Pipe Flange Gaskets
Material selection, bolt torque and installation guidance for Class 125/150 rubber flange gaskets.
Pipe flange gaskets create a static seal between two bolted pipe flanges. The gasket material must match the pipe media, while the profile — full-face or inner-bolt-circle ring — must match the flange geometry and bolting practice. This application guide covers selection, bolt torque, surface finish and common mistakes for low-pressure rubber pipe flange gaskets. For most water, oil and chemical piping in Class 125/150 flanges, the decision starts with three questions: What is flowing in the pipe? What is the maximum temperature? And is the flange flat-face or raised-face? The answers point to EPDM for water, NBR for oil, FKM for chemicals and high heat, and PTFE envelope when no elastomer survives the media. Bolt torque is as important as material. Uneven tightening creates high spots that over-compress the gasket and low spots that leak. Tighten in a star pattern in stages, and verify that the flange remains parallel after the first thermal cycle. Rubber pipe flange gaskets are single-use: reuse after disassembly is not recommended.
Application Requirements
Recommended Materials
EPDM
Water, wastewater, steam and outdoor piping.
Temp: −50°C to +150°C
Specify WRAS grade for potable water. Not for oil or fuel.
NBR
Oil, diesel fuel, hydraulic fluid and lubricant lines.
Temp: −40°C to +120°C
Use 80–90 Shore A for higher pressure or smaller flange gaps.
FKM
Chemical process lines, hot oil and aggressive fuels.
Temp: −20°C to +200°C
Not for steam or hot alkalis. High-fluorine grades for aromatics.
Design Tips
- 1.Verify the flange class and facing before selecting gasket profile. Full-face gaskets suit flat-face flanges; ring gaskets suit raised-face flanges.
- 2.Measure the bolt circle and number of bolts. The gasket must either clear the bolts (ring) or have holes that align (full-face).
- 3.Choose gasket thickness based on flange stiffness and surface condition. Warper flanges need thicker, softer gaskets; stiff flanges can use thinner, harder gaskets.
- 4.Tighten bolts in three stages using a star pattern. Final torque should achieve 15–30% compression without exceeding bolt yield.
- 5.Check flange parallelism after the first heat-up or pressure test. Retorque only if the gasket supplier recommends it for the material.
- 6.Replace the gasket every time the flange is opened. Compressed rubber does not recover enough to reseal reliably.
Common Sizes
| Size | Typical Use |
|---|---|
| 1/2" – 2" NPS | Common instrument and process lines; ring gaskets typical on raised-face steel flanges. |
| 3" – 12" NPS | Main process piping; full-face gaskets common on cast-iron water flanges. |
| Custom | Specialty manways, vessel nozzles and equipment connections. |
Frequently Asked Questions
What is the best material for a pipe flange gasket?
EPDM for water and steam, NBR for oil and fuel, FKM for chemicals and high temperature. Match the material to the media first.
How do I calculate bolt torque for a pipe flange gasket?
Use the equipment manufacturer's specification if available. Otherwise, target 15–30% gasket compression and tighten in stages with a star pattern. A typical M8 bolt may need 20–40 Nm and an M12 bolt 40–80 Nm for standard rubber gaskets.
Can I reuse a pipe flange gasket?
No. Rubber and elastomer gaskets take permanent set and should be replaced every time the flange is opened.
What surface finish is required for a rubber pipe flange gasket?
Typical Ra is 1.6–6.3 µm. Very smooth finishes are unnecessary; rough or scored surfaces create leak paths.
What is the difference between a pipe flange gasket and a ring gasket?
A pipe flange gasket is any gasket used on a pipe flange. A ring gasket is a specific profile that sits inside the bolt circle. Pipe flange gaskets can be full-face or ring type.
Need Pipe Flange Gaskets?
Send the pipe size, flange class, material and quantity. We supply full-face and ring gaskets to ASME B16.21 or your drawing.