A flange gasket is the deformable sheet or ring seated between two mating flange faces. When stud bolts are torqued, the gasket flows into surface imperfections and creates the seal. Choosing the right gasket material and style matters as much as choosing the flange itself.
Common Flange Gasket Types
| Gasket | Material | Best For |
|---|---|---|
| Non-metallic (sheet) | EPDM, NBR, PTFE, graphite sheet | Low pressure, water/air/chemical lines, FF and RF faces |
| Spiral wound | Metal strip + graphite/PTFE filler | RF faces, steam, hydrocarbons, temperature cycling |
| Ring joint (RTJ) | Soft iron, low-carbon steel, 304/316 | RJ facing, high pressure/temperature, oil & gas |
| Kammprofile | Grooved metal core + graphite facing | Heat exchangers, uneven faces, high seating loads |
| Jacketed | Metal jacket + soft filler | Heat exchangers, manways, valves |
Matching Gaskets to Flange Faces
- Raised face (RF) – spiral wound or sheet gaskets; the industry default
- Flat face (FF) – full-face soft gasket only; a hard ring gasket will crack cast-iron equipment
- Ring joint (RJ) – metal RTJ ring, machined groove in the flange face
- Male-female / tongue-groove – confined gasket types (sheet, spiral) that cannot blow out
Flange Gasket Size Chart Basics
A gasket is specified by: flange size (NPS/DN), pressure class, facing type, ID/OD dimensions and thickness (typically 1.5-4.5 mm). For RF flanges the gasket OD sits inside the bolt circle; for FF flanges it covers the full face including bolt holes. Our flange size charts list the bolt-circle and raised-face dimensions you need to size gaskets for Class 150-2500 flanges.
Installation Tips to Prevent Leaks
- Clean both faces; remove old gasket material and scratches across the seal line
- Center the gasket – an off-center gasket is the #1 leak cause on RF joints
- Torque stud bolts in a star pattern in 3-4 passes to the specified value
- Re-torque after the first heat-up cycle on steam and hot-oil lines
FAQ
What is the best gasket for a water flange?
EPDM or NBR sheet gasket, full-face on FF flanges or IBC style on RF flanges, works for most water service up to Class 300.
Can I reuse a flange gasket?
No. Gaskets take a permanent set when compressed; reusing one risks immediate leakage. Always fit a new gasket when a joint is opened.
Spiral wound vs sheet gasket – which to use?
Use spiral wound with RF flanges for steam, oil and cycling temperatures; sheet gaskets are fine for water, air and low-pressure chemical lines.
We supply flanges machined for all gasket styles – ask for a quote with your line conditions and we will recommend facing + gasket combination.