home territory. Modern systems disinfected with chloramine are tougher on rubber than plain chlorine ever was, which is why peroxide-cured EPDM grades exist; that is what to spec for long service on treated municipal water. Anything on the potable side should carry NSF/ANSI 61 certification. The trap that generates more warranty calls than any other in this trade: EPDM plus any petroleum grease or oil equals a swollen, failed seal, sometimes within days. Lubricate EPDM with silicone grease only, and keep pipe dope and petroleum-based lubricants away from it. We stock chloramine-resistant FDA/NSF-61 EPDM for exactly this service, plus FDA/NSF-61 nitrile for fittings that see both water and petroleum exposure.

Semiconductor

Wafer fabs fight two enemies at once: plasma chemistry that eats elastomers, and particles, because a seal that sheds is a seal that scraps wafers. Standard elastomers, even standard FKM, erode in etch and deposition chambers and shed exactly the contamination the process cannot tolerate. The industry answer is high-purity white and off-white FFKM: Simriz® 486CP is the plasma-resistant workhorse for CVD, PVD, etch, and ash chambers, cleaned and packaged for the fab, and Simriz® 508/508CP is the step up for high-energy and remote plasma service on chamber lids, windows, and gate valves. The trap is treating these as interchangeable with black FFKM: filler chemistry drives particulation and plasma erosion, so the semiconductor grades earn their keep. See the full lineup on our FFKM page, and contact us for 508/508CP quotes.

Chemical Processing

This is the compatibility-chart industry: no default compound survives every stream, so every seal decision starts at the chemical compatibility chart. The usual ladder runs FKM as the base for acids, hydrocarbons, and solvents, then Viton® Extreme ETP when ketones, amines, or bases enter the picture, then FFKM when the chemistry gets broad, hot, or both. For the nastiest static service, PTFE and PTFE-encapsulated O-Rings put a chemically inert jacket around an elastomer core. The trap is mixture blindness: a compound rated A for each ingredient can still fail in the blend, and cleaning cycles, trace catalysts, and temperature excursions all change the answer. Check the chart at operating temperature, not room temperature. Shop Viton® ETP O-Rings, PTFE O-Rings, and Teflon™ encapsulated O-Rings.

Not sure where you fit?

Plenty of applications straddle two industries, and plenty of drawings just say “rubber.” Tell us the fluid, the temperature, the pressure, and any spec or certification on the print, and we will match the compound: contact The O-Ring Store. We have been sorting this out over the counter for years, and the five minutes it takes to ask is cheaper than the teardown it takes to guess.