Choosing gaskets correctly: flat, spiral wound and ring joint
The best flange joint is useless if the gasket does not suit. Four variables decide: pressure rating, temperature, medium and the form of the facing. Leave one out and the joint leaks – usually only once in service.
The types compared
| Type | Standard | Rating | Typical use |
|---|---|---|---|
| Flat gasket | EN 1514-1, DIN 2690 | up to PN 40 | Water, compressed air, general service lines |
| Spiral wound | EN 1514-2 | up to PN 160 | Steam, process, fluctuating conditions |
| Kammprofile | EN 1514-6 | up to PN 160 | Where low surface pressure is required |
| Metal ring joint | ASME B16.20 | Class 150–2500 | Petrochemicals, high pressure, RTJ groove |
Gasket materials and their limits
The material determines what temperature and medium the gasket will tolerate. The figures below are guide values – the actual limit depends on pressure, medium and surface pressure.
| Material | Temperature (guide) | Strengths | Limits |
|---|---|---|---|
| Fibre reinforced | up to approx. 200 °C | economical, widely available | limited chemical resistance |
| PTFE | approx. −200 to +200 °C | almost universally resistant | tends to creep, needs retightening |
| Graphite | up to approx. 450 °C in air | high temperature, good recovery | oxidises in air, mechanically delicate |
| EPDM | up to approx. 150 °C | water, hot water, low-grade steam | not for oils and greases |
| FKM | up to approx. 200 °C | oils, fuels, many chemicals | not for hot water and steam |
Common mistake: EPDM and FKM almost exclude one another. EPDM is at home in water and steam but fails with oil. FKM is exactly the other way round. Picking “the better gasket” without looking at the medium often means picking the wrong one.
The facing must match
A gasket is designed for a particular facing. Form B1 – the standard raised face for all PN – calls for a different gasket than tongue and groove or an RTJ groove. With spiral wound gaskets, inner and outer rings are added: the outer ring centres the gasket and prevents over-compression, the inner ring protects the winding against inward blow-out.
Which form your flange has is explained in flanges to EN 1092-1; the dimensions are in the flange dimension tables.
Installation matters too
Even the correct gasket will not seal if fitted badly. Three points from practice:
- Tighten crosswise in stages – not one bolt after another, or the flange will cock.
- Do not reuse gaskets. Flat and spiral wound gaskets are single-use items; they have already bedded in.
- Retighten after start-up where material and operating conditions call for it – particularly with PTFE.
From one order
We supply the gasket together with the flange joint and the bolting – matched to pressure rating, temperature, medium and facing. It sounds like a detail and is regularly the reason a line does not get finished on site.
On the matching bolting: bolts and studs for flanges. The full range under flanges, fittings and connections.
Frequently Asked Questions
Which gasket for which pressure rating?
Flat gaskets to EN 1514-1 up to about PN 40, spiral wound and kammprofile gaskets up to PN 250, metal ring joints to ASME B16.20 for high pressure in Class 150 to 2500.
Up to what temperature does graphite hold?
In air to about 450 °C, because graphite oxidises above that. Excluding air the limit is higher. The exact figure depends on medium, pressure and surface pressure.
EPDM or FKM?
EPDM for water, hot water and low-grade steam, but not for oils and greases. FKM for oils, fuels and many chemicals, but not for hot water and steam. The two largely exclude one another.
Can gaskets be reused?
No. Flat and spiral wound gaskets are single-use items; they bedded in when first tightened. A new gasket belongs in every reassembly.
What are inner and outer rings on spiral wound gaskets for?
The outer ring centres the gasket and prevents over-compression, the inner ring protects the winding against inward blow-out.
Do you need exactly these parts?
Grade, size, pressure rating and quantity are enough – you usually receive your quote the same day, with an inspection certificate 3.1 on request.
Request a quote