Overview
Sealing elements are best classified by construction rather than chemistry. The four families of gasket types are non-metallic soft gaskets, semi-metallic gaskets such as spiral wound and camprofile, solid metallic gaskets including ring joints, and special moulded or fabricated forms. Each family suits a different pressure and temperature band.
Why Construction Matters More Than Chemistry
Two seals can share one compound and behave nothing alike in service. A 3 mm elastomer sheet cut full face and a moulded ring in a machined groove may both be nitrile, yet one lives on flange bolt load and the other on controlled squeeze. Sorting gasket types by construction tells you how a joint generates contact stress and how well it holds it.
Chemistry answers a separate question, which is what the seal can safely touch. Fix the gasket material against the media and the cleaning regime once the construction family is settled.
Family 1: Non-Metallic and Soft Gasket Types
Soft gaskets are cut or moulded from one sheet or compound and depend entirely on flange bolts for their sealing stress.
A rubber gasket cut from nitrile, EPDM or neoprene sheet handles water, air, mild chemicals and low-pressure flanges, with sheet from 1 mm to 12 mm thick and hardness commonly 40 to 80 Shore A. Compressed fibre sheet accepts higher seating stress and copes with steam and oils. A PTFE gasket, virgin, expanded or filled, gives broad chemical resistance across a service range in the region of -200 degC to +260 degC, a natural fit for pharmaceutical lines. Graphite sheet takes higher temperatures and resists creep relaxation. Cork and cork-rubber suit transformer covers and gearbox faces.
Full Face Versus Inside Bolt Circle
Soft sheet is cut two ways. A full face gasket covers the whole flange face and is bolt-holed, which suits flat face flanges and cast iron or GRP bodies that flex under an off-centre load. An inside bolt circle cut stops short of the bolts, putting the same load on a smaller area and lifting seating stress.
Family 2: Semi-Metallic Construction
Semi-metallic designs combine a metal element for strength with a soft filler for conformity. The spiral wound gasket is the most widely used, built from a V-profile metal strip wound with filler tape, normally fitted with inner and outer rings and covered by ASME B16.20. Camprofile, also written kammprofile, uses a grooved metal core faced with graphite or PTFE, giving good recovery at modest bolt load on heat exchangers. Metal jacketed and corrugated designs support a soft filler for moderate duty. All of these gasket types need a reasonably rigid flange.
Family 3: Solid Metallic Construction
Past the semi-metallic ceiling, the seal becomes metal against metal. A solid flat metallic gasket in soft iron, copper or stainless steel works only on rigid flanges with high bolt load. Ring joint gaskets seal by controlled plastic deformation inside a machined groove, in oval and octagonal R styles plus pressure-energised RX and BX, the latter for API 6BX classes, with ring numbers such as R11, R24 and R39. Lens and weld rings cover near zero-leak duty.
Family 4: Special and Fabricated Forms
Plenty of sealing work never involves a flange. These gasket types answer to the groove and the profile rather than to a flange standard. O-rings and moulded profiles sit in machined grooves on pump housings, hydraulic cylinders and valve bodies, with squeeze usually designed in the 10 to 30 per cent range. Die-cut sections close switchgear doors and inspection covers. Extruded lengths joined into a frame seal long perimeters, and bonded, or sponge sections handle weather and dust.
Comparing Gasket Types by Construction Family
Treat every range below as indicative, because the real limit depends on compound, filler, flange rating and duty cycle. The four types of gasket construction differ most in the seating stress each one demands.
| Construction family | Approximate temperature | Approximate pressure | Typical duty |
|---|---|---|---|
| Non-metallic soft sheet | Ambient to roughly +200 degC, PTFE to +260 degC | Low to moderate, Class 150 and 300 | Water, air, dilute chemicals, food lines |
| Semi-metallic | Roughly -100 degC to +500 degC with graphite filler | Moderate to high, most flange classes | Steam, hydrocarbons, heat exchangers |
| Solid metallic gasket and ring joint | +500 degC and beyond | High to very high, API 6A equipment | Wellheads, boiler headers |
| Special and fabricated forms | Tied to the elastomer, roughly -60 degC to +230 degC | Low; housing carries the load | Pump housings, cylinders, enclosures |
How Specifiers Move Up and Down the Ladder
- Pressure class and temperature: ASME B16.5 Class 150 joints often seal on soft sheet, while Class 600 and above call for semi-metallic or solid construction.
- Media and cleaning regime: acids, solvents and CIP cycles in a dairy plant narrow the gasket material field fast, and FDA 21 CFR 177.2600 or USP Class VI compliance may apply.
Flange type and rigidity matter just as much. A thin stamped cover, a plastic flange or an ageing cast iron body cannot deliver the seating stress a wound seal demands, so soft construction and a full face cut are the answer. Bolt load is the input most often ignored. A gasket seals only when the bolts generate its minimum seating stress and hold it after creep relaxation, which is what the m and y factors describe. The DeePee Rubber team works through the same checks.
Why Buyers Across India Choose DeePee Rubber
Specifying the family is only half the job. The part still has to be made to the correct dimensions and tolerance, from a compound suited to the duty. DeePee Rubber has been manufacturing industrial rubber products and precision sealing components since 1965, with over five decades of experience supporting automotive, pharmaceutical, food processing, chemical and oil and gas customers across India. That application-focused approach turns a shortlist of gasket types into a part that performs. Share your drawing, flange details or operating conditions with the DeePee Rubber team and request a quotation.
Conclusion
A sealing decision made on construction rather than habit rarely goes wrong, which is why gasket types are best grouped this way. Once the flange class, temperature, media and joint stiffness are known, the family almost selects itself and the compound choice narrows. The step most plants skip is confirming that the bolts can hold the stress the chosen construction needs. Get that right, and a rubber gasket on a water line will last as well as a wound seal on a steam header, and the next shutdown will be shorter for it.
Key Takeaways
- Classify gasket types by construction first, then match the compound to the media.
- Full face cuts suit non-rigid flanges; inside bolt circle lifts seating stress.
- Semi-metallic construction bridges soft sheet and solid metal on mid-pressure piping.
- A PTFE gasket covers wide chemical resistance, while graphite answers high temperature.
- Bolt load and flange rigidity cause more joint failures than compound choice does.
Frequently Asked Question
Four construction families cover the field: non-metallic soft gaskets, semi-metallic gaskets, solid metallic gaskets and special fabricated forms. Every commercial sealing element fits one of them.
Start with pressure class and temperature, then check media, flange rigidity and bolt load. Soft sheet suits low-pressure flanges, semi-metallic covers mid- and high-pressure piping, and metal is kept for severe joints.
Yes. An O-ring is a moulded seal that works by squeeze inside a machined groove rather than by bolt load across a flange face. It belongs to the special forms family.
Compressed fibre and graphite sheet handle lower pressure steam on utility lines and secondary headers. For main steam headers, a spiral wound gasket or a cam profile is the normal choice. Elastomer sheet is generally unsuitable above light utility duty.
