Overview
Sealing performance turns on five variables, and each narrows the choice: the media contacted, the continuous and peak temperature, the pressure and available bolt load, the regulatory duty, and the mechanical conditions at the joint. Sound gasket material selection answers all five before a compound is named.
The Five Questions That Decide Every Seal
- Media chemistry. Everything touching the seal, cleaning fluids included. A dairy CIP cycle running caustic and acid is harsher than the milk.
- Temperature, continuous and peak. A jacket touching 180 degC on a steam purge is specified at 180 degC, not the 110 degC it normally runs at.
- Pressure and bolt load. A light flange cannot generate the seating stress a hard sheet needs, so a softer compound seals where a harder one fails.
- Regulatory duty. Potable water, food contact and pharmaceutical service carry compliance references that cut the shortlist early.
- Mechanical duty. Vibration, thermal cycling, joint movement and dismantling frequency all change the answer.
Work through those and the gasket material shortlist collapses to two or three candidates, the inputs the DeePee Rubber team asks for.
Elastomer Families and Where Each Belongs
Families differ less in appearance than in what destroys them, and the gasket rubber used for flat flange work sits between 40 and 80 Shore A.
Natural rubber gives excellent tear and abrasion resistance and seals at low bolt load, keeping it in water works and slurry flanges. Oils, ozone and sunlight ruin it. Nitrile is the default wherever oil is present, and covers hydraulic fluid, diesel and grease in a rubber gasket for pump covers and gearbox joints.
Neoprene sits in the middle, with moderate oil resistance and useful refrigerant compatibility. Butyl belongs where gas permeability matters. Fluoroelastomer, FKM or Viton, buys chemical range at higher cost for fuel and solvent duty.
EPDM handles hot water, steam, glycols and dilute acids and alkalis, which makes an EPDM gasket the routine choice for potable water and HVAC flanges. Mineral oil destroys it.
Silicone holds the widest dry-heat span of the common elastomers, so a silicone gasket suits ovens, food equipment and electrical housings. Tear strength is low.
Service Ranges at a Glance
Every figure moves with compound, filler loading and duty cycle, so confirm against service conditions.
| Material | Range | Strengths | Weaknesses |
|---|---|---|---|
| Natural rubber | -50 to +80 degC | Water, abrasion | Oils, ozone, sunlight |
| Nitrile | -30 to +120 degC | Oils, fuels, greases | Ozone, weathering |
| Neoprene | -40 to +110 degC | Refrigerants, weathering | Aromatics, oxidisers |
| EPDM | -50 to +150 degC | Hot water, steam, glycols | Mineral oil, fuels |
| Silicone | Silicone | Dry heat, ozone, food | Wet steam, hydrocarbons |
| FKM (Viton) | -20 to +200 degC | Fuels, solvents, oxidisers | Ketones, esters, cold |
| PTFE | -200 to +260 degC | Universal chemical resistance | Cold flow, no recovery |
When Gasket Material Moves Beyond Rubber
Above roughly 200 degC, in strong oxidising chemistry, or where flange loads are high, the elastomer families run out. PTFE leads the alternatives, supplied as virgin sheet, expanded PTFE, filled grades and envelope forms, and picking the wrong form is the usual reason a PTFE gasket disappoints.
Flexible graphite handles high-temperature steam and takes bolt load without the cold flow of virgin PTFE. Compressed fibre sheet remains the workhorse for general steam and water flanges. At the top of the pressure scale, a metallic gasket carries the load, governed by flange standards.
Properties That Decide Service Life
Chemical compatibility usually gets checked. The mechanical properties that decide how long a gasket survives often do not.
Compression set measures the thickness a compound never recovers after being held compressed at temperature, which explains a joint that sealed at commissioning and weeps after the first shutdown. Stress relaxation and creep are the same loss from the bolt side.
At 40 Shore A, a compound conforms to a rough or warped face. At 80 Shore A, the same gasket rubber resists extrusion but needs far more bolt load.
Tear strength governs handling, permeability decides gas service, and swell undoes both, since a compound that gains volume loses hardness and sealing force. No gasket material review is complete without all three.
Mismatches That Show Up as Field Failures
Four pairings cause most avoidable leaks, each one a gasket material chosen without checking a question above. EPDM in mineral oil swells, softens and extrudes within weeks. Nitrile in ozone or sunlight cracks at the surface and works inward. Silicone in pressurised steam hydrolyses, and in hydrocarbons it swells badly. Virgin PTFE under sustained load in a cycling joint cold flows, the bolts relax and the joint weeps, which expanded and filled grades correct.
ASTM D2000 and Compliance References
Naming a family alone is not a specification. ASTM D2000 gives a shared line-call format for rubber, coding type and class by heat and oil resistance, then adding suffix requirements for compression set, fluid ageing and low temperature. A note reading “EPDM 70 shore” does not.
For food and pharmaceutical duty, buyers ask about FDA 21 CFR 177.2600 for repeated food contact and USP Class VI for biological reactivity. Both apply to a compound rather than a family, so a compliant gasket material is confirmed by grade.
Why Buyers Across India Choose DeePee Rubber
Specifying a seal is half the job. The other half is a manufacturer who reads operating conditions the way your team does. DeePee Rubber has produced industrial rubber products and precision sealing components since 1965, with over five decades of experience across automotive, pharmaceutical, food processing, chemical and OEM manufacturing in India. That depth matters when a duty sits at the edge of a family’s range, and the right gasket material becomes a judgement call. Share your drawing, or the media, temperature range, pressure class and flange detail, and the DeePee Rubber team will return a recommendation and a quotation.
Conclusion
Material selection is a discipline of elimination. Work through media, temperature, load, compliance and mechanical duty in that order, and the field narrows quickly, usually before anyone opens a catalogue. The failures that reach a maintenance log are rarely exotic. They are EPDM meeting oil, nitrile left in sunlight, silicone in wet steam, virgin PTFE holding bolt load through a thermal cycle. Every one was avoidable at the drawing stage. Record the duty conditions, name the compound precisely, and confirm the gasket material against the real service envelope rather than the family average.
Key Takeaways
- No single gasket suits every joint, so answer media, temperature, bolt load, compliance and mechanical duty before naming any compound for a whole plant.
- A silicone gasket belongs in dry heat, food and electrical duty, never in pressurised steam or fuel.
- Above elastomer limits, move to PTFE, graphite, compressed fibre or a metallic gasket.
- Compression set, stress relaxation and hardness decide service life as much as chemistry.
- Put an ASTM D2000 line call on the drawing, and confirm every gasket material grade against FDA or USP references.
Frequently Asked Question
For hot water, low-pressure steam and glycol systems, EPDM is the routine answer, at roughly -50 degC to +150 degC. That makes an EPDM gasket the usual pick for potable water and HVAC flanges. Above that, graphite and compressed fibre take over.
Rarely. Standardising reduces stores complexity, then fails the moment one line carries oil and another caustic. Group joints by duty, and hold two or three compounds covering every group.
Give media, continuous and peak temperature, pressure class, flange standard, dimensions and any compliance requirement. Add an ASTM D2000 line call where the duty is critical.
No. A PTFE gasket wins on chemical range and temperature, but it has almost no elastic recovery, so it creeps under load and cannot follow a moving flange. Elastomers recover, which a vibrating joint needs.
