Overview
Metal sealing replaces soft materials where the duty is severe. A metallic gasket deforms plastically under high bolt load, in solid, ring joint, camprofile, corrugated, jacketed or wound forms, and is specified where temperature, pressure class, fire safety or media hazard exceeds elastomer limits, typically on refinery and wellhead flanges.
When Soft Sealing Stops Being Enough
Most joints start soft and stay soft until the duty forbids it. Nitrile holds to roughly 120 degC and EPDM to around 150 degC, depending on compound and media. Past those bands, gasket rubber hardens, takes a compression set and loses the recovery that kept the joint tight.
Pressure class matters as much. A rubber gasket performs well in Class 150 water and air service, but at Class 600 and above the contact stress needed exceeds what an elastomer can carry without extruding. Add flammable media, a fire-safe requirement, or severe thermal cycling, and a metallic gasket becomes the answer.
The final check is mechanical. A thin flange with few bolts cannot deliver the seating stress metal demands, so flange design constrains the choice as firmly as the process itself.
Which Metallic Gasket Family Fits Which Duty
Metal sealing is not one product. Set beside the soft sheet and moulded options that fill most of the wider range of gasket types, seven families cover industrial practice.
| Family | Typical duty |
|---|---|
| Solid flat metal | Small bore, high pressure |
| Ring joint (R, RX, BX) | Wellhead, Class 900 up |
| Lens ring | High-pressure hydrogen |
| Camprofile | Exchangers, thermal cycling |
| Corrugated metal | Large diameter, lower bolt load |
| Metal jacketed | Exchanger channel covers |
| Spiral wound | Refinery and power piping |
A solid flat ring is the simplest and most demanding, asking the highest seating stress of all. Ring joint styles seat in machined grooves, in oval and octagonal R plus RX and BX.
Lens rings concentrate load on a narrow line, producing high local stress from modest bolt load. Camprofile, also written kammprofile, pairs a serrated core with a graphite or PTFE facing, so the core carries load while the facing seals. Corrugated metal multiplies contact lines and seals at lower bolt load when faced. Jacketed rings wrap a soft filler in a thin shell. The spiral wound gasket is the semi-metallic default across general piping.
Seating Stress, Bolt Load and the m and y Factors
An elastomer seals by flowing into surface imperfections at low stress. Metal does not flow; it yields. A gasket seal made in metal depends on plastic deformation at the contact face, which requires seating stress an order of magnitude above what gasket rubber needs.
Bolt count, bolt diameter and flange thickness decide how much stress reaches the seating face, and a thin flange bows between bolts and leaks at mid-span. Rubber springs back as the joint relaxes; metal largely does not, so a metallic gasket depends on the bolts holding load rather than the seal chasing the flange. The ASME method puts this in two numbers: m, the maintenance factor tied to internal pressure, and y, the minimum stress needed to seat the joint.
Picking the Metal
The gasket material follows the fluid and the temperature. Soft iron and low carbon steel seal easily and cost little but corrode. 304 and 316 stainless cover general and mildly corrosive service. 321 and 347 resist sensitisation at furnace temperatures. Monel suits hydrofluoric acid and seawater; Inconel suits hot oxidising duty and titanium chlorides.
One rule governs all of them. The gasket material must always be softer than the flange facing. A ring harder than its seat cuts a groove into a component worth many times more, turning a small saving into a machining job.
The Standards That Frame the Choice
ASME B16.20 is the reference for a metallic gasket in pipe flanges, along with semi-metallic forms, and covers ring joint, spiral wound and jacketed rings. ASME B16.5 and B16.47 define flange dimensions and classes 150, 300, 600, 900, 1500 and 2500. API 6A and API 6B govern wellhead flanges and ring grooves.
Where Metal Sealing Earns Its Place
Oil and gas is the natural home, from wellheads under API 6A to export lines. Refineries use metal on hot hydrocarbon, hydrogen and steam service where a soft sheet would carbonise inside one run. Power plants specify it on main steam lines. Chemical reactors need a metallic gasket on vessel covers that cycle between ambient and reaction temperature. Heat exchanger duty is its own category, where thermal shock and bundle pulling favour camprofile and jacketed forms.
Handling and Installation Discipline
A perfect gasket cannot rescue a damaged face. Grooves and raised faces need the finish called out in the flange standard, and a radial scratch across the seating band is a leak path no bolt load closes. Treat every metallic gasket as single-use, since metal has yielded once and will not deform the same way twice. Store rings flat, dry and packaged.
Where Soft Sealing Remains the Right Answer
Metal is not universally better. A rubber gasket costs a fraction as much, conforms to imperfect flanges, needs far less bolt load and can be cut on site. For water, air, low-pressure chemicals and equipment covers, an elastomer beats a metallic gasket on cost and practicality.
Why Buyers Across India Choose DeePee Rubber
Specifying a seal starts with the duty, not the catalogue. DeePee Rubber has engineered sealing components since 1965, with over five decades of experience serving manufacturing, automotive, chemical, pharmaceutical, food and oil and gas customers across India. That view matters at the boundary between soft and metal sealing, because the honest answer is sometimes a metallic gasket and sometimes an elastomer part that costs far less and lasts the same shutdown cycle. Where the duty sits in rubber territory, share your flange standard, facing, media and operating range, with a drawing. The DeePee Rubber team will return a recommendation and a quotation.
Conclusion
Metal sealing is a response to duty, not a badge of quality. The decision turns on physical facts: how hot the line runs, what class the flange carries, how hazardous the media is, and how much bolt load the flange can honestly deliver. Once metal is the answer, the family, the alloy and the flange finish carry the outcome, and installation discipline settles the rest. Where those conditions are absent, an elastomer stays cheaper, faster to fit and perfectly reliable, and reaching for metal only adds cost. Bring the operating conditions early, and the specification settles itself.
Key Takeaways
- Move to metal when temperature, pressure class, media hazard or fire safety passes elastomer limits.
- Seating stress, bolt count and flange rigidity decide success as much as the ring.
- Keep the metal softer than the flange facing, and match it to the media.
- ASME B16.20, B16.5, B16.47 and API 6A or 6B are worth quoting on enquiries.
- Compare the wider range of gasket types first, since soft sealing is often adequate.
Frequently Asked Question
Move to a metallic gasket when temperature exceeds what the polymer tolerates, the pressure class runs 600 and above, the media is flammable, or a fire-safe joint is required.
A camprofile has a solid serrated core faced with graphite, so it carries load and resists blowout by itself. A spiral wound gasket is a wound strip and filler held by rings, and it tolerates flange movement better.
No. A metallic gasket seals by deforming plastically, and that happens once. Refitting a used ring leaves the old impression fighting the new flange position, a common cause of repeat leaks.
Tighter than soft sealing tolerates. A gasket seal in metal relies on close contact over a small area, so grooves and faces must meet the specified finish.
