Detail page · Gaskets
Graphite gaskets: the problem-solver for steam, heat and acids
Where fibre gaskets become brittle and PTFE hits its temperature limit, graphite is just getting started: flat gaskets made of expanded natural graphite seal from deep cold to high-temperature service, survive temperature cycling without cold or hot flow, and tolerate almost every medium. This page explains the laminate construction with a stainless steel insert, why the temperature limit is an oxidation limit - and where graphite has its few weaknesses.
- Material
- expanded natural graphite, ≥98 % C
- Temperature
- approx. −200 to 450 °C (more conservative when oxidising)
- Construction
- laminate with stainless steel insert
- Strengths
- steam · heat-transfer oil · acids · alkalis
Construction: graphite foil plus stainless steel insert
The starting material is expanded natural graphite: graphite flakes are chemically expanded and compacted into a flexible foil (typical density of the facing 1.0 g/cm³, purity to DIN 51903 at least 98 % carbon). Pure graphite foil, however, would be too delicate for flange gaskets - so it is almost always processed as a laminate with a stainless steel insert, in two ways:
- Glued to a smooth sheet: the graphite layers are glued to a smooth stainless steel sheet. The adhesive content is under 1 % of the graphite amount - chemical and thermal resistance remain practically unaffected.
- Adhesive-free on a tanged sheet: the foils are rolled onto a tanged sheet - a thin sheet (typically 1.4401, 0.10 mm) from which fine tangs are punched out during perforation and grip the graphite purely mechanically. With no organic components at all: no ageing, no embrittlement.
An anti-stick finish (as a surface coating or impregnation, depending on the manufacturer) prevents sticking to the sealing faces and makes later removal easier. For gas and water applications, an inner eyelet made of stainless steel is also common, which qualifies the gasket as blow-out-safe.
Oxidation limit instead of melting point
The most important peculiarity of graphite: its temperature limit is not a melting point but an oxidation limit. With access to oxygen, the carbon starts to burn off slowly at high temperatures - which is why data sheets state conservative values for an oxidising atmosphere (roughly 350 to 450 °C depending on manufacturer and assessment basis), while considerably higher temperatures are possible under an inert atmosphere or in oxygen-free media. This explains the seemingly contradictory temperature figures in different catalogues. At the low end, the service range extends to around −200 °C and below - graphite stays flexible across the whole range, without cold or hot flow and without swelling or shrinking.
In practice this means: for steam, hot water and heat-transfer oil, graphite is the standard solution above the limits of fibre materials; for permanently oxidising applications above around 500 °C, mica (up to 900 °C) takes over - the temperature ladder is shown on the gaskets overview. On the pressure side, graphite laminates reach high PN ratings depending on the number of inserts; the service limit is always a system value made up of pressure, temperature, flange and bolting - not a single material property.
Chemical resistance: almost everything - except oxidisers
Homogeneous graphite is resistant to almost all classes of media: steam of every kind, seawater and salt solutions, mineral, hydraulic and heat-transfer oils, fuels, organic solvents, alkalis - and, as a distinguishing feature among soft gaskets, also non-oxidising acids such as hydrochloric, phosphoric, hydrofluoric or acetic acid. Its limit is exclusively strongly oxidising media: conditionally resistant to, for example, nitric acid, sulphuric acid under 70 % or hydrogen peroxide; not resistant to concentrated and fuming sulphuric acid, aqua regia or fluorine.
For the laminate, a second rule of thumb applies: it is not the graphite but the metal insert that limits resistance. A tanged sheet made of 1.4401, for example, cannot tolerate hydrochloric acid, hydrofluoric acid, chlorides or hypochlorites - for such media, homogeneous graphite or a laminate with an insert made of Hastelloy or titanium is chosen instead. Resistance must therefore always be checked for both components.
Typical properties of common graphite laminates
| Property | Typical value | Test standard |
|---|---|---|
| Density of the graphite facing | 1.0 g/cm³ | – |
| Purity (carbon content) | ≥ 98 % | DIN 51903 |
| Total chloride | ≤ 25–50 ppm | – |
| Insert (tanged sheet) | 1.4401 / 1.4404, approx. 0.1 mm | – |
| Compressibility | approx. 25–45 % | ASTM F36 |
| Recovery | approx. 10–20 % | ASTM F36 |
| Residual stress under compression (300 °C) | min. 46–48 MPa | DIN 52913 |
| Thickness increase in oil (IRM 903) | max. 2 % | ASTM F146 |
| Standard thicknesses | 0.8 / 1.0 / 1.5 / 2.0 / 3.0 mm | – |
The values come from the data sheets of two common grades and are given as ranges - the current data sheet of the specific product governs for design purposes. Common approvals and tests in this product segment: DVGW (gas), fire-safe tests (API 6FA or BS 6755-2) and BAM tests for oxygen applications. Suitability for drinking water and food contact must be demonstrated per product.
Installation: three graphite specifics
- Scratch-sensitive: do not work graphite surfaces with scrapers or wire brushes; do not install damaged gaskets. The stainless steel insert protects during handling, not against scratches on the sealing face.
- Handle dry: never install graphite gaskets wet or damp - trapped moisture flashes to vapour on start-up and can damage the gasket.
- Do not grease: as with all flat gaskets, lubricant belongs only on bolts and nuts - on the gasket it destroys the permissible pressure reserve. The factory anti-stick finish takes care of release for removal.
Otherwise the general rules from the installation guide apply: flanges parallel, gasket centred, tighten in a cross pattern in stages, retighten only cold, no reuse.
Frequently asked questions about graphite gaskets
What is a graphite gasket?
A flat gasket made of expanded, pre-compressed natural graphite. For flange gaskets, graphite is almost always used as a laminate with a stainless steel insert: either graphite foils glued to a smooth sheet (adhesive content under 1 percent) or rolled adhesive-free onto a tanged sheet, whose punched-out tangs mechanically grip the graphite. The insert (typically 1.4401, 0.1 mm) gives the scratch-sensitive graphite stability for handling and installation.
Up to what temperature can graphite seal?
Graphite's temperature limit is not a melting point but an oxidation limit: with access to oxygen, the material starts to burn off from around 350 to 450 °C depending on conditions - manufacturer figures in this range therefore differ depending on the assessment basis. Under an inert atmosphere or in an oxygen-free medium, considerably higher temperatures are possible; the lower limit extends to around −200 °C and below. For permanently hotter oxidising applications above around 500 °C, mica (up to 900 °C) is the alternative.
Which media is graphite resistant to - and where not?
Homogeneous graphite is resistant to almost everything: steam of all kinds, hot water, heat-transfer and mineral oils, fuels, solvents, alkalis and - as a special feature - also non-oxidising acids such as hydrochloric, phosphoric and hydrofluoric acid. Its limit is strongly oxidising media: concentrated sulphuric acid, nitric acid, aqua regia, moist chlorine. In the laminate, the metal insert additionally limits resistance - a 1.4401 tanged sheet, for example, cannot tolerate hydrochloric acid or chlorides; for such media, choose homogeneous graphite or an insert made of Hastelloy or titanium instead.
What is the difference between glued and adhesive-free graphite laminate?
In the glued laminate, the graphite layers are glued to a smooth stainless steel sheet - with an adhesive content under 1 percent of the graphite amount, which has practically no effect on resistance. In the adhesive-free laminate, the foils are rolled onto a tanged sheet and held purely mechanically - with no organic components at all, which rules out ageing and embrittlement. Both constructions are common in the market (e.g. KLINGER PSE with a tanged sheet, SIGRAFLEX adhesive-free with one or two tanged sheets).
What should be watched when installing graphite gaskets?
Graphite is scratch-sensitive - handle the gasket and sealing faces carefully, no scrapers or wire brushes across the sealing face. Never install wet or damp, and never grease it; many grades carry a factory anti-stick finish for easier later removal. Otherwise, the general flat-gasket rules apply: flanges parallel, gasket centred, lubricate the bolts (not the gasket!), tighten in a cross pattern in stages, retighten only cold, no reuse.
More detail and our range
We supply graphite and fibre gaskets to match your flanges and bolts - as a standard cut to EN 1514-1/DIN 2690 or a special cut to drawing.
Technical basis: manufacturer documentation from KLINGER (KLINGERgraphit Laminate PSE data sheets, graphite resistance table, Flachdichtungen training material 2018) and SGL Carbon (SIGRAFLEX UNIVERSAL data sheet). Properties given as ranges across several data sheet revisions; where revisions differed, the more conservative figure was used. All information without guarantee - the manufacturers’ current technical documentation always prevails. Editorially reviewed: August 2026. Standards and manufacturer status considered: July 2026.